PAUL SCHERRER INSTITUT ISSN 1423-7296 March 2001
Scientific Report 2000 Volume I Particles and Matter
ed. by: J. Gobrecht, H. Gaggeler, D. Herlach, K. Junker, P.-R. Kettle, P. Kubik, A. Zehnder
CH-5232 Villigen PSI Switzerland Telephone: +41 56 310 21 11 Telefax:+ 41 56 310 21 99 http://www.psi.ch PLEASE BE AWARE THAT ALL OF THE MISSING PAGES IN THIS DOCUMENT WERE ORIGINALLY BLANK TABLE OF CONTENTS
Introduction. i Laboratory for Particle Physics 3 Foreword 4 Particle Physics Theory Theory (I) 5 Theory (II) 6 Theory (III) 7 Experiments Search for muon - electron conversion on gold 8 A precise measurement of the K+ —> 7t°e+v decay rate 9 Does the KARMEN time anomaly originate from a beam-correlated background 10 Precision measurement of the mass of the charged pion 11 A precision measurement of the michel parameter % in polarized muon decay 12 Precision measurement of singlet (ip capture in hydrogen 13 Pionic hydrogen 14 Rare A^-decays in flight (Brookhaven AGS E865) 15 Higgs candidates in eV interactions at -JJ = 206.6 GeV 16 Nuclear Physics Test of supersymmetry using in-beam spectroscopy of1% Au 17 Study of 100Ru at the philips cyclotron and at SINQ 18 Modelling fission in nuclear reactions: I reaction cross-sections 19 Modelling fission in nuclear reactions: II mass distribution 20 Measuring itD3He fusion 21 Atomic Physics High-resolution study of heavy-ion-induced thorium and uranium Ly x-ray spectra 22 First direct observation of long-lived 2S-states in muonic hydrogen 23 Detectors and Experimental Facilities Development work for the CMS pixel detector 24 Development of event triggers for CMS based on the picel detector 25 Polarized nuclei in plastic scintillators: New tools for spin physics 26 An ultracold neutron facility at PSI 27 The low energy muon beam for the muonic hydrogen lamb shift experiment 28
Laboratory for Astrophysics 29 Foreword 30 The first year of XMM-Newton 31 XMM-Newton: from calibration to first results 32 Free-floating planets in stellar clusters 33 Spatial analysis of solar type III events associated with narrowband spikes at metric wavelengths 34 Hard x-rays and decimetric radio correlations 35 Shape and geometry of galaxy clusters and the SZ- effect 36 Baryonic dark matter in clusters and spiral galaxies 37 First data from SREM in space 38 Repairing the imaging system of the high-energy solar spectroscopic imager (HESSI) after JPL-mishap 39 Star calibration of the HESSI roll angle system (RAS) 40 The aspect data proccesor (ADP) for the HESSI imager 41 The HESSI solar aspect system (SAS) 42 Fabrication of transition edge sensors (TES) devices 43 Arrays of superconducting photon detectors 44 Transition edge sensors for astronomical applications 45 Operating of the proton irradiation facility - concise summary 46 Standard radiation environment monitor SREM as a successful example of technology transfer and industrial cooperation 47 Comparison of calibration results from PROBA standard radiation environment monitor with Monte-Carlo simulations 48 Laboratory for Muon Spin Spectroscopy 49 Foreword 50 Superconductivity Oxygen isotope effect on magnetic penetration depth in underdoped YxPr1.xBa2Cu3O7.7 51 Magnetism in tetragonal La2.x.ySrxREyCuO4 52 Cation size disorder-induced crossover from superconductivity to magnetic order in Li 85M0.i5CuO4 53 Low energy excitations and inhomogeneous magnetism in electron doped cuprates 54 Effect of an applied current on the flux line lattuce of NbSe2 55 Flux line lattice of 3d superconductors 56 Magnetism (partial overlap with Superconductivity) Magnetic ordering in ammoniated alkali fullerides 57 Spin dynamics in novel transition metals 58 Effects of dimensionality and quantum criticality on heavy-fermion superconductivity and magnetism 59 Glassy spin dynamics in non-fermi-liquid UCu5.xPdx, x = 1.0 and 1.5 60 Study of the magnetic properties of Ce3Pd20Si6 and Ce3Pd20Ge6 compounds 61 \iSR magnetic studies of the heavy fermion compound Ce7Ni3 62 Magnetic properties of CeNiSn doped with Cu or Pt 63 \iSR studies of the Kondo insulators Yb!_xLuxB12 64 The magnetism of YFe6Al6 65 Macroscopic and local magnetic moments in Si-doped CuGeO3 with neutron and [iSR studies 66 Spin fluctuations in the triangular antiferromagnet CsNiBr3 67 Low temperature spin fluctuations in spin-liquid Yb3Ga5Oi2 68 Study of U- and RE-intermetallic compounds exhibiting quadrupolar and magnetic order 69 Comparative study of the magnetic properties of rare earth intermetailic compounds, complementing neutron scattering experiments 70 Magnetic correlations in one dimensional spin systems 71 \iSR and spin-vacancy-induced magnetism in low-dimensional quantum systems 72 \iSR studies of the electron-doped Ca^ SmxMnO3 73 Zero and longitudinal field relaxation in low doping manganites: search for static and dynamic ferromagnetic clusters 74 A [iSR study of the low temperature magnetic properties of the molecular cluster Fe8 75 \iSR on monodisperse nano-scale Pd clusters at low temperatures 76 Study of the dynamic and structure features of magnetism in holmium 77 Spontaneous magnetic ordering in sodium electro sodalite 78 Formation of Condon domains in lead at very low temperatures 79 Semiconductors and Liquid Crystals HSR dynamics of liquid crystals studied by ALC 80 HSR in II-VI solar cell materials 81 Muon(ium) in nitrogen-rich diamond with H2/H3 centres 82 Measurement of relaxation rate and paramagnetic frequency shift of the negative muon spin precession in silicon 83 Chemistry Hydrocarbon activation in zeolites; insights through EPR and jiSR 84 "The blue-ridge mountains of Virginia" 85 ALC-jiSR on aza-cyclohexadienyl radicals in pyridinium salts 86 Interactions of cosurfactants with surfactant bilayers 87 Research and Development with Low Energy Muons Diffusion of muons in metallic multilayers 88 Emission of epithermal muons from a patterned moderator 89 Thickness dependence of the efficiency of s-Ar and s-N2 moderators 90 Anew surface muon beam 91
Laboratory for Micro and Nano Technology 93 Foreword 94 Nano Factory and X-ray Optics Rheology and pattern formation during hot embossing of thin polymer films 95 Nanofabrication with hot embossing and electroforming 96 V-groove replication: a tool for quality control of a compact disc injection molding process 97 Laser ablation lithography using diffractive phase masks 98 High resolution scanning x-ray fluorescence microscopy 99 Tunable wet etched diffractive optics for hard x-rays 100 Micromechanical cantilevers for thermal analysis 101 Silicon Based Nanomaterials and Nanoelectronics Single hole transistor in a p-Si/SiGe quantum well 102 Electro- and photoluminescence of C-induced Ge islands embedded in Si 103 Optical and structural analysis of Ge quantum dots embedded in strained Si quantum wells grown on patterned substrates 104 Modeling of the c(4x4) surface reconstruction 105 Strain fields in C-induced Ge dots 106 Modifications of the Si (100) surface 107 Thermophotovoltaics - system, photocells and potential 108 TEM investigation of an ordering phenomenon in Alo.5Gao.5As 109 Application of the quantum cascade laser principle to the Si/SiGe material system 110 Structural investigations of Si/SiGe cascade samples Ill Formation of arbitrary 3-dimensional nano-structures from strained Si/SiGe double layers 112 Molecular Nanotechnology Photolithographic generation of protein micropatterns 113 Deposition system for single molecule experiments 114 Extracellular stimulation of neurons cultured on microelectrode arrays 115 Nanostructred chips for the analysis of individual proteins 116 Electrochemistry of stacked layers of redox labeled proteins 117 Production and redox labelling of antibodies against B-lactam antibiotics 118
Laboratory for Radio- and Environmental Chemistry 119 Foreword 120 Heavy Elements Fluoride complexation of rutherfordium (Rf, element 104) 121 Thermochemical predictions of the chemical properties of bohrium (Bh, Element 107) 122 Stability of group 8 tetroxides MeO4 (Me=Ru, Os, Hs) and their adsorption behavior on quartz 123 Evaluation of the enthalpy of adsorption of OsO4 on quartz 124 The interaction of element 112 with metal surfaces 125 A first attempt to chemically identify element 112 126 On-line thermochromatographic studies of radon as a presumable pseudohomologue of the elements 112 and 114 127 Vander Waals interaction of atoms of elements 112, 114, and 118 with solid surfaces 128 Semi-empirical calculation of adsorption entropies 129 Selective gas-phase transport of short-lived, carried-free iodine isotopes from a 252Cf fission source 130 a-peak shift in cooled PIN-diode detectors 131 Surface Chemistry Transport yields of selenium nuclides at the SINQ gas-jet facility 132 Reaction of HO86Br with sodium bromide aerosol 133 The adsorption of NO, NO2 and HONO on ice 134 The adsorption of peroxyacetyl nitrate on ice 135 The reaction of HNO3 with sea-salt aerosol particles 136 Modelling the heterogeneous reaction of NO2 on diesel soot 137 Measurement of the HONO emission from a diesel engine 138 Significant nitrite formation in diesel exhaust 139 Analytical Chemistry An Alpine ice-core record of anthropogenic HF and HC1 emissions 140 North-South deposition gradients of trace species in the Alps 141 Electrical conductivity measurement on an ice core from the Illimani (6430 m, 16°39'S, 67°47'W), Bolivia 142 Seasonal record of glaciochemical and isotopic signals in a shallow ice core from Chimborazo, Ecuador 143 Glaciological and chemical survey at glaciar Esmeralda, Chile 144 The influence of sublimation on stable isotope records recovered from high altitude glaciers in the tropical Andes 146 Analysis of dust layers in an ice core from Cerro Tapado, Chile 147 First glacio-chemical investigation of Belukha glacier in the Siberian Altai 148 Continuous melting and ion chromatographic analyses of ice cores 149 Preliminary results of trace element analysis in ice cores by continuous ice melting (CIM) ICP-MS 150 First approach to determine concentrations of mercury in ice cores by cold vapour ICP-MS 151 Determination of total dissolved silicon for 32Si dating of glacier ice 152 Applicability of TXRF for trace element analysis in ice samples 153 7Be and 10Be concentrations at the high-alpine site Jungfraujoch 154 A new Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) for trace element analyses 155 Cement Chemistry Cement Chemistry: Quality control and developments 2000 156 IV
Project Radwaste Determination of the radionuclide inventory in accelerator waste 157 High and intermediate energy nuclear data for accelerator-driven systems (HINDAS) 158 Measurement of radionuclide contents in activated graphite 159 Laboratory for Ion Beam Physics i6i Foreword 162 The PSI/ETH Tandem accelerator facility 163 Investigation of natural 10Be/Be ratios with accelerator mass spectrometry (AMS) 164 Dendrochronological and radiocarbon dating of the Scythen burial place in the Pazyryk Valley in the Altai Mountains, South Siberia 165 Biosphere 2 ocean radiocarbon experiment 166 Variations in atmospheric 14C content 40,000 ago and radiocarbon age of Heinrich event 4 167 Late Pleistocene sequences of the Black Sea shelf: Calibration by AMS 14C dating 168 A Late-Glacial and early Holocene environment and climate history for the Neuchatel region (Switzerland) 169 The application of in situ cosmogenic nuclide exposure dating (10Be, 26A1), to glacial deposits of the last deglaciation in the southern Andes of Chile 170 Slip rates of active thrusts at the northeastern margin of Tibet (China) as revealed by 21Ne and 10Be exposure ages of Late Pleistocene alluvial fans 171 Cosmogenic nuclide erosion assessment of tropical highlands (Sri Lanka) 172 Can we use cosmogenic nuclides to date stone artifacts? 173 A 30,000 year erosion rate record from cosmogenic nuclides in river terrace sediments in the Massif Central, France 174 Last major advance of Taylor Glacier into Central Beacon Valley, Antarctica, at least 4 Ma ago 175 Constraints for the latest glacial advance on Wrangel Island from surface exposure dating 176 Cosmogenic isotope constraints on erosion rates in the Himalaya 177 Detection of the 205 year solar cycle during the last ice age 178 Air-firn-transfer of 10Be on Polar ice sheets 179 Ice core recovery from the South Inilchek Glacier (Kyrghyzstan) 180 Paleomagnetic field reconstruction based on cosmogenic 36C1 in the GRIP ice core 181 Composition-dependent scavenging of 10Be by marine particles 182 10Be sedimentation and transport processes in the South Atlantic 183 10Be and Pb-time-series of a Fe-Mn crust from the Tasman Basin, south-western Pacific 184 10Be / 7Be ratios at the high-alpine site Jungfraujoch 185 129I in rain water near Zurich 186 Prospects of 129I as an environmental tracer 187 Beryllium liquid alloy ion sources for focused ion beam implantation 188 A GePd liquid alloy ion source for focused ion beam implantation 189 Nanostructued materials by selective surface activation using focused ion beam implantation 190
List of publications 191 Contributions to conferences and workshops 216 Lectures and courses 243 Awards 245 INTRODUCTION
Our most important resources are people, scientists with stimulated light emission from SiGe-heterostructures with a innovative ideas, engineers with an impetus to produce a fi- largely recognized publication in Science and several spon- nal product and technicians with pragmatic solutions to help taneous reactions from semiconductor industries. Also other us to be faster than the competition and within budget. We techniques and devices could be transferred to industry as feel presently the good economy through the difficulty to re- for instance superconducting tunnel junction detectors devel- cruit new people at all levels. We have therefore to increase opped for astrophysics with application in protein Time-of- the training of people and facilitate migrations within the in- Flight Mass Spectrometry to mention one. stitute. The Paul Scherrer Institut devotes 60% of its resources The year 2000 was the first year under the new regime to the user laboratory function. We consider it as important, of a global budget. This implied a change in the culture of that we keep our facilities at the forefront of the technology project management. Project leaders have to optimize the and constantly improve on it. It has been decided to rebuild full project including at first sight invisible or hidden cost the yuE4-beam and optimize it for highest intensity of low such as services from the infrastructure and logistic departe- energy muons. A factor of about 5-10 will be achieved in ment. Also the operating costs have to be taken into account 2003/2004 and will serve primarily the ultra low energy //SR at a much earlier stage. As any change in culture takes its facility, where we can stop fully polarised muons in thin sur- time we have to improve in the coming years. faces. A new international users group for this unique facil- ity has been formed and a significant contribution to this new A partial answer to the mentioned challenges above is a beam line has been granted by the German BMBF. PSI likes stronger collaboration within the institute. We experience to thank for this generous support. already a few excellent examples such as a collaboration of scientists and technicians from Particle Physics, Micro- and The majority of the publications in 2000 address ques- Nanotechnology and SLS to produce pixel detectors for use tions in basic research. They pave the way for the long term at SLS, the development of advanced x-ray optics for SLS future of science and technology or equal importantly con- and other light sources by people from Nanotechnology, an tribute to the understanding of nature, the origin of mass and increased collaboration between Radiochemistry and Ion forces or the dynamics of our universe. The price for basic Beam Physics. Also collaborations beyond the departement research is justified if it is of high quality. In the year 2000 are increasing in strength where we like to mention common three laboratories have been reviewed by a team of inter- users meetings of the Muon Spin Rotation (/iSR) and national experts; the laboratories of Particle Physics, Muon Neutron Scattering communities, the help of the detector Spin Rotation, and Micro- and Nanotechnology have demon- group of Particle Physics for instruments at SINQ, and strated world class results and received suggestions for fur- the collaboration between Molecular Nanotechnology and ther developments. Electrochemistry from General Energy departement.
Equally, we should further strengthen our link to indus- try. The front page of this report is about one of the high- lights of this year. We could demonstrate the first electrically Laboratory for Particle Physics Foreword Particle Physics Theory Experiments Nuclear Physics Atomic Physics Detectors and Experimental Facilities LABORATORY FOR PARTICLE PHYSICS
Kurt Gabathuler
The year 2000 marked the closing of the Large Electron- cessfully searched for in pion decay. The anomaly found at Positron Collider LEP at CERN, which ultimately achieved Rutherford, however, might recently have been explained by a centre-of-mass energy of 209 GeV. This facility has greatly members of our laboratory, the effect being assigned to a tiny contributed to the sharpening of the picture of elementary admixture of nitrogen in the organic scintillator used for de- particles and their interactions. A Standard Model fit to the tection of the neutrino interactions. high quality data now available allows one to predict the mass of the so far elusive standard Higgs boson to within A new precision measurement of the pion mass relative a range between 113.5 GeV/c2 (from direct search) and 170 to the muon mass has achieved a statistical accuracy of 1 GeV/c2 (95% CL). ppm by detecting x-ray transitions in muonic oxygen and pi- onic nitrogen atoms simultaneously. Both x-ray lines could At LEP, PSI was a member of a collaboration running be registered by Bragg scattering in the same geometric con- the L3 detector and contributed to the construction of the for- figuration of a crystal spectrometer, thus avoiding system- ward muon chambers. In the last months of running LEP a atic uncertainties. This experiment greatly benefited from possible hint of a Higgs signal at 115 GeV/c2 was reported, the new cyclotron trap enhancing the atom formation rate, which led to a one-month extension of LEP operation be- and from using spherically curved crystals. With the same yond the long anticipated shut-down date. A request for a apparatus, a preliminary experiment was performed on pio- further extension was however rejected as it seemed ques- nic hydrogen, where the rate of registered x-ray transitions tionable that it would be possible to resolve the ambiguous could be enhanced by a factor of 10 with an improved peak- present signal at LEP within a reasonable time and cost, and to-background rate, thanks to optimized shielding. not cause a delay in the construction of the Large Hadron Collider LHC, which is to succeed LEP. Indeed, LHC with The year 2000 saw two retirements of distinguished SIN/ its centre-of-mass energy of 14 TeV is not limited in energy PSI veterans closely related to our laboratory. Milan Locher and will therefore be able to cover the predicted mass win- joined SIN in 1970 and acted for many years as head of the dow of the Higgs particle. theory group. His scientific interest was concentrated on low energy hadron interactions. He served, since the seventies, PSI is a member of the CMS collaboration, now prepar- as scientific secretary of our Research Committee, where his ing its multi-purpose experiment at LHC, which is scheduled careful wording of the often very difficult committee recom- to become operational in about five years. Our laboratory has mendations were very much appreciated, as well as his ex- a major responsibility for the development and construction pertise in the judging of the many pion- nucleus and pion- of the pixel vertex detector and the electromagnetic calorime- nucleon proposals. Wilfred Schoeps joined SIN in 1968 and ter ECAL. These two subdetectors are particularly suited to is known to all experimentalists at the PSI accelerators as the search for the Higgs around 115 GeV/c2. The most the promoter and designer (together with his group) of stan- promising decay mode of a light Higgs particle is H —> 77, dardised, high performance NIM and CAMAC electronics. for which a high performance ECAL is mandatory. With ef- Hundreds of his NIM and CAMAC modules are still in use ficient, high purity b-tagging by the vertex detector in asso- today in numerous experiments at PSI. In fact, some of the ciated Higgs production Htt, the main decay mode H —> bb designs have been licenced out to commercial firms. for the case of a light Higgs could be singled out from the large background. In October, the activities of the Laboratory for Particle Physics were presented, both in written and oral form, to Concerning the experimental programme at the PSI ac- the reviewing Plenary PSI Research Committee (F0K0). In celerator, 2000 was certainly a productive year for all exper- the summary of the deliberations and recommendations, the iments seeking high-statistic data. Two experiments involv- committee stated: "Considering the human and financial re- ing ordinary muon decay and utilizing polarisation measure- sources, PSI's programme in particle physics is, overall, a ments completed their data taking phase. This concludes a good balance between in-house and external engagements... long term programme of looking for effects beyond the Stan- The traditional user lab. function in particle physics can only dard Model in this purely leptonic process. be maintained if new innovative projects at PSI's proton ring are actually implemented in the near future and opportunities In the last few years, the existence of a neutral parti- for new proposals are kept open." The two new initiatives on cle of 33.9 MeV/c2 has been claimed by the KARMEN the forbidden decay [i —> e + 7 and on the electric dipole collaboration while looking at neutrino induced reactions at moment of the neutron are examples of such new innovative the Rutherford Laboratory. At PSI, this particle was unsuc- projects. THEORY (I)
E. Accomando, C. Alexandrou1, A. Denner, St. Diirr, D. Graudenz2, Th. Jensen3, K. Junker, M. P. Locher4, V. E. Markushin, M. Melles, St. Pozzorini3, R. Rosenfelder, M. Spira, O. Wigger5
1 now: Department of Natural Sciences, University of Cyprus, CY-1678 Nicosia, Cyprus 2 now: McKinsey Consulting, Hamburg 3 PhD student 4 retired 5 now: Physik-Institut der Universitat Zurich
In this year the Theory group organized again the tra- ditional summer school in Zuoz. The "Phenomenology of Gauge Interactions" was covered and discussed by leading experts in this field - both from an experimental and theoret- ical point of view. The scientific proceedings are available as
Proceedings of the Summer School on Phenomenology of Gauge Interactions, eds. Dirk Graudenz and Valeri Markushin, Zuoz (Engadin), Switzerland, August 13 - 19, 2000, PSI-Proceedings 00-01, ISSN 1019-6447.
At present the Theory group works mainly in the follow- ing fields: exotic atoms (nuclear, atomic and molecular ef- fects), strong interaction physics at low energy (mesonic res- onances, antiprotons), nonperturbative methods in field the- ory (variational methods, lattice gauge theory), and the Stan- dard Model of particle physics (Higgs physics, electroweak radiative corrections) together with its extensions. 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 M^ (GeV) Below and in the following contributions a few examples are presented in more detail; for further topics see the detailed list of publications which also includes the work done in col- Figure 1: The calculated nn invariant mass distribution in laboration with visitors. the decay
The structure of scalar mesons The decay
E. Accomando, C. Alexandrou, A. Denner, St. Diirr, D. Graudenz, Th. Jensen, K. Junker, M. P. Locher, V. E. Markushin, M. Melles, St. Pozzorini, R. Rosen/elder, M. Spira, O. Wigger
Variational Worldline QED MSSM Higgs Boson Production in 77 Collisions Non-perturbative methods are urgently needed for many The heavy neutral Higgs bosons H, A in the minimal su- strong-coupling problems in quantum field theory. Following persymmetric extension of the Standard Model can be pro- Feynman's successful treatment of the polaron problem in duced as single resonances at high-energy 77 colliders. The condensed matter physics the same variational principle was prospects of the search for these particles have been studied applied to quenched QED in the worldline formulation. New in bb and neutralino-pair final states [4]. The Higgs bosons features arise from the description of fermions by Grassmann can be found with masses up to 70-80% of the initial e±e~ trajectories, the supersymmetry between bosonic and fermi- collider energy for medium values of tg/?, i.e. in areas of the onic variables and the much more singular structure of a supersymmetric parameter space not accessible at other col- renormalizable gauge theory like QED in 3 + 1 dimensions. liders. In a fine scan of the resonance region the two Higgs As trial action a general retarded quadratic action is taken bosons A and H can be disentangled at least in part of the su- with free retardation functions. From the variational equa- persymmetry parameter space. This is shown in Fig. 2. If the tions for these functions a remarkably simple, non-perturba- supersymmetry parameters ft, M2 are favourable, the steps in tive, gauge-invariant solution for the anomalous mass dimen- the resonance formation curve are clearly visible. However, sion 7™ (a) in the MS-scheme has been derived [1]. this theoretical analysis must be backed by future experimen- tal simulations including detector effects. 2.0 4 3-loop/
1.5 AJ y' M2/n = 200/-200\ \200/200GeV . Dyson— Schwinger 0.8- 1 AI/ w/o SUSY \ \«-H J 0.5 background ...... _* .T..™,.7.._._.^ 0.4- 395 396 397 398 399 400 401 402 403 404 405 4-loop\ e [GeV] Figure 2: Threshold scans for H, A production as a function 0.0 of the e±e~ collider energy with final decay into bb pairs. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 The cross sections are defined in bb mass bins of ± 2 GeV a around the maximum of the 77 luminosity. Increasing the
Figure 1: Anomalous mass dimension jm as function of the energy stepwise from below, the Higgs boson A is produced coupling constant a in quenched QED. The variational result first, followed by the combination of A and H, while finally is shown as a solid curve while the solution from the Dyson- H is left before the scan leaves the resonance region. Schwinger equations in rainbow approximation and Landau gauge is indicated as a dot-dashed line. The curves labeled "n-loop" show the results up to n-loop perturbation theory. REFERENCES The Pade estimation of the 5-loop result is also shown. [1] C. Alexandrou, R. Rosenfelder and A. W. Schreiber, PSI-PR-00-05; Phys. Rev. D 62, 085009 (2000). For small couplings the variational result can be com- pared with recent four-loop perturbative calculations [2] while [2] K. G. Chetyrkin, Phys. Lett. B 404,161 (1997); J. A. M. at large couplings one finds that 7m (a) becomes proportional Vermaseren et al, Phys. Lett. B 405, 327 (1997). to y/a (see Fig. 1). The anomalous mass dimension shows no obvious sign of the chiral symmetry breaking observed in [3] V. A. Miransky, II Nuov. Cim. 90 A, 149 (1985); (gauge-dependent) Dyson-Schwinger calculations [3], how- A. Kizilersu et al., hep-th/0010161. ever it is found that a perturbative expansion of 7 (a) di- m [4] M. M. Miihlleitner, M. Kramer, M. Spira and verges for a > 0.7934. The calculation of physical observ- P. M. Zerwas, PSI-PR-00-19, hep-ph/0101083. ables or application to bound state problems seems also fea- sible within the variational worldline approach. THEORY (III)
E. Accomando, C. Alexandrou, A. Denner, St. Diirr, D. Graudenz, Th. Jensen, K. Junker, M. P. Locher, V. E. Markushin, M. Melles, St. Pozzorini, R. Rosen/elder, M. Spira, O. Wigger
W-pair production 21/07/2000 While the limelight in the last running period of the elec- LEP Preliminary tron-positron collider LEP was on the search of the Higgs 20 boson, other interesting physical processes such as W-pair RacoonWW / YFSWW 1.14 production were studied as well. This allowed one on the Gentle 2.1 (±0.7%) one-hand to measure the mass of the W-boson with a preci- 4 :< sion of 0.5% and on the other hand to investigate the non- abelian gauge interaction at the level of 5%. The total cross section for W-pair production was measured at the per-cent level. 10 These precision measurements require adequate theoreti- cal predictions. Since the W bosons can only be detected via their decay products, they have to be treated as resonances in the full four-fermion processes e+e~ —> W+W~ —> 4/. Moreover, radiative corrections need to be included. To a- chieve a theoretical accuracy at the per-cent level, the uni- versal radiative corrections, which comprise renormalization 210 effects (running or effective couplings), the Coulomb singu- larity at the W-pair-production threshold, and initial-state ra- diation (ISR) in leading-logarithmic approximation, are not sufficient. Figure 1: Total W-pair production cross section at LEP2 as During the last years a calculation of non-universal cor- given by the LEPEWWG [6] rections was performed at PSI and implemented into a Monte Carlo generator, called RACOONWW [1]. First results of REFERENCES this generator had already been published at the end of 1999 [2, 3,4]. RACOONWW was further developed during the last [1] A. Denner, S. Dittmaier, M. Roth and D. Wackeroth, year. The leading higher-order initial-state corrections have PSI-PR-00-11, Nucl. Phys. B 587, 67-117 (2000). been implemented. Within the LEP2 Monte-Carlo workshop [5] the generator was compared with other programs, and its [2] A. Denner, S. Dittmaier, M. Roth and D. Wackeroth, theoretical uncertainty was estimated. It allows to calculate PSI-PR-99-29, Phys. Lett. B 475, 127-134 (2000). the total cross section with an accuracy of 0.4 % and the cor- [3] A. Denner, S. Dittmaier, M. Roth and D. Wackeroth, responding distributions with an accuracy of 1%. Finally, a PSI-PR-99-30, J. Phys. G 26, 593-599 (2000). first version of RACOONWW has been made available for the experimentalists. Our results indeed show that the non- [4] A. Denner, S. Dittmaier, M. Roth and D. Wackeroth, universal corrections reduce the cross section by about 2%. PSI-PR-99-34, hep-ph/9912447, EPJdirect Vol.2, C4, 1-10 (2000), DOI 10.1007/sl010500c0004. Figure 1 shows the present experimental data points for the total W-pair-production cross section as given by the LEP [5] W. Griinewald, G. Passarino et al., hep-ph/0005309, in Electroweak Working Group [6] for the Summer 2000 con- Reports of the working groups on precision calculations ferences. The data are in good agreement with the Standard- for LEP2 physics, eds. S. Jadach, G. Passarino and Model prediction as obtained from RACOONWW and a sim- R. Pittau, CERN 2000-009, p. 1-135. ilar generator YFSWW [7]. [6] Homepage of the LEP Electroweak Working Group, Below a centre-of-mass energy of 170 GeV, the predic- http://lepewwg.web.cern.ch/LEPEWWG/. tion in Fig. 1 is continued by GENTLE [8], which does not include the non-universal electroweak corrections. GEN- [7] S. Jadach et al, Phys. Lett. B 417, 326 (1998); TLE is tuned to reproduce the prediction of RACOONWW Phys. Rev. D 61 (2000) 113010 . and YFSWW3 on the total cross section at LEP2 within a few per mill. Quite recently an improved Born approxima- [8] D. Bardin et al., Phys. Lett. B 308, 403 (1993); tion has been implemented into RACOONWW which allows Comput. Phys. Comm. 104, 161 (1997). a similar extrapolation down to the W-pair production thresh- [9] A. Denner, S. Dittmaier, M. Roth and D. Wackeroth, old [9]. PSI-PR-01-01. SEARCH FOR MUON - ELECTRON CONVERSION ON GOLD
W. Bertl2, R. Engfer3, E. A. Hermes3, T. Kozlowski3, G. Kurz3, J. Kuth1, G. Otter1, F. Rosenbaum2, N. M. Ryskulov2, A. van der Schaaf, P. Wintz3,1. Zychor3
R-87-03, SINDRUM II COLLABORATION: AACHEN1 - PSI2 - ZURICH3
Observations on solar and atmospheric neutrinos indicate SINDRUM run2000: |xe conversion on gold that neutrinos mix so lepton flavor would not be conserved. SINDRUM 11 tests lepton-flavor conservation by a search for yue conversion in muonic atoms. The process would result in electrons at fixed momentum (depending on atomic number) around 100 MeV/c. In recent years a dedicated beamline was brought into operation in the TTE5 area. The major element is a 9 m long superconducting magnet. In spring 2000, after a long series of modifications, reliable operation of this PMC magnet was obtained. In the following months data were taken on gold. Conversion on a heavy nucleus might be enhanced relative to a medium Z target, such as titanium [1]. See Fig. 1 for a description of the experimental setup.
A exit beam solenoid F inner drift chamber 1m B gold target G outer drift chamber C vacuum wall H superconducting coil histogram: D scintillator hodoscope I helium bath ue conversion at B=10" E Cerenkov hodoscope J magnet yoke - u"Au —> e'Au
85 90 95 100 105 e" momentum (MeV/c)
Figure 2: Momentum distributions for three different beam momenta and polarities: (i) 53 MeV/c negative, optimized for n~ stops, (ii) 63 MeV/c negative, optimized for n~ stops, and (iii) 48 MeV/c positive, for /x+ stops. The 63 MeV/c data were scaled to the different measuring times. The /x+ data SINDRUM II were taken at reduced spectrometer field.
Figure 1: The SINDRUM II spectrometer during the year distribution expected from muon decay in orbit. Two events 2000 measurements. Muons are transported to the gold target were found at higher momenta, but just outside the region with the help of a 9 m long superconducting solenoid coupled of interest. The agreement between measured and simulated + directly to the spectrometer magnet. positron distributions from /i decay gives us confidence in the momentum calibration. At present we have no hints about Radiative pion capture (RPC), followed by e+e~ pair the nature of the two high-momentum events: they might be production, can be a major source of background. A pion induced by cosmic rays or RPC, for example. Both processes reaching the gold target has a chance of order 10~5 to pro- result in flat momentum distributions such as shown by the duce an electron in the energy region of interest, so the pion data taken at 63 MeV/c (see Fig.2). stop rate must be below one every ten minutes. At the PMC Presently we are still studying the various rates and ef- entrance the beam contains similar amounts of muons and ficiencies that enter the calculation of the new limit on the pions. Since the pion range in matter is about half as large as branching ratio. As a preliminary result we obtain a single- the corresponding muon range the pion contamination can be event sensitivity slightly below 2 x 10~13 which corresponds reduced strongly with the help of a moderator at the PMC en- to a 90% C.L. upper limit below 5 x 10~13. This constitutes trance. Only one out of 106 pions may cross this moderator. an improvement by two orders of magnitude of the previous Typically 99.9% of them would decay before reaching the best result on a heavy target [2]. target. The requirement puts strong constraints on the high- momentum tail transported by the beam line which could be REFERENCES met after a careful optimization of the beam settings. During an effective measuring period of 75 days about [1] T. S. Kosmas, Z. Ren and A. Faessler, 4 x 1013 muons stopped in the gold target. Figure 2 shows Nucl. Phys. A 665,183 (2000) and references therein. as a preliminary result various momentum distributions. The [2] SINDRUM II Collaboration, W. Honeckeref ah, main spectrum, taken at 53 MeV/c, shows the steeply failing Phys. Rev. Lett. 76, 200 (1996). A PRECISE MEASUREMENT OF THE TT+ -»• 7r°e+i/ DECAY RATE
E. Frlez1, J. E. Koglin1, W. Li1, R. C. Minehart1, B. E. Norum1, D. Pocanic1, S. Ritt1''2, O. A. Rondon-Aramayo1, L. C. Smith1, W. A. Stephens1, K.O.H. Ziock1, W. Bertl2, Ch. Broennimann2, J. F. Crawford2, M. Daum2, R. Horisberger2, D. Renker2, D. Sawannakachorn2, R. Schnyder2, H. P. Wirtz2, T. Kozlowski3, B. G. Ritchie4, V. A. Kalinnikov5, N. V Khomutov5, A. S. Korenchenko5, S. M. Korenchenko5, N. P. Kravchuk5, N. A. Kuchinsky5, D. Mzhavia6, Z. Tsamalaidze6,1. Supek7
R-89-01.1, PIBETA Collab: U. VIRGINIA1 - PSI2 - SWIERK3 - ARIZONA ST.4 - DUBNA5 - TBILISI6 - IRB ZAGREB7
The PIBETA experiment aims to measure the pion beta cuts we find > 14,000 clean IT/3 events. Relaxing the soft- decay (ir+ ->• ir°e+v) branching ratio to about 0.5 % in its ware cuts (presently under study) results in ~ 20 % more current phase. The best experimental value at present has er- final events in the current sample. Typical signal-to-back- ror limits of ~ 4 %, far exceeding the theoretical uncertainty ground ratio spectra for the n/3 events are shown in Fig. 1. of < 0.15%. 2000 Partial Vy Analysis Results — Preliminary
During the year 2000 we have successfully continued CO taking data at the ir+ stopping rate of ~ 9 x 105/s. We £600 s have also: (i) fully automated the timing offset adjustment 1670n*-»e *vy Events \ 1 -Arm HT Trigger E,>63 MeV \ S/3- = 13.8 and detector gain matching procedures, (ii) implemented the E.,>1E MeV i \ domino sampling chip readout for all PMT signals, and (iii) .2 400 0.*,>1 completed implementation of near-100 % experiment auto- 1" mation, requiring that only a single experimenter be physi- / \ ji \ cally present and on call at the PSI site while running. 200 \ t' V 2000 Partial 7T/? Analysis Results - Preliminary B
'... .*.?::.•*:•:-vt ^.. s 71 H 14500 Events -10 -5 5 10 3/B>250 i \ t(e')-t( ) (ns) 2000 1 k- 7 / \ / \ 2000 Partial n*—>eVy Analysis Results - Preliminary E m f \ S > 7959 TV*->e*i/j Events * 2—Arm HT Trigger 1000 ±j / \ Er>53 MeV S/3 > 250 = 2000 1 \ 5 E.,>53 MeV / V E *** J 8 > / n z -10 -5 10 1000 4 >) (ns) / * 2000 Partial 7T/? Analysis Results - Preliminary '/ B 0 i-v-v, :• -10 -5 5 10 14500 Events ^ 1500 t(e')-t(7) (ns) — Simplified GEANT E 1000 Figure 2: e-7 timing difference in a subset of the 1-arm trig- ger 7T+ —> e+vy data (top). Comparable distribution for the 2-arm data is virtually background-free (bottom). 500 We have simultaneously recorded a large set of radia- tive decay events for the processes n+ —>• e+v-f and /i+ —>• Veo 165 170 175 180 185 e+vvy. In its current phase the PIBETA experiment will in- B7l72 (deg) crease the existing world data set for these processes by more than an order of magnitude. Fig. 2 illustrates the quality of Figure 1: 7-7 time difference for pion beta decay events (top) our data by showing preliminary results of the partial data and 7-7 opening angle distribution (bottom) projected from analysis of the radiative pion decay. We anticipate significant the analyzed fraction of our 2000 data set. Signal to back- physics results from the analysis of these data, addressing is- ground ratio exceeds 250. sues of non-(y — A) terms in the weak interaction and pion structure (FA/FV, polarizability). Our most important accomplishment in 2000 is the ac- In summary, during the year 2000 the apparatus was sta- quired statistics of clean pion beta (TT/?) decay events, keep- ble and performed as designed and on schedule. We are cur- ing the experiment on schedule for the ~ 0.5 % phase. With rently in the process of evaluating a first ~ 1 % result for the <40 % of the data replayed and the most stringent off-line pion beta decay branching ratio. 10
DOES THE KARMEN TIME ANOMALY ORIGINATE FROM A BEAM-CORRELATED BACKGROUND
F. Atchison1, M. Daum1, P-R. Kettle1, C. Wigger1
R-96-05, PSI1
In a recent letter[l] we present arguments for the exis- y(t) = A • e(-*/2-2M») + B for t > TC. Here, A is the initial tence of a beam-correlated neutron background in the KAR- rate of the exponential decay, B is the beam-correlated back- MEN detector that could contribute to an excess of events, ground from reaction (3), and TC is the linear risetime of the known as the KARMEN time anomaly [2]. The speculative neutron capture rate. A fit to the data of Ref.[2] results in a explanation was that these events could be generated by hith- X2 of 15.5 for 16 DOE erto unobserved neutral massive X-particles originating from If we restrict our fit to the shorter 5 [is time window, as the ISIS target via the rare pion decay process, TT+ ->• fi+X. used in the original analysis[2], in order to be less depen- Our basis is that the KARMEN detector can respond to dent on fluctuations of the background, we obtain a \2 of 8.7 the 10.8 MeV 7-energy from neutron capture by 14N. Ther- for 7 DOE These fits demonstrate that the enhancement re- mal neutrons will originate from moderation of fast neutrons ported in Ref. [2] is not significant after introducing a beam- (Tn < 10 MeV) in the liquid scintillator. These fast neu- correlated background. trons are produced from medium energy interactions (Tn > 100 MeV) in the KARMEN iron shield. The liquid scintil- 250 10 lator (PPP) used in the KARMEN detector consists of 75 % o (volume) paraffin oil, 25 % pseudocumene and 2 g/1 PMP (1- 200 - phenyl-3-mesityl-2-pyrazoline)[3, 4]. The chemical formu- lae of the components are (i) paraffin oil, taken as CnH24, (ii) pseudocumene C9H12, (iii) PMP Ci8H2oN2. The nuclear densities in the liquid scintillator material (in units of nuclei/A3) are 0.071 for hydrogen, 0.036 for car- bon and 9.1 • 10~6 for nitrogen leading to the ratio of atomic abundances of UH '• nc '• TIN ~ 7800 : 4000 : 1. It is this nitrogen that can capture neutrons via the reaction 50 14 15 N(n,7) N (1) with an integral 7-energy of 10.8 MeV. The thermal neutron cross-section for this reaction is a «75 mb. The lower en- ergy cut applied to the events in the KARMEN analysis is HMeV[2] with an energy resolution of a /E = 11.5%/VE E Figure 1: [3] (E in MeV), which is 3.5 % or 380 keV for E = 11 MeV. KARMEN data of Ref. [2] fitted with the function y(t) = Thus, the 10.8 MeV 7-events from reaction (1) will be ac- A-e-t^-^ + B-t/Tc foxt
PRECISION MEASUREMENT OF THE MASS OF THE CHARGED PION
D. F. Anagnostopoulos1, G. Borcheri2, J.-P. Egger3, D. Gotta2, M. Hennebach2, P. Indelicate)4, Y.-W. Liu5, B. Manil4, N. Nelms6, L M. Simons5, A. Wells6
R-97-02, IOANNINA1 - JULICH2 - NEUCHATEL3 - PARIS4 - PSI5 - LEICESTER6
A series of experiments to determine the mass of the neg- The pion beam of the TTE5 channel at PSI was injected atively charged pion was finished by a high-statistics mea- into the cyclotron trap II [3], the basic idea of which is to surement in summer 2000 ([1] and expts. R-94.01 and R- wind up the range curve in a weakly focusing magnetic field. 97.02). Here, pionic and muonic transitions from nitrogen In the case of pions, deceleration has to be fast because of the and oxygen were measured. The muonic line served as en- short life time. The energy loss of the pions is then achieved ergy calibration because the muon mass is known to more by thick degraders. About 1% are stopped in a thin-walled than one order of magnitude better than the pion mass [2]. gas-filled target container in the center of the trap at a pres- The circular transitions, TTN(5<7—4/) and /j,O(5g—4/), are sure of 1.4 bar. Length and diameter of the gas cell are not affected by finite-size effects and hence not distorted by 220 mm and 60 mm. Muons, originating from pion decay strong interaction. Furthermore, using dilute targets, electron shortly before capture, are slow enough to be stopped in the refilling is suppressed, thus avoiding any energy shifts from gas cell as well. With a set-up, optimized for muons, the satellite transitions. count rate for muonic atom X-rays is about 4% of the one for pionic atoms. Because of the high pion flux of several 109s^1, this method is still superior to a direct use of a muon 1800 channnel. X- Si 220 reflection *• • The X-rays were reflected in second order by a spheri- 1400 cally bent silicon Bragg crystal cut along the 110 plane and having a radius of curvature of 2.985 m. The X-rays were 1200- recorded in a newly set-up large area detector array of 2 x 3 ' 1000 Charge-Coupled Devices (CCDs). The sensitive area of one 2 800 chip is 24 x 24 mm or 600 x 600 pixels of 40 yum [4]. • 600 CCDs allow an efficient background reduction by analyzing the hit pattern and applying simultaneously a narrow cut on 400 the deposited charge. Such an analysis is essential for low- 200 -I rate experiments in accelerator environments [5, 6]. The aim of the experiment is to reach an accuracy of 1 200 400 600 800 1000 1200 about 1 ppm for the mass of the charged pion, which re- pixel i 40 ^.m quired the accumulation of about 10000 events in each of Figure 1: Simultaneously recorded reflections of the 5-4 the two fines in a running period of several weeks. With a transitions in TTN and /iO using a silicon crystal of 90 mm count rate of about 15 per hour and transition by using an diameter. The sensitive area of the CCD array (not drawn in N2/O2 gas mixture of 90%/10%, the simultaneous detection scale) is 48 x 72 mm2. of both fines (Fig. 1) inherently avoids systematic errors aris- ing from the long-term stability of the experimental set-up. After correcting for the curvature of the image, the reflec- tions are projected to the axis of dispersion (Fig. 2). The distance between the pionic and the muonic lines results in the ratio of the masses of the pion and the muon.
REFERENCES [1] S. Lenz et al., Phys. Lett. B 416, 50 (1998). [2] D. E. Groom et al., (PDG), Eur. Phys. J. C 15, 1 (2000). [3] IKP Annual Report 1997, p. 85 (1997). [4] EEV, England, CCD22 with frame buffer.
400 600 800 1000 1200 [5] D. Gotta et al., Nucl. Phys. A 660, 283 (1999). pixel & 40 (Lin [6] J-P. Egger, Hyperfine Interactions 119, 291 (1998). Figure 2: Projection of the TTN and /iO reflections to the axis of dispersion. 12
A PRECISION MEASUREMENT OF THE MICHEL PARAMETER £" IN POLARIZED MUON DECAY
P. Van Hove1, J. Deutsch1, J. Govaerts1, P. Knowles1 ,R. Medve1, A. Ninane1, R. Prieelsx,J. Egger2, F. Foroughi2, X. Morelle2, L. Simons2, N. Danneberg3, W. Fetscher3, M. Hadri3, C. Hubes3, K Kirch3, K Köhler3, A. Kozela3, J. Lang3, O. Naviliat3,J. Sromicki3.
R-97-06, LOUVAIN1 -PSI2 -ZÜRICH3
Michel parameters describe the various observables in muon- decay. Most of them are known to have values close to the Standard Model (SM) ones with precisions better than a few percent. One notable exception is the parameter £", or the combination (/ = £" /££' - 1) which is zero in the SM. This combination governs the angular and energy dependence of the positron longitudinal polarization in polarized muon de- cay:
# Measurements # Measurements
Figure 2: ANI and Bhabha experimental asymmetry for a where 0 < x < 1 is the normalized energy and z = cos 6, series of 20 measurements of one 1 hour data taking each. 6 being the angle between the muon spin and the positron Each point corresponds to one foil and is computed from momentum, the parameters £, £', £" are all equal to 1 in the two data files of opposite magnetization. The big dots cor- SM. As can be seen in this formula, values of a; close to 1 and respond to processes occuring in the 2nd foil. As is clearly z close to -1, strongly enhance the impact of a non vanishing seen, the analyzing power changes sign between Bhabha and (£" /££' — 1) on PL for highly polarized muons. ANI events In order to avoid the need to determine the absolute polariza- tion with high precision, we will undertake relative polariza- tion measurements. form magnetic field section is performed using three planes of double sided silicon strip detectors resulting in an energy Xn polarized) A = 1 + exp -f (2) resolution of about 1 MeV FWHM. The figure 1 shows the unpolarized) ± T ^-exp amplitude distribution of signals from the p side and the n where Aexp is an energy dependent experimental value and side of one of these detectors. is obtained by : The positron polarimeter, based on the spin dependence of Bhabha scattering (BB) and annihilation in flight (AIF) of _ N(Pß(backward)) positrons on polarized electrons, consists of 2 Vacoflux foils ^exp (3) with opposite magnetization and interleaved wire chambers allowing to determine the nature of the interaction and the where N(P ) is the number of positrons incident on the po- ß foil in which it took place. It should be noted that BB and larimeter for a given number of muons having a polarization AIF have opposite analyzing powers. Pß. Six weeks of measurement are expected to provide a limit of 0.5% on/. A sample of events recorded in the last test with the com- plete setup were roughly analyzed. The rate asymmetry for The full setup is described in [1]. Muons from the nE3 beam Bhabha and annihilation events originating from each foils line at PSI, backward polarized at 95%, are stopped in targets for runs with opposite magnetic polarization is show in fig- that either maintain (Al) or destroy (S) the muon polarization. ure 2. The most energetic positrons of the Michel spectrum are se- lected using solenoidal magnets. A tracking inside a uni- During 6 weeks, in September-August 2000, we performed the production run of the experiment. The reconstruction ef- ficiency of the positron tracking was close to 80% which is the highest possible efficiency taking into account the dead regions of the telescope. The wire chambers worked with an efficiency close to 99 %. Due to acquisition adjustment and beam handling, we recorded about 50% of the expected statistic. Data are now under analysis.
REFERENCES Figure 1: Amplitude distribution of signals recorded from A) [1] P. Van Hove, Ph. D. Thesis, UCL 2000, unpublished. one p-strip and B) from one n-strip. 13
PRECISION MEASUREMENT OF SINGLET /xp CAPTURE IN HYDROGEN
V.A. Andreev1, D. V. Balin1, T. Case3, K. M. Crowe3, J. Deutsch8, P. U. Dick:2, A. Dijksman2, J. Egger2, D. Fahrni2, A. A. Fetisov1, V. A. Ganzha1, J. Govaerts6, F J. Hartmann5, W. D. Herold'2, V. I. Jatsioura1, P. Kammel4, A. G. Krivshich1, 1 1 2 2 1 6 1 E. M. Maev , O. E. Maev , V. E. Markushin , C. Petitjean , G. E. Petrov , R. Prieels , S. M. Sadetsky , G. N. Schapki,in R. Schmidt2, G. G. Semenchuk1, A. A. Vorobyov1, N. I. Voropaev1
R-97-05, GATCHINA1 - PSI2 - BERKELEY3 - URBANA4 - MUNICH5 - LOUVAIN6
In this experiment a 1 % precision measurement of the electronics was also developed and tested together with the singlet capture rate As in the process ßpis —> n + vß is prototype TPC. As a special example, Fig. 1 shows a 60 /xs proposed. The rate As is very sensitive to the weak formfac- time slice with a ß~ stop in the TPC and the decay electron tors of the nucleón, in particular to the induced pseudoscalar emerging at 5 cm from the muon stop location ("diffusion coupling constant gp. The determination of gp will be a rig- event"). This is one of the event types which we must have orous test of modern effective field theories of low energy under full control in the final measurement. QCD [1]. Previous attempts with liquid H2 targets and direct neutron observations could not reach high enough precision because of p¡ip molecule formation in liquid H2 (ortho-para transitions) and because of limited calibration accuracy of neutron counters. Our method is based on a very precise lifetime measure- ment of n~ in hydrogen gas and the comparison with the free + ß decay constant (Ao). The rate As is then determined as the difference between the inverse pTp lifetime and Ao. The pT experiment must be performed in ultraclean, deuterium- depleted H2 gas (protium). Otherwise, the transfer of pT to impurities would induce distortions of the time slope. Trans- fer to deuterium would lead also to distortions due to very large diffusion of ¡id atoms caused by the Ramsauer-Townsend Figure 2: Design drawing of the new clean TPC (stereoview), 3 effect. the sensitive volume is 15x12x30 cm
To achieve 1% precision in As, the exponential time dis- Based on the experience gained in the test runs and on the tribution of //-e decays must be determined with a precision data analysis, we have designed the final apparatus with an better than 10~5 requiring a statistics of at least 1010 an- ultra clean TPC as its center part (Fig. 2). The TPC with 2 alyzed good events. Events from muon stops outside the entrance chambers will be mounted in a hydrogen pressure H2 gas must be strongly suppressed. Moreover, the system- tank with thin cylindrical Aluminum walls (d~2 mm). Elec- atics of the electronic time measurement must be carefully tron detection and tracking will be made outside the tank with checked. two Sindrum chambers and a scintillator hodoscope. This ar- run= 224 event=1282 disp= 26 rangement removes dangerous electronic cross talk between muon and electron tracks and allows observation of the /xe decays in a cylindrically symmetric geometry with a solid
I I ; I angle of 75%. y(m-F Our system is designed to handle muon stop rates up to 50 kHz. The electrical field in the TPC is ~2.3 kV/cm, cor- I * responding to 0.5 cm//js drift velocity. The negative charges from ionizing particles drift down to a plane of 75 anode wires and 32 perpendicular cathode strips where the signals are amplified and read out. All test runs were made so far with regular clean hydrogen which is not good enough for the I I : * I 5 10 15 20 25 capture measurement. In the meantime, however, our chem- x (e-PC) istry group demonstrated successfully the production of ultra I I ; I clean protium at impurity levels below 10~8. In fall 2001, we expect to be ready for runs with the final TPC. REFERENCES Figure 1 : Display of a diffusion event observed in the TPC [1] J. Govaerts and J.-L. Lucio-Martinez, To meet all these challenges, we developed in 1997-2000 Nucl. Phys. A 678, 110 (2000). a time projection chamber (TPC) and several proportional chambers operating in pure H2 gas of 10 bar and success- [2] PSI Ann. Rep 1997,1, 32; PSI Sci.Rep. 1998,1,20; PSI fully tested them on the yuE4 beam [2]. A new data collec- Sei. Rep. 1999,1, 15; tion system with continuously operating deadtime-free TDC P. Kammel et al., Nucl. Phys. A 663/A 664, 911c (2000). 14
PIONIC HYDROGEN
D. F Anagnostopoulos1, G. Bordiert2, W. Breunlich3, M. Cargnelli3, H. Fuhrmann3, D. Gotta2, M. Giersch3, A. Gruber3, M. Hennebach2, P. Indelicato4, T. Jensen5'6, Y.-W. Liu6, B. ManilA, V. E. Markushin6, J. Marton6, N. Nelms7, L. M. Simons6, H. Zmeskal3
R-98-01, IOANNINA1 - JÜLICH2 - VIENNA3 - PARIS4 - ZÜRICH5 - PSI6 - LEICESTER7
The measurement of the hadronic shift and broadening els = 7.080 ± 0.035 eV (attractive) (1) of the ground state in pionic hydrogen gives access to fun- damental properties of the pion-nucleon interaction. On- which is in agreement with the result of the previous experi- going improvement in the calculation of strong-interaction ment eu = 7.102 ± 0.038 eV [7]. phenomena by Heavy-Baryon Chiral Perturbation Theory al- From the limited statistics of the engineering run, no con- lows predictions with an accuracy of a few per cent, which clusions can be drawn on density effects yet. A high-statistics should be experimentally tested (see [1, 2] and references run for the shift measurement is foreseen in summer 2001. therein). Further measurements will investigate in detail the pressure New techniques that have been originally developed for dependence of the line widths of various pionic hydrogen the precision spectroscopy of X-rays from antiprotonic hy- transitions to establish the pure hadronic effect with the en- drogen [3] and for the determination of the charged pion visaged accuracy. mass [4] will be used in a new series of measurements [5,6]. The final aim is to achieve an accuracy for the hadronic broadening Tis of about 1 %, which is an improvement of al- most one order of magnitude as compared to previous pre- cision experiments [7]. A similar improvement is also ex- pected for the hadronic shift eis. The first goal of the new experiment is to establish a shift value independent of pressure. Such a pressure dependence could originate from the formation of complex molecular structures like (irpp)+pee [8]. The irO(6h—5g) transition, which is not affected by the strong interaction, serves as en- ergy calibration. At lower pressures, a simultaneous mea- surement of both the hydrogen 3p-ls and the oxygen line is possible. This allows an energy calibration basically free of systematic errors. 240 In late 2000, an engineering run took place at the TTE5 Figure 1: Simultaneously recorded reflections of the high-intensity pion channel at the Paul-Scherrer-Institut (PSI). TTO(6—5) calibration transition and the 7r~p(3—1) transition. The experimental set-up was similar to the one used for the pion mass measurement [4]. As target, a cryogenics sys- The spectrum displays about | of the total statistics accumu- tem was installed in the center of the cyclotron trap, where lated for the H2/O2 mixture. about 1 % of the incoming pions are stopped in gas at normal temperature and pressure. Higher densities are achieved by cooling. The X-rays were reflected in first order by a spher- REFERENCES ically bent silicon Bragg crystal cut along the 111 plane. To [1] N. Fettes, U.-G. Meissner, keep aberrations small, the crystal was covered by an aper- Nucl. Phys. A 676, 311 (2000); hep-ph/0101030. ture restricting the reflecting area horizontally to 60 mm. A large-area array of Charge-Coupled devices (CCDs) served [2] V. E. Lyubovitskij, A. Rusetsky, as an X-ray detector. The response function of the spectrom- Phys. Lett. B 494, 9 (2000). eter was obtained from the TTC12 (5
RARE K+-DECAYS IN FLIGHT (BROOKHAVEN AGS E865)
R. Appel4, G. S. Atoyan5, B. Bassalleck2, D. R. Bergmann4, D. N. Brown3, N. Cheung3, S. Dhawan4, H. Do4, J. Egger7, S. Eilerts2, C. Felder3, H. Fischer2, M. Gach3, W. D. Herold7, V. V. Isakov5, H. Kaspar4'7, D. E. Kraus3, D. M. Lazarus1, P. Lichard3, L. Leipuner1, J. Lowe2, J. Lozano4, H. Ma1, W. Menzel6, S. Pislak4'8, A. A. Poblaguev5, V. E. Postoev5, A. Proskurjakov5, P. Rehak1, P. Robmann 8, Alexandre Sher 3, Aleksey Sher 8, /. A. Thompson3, P. Truöl4'8, A. Walid4, H. Weyere'7, M. E. Zeller4
E-91-02.1, BNL1 - NEW MEXICO2 - PITTSBURGH3 - YALE4 - INR MOSCOW5 - BASEL6 - PSI7 - ZÜRICH8
Experiment E865 at the Brookhaven AGS [1] was set Sher, University of Zürich), the analysis of the final Kviie up primarily to search for the lepton flavor violating decay data set taken in 1998 has not been completed yet. We expect + + + K —>• ir n e~ (K^ue) [2] with more than an order of mag- however to improve the sensitivity by at least a factor of three nitude increased sensitivity. The flexibility of the apparatus beyond our published limit of 2.8 x KT11 [2]. allowed also to obtain high statistics event samples on the The analysis of the Ke4 data, performed by S. Pislak, has following decay modes, where existing data were scarce: been completed and lead to the new, quite precise value for the s-wave TTTT scattering length [7]: •K ' e ' e (i™) [3]| (K,,,) [4]; ag = 0.228 ± 0.012 (stat.) ± 0.003 (syst.). + + + + + + 7r 7r~e z/e (Ke4); ß e 'vu ;e e e ve Figure 1 shows the phase shift difference ¿§ ~^l as a function From the K„ and the K ± data we have also extracted con- ßli e of the 7T+7T~ invariant mass extracted from our data in com- siderably reduced upper limits for other lepton flavor vio- parison to those from an older experiment [8] with twelve lating decay modes like 7r+e+\iT, n~/i+e+, n~ß+ß+, and times less statistics, which measured a^ = 0.26 ± 0.05. 7T-e+e+ [5]. Aside from the scattering length, which agrees well with the latest prediction from chiral QCD perturbation theory (ChPT) ag = 0.220 ± 0.005 [9], we have also extracted the momentum transfer dependence of the axialvector and vector decay form factors, which are an essential ingredient for the determination of the coefficients of the ChPT Hamiltonian to order O(p4) [10].
REFERENCES [1] R. Appel et ai, submitted to Nucí. Instrum. Meth.,(January 2001). [2] R. Appel et ai, Phys. Rev. Lett. 85, 2450 (2000). [3] R. Appel et al, Phys. Rev. Lett. 83, 4482 (1999). [4] H. Ma et al, Phys. Rev. Lett. 84, 2580 (2000). i.28 0.3 0.32 0.34 0.36 0.38 Mm [GeV] [5] R. Appel et al, Phys. Rev. Lett. 85, 2877 (2000). [6] S. Adler et al, Phys. Rev. Lett. 85, 2256 (2000); S. Heintze et al, Nucl. Phys. A 149, 365 (1979). Figure 1 : Phase shift difference SQ — S\ as a function of the + 7T 7T~ invariant mass. The curves shows the result of the [7] S. Pislak ef a/., to be published; fit from which the scattering length was extracted (Geneva- M. Zeller, Proc. Chiral Dynamics 2000, Saclay: ref. [8]). TJNL, Newport News, VA (July 2000); P. Truöl, Proc. Int. Conf. Heavy Quarks at Fixed Target The analysis of the Kivl, data is still in progress. Pre- liminary results indicate, that we will be able to determine (HQ2K), Rio de Janeiro, Oct. 2000, hep-ex/0012012. for the first time separately the electroweak vector and axi- [8] L. Rosselet et al, Phys. Rev. D 15, 574 (1977). alvector kaon formfactors Fy and FA , while previous exper- iments [6] with real photons in the final state were sensitive [9] G. Colangelo et al, Phys. Lett. 488, 261 (2000). to\FA+ Fv\ only. [10] G. Amoros et al, Phys. Lett. B 480, 471 (2000); Though considerable progress in the reduction of the im- Nucl. Phys. B 585, 293 (2000). mense amount of data has been made last year (Thesis A. 16
HIGGS CANDIDATES IN e+e~ INTERACTIONS AT = 206.6 GeV
A. J. Barczyk1, K. Deiters1
L3 Collaboration, PSI1
In a search for the Standard Model Higgs, carried out on The search for the Standard Model Higgs boson at LEP 212.5 pb~x of data collected by the L3 detector [1] at the is based on the study of four distinct event topologies repre- highest LEP centre-of-mass energies, including 116.5 pb^1 senting approximately 92% of the HZ decay modes: qqqq, above T/S = 206 GeV, an excess of candidates for the pro- qqvV, qql+l~ (l=e,/i,r) and T+r~qq. With the exception + cess of HZ —> T T~ qq7 the analyses for each channel are opti- mized for H —>• bb, since this represents about 74% of the e+e- ->• Z* ->• HZ Higgs branching fraction in the mass range of interest. The details of the analysis will be presented in a forthcoming pub- is found for Higgs masses near 114.5 GeV. Smaller produc- + lication. tion processes through W W~ and ZZ fusion, are also con- sidered. All significant signal decay modes are investigated. Four-fermion final states from W- and Z-pair production, as By combining all the search channels, we compute the well as e+e~ —> qq{^), make up the largest sources of back- confidence level for the data to be compatible with signal ground. plus background or background only. Our data indicate the most likely mass of the Higgs candidates to be 114.5 GeV. For an assumed Higgs boson of this mass, the confidence level to be consistent with a background only hypothesis is calculated to be 0.09, equivalent to 1.7 standard deviations 10- from the background expectation. The confidence level to be consistent with signal plus background is 0.62. Figure la) d shows the signal-to-background ratio for all channels com- bined assuming a Higgs mass of 114.5 GeV. After a cut on a the final discriminant, Figure lb) displays the number of > -I events versus the signal efficiency. The excess of data is con- 10 - sistent with the signal expectation.
In data collected with the L3 detector at ^/s = 206.6 GeV, we have observed an excess of events above background which is compatible with a Standard Model Higgs boson of mass 114.5 GeV. High-weight events are seen in different decay channels qq~v~U and qqqq which are characteristic of Higgs production together with a Z boson. These data from Data L3, together with those of other LEP experiments [2] suggest Background the first observation of the Higgs boson. Signal + Background REFERENCES [1] L3 Collaboration., B. Adeva et al., Nucl. Inst. Meth. A 289, 35 (1990); J. A. Bakken et al., Nucl. Inst. Meth. A 275, 81 (1989); 0. Adriani et al., Nucl. Inst. Meth. A 302,53 (1991); B. Adeva et al., Nucl. Inst. Meth. A 323, 109 (1992); 0.05 0.1 0.15 0.2 0.25 K. Deiters et al., Nucl. Inst. Meth. A 323, 162 (1992); Signal Efficiency M. Chemarin et al., Nucl. Inst. Meth. A 349, 345 (1994); M. Acciarri et al., Nucl. Inst. Meth. A 351, 300 (1994); G. Basti et al., Nucl. Inst. Meth. A 374, 293 (1996); Figure 1: a) The logarithm of the signal-to-background ra- A. Adam et al., Nucl. Inst. Meth. A 383, 342 (1996). tio for all channels combined assuming a Higgs mass of 114.5 GeV. The total number of events is also indicated, cor- [2] LEP Higgs Working Group, responding to a signal efficiency of 31.4%. b) The number of "Standard Model Higgs Boson at LEP: Results with the events above a cut on the final discriminant, versus the signal 2000 Data, Request for Running in 2001", efficiency. Submitted to the LEP Committee and the CERN Re- search Board (2000). 17
TEST OF SUPERSYMMETRY USING IN-BEAM SPECTROSCOPY OF 196Au
F. Corminboeuf, M. de Huu1, L. Genilloud1, G. Graw3, J. Groger2, C. Gunther1, J. Jolie1, A. Metz3, N. Warr1, T. WendeP,
Z-95-05, FRIBOURG1 -BONN2-LMUMUNCHEN3
Symmetry is an important concept in physics. In finite (d, t) and polarised (d, a) reactions [5]. In a later stage 7 — 7 many-body systems, it appears as time reversal, parity and coincidences were measured at the Yale WNS tandem ac- rotational invariance but also in the form of dynamical sym- cellerator. These studies allowed the observation of many metries. In the field of dynamical symmetries, a remarkably new excited states, among which 25 excited negative parity versatile model was elaborated in the mid seventies by Arima states below 500 keV. and Iachello [1]. This Interacting Boson Model considers 2N Figure 1 shows the resulting energy spectrum for the low- valence nucleons which are coupled to TV nucleon pairs as s est negative parity states in 198 Au [6]. The excited states are (I = 0) and d (I = 2) bosons. The even-even nucleus is, then, assigned by combining all experimental data. In view of the described in a space spanned by the irreducible representa- extreme complexity of odd-odd nuclei in this mass region, tions (irreps) [N] of UB (6). The model turned out to be very one can conclude that a good agreement between theory and successful for medium-heavy and heavy nuclei. Moreover, a experiment is obtained. This provides a strong argument for number of nuclei have low-lying spectra, which resemble in the existence of dynamical supersymmetry in atomic nuclei. detail one of the three dynamical symmetries of the model. This work was supported by the Swiss National Science In these cases, the model has an analytic solution. Foundation and the DPG (grants IIC4 Gr 894/2 and Gu 179/2). A further step towards unification was made in the early eighties when Iachello and coworkers introduced (dynami- cal) supersymmetry to connect odd-even and even-even nu- clei by embedding a Bose-Fermi symmetry into a graded Lie algebraU(6/M) [2,3]. The supersymmetricirrep [AT}, then, spanned a space that describes both an even-even nucleus with N bosons and an odd-A nucleus with N — 1 bosons and the odd fermion. If a common set of parameters describes the excited states of such two nuclei, one concludes that the nuclei exhibit a (dynamical) supersymmetry. Van Isacker et al. [4] introduced an extension of this model allowing the description of a quartet of nuclei, using the same algebraic form of the hamiltonian. This extended supersymmetry (or neutron-proton super- Figure 1: Comparison between the predicted and measured symmetry) deals with boson-fermion and neutron-proton de- level scheme of198 Au grees of freedom. The quartet of nuclei consists of an even- even nucleus with (J\fv + Af^) bosons, an odd-proton and an odd-neutron nucleus, both with (J\fv +A^) -1 bosons and an odd-odd nucleus with (Nv + Afv) — 2 bosons. The extended REFERENCES supersymmetry relates the often very complex structure of [1] F. Iachello, A. Arima, The interacting boson model, the odd-odd nucleus to the simpler ones of even-even and (Cambridge University Press, Cambridge), (1987). odd-A systems. It was realised from the beginning that the ultimate candidate for the test would be the odd-odd nucleus [2] F. Iachello, Phys. Rev. Lett. 44, 772 (1980). 198 Au [4] since the quartet i94,i95pti95,i96Au contams tne nuclei 194pt-195Pt which are considered to be the best exam- [3] A.B. Balantekin, I. Bars, F. Iachello, ple of the U(6/12) supersymmetry. Nucl. Phys. A 370, 284 (1981). Since the experimental level scheme of 196Au was still 196 [4] P. Van Isacker, J. Jolie, K.L.G. Heyde, A. Frank, poorly known, an experimental study of Au was started in Phys. Rev. Lett. 54 , 653 (1985). 1995 in a Fribourg/Bonn/Munich collaboration. The exper- imental program included in-beam gamma-ray and conver- [5] A. Metz, J. Jolie, G. Graw , R. Hertenberger, J. Groger, sion electron spectroscopy following the reactions 196Pt(d,2n) C. Gunther, N. Warr, Y. Eisermann, and 196Pt(p,n) at the cyclotrons of the PSI (Viiligen, Switzer- Phys. Rev. Lett. 83, 1542 (1999). land) and at the University of Bonn. In parallel high reso- lution transfer experiments were performed at the Tandem [6] J. Groger et al., Phys. Rev. C 62 , 064304 (2000). accelerator of the TU/LMU Miinchen using (p,d), polarised 18
STUDY OF 100Ru AT THE PHILIPS CYCLOTRON AND AT SINQ
F. Corminboeuf1, S. Drissi1, L. Genilloud1, J. Jolie1, J. Kern1, H. Lehmann1, N. Warr1,
Z-96-04, FRIBOURG1
In the framework of the Interacting Boson Model [1], vi- brational nuclei are described by the U(5) dynamical sym- metry. New interest in the study of vibrational nuclei arose after experiments on 112Cd isotopes at PSI showed that they exhibited a multiphonon structure up to high phonon num- bers [2]. The systematics of vibrational nuclei along the nu- clear chart was studied by J. Kern et al. [3] and 100Ru was proposed as a possible candidate for a vibrational nucleus. This possibility was especially attractive, because this nu- cleus is situated far from a closed shell and as such its struc- ture should be rather free of particle-hole excitations. There- fore a systematic study of 100Ru was undertaken. The in-beam experiments consisted of the measurement of 7-ray excitation functions, 7-ray angular distributions and 77-coincidences. The excited nucleus 100Ru was produced by bombarding a 97.6% isotopically enriched 98Mo target, with a beam of a particles from the Philips variable energy cyclotron. In order to also extend the knowledge on high- energy low-spin states a second series of experiments was started using the cold neutron beam at the PGA installation of SINQ. Here a 150 mg 98.1% enriched "Ru target was used. The detailed set-up is shown in Figure 1.
Neutron beam 12600 13000 13400 13800 14200 14600 from SINQ CHANNELS
Anti-Compton Pair Figure 2: Primary gamma-ray spectrum observed using the Spectrometer Spectrometer pair spectrometer of the PGA installation at SINQ. neutron lens combined with crystal spectrometer data on secondary gamma rays obtained at ILL. In this way 36 new levels could be ob- served [5]. Comparison with the U(5) symmetry revealed no two particle-hole intruding states below 1.7 MeV and the need for a small SU(3) breaking of the U(5) symmetry [5]. We acknowledge the staff of the Philips cyclotron and of 1.11 1 1 SINQ for the excellent beams they provided. This work was supported by the Swiss National Science Foundation.
REFERENCES Figure 1: PGA set-up used at SINQ to measure the primary capture gamma rays. [1] F. Iachello, A. Arima, The interacting boson model, (Cambridge University Press, Cambridge), (1987). The very small target mass and capture cross section was [2] M. Deleze, S. Drissi, J. Jolie, J. Kern, J. P. Vorlet, compensated by the use of the neutron focusing lens of the Nucl. Phys. A 554,1 (1993). PGA installation [4], which permitted to enhance the neutron flux of 6.9x107 on the target by a factor 6.4. The primary [3] J. Kern, P. E. Garrett, J. Jolie, H. Lehmann, gamma-rays were then observed using the pair spectrometer Nucl. Phys. A 593, 21 (1995). of the PGA installation. These primary gamma-rays, which attain energies of several MeV, reveal directly the excited [4] M. Crittin, J. Kern, J.-L. Schenker, states in 100Ru, because the capture state at 9.673 MeV has a Nucl. Instrum. Meth. A 449, 221 (2000). well-defined energy. Figure 2 shows the observed spectrum [5] L. Genilloud, H. G. Borner, F. Corminboeuf, Ch. Doll, in the energy domain of 6.5-8.5 MeV. S. Drissi, M. Jentschell, J. Jolie, J. Kern, H. Lehmann, To construct the final level scheme, the PSI data were N. Warr, Nucl. Phys. A 662,3 (2000); A 669,407 (2000) 19
MODELLING FISSION IN NUCLEAR REACTIONS: I REACTION CROSS-SECTIONS
F. Atchison1 1Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
1 Introduction that special treatment is required for large fissility nuclei. Semi-empirical formulae have been developed[l] that yield These are handled using the Vandenbosch, Huizenga[6] cor- (i) the ratio of the fission and neutron emission widths in the relation to give the asymptotic fission probability, with a double- de-excitation of states over a large range of nuclear charge, humped fission barrier and a Fermi distribution for the low- mass and excitation-energy and (ii) the nuclear states of the lying neutron states to describe the threshold region. associated scission products; these allow fission to be treated Calculations of fissioning systems consistently in calculations of nuclear reactions. Full details of the physics, formulae and parameter value se- Absolute cross-section values are obtained using the fission lection are given in [1] together with a selection of compar- formulation in a new evaporation code capable of handling isons between measured and calculated values. the wide range of nuclear states involved. Description of As an example of the capability of the new formulation to the entrance channel is made using either the optical-model reproduce low energy neutron induced fission, the calculated and pre-equilibrium emission routines from the ALICE95[2] and experimental values for the fission cross-section in the code or the MECC7 intra-nuclear cascade code of Bertini[3]. threshold region for 238U and 232Th are shown below. The 2 Theoretical considerations entrance channels were calculated using the optical model routines from [2]. 2.1 General considerations The basic assumptions made about the fission process are (i) that it is relatively slow and so competes only with evap- oration and similarly depends only on the immediate nuclear state and not how it was reached, (ii) it is mainly a collec- tive process but with some influence from shell and single particle effects, (iii) it involves barrier penetration; traversal of the fission barrier (and hence determination if the system will fission) occurs at deformations well before actual scis- sion, which means that the process can be separated into two independent steps, crossing the barrier and formation of the Neutron Energy CMBV> scission products. An important consequence of the first assumption is that all stages of the de-excitation need to be allowed to contribute which means that reactions involving high excitation ener- gies (e.g. those induced by medium energy particles) need a treatment of fission for a wide range of nuclear states. The collective aspects of the fission process are described by the liquid-drop model; this means that (i) the fissility (Z2/A) is a good parameter for formulae to interpolate/extrapolate fission parameters, (ii) the shape of the deformation energy potential function is parabolic and the penetrability may be Figure 1: Calculated and measured total fission cross- solved explicitly. Shell effects are significant at low excita- sections for neutron interactions with 238U and 232Th. tion energies and lead to many of the actinides having double humped fission barriers. 2.2 Reaction width REFERENCES Channel widths are calculated from the ratio of the open [1] F. Atchison, PSI-report 98-12 (1998). channels to contributing states multiplied by some suitable vibration period (Willets[4]). Calculation of the fission width [2] M. Blann, Private communication (1995). is reasonably clear near the nuclear ground state and at large [3] H.W. Bertini, M.P. Guthrie, excitations when it reduces to the standard statistical model Nucl. Phys. A169, 670 (1971). treatment[5]. In this latter case, values for open parame- ters (level density parameters and fission barriers) have been [4] L. Willets, Phys Rev. 116, 372 (1959). fixed by fitting measured excitation functions to formulae de- [5] N. Bohr, J.A. Wheeler, Phys. Rev. 56, 426 (1939). rived using the statistical model and then constructing poly- nomials, using the fissility as parameter, to derive values for [6] R. Vandenbosch, J.R. Huizenga, Paper P688, Proc 2nd unmeasured nuclear states. Geneva Conf on the Peaceful use of atomic energy, Difficulties occur for low excitation energy states which means Vol. 15, Geneva (1958). 20
MODELLING FISSION IN NUCLEAR REACTIONS: II MASS DISTRIBUTION
F. Atchison1 1Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
Introduction Full details of the physics, formulae and parameter value se- lection are given in [2] together with an extensive selection The results from a uniquely detailed study of the fission of of comparisons between measured and calculated values. W, Au, Pb and Th induced by 190 MeV protons have been publishedfl] recently. The particularly interesting feature 3 Calculation is the inclusion of production cross-sections for several iso- Absolute cross-section values for these medium energy inter- topes of the same element for the four systems; this allows actionsfl] have been obtained using the fission formulation a searching test of the predictive powers of the recently de- in a new evaporation code, which can handle the wide range veloped semi-empirical fission formulae[2] in the medium energy range. of nuclear states involved, and the MECC7 intra- nuclear cas- cade code of Bertini[3] to calculate the entrance channel. 2 The selection of scission parameters The accompanying figure shows the calculated and measured The broad features of the partitioning of energy, charge and isotopic variation of production cross-section for the same nucleons between the scission fragments are known from ex- five elements (Zn, Rb, Y, Nb and Sb) as produced by inter- periment. The main features that are incorporated into the actions with the Au, Pb and Th targets; the calculated (abso- modelling are (i) scissions are complete and into two frag- lute) cross-section values are shown as a continuous curve. ments, (ii) large fissility nuclides divide their mass asymmet- The agreement between the experimental results and calcu- rically at low excitation energies (the peaks have a width of lation is rather reasonable. several AMU with edges that are Gaussian in form but the distributions are not simple Gaussian functions and the en- REFERENCES ergy partition between the two fragments is non- uniform), (iii) at higher excitation energies competition comes from an [1] M.C. Duijvestijn, AJ. Konig, J.P.M. Beijers, A. Ferrari, increasing and eventually dominant contribution from sym- M. Gastal, J. van Klinken, R.W. Ostendorf, metric division (It is assumed that only the symmetric mass- Phys. Rev. C 59, 776 (1999). division occurs for elements below Radium), (iv) nuclear [2] F. Atchison, PSI-report 98-12 (1998). charge selection is made on the basis of "equal displace- ment from stability", with 0.78 charge unit standard devia- [3] H. W. Bertini, M. P. Guthrie, tion Gaussian distributions. Nucl. Phys. A 169, 670 (1971).
85 95 105 115 90 100 110 120 110 120 130 140
Fig. 1. Calculated and measured cross-sections for the production of Zn, Rb, Y, Nb and Sb isotopes in 190 MeV proton interactions with Au, Pb and Th. 21
MEASURING /xD3He FUSION
M. Augsburger1, V. F. Boreiko2, V. M. Bystritsky2S, W. Czaplinski5, A. Del Rosso1, C. Donche-Gay1, M. Filipowicz5, O. Huot1, P. Knowles1, F. Mulhauseris, V. N. Pavlov2, F. M. Pen'kov2, C. Petitjean3, N. P. Popov4, V G. Sandukovsky2, L. A. Schaller1, H. Schneuwly1, V. A. Stolupin2, J. Wozniak5
R-98-02, FRIBOURG1 - JINR2 - PSI3 - MÜNCHEN4 - CRACOW5
The goal of this experiment is to measure the fusion rate Strong evidence for the fusion can be seen in the com- of the /id3 He molecule via the reactions parison of the distribution of events in the dE/dx-E plane (Figs. 1, 2). Of note are the excess of events (i.e., events 3 above the expected background level) in the expected energy /Lid+ He ^ [i + a(3.7 MeV) + p(14.6 MeV) (1) region 9-13 MeV seen in Fig. 2. The excess events, if at- ^ /x5Li + 7 +16.4 MeV. (2) tributed to the fusion reaction Eq. (1), correspond to a fusion rate A/ = 3(2) x 105s~1. Clarifying the provenance of these The main process, the production of 14.6 MeV protons, should events and reducing the uncertainty on the result is now the lead to the determination of the fusion rate A/. focus of our work on this experiment. In September-October 1999, our collaboration performed a five week experiment in the [iE4 channel at PSI. This time was planned as one week setup and 4 weeks data production, and this was achieved. Measurements with pure deuterium, pure helium, and mix- tures of deuterium and 5% 3He were performed. Two dif- ferent pressures were used in the mixture to obtain relative liquid hydrogen densities $ = 0.0573 and $ = 0.168. Data for a total of 1.2 x 1010 good muons for the low density mea- surement were collected. The target was designed for the installation of three (dE/dx — E)-Si detector pairs, namely Sijjp, SIDO, and SIRI, located above, below, and to the right of the beam. The £7—Si detectors are 4 mm thick, whereas the dE/dx-Si de- tectors have a thickness of 360 [im. Using these detector pairs protons could be separated from other charged parti- 0 5 10 15 20 cles, like deuterons. Scintillators are located above (Eup), Energy in E (MeV) below (Epo), to the left (ELE), and right (ER/) of the beam. They detect the muon decay electrons coming from the tar- Figure 2: The same data as Fig. 1 with the added requirement that get. Details about the target and setup can be found in Refs. [ 1, a muon decay electron be seen between 0.2 to 5 [is after the proton event. Contours are spaced 2 counts apart. 2,3].
In conclusion, we have seen proton events with charac- teristics consistent with the fusion Eq. (1). The analysis is currently focusing on the details necessary to prove conclu- sively that the signal is from fusion. The continuation of the experiment to look for [id + 4He fusion can only be evaluated after the complete analysis of the present data.
REFERENCES [1] A. Del Rosso et ai, Hyperfine Interactions 118, 177 (1999). [2] M. Augsburger et al., PSI Sei. Rep. 1999,1, 16. 10 15 20 25 30 Energy in E (MeV) [3] V. F. Boreiko et al, Nucl. Instrum. Meth. A 416, 221 (1998). Figure 1: Events in the dE/dx-E plane between 0.1 [is and 3 [is after the arrival of the muon. Electrons are seen in the lower left of the plot; contours are spaced 200 counts apañ. 22
HIGH-RESOLUTION STUDY OF HEAVY-ION-INDUCED THORIUM AND URANIUM Lj X-RAY SPECTRA
D. Banas1, D. Castella2, D. Chmielewska3, D. Corminboeuf ', J.-Cl. Dousse2,1. Fijal3, J. Hoszowska4, M. Jaskola3, A. Korman3, T. Ludziejewski3, Y.-P. Maillard2, O. Mauron2, M. Pajek1, M. Polasik5, P.-A. Raboud2, J. Rzadkiewicz3 andZ. Sujkowski3
Z-99-05, KIELCE1 - FRIBOURG2 - SWIERK3 - GRENOBLE4 - TORUN5
In asymmetric collisions of heavy-ions with atoms multi- ple vacancy states are formed as a result of the strong Coulomb interaction between the projectile nuclear charge and the elec- trons of the target atoms. Rich and valuable information about the heavy-ion-induced multiple ionization and the dy- namics of the collisions can be gained from the observation of the satellite structure characterizing the target x-ray emis- sion spectra. For studying the M- and ./V-shell multiple ion- ization, the L — N and L — O x-ray transitions are well suited because their energies are strongly influenced by the number of vacancies in the outer shells. We report on high-resolution measurements of the satel- lite structure accompanying several Lj x-ray transitions in Th and U metallic targets excited by impact with 230 MeV and 360 MeV oxygen ions. The measurements were per- formed at the variable energy cyclotron of PSI by means of high-resolution x-ray spectroscopy, using the transmission Dumond type bent crystal spectrometer installed in the area NE-B for the observation of the target x-ray emission. The instrumental broadening of about 10 eV of the spectrome- ter allowed us to resolve the M satellites of the L% — N4,
L\ — N2 and L\ — N3 transitions in both U and Th. More- 19.4 19.5 19.6 19.7 19.8 19.9 20.0 over, in the 360 MeV oxygen-thorium collision, resolved TV Energy [keV] x-ray satellites of the L-2 — O 4 transition could be observed, to our knowledge, for the first time (Fig. 1). Figure 1: High-resolution L\ — N¡ and Li — O 4 x-ray spec- The measured x-ray spectra contained information on the tra of Th excited by impact of 360 Mev O7+ of 360 Mev ionization probabilities for M-, N-, and O-shells at the mo- O7+ ions. Comparison with results of simulation calcula- ment of the L-x-ray emission. By applying adequate correc- tions. Note the resolved N- satellites of the L2 - O4 transi- tions for the vacancy rearrangement processes occuring in tion. The L2 absorption edge is shown enlarged in the inset. the target atoms prior to the L x-ray emission, the ionization probabilities for the direct Coulomb excitation at the moment of the collision can be deduced. The results will be discussed in terms of available theoretical approaches such as the geo- metrical model and the semiclassical approximation (SCA). Energies and intensities of the observed x-ray diagram and satellite lines will be compared to theoretical predictions of multiconfiguration Dirack-Fock (MCDF) calculations. 23
FIRST DIRECT OBSERVATION OF LONG-LIVED 2S-STATES IN MUONIC HYDROGEN
H. Daniel1, F J. Hartmann1, P. Hauser3, F. Kottmann2, V. E. Markushin3, M. Muhlbauer1, C. Petitjean3, R. Pohl2'3, W. Schott1, D. Taqqu3,
R-97-04, TU MUNICH1 - ETH ZURICH2 - PSI3
An experiment is being under preparation at PSI to deter- a quenched np(2s) mine the Lamb shift (25 — 2P energy difference) in muonic b Coul. de-excit. n—>2 hydrogen atoms. It is based on the availability of a suffi- c Coul. de-excit. n—>3 ciently high population of long-lived //p(25) atoms. Un- d continuum 1/128..64 eV til recently there was only indirect experimental evidence for their existence. It resulted from the analysis of the up kinetic energy distributions measured at hPa H2 pressures which showed that a considerable part of the yup(25) atoms is slowed down below the 25 — 2P energy threshold where collisional 25-quenching is forbidden in first order[l]. The principle of the kinetic energy experiment is to mea- sure the time-of-flight (TOF) of yup atoms, produced near the axis of a 20 cm long cylindrical gas target, to the gold-coated wall. The muon is there transferred to gold and /iAu X- rays of MeV energies are emitted which are detected by a large Csl crystal surrounding the target. Various target diam- Figure 1: Early part of the TOF spectrum taken at 64hPa eters between 7 mm and 58 mm were used. Smaller targets H2 pressure in the 58 mm diameter target, together with a are more sensitive to smaller kinetic energies, and the use of set of calculated functions fitted to the data. The thick func- different target diameters allows a consistency check of our tion corresponds to the resonantly quenched //p(25) result- method [2]. ing in a 900 eV kinetic energy component convoluted with a (fitted) 25 lifetime. The full fit function includes, besides The TOF spectra were fitted with a superposition of Mon- a "continuum"-energy distribution, some discrete high en- te Carlo generated time spectra for individual kinetic ener- ergies from low-n Coulomb deexcitation. The dashed peak gies. The resulting distribution of kinetic energies extend indicates the measured stop time distribution. The measured from below 1 eV up to several tens eV, depending on gas background and a kinetic energy scale corresponding to the pressure. The mean value steadily increases from ~ 2 eV TOF are also shown. at 0.25 hPa to ~ 6 eV at 16 hPa. The pressure dependence demonstrates the importance of collision-induced accelerat- ing cascade processes at high n-levels which are attributed to minary results from a detailed analysis confirm the fraction radiationless Coulomb-deexcitations where the muon transi- of ~ 1.5% of long-lived /xp(25) atoms previously found by tion energy is transformed to kinetic energy of the colliding the indirect method. Simultaneous analysis of the time distri- atoms. butions measured at 16 and 64 hPa for 20 and 58 mm target Surprisingly the TOF spectra measured at 16 and 64 hPa diameters will provide also information on the yup(25) life- show a pronounced component at early times, correspond- time. ing to /ip energies of nearly 1 keV (see Fig. 1). After a The present data are the first direct observation of metastable careful analysis of these data it became clear that this cor- yup(25) atoms. They give also evidence for a new molecu- responds to an effect which was predicted by Froelich and lar cascade process which is predicted to be important also at Flores-Riveros [3]: High-energetic (~ 1 keV) /xp(15) atoms higher levels n > 2 for gas pressures above 1 bar [4]. are produced by resonant molecule formation from the 25- state and subsequent autodissociation REFERENCES
H2 [1] R. Pohl et al., Hyperfine Interactions 127, 161 (2000). /up(15)+p [2] F. Kottmann et al., Hyperfine Interactions 119, 3 (1999). In this process, which has been discussed in more detail in [3] P. Froelich and A. Flores-Riveros, ref.[4], the 25 — 15 energy difference of ~ 2keV is shared Phys. Rev. Lett. 70, 1595 (1993). among the /xp(15) and one proton. This results in /up(15) atoms with a kinetic energy of ~ 900 eV. [4] S. Jonsell, J. Wallenius, P. Froelich, Similar components of fast //p(15) atoms were also mea- Phys. Rev. A 59, 3440 (1999). sured at 16 and 4 hPa, where the 25-lifetime is longer. Preli- 24
DEVELOPMENT WORK FOR THE CMS PIXEL DETECTOR
C. Amsler3, M. Barbero4'1, R. Baur1, W. Berti1, R. Eichler1, W. Erdmann2, K. Gabathuler1, R. Horisberger1, R. Kaufmann3'1, D. Kotlinski1, B. Meier2, Ch. Regenfus3, J. Rothe1, P. Riedler3, R. Schnyder1, S. Streulï2, L. Tauschet
E-94-09, SWISS CMS PIXEL COLLABORATION PSI1 - ETHZ2 - ZÜRICH3 - BASEL4
The pixel detector as the innermost detector element in The module was tested with a set of x-ray sources (see CMS has the task of tagging long-lived reaction products, Fig. 2). The copper line corresponds to signals of 2220 elec- e.g. b quarks and T leptons, and to find secondary vertices. trons and the spectra were recorded with the pixel thresholds The pixel modules consist of a 6.4cmx 1.6cm Si pixel sensor of about 1000 electrons (however with an increased peaking with 150 ¿urn square pixels, which are read out by two rows of time of 45 ns). eight electronic chips. Each of the 44,096 pixels on the sen- sor is connected via a bump bond to its own readout circuit on the readout chips (pixel unit cell PUC). Before module production can start in the year 2003, ex- tensive R&D work must be performed, the main part of it concerning the readout chip. A complete precursor chip in radiation-hard technology with 36x40 pixels has been de- signed and sent to fabrication in July 2000. It features the full readout architecture for the LHC environment and incor- porates all the functions needed for full luminosity readout. The programming interface and the voltage control section is however not yet implemented. On the chip the PUC's are organized in columns. A "col- umn drain architecture" initiates immediate data transfer from the PUC's to a perifery located at the end of the column, Figure 2: Response of pixel module to various x-ray lines where the complex task of data buffering and trigger verifica- (see text) tion is performed, allowing to use a rather simple PUC whith only 140 transistors. The chip dimensions are 5.4mmx 7.8mm Concerning the sensors a novel open atoll structure of with a transistor count of about 225,000. It is expected to be p-stop rings around the n-pixels has been implemented. This delivered in February 2001. provides a high resistive path between the pixels, which should A first pixel module with six readout chips of simpler prevent the charging-up of pixels where the bump bond fails. readout architecture has been bump-bonded and operated (see Measurements with irradiated detectors show a dramatic in- Fig. 1). With this module, possible problems arising from in- crease of the inter-pixel resistance with fluence. (see Fig. 3. Consequently an unconnected pixel will be at a growing po-
CSEM 7888SR
1O"> -¡
fluence [7t cm"2]
Figure 3: Inter-pixel resistance as a function of pion fluence for different detector bias voltages Figure 1 : Pixel module with six readout chips on a testboard tential with increasing fluence, which could discharge to the PUC over the small distance of 15 /im and disturb the neigh- terferences between the chips due to large, transient power bourhood. Studies with a point laser are underway to map surges and from minimal power filtering due to a restricted the behaviour of a region of pixels around an unconnected material budget could be addressed. Remedy was found with pixel. a rather small budget of electric capacitance. 25
DEVELOPMENT OF EVENT TRIGGERS FOR CMS BASED ON THE PIXEL DETECTOR
M. Barbero1'2, R. Horisberger1, D. Kotlinski1, R. Schnyder1,
E-94-09, CMS COLLABORATION, PSI1 - BASEL2
LHC at full luminosity generates around 1000 particles from proton-proton collisions every 25 ns. These produce Pixel reconstruction, h(5OO)—>-c-c, high-luminosity a very large amount of raw data in the detectors, of which, however, only a small fraction is of interest. Therefore a selective filtering must be applied. The high resolution, 3- dimensional space points from the pixel detector, allowing for precise pattern recognition, are very useful for triggering interesting events. Unfortunately the complete pixel detec- tor data cannot be read out at each collision. Therefore two possible triggering schemes are considered. A 1st level trig- ger which uses reduced pixel information and a 2nd/3rd level trigger which uses the full pixel information. The 1 st level pixel trigger uses the hit multiplicity infor- mation. The readout mechanism of the pixel chip is organ- ised in double-columns; we use this feature to combine the pixels into 300 \im x 8 mm pseudo-strips. Figure 2: The reconstructed tracks versus pseudo-rapidity. Only pixel hits are used in the track reconstruction of TT events at the full LHC luminosity. The solid fine shows the reconstructed tracks, the dashed line shows all Monte Carlo - 100 optical fibres tracks which have at least 3 pixel hits. The dotted line shows Monte Carlo tracks with at least 1 pixel hit.
With three pixel hits, per particle track, one can find tracks even at the full LHC luminosity with a high efficiency (above 90%) for most types of LHC events. This can be seen in Fig- analog coded chip address ure 2 where the reconstructed tracks are plotted versus the track pseudo-rapidity for the 500 GeV Higgs —>• TT event # jets ( z, I
POLARIZED NUCLEI IN PLASTIC SCINTILLATORS: NEW TOOLS FOR SPIN PHYSICS
B. van den Brandt1, E. I. Bunyatova2, P. Hautle1, J. A. Konter1 and S. Mango1 1 Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland 2 Joint Institute for Nuclear Research, Dubna, Head P.O. Box 79, 101000 Moscow, Russia
New possibilities for the measurement of spin-dependent observables in nuclear and particle physics are offered by the development of polarizable plastic scintillators. A polarized scintillating target is an instrument in which the hydrogen nuclei (or other nuclei of interest) in a piece of scintillator can be dynamically polarized at very low temperatures and the light produced in the scintillator by scattered particles can be forwarded to a photomultiplier at room temperature [1, 2]. One such instrument has allowed e.g. to measure the neutron-proton spin correlation parameter at forward angles at 68 MeV [3] and the analyzing powers in 7rp*-scattering at 45-87 MeV [4], thanks to the coincident detection of the low energy recoil proton in the target itself. The light output and the polarization achievable in a block of scintillator are determined by the doping and production process [2]. We achieve now routinely 80% proton polariza- tion at 2.5 T and below 0.3 K in blocks ofl8xl8x5 mm of PS-based scintillator. A nominal concentration of 2 x 1019 paramagnetic centres/gram was found to give high degrees of Figure 1: A polarizable scintillating block of 18x18x5 mm, polarization in a reasonable time. For a sample in which 80% mounted in the mixing chamber. and more polarization could be obtained, 85 minutes were enough to reach + 60% and 135 minutes to reach + 70%. We measured the proton spin-lattice relaxation time Tip of a se- ries of samples with different concentrations of TEMPO at about 100 mK in magnetic fields of 0.4 and 0.8 T. Samples with a TEMPO concentration of 7 x 1018 p.c./g had at 90 mK a proton relaxation time of 70 hours in 0.4 T, and of 230 hours in 0.8 T, but needed one day and more to reach full polariza- tion at 2.5 T. In 98.7% deuterated polystyrene-based scin- 20 40 60 tillator, containing the non deuterated additives p-terphenyl time [h] (1.5 wt.%) and l,4-di-(2-(5-phenyloxazolil))-benzene (0.15 wt.%), a deuteron polarization of 25% could be obtained at Figure 2: Time histogram of the proton polarization in a scin- 2.5 T. tillating block as shown in fig. 1. The scintillation characteristics of the blocks have been 90 determined with a Sr-source and with protons of energies a period of two months, proving to be very robust and reli- ranging between 5 and 12 MeV. The light output of the latest able. A reasonable polarization could be achieved (s. fig.2) probes reaches up to 30% of the one of the undoped mate- and the base temperature attained was 65 mK. rial. Protons of energy down to 1.5 MeV can be detected with an energy resolution degraded to about 25 % of the one REFERENCES of the untreated material and an almost unchanged timing [1] B. van den Brandt, E.I. Bunyatova, P. Hautle, resolution. The light extracting system has been investigated J.A. Konter, S. Mango, with a raytracing program. Accordingly, an improved target holder has been constructed (s. fig.l), and the diameter of Proc. of SPIN96, Amsterdam, Sept. 10-14,1996, 238. the 1150 mm long lightguide has been increased to 19 mm. [2] B. van den Brandt, E.I. Bunyatova, P. Hautle, The hydrogen-free light collecting quartz transition (diam- J.A. Konter, S. Mango, eter 19 mm) between the scintillator and the lightguide is Nucl. Instrum. Meth. A 446 , 592 (2000). visible above the scintillator, around which the NMR coil is wound. The microwave guide (with white PTFE cone) can be [3] S. Buttazzoni et al., PSI Sci. Rep. 1998,1, 23. seen in the center of the figure. A rutheniumoxide thermome- ter is hanging below the scintillator. The lightguide is con- [4] R. Bilger et al., PSI Ann. Rep. 1997,1, 22. tained in a tight-fitting stainless steel tube inside the (white) ceramic bobbin, on which the continuous heatexchanger cap- illary is wound. The system has been operated recently over 27
AN ULTRACOLD NEUTRON FACILITY AT PSI
F Atchison1, B. Van den Brandt1, M. Daum1, W. Gloor1, G. Heidenreich1, R. Henneck1, P. Hautle1, St. Joray1, K. Kohlik1, J. A. Konter1, S. Mango1, H. Obermeier1, Ch. Perret1, U. Rohrer1, H. J. Temnitzer1, A. Fomiri2, S. Kalcheva2, A. Kharitonov2, M. Lasakov2, V. Mityukhlaev2,1. Potapov2, M. Sazhin2, A. Serebrov2, G. Shmelev2, V. Shustov2, R. Taldaev2, D. Tytz2, V. Varlamov2, A. Vasiliev2, A. Zakharov2, K. Bodek3, J. Smmicki3, P. Geltenbort4, S. Kistryn5, A. Magiern5, D. Pocanice, E. Frleze
R-00-03, PSI1, PNPI2, ETHZ3, ILL4, Cracow5, Virginia6
During the recent years most attention in physics with ultracold neutrons has been focused on two experiments, the high sensitivity search for time reversal violation via the mea- surement of the electric dipole moment of the neutron (EDM) and the decay asymmetry and lifetime of the neutron. These experiments rely heavily on long observation times of an en- semble of stored neutrons, and were the driving force behind the development of techniques for the production and storage of ultracold neutrons (UCN), i.e. neutrons with an extremely low speed (< 8 m/s). The main impact of the search for the neutron EDM is the exclusion of a variety of proposed mech- anisms for CP violation. Solving this puzzle is expected to provide an access to physics beyond the Standard Model and therefore it ranks at the highest priority. Recently, theories including Supersymmetry, multiple Higgs boson exchange, Figure 1: left-right symmetric models, and attempts to understand the Scheme of the PSI/PNPI Spallation Ultracold Neutron baryon asymmetry in the universe, predict a finite value of Source and Neutron EDM spectrometer the neutron EDM in the range between 10~28 and 10~25ecm; this is just at the verge of the present experimental limit of 6-lCr26ecm. Estimations [2] and Monte Carlo studies [3] show that These important experiments are hindered by a low den- a UCN density of more than 103 UCN/cm3 can be deliv- sity of ultracold neutrons presently available for experiments. ered to the experiments using the proposed method. This is Recently, an attractive solution of these problems has been ~ 2 orders of magnitude more than in experiments at the re- proposed [1]. It is based on a pulsed spallation source, cus- actors in the Institute Laue Langevin, Grenoble and in the tomized to the needs of UCN production. The proposed St. Petersburg Nuclear Physics Institute, Gatchina, which scheme solves a contradiction between the high neutron ther- are at present the world leading centers in ultracold neutron mal flux flowing into the solid deuterium moderator and an research. With these improvements at the new facility, we average heat load in such a moderator. intend to measure the electric dipole moment (EDM) of the At PSI, we are building such a new type of ultracold neu- neutron with a sensitivity of about 10~27 ecm, an improve- tron source. The essential elements are a pulsed proton beam ment by more than one order of magnitude. The Paul Scher- with a high intensity and a very low duty cycle, a heavy el- rer Institute with its superior proton beam is an ideal place to ement spallation target and a large moderator consisting of realize such a new UCN source, which is a prerequisite for a solid deuterium kept at a temperature of about 8 K. For the next leap in the EDM and lifetime experiments. Production of ultracold neutrons, the proton beam is directed for a time period of the order of few seconds onto a lead spallation target to generate a high density neutron pulse in REFERENCES a moderator assembly dedicated to the production of ultra- [1] A. P. Serebrov, V. A. Mityukhlaev, A. A. Zakharov, cold neutrons. The lead target is cooled by heavy water and T. Bowles, G. Greene and J. Sromicki, surrounded by a premoderator and neutron reflector consist- JETPLett. 66, 803(1997). ing of ~4 m3 of heavy water. About 301 of solid deuterium at ~8 K is used as the cold moderator for the production of [2] J. Sromicki, A. P. Serebrov, International Symposium ultracold neutrons. The emerging neutron gas, with a den- on Weak and Electromagnetic Interactions in Nuclei, sity reaching saturation level in the solid may be directed WEIN 98, Santa Fe, NM, June 1998, World Scientific, to a dedicated experiment located as close to the production in press. target as the secondary radiation field allows [1]. The ultra- cold neutrons are then observed and/or counted over a period [3] I. Potapov, V. Kuzminov, comparable to the neutron lifetime in the experiments. Af- contributions to the "First UCN Factory Workshop", ter the density of the UCN in the experimental stations has Pushkin, Russia, January. 19-22, 1998. dropped significantly, a new proton pulse generates the next ultracold neutron packet, and the whole cycle is repeated. 28
THE LOW ENERGY MUON BEAM FOR THE MUONIC HYDROGEN LAMB SHIFT EXPERIMENT
F Biraben1, C. A. N. Conde2, C. Donche-Gay3, T. W. Hänsch4, F J. Hartmann5, V.-W. Hughes8 O. Huot3, P. Indelicato1, Y.-W. Liu6'7, P. Knowles3, F. Kottmannss, F. Mulhauser3, F Nez1, C. Petitjean7, R. Pohf R-98-03, PARIS1 - COIMBRA2 - FRIBOURG3 - MPI MUNICH4 - TU MUNICH5 - YALE6 - PSI7 - ETH8 - PRINCETON9 For the realisation of the /ip Lamb shift experimentfl] a keV, cross the thin gas target and are detected in a down- low energy muon beam line has been built, tested and op- stream microchannel plate (MCP) providing a second muon erated successfully. It consists of the cyclotron trap for the signal. The TOF information from the two time signals pro- production of the low energy muons [2], the muon extraction vides optimized triggering on muons stopping in the target. channel (MEC) for the transport and the selection of the low Figure 2 shows the time spectrum of the second signal energy muons and the PSC solenoid with two transmission relative to the first one in absence of a target. The first peak, detectors for the muon trigger (Fig. 1). which disappears when the last foil voltage is set to zero, defines the TOF trigger signal. The later signals are induced ]Cyclotron Trap by muons stopping in the MCP. The measured muon energy is predominantly between 5 keV and 20 keV. 4000 - 3500 3000 it / s l-i with signal in both stacks t s i n 10n a '- i ¡a. without signal in stack 2 >1500 1000 2nd Stack X Sointillator 500 T^^^T ^T electrons ExB Plates ; it ^' "~ i-, / from n decay 1st Stack ^—~-, B - 0.15 Tesla n _v i , , , i , , , i , , , i , , , i , , , i 0.6 0.8 1.2 1.4 1.6 time/jj.s Figure 1: Set up of the low energy muon channel. Figure 2: Time of flight spectrum measured between first The MEC is a curved magnetic channel where large ad- entrance detector (first foil stack - scintillator - PMT) and justable normal conducting coils provide a field that trans- second detector (foil - MCP). The spectrum can be decom- ports particles adiabatically whose momentum is between 1 posed in contributions from TOF trigger electrons , muons and 3 MeV/c (5 to 45 keV muons). For the efficient elim- stopping in the MCP and electrons from muon decay in the ination of the large amount of low energy electrons present MCP. in the initial beam, two special electron beam dumps (not In a seperate measurement, the MCP was replaced by a shown in Fig. 1) have been installed downstream and up- Ge(Li) diode with a Be window. From the measured inten- stream. The device was tested and adjusted. It provided more sity of the yuBe x rays the muon beam intensity was deduced. than 90% transmission for the low energy muons. No contri- It agrees with the results of a Monte-Carlo simulation ap- bution of low energy electrons was detected downstream. plied to the used foil thickness in the cyclotron trap. It in- The outcoming muons enter the superconducting 5 T so- dicates that with the fully optimized foil configuration in the lenoid (PSC) where they first cross a new type of transmis- cyclotron trap, a beam rate of 100 n~ I ( cm2 . keV . mA . s) sion detector. It is based on a stack of ultrathin carbon foils will be obtained as predicted. Finally, a 4 mbar gas target with 1.8 kV voltage between them to compensate for the was introduced and the observation of muonic x rays from muon energy loss [3]. Secondary electrons are emitted and gas stops completed the full operation of the beamline. accelerated towards a downstream plastic scintillator con- REFERENCES nected to an external PMT via a long light guide. Betweeen the stack and the scintillator an E x B drift space induce a [1] R. Pohl et al., Hyperfine Interactions 127, 161 (2000). transverse drift (greater for the muons than for the electrons) allowing the muons to pass the scintillator. A 70% muon de- [2] P. deCecco et al., tection efficiency could be measured. Further downstream Nucí. Instrum. Meth. A 394, 287 (1997). the muons cross a second foil stack placed in front of the tar- [3] M. Mühlbauer et al., get. The emitted secondary electrons, accelerated to a few Hypfine Interactions 119, 305 (1999). 29 Laboratory for Astrophysics 30 LABORATORY FOR ASTROPHYSICS A. Zehnder Highlights for the Laboratory for Astrophysics (LAP) in 2000 were the delivery of the flight hardware ofHESSI, the repair work following the mishap at Jet Propulsion Laboratory in Pasadena, the successful turn-on of the reflection grating spectrometer on board of the XMM-Newton X-ray satellite and the following calibration phase. The developments of cryodetectors for astrophysical applications, our long-term goal, resulted in the first observation of visible light by a superconducting strip detector array. Following the successful launch of the ESA cornerstone The third flight hardware, the ESA-financed, PSI-designed mission XMM-Newton X-ray telescope on Dec. 10, 1999 and Contraves/Space-built Standard Radiation Environment from Kourou by a powerful Ariane 5 rocket, we were eager Monitor (SREM) was successfully launched on Nov. 16, by to learn how the PSI-subsystem of the reflection grating an Ariane 5 rocket on one of two UK satellites, STRV-lc spectrometer (RGS) detector housing, the door mechanism, and STRV-ld. The results received on ground during the the CCD front-end electronics and the passive CCD cooling initial phase proved that the SREM design and production system were operating in space. All the devices were turned fulfilled the goal. This is shown in the contribution First on without problems, and the commissioning and Data from SREM in Space'. Unfortunately both UK- calibration phase could start in time. The astrophysics satelhtes STRV-lc and -Id stopped transmitting data and group of LAP was responsible for the key program 'cool accepting commands owing to unknown reasons. However, and hot stars' and was actively engaged with software ESA additionally procured six SREMs from development for the in-flight calibrating of the RGS Contraves/Space and therefore, in the future, we will instrument. Their contribution in the present annual report receive radiation data from SREM's on satellites like entitled The first year of XMM-Newton' and 'XMM- PROBA and INTEGRAL. Newton: from Calibration to First Results' give an overview of this so far very successful mission. The program for the The ESA Center of Excellence, the Proton Irradiation guaranteed observing time started in fall and PSI, the ETH, Facility (PIF), for the qualification of space electronics and the University of Zurich and the Observatory of Geneva are components had again a successful year with a long list of profiting from it. The proposed live time of XMM-Newton external users from universities, agencies and industries. is 10 years and should deliver exciting results, leading to a However, a decision for the relocation of PIF in connection better understanding of stellar, galactic and extragalactic with PROSCAN is pending and needs to be taken in order astrophysics. The astrophysical contributions, as well as the to guarantee the users long-term operation. list of publications and conference reports of the members of the small astrophysics group of LAP display their At the beginning of the year 2000, a decision was made to productivity that is based on the hardware efforts made at strengthen the development of cryogenic detectors in favor PSI over the last 10 years. of further space-borne hardware projects. The work on these detectors should be expanded from the X-ray into the PSI built the imager and the aspect system of the High optical wavelength region. Moreover, the development of a Energy Solar Spectroscopic Imager HESSI. It was multi-pixel detector should be initiated. As explained delivered in time and the integration into the spacecraft was above, the HESSI mishap was using up the available well under way for the proposed launch of July 2000. All manpower resources and consequently slowed down the the subsystems and the mechanical parts had passed the work on cryodetectors. However, as shown in the three acceptance tests. However, during the shock tests on the contributions of the group, a 2x8 superconducting vibration test facility at the Jet Propulsion Laboratory (JPL) tunneling junction (STJ) strip-detector array was produced that had qualified a number of very famous spacecrafts, an with such good characteristics that it could be accident occurred. A malfunction of the apparatus led to commercially sold. It produced encouraging results for the severe damages of the HESSI instrument. The contribution detection of biological macromolecules. With a similar STJ 'Repairing the imager of HESSI after JPL-mishap' gives strip detector we observed optical photons for the first time. details. The repair, re-alignment and re-calibration work This was possible by the use of a vastly improved low- kept us busy during 2000. The HESSI contribution of the noise preamplifier. A few thousand excess charges were Solar Aspect System (SAS) and the Roll Angle System measured after absorption of a single photon. This result (RAS) as well as the Aspect Data Processor (ADP) show must be compared with the few charge carriers produced in that the system is now well calibrated and well understood. a Si-semiconductor after absorption of a photon. It thus Integration into the spacecraft started again in October clearly demonstrates the potential of STJ detectors. 2000 and we are looking forward to a successful launch of HESSI on March 28, 2001. 31 THE FIRST YEAR OF XMM-NEWTON M. Giidel1, M. Audard1, and the RGS Consortium2'3'4 PSI1 - SRON/NL2 - COL UNIV/USA3 - MSSL/UK4 XMM-Newton has observed various astrophysical objects during its first year. A large amount of the observing time was spent to perform feasibility tests and to obtain high-quality science data. Following the inital commissioning and calibration pha- ses, XMM-Newton went through a long series of observa- tions to test the performance of the instrument under realistic conditions. For the Reflection Grating Spectrometer Team, these included, among others: i) testing temperature, ele- mental abundance, and line broadening sensitivity in line- dominated spectra of stellar coronae and wind sources; ii) obtaining a set of complex spectra from active galactic nu- clei to disentangle the different components; iii) testing high- resolution spectroscopy with extended objects, namely su- pernova remnants and galaxy clusters; iv) obtaining fields with weak sources to measure background and test spectros- copy at its limits. 10 12 14 16 18 20 22 24 26 28 First Ionization Potential (eV) Most of these tests provided extremely satisfying results. With the calibration at hand, the RGS stands up to its expec- Figure 2: Elemental abundances (relative to O) in the coronae tations. Measurements of spectral line shifts and broadening of HR 1099 increase with increasing first ionization potential requires spacecraft stability which was, for the time being, measured by the centroid stability of the EPIC point source Castor system [2]. Castor consists of 3 binaries that were images. Most of the time, spacecraft jitter was found below for the first time seen as separate, strongly variable X-ray 1" over several hours. sources. One of the systems, the binary YY Gem, shows to- The performance verification data were exploited for their tal eclipses between its two identical, low-mass stars every scientific content. The observation of the 'First Light Tar- 9.5 hrs. Through X-ray light-curve inversion covering a full get' HR1099, a binary star system consisting of two roughly stellar orbit, the spatial coronal structure of the binary system solar-like stars, resulted in the detection of unexpected ele- was reconstructed. The main findings were i) rather extended mental abundances in the coronal plasma. The abundances coronae, with scale heights that are compatible with the high of the elements (relative to the putative photospheric com- average temperature of 5-10 MK measured by spectroscopic position) increase with increasing First Ionization Potential means; and ii) inhomogeneities in the corona that are concen- (FIP), which is contrary to previous findings in the solar co- trated at relatively low stellar latitudes (within ±50°). The rona, in the solar wind, and in cosmic rays. Our speculation latter geometry corresponds to the Sun but differs from pre- is that high-FIP-enriched flares as occasionally seen in the dictions made for this type of star (magnetic fields concen- Sun are reponsible for this abundance pattern [1]. trated at the poles). A particularly rich XMM observation was devoted to the Figure 3: Reconstructed X-ray image of the YY Gem binary. REFERENCES 7 8 9 10 11 12 13 14 15 IS 17 18 [1] A. C. Brinkman, E. Behar, M. Giidel, et aL Wavelength (A) Astron. Astrophys. 365, L324 (2001). [2] M. Giidel, M. Audard, H. Magee, et al., Figure 1: Extract from the RGS spectrum of HR 1099 Astron. Astrophys. 365, L344 (2001). 32 XMM-NEWTON: FROM CALIBRATION TO FIRST RESULTS M. Audard1, M. Gtidel1, and the RGS Consortium2 PSI1 - SRON/NL2 - COL UNIV/USA3 - MSSL/UK4 After the successful launch of the XMM-Newton Observatory on December 10, 1999, the satellite and its scientific instruments have been thoroughly tested during a two-month long commissioning phase. We have spent three months at SRONin the Netherlands to take part in the calibration and performance verification phase of the RGS instruments. This effort is now ongoing at PSI. The validation of the calibration procedures has been performed on the first data sets and first results have been successfully obtained. The XMM-Newton Observatory has been successfully trum [5]. The reconstructed emission measure distribution launched at the end of 1999 [1]. After two months of com- peaked around 7 MK, consistent with previous EUVE and missioning phase during which various tests of functionality ASCA results. For the first time for an X-ray spectrum from have been performed, the calibration and performance phase a stellar corona, we have applied the temperature diagnos- began. We actively participated in this phase at SRON, The tics of dielectronic recombination satellite lines to the He- Netherlands. Issues addressed were: the wavelength scale, like O vii triplet to constrain the cool plasma temperature. the effective area, the line-spread function, the CCD model. From line ratios of the same triplet, we derived an average The wavelength scale has been validated and the present ac- density for the cool (2 MK) coronal plasma smaller than curacy is within 8 mA or 4 arcseconds in pointing indepen- 109 cm"3. The "hotter" (7 MK) Mg triplet tentatively in- dent of off-axis angle [2]. The residual uncertainty is be- dicated a much higher density around 1012 — 1013 cm"3, lieved to originate from the present non-inclusion of attitude suggesting bi-modality of the coronae of Capella. correction. We continue to take an active part in the deter- mination of the wavelength scale: we will analyse attitude- corrected data as soon as they become available. PSI is mainly responsible for the testing and vahdation CAPELLA of the XMM-Newton Science Analysis System (SAS) which XMM-Newton/RGS allows for the reduction, cahbration and analysis of XMM- -Newton data. Basically, we test all RGS-related tasks (e.g., RGSFRAMES, RGSANGLES, RGSPROC, RGSRMFGEN, etc), in collaboration with SAS developers. We are also involved in the EPIC MOS and pn software testing. To further con- tribute to this effort, PSI has been invited to join the XMM- Newton SAS Working Group. The testing and validation of the cahbration procedures 14 _ 16 were performed on various data sets obtained during the three Wavelength (A) early phases of XMM-Newton. Of particular interest was a large flare that occurred during the observation of the bi- Figure 1: Extract from the RGS spectrum of Capella. Major nary system HR 1099, the RGS first-light target [3]. Time- emission lines have been labeled. dependent spectroscopy has been performed to derive ele- mental abundances and their variations during the various stages of the flare. The reconstructed temperature structure REFERENCES of the coronae of HR 1099 suggested two different compo- nents: a very hot plasma (up to 100 MK) that evolves rapidly, [1] M. Audard, L. Grenacher, M. Giidel, et al., and a stable quiescent plasma. The coronal abundance of PSI Sci. Rep. 1999,1, 27 (2000). low-first-ionization-potential elements such Fe and Si have been found to significantly increase during the flare, while [2] J. R. Peterson, M. Audard, RGS-COL-CAL-00011, the Ne (high-FIP) abundance did not show significant varia- Columbia Astrophysics Laboratory (2000). tion. This increase of low-FIP elements during the flare is to contrast with the apparent anti-FIP effect (high-FIP elements [3] M. Audard, M. Giidel, R. Mewe, have larger abundances than the low-FIP elements, relative to Astron. Astrophys. 365, L318 (2001). their solar photospheric abundance) found in the "quiescent" [4] A.C Brinkman, E. Behar, M. Giidel, et al., spectrum of HR 1099 [3, 4]. Astron. Astrophys. 365, L324 (2001). The high signal-to-noise ratio of the bright star Capella [5] M. Audard, E. Behar, M. Giidel, et al., allowed us to study the faintest features in its X-ray spec- Astron. Astrophys. 365, L329 (2001). 33 FREE-FLOATING PLANETS IN STELLAR CLUSTERS K.W. Smith1'2 PSI1 - ETH ZURICH2 The discovery of numerous extrasolar planetary systems in a disc around a young star, but must have formed from in the solar neighbourhood (Mayor & Queloz 1995, Marcy independent collapse. & Butler 1996) has revolutionised our ideas of the planet for- mation process and how it can vary from system to system. Specifically, the fact that most of the systems found contain .' 1 ' ' T 1 | , , , | 1 1 ,_ relatively massive planets at small separations, in contrast to our solar system, has engendered significant research into possible orbital migration. More recently, the discovery that there appear to be no such close systems in the globular clus- ..--••• ter 47 Tuc (Brown et al 2000, Gilliland et al 2000) implies - *1'"'\ — a significant difference in planetary formation which could "•;• : be due to the stellar environment. There are three likely ex- -100 -50 -, 111 , i,/,, i, planations for this. Firstly, planet formation may not be effi- -100 -50 0 50 100 -20 0 20 40 60 80 cient in globular clusters due to their poor metallicity. Sec- 1 ' 1 l -:...rv • • • i • • • 1 1 L ond, UV radiation from clusters of O stars may destroy pro- 0 0 .... ~ toplanetary discs at an early stage, as seems to be occurring •'..' 1 ' -50 ; in the Trapezium (Armitage, 2000). Thirdly, close encoun- •• - -50 - ters between stars lead to a lack of close planetary systems. / .-- • This may be because planetary formation is itself impeded, -100 \ j -_ - - / because the inward migration of planets is hampered subse- 100 — -150 - / \ quent to planet formation, or because the planetary systems : , , 1 r are destroyed by disruptive encounters (Bonnell et al, 2001). i 1 r 0 50 100 0 50 100 This last scenario could then lead us to expect a population of liberated planets in the cluster. Recently there has been a reported detection of a population of substellar objects in Figure 1: Examples of encounters between planetary systems a Orionis (Zapatero-Osorio et al, 2000) that could be due to and a star. (Clockwise from top left): (a) The planet is liber- stellar encounters. ated entirely, (b) The planet is retained by its parent, (c) The We have simulated encounters between planetary systems planet is exchanged, finishing bound to the perturbing star, and single stars in three different clustered environments. (d) Finally, the planet is again exchanged, and the final orbit These were intended to resemble a globular cluster, open is extremely eccentric. cluster and a young star forming cluster, such as a Orionis. We found that in globular clusters a relatively high fraction of any planetary population with orbits outside 1AU is likely REFERENCES to be liberated by encounters over the cluster lifetime, and furthermore that the majority of these systems should be re- [1] P. Armitage, tained in the cluster at least until they are lost through two Astron. Astrophys. 362, 968 (2000). body relaxation after several thousand crossing times. In the less dense environments of an open cluster or young [2] I. A. Bonnell, K. W. Smith, M. B. D. Davies and star forming cluster, planet liberation was found to be less ef- K. D. Home, MNRAS, in press. ficient, although still capable of producing a significant pop- [3] T. M. Brown, et al., ulation of free floating planets. However, it was found that Astron. Astrophys. Suppl. 196, 203 (2000). these objects were liberated at too high a velocity to remain bound in the cluster. In each case, only a fraction of a per- [4] R. L. Gilliland, et al., cent of the planetary population was liberated but remained Astrophys. J. 545, L47 (2000). bound to the cluster. This suggests that there should not be substantial numbers of free floating planets in such environ- [5] G. Marcy and P. Butler, ments. Furthermore, any such objects which were observed PASP 112, 137 (2000). in stellar clusters would be expected to have a higher veloc- [6] M. Mayor, and D. Queloz, Nature 378, 355 (1995). ity than the cluster stars, and so to be found predominantly in the outer regions far from the cluster core. [7] M. R. Zapatero-Osorio, V. J. S. Bejar, E. L. Martin, R. This result implies that the substellar objects recently Rebolo, D. Barrado y Navascues, C. A. L. Bailer-Jones found in a Orionis are not after all planets which formed and R. Mundt, Science 290,103 (2000). 34 SPATIAL ANALYSIS OF SOLAR TYPE III EVENTS ASSOCIATED WITH NARROWBAND SPIKES AT METRIC WAVELENGTHS G. Paesold1*2, A. O. Benz1, K.-L. Klein3, N. Vilmer3 ETH ZURICH1 - PSI2 - OBS. of PARIS3 The spatial association of narrowband metric radio spikes with type III bursts is analyzed. The analysis addresses the question of a possible causal relation between the spike emission and the acceleration of the energetic electrons causing the type III burst. The spikes are identified by the Phoenix-2 spectrometer (ETH Zurich) from routine solar observations in the frequency range from 220 MHz to 530 MHz. Simultaneous spatial information was provided by the Nancay Radioheliograph (NRH) at several frequencies. The 3-dimensional geometry of the single events has been reconstructed by implying different coronal density models. 92/08/18, III/IV Millisecond narrowband radio spikes are structures in the radio spectrum of the Sun forming a distinct class of flare emission. The term 'narrowband, millisecond spikes' refers to short (few tens of ms) and narrowband (few percent of the center frequency) peaks in the radio spectrogram. They can be observed in the range of 0.3 to 8 GHz and occur mainly during the impulsive phase of a solar flare. Since the spike emission is often associated with enhanced hard X-ray emis- sion it is generally assumed that spikes are closely related to the actual process of energy release in solar flares. A subclass of spikes found at metric wavelengths cor- relates with type III bursts. They have been called 'metric spikes' in the literature (e.g. Giidel & Zlobec [3]). They oc- cur in clusters usually at frequencies slightly higher than the start frequency of the type III burst and can be shifted in time -1.0 -0.5 0.0 0.5 1.0 -0.20-0.18-0.16-0.14-0.12-0. II with respect to the type III extrapolated in frequency (Benz E-W coord, in solor rodii E-W coord, in solor rodii et al. [1]). Figure 1: Upper right: Observed position of three frequen- Previously published spatially resolved observations of cies: triangle - 164.0 MHz, square - 236.6 MHz and x - metric spike events (Krucker et al. [4]) found the spike sources 327.0 MHz. Upper left: side view from far to the West. at high altitudes and suggest a model of energy release tak- Lower right: top view from far above the North. Lower ing place in or close to the spike sources. Escaping beams left: location of upper right panel on the Sun. of electrons cause the type III emission. Thus a scenario is conceivable, in which the spikes may be a direct signature of the accelerator. exhibits a very suggestive situation: two consecutive type III Using two dimensional spatially resolved data from the bursts originate in the same spike source. The situation is Nan§ay Radioheliograph (NRH), it is possible to reconstruct depicted in Fig. 1. Energetic electrons appear to be injected the spatial configuration of the event and the relative position into different and diverging coronal structures from one sin- of the spike source with respect to the type III trajectory. The gle position. Such a magnetic field geometry is the standard main purpose of this work is to answer the question whether ingredient of reconnection. These observations are consistent the geometry of the events supports the picture mentioned with the hypothesis that metric spikes may be a signature of above. particle acceleration. Four new events of type III associated metric spike events have been found and analyzed. In addition, three separate REFERENCES events on 92/08/18 that are already published in Krucker et al. ([4]) using VLA observations have been investigated us- [1] A. O. Benz, P. Zlobec, M. Jaeggi, ing older data from Nancay. Astron. Astrophys. 109, 305 (1982). In all analyzed events the spike sources are always lo- [2] A .0. Benz, A. Csillaghy, M. J. Aschwanden, cated at positions coinciding with expected locations from Astron. Astrophys. 309, 2291 (1996). extrapolated type III trajectories to lower altitudes. These observations thus strongly support a model for radio spikes [3] M. Giidel, P. Zlobec, occurring in the course of type III beam propagation or near Astron. Astrophys. 245, 299 (1991). its origin, consistent with independent spectrogram observa- tions (Benz et al. [2]). They add further evidence for spikes [4] S. Krucker, A. O. Benz, M. J. Aschwanden, being a signature of the mechanism accelerating electron Astron. Astrophys. 317, 569 (1997). beams that cause type III bursts. One of the 92/08/18 events 35 HARD X-RAYS AND DECIMETRIC RADIO CORRELATIONS Pascal Saint-Hilaire1'2, Arnold O. Benz1 ETH ZURICH1-PSI2 Hard X-rays from the Sun are emitted during the impul- It is interesting to note that the most important decimetric sive phase of flares. They are often accompanied by unpolar- radio emissions are by the CME itself, and not by the plasma ized type III radio bursts in the decimetric range at the very during the flare (hard X-ray peak). onset of the flare, and then pulsating continua appear. The There are many more as yet unexplained features, like the temporal relation for one of the observed flares is shown in presence of low-frequency type III bursts around UT 12:18 Figure 1. shooting out more than 100 arcseconds to the right of the active region. This project is pivotal as a preparation for Hessi hard X- ray observations. The image reconstruction using Yohkoh HXT data as presented here will be refined greatly with Hessi (resolution at this energy range is twice better than HXT's). Hessi will also provide much better hard X-ray spectra (HXT only has four channels, spanning the 14-93 KeV range). 300 Figure 1: BATSE Hard X-ray lightcurve, and PHOENIX-2 radiospectrogram (stokes I) from ETH's Bleien Observatory) In preparation for the Hessi mission, we have started a projet to compare several such flares, and to find the essential ingredients related to particle acceleration and the generation -900 -800 -700 -600 of hard X-ray emission. X (orcsecs) Fig. 2 depicts the same flare that occurred on September 8th, 1999 as observed with the TRACE ultraviolet/extreme- Figure 2: TRACE 1600A picture (CI, Fell and some ultraviolet satellite. The TRACE image shows a two-ribbon continuum), with Hard X-ray overlay from Yohkoh HXT flare (brightest areas), and the early phase of an expanding (thin, black contours : 23-33 KeV range), and from the coronal mass ejection (CME). The latter can be noticed be- Nancay Radioheliograph (thick contours, red=164MHz, or- tween the radio sources (contour overlays) and the bright ange=236.6MHz, yellow=327MHz, green=410.5MHz, pur- flare. The three radio frequency contours to the right of the ple=432MHz, representing the top two percent of the radio active region correspond to the first pulsating continuum. This flux at each frequency). The time, 12:15:10, corresponds emission stays mainly on top of the active region through- to the peak of the hard X-ray emission in Figure 1. The out the episode of hard X-ray emission. The two lowest fre- TRACE image shows a two-ribbon flare (brightest areas), quency contours, located further south, correspond to type and the early phase of an expanding CME. The three radio III radio bursts attributed to fast electron beams. The type III contours to the right correspond to the first pulsating contin- bursts are present just when the magnetic energy is being re- uum whereas the radio contours to the south are related to leased (as evidenced by the hard X-ray rise). Later on, as the type III radio bursts. The fact that the two hard x-ray foot- CME is expelled towards the upper layers of the corona at a points are not precisely located right on top of the two-ribbon speed of about 1000 km/s, the radio sources at all frequencies tracks (they are about 10 arcseconds to the right) can easily slowly follow the wake of the CME, way up into the upper be attributed to the pointing inaccuracy of TRACE. corona. 36 SHAPE AND GEOMETRY OF GALAXY CLUSTERS AND THE SZ EFFECT L. Grenacher1'2, Ph. Jetzer1'2'3, P. Koch2, R. Piffaretti1'2, D. Puy1'2, M. Signore5 PSI1 - ZURICH2 - ETH ZURICH3 - OBS. of PARIS5 The Sunyaev-Zel'dovich (SZ) effect is the change in en- rc 2 4 6 8 10 e xt ergy experienced by cosmic background photons when they e y (in %) 29 15 12 9 7 scatter on the hot gas in galaxy clusters. By combining the eeg (in %) 4 1 0.4 0.2 0.1 SZ intensity change and the X-ray emission observations, e xt e x and solving for the number density distribution of electrons Table 1: Relative errors e y on the {/-parameter and e s ^ on the responsible for both these effects, the angular diameter dis- surface brightness assuming fi = 2/3 and a spherical cluster. rc is tance to galaxy clusters can be derived. Assuming a cosmo- the core radius in kpc. logical model, this leads then to an estimate of the Hubble constant. 1 1 units of the core radius rc, leads to Ho ~ 45 km s Mpc Recently, Mauskopf et al. [1] determined the Hubble con- which is well below the value found by Mauskopf et al. [1]. stant from X-ray measurements obtained of the cluster Abell 1835 with ROS AT and from the corresponding millimetric observations of the SZ effect with the SZ Infrared Eperi- Geometrical effect ment (SUZIE) multifrequency array receiver. Assuming an Some observations with ROS AT of rich clusters have revealed infinitely extended spherical gas distribution with an isother- that on large scales the X-ray distribution has an elliptical hs mal equation of state, they found a value of H° = 59±28 shape. The influence of the geometrical shape of the cluster 1 1 km s^ Mpc^ for the Hubble constant. profile on the investigated quantities induces a relative error If we suppose other physical characteristics of the cluster on the y parameter of up to 10%, depending on the line of such as: finite extension or aspherical distribution for the sight and the shape of the cluster. density, we find accordingly other estimation of the Compton The effect on the Hubble constant is shown in Figure (lb) for parameter y and the surface brightness, and so a relative er- an ellipsoidal geometry [3] for different axis ratios, where we ror with respect to the classical configuration (i.e. spherical compare again with the value obtained by Mauskopf et al. distribution with an infinite extension). Thus, we define two [1]. family of relative errors: • CyXt = 1 — (yi/yoo) where y^ is obtained for an infi- nite extension and yi for a cluster extension I. Here we consider an isothermal profile and a spherical distribu- tion. om • tf = 1 - ilVsph) where ysph is the Compton parameter obtained for a spherical distribution and yeu the one for an ellipsoidal distribution, with an infinite extension and an isothermal equation of state for the two distributions. Of course, the same analysis for the relative error applies also on the surface brightness Sx • 0 20 40 60 Cluster extension 1 (in units of r) Finite extension of clusters Figure 1: The Hubble constant as a function of the cluster Since the hot gas in a real cluster has a finite extension, each extension and the axis ratio. of the observed quantities, the Compton parameter and the X- ray surface brightness, will be smaller than those estimated REFERENCES assuming I —> oo. In Puy et al. [2] we have analysed [1] P. Mauskopf, P. Ade, W. Allen, et al., the influence of this correction for the simplest cluster case: Astrophys. J. 538, 505 (2000). isothermal fi = 2/3-model with a spherical density profile, and a fine of sight going through the cluster center. In Table 1 [2] D. Puy, L. Grenacher, Ph. Jetzer, M. Signore, we give the relative error on the y-parameter and the surface Astron. Astrophys. 363, 415 (2000). brightness for different finite extensions of the cluster. In Figure la we show the influence of the finite extension [3] L. Grenacher, Ph. Jetzer, R. Piffaretti, D. Puy, I using the same input parameters of Mauskopf et al. [1]. For M. Signore, Proceedings of the SZ Toulouse Workshop, astro-ph/0010512 a spherical geometry, Ho displays a strong dependence on the cluster extension [3]. An extension of I ~ 10, given in 37 BARYONIC DARK MATTER IN CLUSTERS AND SPIRAL GALAXIES L. Grenacher1 >2 PSI1 - ZURICH2 The thesis, done under the supervision of Prof. Ph. Jet- calculate the optical depth and the number of events towards zer, deals with different footprints of baryonic dark matter. the Galactic bulge and some directions towards the spiral For this purpose we investigate three environments on differ- arms [5]. Using the events found by the MACHO collabo- ent scales: ration during their first year of observation towards Baade's Window we estimate the mass functions for the bulge and • the intracluster gas (ICG) is used as a tracer of the dark disk populations following the mass moment method. We matter distribution in galaxy clusters, find that the mass function can be well described by a de- creasing power-law with slope a ~ —2.0 in both cases and a • the fate of the gas in cooling flows in the central re- minimal mass of ~ 0.01 M for the bulge and ~ 0.02 M gion of clusters is investigated, as well as the molecu- 0 0 for the disk, respectively. Assuming that the obtained mass lar clouds in the cooling flow. function for the disk is also valid in the spiral arms, we find • low-mass stars, observed in microlensing experiments, that the expected number of events towards the spiral arms is are used to determine galactic parameters. in reasonable agreement with the observations. We study the Sunyaev-Zel'dovich (SZ) effect and the X- ray surface brightness for clusters of galaxies with a non- \ rcool spherical mass distribution [1]. In particular, we consider the \ \ \ influence of the shape and the finite extension of a cluster, \ \ as well as of a polytropic equation of state on the Compton 11 \ parameter, on the X-ray surface brightness, and on the de- termination of the Hubble constant HQ . It is found that the \ \ non-inclusion of such effects can induce errors up to 30% in \\ \v \ \ the various parameters and, in particular, on the Hubble con- S loo \ ^ \ ^ • stant value, when compared with results obtained under the \ \ \\ ^^ isothermal, infinitely extended and spherical shape assump- . \ tions. On the other hand, for a given Ho, the temperature decrement given by the SZ-effect allows predictions of the X-ray surface brightness and thus gives information on the 6 8 10 12 shape of the density profile of the cluster, which in turn gives Equilibrium Temperature [K] improved constraints on the total mass. Figure 1: Equilibrium distance as a function of cloud tem- In many clusters of galaxies there is evidence for cool- perature in the cooling flow environment of the cluster PKS ing flows in the central regions. The ultimate fate of the gas 0745-191 for different CO abundances. CO is the main which cools is still unknown. A possibility is that a fraction cooling agent in this range of temperature. of the gas forms cold molecular clouds. We discuss the mini- mum temperature which can be reached by clouds in cooling flows by computing the cooling function due to Hi, HD and REFERENCES CO molecules [2]. As an example, we determine the mini- [1] D. Puy, L. Grenacher, Ph. Jetzer, M. Signore, mum temperature achievable by clouds in the cooling flows Astron. Astrophys. 363, 415 (2000). of the Centaurus, Hydra and PKS 0745-191 clusters [3] [4]. Our results suggest that clouds can reach very low temper- [2] D. Puy, L. Grenacher, Ph. Jetzer, atures - less than ~ 10 K - which would explain the non- Astron. Astrophys. 345, 723 (1999). detection of high excited CO rotational transitions in these clusters. We show in Figure 1 the equilibrium distance of [3] L. Grenacher, Ph. Jetzer, D. Puy, Proceedings of the cold molecular clouds in a cooling flow environment with re- Large scale structure in the X-Ray Universe meeting, spect to the center of the cluster PKS 0745-191. The heating Atlantisciences 371 (2000). induced by the hot ICG is equal to the cooling due to transi- tions between excited rotational levels. The equilibrium posi- [4] L. Grenacher, Ph. Jetzer, D. Puy, Proceedings of the Clustering at High Redshift conference, tion is shown inside the cooling radius rcooi for different CO abundances r/co, given with respect to the Hi abundance. ASP Conference Series 200,444 (2000). [5] L. Grenacher, Ph. Jetzer, M. Strassle, F. De Paolis, In the context of microlensing searches in our Galaxy, we Astron. Astrophys. 351, 775 (1999). 38 FIRST DATA FROM SREM IN SPACE P. Buhler1, C. Eggel1, W. Hajdas1, N. Schlumpf, A. Zehnder1, E. Daly2, A. Mohammadzadeh2, P. Nieminnen2, J. Schneider3 PSI1 , ESA/ESTEC'2 , Contraves Space3 The Standard Radiation Environment Monitor, SREM is by the radiation environment model AE8 from NASA. This a particle detector developed for satellite applications [1]. It example demonstrates the power of SREM for monitoring measures high energy electrons and protons of the space en- and characterizing the electron space radiation environment. vironment with a fair angular and spectral resolution and pro- vides the host spacecraft with radiation information. SREM was developed and manufactured by Contraves Space in co- 10s 22/11/2000,13:13:01.950 R = 5.33 [RE] . L = 5.50 [RE] operation with Paul Scherrer Institute under a development X '•, contract of the European Space Agency. SREM is the suc- X-. | 106 cessor of REM [2]. x:-. On 16 November 2000 a first SREM instrument was laun- X, •- \ • • •. _ ched aboard the UK-satellite STRV-lc into space by an Ariane- "B IO4 SREMX\''-..^ - 5 rocket. The satellite reached its foreseen Geostationary ( Transfer Orbit, GTO with apogee and perigee altitudes of 4-( Xri 600 and 39000 km, respectively, an inclination of 6°, and a _ 2 B. := BO MeV v period of approximately 12 h (figure 1). During the check- 10 A = 3.10e-;-06 I /cm'TMt-V/^. xx out of all STRV-lc experiments, SREM has been switched i ... i xi . "^ on and was operated for a short period. The data received 4 6 10° during that period indicate that the instrument works well. Energy [MeV] Figure 2: Comparison of the differential electron spectra \GEO measured with SREM and predicted with the standard radia- tion environment model AE8 from NASA. In case of SREM 2 /^ \\ the spectrum is approximated by an exponential function and a step-function. / \ 12 : Prior to launch the instrument was fully calibrated at the * ° / : Proton Irradiation Facility, PIF of PSI. In addition the in- \ A strument including the host spacecraft were simulated with GEANT to accurately determine the response functions to -2 . X si •_ electrons at energies between 0.5 to 10 MeV and to protons GTO" -""" / in the 10 to 600 MeV range. These are needed to compute the incident particle spectra from the measured detector count -2 2 4 rates. XSM [RE] In order to ease the exploitation of the scientific data we developed the Data Management and Analysis System, Figure 1: GTO of Strvlc on 22 November 2000. The red dot DMAS. DMAS is a software tool written in PV-WAVE, which marks the position of the satellite at 13:13 when the electron allows to maintain the databases of multiple SREMs but also spectrum shown in figure 2 was taken. other space science data sets. DMAS is modular and can be The orbit of Strv-1 c is ideal for investigations of the radi- updated to work with new experiment data. It includes instru- ation belts, because it covers a large spatial area and allows ment specific functions for the reduction of the raw data and to trace the radial distribution of the trapped particles. Es- general functions for e.g. the computation of earth magnetic pecially now, during solar maximum it allows to investigate field parameters and satellite orbits. A GUI allows to de- the influence of spontaneous solar ejections on the Earth's fine experiment parameters, execute data analysis functions, magnetosphere. The Strv-lc/SREM data promises to be a display the data, and to produce data products for the presen- valuable extension of the database obtained by REM aboard tation on the Internet. Strv-lb from 1994 to 1998, which covered the last solar min- Further SREMs will be launched aboard Proba in 2001 imum period. and the ESA M2 mission Integral in 2002. News and data Figure 2 shows an example of an electron spectrum mea- can be found at sured by SREM aboard Strv-lc during the commissioning http://wwwl.psi.ch/www_srem_hn/srem_home.html. phase. The position of the satellite during the measurement REFERENCES is indicated in figure 1 by a red spot. The satellite is at a dis- tance of 5.3 Rg from the center of the earth, in the outer radi- [1] W. Hajdas, PSI Annual Report (1997). ation belt zone. The SREM spectrum is plotted in red and is [2] P. Buhler etal., approximated by an exponential function and a step-function. Nucl. Instrum. Meth. A 368, 825 (1996). The black dotted line shows the electron spectrum described 39 REPAIRING THE IMAGING SYSTEM OF THE HIGH-ENERGY SOLAR SPECTROSCOPIC IMAGER (HESSI) AFTER JPL-MISHAP K. Thomsen, F. Burri, R. Henneck, A. Mchedlishvili, P. Ming, J. Welte, A. Zehnder (PSI), A. Bern (ETH-Z), in colla- boration with the Space Science Laboratory Berkeley, Goddard Space Flight Center, and the University of Delft During the vibration test of the HESSI space craft the satellite was partly destroyed due to malfunctioning of the test facility; after refurbishment and realignment the imaging system was brought back to a flight-worthy condition HESSI is a Small Explorer NASA mission with a single 21, 2000, the HESSI spacecraft was subjected to a series of instrument on a small spin-stabilized spacecraft in low vibration tests at JPL as a part of its flight certification earth orbit. The primary scientific aim of the mission is to program. The structural qualification test, denoted as the explore the basic physics of particle acceleration and sine-burst test, subjected the spacecraft to a major over test explosive energy release in Solar Flares. HESSI will that resulted in significant structural damage. A sticking produce hard X-ray images with an angular resolution as bearing of the shaker facility was found to be the culprit of fine as 2 arc-seconds and a temporal resolution on the order the accident. The central imager support ring was broken in of 10 ms; a detailed image can be obtained in 2 seconds. At two at about its design load; the imager got almost the same time HESSI will provide energy resolution below completely loose and started to hammer, which resulted in 1 keV over the range from 3keV to 400 keV. For the first severe peak loads for the whole imaging system as well as time HESSI will perform hard X-ray and gamma-ray it destroyed two of four solar panels. imaging above 100 keV with an energy resolution of a few keV up to energies as high as 20 MeV. IMAGER Ti RINGS complete burst history The imaging capability of HESSI is based on a Fourier- transform technique using a set of 9 pairs of grids spaced 1.55m. Transmission through a grid pair is modulated as the spacecraft rotates around its axis. The different grid pairs have different slit widths. For the finest grid pair a relative twist alignment and its stability to better than 20 arcsec is mandatory to yield sufficient modulation depth. Given the exact timing of single photons together with the precise knowledge of the aspect of the imager it is possible to reconstruct an image of the source. A Roll Angle System -7X(OK) - -10X a 4 kHz (PSI top ring) 11X @4 kHz (PSI bottom) RAS and a Solar Aspect System SAS, allow for aspect reconstruction to arcmin and arcsec, respectively. Fig. 2: Accelerations as measured on the imager end rings The energy resolution of the instrument is achieved by using Ge detectors at liquid nitrogen temperature. HESSI will have the best angular and spectral resolution of any The spacecraft was disassembled and the PSI-built hard X-ray or gamma ray instrument flown so far. components were sent back to Switzerland for repair. Here the imager was taken apart and the individual components were subjected to detailed investigations and tests. No part was really destroyed; only the strut fittings, the tray mounts, and the mounts of grid #6 were slightly deformed. The surface of the a carbon fiber reinforced plastic (CFRP) imager tube showed two marks from the hammering against the sharp corner of the imager support ring but no deterioration of its structural integrity could be detected. Strut fittings were successfully reworked manually, the tray and grid mounts were replaced by spares. The RAS as well as the SAS units were found intact. Functional tests including thermal cycling of the RAS and SAS electronics verified the healthy condition of the aspect systems. With their acceptable status fully confirmed the RAS and the imager components were cleaned anew, reassembled and aligned. After verification of the alignment with an end-to-end gridlet test the flight hardware was sent to Berkeley for Fig. 1: Overview of HESSI imager, view of grids expanded integration with the rebuilt spacecraft. on top, Roll Angle System visible at bottom leftOn March 40 STAR CALIBRATION OF THE HESSI ROLL ANGLE SYSTEM (RAS) R. Henneck,, J. Bialkowski, F. Burri, M. Fivian, W. Hajdas, A. Mchedlishvili, P. Ming, K. Thomsen, J. Welte, A. Zehnder, (PSI), G. Hurford (UC Berkeley), D. Curtis (UC Berkeley), D. Pankow (UC Berkeley) We describe the calibration of the HESSI RAS at the Jungfraujoch. We determined the width of the point spread function (PSF) to be about 0.9 arcmin rms and the sensitivity to be as predicted (weakest object seen has mv=3.65). The Roll Angle System (RAS) is part of the HESSI object. Although a number of random events are present in instrument [1] to be launched by March 2001. It will this 'raw data plot' the true celestial objects can be easily provide information on the roll angle of the rotating separated by the requirements (a) of the correct periodicity spacecraft (15 rpm). Precise knowledge (1 arcmin at la) of and (b) to follow a nearly straight line. this angle is a necessary ingredient for image reconstruction. The RAS is a star camera which points 2000 radially outwards and observes stars at 75° from the sun direction. Stars within a field-of-view of 30° x 1.4° are focussed by a lens onto a 2048 pixel line CCD. The passage of a star image over the CCD (orthogonally) will produce a signal in several pixels and the timing of this signal defines the roll angle, once the star has been identified via its pixel position and amplitude (for more detail see Refs. [2], [3]). Ground calibration of the assembled flight model was performed at the Jungfraujoch Research Station at an c 1000 - altitude of 3600 m. This location combines better atmospheric ,seeing' with the beneficial side effect of convenient CCD cooling. The RAS was mounted on a horizontally rotating support and could be set to scan the sky continuously over about 50° between two end- switches. Due to a longer delay at one end-switch the characteristic periodicity shown in Fig.2 was obtained. Fig.2: CCD position vs. time for Hipp. 25336 (mv=1.64), Hipp. 30343 (mv=2.89), Hipp. 29655 (mv=3.65), Hipp. 25428 (mv=1.65) together with Hipp. 21421 ('Aldebaran', mv=0.87)), Jupiter, Saturn and Hipp. 23015 (mv=2.69) (from bottom to top). The periodic long / short time structure is characteristic for the azimuth of each object and is due to a # laser measurement at 670 nm ^prediction, 'sampled'with 1 pixel resolution longer delay at one end-switch. a planets (Jupiter, Saturn) X stars (Aldebaran, Capella) Fig.l: PSF rms versus angle of incidence. Stellar scintillation introduced a large amount of amplitude spread which made the determination of the PSF width and of the RAS sensitivity from weak objects (mv>l) Focal length adjustment was achieved by minimizing the unreliable. For Aldebaran we took 4 measurements for width of the point-spread-function (PSF) upon varying the which the effective sensitivity varied between 74% and focal length. Doing this for several sources with different 81% of the nominal prediction. We therefore consider 80% spectra resulted in a PSF which is independent of CCD a lower limit taking into account the possibility of some position, as intended (see Fig.l). The predicted width residual haze that we cannot exclude. Thus, the RAS (triangles) of the PSF as a function of incidence angle, sensitivity is as predicted and the required accuracy will be calculated with the CCD responsivity spectrum and achievable. .sampled' with 1 pixel resolution agrees reasonably with a lab measurement using a red laser collimator (diamonds, REFERENCES: with trendline). [1] R.P Lin et al, SPIE Proc. 3442, 2-12 (1998). Fig.2 shows CCD position versus time, plotted with enough [2] R. Henneck et al, SPIE Proc. 3765, 518-523 (1999). time resolution to see the characteristic periodicity of each [3] M. Fivian et al, SPIE Proc. 4012, 518-523 (2000). 41 THE ASPECT DATA PROCCESOR (ADP) FOR THE HESSI IMAGER A. Mchedlishvili, J. Bialkowski, M. Fivian, R. Henneck, K. Thomsen, A. Zehnder, (PSI), D. Curtis (UC Berkeley). We describe the design and software of the HESSI Aspect Data Processor (ADP). It controls 4 CCD detector units and is capable to do complex processing on an input rate of 2 Mword/s, corresponding to a frame rate of 0.5 kHz. The ADP is part of the aspect system of the HESSI It is driven by an internal sequencer. Upon request set instrument [1]. It controls the front-end of the Solar Aspect every its by incoming SAS/RAS data, the sequencer moves System SAS [2] and of the Roll Angle System RAS [2], the data into interface memory, starts the processes to find makes preliminary on-board processing of CCD images Solar limbs and star events and if requirements are met the and controls the data transfer between the front-ends and the Instrument Data Processing Unit (IDPU). pixel addresses are saved in memory. At the end of each image the sequencer generates an interrupt for the DSP, The SAS data represent intensity profiles of a Sun image, which does general processing and moves the formatted which is intersected by a 2048 pixel line CCD. Three SAS data into FIFO. The FIFO can accommodate 192 images, CCD are intersection the Sun image at 120°. The ADP sufficient to equalize the data flow, unless the IDPU stops determines the edges or 'limbs' of this profile by selecting to acquire data. N pixels above/below a selectable threshold, ignoring The 3rd part has an internal hardware timer, which gets however Sunspots and spurious signals. This is done at absolute time from the spacecraft and passes it to the DSP 128Hz, the resulting pixel positions, amplitudes and times to synchronize all data collection procedures. are sent to ground. The RAS scans the sky for stars images on a linear CCD, which appear periodically as HESSI Boot so f tw a re rotates at 15 rpm. Snapshots are taken every 10 ms. The fro m EEPROM ADP selects all pixels above a pixel dependent, selectable threshold, which correspond to a star image. It ignores In itialyze DSP extended 'high' regions caused by the Earth or Moon. and hardware Since the timing of a star is the crucial information, the pixel-corresponding amplitudes before and after the triggering images are recorded as well. Using spatial and time summation of consecutive pixels and images can improve the sensitivity. The ADP creates the different data formats, gets absolute time from the spacecraft, synchronizes the aspect data, S AS generates status of health information and is ready to mage image communicate by messages with the IDPU at any time. Figure 2: ADP on-board software structure. The ADP has three independent parts (see Fig.l) with the processing power distributed accordingly. It contains a DSP Fig.2 shows the structure of the software. After rebooting (SMJ320C50GFAM50) for on-line data processing and 3 and initialisation, the DSP goes in loop and waits for flags. FPGAs (A14100) to realize hardware level of data Flags are generated by the end of the SAS/RAS images, by processing and communication with the IDPU. The central messages and FIFO operations in corresponding driver part with the DSP also controls and monitors the activity of programs, which are speed optimised and can process any the other two parts. event in -lits time intervals. To increase the processing After initialization, the SAS-RAS I/F acts as an rate, bad events are masked and ignored by the drivers. independent unit and becomes responsible for functioning The processing software contains four independent of the SAS/RAS front-ends. subroutines, which are accessed via flags. The subroutines are not interruptible and single event processing should be completely finished. However, even with this limitation we event DSP memory achieved full limb and star event determination at 128 Hz, Busi/f including periodic down-loading of the whole, raw images Power and MUX FIFO control at about 40 Hz. The status of the ADP program is SAS Bus controlled and monitored by the IDPU, which can upload RAS control I/F new software or update old one. JLT FIFO Power The ADP was found to work properly during all ground control calibration of SAS and RAS and during the full flight- memory J qualification program on the assembled spacecraft. Figure 1: ADP general scheme. REFERENCE: [2] M. Fivian et al, SPIE Proc. 4012 518-523 (2000). 42 THE HESSI SOLAR ASPECT SYSTEM (SAS) M. Fivian1, W. Hajdas1, R. Henneck1, A. Mchedlishvili1, P. Ming1, K. Thomsen1, A. Zehnder1, G. Hurford2, D. Curtis2, B. Dennis3 PSI1 - UC-BERKELEY2 - GSFC- GREENBELT3 We describe the design, performance and the pre-flight calibration of the HESSI Solar Aspect System. It is based on the optical observation of the Sun image with three linear CCDs and it will provide a position determination with accuracy < 0.4 arcsec. The Solar Aspect System (SAS) is part of the HESSI in- Calibration of the Geometry strument [1] to be launched by March 2001 at the maximum For ideal circumstances and with exactly known posi- of Solar activity. In order to reconstruct images with a resolu- tions (lens optical center, CCD pixel location), the mid-perpen- tion of 2 arcsec, the relative pointing of the imager has to be dicular of the 3 chords (i.e. the straight line between the two known with a precision of < 0.4 arcsec (on a 1 a level) at any limbs on each CCD) would intersect in one point, the mo- time. The SAS consists of 3 identical lens/sensor subsystems mentary Sun center position. Given the accuracy of our di- (spaced at 120 degrees) and provides a high rate (< 128 Hz) mensional measurements and given thermal and mechanical of information on the Solar pointing of the rotating spacecraft instabilities, the mid-perpendiculars usually do not intersect (15 rpm). Each SAS subsystem is based on focussing the Sun in one point but form a residual triangle. The best guess for through a narrow bandwidth filter (at 670 nm) onto a 2048- the Sun center is then the center of gravity of the three inter- element x (13 /xm)2 linear CCD. For each image, there are sects of the mid-perpendiculars. The size and shape of the tri- two limb crossings where the Sun image intersects the CCD. angle depend sensitively on the position of lenses and CCDs. After integration of the image for pa 500 /is (programmable), Since every momentary Sun center is overdetermined, the six a digital thresholding algorithm is used to select N pixels at measured radii and the residual triangle form a set of not self- the Solar limb for inclusion in the telemetry. [2] consistent parameters, which can be used for calibration of the SAS pointing. Therefore, the following calibration algo- Ground Based Measurements rithm has been designed [4]: For calibration, the imager with the integrated SAS sub- systems was pointed directly at the Sun. Setting an initial 1. Assume that the first lens/CCD subsystem is in correct pointing ahead of the Sun image motion, the drift of the Sun position. over the FOV (pa 1 degree) gives a well defined trajectory in the SAS image plane. Aquiring images for every integration 2. Minimize the variance of the size of the residual trian- cycle, Sun profiles were obtained. The Solar limbs (i.e. the gle by varying the two undefined angles. angle over which the intensity rises from zero to about 50 % 3. Minimize the size of the residual triangle by varying of the maximum intensity) were fitted with an error function the shift along the CCD of one of the two other CCDs. adding a linear background. [3] 4. Minimize the variance of the radii by varying the three before fitting of geometry after fitting of geometry shifts perpendicular to the CCDs. As shown in Fig. 1, these three minimization algorithms lead to a set of calibration parameters which is self-consistent. Using the ground based measurements, the geometry of the SAS could easily be calibrated to an accuracy of 5 arcsec for the angles between the CCDs and 1.5 yum for the components of the CCD positions. Therefore, the relative pointing is ex- pected to be better than 0.2 arcsec. The offset to the telescope axis and thereby the absolute pointing will be drawn from our dimensional measurements of all features of the imager. 50 100 50 100 REFERENCES time [sec] time [sec] [1] R. P. Lin et al, SPIE Proc. 3442,2 (1998). Figure 1: The left column shows the 6 measured Solar radii (upper plot) and the size of the residual triangle (lower plot), [2] R. Henneck et al, SPIE Proc. 3765, 771 (1999). i.e. the square root of the area of the triangle, for the nominal geometry of the SAS lenses and CCDs. The plots in the right [3] M. Fivian et al, PSI Ann. Report I, 39 (1999). column show the same variables after fitting of the geometri- [4] M. Fivian et al, SPIE Proc. 4012, 518 (2000). cal parameters of the SAS subsystems. 43 FABRICATION OF TRANSITION EDGE SENSOR TES E. C. Kirk1, J. E. Olsen1, Ph. Lerch1, A. Zehnder1, H. R. Ott2 PS^-ETH ZURICH2 This contribution describes the fabrication process of the TES photon detector [1]. The process [2] takes place upon a 1 mm x 1 mm x 250 nm thick pre-fabricated silicon nitride membrane. With cautious handling, the membrane with- stands most normal fabrication steps, e.g. heating to 700 degrees C, photoresist spinning, patterning and development, film deposition and wet etching. The fabrication process may not include steps which touch the membrane (contact lithog- raphy), ultrasonic cleaning or strong jets of air or liquid. The Mo and Au thermometer bilayer is sputter-deposited across the entire chip surface in an ultra-high vacuum sys- tem. Mo is a superconductor with a transition temperature (Tc) of 0.92 K. This can be tuned to the lower Tc required for the thermometer by the addition of a layer of Au. The t. -?•:. film thicknesses we have used in these devices are 40 nm of Mo and 180 nm of Au. The Mo is deposited at 700 degrees Figure 1: Picture of a TES device on its silicon ni- C, after which several hours are required to bring the sub- tride membrane: a=thermometer+absorber (smaller square), strate down to room temperature before the Au is deposited. b=contacts, c=membrane, d=substrate. The quality of the interface between the two metals is criti- cal for the strength of the proximity effect and therefore the Tc of the thermometer. To achieve a clean, reproducible in- terface, the surface of the Mo is sputter-cleaned immediately Thermometer: Mo/Au bilayer before starting the Au deposition. Transmission electron mi- . Size: 420 (lm X 420 (lm X 40 nm Ms, Tc « 120mK, Cv O.epJ/K croscopy of a cross-section through the bilayer shows the Sypereersdueirsg sontaof tay« roughness of the thinnest film (Mo) to be a few percent of its thickness. A constant film thickness is important for the _™ sharpness of the transition. BUJ The bilayer is etched away to leave a thermometer in the centre of the membrane. Figure 2: Schematic cross-section of the TES device. To connect to the thermometer, superconducting leads must be deposited on the chip. The preferred interconnect thick (approaching 1 yum) square of Au covering most of the material is Nb, because its Tc is well above that of the ther- mometer. In order to deposit only where interconnects are thermometer. For processing reasons this is best not done in required, the thermometers and other surface areas are pro- the initial deposition. If an absorber is required, the Mo film tected by a photoresist mask. At this stage, the excellent ther- thickness should be chosen such that the maximum Au thick- mal isolation properties of the silicon nitride membrane, es- ness is required to tune it to the final Tc. Figure 1 in [1] shows sential for functioning of the TES device, present a problem. that, as the Au thickness is increased, the effect on the Tc of Nb has too high a melting point to be deposited by thermal adding further Au is reduced. Otherwise, the area under the evaporation and must be sputtered, a process creating con- absorber has a lower Tc than the surrounding thermometer siderable heat. Keeping the membrane below the tempera- material, reducing the sharpness of the measured transition. ture at which the photoresist mask deforms is a challenging task. Thermally-evaporated Al contacts present fewer depo- sition problems and are currently in use, although they are REFERENCES less satisfactory because of their lower Tc and the step cov- erage where they meet the thermometer. [1] J.E. Olsen, E.C. Kirk, Ph. Lerch, A. Zehnder, H.R. Ott, Sci.Rep.2000,1, this Volume. If the energy of the photon to be detected is high enough for it to pass through the device, it may be necessary in a fi- [2] E.C. Kirk, Ph. Lerch, J. Olsen, A. Zehnder, H.R. Ott, nal processing step to add an absorber in the form of a very Nucl. Instrum. Meth. A 444, 201 (2000). 44 ARRAYS OF SUPERCONDUTING PHOTON DETECTORS Ph. Lerch1, E. C. Kirk1, J. E. Olsen1, A. Zehnder1, H. R. Ott2 PS^-ETH ZURICH2 Superconducting tunnel junctions (STJ) have reached per- formances that allow their use in scientific instrumentation. With soft x-rays, individual pixels have shown energy re- solved photon counting with an energy resolution approxi- mately an order of magnitude better [ 1 ] than the one obtained with state-of-the-art Ge detectors. Count rates up to 104 cps have been demonstrated as well. At lower energy, they com- bine a modest energy resolving power with fast response and high detection efficiency from the NIR to the EUV band. This makes this type of detector an interesting alternative to the present generation of detectors used in UV/optical astron- omy, such as CCDs and micro-channel plates. In order to fully exploit the unprecedented sensitivity of this class of detectors, one wishes to be able to pack several pixels into arrays in order to build an imaging instrument in which every pixel has its intrinsic resolution in energy. A technology demonstrator including an array of 6 x 6 pixels with parallel readout has been built by an ESA collaboration [2]. Each pixel counts single visible photons with a resolu- Figure 1: Optical micrograph of a 2 x 8 superconducting tun- tion of about 10 % at 2 eV. neling junction system. The 400 /im long strip absorbers, in- An STJ is an active device that does not store its infor- clinated at 45 degrees, are made out of high quality Ta or Nb, mation. Thus, unlike pixels used in CCD cameras, the par- 2 2 the 30 by 30 yum junctions placed at each end of the strips allel readout of N x N pixels requires N channels. Since are made out of Al/AlOx/Al/Nb. every pixel is operated in a deep cryogenic environment, the thermal load imposed by wiring all the pixels to their read- out channel is going to limit the maximum number of chan- One disadvantage of the readout scheme based on the nels. Several readout approaches like the matrix connection charge division mechanism is its intrinsic low speed. The scheme, frequency or time multiplexing are currently inves- diffusion rate D of quasiparticles in Ta [4] is only 8 to 10 tigated worldwide. cm2/sec. The precise origin of this low diffusion rate remains By separating the photon collection from the signal mea- unclear. A photon absorbed near one end of a strip of total surement functions within the device, we hope 1) to reduce length L generates quasiparticles. A large fraction will be the number of STJs without reducing the photon collection registered by the closest junction, another fraction needs a 2 area in the same proportion and 2) to limit the influence of time r = L /D to reach the other STJ where it generates the (still not completely understood) energy resolution degrading "coincidence" signal. Using L = 0.1 cm, we obtain r « 1 processes that gain in importance with energy. We built 2x8 mSec, equivalent to a count rate of 1 kHz. arrays and tested individual elements of them. Each element is a ID-strip of superconducting material (Nb or Ta) which REFERENCES acts as photon absorber. The energy of an absorbed photon generates an electric charge by the break-up of Cooper pairs. [1] S. Friedrich, et al, IEEE Transactions on This charge diffuses in the absorber, is collected - and am- Applied Superconductivity 9, 3330 (1999). plified - by 2 STJ devices microfabricated at each end of the [2] S. Kraft, P. Verhoeve, N. Rando, A van Dordrecht, strip. Each STJ delivers a signal proportional to a fraction of A. Poelaert, R. den Hartog, A. Owens, M. Bavdaz, the "primeval" electric charge that is dependent on the posi- A. Peacock, Nucl. Instrum. Meth. A 436, 238 (1999). tion of impact in the absorber. Coincidence measurement of these two signals enables to measure the energy as well as the [3] E. C. Kirk, Ph. Lerch, J. Olsen, A. Zehnder, H. R. Ott, impact location on the absorber [3]. STJs, which have about Nucl. Instrum. Meth. A 444, 201 (2000). 100 pF of capacitance, are readout by charge sensitive am- plifiers that have best equivalent noise charge of about 1000 [4] Th. Nussbaumer, Ph. Lerch, E. Kirk, A. Zehnder, e. We measured a responsivity of 2500 e/eV at 2 eV (red) R. Fiichslin, P. F. Meier, H. R. Ott, with a Nb absorber and obtained an energy resolution of 45 Phys. Rev. B 61, 9719 (2000). eV together with a position resolution of 5 microns on a total length of 200 microns at 6 keV. 45 TRANSITION EDGE SENSORS FOR ASTRONOMICAL APPLICATIONS J. E. Olsen1, E. C. Kirk1, Ph. Lerch1, A. Zehnder1, H. R. Oti2 PSI1 - ETH ZURICH2 We are developing superconducting transition edge sen- sors (TES) for the energy resolved detection of single pho- 'bias tons in the energy range from visible to X-Ray. The best resolution reported with similar /^calorimeters is 4.5 eV at 6 SQUID-Array Readout keV [1]. These devices are operated around Tb ss 100 mK. FVFUT=O II I CO When a photon of energy E1 hits the absorber of known heat capacity Cy, its energy is transformed into heat. A Sensor thermometer is then needed to measure the temperature rise Shunt IV 2mQ AT = E7/Cy proportional to the collected energy. The sharp transition (a = dlogR/dlogT m 100) of a supercon- ductor provides such a sensitive thermometer in a small tem- perature range (pa 2 mK). We use superconducting Mo/Au bilayers in which the transition temperature of Mo (Tc = 920 2.2 K mK) has been reduced to about 120 mK by proximity effect 100 mK [2]. Fine tuning of the deposition parameters is required to establish reproducible and sharp transitions (figure 1). As an alternative, an Ir (bulk Tc = 12 mK) monolayer was used Figure 2: The TES SQUID readout circuit. [3]. The bilayer is deposited on a 250 nm thick S13N4 mem- resistance RN ~ 50 mtt. A significant part of the current brane (see figure 1 b) in [4]) that provides a weak thermal flows through the shunt and if T < T , a dynamical equilib- link (G pa nW/K) to the heat bath (substrate). After an im- b c rium is established. The power permanently dissipated in the pact, the detector returns to equilibrium temperature with its thermometer flows to the substrate through the heat link G. intrinsic time constant To = Cy/G. To detect higher energy This operation mode is called ETF: the increase of the resis- photons, a Au absorber in good thermal contact with the bi- tance of the device due to the deposition of E is registered layer needs to be deposited on top of it. y as a decrease (V = cst) of the current flowing through the sensor. The device will rapidly return to its equilibrium tem- perature. The effective time constant that can be achieved is 30 • much smaller than To. 800 ETF requires a low-resistance readout scheme, achieved 20 • i \ fm l 1 with superconducting electronics, e.g. Superconducting Quan- a 10 tum Interference Devices (SQUID). 600 The electrical performances of bilayers deposited on mem- 118 120 122 124 ; : \\ T [mK] ; branes were measured, however stray impedances (sa 30 mfl) in the superconducting detection circuit precluded irradiation 400 j- m •j X experiments to be successfully performed. H Mo-Au: ds = 43 ntti \ ntti X A Mo-Au: ds = 43 ^ : 200 - ™h Mo-Au: ds = 51 nm REFERENCES guide 1 i i i i i i [1] K. D. Irwin, G. C. Hilton, J. M. Martinis, 50 100 150 200 S. Deiker, N. F. Bergren, S. W. Nam, D. A. d (Au) [nm] Rudman, D. A. Wollman, Nucl. Instrum. Meth. A 444, 185 (2000). Figure 1: Transition temperature of a Mo/Au bilayer as a [2] U. Nageletal. function of Au thickness. The inset shows the transition as J. Appl. Phys. 76 (7), 4262 (1994). measured with SQUID readout cicuit. [3] M. Frank, D. Dummer, S. Cooper, By biasing the detector with a voltage instead of the clas- J. Igalson, F. Proebst, W Seidel, sical current bias, an electro-thermal feedback (ETF) is achie- Nucl. Instrum. Meth. A 345, 367 (1994). ved. For that purpose, a shunt resistor is placed in parallel [4] E. C. Kirk, J. E. Olsen, Ph. Lerch, with the detector, as shown in figure 2. Its resistance must A. Zehnder, H. R. Ott, be an order of magnitude smaller than the bilayer's normal PSI Sci. Report 2000,1, this Volume. 46 OPERATING OF THE PROTON IRRADIATION FACILITY - CONCISE SUMMARY W. Hajdas, K. Thomsen, A. Zehnder (PSI), R. Harboe-Sorensen (ESA-ESTEC) All PIF experiments in the year 2000 were conducted in two new areas: NEB and PKC2. Beam activities utilized more than 90 shifts giving a 10% increase comparing to 1999. Different experiments were grouped into 42 test blocks resulting in 77 proton and gamma-source exposure days. Majority of tests aimed to qualify and calibrate devices and radiation monitors for forthcoming satellite missions like HESSI, INTEGRAL, PROBA and ROSETTA. PIF experiments in the year 2000, similarly as in 1999, Astrophysics, is preparing the HESSI launch in March extended through a long period from 2 February to 15 2001. Industrial research labs also carried out several large December. Researches from 17 institutes, industrial labs, experiments. The ABB Semiconductors tested sensitivity of and space agencies were involved in the irradiation tests. power devices for upsets induced by ionizing particles on These were arranged into 42 irradiation blocks of variable earth. The Marconi Applied Technologies verified number duration within which about 25 different types of tests and of Charge Coupled Devices (CCDs) to find best candidates calibrations were performed. It resulted in more than 90 for space usage. French firm TRADE, contracted by ESA, proton beam shifts distributed over about 70 days. Up to irradiated and characterized hundreds of optocouplers now it is the largest number of shifts in the whole PIF foreseen for e.g. telecommunication satellites. In addition, 60 activity record. It prominently extends behind the originally device functionality quick testing (SREM) with Co source designed upper limit of the beam time set to 60-70 shifts. became a routine extension to standard PIF operation. The most important novelty in the year 2000 was that PIF Table 2: Selected PIF experiments exposures utilized two new irradiation areas. The high- energy test site moved to the PKC2 area giving room for • SREM radiation monitor calibration construction works of the PROSCAN project. Similarly, • SRAM/DRAMs proton SEU characterization the parasitic use of the OPTIS was replaced by a new stand • Radiation damage of various CCDs in the NEB area. It made utilizing of beams much easier, prevented interference and lowered waiting time for the set- • Dose effects in photo-, laser-, and avalanche diodes up. Obviously, the future goal is to merge both low and • FPGA total dose and SEE testing high-energy site together into a single one. This facility will • Optocouplers rad-hardness determination be more user and operator friendly and cover the whole • Activation measurement of Ta, Ti, Cu, W, and Al range of energies from 0 to 250 MeV. First steps are already in a design phase in frame of the new biomedical • Radiation damage in crystal frequency shifters cyclotron project (PROSCAN) and its test areas. • Radiation effects in power MOSFETs Table 1: Beam time and test area utilization by PIF • Performance studies of PC error correcting software • Radiation damage in novel solar cell technologies PKC2 NEB "Co Total • Dose effects in power supplies for LHC Beam blocks 22 14 6 42 Table 3: Users and collaborations Shifts 64 25Y2 6Y2 92i/2 No Research Institution IRRADIATION EXPERIMENTS 2000 1 ESA / ESTEC, The Netherlands The most important trend seen in PIF activities in the year 2000 is a larger than before participation of groups from 2 PSI / GSFC / Berkeley University Switzerland. They represent about a complete spectrum of 3 ETH, Zurich conceivable users starting from universities - University of 4 University of Bern Bern through scientific institutes as CERN and industry that was represented by ABB and Contraves Space AG. As 5 ABB Semiconductors, Lenzburg usually, the largest amount of beam time was reserved for 6 Contraves Space, Zurich European Space Agency (ESA) related activities. It was 7 CERN, Genf mainly used to characterize several electronic devices and calibrate new generation of radiation monitors - SREMs. 8 HIREX, France Several missions either use them already (STRV-lc) or will 9 TRAD, France place them on board for dose and particle spectra measurements (INTEGRAL, PROBA, ROSETTA, ISS). 10 ALCATEL, France and Norway The next large activity is motivated by background studies 11 ASTRIUM, France and Germany of the HESSI satellite and relates with spacecraft materials 12 SAAB, Sweden activation during passages through the South Atlantic Anomaly. Together with NASA-GSFC and Berkeley 13 Marconi Applied Technologies, UK University, the PSI, represented by Laboratory for 47 STANDARD RADIATION ENVIRONMENT MONITOR SREM AS A SUCCESSFUL EXAMPLE OF TECHNOLOGY TRANSFER AND INDUSTRIAL COOPERATION W. Hajdas, P. Biihler, N. Schlumpf, A. Zehnder (PSI), L. Adams, E. Daly, P. Vuilleumier (ESA), HJ. Schneider (CSAG) The Standard Radiation Environment Monitor (SREM) was developed under a partnership of European Space Agency (ESA), PSI and Contraves Space AG (CSAG). Successful teamwork resulted in production of 10 devices under an ESA contract. First SREM is by now in space onboard of the STRV-lc satellite and future missions are already planned. PSI is responsible for response modeling as well as calibration of the whole production batch. Remarkable achievements of first Radiation Environment with respect to requirements of radiation dosimetry and Monitors (REMs) that flew on MIR and STRVlb satellites spectroscopy, by PSI. Calibrations were performed using encouraged continuation of the program and further PSI Proton Irradiation Facility (PIF) and the results were development of such detectors. ESA issued a bid with compared with theoretical response obtained with extensive specification requirements for a new monitor while PSI Monte Carlo simulations fabricated its reduced model and conducted preliminary After successful completion of the first part of the project, tests with particles. Several industrial firms contacted PSI ESA decided to use the 1st SREM on board of the STRV- LAP acquiring technological details needed for monitor lc mission. The satellite was launched in November 2000 design and construction. The best proposal came from the by UK Defense Research Agency. In addition, PSI LAP Swiss firm Contraves Space AG and was selected by ESA. entered a scientific collaboration of the ESA INTEGRAL Near locations of PSI and CSAG allowed for very frequent project (International Gamma-Ray Astrophysics and productive contacts. The PSI provided expertise in Laboratory) scheduled for 2002. The INTEGRAL SREM - field of electronic design, detector optimization as well as IREM was quickly adapted to the mission requirements by response modeling and tests. Close teamwork carried CSAG and PSI and is already delivered to the prime project through the whole development phase when our team contractor - ALENIA SPAZIO - for integration. attended weekly progress meetings. Contraves fabricated first model of SREM in November 1996 - see Photo 1. Because ESA considered having SREMs as a basic radiation monitoring equipment for its missions, a purchase order of 8 SREMs was issued to CSAG. PSI LAP was subcontracted with a task of calibration and verification of performances. First two devices for PROBA and ROSETTA were already tested. The PROBA - Project for On-Board Autonomy - spacecraft will fly in summer 2001 as a part of the ESA Technological Demonstration Program. Another calibrated SREM will conduct radiation measurements on board of the ROSETTA mission to be sent in 2003 to study the nucleus of comet Wirtanen. Other ESA missions with SREMs are shortly listed below: • SMART-1 - 1st European mission to the Moon flying with use of the Solar Electric Propulsion (2003). • Mars Express - 1st European flight to Mars (2003) • FIRST - infrared laboratory studying how stars and galaxies were born (2007) • Mercury Orbiter - (2009) Photo. 1: SREM Engineering Model • International Space Station - still under discussion in frame of the Technology Exposure Facility project The most important improvements in the new SREM Beside activities related to hardware qualification and design are: smaller weight and dimension, lower power calibration in frame of CSAG-PSI contract, PSI LAP began consumption and capability of detecting very high particle detailed preparations towards analysis of data from space. fluxes. The proton and electron spectroscopy is further It includes improved SREM response functions in which refined and, in addition, the monitor provides directional the satellite mass distribution is taken into account. sensitivity. Programmable alarm flags for high/low dose Moreover, software analysis packages are developed for the rates inform the mission about radiation hazard while a set Integral Science Data Center in Genf. There is also a firm of external RADFETs enables dose determination at seven interest in development of yet another family of radiation distinct satellite locations. monitors by ESA-CSAG and PSI collaboration. The prime First engineering and pro-to-flight exemplars of SREMs goal is to design a minimum intrusive, light instrument with were intensively tested and characterized by CSAG and, very powerful spectroscopic capabilities. 48 COMPARISON OF CALIBRATION RESULTS FROM PROBA STANDARD RADIATION ENVIRONMENT MONITOR WITH MONTE-CARLO SIMULATIONS C. Eggel, W. Hajdas, A. Zehnder (PSI) The Standard Radiation Environment Monitor (SREM)for PROBA satellite was calibrated at the Proton Irradiation Facility (PIF) in PSI. For measurements of proton spectra and angular distributions, the detector suite was irradiated with protons at various energies and different angles. The detector response was compared with corresponding Monte Carlo Simulations. The agreement between laboratory results and theory is very good. SREM - Standard Radiation Environment Monitor was II. SIMULATION PROCEDURE developed in partnership between ESA-PSI and Contraves Monte Carlo simulations of the SREM response are Space AG (Zurich). First monitors e.g. for ROSETTA, performed using CERN code GEANT. Simulations are PROBA and STRVlc missions are already manufactured carried out for exactly the same energies as in the by Contraves, calibrated by PSI and delivered to ESA. The experimental case and with sufficient statistics. Angular SREM is a space dedicated detector system for on-board position of the SREM is changed to cover the whole set of particle spectroscopy and dosimetry. Its calibrations are proton incidence angles. Detector areas were first re- performed using the PSI Proton Irradiation Facility in measured during the experiment and their values were set PKC2 Area, and gamma and electron radioactive sources. for simulations. Separate computations were done to find They provide a final check of instrument detection system out the fluency at the positions of the detectors heads as qualifications, give ultimate verification of the SREM well as at the beam center in order to assure the same response function and provide input for its adjustment. The conditions as in the experiment. By these means, the 1st objective is to measure monitor's parameters: energy correctness of computational setup could be verified and thresholds, detector area and dead time corrections and the SREM sealers values normalized properly. 2nd one is to provide a reference data for full set of energies and incoming angles. It is done using the same particles III. RESULTS COMPARISON and spectra as in space and results in having an accurate model of the SREM response. An accurate monitor's The agreement between experimental data and simulation computer model was constructed to compute full response results is in general very good - see Fig. 2. Though, in a matrix for protons, electrons and heavier ions for the whole few cases 10-20% differences can be seen. It is due to fine- energy range met in space. tuning of SREM discriminators and its material bulk distribution as well as beam uniformity and divergence. I. TEST FLOW AND CONFIGURATION Simulation 300 MeV / 0 deg Essential parts of the calibration procedure are shortly Experiment 300 MeV / 0 deg listed below. 1. Short Functional Test, "Co and Cosmic Ray check 2. Low energy response at 0° 3. Thresholds determination 4. Detector area measurement 5. Dead-time determination 6. Full response calibration/set of energies and angles The high-energy tests are performed with protons using five energies in the range 50.8 to 300 MeV while TC1 SI 2 513 514 515 TC2 525 01 C2 C3 C4 TC3 532 533 S34 calibrations at nine lower energies, 12.5 MeV to 60 MeV, Sealer are done using 60 MeV initial energy setup. For the 300 MeV setup the detector was irradiated at 12 angular Fig. 2: Experiment compared to Monte Carlo Simulation configurations covering the whole range polar angles for Proba SREM at energy 300 MeV and angle 0°. 0=(O° -180°) and selected azimuth angles (0°-270°). The low energy setup was used for measurements from the front V. CONCLUSIONS only as the collimators cut off protons coming from a side. For flux normalization purposes, measurements at different The numerical simulations of the detector response and the energies are performed with two plastic detectors in computer model of the SREM have proven to be positions corresponding to SREM detector heads, exactly adequately exact. They can be used to obtain full SREM as during calibration runs. Ionization chambers monitor the response matrix. In addition, they greatly support and assist proton beam current at the same. It allows for calculations in refined analysis of data from space. Simulations are now of normalisation factors so one can relate SREM sealer carried on for the application of SREM on boards of response to the corresponding proton fluence. INTEGRAL and PROBA satellites. 49 Laboratory for Muon Spin Spectroscopy Foreword Superconductivity Magnetism Semiconductors and Liquid Crystals Chemistry Research and Development with Low Energy Muons 50 LABORATORY FOR MUON-SPIN SPECTROSCOPY D. Herlach Research at the Laboratory for Muon-Spin Spectroscopy been designed to fully exploit the potential of the LE-yuSR (LMU) uses positive and (occasionally) negative muons (p+, techniqhe but will also be available for other experiments re- H~) as local magnetic probes in matter. The experimen- quiring highest intensity polarised /x+ beams. The project tal techniques referred to as [iSR (for Muon-Spin dotation, found strong support from the PSI Research Commission Relaxation, Resonance or Research) are universally applica- (FoKo) and has been approved by the PSI directorate. The ble since the polarised muons available at meson factories construction of this beam, which is planned to be installed in such as the PSI proton accelerator complex can be implanted /xE4 in 2003, will be funded to a substantial proportion by in any material. the German Mininistry for Education and Research (BMBF) The muon is a very sensitive probe of both static and dy- through the Technical University of Braunschweig and the namic magnetic properties of materials: due to its mean life- University of Konstanz, and by the British EPSRC through time of 2.2 /is and a gyromagnetic ratio of 2?r-135.5 MHz/T, the University of Birmingham. the accessible magnetic fields and widths of field distribu- In October the LMU reported to the plenary FoKo. The tions range from ~ 10 /zT to several Tesla, and the time scales result of the evaluation was very positive. In particular, the for dynamic properties from pico- to milliseconds. As a commission acknowledged the large number of high-quality + 'light isotope' of the proton (mM = 0.1 lmp) the yU can form yuSR publications, though recommended to take measures for the hydrogen-like atom Muonium (/i+e~) which may substi- keeping track of all publications based on work using the tute for hydrogen in insulators and organic materials, provid- yuSR facilities. The FoKo appreciated the presented scien- ing a very sensitive spin label. tific highlights and the demonstration of the complementary At present, our laboratory maintains and further devel- role of /uSR vis a vis of other experimental techniques, such ops six state-of-the-art /iSR instruments: three for surface- as neutron scattering and NMR, and particularly acknowl- muons (4.2 MeV /i+), one for decay-channel muons (7-60 edged the original development of bulk /iSR using muons on MeV /i+ or yU~), an avoided-level-crossing (ALC) spectrom- request. The availability of low energy muons opening /iSR eter, and the unique low-energy-muon beam and spectrome- to the investigation of surface problems, thin films, layered ter (LE-/xSR) for fj,+ of tunable energy between 0 and 30 keV. structures, magnetic nanoparticles etc. was highly appreci- Two instruments are permanently installed at the TTM3 beam ated. which is equipped with a spin rotator and a beam-sharing de- The user programs involve a large variety of topics in vice (MORE) that allows one to extract one muon from the condensed matter research. The majority of the proposals is beam upon request of one of the spectrometers, thus provid- devoted to magnetism and superconductivity. Effort is put on ing unique sensitivity to small magnetic field differences and the study of new materials such as high spin molecules, low extending the measurable characteristic times into the mil- dimensional magnetic systems, organic superconductors, con- lisecond range at 1 ns time resolution. ducting polymers, liquid crystals and novel solar cell materi- Five of the instruments are operated as a User Facility als. for which the yuSR group provides scientific and technical During the year 2000, more than one hundred articles support. In 2000, 65 research proposals of groups from PSI, based on //SR work performed at PSI have been published, Swiss universities and from abroad have been active, using of which six in Physical Review Letters. Major achievements roughly 50% of the total beam time allocated to approved have been obtained in the determination of microscopic prop- experiments at the target M and E beam lines. About 225 erties of superconductors. In particular, evidence has been scientists from 96 institutions in 21 countries are involved in found for ferromagnetic-fluctuations mediated superconduc- the /uSR proposals. tivity in UPt3 and for unconventional superconductivity in Together with collaboratoring groups from the Universi- (U,Th)Bei3. Another highlight is the observation of a large ties of Birmingham, Konstanz and Zurich, the Technical Uni- oxygen-isotope effect on the magnetic penetration depth in versity of Braunschweig and ETH Zurich - some of whom underdoped Ya;Pri_a;Ba2Cu3O7_5. Low energy muons have also provide funding and manpower and participate in the de- been used for a direct determination of the depth-resolved velopment of the LE-//SR technique - the LEM group uses profile of the magnetic field entering a superconductor (both their unique beam and spectrometer to apply the advantages inside and outside of the sample) with a few nanometers res- of/xSR to thin films and layered structures, near surfaces and olution. But as the reader may see by going through the fol- as a function of implantation depth on a nm scale. lowing 41 reports, there are many other significant contri- In 2000, a proposal and design for a new surface-muon butions of yuSR to topics of current interest, some of which beam to be installed in the present yuE4 channel has been closely related to environmental and technological problems. worked out. This beam - which is expected to provide ten times the muon flux of the present TTE3 beam - has primarily 51 OXYGEN ISOTOPE EFFECT ON MAGNETIC PENETRATION DEPTH IN UNDERDOPED YxPr1_xBa2Cu3O7_(5 A. Shengelaya1, R. Khasanov1'2, H. Keller1, E. Morenzom2, K. Conder3, and I. M. Savic4 RA-90-07, ZURICH1 - LMU/PSI2 - LNS/PSI3 - BELGRADE4 There is increasing evidence that a strong electron-pho- l.C non coupling is present in cuprates [1], which may lead to the formation of polarons (bare charge carriers accompanied by local lattice distortions) [2]. However, it is not clear whether these normal-state polaronic carriers condense into Cooper pairs. To show that this occurs, it is necessary to demon- strate that the effective mass of supercarriers m* depends on the ionic mass M. In conventional superconductors, only the 'bare' charge carriers condense into the supercarriers, and the supercarrier mass is essentially independent of M. According to the London model the magnetic field pen- o.d etration depth A in superconductors is proportional to the effective mass m* of the superconducting carriers. Thus the isotope dependence of m* can be determined from the isotope dependence of the penetration depth. Previous ex- Figure 1: Temperature dependence ofthe/iSR depolarization 16 18 periments indicated that in cuprate superconductors A is in- rate a for the O and O samples of Yo.6Pro.4Ba2Cu307. deed isotope dependent. However, in all these experiments A The back exchange data (x) demonstrate the intrinsic char- was extracted indirectly - from the Meissner fraction [3], and acter of the oxygen isotope effect. The right vertical axis from the reversible part of a torque magnetometry signal [4]. shows the value of Aa&, calculated from the formula (1). The /uSR technique is one of the most direct and accu- Our experiments are the first direct demonstration of an rate methods to determine the penetration depth in super- isotope effect on the magnetic penetration depth in cuprate conductors. Detailed /iSR investigations of polycrystalline superconductors. This implies that lattice vibrations play an important role in the occurence of high-T superconductivity. high-Tc superconductors have demonstrated that A can be c obtained from the gaussian muon spin depolarization rate a(T) ~ 1/A2(T), which probes the magnetic field distri- In a further step of research we propose to continue the bution in the mixed state. For the highly anisotropic super- study of the oxygen isotope effect on the penetration depth in conductors (like HTSC-cuprates) A is solely determinated by Yi_a;Pra;Ba2Cu3O7 as a function of Pr doping, and to mea- the shortest penetration depth Aa& and according to [5] sure directly the magnetic penetration depth in the Meissner state of thin films by low energy yuSR. Such experiments can \ab{nm) = 224/. (1) provide crucial information about the nature of the doping- induced charge carriers in cuprates. We used the transverse-field /iSR technique to measure the isotope dependence of A in Yi_xPrxBa2Cu3O7 samples with REFERENCES two oxygen isotopes 16O and 18O. [1] Proc. Int. Workshop on Anharmonic Properties o Fig. 1 shows the temperature dependence of the transverse- Tc Cuprates edited by D. Mihailovic, G. Ruani, field muon spin depolarization rate a for Yo.ePro.4Ba2Cu307 E. Kaldis, and K. A. Miiller, 118-146 sample with two oxygen isotopes. This sample has a Tc of (World Scientific, Singapore, 1994). 16 45 K. One can see that below Tc the O sample has a higher depolarization rate compared to the 18O one. We also mea- [2] A. S. Alexandrov and N. F. Mott, sured a sample with smaller Pr concentration x=0.3, where Int. J. Mod. Phys. 8, 2075 (1994). the isotope effect also exists, but it is smaller compared to [3] G. M. Zhao et al., Nature 385, 236 (1997). the x=0.4 sample. The calculations of the isotope shift in a 2 2 and correspondingly in A give Atr/tr = AA~6 /A~6 = 3.7% [4] J. Hofer et al., Phys. Rev. Lett. 184, 4192 (2000). for Pr 0.3 and 6.9% for Pr 0.4 respectively. [5] P. Zimmerman et al., Phys. Rev. B 52, 541 (1995). 52 MAGNETISM IN TETRAGONAL La2_x_ySrxREyCuO4 H.-H. Klaufi1, W. Kopmann1, D. Baabe1, D. Mienert1, H. Luetkens1, F. J. Litterst1, M. Hucker2, B. Buchner2 RA-93-05, BRAUNSCHWEIG1 - KOLN2 In this proposal we study the magnetic phases in the Rare Earth doped high-Tc system La2-xSrxCu04 (LSCO). The partial substitution of the La-Ion with Nd or Eu leads to a structural modification at low temperatures: the low temper- ature orthorhombic (LTO) phase is replaced by a tetragonal phase (LTT). In the LTT phase a new kind of incommen- 0 25 30 35 40 surate stripe like magnetic order was observed [1]. /z+SR Temperature (K) Temperature (K) as an outstanding method to observe inhomogeneous local magnetic order has played an important role, e.g. the ex- Figure 1: Gaussian relaxation rate a in 2kG transverse field on Lai.8-ySro.2EuyCu04. istence of magnetic order in La2-x-ySrxREyCu04 in an extended carrier doping range (x < 0.20) has been shown in this project and the magnetic phase diagram of the LTT with a stronger Eu-doping. Only for the samples with y = 0.20 phase has been established [2, 3]. The structural transition and 0.23 a nonzero spontaneous muon spin precession could from LTO to LTT is accompanied by a change from a su- be fitted to the time spectrum. perconducting to a magnetically ordered ground state with nearly identical transition temperatures. This can be inter- preted as evidence for a common coupling mechanism. A X (a . .10 The aim of the experiments in 2000 was to clarify the IN y= .17 • reason for the charge carrier doping dependent change from (L) .20 * T3 1.5 i: \ Y= : .23 + stripe like magnetism to superconductivity. In Lai.g_xEuo.2 Y= H i i \ SrxCuO4 this is observed at a; = 0.20. One possible expla- ft nation is the gradual decrease of the LTT tilt pattern of the 1 CuOg octahedra with increasing Sr-concentration causing a 1 ^ \ crossover to the superconducting phase at a Sr concentration (1) x corresponding to a critical tilt angle [4]. Alternatively the 0.5 • - ur x % *•**. X intrinsic charge carrier doping itself might be responsible. In 0 a comparitive study of different high-T^-systems a common iH n quantum critical point has been extracted in a number of ex- Q) 4 6 8 10 perimental properties at a hole concentration of 0.19 [5]. PS Frequency(MHz) We studied a series of La2-x-ySrxREyCu04 samples at the GPS spectrometer with a fixed carrier concentration of Figure 2: Fourier transforms of zero-field //SR spectra mea- x = 0.20 and different Europium content y between 0.10 and sured on Lai.8_ Sro.2Eu Cu04 at 1.8 K. 0.23 thereby increasing only the LTT tilt angle of the CuO@ y y octahedra. We studied the relaxation rate in 2kG transversal In conclusion the presented data clearly prove that phe- field (TF) experiments as a measure of the magnetic penetra- tion depth A in a bulk superconducting phase and of a critical nomenologically the LTT tilt angle of the CuO6 octahedra is magnetic relaxation at a magnetic phase transition. Figure 1 responsible for the change from susperconducting to mag- shows the gaussian relaxation rate a oc A~2. For y =0.10 an netic ground state. A quantum critical point at a specific increase of a below 22 K indicates the bulk superconducting charge carrier concentration x is not observed in La2-x-y Srx state with a small magnetic penetration depth. For increased EuyCu04. y a is reduced between 5 and 20 K indicating a larger field penetration or a reduced superconducting carrier density. Be- REFERENCES low 5 K a strong increase of a is due to magnetic relaxation. [1] J. M. Tranquada et al., Nature 375, 561 (1995); This relaxation is strongly enhanced in systems with y = 0.20 M. von Zimmermann et al., and 0.23. These data show that it is indeed possible to tune Europhys. Lett. 41, 629 (1998). the electronic behavior from susperconductivity to magnetic order by increasing the LTT tilt angle. [2] W. Wagener et al., Phys. Rev. B 55, R14761 (1997). In addition ZF-measurements have been performed to de- rive a sublattice magnetization from the spontaneous muon [3] H.-H. KlauB et al., Phys. Rev. Lett. 85, 4590 (2000). spin precession in a magnetically ordered state. Figure 2 [4] B. Buchner et al., Phys. Rev. Lett. 73, 1841 (1994). shows some Fourier spectra at base temperature (1.8 K). The width of the observed static local field distribution increases [5] J. L. Tallon and J. W. Loram, cond-mat/0005063 (2000). 53 CATION SIZE DISORDER-INDUCED CROSSOVER FROM SUPERCONDUCTIVITY TO MAGNETIC ORDER IN L185Mo 15C11O4 /. A. McAllister1, J. P. Attfield1, K. Prassides2, S. Rouziere2, A. Lappas3 RA-99-12, CAMBRIDGE1 - SUSSEX2 - FORTH CRETE3 Cation size mismatch (tr2) is known to alter the super- additional fast relaxation, which disappeared on heating was conducting and structural properties of the L1.85M0.15C11O4 evident in samples 3 and 4. On the other hand, a sponta- 2 + single-layer high-rc cuprates [1]. Tc decreases as a in- neous precession of the /i spin at low temperatures was ob- creases and structural transitions to the lower temperature served for samples 5-8, LI and L5, providing unambiguous LTO1, LTO2 and LTT forms [2] occur at progressively higher evidence of the development of long range magnetic order. temperatures. Earlier studies suggest that the lowest temper- The frequency of the observed oscillations at 2 K increases ature form, LTT, is responsible for the suppression of super- with a2, as shown in Figures 1 and 2. The fraction of the conductivity [3]; this phase has been found to nucleate at the magnetic component (extracted from the asymmetry) also in- LTOlandLTO2. creases with a2 but decreases with increasing temperature A preliminary yU+SR study revealed a fast relaxing com- (Figure 3). ponent of the muon spin depolarisation, due to the slowing down of the spin fluctuations. A more comprehensive study of this magnetic behaviour was subsequently carried out on the General Purpose Spectrometer and the Low Temperature 2 Facility at PSI. The compositions, a and 7"c's of the materi- als studied are given in Table 1. Structural behaviour, studied by neutron diffraction is described elsewhere [1]. A site composition aA T No. 1 c 2 Table 1: A-site compositions, (tr ), Tc's and sample numbers of the L1.85M0.15Q1O4 materials studied by /x+SR T(K) Figure 3: Fractions of magnetic (closed symbols) and non- magnetic (open symbols) components for samples 3-8, as determined from the ZF asymmetries. Increasing a2 in the L1.85M0.15G1O4 series causes mi- croscopic structural phase separation, with one phase sup- porting magnetic LRO and the other, superconductivity. REFERENCES [1] J. A. McAllister et al., Phys. Rev. Lett. 83, 3289 (1999). Time (us) [2] D. M. Paul et al., Phys. Rev. Lett. 58, 1976 (1987). + M. Onoda etal, Jpn. J. Appl. Phys. 26, 363 (1987). Figure 1: ZF-yU SR data at 2 K for samples 3-8. J. D. Axe et al, Phys. Rev. Lett. 62, 2751 (1989). In ZF-/i+SR experiments, sample 1 showed only the slow [3] A. Lappas et al., relaxation expected for a superconducting material, while an J. Phys.: Condens. Matter 12, 3401 (2000). 54 LOW ENERGY EXCITATIONS AND INHOMOGENEOUS MAGNETISM IN ELECTRON DOPED CUPRATES D. Baabe1, H.-H. Klaufi1, D. Mienert1, M. Birke1, P. Adelmanri2 and F. J. Litterst1 RA-94-12, BRAUNSCHWEIG1 - KARLSRUHE2 Introduction: Nd2-y Ce^CuC^ (NCCO) is the prototype Inhomogeneous magnetism in magnetic NCCO: Since electron-doped high-Tc cuprate crystallizing in the tetrago- an incommensurate stripe-like magnetic order has been found 3+ 4+ nal T' structure. By substitution of Nd with Ce elec- inLa2-x-yREa:Srj/Cu04 [2], [3] we investigated compounds trons with predominantly Cu-3d character are added to the of RE2-j/Cej/Cu04 (RE = Nd, Pr, Eu) with y < 0.125. Last system. This affects the Cu-3d magnetism and changes the year we found an anomalous broadening for the 1/8 com- Nd-4f spin system by diluting it. Specific heat measurements pound below 30 K. In 2000, we have performed an addi- on Nd2CuO4 from Brugger et al. [1] have shown a Schottky tional set of experiments on polycrystalline (Nd,Pr,Eu)CCO type anomaly with a peak maximum at m 1.4 K. With Ce compounds at the GPD spectrometer. The temperature de- doping the peak maximum is shifted to lower temperatures pendence of the ZF spontaneous muon spin precession fre- and a large Sommerfeld constant develops gradually in non quency v was observed for compounds NCCO with y = 0.05 magnetic NCCO. and 0.10. For NCCO with y = 0.10 a fit with one frequency Low energy excitations in non magnetic NCCO: In was not suited to account for the data. The appearance of a 2000 we performed longitudinal field /i+SR experiments on second frequency at T pa 25 K (Fig. 2) reflects the onset of a polycrystailine specimens of NCCO with y = 0.1575 and 0.19 broadening of the static field distribution as found for y = 1/8 at the LTF spectrometer to study the spin dynamics of the at pa 30 K [4]. Contrarily for NCCO with y = 0.05, no second observed low energy excitations. As reported in 1999 we ob- served an increasing relaxation rate which saturates below w 0.5 K for all investigated compounds with y > 0.15 indicat- ing the low energy excitations from the viewpoint of /x+SR. Consequently, the decoupling experiments were performed in this low temperature regime at T m 75 mK. In the fast dy- namic limit the Redfield approach leads to a magnetic field dependence of the relaxation rate A as 1 •B2 a • v A c 50 100 with a proportional to the 2nd moment of the static field temperature (K) distribution A. The results for NCCO with y = 0.1575 at T = 50 mK are plotted in Fig. 1 (left) and shows good agree- Figure 2: Spontaneous muon spin precession frequency in ment with the expected power law. From this diagram the zero external magnetic field vs. temperature for NCCO with fluctuation rate vc was calculated and plotted in Fig. 1 (right). y = 0.10. A moderately fluctuating spin system for NCCO with y = 0.15 frequency was observed. A comparison with also measured compounds Pr2_j/Cej/Cu04 with y = 0.05, 0.10 and 0.125 excludes an important role of the Nd magnetic moment on this anomaly and supports the assumption of an electronic phase separation. REFERENCES [1] T. Brugger ef al., Figure 1: 1/A vs. B2atT = 50 mK of NCCO with y = 0.1575 Phys. Rev. Lett. 71, 2481 (1993). (left). Calculated fluctuation rate vc vs. Ce content y of com- pounds NCCO (right). [2] J. M. Tranquada e? aZ., Nature 375, 561 (1995). beyond the antiferromagentic ordered regime (y pa 0.13) is [3] W. Wagenere?a/., observed. This mirrors the proximity to the magnetic or- Phys. Rev. B 55, R14761 (1997). dered regime and still existing short range correlations. The surprisingly sharp transition from a vc of MHz to GHz by [4] D. Baabe et al., changing y from 0.15 to 0.1575 may indicate a quantum crit- J. Magn. Magn. Mat., in print (2001). ical point. 55 EFFECT OF AN APPLIED CURRENT ON THE FLUX LINE LATTICE OF NbSe2 A. Yaouanc1, P. Dalmas de Reotier1, P. C. M. Gubbens2, C. T. Kaiser2, F. Lefloch1, P. L. Gammel3, A. Amato4 RA-99-10, CEA GRENOBLE1 - TU DELFT2 - BELL LABORATORIES3 - PSI4 In October 1999 we managed to observe the effect of an 4.7 K with the purpose to test the validity of the prediction electrical current on the flux line lattice in NbSe2. However, made in Fig. 2 concerning the transverse correlation length. the signal arising from the muons implanted outside the sam- Because the yuSR measurements have been done on the sam- ple, i.e. the background signal, was relatively large. In Oc- ple used for the small angle neutron scattering experiment tober 2000 we attempted to study the effect of a current with [1], any direct comparison between the muon and neutron a sample configuration designed to drastically reduced the data is meaningful. background. Unfortunately, because one of the soldering of the current wire was damaged, it occurs that any current of sufficiently large intensity (to be of interest) was heating the sample through the contact resistance. This means that we did not manage to perform better experiments than last year. i i i i i i i i i i i i i i i i i i i i i i i i i i i i • • • 10 2.0 - - 1.5 . . Bex,= 50 mT ~ -. T = 2 IK • 1.0 • Q 0.5 - - 0.0 i , . . , i . . , , i . , , . i , . . , i . . 40 45 50 55 60 65 70 Magnetic field (mT) Figure 1: one of the field distribution measured on a single crystal of NbSe2. The external field intensity is 50 mT. A 1000 field cooling procedure was used. The observed structure at H(Oe) 50 mT arises from the muon implanted outside the sample. In Fig. 1 we present a typical field distribution deduced Figure 2: The field dependence of the longitudinal corre- from a /xSR spectrum using the maximum entropy algorithm. lation length £L measured at 4.7 K by small angle neutron It is visible that the background signal is small. We decided scattering these values on a linear plot with theoretical pre- it was worthwhile to study the disorder of the field distribu- dictions. The dotted line is the prediction for the transverse tion by measuring at low temperature the distribution as a correlation length and the open circle is the result of a deco- function of the field intensity. Fig. 2 shows that the corre- ration experiment. lation length along the applied field direction increases with the field and the correlation length perpendicular to the field REFERENCES direction is also expected to increase at high field. We are [1] U. Yamn etai, presently analysing two sets of field scans taken at 2.1K and Phys. Rev. Lett. 73, 2748 (1994). 56 FLUX LINE LATTICE OF 3D SUPERCONDUCTORS P. Dalmas de Reotier1, A. Yaouanc1, P. C. M. Gubbens2, S. J. Harker2, A. Amato3 RA-00-01, CEA GRENOBLE1 - TU DELFT2 - PSI3 The discovery of high temperature superconductivity in cuprates has refocussed attention on the nature of the mixed state of type-II superconductors in general. It is now apparent that the understanding of the physical properties of the vor- tex state in high Tc superconductors requires a better under- standing of that state for 3D conventional superconductors. In recent years surprising discoveries have been made for these latter compounds. For example, the small angle neu- tron scatterring (SANS) technique has revealed the square flux line lattice (FLL) at high field for RENi2B2C [1] and V3Si [2]. The transverse field yuSR technique has confirmed the STM result [3] that the core size in NbSe2 shrinks as the field increases in the low field regime [4]. In addition, this /xSR study has proven that the London penetration depth in the flux line lattice phase is field dependent. The results obtained recently by the Vancouver /iSR group have nicely shown that the yuSR technique can yield essential information on the FLL. Surprisingly, the results obtained by the /uSR and SANS techniques are not discussed on the same footing. In particular the effect of disorder is not described with the same physical principle: the correlation length con- cept. The purpose of this proposal is to probe the FLL of con- ventional 3D superconductors by the transverse /xSR tech- nique and compare the results obtained by the /xSR and SANS techniques. The effect of disorder on the field distribution will be modelled using the correlation length concept. In 2000 we intended to focus our attention on the high-K 50 60 70 80 90 100 110 cubic superconductor VsSi (Tc ~ 16 K). The reasons are Magnetic field (mT) as follows. The physical properties of its FLL is now of much interest. The SANS technique has shown that its crys- Figure 1: Some field distributions measured on a single crys- tal structure depends on the field orientation and its intensity tal of V3Si (Tc = 16 K) with the field applied along the [100] [2]. These results are largely but not completely in agree- crystal direction. The external field intensity is 75 mT. A ment with a recent theory which accounts for the nonlocal field cooling procedure was used. character of the electrodynamics [5]. A detailed theoretical prediction has been presented recently for the temperature dependence at low temperature of the core size (the Kramer- REFERENCES Pesch effect) [6]. [1] P. C. Canfield et al, However, due to an accelerator breakdown, we managed Phys. Today 51, No. 10, 40-46 (1998). to record only 8 spectra from 20 K down to 2.1 K using [2] M. Yethiraj et al., Phys. Rev. Lett. 82, 5112 (1999). a field cooling procedure. Some field distributions derived from the spectra using the maximum entropy algorithm are [3] U. Hartmann et al, SPIE Conf. Proc. 1855, 140 (1993). presented in Fig. 1. The typical expected asymmetry of the distribution is observed, reflecting the influence of the core [4] J. E. Sonier et al, Phys. Rev. Lett. 79, 1742 (1997). size. The peak at about 75 mT observed for the two distribu- [5] V. G. Kogan et al, Phys. Rev. Lett. 79, 741 (1997). tions recorded in the superconducting regime arises from the muon implanted in the sample holder. We are now analysing [6] N. Hayashi et al., Phys. Rev. Lett. 80, 2931 (1998). these spectra. 57 MAGNETIC ORDERING IN AMMONIATED ALKALI FULLERIDES T. Takenobu1,1. Mauriri2, K. Prassides2, A. Lappas3, A. SchenckA, Y. Iwasa1 RA-93-03, JAIST1 - SUSSEX2 - FORTH CRETE3 - ETH ZURICH4 Recent progress in the synthesis of fullerene intercala- tion compounds has afforded a huge variety of materials. Among them, the ammoniated alkali fulleride (NH3)K3C6o provides a novel opportunity to investigate the correlation between molecular rotation and electronic properties, which is one of the most unique aspects of fullerene based solids. (NH3)K3C6o is synthesized by intercalation of neutral am- monia molecules into fee K3C60, which is a superconductor with Tc= 19 K. The structure of (NH3)K3C60 is very similar to that of K3C6o except for a slight orthorhombic distortion induced by ammoniation. Interestingly, despite the similar crystal structures, the electronic ground state of (NH3)K3C6o is that of an antiferromagnetic insulator with TN= 40 K, as 0.00- shown by zero-field/longitudinal-field yU+SR [1]. The mag- netic moment is on the order of 0.7 yU^/molecule. The sup- pression of superconductivity and the metal-insulator transi- + Figure 1: Evolution of the zero-field (ZF) yU spin polariza- tion in (NH )K C o are thus associated with effects of mag- 3 3 6 tion, P^it) at 5 and 80 K for (NH )KRb C . netic origin, providing an important analogy with the phe- 3 2 60 nomenology in organic and high-Tc superconductors. Recently, we have succeeded in synthesizing an isostruc- perature is described by the equation of the conventional 3D 33 tural series of (NH3)A3C6o compounds, where A is amixture Heisenberg antiferromagnet: v^= v0 [l-(T/TN)]° , with of K and Rb ions, in which the interfullerene separation is 1/0= 0.62(2) MHz and TN= 50(1) K. further substantially expanded. We observed similar behav- ior between (NH3)K3C60 and (NH3)A3C60 in electron spin resonance (ESR) measurements [2]. Thus the systematic cor- 1 1 I 1 1 1 1 relation between the structure and the magnetic properties in - this series of compounds is crucial in obtaining a compre- hensive understanding of the role of degenerate molecular 1 i orbitals in determining the properties of fullerene solids. In i this work, we have undertaken a preliminary investigation of the low-temperature ground state of some members of the - (NH3)A3C6o series by the /z+SR technique with the GPS spectrometer. Fig. 1 shows the time-dependent zero-field //+SR spec- 1 1 tra of (NH3)KRb2C60 at 5 and 80 K. No oscillating signal is f i i i i present at temperatures of 80 K and above. However, at lower 0 10 20 30 40 50 SO 70 SO temperatures, the shape of the /x+ SR spectra changes and we Temperature ( K ) observe a short-lived oscillating signal. In fitting the data, we employ a strongly-damped oscillating polarization signal Figure 2: Temperature dependence of the ZF muon preces- superimposed on a slowly relaxing component. The observa- sion frequency, v^ in (NH3)KRb2C6o. tion of a yU+ Larmor precession frequency u^ in zero external field indicates the onset of magnetic order, where the spon- We also collected time-dependent ZF-yU+SR spectra for taneous magnetization is proportional to v^. The frequency, (NH3)Rb3C6o as a function of temperature and observe sim- v^ is 0.57(1) MHz at 5 K, corresponding to a static local field ilar evidence for a transition to a low-temperature LRO mag- at the muon site, < B^ >= 42.1(1) G. In addition, the depo- netic state around 57 K. More detailed analysis of the data is larization rate of the oscillating component, Ai has a value of currently in progress. 2.5(1) fis^1 at 5 K, implying a distribution of local field with a width < 5B2 >1/2 ss 25 G, only smaller than < B^ > by a factor of 1.6. A similar local field with a large spatial inho- REFERENCES mogeneity is observed in (NH3)K3C6o [1]. Fig. 2 shows the [1] K. Prassides et al., J. Am. Chem. Soc. 121,11227 (1999). temperature dependence of the muon precession frequency and the depolarization rate of the magnetically ordered com- [2] T. Takenobu et al., Phys. Rev. Lett. 85, 381 (2000). ponent in (NH3)KRb2C6o. The variation of v^ with tem- 58 SPIN DYNAMICS IN NOVEL TRANSITION MAGNETS R. H. Heffner1, J. E. Sonier1, J. Sarrao1, D. E. MacLaughlin2, G. J. Nieuwenhuys3, O. O. Bernal4 RA-98-04, LOS ALAMOS1 - RIVERSIDE2 - LEIDEN3 - CALIFORNIA STATE4 When La2CuC>4 is doped with Sr, antiferromagnetism We also confirmed the coexistence of magnetism and su- (AFM) is destroyed at about 3% Sr content; beyond 3% a perconductivity in La2-xSrxCiii_zLiz04+y, for x = 0.15 so-called spin-glass phase exists, which has been shown by and y = 0.02. Niedermayer et al. [1] to coexist with superconductivity be- tween about 6 and 10% Sr doping. Recent measurements by Panagopoulos et al. [2] seem to show that this phase may ex- ist as high as 18-19% Sr doping. Both Li doping on the Cu site (Li1+ replaces Cu2+) and Sr doping on the La site de- stroy long-range AFM order at the same rate; e.g., T/v —> 0 at about 3% Li doping. [3] Beyond 3%, Li doping in La2Cui_zLizC>4 also leads to short-range, quasi-static mag- netic order, as found previously by us in both polycrystals 100 • T poly and single crystals with z < 0.10. N T xtal :AFM • N A poly There are significant differences in the Li- and Sr-doped T« La2CuC>4 materials, however. Although Sr doping leads to A Tn xtal superconductivity, Li-doped La2CuC>4 remains an insulator • T xtal out to at least z = 0.50. Thus, the similar depression of r T/v is remarkable in view of the very different mobilities of 10 A the Li- and Sr-doped holes. Furthermore, neutron scatter- ing has established that when sufficient numbers of holes are introduced into the CuO2 planes the dynamic magnetic cor- relations become incommensurate with the underlying lattice "Glass1 in all previously investigated La2-xAxCui_zBzO4+y (A = Sr or Nd, B = Zn) materials except B = Li. Recent inelastic scattering on z = 0.10, a; = 0, Li-doped 214 show only com- mensurate magnetic correlations for T > 15 K, the range of 1 temperatures measured. [4] 0.00 0.04 0.08 0.12 Nominal Li concentration z Our principal goal during 2000 has been to map out most of the phase diagram for Li-doped La2CuO4. As shown in Fig. 1, we have largely succeeded in doing this, although the Figure 1: Temperature versus Li concentration. T/v = Neel freezing temperatures for the concentrations > 10% Li are temperature, TQ or Tp = freezing temperature (glass state). not yet well established. Panagopoulos et al. [2] have ar- gued that there exists a characteristic temperature for the spin fluctuations in Sr-doped La2Cu04 which vanishes above a REFERENCES critical Sr concentration xc = 0.19. This concentration cor- responds to the doping at which the normal state pseudogap [1] Ch. Niedermayer et al, Phys. Rev. Lett. 80, 3843 (1998). also vanishes. From this they conclude that xc is a point of quantum criticality associated with the competition be- [2] C. Panagopoulos et al., preprint, 2000. tween spin fluctuations and superconductivity. In view of the similarity between the phase diagrams for Li- and Sr-doped [3] L. P. Le, R. H. Heffner et al., La2CuC>4, and the fact that no superconductivity exists in Phys. Rev. B 54, 9538 (1996); the Li-doped system, it is very important to pursue this com- B. J. Suh, et al., Phys. Rev. Lett. 81, 2791 (1998); parison as far as is feasible. J. L. Sarrao, et al., Phys Rev. B 54, 12014 (1996). [4] W. Bao, et al., Phys Rev. Lett. 84, 3978 (2000). 59 EFFECTS OF DIMENSIONALITY AND QUANTUM CRITICALITY ON HEAVY-FERMION SUPERCONDUCTIVITY AND MAGNETISM R. H. Heffner1, J. E. Sonier1, J. Sarrao1, D. E. MacLaughlin2, G. J. Nieuwenhuys3, O. O. BernalA RA-00-16, LOS ALAMOS1 - RIVERSIDE2 - LEIDEN3 - CALIFORNIA STATE4 We have carried out a survey of three materials in a new 0.2 CeRh Ir In • • family of heavy fermionmaterials[l]: CeRhIn5 (undergoing ; o5 o.5 5 magnetic order at T = 3.5 K), Celrlii5 (a superconductor 0.1 m H =0 : below Tc = 0.4 K) and CeRho.5Iro.5In5 (a superconductor 0.0 • • • ••••• app : below Tc = 0.8 K, undergoing magnetic order at Tm = 3.8 1.0 K). In CeRhlns the Ce moments are AFM aligned in the a-b • • • ••••• • plane, but rotate 107 degrees for each unit cell distance along T : m the c-axis [2]. Our /iSR measurements in CeRhlns show two 0.5 - • muon frequencies below Tm. • ! 0.0 •• . 1.0 In CeRho.5Iro.5In5 our most significant discovery is that ; • • • ••••• • the magnetism and superconductivity coexist microscopically. • • . : 0.5 - • J Fig. 1 shows the temperature dependence of the spin-lattice T i C relaxation rate 1/Ti, the amplitude of the single observed 0.0 i,|, i . i i . i . i . i oscillating signal Aosc, the /xSR frequency v^ and the in- • homogeneous linewidth A. All four of these quantities pass 3 smoothly through the superconducting critical temperature 2 Tc = 0.8 K, indicating very little influence of the supercon- i \ ductivity on the magnetism. Between T = 3.5 and 3.9 K, 1 we observe only a Kubo-Toyabe (KT) relaxation rate; i.e., 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 the oscillating amplitude is too small to be observed and the T(K) fluctuations are too fast to damp the nuclear KT rate. The magnetic structure has not been determined in this system, but is likely to be complicated based on neutron scattering Figure 1: Temperature dependence of zero field fit to measurements in CeRhlns. Specific heat measurements in /xSR relaxation function Aosc exp(—At) COS(2TTZ^£ + M) + our laboratory are consistent with all of the Ce atoms par- ticipating in the superconductivity. Thus, this system is evi- dentially one in which a fraction of the crystal-field ground- state moment is itinerant (and becomes superconducting) and a fraction is localized and magnetically ordered. We also carried out Knight shift measurements for H = 6 kOe parallel to the c-axis in Celrlns (Fig. 2) and 81.4 CeRho.5Iro.5In5 from T = 2 -300K. 81.3 8 1 .2 REFERENCES 81.1 [1] J. D. Thompson, R. Movshovich, Z. Fisk, F. Bouquet, Celrln5 N. J. Curro, R. A. Fisher, P. C. Hammel, H. Hegger, M. 81.O F. Hundley, M. Jaime, P. G. Pagliuso, C. Petrovic, N. E. m Phillips and J. L. Sarrao, 8O.9 J. Magn. Magn. Mat. , to be published. O 5O 1OO ISO 2OO 25O 3OO [2] Wei Bao, private communication, Los Alamos, 2000. Figure 2: Temperature dependence of the two frequencies observed in transverse field of 6 kOe. 60 GLASSY SPIN DYNAMICS IN NON-FERMI-LIQUID UCug^Pd,., x = 1.0 AND 1.5 D. E. MacLaughlin,1 O. O. Bernal,'2 R. H. Hejfner3 G. J. Nieuwenhuys,4 M. S. Rose,1 J. E. Sonier3 B. Andraka,5 R. Chau,6 M. B. Maple6 RA-00-15, RIVERSIDE1 - LOS ANGELES2 - LOS ALAMOS3 - LEIDEN4 - GAINESVILLE5 - SAN DIEGO6 Local/-electron spin dynamics in the non-Fermi-liquid heavy-fermion alloys UCus-^Pdj;, x = 1.0 and 1.5, have been studied using muon spin-lattice relaxation. The sample-averaged asymmetry function G(t) exhibits the scaling G(t, H) = G(t/H7) expected from glassy dynamics. Our results put an upper bound of ~10~3 /x ion on static magnetism in either alloy above 0.05 K, and strongly suggest quantum spin glass behavior in this system. /xSR and other experiments [1,2] have demonstrated the UCu3.5Pd,5T=0.05K importance of structural disorder in the breakdown of Fermi- 20 liquid theory in certain /-electron intermetallic compounds and alloys. Disorder-driven mechanisms have been consid- ered for the non-Fermi-liquid (NFL) properties of some of these systems, and it is natural to consider the possibility of extremely disordered or "glassy" behavior. On theoreti- AH=13Oe cal and experimental grounds it is known that glassy dynam- 10 O51 Oe ics lead to long-time correlations with distinct signatures as £ Y160Oe > • 400 Oe the freezing or "glass" temperature Tg is approached from • 1.0 kOe above [3]. In a spin glass the spin autocorrelation function A2.5kOe q(t) = (Sj(t)-Sj(O)) is theoretically predicted to exhibit power-law (q(t) = ct~a) or "stretched-exponential" (q(t) = 3 0 -4 cexp[—(Ai)' ]) behavior. Power-law correlation has been 10 10" 10-2 10" 10u found in spin-glass AgMn using /iSR [3]. 0.7 t/H Our /xSR experiments suggest that spin correlations in the NFL alloys UCu5_xPdx, x = 1.0 and 1.5, are indica- tive of glassy spin dynamics. The sample-averaged muon Figure 2: Data of Fig. 1 plotted versus the scaling vari- asymmetry G(t,H), shown in Fig. 1 for UQ^.sPdi.s, is able t/H-t, 7 = 0.7. strongly sub-exponential, indicating a quenched inhomoge- ing found in the inelastic neutron scattering (INS) cross sec- UCu35Pd15 7= 0.05 K tion [4], although the connection with glassy dynamics has not been previously noted. The present measurements ex- tend by three orders of magnitude the frequency range over which power-law correlations are observed in UCus-^Pd;,;. Zero-field /iSR shows no sign of static magnetism or spin freezing in either alloy down to 0.05 K. By definition NFL behavior is a property of the lowest- lying excitations of a metal, to which a low-frequency probe such as /uSR is extremely sensitive. The strong disorder, glassy behavior, and absence of a phase transition in UCus-^Pda; all strongly suggest that these alloys are quan- H=0 tum spin glasses [5]. 8 Time t ((is) REFERENCES [1] O. O. Bernal et al, Phys. Rev. B 54, 13000 (1996); Figure 1: Field dependence of sample-averaged muon asym- D. E. MacLaughlin etal, Phys. Rev. B 58,11849 (1998). metry relaxation function G(t) in UCu3.5Pdi.5, T = 0.05 K. [2] C. H. Booth et al., Phys. Rev. Lett. 81, 3960 (1998). neous distribution of relaxation rates, and obeys a time-field [3] A. Keren, P. Mendels, I. A. Campbell, and J. Lord, scaling relation G(t, H) = G(t/H"<) (Fig. 2) for applied Phys. Rev. Lett. 77, 1386 (1996); D. E. MacLaughlin, magnetic field H between 13 Oe and 1 kOe. The field depen- Phys. Rev. Lett. 51, 927 (1983). dence corresponds to a measurement of the Fourier transform of q(t) over the frequency range "j^H^-ir K, 200 kHz-14 [4] M. C. Aronson et al., Phys. Rev. Lett. 75, 725 (1995). MHz. Power-law behavior of q(t) is implied by the observa- [5] D. R. Grempel and M. J. Rozenberg, tion 7 < 1 [3], and also by the temperature-frequency scal- Phys. Rev. B 60, 4702 (1999). 61 STUDY OF THE MAGNETIC PROPERTIES OF Ce,Pd,nSiß AND Ce,Pd2nGeß COMPOUNDS A. Amato1, Ch. Baines1, V. N. Duginov2, A. V Gribanov3, K. I. Gritsaj1, D. Herlach1, A. A. Nezhivoy4 V. N. Nikiforov3, V Yu. Pomjakushiri2, A. N. Ponomarev4, Yu. D. Seropegin3, U. Zimmermann1 RA-97-04, PSI1 -DUBNA2 -MOSCOW3 -KURCHATOV4 Ternary rare earth compounds R-T-X (R: rare earth metal, T: transition element, X: Si or Ge) deserved recently con- siderable attention due to their interesting properties such as heavy fermion state, non-Fermi liquid behaviour, super- conductivity, mixed valence, Kondo phenomena, anomalous magnetic ordering. Cerium phases are known to exhibit these features particularly frequently. The competition between magnetic and Kondo interac- tions was traditionally considered to result in either a mag- netic ground state with full suppression of Kondo features, or in a non-magnetic Kondo ground state. However, in the last decade it has been found that there are many f-electron compounds in which magnetic ordering coexists with Kondo 0.0 behaviour. The Ce3Pd2oX6 (X = Ge, Si) systems belong to 0.0 0.2 0.4 0.6 0.8 1.0 them. Temperature, K Preliminary results of our previous experiments with the compound CesPcboSie have been published [1]. Last year 3.0 we concentrated our efforts on Ce3Pd2oGe@. It is known Ce3Pd20Ge6 that there are two separated cerium subsystems in this com- -4.0 pound [2]. One of the subsystems involves Ce3+ ions in Ce2 T = 50 mK CO positions which form 'small cubes' inside the unit cell. Ions U of each cube make up magnetic 'molecules' with a magnetic 3.0 moment that increases with decreasing temperature and un- dergo antiferromagnetic-like ordering at Tmagn. g 2.0 The second cerium subsystem consists of Ce 1 ions. These ions are less magnetically active because they have Ge as O 1.0 a nearest neighbors. The Cel atoms may mostly play the role cu of Kondo scattering centers for the conduction electrons. Q 0.0 Zero-field /iSR measurements were undertaken to gain 0.0 0.1 0.2 0.3 0.4 0.5 information about the magnetic ordering at low temperatures Longitudinal field, T using the LTF-setup. The depolarization function was repre- sented by an exponential. The temperature dependence of the Figure 1: Top: Temperature dependence of the muon spin muon-spin depolarization rate is shown in Fig. 1 (top). Below relaxation rate. Bottom: The recovery of the muon spin po- 0.4 K the increase of the depolarization rate represents the de- larization in longitudinal magnetic field. velopment of quasi-static ordering of magnetic moments of electronic origin most probably randomly oriented. We observe a recovery of the polarization in longitudinal- Further experiments at low magnetic fields are required field measurements, with fields up to IT (Fig. 1, bottom). for a detailed study of the dynamic properties of the internal This proves the dynamic nature of part of the muon-spin de- magnetic field. It seems that all magnetic anomalies can be polarization. More detailed experiments are planned at low observed only at sufficiently low magnetic field. longitudinal magnetic field. We also performed transverse-field //SR measurements REFERENCES in an external field of 3 kOe. The temperature dependence of [1] V. N. Duginov et al, Physica B 289, 43 (2000). the magnetic field seen by the muons is similar to the one in Ce3Pd2oSÍ6. [2] V. N. Nikiforov et al, Low Temp. Phys. 24, 565 (1998). 62 MAGNETIC STUDIES OF THE HEAVY FERMION COMPOUND Ce7Ni3 A. Kratzer1, D. R. Noakes2, G. M. Kalvius1, E. Schreier1, R. Wdppling3, K. Umeo4, T. TakabatakeA, H. v. Lohneysen5 RA-98-05, TU MUNCHEN1 - VIRGINIA STATE2 - UPPSALA3 - HIROSHIMA4 - KARLSRUHE5 Ce7Ni3 exhibits intermediate valence (IV) at high and low field (TF = 0.025 T) was measured just above T^. We heavy Fermion (HF) properties with 7 = 9 J/(mol K2) and observed again two signals with opposite Knight shifts and an antiferromagnetic (AFM) ground state (T/v pa 1.9 K) at cosine angular dependences. Their relative separation in fre- low temperatures. One distinguishes three different Ce sites quency has increased from 20% at 3 K to 37% at 2K, giv- in its hexagonal Th7Fe3 crystal structure, labeled Cei (one ing strong evidence for a critical divergence of both Knight atom/unit cell with trigonal point symmetry), Ce2 and Ce3 shifts (both three atoms/unit cell with monoclinic symmetry). It had been suggested that Cei is responsible for AFM order, Ce2 for the HF behavior and Ce3 for the IV contributions [1]. A recent neutron study [2] reports two successive mag- netic transitions at TN = 1.8 K and TM = 0.7 K. Below TN a single-k incommensurate (IC) spin structure is formed, with a temperature dependent modulation of moments along the c-axis. All three Ce sites are involved but with different rms moments (0.46, 0.7 and 0.1/xs for Cei, Ce2, Ce3, respec- 0.5 1.0 1.5 tively). Below TM a coexistence of a commensurate and the Temperature (K) IC structure is proposed. The AFM order vanishes at applied pressure of Pc «0.32GPa. Simultaneously non Fermi liquid Figure 2: Left: ZF-spectrum at 1.8 K for c SM. The inset (NFL) behavior appears [3]. shows the case for c || SM. Right: Temperature dependence of the spontaneous precession frequency Below TN heavily damped oscillatory muon spin preces- 0.5- Ce7Ni3 ZF 5? sion signals are seen for c _l_ SM (see Fig. 2, left, for an exam- ••••-0 c perp S g 0.4- fl ^ c par Sfl ple). They were fitted with a Bessel type oscillation in accor- 5 0.3- dance with the IC spin structure. These types of fits were un- satisfactory. They required a phase shift near 180° and thus 2 5 °- ' missed the early channels. Adding a monotonically decaying 1 0.1- * Gaussian relaxation remedied the situation, but had no theo- retical base. The likely conclusion is that a more complex 0.0- 01 23456789 10 11 12 spin arrangement than a simple IC modulation exists. An ad- Temperature (K) ditional complication are the two muon stopping sites, but, as stated, their immediate neighborhood of magnetic ions is Figure 1: Temperature dependence of the ZF-relaxation rate identical and differences are expected to be small. Indepen- above TJV dent of these fit problems one easily derives the temperature spectra were measured at the GPS facility using sin- dependence of the precession frequency (Fig. 2, right). It gle crystalline samples. The data are fully consistent with a reflects the order parameter of a second order phase transi- magnetic transition at T/v =1.85 K. The ZF relaxation rate tion. The saturation field is roughly 0.15T, a low value, but for T > TN (Fig. 1) shows critical behavior (i.e. follows a in agreement with the comparatively small Ce moments de- critical power law) typical for a second order transition. The tected by neutrons. No significant change in spectral shape critical exponent was found to be w pa 1. One further no- was seen around TM = 0.7 K. If this second transition exists tices a distinct dependence of relaxation rate on crystal ori- at all, then the spatial arrangement of Ce spins around the entation, meaning that magnetic anisotropy persists, leading muon changes only very little. The inset to Fig. 2, left reveals to non isotropic paramagnetic spin fluctuations in the vicinity that the spontaneous spin precession seen for c _L S^ is ab- of TN. The Knight shift in TF = 0.6 T between 3 K and 300 K sent for c || SM. This confirms that the moments are oriented was studied in a separate set of experiments [4]. Two signals, predominantly in c direction. Further work is in progress. one with positive, the other with negative Knight shift were observed. Both show a simple cosine angular dependence REFERENCES but with opposite phases. They were interpreted in terms of two muon stopping sites. Both are tetrahedrally coordinated [1] O. Trovarelli et al., Physica B 206, 243 (1995). b sites. Their nearest neighbor shells are identical (one Cei and three Ce3 ions), but the next nearest neighbor shell ( 3 Ni [2] H. Kadowaki et al., J. Phys. Soc. Jpn. 69, 2269 (2000). ions vs. 3 Ce2 ions) are different. The occupation of the two [3] K. Umeo et al., J. Phys. Cond. Mat. 8, 9743 (1996). sites by the muon is temperature dependent. As an extension to this work, the angular dependence of the Knight shift in [4] A. Schenck et al., submitted for publication (2000). 63 MAGNETIC PROPERTIES OF CeNiSn DOPED WITH Cu OR Pt G. M. Kalvius1, E. Schreier1, G. Grosse1, A. Kratzer1, D. R. Noakes2, R. Wäppling3, Y. Echizen4, T. Takabatake4, H. v. Löhneysen5, A. Amato6, Ch. Baines6 RA-99-03, TU MÜNCHEN1 - VIRGINIA STATE2 - UPPSALA3 - HIROSHIMA4 - KARLSUHE5 - PSI6 CeNiSn is a non magnetic Kondo semi-metal. Replac- is roughly the same as in CeNiSn [3] at base temperature, the ing Ni in part by Cu or Pt induces magnetism when a certain absence of a temperature dependence is a distinct difference critical concentration is exceeded. The absence of long- or signaling a definite change in electronic structure whose ori- even short-range magnetism in CeNiSn [1] is due to the dom- gin may be the loss of coherent AFM spin excitations with inance of Kondo interaction over RKKY coupling (TK > crystallographic disorder [4]. Furthermore, we find a linear TRKKY)- The magnitude of TK is determined by the de- field dependence of the Knight shift, again contrasting the be- gree of hybridization of the Ce 4/ state with the conduction havior of CeNiSn where a slight curvature is present. In the electron sea. The nominal picture is, that the introduction of pure material the spin correlations at low temperatures are Cu or Pt widens the unit cell which weakens the hybridza- weak and respond to even small external fields. The addition tion and in turn reduces TK below TRKKY when exceeding of Cu strengthens the correlations. The corresponding stud- the critical concentration. The transition temperature (TM) ies for the magnetic compounds with x = 0.08 and 0.2 are into a magnetic state is determined as the temperature where summarized in Fig. 2. The Knight shift in the paramagnetic the muon spin relaxation rate (in ZF) exhibits a sharp up- regime of the x = 0.2 compound exhibits a clear tempera- turn. For CeNii-^Cu^Sn we had found earlier [2] a crit- ture dependence, reflecting weak critical behavior. At TM a u ical concentration x^r « 0.07. In the present work we jump of Knight shift occurs. Both features are barely visi- studied CeNio.74Pto.26Sn which was found to be magnetic ble in the x = 0.08 material which obviously is only weakly (TM = 1.5 K) while the compound with x = 0.2 is non mag- magnetic. The TF relaxation rates show little critical behav- netic. This leads to x^ K, 0.23. Fig. 1 (which supersedes ior for both compounds, but a distinct field dependence in the the corresponding figure shown in [2]) shows that in order to paramagnetic regime which vanishes at the transition point. create a magnetic state one needs a volume expansion about In the magnetic regime the internal field fully dominates the twice as large when doping with Pt relative to Cu, mean- applied field in both cases. The ZF spectra at low tempera- ing that volume increase is not the only mechanism inducing tures for x > 0.07 are characterized by a monotonie gaus- magnetism in the CeNiSn series. Pt is isoelectronic to Ni, but sian decay of muon spin polarization, implying a disordered Cu contains one additional 3d electron. One concludes that cluster-type magnetic state [5]. an increase of d electron density helps to move towards the onset of magnetism. CeNi0.8CU0.2Sn in TF=2kG 8- -0.35 7- -CeNilxCuxSn -0.4G 6- CeNii-xPtxSn 5- -0.45 I 1- * 2kG TF 4- » ZF c o •JB 3- CO 2- 1- 0.0 0.4 0.8 1.2 1.6 2.0 0 œ 0- Temperature (K) O) 1 I CO 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Figure 2: //SR Knight shift and TF relaxation data for xoiforCu| |xcrforPt CeNii-zCu^Sn with x = 0.08 (left) and x = 0.2 (right). The ZF data are taken from previous studies. Volume Increase (%) Figure 1: Volume dependence of T M for CeNii-^Cu^Sn and REFERENCES CeNii-^Pt^Sn. The numbers at the data points give the val- ues of x. [1] A. Kratzer et ai, Europhysics Lett. 19, 649 (1992). In addition, we have performed /iSR Knight shift and [2] G. M. Kalvius et al, Physica B 289-290, 256 (2000). TF relaxation rate measurements for CeNii-^Cu^Sn com- [3] G. M. Kalvius et al, Physica B 206-207, 807 (1995). pounds with x = 0.065,0.08,0.2 (i.e. just below, just above the onset of, and well inside the magnetic regime). A small [4] A. Briickel et al, Physica B 240,199 (1997). Knight shift exists for x = 0.065, but without any tempera- ture dependence. Although the magnitude of the Knight shift [5] D. R. Noakes, J. Phys: Cond. Matt. 11,1589 (1999). 64 /LtSR STUDIES OF THE KONDO INSULATORS Ybi_xLuxB12 G. M. Kalvius1, E. Schreier1, A. Kratzer1, D. R. Noakes2, R. Wdppling3, F. Iga4, T. Takabatake4, H. v. Lohneysen5 RA-99-04, TU MUNCHEN1 - VIRGINIA STATE2 - UPPSALA3 - HIROSHIMA4 - KARLSRUHE5 High purity single crystalline samples of the Kondo insu- lators Ybi-^LuxB^ (x =0,0.125,0.5,1) were studied be- tween 1.8 and 300 K at the MORE facility with the aim to get information on local magnetic properties as a function of gap closure which is induced by the partial replacement of Yb by Lu [1]. Previously published yuSR data [2] of a powder sam- ple of YbBi2 were interpreted in terms of the development of extremely weak slowly dynamic (~ 60 MHz) magnetic cor- relations of Yb moments of less than 10~2 HB below ~ 10 K. This conclusion was based on LF=200 G relaxation data, the ZF spectra being fully dominated by dipolar couplings to the 0.00 nuclear moment of nB. We were unable to confirm the con- 50 100 150 200 250 300 Temperatur (K) YbB12 0.2 Figure 2: Temperature dependence of the LF=100G relax- \ ation rate in Ybi_a:Lua:Bi2 \ £• o.o »3»B^2K CD = The probable explanation is fast motional narrowing be- | 0.2 tween the two muon surroundings leading to a single qua- \ \ sistatic relaxation function. A site change may be another scenario which cannot be excluded. It could be initiated by 0.0 (*£,20K. molecular rearrangement which would explain the peak in 0 5 10 15 0 5 10 15 20 low LF relaxation rate. In summary, our data suggest that the Time (us) Figure 1: Raw ZF-yuSR spectra of YbBi2 elusions of [2]. First, we observed significant changes in ZF spectral shape with temperature (Fig. 1). Characteristic tem- peratures for changes are ~20K, ~100K and ~150K. This contradicts the interpretation of [2] using a single site nuclear Kubo-Toyabe (KT) relaxation with A ss 0.5 fj,s~1. Second, this single parameter set was not able to reproduce the spectra in low LF (5 to 50 G). Third, we could not confirm the drop 20 40 60 80 100 120 in LF=100 (or 200) G relaxation rate near 10 K. In contrast, Temperature (K) we found that this rate suddenly peaks sharply at 150 K. The observation that for LF > 1000 G the relaxation rate is close Figure 3: Temperature dependence of the relative intensity to zero at all temperatures agrees with [2]. It means, one ai. deals with comparatively slow dynamical effects. Fourth, we features of the /xSR spectra of Ybi_xLuxBi2 arise mainly found no systematic differences in the spectra of the various from molecular dynamics (probably within the B12 clusters) Ybi_a;Lua;Bi2 compounds with Yb content. Similarly, there and that Yb carries no detectable moment. This is supported is no contrasting behavior in the LF=100 G relaxation rate of by recent m Yb NMR measurements [3] where a minimum different Ybi_a;Lua;Bi2 compounds (Fig. 2). This excludes of 1/Ti was seen around 15 K which ties in with the tem- magnetic correlations as its origin. The ZF and low LF spec- perature dependence of ZF-//SR spectral shape. The NMR tra are difficult to fit. Below ~ 100 K, best results were ob- results on the m Yb sites differs from those at the nB sites tained with a sum of two (nuclear) Gaussian KT functions requiring an additional relaxation process for the B ions. (double relaxing with the additional relaxation present in the LF data) of widths Ai =0.52(1) jus1 and A =0.13(l)/xs"1 2 REFERENCES with temperature (but not field) dependent intensities a\ and a2 of the signal components (see Fig. 3). Above ~100K a [1] F. Iga et al, J. M. M. M. 177-178,156&377 (2000). single site static KT function with roughly the weighted av- erage of widths at 100K (A =0.22(1)/L THE MAGNETISM OF YFe6Al6 E. Schreier1, G. M. Kalvius1, F. E. Wagner1, U. Zimmermann2, D. R. Noakes3, R. Wdppling4, W. Schdfer5,1. Halevy8, J. Gaf RA-00-04, TU MUNICH1 - PSI2 - VIRGINIA 3 - UPPSALA4 - BONN5 - BEN GURION8 The RFe@Al6 (R = rare earth) spinels crystallize in the sets in, cannot be decided on yuSR data alone. Mossbauer ThMni2 structure where four lattice sites can be distinguished. spectroscopy comes to aid. Typical spectra are shown in Site 2a contains all R ions, site 8i only Al, site 8/ only Fe Fig. 2. We shall not discuss the (still preliminary) fits to the while site 8 j is randomly occupied by Fe and Al in equal pro- spectra at this stage. At low temperature all iron atoms ex- portion. We had previously studied the R=Tb, Ho, Er com- hibit magnetic hyperfine splittings in accordance with long- pounds which are known ferrimagnets (T/v ~ 340 K) and range ordered magnetism. A considerable field distribution found evidence for frustration due competing exchange in- is visible here as well. The Zeeman splitting of the ma- teractions [1]. Unpublished neutron diffraction results on jority of Fe atoms collapses towards 60 K, but a small por- YFegAlg gave no indication for the presence of long-range tion remains unaffected. Up to 320K a coexistence of mag- order. In addition, line shape analysis provided even no con- netically ordered and very short range-ordered, or otherwise clusive evidence for any short-range order. If correct, these highly correlated paramagnetic states exists. Beyond 320 K results mean that the absence of a magnetic 2a sublattice pre- the Mossbauer spectra show no longer magnetic splittings, vents magnetic order altogether, although the Fe containing the pure paramagnetic state has been reached. The resid- 8/ sublattice is considered the driving force for magnetism ual quadrupole doublet exhibits a distinct asymmetry which in all RFe6Al6 materials. To gain more insight into the sit- most probably arises from slow paramagnetic spin fluctua- uation from a local point of view, we employed yuSR and tions (paramagnetic relaxation spectrum). Slow spin fluctua- Mossbauer spectroscopies. The yuSR data were taken at the tions tie in with the still large muon spin relaxation rate seen GPS (He-flow cryostat down to 1.8 K) and GPD (N2-flow above the final magnetic transition of 320 K. In summary the cryo-oven up to 400 K) facilities. local magnetic data clearly show the existence of different kinds of magnetic order in YFegAlg. The discrepancy to the YFeeA'e neutron data remains a mystery. 0.15- 0.10- 0.05- a LF=50G * ZF 0 00- a GPS LF=50G 4- s * GPS ZF X GPD ZF 3- 2- 1- ^ ••>- 0- ! 100 200 300 400 Temperature (K) Figure 1: Temperature dependences of the /iSR signal amplitude (top) and relaxation rate (bottom) in YFegAlg. A large loss of yuSR signal amplitude occurs around 60 K (see Fig. 1 -top). This points strongly towards an onset of long-range ordered magnetism. The signal at 50 K and below can be understood as the 1/3 longitudinal part of the typical /xSR spectrum of an ordered magnet. The oscillatory trans- verse part is damped too rapidly by excessive field distribu- tions. The variation of muon spin relaxation rate with tem- perature is shown in Fig. 1 - bottom. It shows critical behav- -4 0 4 ior on approach to 60 K and thus confirms the conclusion of Velocity (mm/s) presence of a magnetic transition. The behavior of relaxation rate at lower temperatures reveals the typical approach to Figure 2: 57Fe Mossbauer spectra of YFegAlg at various tem- the quasistatic limit of ordered magnetism. Between 60 K< peratures. T <320K one observes a relaxation rate much too large for a free paramagnet. At least strong spin correlations must be present. The rate drops in the vicinity of 320 K. Whether this REFERENCES is due to another phase transition or whether muon diffusion [1] G. M. Kalvius et al. Physica B 289-290,225 (2000). 66 MACROSCOPIC AND LOCAL MAGNETIC MOMENTS IN Si-DOPED CuGeO3 WITH NEUTRON AND /zSR STUDIES F. Semadeni1, A. Amato1, B. Roessli1, P. Boni1, C. Baines1, T. Matsuda1, K. Uchinokura2, G. Shirane3, RA-00-10, PSI1 - TOKYO2 - BROOKHAVEN3 Since the first observation that the inorganic compound 0.6 0.6 CuGeO3 undergoes a spin-Peierls (SP) transition [1], an ex- tensive study of the doped system has been undertaken. Site 0.5 0.5 (Cui_ M GeO ) [2] and bond (CuGei_ Si O ) doping [3] x x 3 x x 3 0.4 studies have revealed the existence of a new antiferromag- netic phase below the SP ordering temperature TSP- In the 3 0.3 present work we report a detailed study of the phase dia- Is °- gram of Si-doped CuGeO3 single crystals by means of neu- 0.2 0.2 tron diffraction as well as zero-field field muon spin rota- O (x ff (neutrons) _ tion (/iSR). The different signals observed with the neutrons, 0.1 e 0.1 • AOSCA (\iSK) namely the AF and SP superlattice peaks, are interpreted in 0.0 0.0 terms of volume fractions via the analysis of the zero-field 0.00 0.01 0.02 0.03 0.04 0.05 muon spectra. Finally, the local magnetic moment measured Si concentration x by /iSR is compared with the macroscopic order parameter obtained by neutron diffraction. Selected samples (0.82%, Figure 2: The order parameter fj,eff as a function of Si dop- 1.7%, 2.38% and 3.8%) belonging to the series of single ing x measured with the neutron diffraction method (open crystals measured with neutrons have been investigated by circles). The effective magnetic moment determined by /iSR muon spin rotation spectroscopy in the three temperature re- is also shown. The dashed line is a guide to the eyes. gions that have been determined with neutron and suscepti- bility measurements, according to the experimental T-x dia- gram presented in Fig. 1. The values obtained from the vari- an oscillating and relaxing part. The good agreement be- ous techniques are found to be in good agreement, indicating tween neutron and /iSR results (see Figs. 1 and 2) allows that the muon and the neutrons observe a magnetic ordering to associate the precessing signal, referred to Aosc, with the at the same transition temperature. The observation of the dimerised-AF phase in the low doping regime, and with the uniform-AF phase in the high doping regime. The purely relaxing signal, Ar;x, is attributed, for x < 1.23%, to the re- • i • gions where the lattice dimerisation is maximal. However, 14 X TN (neutrons) for higher doping concentrations, this amplitude does not T (HSR) 12 - ""*= j o N disappear. It is thought to arise from an increase of static 10 o TN (X) J magnetic disorder that is induced by high doping. The com- T • TSp 00 pilation of information provided by neutron and /iSR have g 8 - in TSp (neutrons) provided a detailed insight about the origin of the various H 6 - - magnetic and non magnetic contributions observed in the Si- 4 —j=s : doped CuGeO3. The analysis of the zero-field muon spec- tra has confirmed the spatial inhomogeneity of the staggered 2 - 2 magnetisation that characterises the antiferromagnetic super- n • • • ••• lattice peaks observed with neutrons. The variation of the 0.00 0.01 0.02 0.03 0.04 0.05 macroscopic order parameter with doping can be understood Si concentration x by considering the evolution of the local magnetic moment as well as of the various regions contributing to the muon Figure 1: Temperature-concentration phase diagram of the signal. Si-doped CuGeO3. The AF ordering temperature TJV and the spin-Peierls transition temperature TSP have been deter- mined by susceptibility [4] and neutron diffraction experi- REFERENCES ments. The Tjy determined by /iSR measurements are also [1] M. Hase et al., Phys. Rev. Lett. 70, 3651 (1993). reported. The dashed lines are a guide to the eye. [2] See for ex.: S. Coad et al., SP dimerisation in susceptibility data for the samples in the J. Phys.: Condens. Matter 8, 6251 (1996). low doping regime is also confirmed by neutrons. The dis- crepancy between both methods is due to the fact that the [3] L. P. Regnault et al., Europhys. Lett. 32, 579 (1995); SP superlattice peak that is measured with neutrons becomes K. Hirota et al., J. Phys. Soc. Jpn. 67, 645 (1998). extremely small while approaching the critical concentration. [4] See for eg.: T. Masuda et al., Furthermore, we emphasise that TSP is not observed above Phys. Rev. B 61, 4103 (2000). x=1.2%. Below Tjy, the muon signal is found to consist of 67 SPIN FLUCTUATIONS IN THE TRIANGULAR ANTIFERROMAGNET CsNiBr3 P. C. M. Gubbens1, P. Dalmas de Reotier2, A. Yaouanc2, D. Visser1 S. J. Harker1 RA-00-08, TU DELFT1 - CEA GRENOBLE2 CsNiBr3 crystallizes in a hexagonal structure with mag- netic chains forming a triangular array in the plane perpen- CsNiBr3 dicular to the c-axis. This compound displays two magnetic zero field phase transitions. The c-component of the Ni magnetic mo- ment orders at TNI ~ 13.7 K, while the transverse compo- nent orders at TN2 ~ 11.6 K. The mutual magnetic moment canting partially resolves the geometrical magnetic frustra- tion inherent in a crystal structure composed of triangulars. Note that most of the magnetic properties of CsNiBr3 have been inferred from NMR results [1]. 1 .... 1 . • • i • • • • i 1.0 : CsNiBr3 : V zero field •a .2 4 : \v _ 1 Maximu m 0 - 5 10 Temperature (K) 2.0 - • Figure 2: Temperature dependence a) of the maximum mag- | 1.5 netic field at the muon site corresponding to the Bessel depo- •2 larisation function, b) of the exponential damping rate. The ^ 1.0 O) measurements are done below TNi, in the magnetically or- c Q. dered state of CsNiBr3 with the initial muon spin polarisation \ TN2 : perpendicular to the c-axis. I" V : 0.0 5 10 15 A(T) characterizes the additional exponential depolarization Temperature (K) needed to describe the spectra. Remarkably, A(T) = 0 for TN2 < T < TNI • The need for a Bessel function means the Figure 1: Temperature dependence a) of the maximum mag- Ni magnetic moment is sinusoidally modulated below TNI • netic field at the muon site corresponding to the Bessel depo- The extra distribution below TN2 may be the signature of an larization function, b) of the exponential damping rate. The additional modulation of the Ni moment. measurements are done below TNI , in the magnetically or- The measurements in the paramagnetic region indicates that the spin dynamics displays a critical slowing down when dered state of CsNiBr3 with the initial muon spin polarisation parallel to the c-axis. approaching TNi from above. Therefore, while there is still the possibility of recording spectra nearer to TNI , we can already conclude that magnetic frustration does not quench We started the //SR investigation of CsNiBr3 at ISIS. However, we could only take spectra with the initial beam the paramagnetic critical dynamics. This is in sharp contrast to one of the conclusions of the NMR work [1]. asymmetry, SM, perpendicular to the c-axis. Thanks to the spin rotator available at the GPS spectrometer, we have been able to extend the study to the c-axis parallel to SM. The de- REFERENCES polarization function for the two geometries is well described [1] S. Maegawa et al., by the product of a Bessel function with an exponential func- Phys. Rev. B 51, 15979 (1995). tion. In Figure 1 and Figure 2 we present Bmax(T) and A(T), where £?max(T) is the maximum field of the field distribu- [2] P. CM. Gubbens etai., tion corresponding to the Bessel depolarization function and ISIS Annual Report (2000). 68 LOW TEMPERATURE SPIN FLUCTUATIONS IN SPIN-LIQUID Yb3Ga5Oi2 /. A. Hodges1, P. Dalmas de Reotier2, A. Yaouanc2, P. C. M. Gubbens2, S. J. Harker2 RA-00-22, CEA SACLAY1 - CEA GRENOBLE2 - TU DELFT3 In the garnet YbsGasO^, the Yb3+ ion has a well iso- i i i i lated S' = 1/2 crystal field ground state with only a modest 0 Yb3Ga5O12 . " anisotropy. Specific heat measurements [1] evidence the ap- h pearance of short-range magnetic correlations as the temper- _ B = 0.6T ,/ - iitt ( -20 ext ature is lowered below ~ 0.5 K and a A-anomaly at 0.054 K. in 170 y Our Yb Mossbauer measurements show that below the A- co anomaly, the correlated magnetic moments continue to fluc- 0 -40 Y tuate at relatively high rates. YbsGasO^ may thus be clas- O" - // sified as a correlated spin-liquid. This property is associated -60 with the geometrical frustration of the magnetic interactions iv e t i . il/T which arises from the geometric arrangement of the Yb3+ r -80 _ 1 t ions on corner sharing triangular sublattices. Rela t I l - 1 1 1 1 ' ' 0.1 1 Temperature (K) III ! ,—^HIAI : . 3.0 Yb3Ga5O12 ; 2.5 Figure 2: Muon frequency shift measured for Y ; zero-field itSR \ with Bext = 0.6 T. The fine is an eye guide. *? 2.0 B • \ re 1.5 7 • " " 1 • " " " 1 • i • • ' • • • i • • • •' 7 pin e 1.0 3.0 • 0.04 K -: £ I * CO 7 • J 0 2.00 K J Q 0.5 2.5 L t • • : i 1 r X 0.0 - \ N ~ , 2.0 1 \ : B ; \ xx \ 0.01 0.1 1 10 100 1.5 - ®. \ U — Temperature (K) \ / X_J j 1.0 7 \ / Figure 1: Zero-field muon spin relaxation rate, Xz, for 0.5 Dampin g r \y YbsGa5Oi2. The Xz increase below ~ 0.5 K is the signature Yb3Ga5oi2 1 0.0 - of the slowing down of the magnetic fluctuations. Above ~ 1 ... i , ... i , .. i,, .. i , , , . 1 0.5 K the fluctuations are uncorrelated. The drop of Xz above 0.0 0.5 1.0 1.5 2.0 2.5 100 K could result from muon diffusion. External magnetic field (T) In Fig. 1 we present the zero-field relaxation rate ver- sus temperature measured at ISIS and PSI. Below ~ 0.5 K, Figure 3: Xz versus Bext for longitudinal field experi- we observe a slowing down of the magnetic fluctuations. No ments on YbsGa5Oi2. This behaviour of Xz(Bext) does not magnetic phase transition is detected down to 28 mK. Xz seem to have been observed previously. Whereas at 0.04 K shows no particular behaviour at the temperature of the spe- ^z(Bext) starts to decrease as the field increases, at 2.0 K, cific heat A-anomaly. The frequency shift (Fig. 2) shows a the opposite is seen. The fines are eye guides. change of behaviour near 0.5 K, it becomes temperature in- dependent and again there is no change at the temperature of the A-anomaly. Further surprising results are displayed on REFERENCES Fig. 3. A^(Sext) is unusual since in a conventional system we would expect Xz to decrease monotonically as the field is [1] J. Filippi et ah, increased. Our results seem to indicate the applied external J. Phys. C 13, 13 (1980). magnetic field has a strong influence on the Yb3+ magnetic moment dynamics and this influence is quite different at 0.04 and 2.0 K. 69 STUDY OF U- AND RE- INTERMETALLIC COMPOUNDS EXHIBITING QUADRUPOLAR AND MAGNETIC ORDER A. Schenck1, D. Andreica1, F. N. Gygax1, Y. Onuki2 RA-98-16, ETH ZURICH1 - OSAKA2 This years measurements were focused on the systems extensively studied in ZF and LF with the aim to pin down CeAg, PrCu2, GdCu2 and a few measurements on TbCu2, the spin dynamics observed in parallel to the appearance of all available as single crystals. The measurements on CeAg static fields below about 60 K. Due to problems with the could essentially be completed and the data analysis is now cryostat on Dolly these measurements could unfortunately in progress. In particular we have collected all necessary data not be completed. As an example Fig. 1 shows the //SR sig- + to indentify the yU -stopping site(s) in CeAg. Extensive ZF nal at 20 K in LF with P^ (0) andBext parallel to the crys- and LF-measurements show that magnetic correlations set in tallographic &-axis for Bext ranging from zero to 500 G. The already far above To = 5 K, namely below 20 K near the relaxation rate from the non-oscillating component is shown 2 quadrupolar ordering temperature TQ = 15 K. PrCu2 was in Fig. 2 as a function of Bext. It follows a 1/(1 + aB xt) dependence. Note that if Bext is replaced by the total field at the /i+ (By, = B + Bi t) no satisfying fit is achieved. 0.25 ext n We conclude that the observed field dependence is a prop- 0.20 500 G erty of the Pr-4f spin dynamics. ZF measurements on GdCu2 0.15 0.25 0.20 0.15 0.25 0.20 0.15 0.25 0.20 0.15 0.25 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.20 Field (T) 0.15 0.25 Figure 2: Field dependence of the spin lattice relaxation rate 0.20 at 20 K, deduced from the signals in Fig. 2. The solid line 0.15 represents a fit, see text. Also shown is the field dependence at 80 K, i.e. above the onset of magnetic order at ~ 60 K. 0.25 0.20 50 G > y> y^/;> ^ ;.\ below T/v — 40 K produced four spontaneous precession 0.15 VK lf frequencies which confirm a recent determination of the AF- 0.10 structure of GdCu2 by neutron scattering. 0.05 0.00 -0.05 -0.10 Figure 1: LF-/xSR signal at 20 K for various applied fields. 70 COMPARATIVE STUDY OF THE MAGNETIC PROPERTIES OF RARE EARTH INTERMETALLIC COMPOUNDS, COMPLEMENTING NEUTRON SCATTERING EXPERIMENTS P. Schobinger-Papamantellos1, D. Andreica2, F. N. Gygax2, A. Schencli2, P. Duong3, K. H. J. Buschow3 RA-00-11, LFK-ETHZ1 IPP-ETHZ2 - AMSTERDAM3 The magnetic ordering of the PrCoALi compound has been studied by neutron powder diffraction and magnetic D D measurements [1, 2]. Below TN = 17 K only the Pr moments V2 order with a longitudinal amplitude-modulated structure con- TN=17K fined to the c direction. The wave vector q = (0,0,qz) has an : almost T-independent length. At 1.5 K the amplitude of the I - wave is 2.24(4)yUB/Pr atom and qz =0.437(2)= 11/25 giving : vi the possibility to consider a commensurate phase. ZF-, LF- o and TF-/iSR measurements were used to study the magnetic ordering of a PrCoAl4 single crystal with the aim to check the interpretation of neutron results. The ZF signal consists of up 10° 7- to four components with amplitudes Ai, A2, A3, A4 depend- ing on the T-range: Above 30 K one observes two compo- - nents in the signal (Ai,As). Below 30 K one observes three 1 1 1 JL components (Ai,A3,A4) and below 17 K four components. 102 Only one of the components above 30 K shows a frequency Temperature (K) corresponding to a field of 0.05 T at the lowest T. The third component appearing below 30 K is associated with a very Figure 1: T-dependence of the precession frequencies in rapid relaxation probably reflecting a very wide field distri- PrCoAl4. bution and zero average field and the fourth component ap- pearing below 17 K reflects a precession in a much larger in- ternal field of 0.26 T. The T-dependence of the two frequen- der magnetostructural transition where the volume portions cies is displayed in Fig. 1. In contrast to the neutron diffrac- of the two coexisting orthorhombic LT phases display the tion results we find two additional critical temperatures at strongest T dependence as found by x-ray and neutron scat- 30 K and 90 K. tering. According to theory [3] long period structures with a wave • 111111 1 11111 11111 16 _i i i i | i i i i | i 1 ' ' 1 ' vector expressed by a rational fraction p/N where N is odd -•-- may display odd and even harmonics. The possible evolu- 20 - P TN tion of ferromagnetism in such structures [4] is due to the - 12 fact that the number of + and — moments do not match. In •i--- i "" the case of Pr3+ (having an even number of unpaired elec- P YFe E 10 '- ErFe4Ge trons) the ground state may be non-magnetic if the lowest 4 Crystalline Electric Field level is a singlet; so the observed sinusoidal structure may be stable down to 0 K. This may ex- '• plain why no higher harmonics were observed at the lowest 111 ,,, i, ,,, i, 20 40 60 80 T in the powder patterns. T[K] The /uSR experiment cannot yet distinguish between long Figure 2: T-dependence of the ZF amplitudes of the //SR period commensurate or incommensurate structures. To de- signal in the ErFe Ge and YFe Ge compounds. cide on the structure type it is necessary to determine the yU+ 4 2 4 2 site (foreseen for 2001) and to perform dipolar field calcula- tions. In any case the /iSR signal above 17 K demonstrates that short-range order sets already in at much higher T. This REFERENCES effect was not clearly evident in the neutron data. To check [1] L. D. Tung, K. H. J. Buschow. on the possible disappearance of the Pr magnetic moment for J. Alloys Comp. 37, 291 (1999). temperatures close to 0 K or the appearance of a very weak ferromagnetism we intend to extend the /iSR measurements [2] P. Schobinger-Papamantelloset ah, down to below 100 mK. J. Magn. Mag. Mater., in Press. Furthermore the investigation of ErFe4Ge2 and YFe4Ge2 powder samples confirmed the appearance of magnetic or- [3] D. Gignoux, D. Schmitt, Phys. Rev. B 48,12682 (1993). der below T/v (Fig. 2). The anomaly observed in ErFe4Ge2 [4] A.R. Ball et al, J. Magn. Mag. Mater. 119, 96 (1993). in the range 30 - 40 K traces the path of the double first or- 71 MAGNETIC CORRELATIONS IN ONE DIMENSIONAL SPIN SYSTEMS D. Mienert1, H.-H. Klaufi1, D. Baabe1, W. Kopmann1, M. Birke1, H. Luetkens1, F. J. Litterst1, U. Ammerahl2, B. Buechner1'2 and C. Geibel3 RA-99-01, BRAUNSCHWEIG1 -KOLN2 -DRESDEN3 In this work we study the magnetic phases of quasi one Ca dimensional spin- \ -systems as a function of charge carrier LaKCa= — i4 Sr]4 10- a Ca and impurity doping in the family of (Sr, Ca, La)i4Cu24O4i. *L , . This system contains CuO2 chains and Cu2O3 2-leg ladder structures [1]. Because of the large spin gap energy of the nonmagnetic La Ca ladders (A ~ 370 K [2]) for all compounds below RT the 6- I W * '° muon mainly traces the magnetic correlations on the chains. 4- s Starting with Sri4Cu24O4i, a system which exhibits a 1 ' a" of ', "„ °» doping of 0.6 holes per Cu-atom on the chain sites, we inves- 2- tigated the magnetic phase diagram as a function of hole dop- ing on well defined single crystals (Fig. 2). Ca doping leads to a considerable charge transfer from the chains to the ladder hole doping (holes per chai Cu) structures and doping with trivalent elements like La reduces the number of holes and e.g. forLa6Ca8(...) ((...)=Cu2404i) the chain and ladder structures are nominally undoped [3]. Figure 2: The phase diagram shows three different regimes + In the nearly undoped compound LasCagO..) a linear for the magnetism of the chains as studied by /i SR exper- scaling of the Knight shift and susceptibility in 0.6 T TF ex- iments. Only Sri4Cu24O4i shows spin freezing below the periments between «75 K and RT has been used to extract displayed temperature of T=10 K. The other samples seem the dipolar hyperfine coupling tensor Adip,y and a contact to be nonmagnetic or show only a weak nuclear damping downto 1.8 K. term Acontact. A comparison of this tensor with dipole cal- culations leads to a muon site (0,0.18, nil) close to the ladder oxygen atoms above the chains Cu sites (Fig. 1). observed in Sri4(...) [4]. The origin for this observed spin freezing is still not clear. To exclude impurity spin freezing of paramagnetic spins present in all those samples we have performed ZF/LF experiments on two different single crys- tals of a1 — NaV2C>5 with very much different impurity spin content. The observed relaxation is nearly identical and com- pares well with results in [4] (see figure 4). muon sites A Klauss et al., sample 1 • Klauss et al., sample 2 D Fudamoto et al. Figure 1: Muon site extracted from 6 kG transversal field experiments. We investigated several crystals with Ca and La doping in ZF and LF experiments. The observed magnetic transition 0 10 20 30 40 50 temperatures are shown in figure 2. In the undoped system temperature (K) along the chain ferromagnetic nearest neighbour spin corre- lations originating from a nearly 90 degree superexchange Figure 3: Results on two different single crystals of via oxygen atoms and antiferromagnetic interchain coupling a1 — NaV2C>5 in comparison to Fudamoto et al. [4]. is expected. By doping with spin deficiencies the antiferro- magnetic next nearest neighbour coupling ( JNNN = 11.2 meV) dominates the correlations along the chain. REFERENCES a1 - NaV O is discussed as a quarter filled ladder sys- 2 5 [1] K. Kumagai et al, Phys. Rev. Lett. 78, 1992 (1997). tem with a spin gap below 34 K. It is well established that this spin gap formation correlates with a charge ordering. [2] S. Katono et al, Phys. Rev. Lett. 82, 633 (1999). For T > Tco=34 K a single V-site with an average valence of 4.5 is observed, below Too magnetic V4+ and nonmag- [3] T. Osafune etal, Phys. Rev. Lett. 78,1980 (1997). 5+ netic V sites are concluded from different experiments [5]. [4] Y. Fudamoto et al, Phys. Rev. Lett. 83, 3301 (1999). ZF //SR spectra exhibit a spin freezing like magnetic relax- ation with quasi static order below 10 K similar to the one [5] Y. Fagot-Revurat et al, Phys. Rev. Lett. 84,4176 (2000). 72 AND SPIN-VACANCY-INDUCED MAGNETISM IN LOW-DIMENSIONAL QUANTUM SPIN SYSTEMS A. Lappas1,1. Mastoraki1, A. Schenck2, F. N. Gygax2, K. Prassides3,1. Maurin3 RA-00-09, FORTH CRETE1 - ETH ZURICH2 - SUSSEX3 Haldane suggested that the ground state for half-integer ments. For example, in the heavily Mg-doped compound systems can show quasi long-range-order (LRO) whereas, in- (x=0.24), at least 3 spontaneous Larmor precession frequen- teger spin systems have a non-zero energy gap in the spin- cies were resolved in ZF-yuSR, corresponding to local fields excitation spectrum, exhibiting a singlet non-magnetic of < Bf, >~ 20, 120, 220 G. Sizeable field distribution, ground state. An important problem, which merits further < AB2 >x/2~ 29 G, appeared to be due to large spatial in- investigation is related to the question of how the singlet homogeneities. In a preliminar approach, a phenomenolog- ground state can be suppressed and give its place to LRO. ical fit to the 1.82 K ZF data was carried out by the sum of The GPS spectrometer at the TTM3 beamline was employed PM(i) ~ A, cos(uit + 30 SrCu M g (BO ) . 2.5 1M 004 3 2 a LF100G Spin Freezing, Tf~11 K 2.0 * LF300G " X LF500G 1.5 o LF800G - « LF2kG ' \ 3.8 K s "5 0.5 DC k o.o 0.0 *# . .i . .A 10 15 20 25 30 4 6 8 10 Temperature (K) Temperature (K) Figure 1: ZF- and LF-/iSR relaxation rates. Figure 3: ZF- and LF-/iSR relaxation rates. unusual ground state was explored by //SR (ZF/LF) upon chemical substitution of the metal in the NiOg chains by non- REFERENCES magnetic Mg2+. Three samples with compositions through- out the phase diagram (x=0.04/ T/=2.52 K, x=0.12/T/=3.38 [1] Y. Uchiyama et al., Phys. Rev. Lett. 83, 632 (1999). K and x=0.24/T/=3.19 K) were found to display extremely H. Kageyama et al., Phys. Rev. Lett. 82, 3168(1999). rapid ZF depolarisation. All the zero-time asymmetry was [2] A. Lappas et al., Z. Physik B 96, 223 (1994). lost in t<2.2 /xs"1 for all samples with x>0.04. Fig. 2 presents ZF spectra below the 3.2 K antiferromagnetic-like transition [3] D. Andreica et al., Physica B 289, 176 (2000). found in DC susceptibility and neutron diffraction experi- Y. Fudamoto et al., Phys. Rev. Lett. 83, 3301 (1999). 73 STUDIES OF THE ELECTRON-DOPED Cai_xSmxMnO3 T. Chatterji1, D. Andreicci2, A. Schenck2, F. N. Gygax2, R. Suryanarayanan3, R. Revcolevschi3 RA-99-05, GRENOBLE1 - ETH ZURICH2 - ORSAY3 Following the discovery of colossal magnetoresistance (CMR) properties [1] there has been a lot of research in re- 2 - 10 - •= cent years on the hole-doped manganites Lai_xAxMn03, "K i : A fZF A 1 0 where A is a divalent element like Ca, Sr, Ba, Pb. If one con- 0.8 : P'o : r O LF siders AMnO compounds then substituting A by a trivalent CO 4 0.6 3 CD i\ rare-earth can be considered to be electron doping. Electron- 0.4 3 'L 0.2 - doped manganites also show CMR effects. Here the pure 10° i \ 4+ K> 105 110 115 120 125 • compound AMnC>3 contains only Mn ions and has no efl CO X > T(K) : electrons. By doping electrons with trivalent rare-earth el- 1 X2 3+ CD 10" ements efl levels are occupied and Mn ions are created. Ll • Q rn • 01 5 cpW • The properties of electron-doped manganites are much less : ° o Q •—" • 2 studied compared to those of hole-doped analogues but it is 10- i i i i i i i i i i i i i i i i i i i i i i i i already known that the manganites are not symmetric with 95 100 105 110 115 120 125 respect to the hole and electron doping. Here we report the Temperature (K) results of our /xSR investigations on Cai -x SmxMn03. We have performed zero-field (ZF) and longitudinal-field Figure 1: Temperature variation of the muon relaxation rates (LF) yuSR investigations on the electron-doped manganites in Cao.gSmo.iMnOs above and below TCG ~ 110 K. Above Cai-^SnXjMnOs for x = 0.1 and 0.3 on the Dolly and the TCG a stretched exponential function Ae^~xt' is used to fit GPS spectrometers of the Paul Scherrer Institute. The poly- the muon relaxation whereas below TCG two exponentially crystalline samples were pressed into cylindrical pellets of damped components have been used. The insert displays the radius of about 10 mm and thickness of about 2 mm by ap- temperature variation of the exponent (3 of the stretched ex- plying high pressure and temperature. These pellets were ponential above TCG- fixed on a fork-shaped copper sample holder with mylar foils. The sample holder was mechanically fixed to the cold tip be fitted by a single exponential component Ae^xt\ The of the helium flow cryostat. The incident muon beam was 1 perpendicular to the sample plate. The initial muon polari- relaxation rate is about 5 x lO^yUS^ . Fig. 1 displays the sation was parallel to the beam. The ZF-yuSR signals from temperature variation of these muon relaxation rates. The in- Cao.gSmo.iMnOs were recorded on the DOLLY spectrome- sert shows the temperature variation of the exponent j3 which ter at several temperatures in the range from 100 K to 120 K. decreases from about 1.0 (pure exponential) to about 0.3 at The signal showed no oscillations but relaxation which could TCG ~ 110 K. We have also measured the longitudinal field xt dependence ofthe yuSR signal at T = 105 and 120 K. From be fitted by a stretched exponential function Ae^~ ^ for the field dependence at T = 105 K we deduce an internal temperatures above T G ~ 110 K. The relaxation rate which C field spread experienced by the muon of about 1.4kG. The is about 10~1 usec~1 at T = 120 K increases with decreas- / observed strong field dependence at T = 120 K is some- ing temperature and becomes large (10/isec^1) what unusual and is not understood at present. The obser- 110 K. Below TCG ~ 110K the muon signal could be fit- vation of a stretched exponential relaxation function above ted by two exponential components A\e^Xlt^ + A^e^^^ TCG, implying an inhomogeneous distribution of relaxation downtoaboutT = 107 K at which the component Aie(~Alt) rates, could be in line with theoretical considerations that the is lost. The second component A2e^~X2t' survives down to ground state of the manganites may be unstable with respect 100 K. The asymmetry A of the signal is about 0.26 above to the appearance of a phase separation. TCG ~ HO K. Below TCG the asymmetry ofthe two compo- nents are about A\ K, 0.17 and Ai ~ 0.9. The asymmetry of the component which survives below 107 K is about one third REFERENCES of the total asymmetry and hence represents those fi+ which experience internal fields parallel to their spin. We have also [1] Colossal magnetoresistive oxides, ed. Y. Tokura, measured the temperature dependence of the LF-yuSR sig- Gordon and Breach, Science Publishers (2000) nal in a longitudinal field of 0.2 T. The LF-yuSR signal could 74 ZERO AND LONGITUDINAL FIELD RELAXATION IN LOW DOPING MANGANITES: SEARCH FOR STATIC AND DYNAMIC FERROMAGNETIC CLUSTERS R De Renzi1, G. Allodi1, M. Cestelli Guidi1, G. Guidi1, M. Hennion2, L. Pinsard'6, A. CaneiroA, F. Prado4, R. Sanchez4, A. Amato5 RA-99-06, PARMA1 - LBL2 - PARIS SUD3 - BARILOCHE4 - PSI5 The magnetic properties of LaMnO and of its low dop- 3 1.0 ing derivatives are a key to the understanding of the entire manganite phase diagram. The interplay of magnetic inter- 0.8 actions, charge and orbital ordering leads to a very rich phe- nomenology. These features reveal important aspects of the •^0.6 more general transition from the spin-correlated insulating to the metallic state, hence they are a frontier test of condensed >0.4 matter theories. In our second beam allocation (May 2000) we have stud- 0.2 ied the following samples: a single crystal of LaMnO3; mo- saics of single crystals of Lai_xCaxMnO3 (x = 0.08,0.125); 0.0 0.0 a polycrystal of KCuF . 50 100 150 50 100 150 3 T (K) T(K) Our main results are summarized below. Figure 2: Local fields vs. T (dashed lines are fig.l data). Right: Lao.92Ca0.o8Mn03; Left: La0.88Cao.i2Mn03; Tco marks charge ordering. Orbital ordering (OO) plays also an important role in manganites. In OO the planar orbital configuration of Mn3+ may give rise to alternate perpendicular orientations at neigh- bouring sites. Coherent OO states may have subtle implica- tions on magnetism and transport. To clarify this point we extended or studies to a prototype material for OO, KQ1F3, 0.0 where Cu2+ has the same local symmetry of Mn3+. It is a 50 100 150 0 50 100 150 T (K) Temperature (K) quasi-one dimensional antiferromagnet, with weak ferro cou- pling among chains (T/v = 39.5 K, in our sample). Our main Figure 1: Right: Local fields in LaMnO3; Left: Relaxation results consist in the identification of a F-Mu-F center in the rates. Insets show the critical behaviour. paramagnetic state [see J. Brewer et al.7 Phys. Rev. B 33, 7813 (1986)] and of its complex quasi-lD spectrum in the We have identified the two muon sites from dipolar calcu- ordered state. Since we know precisely the muon site, we lations, symmetry arguments and a careful study of the field can now proceed to a thorough study of magnetism in pure dependence of the muon frequencies. This allows us to give and charge doped materials. an absolute estimate of the Mn moment, which agrees with the 4[IB detected by neutrons at T ->• 0[l, 4]. Fig. 1 (left) REFERENCES shows the temperature behaviour of the two local fields and the inset shows the critical behaviour, with critical exponent [1] R. De Renzi, G. Allodi, M. Cestelli Guidi, G. Guidi, ft = 0.36(2) in agreement with Heisenberg 3D. The relax- M. Hennion, L. Pinsard, A. Amato, ation rates, T^1 and T^1 also show a critical behaviour[l, 4], Physica B 289, 52 (2000). evidencing a cross-over to an Ising 3D critical exponent value n = 0.7(1) (Fig. 1, right). The dynamical cross-over is ex- [2] R. De Renzi, G. Allodi, G. Amoretti, M. Cestelli Guidi, pected, since the ordered material does have a full anisotropy S. Fanesi, G. Guidi, F. Licci, A. Caneiro, F. Prado, (spin along a axis). R. Sanchez, S. Oseroff, A. Amato, We have taken more data on two Ca dopings, which both Physica B 289, 85(2000). show an additional magnetic transition at T = Tco (Fig. 2): [3] R. De Renzi and S. Fanesi, Physica B 289, 209 (2000). low temperatures precession frequencies abruptly give way to a single very fast Kubo-Toyabe relaxation. We have pro- [4] M. Cestelli Guidi, G. Allodi, R. De Renzi, G. Guidi, duced preliminary phase diagrams, to be compared with pre- M. Hennion, L. Pinsard, A. Amato, vious self doped LaMnO3+y data[2]. Cond. Mat. 0012158. 75 A fiSR STUDY OF THE LOW TEMPERATURE MAGNETIC PROPERTIES OF THE MOLECULAR CLUSTER Fe8 A. Lascialfari1 ,R. De Renzi2,R. Ullu1, RA-00-19, PAVIA1 - PARMA2 The metal-ion based molecular clusters are constituted of crossing at this angle. This suggests that these anomalies are identical and almost non-interacting molecules. In this way caused by the QTM process which induces local spin fluctu- one can study the properties of a single molecule by using ations seen by the muons. macroscopic amounts of a sample [1]. One of the most in- vestigated systems is the superparamagnet Fe8 [2] which is characterized by a magnetic (high-spin) S=10 ground state. Fe8:Br single crystal T=1.7K At low temperatures the S=10 ground state degeneracy is re- moved by the crystal field and the energy levels can be la- beled by Ms = 0,±l,...,±10. Ms, the magnetic quan- tum number, is the projection of the total spin S along the z anisotropy axis. At temperatures well below that corre- sponding to the energy barrier A/ks ~ DMs2 ~ 27 K, by applying an increasing magnetic field H \\ z7 level crossing conditions among theMs states are produced and phenomena associated with the quantum tunneling of the magnetization (QTM) can be singled out[3]. In the present experiment we studied the intramolecular spin dynamics with muons, a local probe, giving information complementary to that obtained by macroscopic techniques. In order to enhance the signal we aligned three single crys- tals resulting together in a total cross section to the beam of about 5 mm2. Each crystal was aligned with Q ~ 0° and, in a second experiment, 0 ~ 40°, where© is the angle be- tween the easy (anisotropy) axis and the external magnetic 0.015 field. The experiments have been perfomed at T = 1.7 K after 2000 4000 6000 zero-field-cooling of the sample by varying the longitudinal Field (Gauss) magnetic field H. The total muon asymmetry was 0.23 and that of the background was estimated to be around 0.06. The muon asymmetry recovery curves of the sample have Figure 1: Longitudinal relaxation rate A in Fe8 as a function been fitted by a sum of two different contributions, namely of the magnetic field H, for two different angles between H AL and As originating from muons coming from two very and the easy-axis. The dashed lines mark the crossing fields different sites of the crystal. The muons corresponding to at the two angles. the AL asymmetry have a long relaxation time, resulting in a flat curve. They are placed far away from the magnetic cen- tral core of Fe8. These could actually correspond to more REFERENCES than one site, indistinguishable through their muon relax- ation. The muons with As asymmetry have a shorter re- [1] D. Gatteschi, A. Caneschi, L. Pardi and R. Sessoli, laxation time I/A, giving the only decaying part of the total Science 265,1054(1994). asymmetry. They are placed near to the magnetic core. [2] C. Delfs, D. Gatteschi, L. Pardi, R. Sessoli, K. Wieghardt We focused on the X(H) behaviour at T=1.7K. Fig. 1 and D. Hanke, shows for 6 ~ 0° some anomalies in X(H) at H ~ 0.22,0.44 Inorg. Chem. 32, 3099 (1993). Tesla. These values correspond to the first two energy level crossings caused by the applied magnetic field. Analogously, [3] C. Sangregorio, PhD thesis; for 0 ~ 40°, we observed an anomaly at H ~ 0.3 Tesla, C. Sangregorio et al., Phys. Rev. Lett. (1997). which corresponds to the theoretically predicted first level 76 /xSR ON MONODISPERSE NANO-SCALE Pd CLUSTERS AT LOW TEMPERATURES P. C. M. Gubbens1, C. T. Kaiser1, F. M. Mulder1, P. Dalmas de Reotier2, A. Yaouanc2, P. M. Paulus3, L. J. de Jongh3, G. SchmidA RA-99-07, TU DELFT1 - CEA GRENOBLE2 - LEIDEN3 - ESSEN4 The materials we have studied belong to a class of giant ... i.... i. 1 1 • " • • 1 molecular clusters, in which the metal cores are members of a N 0.30 X series of "magic numbers" obtained by surrounding an atom 2, 6 N by successive shells of atoms of its kind [1], [2]. The magic 0.25 - - numbers are 13, 55, 147, 309, 561 and so on. Organic lig- CD 0 ands are necessary to stabilize the particles and for obtaining a monodisperse particle size. Studies of the magnetic sus- mc 0.20 - 0 - o 0 ceptibility and electronic specific heat, which are sensitive to '•a N 0 the electrons at the Fermi level, show a clear size dependence as 0.15 Phen* - ; pd5,1 36O2OO <: and an odd/even effect for the 5, 7 and 8 shell Pd clusters [3]. o Q. 0 ; CD Zero-field This year we have extended our study of the clusters to Q 0.10 the so-calledPd5 compound, i.e. Pd56iPheng602oo- Because i.... i. . , . i . , . , i . , 1,. ,. 1 only a limited sample material (300 mg) is available, the "fly- 0 50 100 150 200 250 300 past" set-up of GPS proved to be very useful. Furthermore, Temperature (K) the MORE device on GPS has been used to monitor the rela- tively low depolarization rate. Figure 1: Temperature dependence of the exponential relax- In a first approximation we have fitted the zero-field data ation rate Xz for Pd5giPhen3602oo in zero-field. with a single exponential characterized by a depolarization rate Xz. In Fig. 1 the temperature dependence of Xz is shown. From room temperature down to 75 K, Xz increases until reaching a plateau. This behaviour is very similar to the Pd2 3.0 sample, and could be due to muon diffusion in the palladium : • Pd56|Phen*36O200 # : 2.5 - oPhen 8 • j core. However, in contrast to Pd2 for which an additional in- : • 0 : crease of Xz is observed below 15 K, a similar effect is not ••_ 5K ° J observed in Pd5. : 0 : The initial asymmetry is reduced, indicating that part of a 1.5 7 • -. the muons form muonated radicals in the ligands surrounding * 1.0 - • ° '• the cluster core. In an attempt to show that a large fraction of the measured signal arises from the Pd core, additional high 0.5 : . ° : field measurements were performed on the Pd5 compound - • • 0 0.0 - 0 0 0 - and the pure ligand sample. In Fig. 2 the areas underneath , ,i 1 1 1 the spectra for both the Pd5 and the ligand sample versus ap- 0.1 1 10 100 plied magnetic field are shown. Both sets of data are clearly External magnetic field B (mT) different at lower fields, indicating some muons in the Pd5 ext sample do indeed measure an effect of the Pd core. More- over, an increase of the area for Pd5 compound and the lig- Figure 2: Field dependence of the area underneath the spectra and Phen seems to start around 0.5 mT, which is about the for both Pd5 and Phen at 5K. same order of magnitude as observed in Pd2. At very high fields both curves are similar. A preliminary analysis of this result indicates that roughly 50% of the muons are located in REFERENCES the Pd clusters and the other half in the Phen ligands. At low [1] G. Schmid (ed.), Clusters and colloids, from theory to field the signal of the muons is mainly composed of the Pd cluster contribution, whereas the contribution of the ligand is applications, VHC, Weinheim, 1994. small. Aim of future analysis will be to separate the Pd-core [2] L. J. de Jongh (ed.), Physics and chemistry of metal from the ligand contribution. This will enable us to obtain cluster compounds, Kluwer, Dordrecht, 1994. both the correlation time and width of the field distribution due to the delocalized electron in the Pd core. [3] Y. Volokitin, et al, Nature 384 (1996) 621; see also N&V ib 612. 77 STUDY OF THE DYNAMIC AND STRUCTURE FEATURES OF MAGNETISM IN HOLMIUM V. N. Duginov1, K. I. Gritsaj1, D. Herlach2, A. A. Nezhivoy3, B. A. Nikolsky3, V. G. Olshevsky1, V. Yu. Pomjakushin1*2, A. N. Ponomarev3, U. Zimmermann2 RA-98-01, DUBNA1 - PSI2 - MOSCOW3 It is known that for 20 K < T < 132 K the magnetic struc- 217 ture of holmium is an antiferromagnetic (AF) helicoid which restructures into a ferromagnetic (FM) helicoid at Tc = 20 K. The spiral structure wavelength along the c-axis and the distance between the basal planes of the crystal lattice are, generally speaking, incommensurate. A phenomenological description of such an incommensurate helicoid is the model of a magnetic spin-slip structure, according to which only six equivalent directions of magnetic moments in the basal planes are possible, corresponding to the hexagonal symme- try. According to the spin-slip model, an individual angle ceind between the directions of magnetization of two neigh- boring basal planes can assume only two values, 0 (doublets planes) or 60° (singlets planes). 205 39 41 43 45 47 In a simple helicoid structure («¿„d = a) all intersti- Temperature, K tial sites are magnetically equivalent, and in a /iSR exper- 132 iment only one muon-spin precession frequency should be observed at a given temperature. In the spin-slip structure, the interstitial fields in different sections of the helicoid are different and the frequency spectrum of the spin precession signal should be more complicated. Zero field measurements were performed on a textured sample of holmium and on a the single crystal which was cut off from the textured sample. High-statistics spectra were measured below the Néel temperature near the spin-slip point. The c-axes of the textured sample were oriented parallel to the polarization of the muon beam. We used the CCR cryo- stat of the GPD spectrometer and performed measurements at temperatures around 96 K, 42 K, and 24 K. At each tempra- 112 ture, about 15-106 events were collected in the 'backward' 93 95 97 99 101 8 Temperature, K and 30-10 in the 'forward' detectors, respectively. The spectra in the AF temperature regime are described Figure 1: Temperature dependence of the muon-spin preces- satisfactorily by a single muon-spin precession frequency. sion frequencies around the 42 K and 96 K spin-slip temper- The temperature dependence of the measured precession fre- ature points. quencies is shown in Fig. 1. The spin-slip transition near 42 K seems to be most suit- able for a yuSR study because it is situated at a smoother part in the case of the single-crystal sample, too. This may be of the Brillouin curve, but it is also evident that significantly connected with the features of the domain structure and/or higher precision is needed for the determination of the muon- different magnetic environments for the muons. spin precession frequencies. The spin-slip point near 24 K is In 2001 we are not planning to perform yuSR experiments distorted by the proximity of an unexplained drop of the spin on holmium because for the data obtained so far a more com- precession frequency not far from Tc [2]. plex analysis and theoretical interpretation is needed first. In earlier experiments with the textured sample [1] we have performed measurements of the form of the muon-spin REFERENCES precession signal in the FM region. In 2000 we have re- peated this experiment with the single-crystal in the 'deep' [1] A. N. Ponomarev et al, Physica B 289, 236 (2000). FM region. Typical statistics was about 5.5-106 in the 'back- 6 [2] E. Schreier et al, Physica B 289, 240 (2000). ward' and 12-10 in the 'forward' detectors. At 6 K and 8 K the muon-spin precession signal proved to be complex 78 SPONTANEOUS MAGNETIC ORDERING IN SODIUM ELECTRO SODALITE R. Scheuermann1, E. Roduner1, B. Grofi1, G. Engelhardt1, D. Herlacli2, A. Schenck3, A. Amatd2, W. Waeber2 STUTTGART1 - PSI2 - ETH ZURICH3 Sodium-doped anhydrous sodium sodalite (sodium-elec- tro-sodalite, SES) represents a unique model system of a body-centered cubic (bcc) lattice of paramagnetic clusters, analogous to F centers in ionic solids. The sodalite frame- work is built by an alternating network of corner-sharing AIO4 and SiC>4 tetrahedra, forming truncated octahedral cages (J3- or sodalite cages) arranged on a bcc lattice. The particu- lar type of F center is a Na3+ ionic cluster (four alkali cations in a tetrahedral geometry sharing one electron) located in- side a /?-cage. At high sodium loadings their large density (« 1021 cm"3) allows one to study their interaction. The ex- change coupling between unpaired electrons leads to an anti- 0 2 4 6 ferromagnetic phase transition, observed in nuclear magnetic f[HS] resonance (NMR), electron paramagnetic resonance (EPR), Figure 1: Spontaneous muon spin precession in SES at low and static susceptibility measurements [1]. temperatures, polarization fitted to Eq. 1. In this work we present results from zero-field muon spin rotation experiments performed at the surface muon beams in 1.4-1 area TTE3 (DOLLY) and TTM3 (GPS) on a powder sample of 1.2- 280 mg black SES (sodium loading « 90 %). As no exter- nal field is applied any muon spin precession is only due to 1.0- internal fields, and anisotropy does not play a role. Fig. 1 £0.8-1 shows the measured forward-backward asymmetry at differ- ent temperatures. Clearly, spontaneous magnetic ordering, 1,0.6- reflected in muon spin precession, sets in below pa 50 K. 0.4- The data were analyzed in the time-domain, best fitted by a three-component polarization function 0.2- -At , 0.0 •a e -rt P(t) = aLe aGe R (1) 0 10 20 30 40 50 7[K] OL reflects the volume fraction of magnetic domains and de- creases with increasing temperature near the phase transition. Figure 2: Temperature dependence of the zero-field preces- The Lorentzian relaxation rate A increases when approaching sion frequency, fitted to Eq. 2. the Neel temperature, indicating a non-uniform local mag- netic field near the phase transition ('melting of magnetic do- The second term in Eq. 1 is ascribed to a fraction of non- mains'). Although the specific site of the muon in the lattice precessing muons in a local field parallel to their spin direc- is not known, the rather small damping rate of the preces- tion and/or to muons in paramagnetic regions. The third term sion signal leads to the conclusion that the field distribution is attributed to muonium formation. A decoupling experi- around the stopping sites is very homogeneous and the pre- ment at 50.4 K clearly shows the existence of a system akin cession signal originates from muons stopped at equivalent to muonium. At low magnetic fields (up to 500 G) the dipolar sites. interaction with the nuclear magnetic moments of 27A1 and 23Na leads to a reduction of the observed muonium asymme- The temperature dependence of the precession frequency try, and GSL + GSQ + 2aR to be less than the full beam asym- v{T) (equivalent to a magnetization curve) shown in Fig. 2 metry. can be fitted perfectly by the expression taken from [2]: REFERENCES [1] V. I. Srdanov et ah, Phys. Rev. Lett. 80, 2449 (1998). u0 = (1.250 ± 0.003) MHz corresponds to a local magnetic field at the muon site of B\oc K, 92 G. TN = (50.51 ± [2] A. Schenck etal, 0.07) K is obtained for the Neel temperature. /? = (0.406 ± J. Phys.: Cond. Matter 10, 8059 (1998). 0.009) is close to the theoretically predicted value of 0.38 [3] J. J. Binney et al, The Theory of Critical Phenomena, for a three-dimensional Heisenberg system [3]. S = (2.59 ± Oxford University Press, Oxford (1992). 0.07) is a phenomenological parameter and reflecting magnon excitations [2] (predicted to be 2 for a cubic system [4]). [4] R. Kubo, Phys. Rev. 87, 568 (1952). 79 FORMATION OF CONDON DOMAINS IN LEAD AT VERY LOW TEMPERATURES G. Solt1, V. S. Egorov2, C. Baines1, D. Herlach1, U. Zimmermann1 RA-94-14, PSI1 - KURCHATOV2 The thermodynamic instability of a uniform system with local fields inside the domains appears as a broadening of very high differential magnetic susceptibility \ = dM/dB > the spectral line (as compared to the uniform state outside 1/4TT leads, in the case of metal single crystals with large the domain sections), resulting in the peaks in Fig. 1. For amplitude de Haas-van Alphen (dHvA) oscillations, to the slightly lower (H < 2.2 T) or higher (H > 2.6 T) fieldsth e break-up of the homogeneous state with the arisal of dia- and sharp peaks of A disappear, indicating that the phase bound- paramagnetic domains [1, 2]. In this state, the occupation of aries for the Condon domain state in the (B, T) plane are, Landau levels and thereby the magnetizations ±MV in the for this 'domain-active' (Q mode, unexpectedly 'steep'. The two kinds of domains are 'frozen', and the response of the quantum oscillations are damped with increasing tempera- system to changes of the applied field consists in varying ture, and the observed peak height oc 8irMp decreases as merely the volumes of the oppositely magnetized regions. shown in Fig. 2. The domain state reappears periodically with the variation of the external field H, the period and the 'domain section' within the dHvA cycle are related to the electron Fermi sur- face (FS). By the use of /iSR the study of the domain phase in Be has become possible [3, 4]. Also, a first observation of domains in white Sn has recently been reported [5]. In fact, for highly pure metal single crystals at sufficiently low tem- perature, Condon domains should always be stable in a given field range determined by the FS geometry. The present yuSR results for Pb shown in Figs. 1 and 2 provide new evidence for this. 0.20 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 temperature T (K) Figure 2: Peak height (proportional to domain magnetization Mp) as function of the temperature, with H kept constant at the first maximum of A in Fig. 1. A more detailed investigation of the domain state and of the phase boundaries in Pb are projected. 0.06 23950 23970 23990 24010 24030 REFERENCES applied field H (Oe) [1] J. H. Condon, Phys. Rev. 145, 526 (1966). Figure 1: Exponential damping rate A (line broadening) of the /xSR signal at T = 20 mK. The distance between the [2] D. Shoenberg, Magnetic oscillations in metals, periodical peaks corresponding to centers of the domain sec- Cambridge University Press, Cambridge 1984. tions is AH pa 34 G. [3] G. Solt, C. Baines, V. S. Egorov, D. Herlach, E. Krasnoperov, U. Zimmermann, The Pb single crystal plate was oriented normal to the ex- Phys. Rev. Lett. 76, 2575 (1996). ternal field if 11 [110]. The period AH PS 34 G corresponds to a dHvA mode with frequency F = H'2/AH Pa 1694 T, [4] G. Solt, C. Baines, V.S. Egorov, D. Herlach, near to the known [6] value i /xSR DYNAMICS OF LIQUID CRYSTALS STUDIED BY ALC S. J. Blundell1, B. W. Lovett1, F. L. Pratt2,1. M. Marshall1,1. D. Reid3, W. Hayes1, RA-97-22, OXFORD1 -ISIS2 -PSI3 The uniaxial nematic (N) mesophase of a liquid crystal [1] is a state of matter which exhibits symmetry properties intermediate between those of a solid (S) and an isotropic liq- uid (I). In the N phase, molecules have translational freedom and orientate preferentially along one particular axis, which is defined by a unit vector called the director, n. Nuclear magnetic resonance (NMR) measurements have elucidated many of the dynamical properties of the N state. The use- fulness of the positive muon, an alternative local magnetic probe, has recently been established in dynamical studies of 29 °C (N) small organic molecules and so we wished to apply this tech- nique to liquid crystals. C(S) CO 1.75 1.8 1.85 1.9 1.95 2.0 2.05 Figure 2: ALC spectra taken from 5CB for four different CD temperatures. •o D "5. crossing. Thus if the muons are implanted with their spins transverse to the field, their spins will precess. Two preces- < sion frequencies are expected, corresponding to the selection c rule A/z = ±1, ASZ = 0, and are obtained by fast Fourier o transform of the raw muon time spectra and their average value is A^. In a field of 200 mT we identified four pairs CD of Mu precession frequencies (not shown). By correlating o these peaks, we obtain a spectrum in A^. Four peaks are o clearly visible in this correlation amplitude spectrum in the I phase, which then broaden with decreasing temperature as is shown in Fig. 1. In the I phase, where D^ is averaged out, 400 420 440 460 480 500 520 540 the peaks correspond to four values of A^. These are due Hyperfine Frequency (MHz) to the four possible inequivalent sites for Mu addition to the 5CB molecule. Figure 1: Structure of 5CB showing four muon positions and In our ALC studies, we observe four AM = 0 reso- corresponding correlation amplitudes obtained from a TF ex- nances, one for each of the four possible Mu addition sites. periment. The cross marks an artifact peak. For the I phase all dipolar parts of the Hamiltonian are aver- aged out, so we expect only the Fermi contact terms to con- To demonstrate the feasibility of applying the muon spin tribute. This is not the case for the N and S phases. We use a rotation/ relaxation (/iSR) technique to nematics we present model [2] of the molecular dynamics to fit these spectra. The the results of measurements carried out on the nematic com- fitted curves are shown in Fig. 2. Further details and also pound 4' -n-pentyl-4-cyanobiphenyl (5CB), whose molecular longitudinal-field data are reported elsewhere [2]. structure is shown in Fig. 1. It has a S-N transition at 24°C and a N-I transition at 35°C. It is chemically the simplest REFERENCES nematic mesogen known and is thus a good choice for this first investigation. In 5CB, as in other organic materials, we [1] P. G. de Gennes and J. Prost, The Physics of Liquid expect muonium (Mu = /U+e~) to form by electron capture Crystals, 2nd edition, Clarendon Press, Oxford (1993). soon after implantation. At high magnetic field (» 20 mT) [2] B. W. Lovett, S. J. Blundell, J. StieBberger, F. L. Pratt, T. the eigenstates of the muon-electron system are well approx- Jestadt, S. P. Cottrell and I. D. Reid, imated by the two particle Zeeman states quantized in the Phys. Rev. B 63, 054204 (2001). field direction, except in the special case of an avoided level 81 IN II-VI SOLAR CELL MATERIALS N. Ayres de Campos1, J. M. Gil1, H. V. Alberto1, R. C. Vilao1, J. Piroto Duarte1, A. Weidinger2, Ch. Niedermayer3, S. F. J. Cox4 RA-97-23, COIMBRA1 - HMI BERLIN2 - KONSTANZ3 - ISIS4 1. ZnO After the discovery of a shallow donor muonium state in CdS [1], a theoretical work predicted the existence of a similar state in ZnO [2]. Experiments recently conducted at ISIS on ZnO powder [3] confirmed the existence of a shallow donor muonium state, with an isotropic component of the hy- perfine interaction of the order of 500 kHz and an ionisation energy of 64 meV. In this project, experiments were conducted in a com- mercially available ZnO single crystal. Transverse-field (TF) measurements were performed in a field of 200 G in the tem- perature range from 2.2 K to 100 K in GPS. The results con- 0.2 0.4 0.6 firm the ionisation temperature and energy previously ob- tained for the shallow state. Fig. 1 shows the envelope re- Time (|a,s) laxation rate corresponding to the hyperfine interaction, the ionisation being made visible as a sharp decrease when the Figure 2: Muon-spin precession in a transverse field of 4kG diamagnetic signal becomes dominant in the time spectra. on HgO powder at 50 K. A temperature scan at a transverse field of 100 G was first performed in the HgO powder sample. The diamagnetic frac- 0.30 tion is observed to increase at the expense of the paramag- netic fraction in the temperature range from 150 to 200 K. This is attributed to the ionisation of the paramagnetic state, as in the case of CdS. The analysis of the data yielded a para- magnetic state ionisation energy EQ = (311 ± 4) meV. 3. ZnSe In longitudinal field repolarization measurements on ZnSe at ISIS [4] full polarization could not be recovered at a field 20 40 60 80 100 Temperature (K) of 4.5 kG. The high longitudinal field, the high time reso- lution (1.25 ns), and the low temperatures attainable at LTF, were combined to verify the existence of that fast relaxing Figure 1: Envelope relaxation rate of the muon-spin preces- component, which would justify the still missing fraction. A sion in a transverse field of 200 G, in a ZnO single crystal. fast relaxation component was indeed observed in the time spectra at fields from 1.5 T up, at 50 mK. A preliminary anal- The shallow muonium signal in the low temperature spec- ysis of these data leads to a spin exchange rate of 50 MHz in tra is not sharp enough to allow the desirable characterisa- the slow-exchange limit, considering an isotropic muonium tion of the hyperfine interaction, possibly due to the presence state as known from transverse field data. of defects in the crystal. The envelope relaxation is seen to decrease with decreasing temperature below 16K, which is probably due to either a second component or a dynamic ef- REFERENCES fect on the paramagnetic signal. [1] J. M. Gil et al, Phys. Rev. Lett. 83, 5294 (1999). 2. HgO A clear muonium paramagnetic signal was observed on [2] C. G. Van de Walle, Phys. Rev. Lett. 85, 1012 (2000). HgO powder, in a survey of several II-VI compounds. Fig. 2 [3] RBI2295 DD ISIS experimental report, October 2000. presents an asymmetry time spectrum obtained on HgO pow- der in a 4kG transverse field and at 50 K, in GPS. The hyper- [4] RBI 1353 ISIS experimental report, April 2000. fine interaction is of the order of 16 MHz, considerably lower than that of Mug^ in Si, but considerably larger than that of the shallow states in CdS and ZnO. 82 MUON(IUM) IN NITROGEN-RICH DIAMOND WITH H2/H3 CENTRES /. Z Machi1, S. H. Cornell2, J. P. F. Sellschop2, K. Bharuth-Ram3 RA-97-24, SOUTH AFRICA1 - WITWATERSRAND2 - DURBAN-WESTVILLE3 Introduction: Much of the understanding of the elec- twice the value it had before some of the A-centres were con- tronic and dynamical behavior of hydrogen in diamond has verted to H2/H3 centres. come from /iSR methods. This is made possible by similar The behaviour of the MUT state is not changed from be- chemical properties of muonium (Mu) with those of hydro- fore to after the production of the H2/H3 centres, as the / gen (H). This allows H states in diamond to be identified by and the A remain (on average) at about 30% and 4.0 fis^1. analogy with the different Mu states. Presented in this work The yU+ has therefore grown at the expense of the missing are the prompt fractions (/) and the spin relaxation rates (A), fraction (MF). The entire strength of the MF is known to be of the /x+ state, after the conversion of some A-centres in a associated with the Mu trapped at the nitrogen related cen- nitrogen-rich type la diamond to H2/H3 centres. tres, as Mux [2]. Clearly, the decoration of the A-centres by vacancies has resulted in less paramagnetic Muj, and more + Experimental: Characterization of a type la diamond re- of the /i species. vealed the presence of about 600 ppm of A-centres (a pair of The absence of a large value of / for the MuT state in two adjacent substitutional nitrogen atoms). H2/H3 centres the previous work had indicated that it was most likely the were produced by irradiating this same sample with 2 MeV /x+ species diffused to the nitrogen related centres and then gamma photons to a dose of 1019 cm"2, and then anneal- trapped there, capturing an electron to form the Mux species. ing at 1270 K for 2 hrs. This procedure results in vacancy It is possible that the trapping of a vacancy at some of the trapping at some A-centres to convert them to H2 or H3 cen- the nitrogen related defects in the present work enables the tres [1] depending on their charge state. The / and A of the trapped /J,+ to remain in the diamagnetic state. The hint of an /x+ states were determined in the temperature range 5-300 K, ALC resonance (see Fig. 2), consistent with trapped /x+ ob- and in applied magnetic fields of 7.5 mT, while those for the MUT state were determined in the range 5-55 K, in 1.0 mT. 100 "Old muons" (averaged over the time range 4-15 |is) Results and Discussion: In our previous work conducted 90 on the current sample (with only A,B-centres), a new para- Temperature = 10K magnetic muonium species, with less than axial symmetry 80 (termed Max) trapped at the nitrogen related defects was 70 shown to form [2]. These results, following the production of H2/H3 centres showed for the first time (in diamond) a non- 60 + negligible relaxation of the yU signal (see Fig. 1), except the 50 data of the chemical-vapor-deposited sample [3] which could not be linked to the current data. Also, previous measure- 40 Resonance at 50 mT ments on vacancy rich samples (even after annealing) did not 30 + show a relaxation of the /i signal. 10 100 Field (mT) 100 0.05 Figure 2: Repolarization curve of old" muons in virgin" state O Prompt Fraction (u.+) type la diamond. Natural diamond (la) + 19 2 • Relaxation rate (u. ) 80 2 MeV photon irradiated (10 cm" 0.04 Annealed (1000°C for 2 hrs) Field = 7.5 mT served in LF-/iSR data for the 'virgin' sample, would there- fore be expected to become more significant in the sample o 60 0.03 1 with some A-centres converted to H2/H3 centres. U- 40 0.02 Conclusion: These results are therefore interesting in 20 0.01 that they are consistent with the observation of dynamical effects involving /i+ in diamond. J0.00 0 40 80 120 160 200 240 280 REFERENCES Temperature (K) [1] Y. Mita et al., J. Phys.: Condens. Matter 2, 8567 (1990). Figure 1: Prompt fractions and spin relaxation rates of the [2] I. Z. Machi et al., Physica B 289/290, 507 (2000). /x+ state in type la diamond with H2/H3 centres. [3] K. Bharuth-Ram et al., In addition, the value of / for the /x+ state displayed Hypfine Interactions 105, 339 (1997). 83 MEASUREMENT OF RELAXATION RATE AND PARAMAGNETIC FREQUENCY SHIFT OF NEGATIVE MUON SPIN PRECESSION IN SILICON T. N. Mamedov1, D. G. Andrianov2, V. N. Gorelkin3, K. I. Gritsaj1, D. Herlach4, O. Kormann5, J. Major5'8, M. Schefzik6, A. V Stoykov1, U. Zimmermann4 RA-97-25, DUBNA1 - MOSCOW2'3 - PSI4 - STUTTGART5'6 As was shown earlier [1, 2] on n- and p-type silicon with generate n- and p-type silicon is caused by interaction of the impurity concentrations from 51012 cm"3 to ~1017cm~3, acceptor magnetic moment with free charge carriers, while the relaxation rate v of the Al acceptor center magnetic mo- in the case of a low concentration of charge carriers (in non- ment depends on temperature as v ~ Tq (qm 3) and is prac- degenerate Si and in Si with isoelectronic impurity) the main tically independent of the type and concentration of impu- mechanism for the acceptor relaxation at T < 60 K is the spin- rity. As the impurity concentration increases approaching lattice interaction. nc, the critical concentration corresponding to the insulator- The spin-exchange scattering cross-sections of electrons metal transition (the Mott transition), there is a deviation (cre) and holes (<7h) on the Al acceptor in silicon are esti- 3 15 2 13 2 of the temperature dependence of v from z/~T . Relax- mated: cre ~ 7-10~ cm and <7h ~ 10~ cm at n- and p- ation of the acceptor center magnetic moment in Si is due to type impurity concentrations close to nc. spin-lattice interaction and exchange scattering of free charge In silicon with 1.14-1019 cm"3 phosphorus impurity there 3 carriers on the acceptor. Deviation of v{T) from the T - are damped and undamped components of the muon polar- behaviour at high impurity concentrations could have been ization at T < 20 K. The presence of the undamped compo- caused by substantial changes in the phonon spectrum of the nent of polarization in degenerate n-type silicon is due to [2] crystal or by an increased role of the spin exchange process. the capture of conduction electrons by the neutral acceptor Measurements carried out in the year 2000 were aiming and its ionization with the rate z/tr comparable with the re- at the study of mechanisms for the relaxation of the acceptor laxation rate of the muon spin in the paramagnetic (neutral) center magnetic moment in highly doped silicon. The tem- state of the acceptor. The ionization rate for this sample is perature dependence of the negative muon polarization has about4-106s"1 atT = 4.2-10K. been investigated for silicon samples with boron (4.1-1018, 1.341019,4.91019 cm"3), phosphorus(1.141019 cm"3) and 19 3 20- germanium (910 cm" ) impurities. The boron and phos- o Si:Ge[9*1019cm3] phorus concentrations were above nc. Germanium in silicon A Si:B[4.1*10l8cm"3] is an isoelectronic substitutional impurity - the valency of 15- • Si:B[1.34*1019cm3; Ge and Si atoms is the same and equal to four. Accordingly, v Si:B [4.9*10'° cm"3] introduction of Ge atoms in silicon does not change the con- . 10- '}, centration of charge carriers. 3 The measurements were carried out in an external mag- K netic field of 0.1 T transverse to the muon-spin direction in 1 5- •H the temperature range 4 - 300 K. *** The temperature dependence of the frequency shift of the 0 muon-spin precession Aui(T)/uio for the germanium-doped 10 20 30 40 50 60 70 silicon sample does not contradict the 1/T-Curie law (see T, K Fig. 1), thus making it possible to determine the hyperfine interaction constant in the muonic MA1 atom: Ahf/27r = Figure 1: Temperature dependence of the frequency shift of (23.6±1.5)MHz. This result agrees with Ah{/2n ~ 26 MHz the muon-spin precession for highly doped silicon samples. - the averaged value for n- and p-type silicon samples with The dashed curve corresponds to AOJ/UQ = C/T with C = impurity concentrations up to ~1017cm-3 studied earlier. (0.16 ± 0.01) K. A decrease of the frequency shift with increasing impurity concentration is observed for boron-doped silicon. AU/UJQ decreasing is possibly due to antiferromagnetic exchange in- REFERENCES teraction of the hole localized on the M Al acceptor with the holes of neighboring acceptor centers (see, e.g. [3]). [1] T. N. Mamedov, K. I. Gritsaj, A. V. Stoykov et.al, In silicon with a high impurity concentration of germa- Physica B 289-290,574 (2000). nium v depends on temperature as T3. This behaviour is analogous to the one for non-degenerate n- and p-type sili- [2] T. N. Mamedov, D. G. Andrianov, D. Herlach et.al., con samples. In silicon highly doped with boron and phos- JETP Lett. 71, 438 (2000). phorus the temperature dependence of the relaxation rate of [3] M. P. Sarachik, D. R. He, W. Le, M. Levy, the acceptor center magnetic moment is weaker than the In- Phys. Rev. B 31, 1469 (1985). dependence. Thus, the present experimental data evidence that the change in the temperature dependence of v in de- 84 HYDROCARBON ACTIVATION IN ZEOLITES; INSIGHTS THROUGH EPR AND C. J. Rhodes1, H. Morris1, T. C. Dintinger1,1. D. Reid2, U. Zimmermannz, C. A. Scott4 RA-93-02, LIVERPOOL1 - UCL2 - PSI3 - ISIS4 The activation of hydrocarbons by oxidation and catalytic is broadly a single location for sorbed molecules; in ZSM5/- cracking forms the basis of the petrochemical industry. The silicalite there are zig-zag channels which provide the lateral catalysts in most common use are the zeolites, which are alu- interconnection of the straight channels, and so molecules minosilicate nanomaterials containing micropores of molec- can be located both within these separate channels and, pref- ular dimensions: these are generally used in their proton- erentially, at the channel intersections. exchanged forms, although transition-metal exchanged zeo- lites find useful applications, for instance in the transforma- We propose that the fraction exhibiting the low reorien- tion of high molecular weight fractions "heavy cuts". tational activation energy is located at the more spacious in- tersection sites (d = 9 A), while that at the higher activation It has been amply demonstrated that such zeolites, when energy is from molecules occupying the channels themselves activated under thermal oxygen conditions, develop redox (d ~ 5.5 A) upon which are imposed greater motional restric- properties and can oxidise spontaneously a variety of hydro- tion. carbons[l]. Controversy exists for benzene, which though reported to form a "dimeric" radical cation in a range of ze- ACKNOWLEDGEMENTS olites, it has not been clear whether this cation is the TT-TT sandwich complex (with the positive hole shared between 2 We thank Professor A. Lund for providing a copy of his intact benzene moieties, or is the biphenyl 7r-radical cation, anisotropic EPR simulation program. Further acknowledge- sinceisotropic simulations of their spectra are very similar[2]. ments are due to the EPSRC, the Paul Scherrer Institute, the On the basis of anisotropic simulations, however, far better European Union, Unilever Research and John Moores Uni- agreement is met with the experimental spectrum, showing versity for financial support of this overall programme of that the "dimer" is, in fact, the biphenyl radical cation. work; CJR further acknowledges the Royal Society of Chem- istry for the award of a J. W.T. Jones Travelling Fellowship. This result demonstrates that C-C a-bond formation can occur in zeolites by a free-radical mediated route. REFERENCES [1] C. J. Rhodes, in Radicals on Surfaces, Since the reorientational dynamics of neutral free radi- ed A. Lund and C. J. Rhodes, Kluwer, Dordrecht, 1995. cal intermediates in zeolites are largely inaccessible to EPR/- ENDOR methods, certainly under conditions pertinent to cat- [2] G. Hiibner and E. Roduner, alytic processes, we have utilised an alternative strategy: the Magn. Reson. Chem. 37, S23 (1999). Longitudinal Field Muon Spin Relaxation method [3, 4, 5, 6, 7]. This employs positive muons as radioactive magnetic [3] C. J. Rhodes, T. C. Dintinger and C. A. Scott, labels for radicals, and is extremely sensitive since it uses Magn. Reson. Chem. 38, 62 (2000). single-particle-counting detection. [4] C. J. Rhodes, T. C. Dintinger and C. A. Scott, Magn. Reson. Chem. 38, 729 (2000). We have studied cyclohexadienyl radicals and dimethyl- cyclohexadienyl radicals as sorbed in zeolites ZSM5, sili- [5] C. J. Rhodes, T. C. Dintinger, I. D. Reid and C. A. Scott, calite and mordenite. For cyclohexadienyl radicals in ZSM5, Magn. Reson. Chem. 38, S58 (2000). silicalite and mordenite, a fraction was detected with a com- mon reorientational activation energy of ca 5 kJ mol~1; how- [6] C. J. Rhodes, T. C. Dintinger, I. D. Reid and C. A. Scott, ever, in both ZSM5 and silicalite there appeared a secondary Magn. Reson. Chem. 38, 281 (2000). fraction with an activation energy of ca 14 kJmol^1. This was absent in mordenite. These differences arise from the [7] C.J.Rhodes, differing internal channel structures of the zeolites, namely Prog. React. Kinet. Mech. 25, 219 (2000). that there are only straight channels in mordenite, hence there 85 "THE BLUE-RIDGE MOUNTAINS OF VIRGINIA" C. J. Rhodes1, H. Morris1,1. D. Reid2, U. Zimmermann3 RA-99-15, LIVERPOOL1 - UCL2 - PSI3 The chemistry of the troposphere is dominated by ox- A Ea A Ea idation reactions, mediated by OH radicals [1]. The plant 11 1 1 12 1 1 kingdom emits enormous quantities of hydrocarbons into the (10 s- ) (kJmor ) (10 s- ) (kJmor ) atmosphere, especially terpenes from forests. Indeed, the a-pinene 8.1±2.4 6.0±0.3 4.8±1.3 13.1±1.7 "Blue-Ridge Mountains" (of Virginia), of Laurel and Hardy /3-pinene 4.5±1.1 6.6±0.9 8.1±2.5 16.0±1.2 fame, appear blue behind the haze caused by the tropospheric oxidation of pinenes and other terpenes [2]. The process Table 1: Reorientational activation parameters measured for of hydrocarbon oxidation involves the partial oxidation of a-pinene and /?-pinene sorbed in activated carbon powder. minute hydrocarbon droplets, and is incomplete, leading to a carbonaceous aerosol - hence the haze. It is a kind of cold combustion, involving the formation and diffusion of hydro- carbon radicals within the developing microporous structure ACKNOWLEDGEMENTS of developing carbon particles. CJR thanks the Royal Society of Chemistry for the award of a J.W.T. Jones Travelling Fellowship. Using Longitudinal Field Muon Spin Relaxation [3, 4, 5, 6, 7], we have investigated the formation of radicals from a REFERENCES variety of terpenes and their interaction with a porous carbon material. The results for a-pinene and /3-pinene are repre- [1] R. P. Wayne, Chemistry of Atmospheres, sentative of this study. Addition of muonium to either pinene Clarendon Press, Oxford (1985). isomer will yield very similar radicals, differing only in the relative position of the muon and a proton. It might be ex- [2] R. P. Turco, Earth Under Siege, pected, therefore, that the reorientational dynamics of these Oxford University Press, Oxford (1997). radicals would also be very similar. [3] C. J. Rhodes, T. C. Dintinger and C. A. Scott, Magn. Reson. Chem. 38, 62 (2000). In both samples two distinct motional regimes are re- vealed, corresponding to radicals sorbed at different sorp- [4] C. J. Rhodes, T. C. Dintinger and C. A. Scott, tion sites within the carbon micropores. The activation en- Magn. Reson. Chem. 38, 729 (2000). ergies and frequency factors are shown in the table, and are indeed identical within error for both fractions for both iso- [5] C. J. Rhodes, T. C. Dintinger, I. D. Reid and C. A. Scott, mers. We propose that the fraction of lower activation en- Magn. Reson. Chem. 38, S58 (2000). ergy (~6kJmol^1) corresponds to molecules that occupy [6] C. J. Rhodes, T. C. Dintinger, I. D. Reid and C. A. Scott, the meso- and macro-pores (i.e. those of dimensions >20 A), 1 Magn. Reson. Chem. 38, 281 (2000). while the fraction at higher activation energy (~15 kJ mol" ) is sorbed within the micropores (4-20 A). [7] C.J.Rhodes, Prog. React. Kinet. Mech. 25, 219 (2000). 86 ALC-MSR ON AZA-CYCLOHEXADIENYL RADICALS IN PYRIDINIUM SALTS B. Beck1, E. Roduner1, H. Dilger1, R. Scheuermann1, P. Czarnecki2 RA-OO-21-a, STUTTGART1-POZNAN2 Avoided-Level-Crossing Muon-Spin-Resonance (ALC- ion independence. The totally different development of line has proven to be an appropriate tool to investigate re- shape around the first phase transitions in contrast leads to orientational dynamics of aza-cyclohexadienyl radicals in py- the conclusion that a differentiation of phase transition types ridinium tetrafluoroborate (PyBF4) [1]. As a variant of mag- with ALC-//SR is possible. Up to now it is not clear whether netic resonance, ALC-//SR interprets the relaxation of a po- only the ordering of the ions is responsible for the ferroelec- larized muon spin-label in the radical as a function of a longi- tricity appearing in the low temperature phases, or whether tudinally applied magnetic field being scanned through avoid- the conventional mechanism of anion lattice displacement to- ed crossings of magnetic energy levels. Muonium (Mu = wards the cation lattice contributes here as well. /x+e~) is chemically a light hydrogen isotope in which the nucleus is a polarized muon. The hyperfine coupling con- (a) PyBF stants in the Mu adduct are related to the resonance fields. 4 Changes in the reorientational dynamics of the radical result in changes of the line shape of the resonances [2]. PyBF4 shows two solid-solid phase transitions of order- disorder character at 7\ = 238.7 K and T2 = 204 K. The first transition is paraelectric-ferroelectric and of second or- der, which is exceptional for multidimensional ferroelectrics [3]. Pyridinium perchlorate (PyClO4), belonging to the same family as the tetrafluoroborate, also reveals two solid-solid phase transitions — but in contrast to the PyBF4 of first order — taking place at 7\ = 248 K and T2 = 232 K [4]. Simi- lar symmetry of the involved phases is thought to be at least partially responsible for the continuous character of a phase transition. But factors driving a transition in a discontinuous way although in a structurally comparable compound are still unknown. Adding muonium to pyridinium cations in the or- tho, meta and para position with respect to the nitrogen atom results in three different aza-cyclohexadienyl radical cations (C5H6NMU"1"). The radicals are expected to perform fast ro- tation around the axis perpendicular to the molecular plane [3, 4]. In the range of 1.8 T to 2.8 T both compounds yield six strong resonances which are identified as Ai and méthylène Ao lines of each radical. The coupling constants for the muons and the méthylène protons calculated from the res- onance positions are identical for both salts. In fig. 1, the or- tho Ai resonance of both compounds and the corresponding 1.85 1.9 1.95 270 280 290 300 line width analysis are displayed. From the Dzz values, char- acterizing the line width, and the line shape we deduce that above 7\ the cations perform fast uniaxial rotation around the Figure 1: ALC-yuSR spectra of ortho Ai resonance (left) axis perpendicular to the molecular plane in both salts. In and axial hyperfine anisotropy of all Ai resonances (right) case of the tetrafluoroborate we observe a dramatic change of PyBF4 (a) andPyClO4 (b). of the reorientational dynamics of the aza-cyclohexadienyl radical between 233 K and 240 K. The evolution of the Dzz values is very smooth, reminiscent of the continuous char- REFERENCES acter of the first phase transition, and indicates a restriction [1] B. Beck et al, Physica B 289-290, 607 (2000). of rotational dynamics with temperature. The perchlorate re- veals this change in dynamics between 244 K and 245 K. In [2] (a) E. Roduner, Chem. Soc. Rev. 22, 337 (1993). contrast to the tetrafluoroborate the alteration is limited to a (b) E. Roduner, Appl. Magn. Res. 13,1 (1997). very small temperature range and is steplike here, reminding [3] I. Szafraniak et al., us of the discontinuous transition. The similar Dzz values for both compounds above T\ demonstrate identical reorien- J. Phys.: Condens. Matter 12, 643 (2000). tational dynamics in the paraelectric phase and therefore an- [4] J. Wasicki et al, Molecular Physics 98, 643 (2000). 87 INTERACTIONS OF COSURFACTANTS WITH SURFACTANT BILAYERS R. Scheuermann1, E. Roduner1, H. Dilger1, B. Beck1,1. M. Tucker2, E. J. Staples2 RA-00-21-b, STUTTGART1 - UNILEVER RESEARCH PORT SUNLIGHT2 Surfactants are amphiphiles which by nature form aggre- gates in order to satisfy the enthalpic and entropic require- ments derived from their structure. Depending on the rela- tive magnitudes of the hydrophilic headgroup and hydropho- bic tail, the molecule will tend to form curved or planar in- terfaces. At low concentrations, surfactant self-aggregation leads to the production of' micelles'. However, when present at sufficiently high concentrations, molecules with small head- group areas and long chains prefer to form bilayer planar in- terfaces which result in one-dimensional lamellar type struc- para- meta-PEA-Mu tures. Temperature and molecular geometry thence dictate 19500 20000 20500 21000 whether the lamellar phase is 'simple' (fig. la), tilted (fig. lb), magnetic field [G] or 'interdigitated' (fig. lc). Figure 2: Ao resonances of the three isomers of the muonated cyclohexadienyl radical PEA-Mu in a solution of PEA in liquid octadecane (top), pure liquid PEA (middle), (a) (b) (c) and in a solution of PEA in water (bottom) at T = 35 °C. In the 'aqueous' environment the resonance positions are shifted to higher fields. The solid lines represent the result Figure 1: Schematic arrangements of surfactant molecules in of a fit of three Lorentzians to the data. different configurations of lamellar phase. ficiently close packed that the cosuractant cannot penetrate Dialkyl chain systems readily form lamellar phases. The the bilayer. For the interdigitated bilayer (fig. 3b) the aniso- alkyl chains can be considered 'liquid' (L ) above a defined a tropy is present even at room temperature, indicating that the temperature. Below this the system is said to be in the L^ tracer molecule is axially aligned within the bilayer. The rel- state with more ordered packing of the hydrocarbon chains. ative intensities of the Ai fines are much larger than observed In the L state the mixing of surfactant components is nearly a with the simple lamellar structure, revealing a significantly ideal. In the Lp state considerable mixing is possible leading higher order of PEA in the interdigitated bilayer. to the formation of defective lamellar phases. In this work avoided level crossing (ALC) /iSR is used to contrast the in- teraction of a cosurfactant, phenylethanol (PEA), with both (a) A simple and interdigitated lamellar structures. The muonated cyclohexadienyl radical derived from PEA exists in three iso- mers (ortho-, meta-, para-PEA-Mu), each of them gives a typical signature in an ALC spectrum (fig. 2). From the appearance/disappearence of the Ai resonance lines or a sudden change of the hyperfine coupling (and hence the resonance field) the local environment of the muonated radical may be deduced. In this instance this means whether PEA resides in an ordered state (co-aligned with the mole- cules in the surfactant bilayer) or in an isotropic environment. In liquid solution of pure PEA a spectrum which is typical of PEA in its rotationally averaged environment is observed, the resonance positions shift to higher field values in an aqueous environment, and to lower field values in an environment of 20000 18000 20000 magnetic field [G] alkyl chains (fig. 2). magnetic field [G] Interdigitated and simple lamellar phase dispersions were Figure 3: ALC spectra of a PEA solution in a surfactant prepared at constant phase volume in water and were mixed forming a simple lamellar phase (a) or an interdigitated with identical levels of PEA. For the simple bilayer (fig. 3a) bilayer (b). The solid fines in (a) serve to visualize the there is no evidence of anisotropy (Ai resonances) until a shift/step of the Ao resonance positions with temperature. critical temperature of 55 °C is reached. This is the tempera- ture at which the alkyl chains of the surfactant 'melt' (LafLp These results demonstrate the potential of ALC-/xSR in phase transition). The implication is that in the simple lamel- studies of systems where the variation of the tracer molecule lar phase below the transition temperature the chains are suf- environment with temperature is dramatic. DIFFUSION OF MUONS IN METALLIC MULTILAYERS H. Luetkens1'2, E. M. Forgan3, H. Glückler2, B. Handke5, R. Khasanov2'6, H. Keller6, J. Korecki5, F J. Litterst1, E. Morenzoni2, Ch. Niedermayer4, M. Pleines'2'4, T. Prokscha2, G. Schatz4, T. Slezak5 RA-94-15, BRAUNSCHWEIG1 - PSI2 - BIRMINGHAM3 - KONSTANZ4 - KRAKOW5 - ZÜRICH6 -E /kT The development of the low energy muon beam at PSI = fo-e a (1) opens the possibility to study the muon diffusion in artificial layered structures of a few ten run thickness [1]. Here, we re- Here, Ea is the activation energy, k is the Boltzmann con- port on the first muon diffusion experiments done in 1999 on stant, and /o is the attempt frequency. For a realistic initial a single 10 nm Cr / 40 nm Au / 10 nm Cr epitaxial trilayer. stopping distribution the Monte Carlo code TRIM.SP [3] has The motivation of these studies is threefold: first, as a ba- been used. The calculated time dependent fraction of muons sic experiment to understand muon diffusion in such systems it is a necessary prerequisite for further LE-//SR studies on magnetic multilayers. Second, they allow to study muon dif- fusion without introducing magnetic impurities in the speci- men as it is normally done in muon diffusion studies of non- magnetic metal hosts. Third, they allow to investigate inter- face effects like diffusion barriers due to different enthalpies of solution, preferential diffusion due to epitaxial strain and the role of disorder at the interface for sputtered samples. The principle of the experiment is shown in Fig. 1. 50 100 150 200 250 300 350 Cr Au A Cr Figure 2: Measured and calculated depolarization rates A as a function of temperature T. in the Au layer is well reproduced by an exponential deflation of muons from the Au layer. As a first approximation we ne- glected any additional interface barriers resulting in infinitely permeable interfaces. The calculated depolarization rates are Depth (nm) compared to the experimental data in Fig. 2. It is visible that Figure 1 : Initial muon implantation profile (solid line) and the diffusion to the Cr layers is strongly suppressed compared time dependent muon distribution due to thermally activated to the literature values of muon diffusion in bulk Au. The diffusion (dashed line). Muons reaching one of the magnetic data could only be reproduced by using extremly small at- (SDW) Cr interfaces immediately loose their spin polariza- tempt frequencies, clearly showing that interface effects are tion [2]. The depolarization of the LE-//SR signal therefore not neglectable. The energy barrier at the interface is ex- directly reflects the time dependent fraction of muons within pected to strongly depend on the enthalpy of solution, H, for the non-magnetic Au. muons in the two connected metals. Since H is related to the interatomic spacing in the metal lattice it is reasonable to as- The measured yuSR spectra are well described by a sin- sume the same qualitative behaviour for muons and protons. gle exponentially damped signal. The temperature dependent First promising results are obtained using proton enthalpies depolarization rate A is shown in Fig. 2. At 125 K, the on- of solution at infinite dilution in the Monte Carlo code giving set of muon diffusion across the plane boundaries is detected a repelling potential for muons at the interface. by the increase of A. The decrease of A at 285 K indicates the magnetic phase transition of 10 nm Cr at a reduced Néel REFERENCES temperature compared to bulk Cr due to the size effect [2]. [1] E. Morenzoni, Appl. Magn. Reson. 13, 219 (1997). Monte Carlo calculations were performed to reproduce [2] H. Luetkens et al, Physica B 289-290, 326 (2000). the experimental data. In these calculations, Arrhenius like hopping between the octahedral interstitial lattice sites of the [3] W.Eckstein, fee Au lattice is assumed. For this thermally activated pro- Computer Simulation of Ion-Solid Interactions, cess the jump rate / at temperature T is given by: Springer Verlag Berlin (1991). 89 EMISSION OF EPITHERMAL MUONS FROM A PATTERNED MODERATOR T. Prokscha and E. Morenzoni, PSI The emission of epithermal (~ 15 eV ) positive muons + (/i ) from a solid argon (s-Ar) moderator is essentially a sur- : moderator face process since the escape depth of these /x+ is of the order lover : direction of of a some ten nanometers [1,2]. Therefore, an increased sur- epithermal face should yield a larger moderation efficiency emod. For the geometry shown in Fig. 1, we observe a gain of 1.48(3) of emod compared to a flat moderator [3]. This is about 15% less than the surface enlargement factor of 1.73. b) A2AAdA> Figure 2: (a) For an isotropic distribution, the escape depth 9 d e of the moderator grating is equal to d{, the escape depth of the flat moderator. The active moderation volume Va, and therefore the moderation efficiency, is increased by the sur- Figure 1: SEM image of a structured silicon moderator 9 substrate with ridge distance d = 30 /im, ridge height face enlargement factor G, Va oc d e • A? • G, where A? is the area of the flat moderator surface, (b) For an extreme h = 20 yum, and angle 2a = 70.5°. The right side shows 9 2 forward distribution, the escape depth d e is reduced with re- a front view of the substrate with a 3 x 3 cm pattern in the 9 spect to d{,d e = d(/G. Therefore, a larger surface does not center. The thickness of the s-Ar layer deposited on the cold + (~ 10 K) substrate is typically a few hundred nm. The in- produce a larger yield of epithermal /x , because the active coming surface /i+ beam is directed upwards from the plane volume does not change. of view. under large angles onto the neighbouring wall. The results of the simulation are summarized in Tab. 1. It can be shown geometrically that the gain in emod equals the gain in surface only, if the angular distribution of the Forward directed distributions like ^^(0) = (1 + cos 0)™ epithermal /i+ inside the moderator layer is isotropic, see with n > 1 yield a gain < 1.48 for R = 1 and can be ex- Fig. 2. For an extreme forward directed distribution e d cluded. The program TRIM.SP yields R = 89% for normal mo + does not change when increasing the surface. In case of an incidence of a 15 eV yU on s-Ar. We conclude, that the isotropic distribution, some /z+ will impinge on the adjacent observed gain in emod for a patterned moderator is a conse- + moderator layer. If the absorption probability for those fi+ quence of i) a nearly isotropic distribution of epithermal fi inside the layer, and ii) a reflection coefficient R ~ 90%. were unity, emoa would also not change with increasing sur- face. Table 1: Simulated gain of e d for different angular dis- We performed a Monte Carlo simulation to investigate mo tributions Fi (@). F (Q) is the distribution of those /x+ in detail the consequences of various angular distributions n 0Ut which are emitted from the moderator and not absorbed in and backscattering probabilities on the emission of epither- the V-groove walls. The backscattering probability R for a mal /i+ from a patterned moderator. The simulation gener- single collision is derived from the experimental gain of 1.48. ates epithermal particles with homogenous stop density and angular distribution Fi {&) with respect to the beam axis n F (Q) gain F {®) R[%] in a flat and patterned moderator layer. The cumulative ef- m out 1 (isotropic) 1.73 cos© 78 fect on the angular distribution arising from collisions with (l + ±cos0) 1.58 COS1'2 0 90 the moderator atoms is taken into account by the appropriate (l + |cos0) 1.52 COS1'3 0 96 choice of the functional dependence of Fin (0). In the case of the patterned moderator, the angular distribution of particles REFERENCES backscattered from the adjacent groove wall is assumed to be cos 0ra, where 0ra is the angle with respect to the surface [1] E. Morenzoni, Physics and applications of low energy normal. The angular distribution of backscattered /x+ calcu- muons, in Muon Science, S. Lee et al. (Eds.), lated with the program TRIM.SP [4], which has been shown IOP Publishing (1999). to predict reliably the distribution of backscattered protons, [2] T. Prokscha et al, PSI Scientific Report 2000, Vol. 1. supports this assumption. Only for grazing incidence at an- gles larger than 70° with respect to the surface normal, specu- [3] T. Prokschaetal, Appl. Surf. Sc. 172, 235 (2001). lar reflection is favored. Due to the geometry of the V-shaped [4] W Eckstein, Computer Simulation of Ion-Solid Interac- grooves this case is very unlikely because only the small frac- tion of yU+ starting near the bottom of the groove can impinge tions, Springer Verlag Berlin (1991). 90 THICKNESS DEPENDENCE OF THE EFFICIENCY OF s-Ar AND s-N2 MODERATORS T. Prokscha1, H. Gluckler1, R. Khasanov1'4, H. Luetkens1'2, E. Morenzoni1, Ch. Niedermayer3, M. Pleines1'3 PSI1 - BRAUNSCHWEIG2 - KONSTANZ3 - ZURICH4 The efficiency of a condensed van der Waals gas moder- ator, measured as a function of the moderator thickness, re- ^ * s-Ar: I _ veals information on the processes involved in the generation 2500 + xVndf 1(3.6 / 10 : of epithermal ( ~ 15 eV) positive muons (// ). We investi- 77.67 ± : 0.8914 S OW 2000 ..... PI : gated the epithermal /i+ yield N J /N™ of solid argon (s- "pi": 36.16± : oISi; P3: 344 7 ± I 6.12 Ar) and solid nitrogen (S-N2) moderators in dependence on 1500 ow the layer thickness. The number of epithermal muons N^ 1000 is determined by a time-of-flight (TOF) measurement, and N™ denotes the number of incoming surface muons. 500 1 I 0 », , , , i , , , , i , , , , As moderator substrate we used a patterned Ag foil as de- 0 25 50 75 100 125 150 175 200 scribed in [1]. Research purity gas was condensed onto the blank substrate (T ~ 10 K). The gas pressure during layer 2500 deposition was ~ 10~6 mbar resulting in a deposition rate - [ | | •z_^_4- i s-N i ^Jf^^ \ 2 2 of ~ 0.1 nm/s. The deposition rate was calibrated offline by 2000 - L L &£L...± L... xVndf 31.57 i' 21 mounting a micro balance at the moderator position and re- pi : 119.2 ± : 3.326 :i4.56± : 0J530 1500 peating the evaporation procedure under the same pressure P3 I 1720.1 ± i 15.62 conditions. After measuring the epithermal /i+ yield for one thickness additional gas was deposited on top of the existing 1000 - \- A NEW SURFACE MUON BEAM E. Morenzoni1, T. Prokscha1, F. Foroughf, K. Deiters2, M. Daunt", D. Renter3, D. Herlach1, C. Petitjean3 PSI: LML^-AEA^LTP3 Over the past years, a beam of polarized low energy mu- The beam has been calculated with TRANSPORT and ons (LEM), which can be implanted at very small and con- the parameters optimized with TURTLE and ray tracing pro- trollable depths on a nm scale below the surface of a sample, grams. The comparison of the acceptances between TTE3 and has been developed at our institute. In order to definitely es- the new beam yields an increase of the muon rate by a factor tablish the emerging LE-//+SR technique, to strengthen the of 10 for the full beam spot, starting with an initial rectangu- leading role of PSI in this field and to cope with the increas- lar momentum distribution of 3% (which corresponds to the ing demand from external users, we have designed and pro- useable momentum width for low-energy muon production). posed to set up a new surface muon beam line optimized to Also in the central region, the gain in muon rate amounts to deliver the highest intensity on a small beam spot. a factor of 10. The suppression factor of positrons over a 3x3 cm2 area is better than 100. The new beam area is large The main motivation for this development was to increase enough to accommodate and render accessible for develop- the intensity of low energy muons, which is directly propor- ment and tests the LEM apparatus also during periods that tional to the flux of incoming surface muons on a 30x30 mm2 are used by other users to perform experiments in this area. area. However, also other programs, such as bulk //+SR and particle physics experiments using low momentum positive After positive review of the PSI research committee the and negative muons will profit from the availability of such a construction of the beam line has been approved. A large beam. fraction (~40%) of the total investment will be funded by the Technical University of Braunschweig and the Univer- Optimum surface and cloud muon intensity and lower sity of Konstanz through the German Ministry for Education positron contamination are obtained with a 90 degree extrac- and Research, BMBF. The new beam line will require a new tion with respect to the target production surface as in the injection chamber and moderator cryostat for the LEM appa- present TTE3 and /iE4 beam lines. ratus, which will be developed and funded in collaboration with the University of Birmingham. After studying different variants the //E4 beam area turned out to suit our purposes best. In order to keep costs and work within reasonable limits we only considered designs leaving the target E region (including the vacuum chamber) untouched and minimizing the impact on other beam lines. This implies that the external dimension of the first focusing element and its distance from target E are fixed at 90 cm and 60 cm, respectively and that the existing shielding channel has to be used to a large extent. A schematic overview of the proposed version is shown in Fig. 1, together with the new area layout. A significant in- crease of the channel acceptance with respect to TTE3, which is limited by the use of a quadrupole of small aperture, is achieved by the use of a normal conducting, radiation-hard solenoid as first focusing element, which rotates the image of target E by about 45°.The solenoid is followed by a beam line consisting of bending magnets (ASK's with increased gap) and large aperture quadrupoles (QSF). Positron separa- tion is achieved by using a wide gap ExB filter at the end of the beam line. The first bending magnet must be positioned Figure 1: Schematic layout (bold lines and filled outlines of at a distance of 3-3.5 m from target E in order to fit into the beam-line elements) of the new /iE4 beam line and area for existing channel. highest intensity surface muons. 93 Laboratory for Micro and Nano Technology Foreword Nano Factory and X-ray Optics Silicon Based Nanomaterials and Nanoelectronics Molecular Nanotechnology 94 LABORATORY FOR MICRO- AND NANOTECHNOLOGY J. Gobrecht The Laboratory for Micro- and Nanotechnology in 2000 achieved several breakthrough-results in its core research activities. At the same time a significant number of new academic and industrial users could be served by the advanced technological services. LMN's overall performance was ranked excellent by external auditors. several of our research projects will be delayed or even In 2000 the LMN continued in its efforts to focus the more seriously endangered. The other concern is the slow research activities in the areas of light emission from but unavoidable ageing of our process equipment which silicon (Si) based nanomaterials and molecular consumes an increasing part of our resources for Nanotechnology for applications in the life-sciences. At the maintenance and repairs. A major investment is same time, our base-laboratory services to external unavoidable in the coming years since we have to keep academic and industrial users as well as other PSI projects pace with the rapidly moving developments in micro- were intensified. processing technologies. This is a prerequisite for applied I am happy to report some major advances and highlights research at the forefront of micro- and nanotechnology. of our research work during the last year: In 2000 an audit of the LMN was requested by the After having set "light-emission" as the major goal for the directorate of PSI. This was conducted in September by area of Si-based nanomaterials, we now can report three internationally recognised external scientists from the electrically stimulated photon-emission from Si-Ge fields of Si-Ge electronics, molecular sciences and quantum cascade structures - to our knowledge the first nanostructuring. In short, the results and recommendations ever reported from this material. Also the luminescence can be summarized as follows: from Ge quantum dots can now be stimulated electrically. • LMN's overall performance is ranked excellent. After tedious solving of technological problems we were rewarded with exciting results from our "single hole • Industrial cooperation should be increased in some transistor" in Si/Si-Ge, also the first of its kind ever areas, particularly in the Si-Ge nanostructures area. realised. In a fruitful cooperation with PSFs energy • Some projects should be reinforced to become over- research department we were able to realise a thermo- critical, in particular in Molecular Nanotechnology. photovoltaic energy conversion demonstrator with a world- record system efficiency of 2.1%. We are satisfied with this very positive outcome and esteem the valuable recommendations by the auditors. In the neuroinformatics project, we observed electro- physiological signals from living neural cells cultivated on Our scientific output in 2000 not only increased in respect structured microchips. In the search for an amprometric to refereed papers, but we also initiated or participated in immunosensor, control was gained over the unexpectedly four patent applications. Another remarkable change complex chemistry of penicillin. In order to bring the occurred in respect to our research partners. Due to the molecular nanojunction-experiments into operation we ending of the SPP "MINAST" in Dec. 99, the six projects could move to a new lab and start assembling the UHV with LMN participation were finished as was the equipment. cooperation with 10 academic and 9 industrial partners. Due to intensive marketing and launching of new proposals In micro- and nanostructuring, an increasingly intensive we were able to compensate this with the start of several and fruitful cooperation with the SLS team in the area of X- new projects in 2000 with numerous new research partners. ray optical devices and detectors developed. For our It seems we are proceeding well towards our goal of advanced, submicron "hot embossing lithography" and becoming one of the recognised and preferred research "nano injection moulding" processes a broad industrial partners in nanotechnology [1]. interest was observed leading to a number of interesting industry research contracts with high potential for I would like to take the opportunity to thank all LMN staff technology transfer. A poster on a joint project with the for their engaged scientific work, for successful fund energy department of PSI on structuring of polymer raising and for taking great care about our academic and surfaces using diffractive optics was awarded at the industrial partners. Equally I thank the PSI directorate for esteemed MNE conference. the continuous support and all our research partners for the fruitful cooperation. Next to all the highlights and successes we are happy to report on in the following pages, there are also a number of Enjoy reading the following pages! problems which have to be solved in order to further enhance our performance: probably the most urgent one is REFERENCE the difficulty in recruiting qualified PhD students, who are and always have been a cornerstone of our scientific [1] Vision 4, Dec. 2000, supplement "Mikrotechnik in der research work. If this situation does not improve in 2001, Schweiz", p. 18 95 RHEOLOGY AND PATTERN FORMATION DURING HOT EMBOSSING OF THIN POLYMER FILMS L.J. Heyderman, M. Aufder Maur, J. Gobrecht, B. Haas, B. Ketterer and H. Schift (PSI) We investigated the viscous flow of thin PMMA films into microcavities during hot embossing in order to optimise the moulding of nanostructured surfaces. The cavities fill by lateral flow of PMMA from the borders of the cavities, and compressive and capillary effects are important. Under certain conditions, periodic patterns form which are strongly influenced by the stamp geometry. Rapid expansion of air results in fractal viscous fingering patterns. The hot embossing process is a low cost, fast method for the replication of structures at the micro- and nanoscale over large areas. In Hot Embossing Lithography, a thin layer of thermoplastic material is used as a resist for subsequent pattern transfer; it is heated above the glass transition temperature so that it assumes a viscous state and can then be shaped under pressure by imprinting with a hard master. Once the polymer has exactly conformed to the shape of the stamp, it is hardened by cooling and the master is demolded. In order to optimise the embossing process for more complex stamp geometries, an insight into the way in which the nano- and microcavities fill during Fig. 2: Polymer pillars formed in stamp cavity. Original embossing is important. The thin film environment also stamp geometry in black (cavity) and white. provides a model system where fundamental effects can be studied. At the high pressures used for embossing, the air in the cavities is compressed and is not observed in the final AFM profile of partially filled cavity embossed structures. However, if the embossing pressure is Position of cavity applied rapidly or the embossing pressure is released before during embossing cooling, an explosive behaviour of the air occurs and a width: 20 um viscous fingering pattern is formed. The final pattern is height: 175 nm fractal in nature due to the high air expansion velocities involved. In the presence of a structured stamp, there is an Schematic Representation of Polymer Flow anisotropic growth of the finger pattern which prefers to grow along the structure edges (see Fig. 3). STAMP POLYMER compression SUBSTRATE t ft t t t Fig. 1: Squeeze flow of polymer into stamp cavity. Under ordinary conditions, a microcavity is continuously filled from the borders during hot embossing of thin polymer films. AFM measurement reveals that both capillary effects, causing the polymer to flow up the cavity Fig. 3: Viscous fingering with structured stamp. walls, and compressive effects, seen as a bowing of the central region, are apparent (see Fig. 1). The observation of pattern formation in polymer thin films is proving to be important for the understanding of The formation of periodic pillar arrays in thin polymer structure formation in the micro- and nanorange, and will films can be induced when a charged mask is placed in help to improve stamp design and processing. close proximity to the molten polymer film. It is known that the period depends on the size of the electrostatic field, FUNDING: SNF (NFP36), PSI. surface tension, Van der Waals interaction, and the polymer REFERENCES viscosity, thickness and molecular weight. We have shown [1] L.J. Heyderman, H. Schift, C. David, J. Gobrecht, that it is possible to tailor the shape and size of the polymer T. Schweizer Micro. Eng., Accepted (2001). pillars by using a specific stamp cavity size and shape. Line sections, dots and rings have been isolated and an example [2] H. Schift, LJ. Heyderman, M. Auf der Maur, of this is given in Fig. 2. J. Gobrecht Nanotechnology, Accepted (2001). 96 NANOFABRICATION WITH HOT EMBOSSING AND ELECTROFORMING L.J. Heyderman, M. Aufder Maur, D. Bdchle, C. David, F. Glaus, J. Gobrecht, B. Haas, M. Horisberger, P. Hdberling, B. Ketterer, T. Neiger and H. Schift (PSI), R. Bischofberger (Applied Microswiss) The nano- and microstructuring possibilities of electroforming in combination with hot embossing lithography are demonstrated. Periodic structures down to 120 nm and feature sizes < 50 nm were replicated. Electrode devices, several mm long, were fabricated with various line widths and heights. Overplating provided a means to increase aspect ratios and decrease gapwidths, and daughter molds with nanoscale fidelity were fabricated by backplating. Hot Embossing Lithography (HEL), also referred to as Lines Dots Holes Nanoimprint Lithography (NIL), can be used to replicate Height: 35 nm Height: 35 nm Depth: 150 nm micro- and nanostractures for a variety of applications, for example electrode structures, Fresnel zone plates and high density magnetic recording media. One of the main advantages of conformal molding over other replication techniques, is that structures with high aspect ratios can be directly reproduced by embossing a thermoplastic material. Structured stamp 400 nm Embossed thin polymer film Seed layer Fig. 2: 400 nm period electroformed structures (original Substrate polymer mask height: 50 nm). (i) Aspect Ratio Cross-section images of some electroplated electrodes are Preserved given in Fig. 3. Here, electrode lines with periods of 1 (J,m were overplated to heights up to six times greater than the (ii) Overplating original polymer galvanoform (45 nm thick), resulting in a decrease in the interelectrode gap from 150 nm to 40 nm. Following removal of the Cr/Ge between the nickel lines HI (Hi) Backplating by RIE, electrical measurements showed that the long parallel electrode fingers were isolated. Fig. 1: Process scheme for HEL with electroforming. To maintain this advantage in subsequent pattern transfer, electroforming rather than lift-off is used because metal structures can be generated with a considerable height and a good surface quality. The possibilities for electroforming of resist structures with an underlying seed layer are shown in Fig. 1. After embossing the residual resist layer is removed by oxygen reactive ion etching (RIE), opening seed layer windows for plating. Depending on the extent of electroplating, either the structure height can be preserved or increased. Daughter stamps can be manufactured by extending the overplating to form a substantial supporting base, providing a robust metal stamp. Fig. 3: Electroplated nickel lines for electrode device. We used a Cr/Ge seed layer which provided a good starting material for subsequent nickel electroplating. Periodic HEL and electroforming is of interest, for example for arrays of lines and dots with periods down to 120 nm and electronic devices where a small gap is required or for feature sizes <50 nm were faithfully replicated, and creating metal sieves with nanoscale holes. It seems likely examples of 400 nm period nickel structures are given in that the dimensions of the electroformed structures can be Fig 2. The surface of the electroplated nickel is smooth further decreased for future nanoscale applications. with a roughness comparable to that of the electroplating FUNDING: SNF (NFP36), PSI. seed layer. Nickel daughter stamps, backplated to a thickness of 100 to 400 u,m, were produced with resolution REFERENCE matching that of the original and were successfully used to [1] L. J. Heyderman, H. Schift, C. David, B. Ketterer, replicate structures in polycarbonate. M. Auf der Maur and J. Gobrecht, Microelectronic Engineering, Accepted for Publication (2001). 97 V-GROOVE REPLICATION: A TOOL FOR QUALITY CONTROL OF A COMPACT DISC INJECTION MOLDING PROCESS H. Schift, F. Glaus, J. Gobrecht, B. Haas and B. Ketterer (PSI), A. D'Amore, D. Simoneta and W. Kaiser (FHAargau and KATZ), M. Gabriel (AWM Werkzeugbau), W. Haese (Bayer AG) Polymer molding is highly suitable for the mass fabrication of high precision micro- and nanostructures. It requires thermoplastic polymers with good molding properties at moderate process temperatures. We show a quantitative approach to the analysis of the molding properties of polymers in the nanorange and indicate which parameters are most important for achieving a good replication fidelity. Thermal injection molding is a key technology for the fabrication of devices with nano structured surfaces. It lliil combines a very high resolution capability with low-cost, mass production potential. In our previous work [1] it has been shown that the replication limit has not yet been reached and that the molding process can be very fast. For future high precision applications it is necessary to broaden our understanding of how nanostructures are molded and which kind of polymers are best suited for nanoreplication. Fig. 2: Injection molded A-ridges on a Compact Disc polymer (see fig. 3). The aspect ratio (relative height) of the molded structures is nearly constant for different structure sizes on the same molded disc. 70 60 y I''-"!i 40- I Fig. 1: V-groove etched into monocrystalline silicon £ 30 3 Our aim was to generate microstructures on a mold with II variable size and defined shape, and to examine a physical property in the nanorange which can be easily measured on 10 the molded structure. Particularly suitable as master structures for this are V-grooves, which can be fabricated in 100 105 110 115 120 125 130 monocrystalline silicon substrates by anisotropical mold temperature [°C] chemical wet etching. This process yields grooves with Fig. 3: Structure height of an injection molded A-ridge very smooth walls and a sharp V-shaped bottom edge (see dependent on the mold temperature (structure fig. 1). Gratings with periods ranging from 120 nm to 5 Lim width 200 nm). were fabricated. The silicon master was inserted into a Compact Disc molding tool from AWM and several Using molds with V-grooves new materials can be tested hundred discs with a diameter of 80 mm were produced and the fidelity of the molding in the micro- and nanorange with cycle times down to 10 sec (see fig. 2). The polymers can be improved. With this knowledge the already large used were polycarbonates from Bayer AG. potential of the injection molding technique for the mass fabrication of nano structured devices can be increased. The degree of molding of replicated V-groove structures was compared for different process parameters, sizes and FUNDING: SNF (NFP36), PSI, FHA, AWM. orientations. The dominant factor which influences the molding fidelity is the strong dependence of the melt REFERENCE viscosity with the mold temperature. Within the [1] H. Schift, A. D'Amore, C. David, M. Gabriel, temperature range given by the molding tool the height of J. Gobrecht, W. Kaiser and D. Simoneta, the A-ridges increases constantly up to temperatures J. of Vac. Sci. Technol. B 18 (6) (2000). slightly below the glass transition temperature of the 98 LASER ABLATION LITHOGRAPHY USING DIFFRACTIVE PHASE MASKS C. David, T. Neiger, P. Haberling, J. Wei, T. LippertandA. Wokaun (PSI) We investigated a fast parallel method for the fabrication of continuous profile structures in polymer surfaces using a XeCl excimer laser. The used quartz phase masks consist of phase gratings with varying duty cycles to control the transmitted zero order flux for different positions on the mask. Using this method, blazed diffractive optical elements were ablated in polyimide films. Intense UV laser pulses can be applied to pattern polymer surfaces. The ablated depth per laser pulse depends on the fluence and the sensitivity of the polymer. Complex patterns over larger areas can be generated by projecting a demagnified image of a mask onto the substrate. Conventional photo masks consisting of absorber structures often suffer from radiation damage. We developed phase masks consisting of gratings etched into quartz substrates. The patterned areas diffract the light out of the aperture of the projection lens without absorption or damage (Fig.l). Substrate (polymer) Photomask with diffracting structures Fig. 1: Set-up for the patterning of polymer surfaces by laser ablation using diffractive masks. The masks are generated using electron beam lithography and reactive ion etching (Fig. 2). The transmitted zero order flux propagating through the lens onto the substrate can be varied by changing the line width and thus the duty cycle of the diffracting structures. This is achieved by a continuous change of the focal setting of the electron-beam lithography tool [1]. To achieve an accurate control of the ablated Fig. 3: SEM micrographs of an array of diffractive micro depth, the threshold and the non-linear response of the lenses. Each lens has a size of 0.8 x 0.8 mm2 and ablated polymer was measured and pre-compensated in the is generated using only a few shots of the excimer mask design. The correction algorithm was implemented in laser. the mask data preparation software. I I The described method opens up the possibility for efficient fabrication of diffractive optical elements with continuous structure profiles [2]. As an example, a micro lens array ablated into a spin-coated polyimide film on a glass substrate is shown in figure 3. The array was formed in a step-and repeat scheme by exposing each lens with a few laser pulses. The lower image shows the desired spherical shape and the steep edges of the polyimide lenses. FUNDING: SNF, PSI. REFERENCES [1] C. David and D. Hambach, Microelectronic Fig. 2: SEM micrograph of diffractive grey tone phase Engineering 46 (1999) 219-222. mask structures with varying duty cycle etched [2] C. David, J. Wei, T. Lippert, A. Wokaun, into quartz. submitted to Microelectronic Engineering. 99 HIGH RESOLUTION SCANNING X-RAY FLUORESCENCE MICROSCOPY C. David, F. Glaus, T. Neiger (PSI), B. Kaulich, R. Barrett, M. Salome and J. Susini (ESRF) Using Fresnel lenses optimised for operation near the sulphur absorption edge at 2472eV photon energy, it was possible to perform X-ray fluorescence microscopy experiments with unprecedented spatial resolution and sensitivity. By imaging zinc sulphide (ZnS) test structures specially fabricated for this experiment, we were able to resolve features with lateral dimensions below 100 nm and to detect sulphur quantities down to 3-10l6g. For many samples the fluorescent X-ray emission resulting from absorption of the incident beam offers useful chemically sensitive information about the system under study. In particular, the vastly reduced Bremsstrahlung spectral background has a trace element sensitivity which can be significantly better than that possible using electron excitation. On the other hand, it is also of interest for concentrated systems as the use of fluorescence emission allows the study of bulk, non-conducting samples which cannot be prepared in suitably thin sections for standard absorption contrast microscopy. The characteristics of the ESRF ID21 X-ray microscopy beamline make it well suited to applying X-ray fluorescence microscopy for studies of sulphur content using both spectrometric and spectroscopic methods in applications such as geochemistry and human biology. The experimental methods being developed depend upon the quality of the microfocussing optics, which must deliver high fluxes into the smallest possible probe size. To meet these demands, the lens diameter has to be matched to the spatial coherence of the undulator source, and its outermost zone structures should be as small as possible. Furthermore, the zone structures have to provide a good diffraction efficiency. Fresnel lenses especially optimised Fig. 2: The ZnS test structures imaged at the ESRF for this purposes have been fabricated using electron beam scanning x-ray microscope in sulphur- lithography and reactive ion etching. The 300 |j,m diameter fluorescence mode. The lower image shows a lenses consist of 900 nm high germanium structures with zoom of structure widths ranging from 75 nm to 100 nm outermost zone width on a Si N membrane [1]. 3 4 175 nm. To investigate the limits of sulphur fluorescence microscopy, a test pattern consisting of 26 nm thick ZnS The sample was scanned with radiation just above the structures was used. To minimise the background signal a sulphur K-absorption edge at 2472 eV. The sulphur K-lines germanium substrate was used. Figure 1 shows scanning X-ray fluorescence (2307-2464 eV) was collected using an electron microscopy (SEM) images of these structures. energy dispersive high-purity Ge detector. Figure 2 shows the resulting scanning x-ray fluorescence microscope images. Even though the fluorescence yield for S K-line emission is only 0.078, structure widths below 100 nm can be resolved. Taking into account the sulphur content of the test structures, this corresponds a sensitivity of better than 300ag(3-1016g). Further high resolution scanning x-ray fluorescence investigations on biological specimens are currently ongoing. ".*. • FUNDING: PSI, ESRF. Fig. 1: SEM images of a ZnS Siemens star. The structures are 26 nm thick, the width ranges from 1 itm down REFERENCE to 50 nm (half pitch). The right image shows [1] C. David, B. Kaulich, R. Barrett, M. Salome, structure widths from 75 nm to 175 nm. J. Susini, Appl. Phys. Lett. 77, 3851 (2000). 100 TUNABLE WET ETCHED DIFFRACTIVE OPTICS FOR HARD X-RAYS C. David, B. Nohammer, B. Haas, J.F. van der Veen (PSI), J. Hoszowska, E. Ziegler, M. Drakopoulos, F. Zontone (ESRF), J.H.H. Bongaerts, M.J. Zwanenburg (Univ. Amsterdam) Electron beam lithography and vertical selective wet etching of silicon has been applied to fabricate linear transmission Fresnel zone plates. By tilting the lens it is possible to increase the effective structure height and to optimise the diffraction efficiency over a wide range of photon energies. Measurements using the lenses as collimators for x-ray waveguiding experiments resulted in a flux enhancement by a factor of 50. Focusing elements for hard x-rays are used either to provide a small spot of radiation for spatially resolving techniques or to concentrate the radiation in order to enhance the flux density in a small region of interest. The main problem with producing highly efficient diffractive lenses for hard x-rays is that the phase shift of matter is Fig. 3: The effective structure height of a linear small, which means that extreme aspect ratios are required diffractive lens can be increased by tilting. for sub-micron structure widths. This is particularly true for materials consisting of light elements, and is therefore why over a wide range of photon energies [1]. The diffraction silicon was formerly considered as unsuited for the efficiency of a 5.5 |j,m high silicon lens was measured as a fabrication of diffractive transmission hard x-ray optics. function of tilt angle for photon energies up to 29 keV (see However, single crystal silicon offers a unique possibility figure 4). The measured values are in good agreement with to fabricate very high aspect ratio structures using a simple calculations based on scalar diffraction theory; they show, wet etching process shown in figure 1. that it is indeed possible to tune the lens over a wide energy range. The lens has been applied to focus 13.3 keV radiation in waveguiding experiments on ordering phenomena of colloid suspensions [2]. An increase in flux by a factor of r b) eleclron-beam exposure 50 was measured compared to measurements performed a) membrane definition .mil development without a lens. Aspect ratio of outermost zone structures 16 20 30 50 100 200 V c) 30 nm Cr lift-off d) orientation-selective wet etching and removal of Cr Fig. 1: Schematic view of the lens manufacturing process. On <110> Si substrates, lines in <112> direction can be wet etched with vertical side The hard x-ray lenses shown in figure 2 were fabricated using this method [1]. The outermost zone width is 324 nm, the zone height is 12 (am, corresponding to an aspect ratio of 40. To increase the aspect ratio even further, the linear lenses can be tilted with respect to the x-ray beam as shown in figure 3. This trick also enables us to vary the effective structure height in order to match the resulting phase shift 10 20 30 40 50 60 70 80 Fig. 4: Calculated and measured efficiency of a 5.5 iim high silicon lens as a function of tilt angle. FUNDING: PSI, ESRF. REFERENCES [1] C. David, B. Nohammer, E. Ziegler: •CO submitted to Appl. Phys. Lett. Fig. 2: SEM images of a linear Fresnel lens fabricated by [2] M. J. Zwanenburg et al.: electron beam lithography and wet chemical Phys. Rev. Lett. 85, 5154 (2000). etching of <110> oriented silicon substrates. 101 MICROMECHANICAL CANTILEVERS FOR THERMAL ANALYSIS J.H. Fabian, C. Padeste, J. Gobrecht, Ph. Lerch (PSI), L. Scandella (NanosurfAG), E. Meyer (Univ. Basel) Micromechanical cantilever devices have been designed and fabricated. Heated cantilevers are used as a thermo gravimetric sensor for the analysis of nanogram weight samples and achieve picogram mass accuracy. To demonstrate the excellent features of the fabricated devices, the thermal gravimetric analysis of 2.7 ng calcium oxalate monohydrate is presented. Analytical chemistry routinely uses thermal gravimetric analysis (TGA) in order to study the change in mass of samples undergoing desorption, adsorption or decom- position processes. We have developed a method based on joule heated micromechanical cantilevers to investigate the thermal behaviour of samples whose masses range between about 100 picograms and several hundred nanograms. Micromechanical cantilevers were attached to a piezo- electric actuator and the bending amplitude measured by an optical beam deflection technique adapted from scanning force microscopy. In the experimental setup (Fig. 1) the resonance frequency of a cantilever with the deposited Fig. 2: 2.7 ng of calcium oxalate were deposited with a sample (Fig. 2) is tracked while the cantilever is heated up. micromanipulator on the cantilever device. CaC2O4 H2O (s) <-»CaC2O4 (s) + H2O (g) CaC2O4 (s) -> CaCO3 (s) + CO (g) CaCO3 (s) <-> CaO (s) + CO2 (g) In the measured TGA curve (Fig. 3) the three decomposition steps can be well resolved; only a small discrepancy in the second step is observed in comparison with the theory. vacuum pump Fig. 1: In the experimental setup, the cantilevers' -1,4 deflection can be determined with < 1 nm 200 400 600 800 accuracy while the device is operated under temperature (°C) vacuum or inert gas conditions. Fig. 3: Temperature dependence of the mass change A variation of the mass of a cantilever-sample system following the decomposition of 2.7 ng calcium induces a shift in the resonance frequency. Since the oxalate monohydrate. temperature of the silicon cantilever can be controlled by The major advantages of a cantilever based system the electrical power dissipated into the device, a sensitive compared with conventional thermal analytical instruments thermobalance is realised. are the high mass sensitivity, the low power consumption for heating the device up to several hundred degrees For that purpose, complete arrays of U-shaped cantilevers Celsius, and the short thermal response time which allows with a p-doped top layer in which joule heat is dissipated us to thermally cycle the device in the kHz range. were micro-machined [1]. In order to optimise the design of the cantilevers for thermogravimetric applications, finite FUNDING: SPP MINAST NOSE, PSI. element simulations of the micro-electro-mechanical device REFERENCES were performed [2]. [1] J.H. Fabian er al., Ultramicroscopy 82, 69 (2000). To demonstrate the performance of our thermobalance, we measured the thermal decomposition curve of calcium [2] J.H. Fabian et al., Proceedings of the 18th CAD-FEM oxalate monohydrate. The chemical reaction occurring in Users' Meeting, International Conference on FEM three steps can be described as follows: Technology, A 1.4.5 (2000). 102 SINGLE HOLE TRANSISTOR IN A p-Si/SiGe QUANTUM WELL U. Dotsch, U. Gennser, C. David, G. Dehlinger, D. Griitzmacher (PSI), T. Heinzel, S. Luscher, K. Ensslin (ETHZ) A single hole transistor is created in a p-Si/SiGe quantum well by applying voltages to nanostructured top gate elec- trodes. The gating is achieved by oxidizing the etched semiconductor surface and the mesa walls prior to evapora- tion of the top gates. Pronounced Coulomb blockade (CB) effects are observed at small coupling of the transistor island to source and drain. Transport through small islands defined in semiconductors The top gate (10 nm Ti and 20 nm Al) was patterned by has been of considerable interest recently. When the island electron beam lithography and subsequent lift-off using is only weakly coupled to reservoirs via tunnel barriers, the thermal evaporation. In Fig.2 the island geometry is shown. Coulomb blockade effect determines the carrier transport. Three split gate electrodes (point contact gates pel, pc2, as Single hole transistors out of p-doped Si/SiGe quantum well as the center gates define the dot with a lithographic wells are of particular interest for several reasons: (i) the size of 500 nm x 800 nm. For pel and pc2, a gap width of material has a large g-factor of geJ= 6.7 and a large effective 150 nm was chosen. mass (m = 0.25 me), (ii) the interaction parameter rs, de- fined as the ratio between the Coulomb energy of two holes 0.010 at their average separation, and the Fermi energy, is very large, i.e., r ~ 4 for typical carrier densities. 0.002 s 0.008 pel: -180mV pc2:+145mV jot' 0.006 43 44 0.004 gate voltage (mV) 0.002 Fig. 1: Schematic cross section through the processed 35 40 45 50 55 60 hetero structure. gate voltage (mV) However, p-SiGe has been notoriously difficult to gate, due Fig. 3: Conductance G through the island as a function of to leakage currents across the Schottky barrier. Here, we Vg, showing CB oscillation. Inset: blow-up of the present the fabrication and characterization of a gated sin- peak at Vg =43 mV (crosses), fitted to a thermally gle hole transistor in a p-SiGe quantum well. Tests have broadened CB resonance (solid line). For these indicated that in our samples, large leakage currents be- measurements, the temperature was 90 mK tween the top gate and the 2-dimensional hole gas can flow across the mesa edge. Therefore, we have deposited a layer At sufficiently large split gate voltages V and V , CB of SiO by thermal evaporation right after the reactive ion pcl pc2 2 oscillations are observed as a function of the center gate etch which defines the mesa, as shown in Fig. 1. voltage V,s.[Fig. 3]. Here, Vsomdmin was kept at 100 jxV. The measured CB resonances can be fitted well to the expres- sion 2 G(VTh) = Gmax cosh" [rj • (F - Fmax)/ kjh ] describing a thermally smeared CB peak in the multilevel transport regime. G^ and Vmai denote the amplitude and the position of the CB resonance, respectively. FUNDING: SPP MINAST (SIMNAD), PSI. Fig. 2: Scanning electron micrograph of the gate geome- REFERENCE try. The Ti/Al gates appear as bright areas. [1] U. Dotsch et al., Appl. Phys. Lett. 78, 341 (2001). 103 ELECTRO- AND PHOTOLUMINESCENCE OF C-INDUCED GE ISLANDS EMBEDDED IN SI A. Beyer, E. Miiller, S. Stutz, H. Sigg, D. Grutzmacher (PSI), K. Ensslin (ETHZ) The deposition of a sub-monolayer carbon on a Si (001) surface and the subsequently growth of Ge leads to an im- mediately 3-dimensional nucleation of small Ge islands. These islands show intense photoluminescence (PL). The external quantum efficiency (EQE) increases with a decrease of the excitation power density from 4xlO'4 to 1.4xlO'2 for an optimised sample. Electroluminescence from Ge islands was observed with an EQE in the 10" range. A promising way to improve the optical properties in indi- land related PL increases with a decrease of the excitation rect semiconductors like silicon is the localisation of charge power density from 4-10"4 to 1.4-102. The inset in figure 1 carriers. The resulting enhanced uncertainty in the momen- compares the integrated PL from the Ge islands and the Si tum of the charge carriers allows optical transitions without TO peak in dependence of the excitation power. The slope the use of phonons. In order to realise a distinct carrier of 0.5 and 0.97 suggests that Auger recombination in the localisation, Ge islands were prepared on the C alloyed Si islands and impurity levels in the silicon are the dominant (001) surface. This technique leads to extremely small Ge non-radiative recombination paths. islands (<15 nm) at moderate deposition temperatures [1]. voltage / current We have grown these islands by molecular beam epitaxy at -2.6V / 309mA a substrate temperature of 460°C using e-beam evaporation -2.4V/245mA of Si and Ge. The carbon was evaporated from a pyrolithic graphite filament. Photoluminescence (PL) measurements -2.2V/182mA at 1.8 K were performed on samples with a stack of 10 -2.0V/124mA island layers. These layers were separated from each other by 8 to 32 nm Si. An annealing step in a H/N2 ambience at 650°C for 10 minutes was applied after the growth in order to enhance the PL intensity due to healed up point defects. H .6V / 30mAJ 1.4V/9mA 0.85 0.90 0.95 1.00 1.05 1.10 1.15 energy [eV] Fig. 2: Electroluminescence (EL) at various bias voltages. U5 Inset: Integrated EL and external quantum effi- C CD ciency (EQE) at various current densities. For the electroluminescence (EL) measurements, devices were fabricated from samples containing a stack of 30 island layers with the PL optimised structure grown on a n- type Si wafer and capped with a 200 nm wide p-doped Si layer. On the front side of the devices aluminium finger 0.9 1.0 1.1 1.2 contacts were fabricated, with a width of 4 iim and spaced energy [eV] by 3 (im covering a device area of 0.134 mm2. Fig. 1: PL at various excitation power densities. Inset: The EL measurements at 15K shown in figure 2 reveal an Integrated PL of the Ge dots and the Si TO peak. broad peak from the Ge islands at 1.04 eV. The external quantum efficiency is plotted in the inset for the various 6 The amount of C and Ge per island layer was varied from current densities and is generally rather low in the 10 0.1 to 0.3 monolayer (ML) and from 0 to 3.4 ML, respec- range. Improvements can be expected by using transparent tively. The strongest PL intensity was found for islands conductive oxide (TCO) contacts instead of the Al finger formed by 0.2 ML of C and 2 ML of Ge grown in layers contacts on the front side. which were separated by 16 nm Si. The PL for such a struc- ture at different excitation power densities is shown in FUNDING: SNF, PSI. figure 1. The large broad peak around 1.0 eV stems from the Ge islands. The Si cause to smaller narrow peaks at REFERENCE higher energies, such as the TO phonon related (Si TO) line [1] O. G. Schmidt, C. Lange, K. Eberl, O. Kienzle, and at 1.09 eV. The external quantum efficiency of the Ge is- F. Ernst, Appl. Phys. Lett. 71, 2340 (1997). 104 OPTICAL AND STRUCTURAL ANALYSIS OF GE QUANTUM DOTS EMBEDDED IN STRAINED SI QUANTUM WELLS GROWN ON PATTERNED SUBSTRATES A. Beyer, E. Miiller, S. Stutz, H. Sigg, C. David, D. Grutzmacher (PSI), K. Ensslin (ETHZ) Ge quantum dots embedded in strained Si quantum wells (QW) were investigated. The dislocation density in the re- laxed SiGe buffer layer was reduced by deposition on mesa lines possibly permitting an elastically strain relaxation. Intense PL signals were observed from Ge dots in the stained Si QW's. It was proven, that these PL stems from the quantum structures by comparing samples before and after etching the Si QW and the Ge dots. Ge quantum dots embedded in silicon have been used in the quenched, presumably because of the high dislocation past to improve the opto-electronic properties of Si based density in the SiGe buffer layer. These PL is assigned to the materials. The idea is to overcome the limitation of the quantum structures grown on top of the relaxed buffer indirect band gap of Si by strong localisation of the carriers layer. We have proved this assumption by removing the in quantum dots. However, the Ge quantum dots provide a quantum structures by an reactive ion etching step in a SF6 strong carrier confinement only for the holes, the electrons plasma. The PL spectra from the remaining SiGe buffer are only weakly confined in the Si. We embedded the Ge layer is plotted as a gray line in figure 1. The X^ line is quantum dots in strained Si quantum wells (QW) grown on quenched due to the etching. Consequently these line is relaxed SiGe buffer layers. The strained Si QW provide a attributed to the quantum structures. Unfortunately, the PL confinement of the electrons in the vicinity of the Ge dots. data do not permit an exact assignment of the recombina- tion path, which give rise to the X^ line. The structures were deposited on planar and patterned sub- strates by MBE. The pattern was created by e-beam lithog- raphy on Si (001) wafers. 2 Lim deep and 1.5 itm wide trenches were etched to define line shaped mesas with widths ranging from 0.5 |im to 4.5 (J,m. The lines were aligned parallel and 15, 30 and 45° off to the [110] direc- tion. Si and Ge were deposited by e-beam evaporation using a substrate temperature of 620°C. First a 1.2 (j,m thick Si08Ge02 step graded buffer layer was grown. On top of this buffer layer Ge islands have been deposited using 7 monolayer of pure Ge, followed by a 2.5 nm thick silicon layer and a 20 nm thick Si08Ge02 spacer layer. These three growth steps were repeated 10 times. Fig. 2: TEM images from structure grown on top of the line shaped mesa. An silicon enrichment on the top corner forms an vertical silicon quantum well. The sample with the smallest mesa width shows an unusual feature in the TEM image in figure 2. A vertical bright thin line through the center of the mesa structure is visible, indicating an enrichment of silicon. Apparently, the growth 0.9 1.0 1.1 rate of si is larger on the top than on the adjacent facets. energy [eV] Consequently, we have grown a self assembled vertical silicon rich quantum well with a width of about 20 nm. Fig. 1: PL at 1.8K of Ge dots in strained Si QW (black This vertical QW acts as an efficient collector for electrons line). The etched and the planar sample confirm and improves the confinement of the electrons in the vicin- our assignments (see text). ity of the Ge islands, leading to intense PL lines. The PL from a patterned and a planar sample are compared FUNDING: SNF, PSI. in figure 1. The planar sample exhibits intense dislocation related PL lines. These lines are strongly reduced in the REFERENCE case of patterned substrates [1]. An intense PL signal la- [1] D. Grutzmacher, R. Hartmann, O. Leifeld, beled with X^ dominates the spectra from the patterned U. Gennser, C. David, E. Miiller, J.-C. Panitz, SPIE sample in figure 1. In the planar sample these signal is Vol. 3630, 171 (1999). 105 MODELING OF THE C(4X4) SURFACE RECONSTRUCTION C. Guedj, O. Leifeld, D. Griitzmacher (PSI), P. Kelires (FORTH), E. Kaxiras and I. Remediakis (Univ. Harvard) The C(4x4) surface reconstruction previously observed by STM was modelled with anharmonic Keating modelling, Monte Carlo modelling, and full Ab Initio quantum mechanics calculations. The lowest energy configuration as well as good agreement with STM data is obtained with a configuration involving surface carbon atoms positioned in second nearest neighbours. Carbon-induced Ge dots can exhibit interesting photolumi- trated in figure 2. The calculated distance between spots nescence and electroluminescence properties, which may (0.64 nm) is reasonably close to the experimental one (0.59 lead to further opto-electronic applications if the techno- nm). In this respect the model described in [1] gives better logical and economical requirements are fulfilled. The agreement, however, the asymmetry between spots is well contribution of carbon is essential but its exact distribution reproduced, as opposed to the modelling suggested in [1]. during and after growth is not precisely known. Carbon Moreover, the overall agreement by this new model with all pre-deposition onto Si(001) lead to the c(4x4) surface re- available experimental data is satisfactorily. construction domains, which were previously interpreted with a model involving surface carbon atoms in first nearest neighbours.[l] However, this model turned out to be in- compatible with recent XPD experiments.[2],[3],[4] There- fore, we searched for another structural arrangement of atoms compatible with all available experiments. Three complementary theoretical tools also indicate that this model, involving carbon atoms in second nearest neighbours, is the most stable among those considered. This structure is represented at the atomic scale in figure 1. 3 - o o a CO § Fig. 2: Comparison between experimental STM image and tn simulated image (top left) obtained from full ab b initio calculations. 0 12 3 4 Distance along [110] (nm) The STM resolution is difficult to estimate and depends on many factors such as tip radius, voltage step resolution, Fig. 1: Top view of the arrangement of atoms considered to resolution of the A/D converter in addition to electrical and explain the c(4x4) surface reconstruction. Atomic mechanical noise. A conclusive answer to the atomic posi- positions are obtained from anharmonic Keating tion of the C atoms in the C alloyed Si surface may be modelling. obtained from grazing incidence x-ray diffraction data. In this newly suggested configuration, carbon atoms are FUNDING: BBW/EU (SiGeNET), PSI. arranged in second nearest neighbour positions, therefore they locally form a zinc-blende silicon carbide. This con- REFERENCES figuration is a local cubic 3C-SiC nanostructure on silicon, [1] O. Leifeld, D. Gratzmacher, B. MuTler, K. Kern, which is more stable than a surface diamond nanocluster. E. Kaxiras and P. C. Kelires, For bulk Si-C solid solutions, it is known that stoechiomet- Phys. Rev. Lett. 82, 5 (1999). ric SiC is the only stable compound of the phase diagram. [2] R. Kosugi, S. Sumitani, T. Abukawa, Y. Takakuwa, In our case, anharmonic Keating modelling, Monte Carlo S. Suzuki, S. Sato, S. Kono, simulations and full ab initio Quantum mechanics simula- Surf. Sci. 412/413,125 (1998). tions demonstrate that this model has a lower energy than [3] M. Ikeda, T. Maruoka, N. Nagashima, the one involving surface carbon atoms in first nearest Surf. Sci. 416,240 (1998). neighbors. Moreover, a reasonable match is found for the [4] M. Stoffel, L. Simon, D. Aubel, J.L. Bischoff, calculated STM image and the experimental one, as illus- L. Kubler, Surf. Sci. 454-456, 201 (2000). 106 STRAIN FIELDS IN C-INDUCED GE DOTS C. Guedj, E. Muller, A. Beyer, D. Griitzmacher (PSI), K. Eberl (MPI Stuttgart) Optical properties of solid-state nanostructures are usually correlated to the amount of strain at the atomic level. Local stresses modify the orbitals shapes and the energy levels. The exact distribution of strain in a heterogeneous medium is usually difficult to estimate. Analysis of high-resolution TEM images may help to get a better insight into the local distortions in various nanostructures. The example of carbon-induced Ge dots is particularly interesting. Electronic-Device properties are directly linked to the mi- that the local increase of parallel lattice parameter is maxi- crostracture of the material, at the atomic scale. In low mal at the peripheral base of the dot. This area corresponds dimensional heterostractures, interatomic distances may to the maximal distortions, where defects are most likely to rapidly change from the substrate to the active layers, and occur. These regions also fix the size of the dot; they repre- the mapping of these distortions is of high interest to under- sent the "elastic fences" where the island would need too stand the resulting physical properties. Carbon-induced Ge much energy to grow bigger. The picture is simpler in the dots are particularily relevant to illustrate this principle, case of 2D systems. For a single layer of Si, xGex epitaxially because rapid fluctuations of strain occur in these nanos- grown on silicon with a thickness below the onset of misfit tructures, and photoluminescence energies depend on the dislocations, the layer is called pseudomorphic when its spatial distribution of stresses. The direct correlation be- parallel lattice parameter is equal to the one of the sub- tween the strain map and the optical properties is a key to strate. In that case, the Moire pattern of figure 1 would control the final optoelectronic properties of the device. consist of a series of parallel lines whithout bending. Therefore, we performed an investigation of strain fields in The picture obtained for the perpendicular distortions is these nanostructures. presented in figure 2. This analysis uses digitized high-resolution transmission electron microscopy images to analytically extract a strain 01 map after proper atomic scale modeling. In parallel, we "'. •••'"•**: [° ] have also implemented a self-Moire technique to obtain a rapid qualitative insight into the strain fluctuations, without -• ;, -; •. *'"•*>.... [T!O]^J the counstraints of extensive analytical calculations. We found that the two methods give basically the same results. An example is represented in figure 1. if: • I/J1] Fig. 2: Self Moire pattern of a carbon-induced Ge dot epi- taxially grown on Si(001). The Moire process is tuned to highlight the distortions of the perpen- dicular lattice parameter. The spacing between the Moire lines is inversely propor- tional to the actual interplanar distance. The highest per- pendicular lattice parameter is obtained at the top of the Ge-rich dot, where Ge atoms are likely to segregate. The dot is in compression. In the underlying matrix, there is an inverse distortion, with a broader spatial extention: this area is tensially strained. The dot elastically differs from its substrate, and the mutual adaptation gives this complex Fig. 1: Self Moire pattern of a carbon-induced Ge dot epi- pattern, both in the parallel and perpendicular directions. taxially grown on Si(001). The Moire process is The simple 2D analysis does not apply anymore, and 3D tuned to highlight the distortions of the parallel lat- band structure calculations must be implemented to calcula- tice parameter. te the resulting band offsets. It may be possible to obtain quasi-discrete levels at the peripheral base of the dots, With this newly developped technique, we can choose to which should noticeably influence the optoelectronic prop- highlight the distortions in the directions either parallel or erties of the system. The tensially strained channel below perpendicular to the substrate. For example, the vertical the dot may be used for a new type of device, called lines of figure 1 are linked to the distortion of the parallel DOTFET, and recently invented by K. Eberl. lattice parameter. When a deviation from perfect lateral periodicity occurs, then the Moire lines bend. We can see FUNDING: BBW/EU-(SiGeNET), PSI. 107 MODIFICATIONS OF THE SI(100) SURFACE O. Kirfel, D. Grutzmacher (PSI), K. Kern (MPI Stuttgart) The deposition of C-induced Ge dots on pre-structured surfaces is expected to lead to the self organised formation of small (-10 nm diameter) Ge dots. Theoretical model calculations show that the reduction in size of the dots might lead to an increase of the radiative recombination processes.' As the size of the dots is of strong importance, the ex- act control of their nucleation and growth is crucial and their formation has to be studied in detail. Previous experiments with Ge deposition on C pre-covered Si(100) showed, that pre-deposition of a 0.11 ML of C prevents the formation of a Ge wetting layer. Ge dots with irregular shape can be found in the C-poor areas after the deposition of 2.5 ML Ge. This could be attributed to an undulating surface strain field caused by the submonolayer of carbon.2 In contrast, the deposition of Ge on bare Si(100) leads to a wetting layer, until a critical thickness of about 4 ML is reached and faceted hut-clusters are formed (Stran- ski-Krastanov growth mode)/ As the growth of Ge clusters and therefore their size is strongly influenced by the pre- deposition of carbon, we started to study the influence of the amount of carbon on the Si(100) surfaces. To analyse the impact of carbon on the Si(100) surfaces, samples with a lOOnm Si buffer (750°C) and a sub- monlayer of C (460°C; 0.05ML, 0.11ML; 0.2ML, 0.3ML) were grown in a MBE and transferred under UHV condi- tion into a STM. Fig. 1: All Samples are Si(lOO) with a submonolayer of A general feature of the pre-deposition of carbon is the C. a) 0.05ML C: First occurrence of c(4x4) recon- enhancement of surface roughness with increasing C cov- struction indicate by white arrows, b) 0.11ML C: erage, demonstrated in figure 1. At a C coverage of 5% of a Areas with elongated pairs of bright spots exhibit a monolayer there are terraces with buckled Si dimers which c(4x4) structure, c) 0.2ML C: Most of the surface often occur when impurities are present. On top of these is c(4x4)-reconstructed. d) 0.3ML C: No c(4x4) terraces are a small number of paired bright spots. This reconstruction and no Si-dimers. spots are characteristic for the c(4x4) reconstruction of the Si, initiated by the C. At a coverage of 0.11ML patches of dimers disappear and the c(4x4) reconstruction starts to be areas with a c(4x4) recontruction appear, separated by areas extruded by a modified reconstruction at 0.2 ML C. At 0.3 revealing buckled dimmer rows (fig l.b). After depositing ML C the c(4x4) reconstruction is completely extruded and 0.2ML almost the complete surface is covered by the only a less ordered surface can be seen. The increase of C c(4x4) reconstructed areas. Buckled Si dimers can hardly coverage is accompanied by an increase in surface rough- be found. Besides the c(4x4) reconstruction, there are areas ness. The larger amount of C itself with the change in the visible where the reconstruction seems to be modified. Two surface reconstruction and also the change in roughness areas exhibiting this modification are circled in figure lc. will impact the surface diffusion length of ad-atoms on the Similar to the c(4x4) reconstruction this modified surface C-modified Si (100) surface. Thus the amount of C pre- exhibits paired bright spots, but the correlation of these deposited allows to control the size of the Ge dots, which is paired spots is different and might be written as a 2x4 re- a crucial parameter in the process of optimising the emissi- construction based on the Si lattice. At a coverage of on of photons. 0.3ML the roughness has increased again. No c(4x4) re- construction and no Si dimers can be found. Generally the FUNDING: SNF, PSI. surface is much less ordered and no clear reconstruction is visible. REFERENCES To summarize, these results show, that first, the Si dimers change to buckled ones accompanied by the first c(4x4) [1] B. Delley and E. F. Steigmeier, reconstruction at 0.05 ML C. Increasing the amount of C, Phys. Rev. B 47 (3), 1397 (1993). the reconstruction of the surface gradually changes from [2] O. Leifeld, E. Miiller, D. Grutzmacher, B. Miiller, and the c(4x4) reconstruction at 0.1 ML to the 2x4 reconstruc- K. Kern, Appl. Phys. Lett. 74 (7), 994 (1999). tion at 0.2 ML. The areas with c(4x4) reconstruction grow and only small areas with buckled Si dimers were found at [3] Y.W.Mo, D. E.Savage, B. S.Swartzentruber, and 0.11 ML C. After this, the buckled Si M.G.Lagally, Phys. Rev. Lett. 65 (8), 1020 (1990). 108 THERMOPHOTOVOLTAICS - SYSTEM, PHOTOCELLS AND POTENTIAL B. Bitnar, G. Palfinger, W. Durisch, D. Griitzmacher, J. Gobrecht (PSI) Thermophotovoltaics is a technique which converts heat into electricity by using a radiation emitter and photocells. We built a small TPV prototype system, which reached a world record system efficiency of 2.1 %. The usability of different photocells in a TPV system is discussed based on IV- measurements. One application of TPV is the integra- tion in residential gas heating systems. We present a cost estimate of the electricity generated by TPV. A TPV prototype system was developed based on a also shows first IV-results for a germanium photocell from 1.35 kW butane burner, a selective emitter made from CESI (Segrate, Italy) illuminated with Er2O3 emitter radia- Yb2O3 and silicon photocells. With this system, components tion. The electrical power is still low, but probably this are tested for future use in a larger demonstration system combination has a large potential for improvements. [1]. In order to roughly estimate the cost of electricity produced Fig.l shows the prototype system mounted onto a conven- by TPV, the cost of the components of a the 20 kW TPV tional butane gas cylinder. The burner in the centre of the system was calculated for three different scenarios: cylindrical configuration is surrounded by the radiation 1. Based on an efficiency of 2.1 % already reached by the emitter, which produces 1.35 kW system, the geometry of the current system, radiation in a narrow emis- the prices of commercially available monocrystalline sion band around 1 jxm solar cells, quartz tube, an emitter and copper blocks wavelength. We measured for cooling the cells. an emitter temperature of 1735 K and a maximum 2. An improved system efficiency of 3 %, which should emissivity of 0.85 [2]. A be feasible without any major breakthrough in technol- cluartz glass tube protects ogy, a reduction of the system diameter and the photo- the photocells from the hot cell area and using a DURAN glass tube. exhaust gas. The tempera- 3. A system efficiency of 5 %. ture of the cells, which are glued onto water-cooled Scenario 1 should be achievable by producing a small se- copper blocks, is below ries of TPV systems with the current technology. Scenario 30°C. 2 presumes the availability of a high efficiency concentra- tor cell. Scenario 3 marks a technological breakthrough like This system produces a low bandgap cell with an efficiency and price comparable 29 W electrical power with to silicon photocells. 1.35 kW thermal input Fig. 1: TPV prototype system power. This corresponds to Table 2 shows the results of the calculation assuming a life- a world record system efficiency of 2.1 %. The photocell time of 20 years, a burner running 1800 hours/year at generator is made from commercially available silicon solar 12 kW, an interest rate of 4V4 % and yearly maintenance cells from TESSAG (Heilbronn). costs of 1% of the investment. Expecting the market break- through of TPV at an investment cost of 1000 to Table 1 shows the result of IV (Current/Voltage)- 1500 Euro/kW , an economic large scale production of measurements of different single photocells under AM 1.5 peak electricity by decentralised TPV generators could be reach- solar irradiation and Yb O/Er O emitter radiation. 2 2 3 able within the next years. Table 1: IV-characteristics of different photocells. Table 2: Cost estimate for a 20 kW TPV system. cell radiation Pmx Isc Scenario 1 2 3 spectrum [mA/cm2] [mV] [mW/cm2] TESSAG AM 1.5 37.4 595 16.0 cost of cells [EUR] 117 59 59 Yb,O, 146 630 50.8 cost of quartz/DURAN glass tube [EUR] 187 59 59 PSI AM 1.5 29.7 630 14.5 cost of emitter [EUR] 62 62 62 Yb,O, 137 679 64.2 cost of cell cooling (copper) [EUR] 121 60 60 CESI Ge AMO 49.5 204 3.38 total investment [EUR] 488 240 240 EUR/kW,,,t 1936 666 400 Er,O3 117 243 10.7 EUR/kWh excluding gas 0.092 0.032 0.019 A photocell optimised for the TPV was produced at PSI. EUR/kWh including gas 0.127 0.067 0.054 Tab.l shows that this cell has an efficiency by Yb O irra- 2 3 FUNDING: PSI, BFE. diation about 26 % higher than the TESSAG cell. REFERENCES Selective Er,O3 emitters have an emission band at 1.55 Jim wavelength and reach in principle a higher radiation power [1] J. C. Mayor et al, PSI annual report 2000. 1 than Yb2O3 emitters at a temperature around 1700 K. Tab.l [2] B. Bitnar et. al, 28" IEEE PVSC 2000. 109 TEM INVESTIGATION OF AN ORDERING PHENOMENON IN Al05Ga05As E. Muller and B. Patterson (PSI) Two types of ordering have been observed in Al05Ga0SAs grown on GaAs (110) substrate. Transmission electron dif- fraction proved the presence of a homogeneous but incomplete CuAu I type ordering while high resolution transmis- sion electron microscopy (HRTEM) revealed compositional striation parallel to the interface. Al05Ga05As grown on GaAs (110) substrate by Molecular Towards the bottom of the layer the number of such stack- Beam Epitaxy is one of the materials known to show order- ing faults appears to be much higher, resulting in stronger ing effects. An ordering of Al and Ga (Fig. 1) in the CuAu I streaking relative to the {110}-spots (Fig. 4). In the diffrac- type structure [1] as well as quasi-periodic composition tion pattern of the substrate neither of the additional variations [2] are reported in the literature. Only one of the intensities is observed. The presence of a homogeneously two phenomena used to be present at a time, however. In a but imperfectly ordered structure of the CuAu I type must sample grown at the former PSI Zurich, an ordering of the therefore be concluded. The quality of the ordering in- CuAu I type was observed by synchrotron X-ray scattering. creases towards the top of the layer. This was confirmed by The additional TEM investigation aimed at a more local X-ray measurements at a thicker sample. characterisation of the ordered material. bo Fig. 1: Ordering of Al and Ga in the CuAu I type structure. Ga : dark circles, As : bright circles, Al: gray cir- Fig. 4: Electron diffraction patterns from the bottom of the cles GaAlAs-layer (left) and from the GaAs substrate (right) Subsequently, the samples were investigated with high- resolution transmission electron microscopy (Fig. 4). Stria- tions running parallel to the interface have been observed Fig. 2: TEM micrograph of a GaAlAs layer (dark gray) on over the whole length of the electron transparent part of the GaAs (HO)-substrat (black) sample (~ 10 |j,m). The AlGaAs layer consisted of flat parts and a relatively large number of pyramids (Fig. 2). Diffraction patterns taken at a constant distance from the GaAs substrate show hardly any variation. Parallel to the growth direction, how- ever, two phenomena can be distinguished: Diffraction patterns from the top of the pyramids (Fig. 3) contain "zincblende-forbidden" intensities at {110}-positions. These prove the presence of the CuAu I type ordered struc- ture. Diffraction patterns from the top of the flat part of the _ -- 20 nm layer show strong {110}-ordering reflections and weak Fig. 4: TEM image: horizontal composition striation in the streaking through these spots along the growth direction (Fig. 3). The streaking is due to the presence of stacking AlGaAs layer (top), but not in the GaAs (bottom) faults within the ordered structure. Calculating the autocorrelation function, two values result: a short-range correlation (1.5 nm), indicating random stack- ing faults [1], and weaker, quasi-periodic oscillations (20 nm) due to composition variations [2]. It is the first time that both ordering phenomena have been observed in the same sample. REFERENCES Fig. 3: Electron diffraction patterns from the top of a [1] T.S. Kuan et al., Phys. Rev. Lett. 54, 201 (1985). pyramid (left) and from the top of a flat part (right) [2] P.M. Petroff et al., Phys. Rev. Lett. 48,170 (1982). 110 APPLICATION OF THE QUANTUM CASCADE LASER PRINCIPLE TO THE Si/SiGe MATERIAL SYSTEM L. Diehl, G. Dehlinger, H. Sigg, U. Gennser, D. Grutzmacher, E. Mttller, S. Stutz (PSI), J. Faist (Univ. Neuchatel), K. Ensslin (ETHZ) The principle of intersubband emission is applied to the Si/SiGe material system, using hole intersubband transition in structures grown pseudo-morphic on Si by molecular beam epitaxy. Cascade structures consisting of three times four repetitions of a five quantum well sequence are investigated. We observed a good agreement between theoreti- cal and experimental transition energies. The present investigation shows that Si/SiGe quantum cascade LEDs have sufficiently narrow linewidths and - in certain cases - high efficiency to be promising candidates for laser applica- tions. The combination of Si technology for both electronics and the good quality of the samples (see next report). For the active optical components has always attracted a great deal emission experiments, the devices were mounted into a He- of interest, but so far, the indirect bandgap of this group IV cooled flow cryostat and held at a temperature of 4 K. The material prevented the fabrication of an efficient light emit- light was collected by f/0.8 optics, sent into a Fourier trans- ter. This obstacle can be circumvented by adopting the form infrared spectrometer (FTIR) and detected by a cooled concept of the Quantum Cascade Laser (QCL) [1] to the HgCdTe detector. An electrical current with a frequency of Si/SiGe material system. QCLs rely on intersubband tran- 100 kHz and a pulse width of 5 (is was supplied to the sitions and tunneling, which are not dependent on the type 0.4x0.4 mm2 large mesa structures. of the bandgap. While the non-polar character of SiGe alloys is an advantage, the large lattice mismatch between Si and Ge, small band offsets in the complex valence band, 1.0 180 / zed ) I - and large effective masses for holes are severe drawbacks for the fabrication of Si-based QCL that has to be over- 160 come. 140 normal i e d E L energ y The structure is a repetition of twelve periods consisting of >, 0.5 i \i 1 120 - A one injector region and one optically active quantum well \ ° 100 120 140 160 180 200 tens i each. As shown in Fig. 1, two heavy hole (HH) states and c Mi \ HH2-HH1 (meV) one light hole (LH) state are confined in the optically active A_ A A n quantum well. The aim of the injector is to fill the upper 0.0 Lig h level HH2 with carriers, which then make a radiative transi- tion down to the ground state HH1. Holes can escape from 50 100 150 200 250 300 350 400 this level via tunneling through a miniband provided by the Energy (meV) injector region of the subsequent period. 0.1 Fig. 2: Electroluminescence spectra for the three different samples. Inset: Measured versus calculated transi- Injector (n+1) tion energy. The electroluminescence signal shows a strongly TM- LH states polarized peak close to the calculated transition energy. This peak could be detected up to temperatures of 200 K. A clear confinement shift is observed, Fig 2. The FWHM of about 25 meV is comparable to the best value reported so -0.3 Valence band edge far in absorption measurements on Si/SiGe QWs. The HH2 HH radiative efficiency of the best of the SiGe is found to be LH -0.4 comparable to GalnAs/AlInAs quantum cascade LEDs [2]. 100 0 -100 -200 -300 -400 -500 -600 Position (A) FUNDING: SNF, PSI. REFERENCES Fig. 1: Valence band structure of one period of a typical Si/SiGe quantum cascade structure. [1] J. Faist, F. Capasso, D. L. Sivico, C. Sitori, A. L. Hutchison, A. Y. Cho, Science 264, 553 (1994). Several intersubband luminescence structures, whose main [2] G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, J. Faist, difference is the Ge content and width of the optical active K. Ensslin, D. Grutzmacher, and E. Miiller, well, were grown by low temperature molecular beam Science 290, 2277 (2000). epitaxy. TEM pictures and x-ray measurements confirmed Ill STRUCTURAL INVESTIGATIONS OF Si/SiGe CASCADE SAMPLES D. Griltzmacher, E. Miiller, G.Dehlinger (PSI), T. Roch, J. Stangl, G. Bauer (Uni. Linz) The structural peculiarities of Si/SiGe quantum cascade structures have been carefully analysed using transmission electron microscopy, x-ray diffractometry and x-ray reflectivity. Special emphasis was put on the determination of strain, the interface roughness and the reproducibility of the well and barrier widths within the stacks of Si/SiGe cascades. An interface roughness of 2 to3 monolayers and a correlation length of 300 +200 nm was established. The large lattice mismatch between Si and Ge of 4% puts severe constrains on the design and the process window for the fabrication of quantum cascade structures. In order to achieve a large confinement potential high Ge concentra- tions are desired. In addition thin Si barriers are required to allow for efficient hole tunnelling from the ground state of the active well into the adjacent SiGe wells. Each cascade Fig.2 : TEM dark field image of the complete cascade contains a SiGe active well and 4 SiGe quantum wells structure, containing 3 stacks of 4 cascades, sepa- separated by 2 nm wide Si barriers from each other. Those rated by 100 nm wide Si layers. 4 wells form a mini-superlattice, with a miniband, which is aligned under proper bias conditions to the ground state of To determine the interface roughness and the reproducibil- the active well of one cascade and to the excited state of the ity of the cascade sequence x-ray diffractometry and re- active well of the adjacent cascade. flectivity measurements have been performed. Fig. 3a Fig.l shows strain situations, which occur during the depo- shows a reciprocal space map of the (113) reflex. Any sition of the Si/SiGe quantum cascade structures on Si lattice relaxation would lead to a deviation of the (1U) line, (100) substrates. The curves separate the regimes for pseu- i.e. the sattelite peaks would not line up with the substrate domorphic growth (below lower line) and lattice relaxation peak located at (113). Hence the reciprocal space map via formation of dislocations (above upper line). The re- clearly proves that the structure is completely strained. gime of meta-stable growth Between these curves is acces- Fig.3b) depicts a reflectivity space map. The reflectivity sible by low temperature deposition. The data a)-e) mark measurements performed at the HASYLAB and at the the situation after a) the growth of a single SiGe active University of Linz indicate an interface roughness of 2-3 well, b) two wells separated by a Si barrier, c) one cascade ML for the topmost quantum wells and slightly lower val- (5 wells, 4 barriers), d) a block containing 4 cascades and ues for the wells at the bottom of the structure. The space e) the whole structure except the topmost Si contact layer. maps, showing the diffusive scattering, indicate a correla- In particular for the latter situation the figure demonstrates tion length of 300 ± 200 nm. This confirms the excellent the huge amount of strain incorporated in the structure. The reproducibility of layer thicknesses and Ge contents in the deposition temperature was therefore reduced to 350°C. grown cascade structures. Molecular beam epitaxy permits deposition of single crystal Si/SiGe layers at these low temperatures. a) 0.54 - m isfil d islocalio n Fig. 1: Critical thickness of SiGe vs. the Ge content; dem- onstrating the strain situation during deposition of a Si/SiGe quantum cascade structure Despite the severe strain in the structures and the low depo- Fig. 3: a) Reciprocal space map of (113) reflex and b) sition temperature no extended defects were obtained by reflectivity space map of a cascade structure transmission electron microscopy (TEM). Fig. 2 shows a cross sectional dark field image of the complete structure. FUNDING: SNF, BBW (EU), PSI. 112 FORMATION OF ARBITRARY 3-DIMENSIONAL NANO-STRUCTURES FROM STRAINED Si/SiGe DOUBLE LAYERS V. Prinz, A. Beyer, C. David, E. Deckardt, B. Haas, B. Ketterer, F. Glaus, D. Grutzmacher (PSI) Complex 3-dimensional nano-structures can be formed by scrolling strained doublelayers. The simplest structures consists of a sacrificial layer, a thin compressively strained SiGe layer and a thin Si cap layer. By etching the sacri- ficial layer the asymmetric strain field in the underetched SiGe/Si bilayer leads to scrolling of these film. Depending on the shape and orientation of the mesa which is underetched a large variety of 3-d nano objects are created. Recently it has been demonstrated that nanotubes and other material for further shaping of the objects by additional nano-objects with cylindrical geometry can be formed by lithography or overgrowth. scrolling strained films such as III/V compounds and Si/SiGe structures [1]. In this study we extended this ap- proach to the formation of arbitrary 3-dimensional nano- objects, which may open up numerous paths for new appli- cations of semiconductor nano-structures. On top of a Si (100) substrate a thick heavily Boron doped film has been deposited, followed by a 10 nm wide un- doped Si layer forming the sacrificial layer. The structure is completed by the growth of a SiGe/Si p-type double-layer. Using e-beam lithography and wet chemical etching mesas of specific shapes were etched. The trenches defining the Fig.2: Scrolled Si/SiGe heterostructures with D = 5|j,m mesa structures were etched through the 3 topmost layers, including the sacrificial layer. Using a solution of NH3OH in water (3.7%) the undoped sacrificial layer is selectively Figure 3 depicts two examples of structures fabricated by etched against the heavily doped Si and SiGe layers. Due to underetching V-shaped mesa structures. The helical spiral the strain relaxation in the double layer these films start to shown in Fig 3 a is fabricated by a thin, highly strained bend up. The curvature will depend on the amount of SiGe/Si double-layer, whereas the tips in figure 3b are the strain, i.e. of the Ge concentration in the SiGe film, and the result of underetching rather thick epitaxial layers with a individual Si and SiGe film thickness', as given by: small lattice mismatch. Those structures might be useful for micromechanical as well as optical structures. Since the tips Dd have atomically sharp edges, use as field emission tips Aa should be possible. with D=diameter of curvature, d=thickness of the double layer, a lattice constant of Si, and Aa difference in the lat- tice constant averaged over the double layer. Fig.l shows ,- *f • ••*" k -* schematically the structure and driving forces for the scroll- ing of the epitaxial double layer. Etch p - Si Fig. 3: a) helical spiral and b) tips fabricated from V- shaped mesa structures Fig. 1: Schematic view of the scrolling mechanism FUNDING: PSI. Figure 2 shows two examples of rings fabricated by this REFERENCE methods. Fig. 2a shows three rings, which are connected at the front end and Fig. 2b shows a top view of a ring which [1] V. Ya. Prinz, S. V. Golod, V. I. Mashanov and A. has been manipulated in such a way, that it forms a cylinder K. Gutakovsky, Inst. Phys.S er. No. 166, 26th standing on the substrate surface. This might be the starting Int. Symp. Comp. Semicond. Berlin, 203 (1999). 113 PHOTOLITHOGRAPHIC GENERATION OF PROTEIN MICROPATTERNS C. Padeste, H. Sorribas, L. Tiefenauer (PSI) Positive resist photolithography in combination with oxygen plasma etching has been explored for the generation of micropatterns of covalently immobilised functional proteins. After plasma etching the surface adjacent to the protein pattern is chemically modified, or a second protein is immobilised resulting in a complementary protein pattern. Patterns of proteins and other molecules on various For neuron culture applications it is of interest to create surfaces are of increasing interest for biosensors and for inert areas adjacent to a protein pattern. Silanes differing in neurobiological applications. Lines of adhesion proteins on hydrophilicity were investigated to produce different surfaces have been shown to guide neurite outgrowth in background areas: a polyethyleneglycol-silane (PEG), a predifined patterns. Photolithographic techniques are well fluorinated alkyl silane (tridecafluorosilane, TFS) and a established to produce patterns with a resolution better than long chain alkyl silane (octadecyltrichlorosilane, ODS). 0.5 (xm. However, development and removal of the Plasma treated glass surfaces were modified with the irradiated resist are done in organic solvents or alkaline corresponding silane and contact angles and adsorption of solutions which may denature proteins. We have further radiolabelled rlgG were measured. Streptavidin covalently developed a published technique for the production of immobilised on glass served as the control surface. protein patterns using positive resist photolithography, where the protein layer is protected with a sucrose film to avoid direct contact with solvents. The technique allows the immobilisation of a second substance, thus creating complementary patterns on one surface. PEG SAv ODS SAv Fig. 2: Spreading of water droplets on glass chips with immobilised SAv (right half) and modified with PEG-silane and ODS, respectively (left half). A correlation of adsorption of IgG with the surface hydrophobicity was found (Table 1). Protein adsorption was ranging from a few percent of a monolayer for the plasma and PEG-treated surfaces to values exceeding a complete monolayer (600 ng/cm2 adsorbed IgG Fig. 1: Complementary line patterns of rabbit-IgG (top corresponds about to a dense monolayer of protein). half) and of streptavidin (bottom). Line widths are 5 |im (left) and 2 |im (right). Table 1: Contact angles and non specific adsorption of rlgG on glass surfaces. The patterning process consists of several steps. A protein Treatment H O contact Adsorbed is covalently immobilised on a glass or oxide surface using 2 angle [deg] IgG [ng/cm2] a silane and a crosslinker. The protein film is embedded in a sucrose layer, which is spin dried at high rotation speed SAv 42 ±2 125 ± 10 and cured in an oven. A photoresist is applied to the surface O,-Plasma 17 ±4 22 ±10 and structured using a lithographic mask. After develop- ment of the irradiated photoresist, exposed sucrose and PEG 33 ±3 28 ±10 protein is removed from the surface in an O2-plasma ODS 131±4 861 ±110 etching step. A second protein can now be immobilised on TFS 104 ±3 524 ± 27 the etched areas. A final lift-off step removes the photoresist. Using the presented techniques patterns of adhesion Complementary lines of different widths were created on molecules can be generated combined with complementary one surface. The used proteins rabbit-IgG and streptavidin PEG-silane areas to suppress non-specific protein (SAv) were visualised by binding rhodamine labelled adsorption. Such structured surfaces will be useful to antibodies and fluoresceine labelled biotin, respectively. establish cultures of dissociated neurons with guidance of The successful specific binding confirmed the biochemical neurite outgrowth by the protein pattern. functionality of the protein patterns. The limit of resolution of the process sequence is in the range of 1 \im (Fig.l). FUNDING: PSI, SPP Biotech, Module Neuroinformatics. 114 DEPOSITION SYSTEM FOR SINGLE MOLECULE EXPERIMENTS T.A. Jung, R. Schelldorfer (PSI), S. Berner, F. Meisinger, M. Brunner (Univ. Basel), H. Suzuki IFP (Univ. Basel and KARC) Molecular material in monolayer or submonolayer surface coverage exhibits distinctively different physical and chemical properties than in solution or in the bulk. Here we describe a system to handle sub-monolayer coverages of molecules like fullerenes and porphyrins. This effort aims at the detailed characterisation of molecular properties at surfaces using Scanning Probe Microscopy(SPM) experiments synchrotron based photoelectron diffraction and spectroscopy techniques. The main goal of this research is to understand structure and properties of molecules at surfaces and interfaces, for example in future molecular devices. A two chamber molecular deposition system was top edge of the steps, and self-organize in almost developped complementary to a pre-existing multi-chamber equidistant spacings. This gives some evidence for residual vacuum system with sample preparation and surface mobility at the room temperature used for the preparation characterization (AES, XPS, STM, LEED, ...) techniques. and observation of these molecules on the Ag(100) Molecular sublimation sources on ,button heaters' and substrate. samples can be interlocked without breaking vacuum (Fig.l). r [j HI in f-rl tni ti inf-i fit ;| oia*m 1 ! |illl |L,I fc nt^t.i It- a. •*-- tf—pl- r m"l>- h- in- ilirn t i ~:~> i ifr i |L in tfi I- w - a\. n i 1-4 n j i^j Fig.l: Schematic representation of the sublimation chamber: In vacuum button heaters with sublimation sources and samples can be transferred and operated next to a quarz crystal microbalance to enable precise depositions. Fig.3: STM image of some percent of a monolayer Cu- n TBPP on Ag(100). The individual molecules are Fig.2: Chemical Structure of Cu -tetra-(di-tertiary-butyl visible as they are lined up at the substrate steps phenyl) porphyrin (Cu-TBPP). with monoatomic height. Preferential adsorption [1] and the corresponding conformational flexure [2] of molecules when deposited on atomically clean substrates are crucial determinants of molecular properties. Molecular flexure and molecule substrate interactions affect any physical, chemical, optical, and electronic property. This is important for our understanding of contacted molecular devices. FUNDING PSI, SNF, University Basel, KARC Japan. Cu-TBPP (Fig.2) has been sublimed onto atomically clean Ag(100) substrate. In a Scanning Tunneling Microscopy REFERENCES image (STM), the porphyrin molecules appear as bright [1] H. Rauscher et. al. Chem. Phys. Lett 303, 363 (1999). spots which are lined up along step edges like pearls on a necklace (see Fig.3). Molecules preferentially adsorb to the [2] T. Jung et. al. Nature 386, 696 (1997). 115 EXTRACELLULAR STIMULATION OF NEURONS CULTURED ON MICROELECTRODE ARRAYS H. Sorribas, L. Tiefenauer (PSI), C. Strieker (Univ. Zurich /ETHZ) Microelectrode arrays have been fabricated, functionalised with cell adhesion molecule and cultures of dissociated neurons established. Cells on electrodes were extracellularly stimulated and the electrophysiological cell response was measured with patch clamp techniques. Microelectrode arrays for extracellular stimulation and smoothness). Electrophysiological characterisation of the recording from neural cells have been developed by several neurons with whole cell patch clamp confirmed that these groups. Such devices can be used to study neural cultured neurons were electrically active. The membrane processing, plasticity and learning, and have also found potential was about -65 mV. Upon stimulation the applications as sensing devices for pharmacologic drug membrane was depolarised in two phases to a value of screening. The low signal intensity recorded with about 60 mV. Extracellular stimulation with 130 (iA pulses extracellular electrodes is partially due to loose sealing of during 100 |is was necessary to generate an action potential the neuron membrane onto the electrode. Functionalisation in the neuron which was recorded with the intracellular of the electrode surface with cell adhesion proteins has electrode (Fig. 2). Stimulation with pulses higher than 350 been tried in order to improve the sealing. Results on (J.A led to electrochemical reactions on the electrode surface extracellular stimulation with extracellular gold electrodes resulting in damage of the electrode and of the cell. on a microstructured chip are presented. Chips with extracellular electrodes were fabricated with stimulating extracellular gold electrode conventional thin film technology. Gold tracks were intracellularly recorded action potential insulated with a 200 nm silicon oxide and a 400 nm silicon nitride layer. The chip was mounted on a printed circuit board. The contact pads on the chip were connected to the printed board via Al-wire bonds. The printed board and the bond wires were embedded in PDMS which is biocompatible (Fig. 1). The surface of the chip was V • -66 mV functionalised with a cell adhesion molecule to promote neurite outgrowth. Dissociated chicken dorsal root ganglia neurons were cultured on such chips for 4-7 days. recording Stimulation glass microelectrode Electrophysiological activity of neuron cells on or close to 100 jis with 130jiA the electrodes was first tested with whole-cell patch clamp. Fig. 2: Action potential recorded intracellularly after The electrode was then connected to a stimulus generator extracellular stimulation and currents between 50 and 350 |J,A were applied during 50-100 |is. The response of the cell was recorded with the intracellular patch electrode. These preliminary results show that the fabricated microstructured electrode array chip can be used for stimulation of cultured neurons. It remains to be shown if extracellular recording is feasible with these chips. Measurement of the gap distance between the neuron cell membrane and the electrode surface with fluorescence interference contrast microscopy revealed that a minimal cell-surface distance of 37 nm can be obtained when the adhesion protein axonin-1 or the peptide RGDC is on the surface [1]. This gap is larger for neurons grown on NgCAM (47 nm) or laminin (91 nm). Whether the tight contact induced by axonin-1 will result also in an improved extracellularly recorded signal has to be shown. Fig. 1: Chip bonded into printed board for stimulation via FUNDING: SPP Biotechnology, PSI. extracellular electrodes. REFERENCE Neurons were cultured on RGDC treated chips. With the applied cell density 5 - 8 of 50 electrodes were covered [1] H. Sorribas, D. Braun, L. Leder, P. Sonderegger and with a neuron. Higher cell densities prevented neurite L. Tiefenauer, J. Neurosci. Met. 104, 133 (2001). outgrowth. Neuron cells for stimulation were chosen according to morphologic aspects (size, shape, membrane 116 NANOSTRUCTRED CHIPS FOR THE ANALYSIS OF INDIVIDUAL PROTEINS L. Tiefenauer, B. Ketterer, B. Haas, H. Schift, L. Heyderman, J. Gobrecht (PSI), O. Dubochet, P. Surbled, T. Hessler (Leister Process Technol.) The aim of this feasibility study is to produce nanochips used for the investigation of individual proteins by light microscopes as well as scanning probe techniques. The regularly arranged openings with diameters from 100 to 400 nm will permit an unhindered mass transport through individual protein assemblies present in biological membranes. Nanoreplication techniques will be developed and transferred to industry. Proteins in biological membranes are crucial for the vital functions of life, especially by regulating intercellular communication and transport of molecules into the cells. Elucidating the structure of individual membrane proteins in their natural environment is therefore an important step towards a better understanding of their functions. Scanning probe microscopy (SPM) techniques are unique tools to image individual proteins. However, membrane proteins are usually mobile (see (1) in Fig. 1) in the membrane and • D D • o o o o o o difficultly to visualize by SPM. Furthermore, mass o o o o o o • • • o o o o o o transport phenomena (2) cannot be investigated, if the o o o o o o inside of the natural membrane is lying flat on a surface (3). • • o o o o o o • investigation- 2 fields Outside I 300 run chip membrane cell membrane protein ••• CH- I? membrane length 0.5 mm 30 nm Inside Fig. 2: Layout of the nanochip. Note that dimensions from mm- to nm-range must be controlled. Fig. 1: Mass transport through membranes (2) requires free access from the inside (3). The processes are developed in close collaboration with the We have therefore designed a nanochip (Fig. 2), which industrial partner. The product-oriented procedure is essentially consists of a 300 nm thick silicon nitride favorized by TopNANO 21 and will facilitate the membrane in which pores in diameters of 100 to 400 nm technology transfer from the research to production places. are regularly arranged. The pores are arranched in investigation fields, which are in the dimensions suitable Production processes for SPM-investigations. 1. Stamp production The challenge of this project is to produce nanosized structures in a sufficient quantity. Lateral dimensions down to 100 nm cannot be generated by conventional photolithography processes. Thus, we have first written the 2. Nanoreplication: stamping nanostructures by e-beam lithography and produced a silicon master stamp (Fig. 3). In a second step the sharp relief is replicated in a resist coated onto a silicon nitride layer using hot embossing. The procedure used for preparing silicon nitride layer on silicon determines the 3. Etching processes mechanical stability of the final thin membrane and must therefore carefully be optimised. The feasibility of the nanoembossing technique has earlier been demonstrated, but further developments are required as it will be done in the synergic nanoreplication project. Resist windows are Fig. 3: Production process: Hot embossing of a resist is opened on the substrate using reactive ion etching. In a followed by dry and wet etching steps. final wet etching process a free standing membrane is obtained. FUNDING: TopNANO21, PSI. 117 ELECTROCHEMISTRY OF STACKED LAYERS OF REDOX LABELED PROTEINS B. Steiger, C. Padeste, A. Grubelnik, L. Tiefenauer (PSI) Streptavidin-ferrocene conjugates were synthesised and utilised as functional building blocks to derivatise electrode surfaces. The analysis of the cyclic voltammograms of the electrodes provided evidence for the biochemical and electrochemical functionality of the conjugates and for the formation of spatially ordered multilayers. The avidin (Av)-biotin technology is a universal molecular anchoring system in the biological sciences. Av-ferrocene IMM1 LSLffLl LSLffLl conjugates immobilised on electrodes can provide a multi- rww^ rww] rwwi rwwi functional base for electrochemical biosensors [1]. The use of the egg white protein avidin, however, is often restricted due to its high isoelectric point and presence of sugar moieties, which may lead to nonspecific interactions. Streptavidin (SAv), a protein isolated from Streptomyces avidinii, is remarkably similar to Av, especially in terms of biotin-binding, but it is only slightly anionic and contains ////////////////// no sugar groups. SAv-ferrocene conjugates (Fc16SAv, Fig. 1) have been synthesised and the SAv-biotin binding was used to form assemblies on gold electrodes. = Ferrocenylated Streptavidin Fig. 3: Schematic picture of the multilayer structure. *,'<> V* This monolayer provided the base for the assembly of successive Fc16SAv layers via biotin-dimers (Fig. 3). To t"t prevent intramolecular bridging, the biotin-dimer was synthesised in situ by first binding 5-(biotinamido) pentyl- amine to the immobilised Fc16SAv layer and then reacting the amino groups with sulfosuccinimidyl-6-(biotinamido) Fig. 1: Polypeptide backbone of the SAv tetramer hexanoate. This procedure was repeated after immo- modified with ferrocenes. Arrows indicate the bilisation of a next Fc16SAv layer. position of the four biotin binding pockets. The tyrosines located at the bottom of the pockets are shown as black stick models. The initial step was the chemisorption of 2-aminoethane- thiol on a gold disk electrode, followed by the reaction of the amino groups with sulfosuccinimidyl-6-(biotin-amido) hexanoate. The next step was the binding of Fc16 SAv to the immobilised biotin groups. Fig. 2 shows that the coverage 400 300 200 1 2 Potential (V vs Ag/AgCI) rFcl6SAv reaches a limiting value of about 3 pmol/cm upon increasing reaction time, indicating the formation of a Fig. 4: Cyclic voltammograms (CV) of a Au electrode in complete monolayer. T was calculated from the area under a pH 7.4 buffer at 0.1 V/s during the assembly of the ferrocene redox peaks (Fig. 4, N=l). Fc16SAv multilayers. CVs were recorded to monitor the growth of the multi- layers. rFcl6SAv as a function of the number of layers gave linear plots with a slope close to 3 pmol/cm2 per layer. An electrode with 4 layers exhibited reasonable stability, the decrease in the CV response being ca. 10% after 7 days. 100 120 140 FUNDING: PSI. REFERENCE Fig. 2: Quantities of Fc16SAv immobilised on a biotin covered Au electrode, T, at various times after the [1] C. Padeste, A. Grubelnik and L. Tiefenauer, electrode was exposed to 200 jig/ml of Fc16SAv. Biosensors and Bioelectronics, 15, 431 (2000). 118 PRODUCTION AND REDOX LABELLING OF ANTIBODIES AGAINST fi-LACTAM ANTIBIOTICS A. Grubelnik, C. Padeste, J.-J. Hefti, L. Tiefenauer (PSI) Antibodies against the fi-lactam antibiotics benzylpenicillin and cloxacillin have been produced and tested in an enzyme immunoassay. In various food samples, we have determined these antibiotics in concentrations below the maximum residue limits of the European community. After purification, the antibodies have been redox labelled with microperoxidase 8 (MP8)for use in an amperometric immunosensor. The (3-lactam antibiotics, in particular the penicillins, are In a second step, these sensitive antibodies have been most frequently used in veterinary medicine. A sensitive, labelled with a redox centre for amperometric detection. As quick and cheap assay would be important for routine redox marker we have chosen microperoxidase 8 (MP8), analysis of samples in food industry as well as for govern- which catalyses the electrochemical reduction of hydrogen mental food control. We are developing an amperometric peroxide. immunosensor that could fulfil these requirements. The immunological recognition is very sensitive and specific and can in principle be applied to any analyte of interest, as long as a suitable antibody is available. The direct amperometric detection has a lot of advantages, but it requires the redox labelling of the antigen or the antibody. The production of sensitive antisera against benzyl- penicillin and cloxacillin, two commonly used antibiotics in veterinary medicine, turned out to be difficult. Since the (3-lactam ring is very reactive, the antibiotic haptens undergo chemical modifications during immunisation and the resulting antisera are insensitive and unspecific. Fig. 2: Structure of the synthesised MP8-DSS conjugate (NHS-activated MP8) used to label the antibodies. In a complex procedure we are able to label the antibodies with up to eight MP8 molecules. This procedure includes a hydrolysed form of the antibiotic protein G purification of the antiserum, labelling of the purified IgG with an activated MP8 derivative (Fig. 2) and subsequent purification of the labelled antibodies on an affinity column. During the labelling step, the binding sites of the antibody have to be blocked with an antigen derivative to protect them against chemical modification. With this method, the antibody molecules retain most of their biological activity and are electrocatalytically active R = as is shown in Fig. 3. cloxacillin benzylpenicillin Fig. 1: Structures of benzylpenicillin and cloxacillin, hydrolysis with penicillinase and synthesis of their BSA conjugates. If the (3-lactam ring is used to conjugate the antibiotic to the carrier protein (BSA), a stable immunogen is formed (Fig. 1). This immunogen is similar to the hydrolysed antibiotic and will induce antibodies against this form. In the enzyme immunoassay, the intact antibiotic can now be Fig 3: Electrocatalytic reduction of H2O, in a flow hydrolysed with penicillinase and thus be detected by the injection system using gold electrodes with antibody. We could demonstrate the sensitivity of this covalently immobilised MP8, IgG-MP8 and IgG. method by analysing milk and honey samples spiked with benzylpenicillin or cloxacillin in concentrations as low as FUNDING: PSI. 0.1 ng/ml. 119 Laboratory forRadio- and Environmental Chemistry Foreword Heavy Elements Surface Chemistry Analytical Chemistry Cement Chemistry Project Radwaste 120 LABORATORY FOR RADIO- AND ENVIRONMENTAL CHEMISTRY H.W. Gaggeler (Univ. Bern & PSI) In the field of heavy element research much effort was In addition, the SINQ-gas-jet device was successfully used devoted to the development of a novel system, IVO (In-situ for production of labelled HOBr and allowed to investigate Volatilization and On-line detection) coupled to a "4-TI the kinetics of the interaction of this molecule with NaBr thermochromatography" detector operated at cryo- aerosol particles. This laboratory study should yield temperatures. Such a technique is mandatory for the important information on heterogeneous processes in the planned new heavy element adventures such as attempts to arctic atmosphere. study, for the first time, the chemical properties of hassium The planning and construction phase of the project (element 108) - in form of its very volatile tetroxide - and PROTRAC came to a positive end. This gives hope that in of element 112 - presumably a very volatile metal. The the first half of the coming year this new device will start scientific steering committee of the Gesellschaft fur operation. Schwerionenforschung approved during its summer meeting a proposal to investigate element 112 produced in The cement chemistry group fulfils R&D work for nuclear the bombardment of a 244Pu target with 48Ca particles. power plants and is mostly financed by external sources. The high competence of this group was recognized by Our environmental research efforts included the partici- external companies resulting in several new projects. pation in several field campaigns. In July, an exploratoring Research results gained in the field of waste disposal led to drilling was performed on a glacier close to the Belukha a patent application. summit in the Altai region. This campaign is the result of a joint project between the Siberian branch of the Russian The group Radwaste Analytics continued the radiochemical Academy of Sciences in Barnaul and PSI. Based on the iso- analyses of irradiated accelerator parts, e.g. targets, beam topic and chemical interpretation of the drilled shallow-firn dump samples and shielding materials. Additionally, first core we decided to continue this project with a deep drilling samples of radioactive SINQ targets (zircalloy and lead) next year. were prepared for analysis. The group cooperates in the EU-Project "High and Intermediate Energy Nuclear Data Besides Siberia, several people from our unit travelled to for Accelerator-driven Systems". different places in South America, first, to Patagonia (Chile) - unfortunately the drilling campaign was not successful due to poor weather conditions - second, to the Cerro Tapado and Cerro del Plomo (Chile) and, third, to the Chimborazo (Ecuador) in collaboration with French colleagues. Obviously, next year much effort will be devoted to laboratory work in order to analyze all these firn and ice samples. Research in the field of surface chemistry with radioactive species celebrated several "breakthroughs". It was possible to produce 13N-labelled peroxyacetyInitiate (PAN) at extremely low carrier concentrations. With this tracer, thermochromatography experiments were conducted that proved to be instrumental in understanding the interaction of PAN with ice crystals in the upper troposphere and lower stratosphere. 121 FLUORIDE COMPLEXATION OF RUTHERFORDIUM (Rf, ELEMENT 104) E. Strub, J.V. Kratz, A. Kronenberg, A. Nahler, P. Thorle (Universitat Mainz), W. Briichle, E. Jager, Z. Li, M. Schadel, B. Schausten, E. Schimpf (GSI Darmstadt),D. Jost, A. Turler (PSI), H.W. Gaggeler (Univ. Bern & PSI), J.P. Glatz (ITU Karlsruhe) The sorption studies of Rf and on-line produced Hf on Anionic Ion Exchangers have been continued by systematically varying the HNOj and the HF concentration. Rf shows typical group 4 behavior but its sorption is influenced by the presence of counter ions like NOj and/or HF2. 261 The distribution coefficient (IQ) of Rf on ion exchange [HNO3] [HF] logKd(Hf) log Kd (Rf) resins at various HNO3/HF concentrations had been studied 0.1 0.01 2.1 0.8 [1]. Rf was eluted at higher HF concentrations from CIX 0.1 0.03 2.1 0.9 than Zr and Hf and rather resembled Th. Up to 1 M HF, Rf 0.1 0.05 2.0 0.8 0.1 0.5 2.1 0.9 was not retained on the AIX also resembling its pseudo- 0.1 1 2.2 0.7 homolog Th. 0.03 0.5 2.2 1.7 Th is known to form no anionic fluoride complexes, while 0.01 0.01 2.1 1.0 Zr and Hf are forming complexes of the type [MF§]2" in HF 0.01 0.05 2.3 1.6 solutions and therefore can be resorbed on AIX resins. 0.01 0.5 2.5 1.6 0.003 0.5 2.7 1.7 We have continued these studiesNow of Rf and on-line 0 0.01 2.5 2.7 produced Hf by systemetically varying both the HNO3 and 0 0.1 2.7 2.4 the HF concentration. If Rf is resembling Th, there should 0 0.5 2.8 1.8 exist no concentration range in which Rf is adsorbed on the It is obvious that the behavior of Rf and Hf in the examined AIX. system are remarkably different. While the Kd values of Rf 261Rf was produced in the ^Cm^O^n) reaction at the PSI 2 248 are varying strongly with both HF and HNO3 concentration, Philips Cyclotron. A 730 |Jg/cm Cm target was bombar- the dependence of the Hf IQ values on the acid concentra- 18 3+ ded with a 0.5 |xApart O beam. The target contained 10% tions is rather weak. Gd thus producing simultaneously short-lived Hf isotopes. Strong adsorption of both elements onto AIX can only be Rf and Hf were transported by a He(KCl) gas jet and col- observed in pure HF solutions with concentrations [HF] > lected for 90 s by impaction on a slider in the Automatic 0.01 M. This indicates the presence of anionic complexes Rapid Chemistry Apparatus ARCA II. The residue was under this condition which is in agreement with [3]. dissolved in 200 \A 0.1 M HNO3/x M HF (x variable) and fed onto the AIX. The effluent was evaporated to dryness as On the other hand, the sorption of the complexes on AIX sample 1. In order to elute remaining Rf from the column, a seems to be influenced by the presence of other anions second fraction (200 |ji) was collected which is known to acting as counter ions on the exchanger resin (NO3~ and/or elute group 4 elements from the column (2 M HC1/0.01 M HF2", see [2]). HF). This fraction was prepared as sample 2. 78-s 261Rf was Thus, Rf shows the typical behavior of group 4 (formation detected by a-spectroscopy. The counting time was 12 min. of anionic fluoride complexes), but the interaction of these Every 8th pair of samples was monitored by additional y- complexes with different counter ions is enhanced with spectroscopy to determine the distribution of Hf. From the respect to Zr and Hf. ratio of the counting rates, the Kd values were calculated. REFERENCES The results are shown in in the table and are also plotted in [1] E. Strub et al., Radiochimica Acta 88, 265 (2000). the 3D graphs below (some values in the plot are interpo- [2] E. Strub, Dissertation Universitat Mainz (2000). lated). [3] Szeglowski et al., Radiochim. Acta 51, 71 (1990). 2,75 2,S 2,25 • 2,5-2,75 • 2,25-2,5 ~f logKd • 2-2,25 1,f? 11,75-2 0,'ri • 1,5-1,75 11,25-1,5 U.U1 • 1-1,25 '!•:'& • 0,75-1 (=.0: P.CS • 0,5-0,75 [HF] 1,1 DHNQ,] 0-5 0.1 0.1 Fig. 1: Sorption on Hf in HNO3/HF solutions on an AIX Fig. 2: Sorption on Rf in HNO3/HF solutions on an AIX resin (Aminex A27 or Riedel de Haen). resin (Aminex A27 or Riedel de Haen). 122 THERMOCHEMICAL PREDICTIONS OF THE CHEMICAL PROPERTIES OF BOHRIUM (Bh, ELEMENT 107) R. Eichler (Univ. Bern & PSI) Extrapolative and empirical correlation methods have been used to predict thermochemical properties of gaseous and solid Bh compounds, which can be formed with Bh in reactive gas mixtures ofO2(g)/H2O(g) and O2(g)/HCl(g). Thermochemical predictions of the behaviour of Bh in gas strumental in selecting the experimental conditions in gas chromatographic studies with reactive gas mixtures of chemical investigations of BhO3Cl [9]. The predictions O2(g)/H2O(g) and O2(g)/HCl(g) are essential for the prepa- revealed BhO3Cl to be thermodynamically more stable and ration and the interpretation of experimental studies of Bh. less volatile than TcO3Cl and ReO3Cl [10]. The presented predictions of the volatility of Bh com- OP (M=O) • pounds are based on the assumption that Bh is a typical 0.6 0.8 1.0 2 2.0 2.2 2.4 member of group 7 of the periodic table and thus homo- 00 - / logous to Tc and Re. The results obtained in gas ' Bh adsorption chromatographic experiments with Tc and Re [1-3] are used to estimate unknown enthalpies of formation of oxide, oxyhydroxide, and oxychloride compounds of Tc 80 - and Re in the solid or gaseous state. Analogous to / predictions made for seaborgium (Sg, element 106) / -5 Re compounds [4] the present approach employs an empirical Re MO3C / 1 '/ correlation between the formation data and the known 60 - / sublimation enthalpies of metallic Tc and Re [5] (e.g. Fig. 1). Subsequent extrapolations of these correlations VTC using predicted sublimation enthalpies of metallic Bh [6,7] yield the formation enthalpies of Bh compounds in solid H[D] • and gaseous states (Table 1). Fig. 2: Empirical correlation of AHsuW of oxychlorides of group 7 elements with calculated dipole moments (|i) and molecular overlap populations (OP) of the MO a molecules MO3C1 (M=Tc,Re) [8]. Extrapolation of AHsubi (BhO3Cl) using |i(BhO3Cl) and OP(BhO3Cl) from [8]. Table 1: Predicted thermochemical formation data of dif- ———-_ ferent Bh compounds in their solid and their gaseous state. Compound AfH°(s) AfH°(g) AHsuW AHads —•- MO ,C 1 [kJ/mol] [kJ/mol] [kJ/mol] [kJ/mol] —- HM°4 BhO2 -444 48 492 -341±21 Tc Bh* Re Bh Bh*O2 -436 33 469 -325±20 600 700 800 900 BhO3 -671 -385 358 -250±18 A^M,,,) [kJ/mol] Bh*O3 -576 -339 237 -168+15 0 HBhO4 -837 -710 127 -93+11 Fig. 1: Empirical correlation of AfH (g) of different compounds of group 7 elements with the standard HBh*O4 -738 -628 110 -81+11 formation enthalpies of the gaseous state of the BhO3Cl -650 -561 89 -74±12 Bh*O Cl -588 -528 60 -58±12 metal (AfH°(M(g))). Extrapolations for AfH°(s) of 3 0 Bh compounds were carried out using AfH (Bh(g)) BhO3Cl (rel) 75...100 [6]andAfH°(Bh*(g))[7]. REFERENCES Finally, the standard adsorption enthalpies of single mole- [1] R. Eichler et al., Radiochim. Acta 87,151-159(1999). cules of Bh compounds on quartz surfaces were deduced [2] T.Hafeli, Diploma thesis, University of Bern (1999). from the macroscopic standard sublimation enthalpies em- [3] R. Eichler et al., Radiochim. Acta 86, 87-93 (2000). ploying the well established correlations between the sub- [4] B. Eichler et al., J.Phys.Chem. A103 (46), 9296 (1999). limation enthalpies of different oxide and oxychloride [5] O. Knacke et al., Thermochemical Properties of Inor- compounds and their standard adsorption enthalpies on ganic Substances, 2nd ed., Springer-Verlag, Berlin quartz surfaces [3,4]. (1991). [6] B. Eichler, Kernenergie 19 (10), 307 (1976). In addition, the standard sublimation enthalpy of BhO3Cl [7] G.V. Ionova et al., Sov. Radiochem 37, 282 (1995). (Table 1, BhO3Cl (rel)) is also predicted by correlating the [8] V. Pershina et al., J. Chem. Phys. A 113,1441 (2000). calculated relativistic molecular properties of MO3C1 (M=Tc, Re, and Bh) [8] with the sublimation enthalpies of [9] R. Eichler et al., Nature 407, 63(2000). the compounds (Fig. 2). [10] For more details see: wwwl.psi.ch/www_lch_hn/Bh_ The estimated adsorption enthalpy of Bh oxychloride on chemistry_prediction.pdf. quartz surface, AHads(BhO3Ci)=-74+12 kJ/mol, was in- 123 STABILITY OF GROUP 8 TETROXIDES MeO4 (Me=Ru, Os, Hs) AND THEIR ADSORPTION BEHAVIOR ON QUARTZ Ch.E. Dullmann, R. Eichler, A. Tiirler (Univ. Bern & PSI), B. Eichler (PSI) In view of a first gas-phase chemistry experiment with hassium (Hs, Z=108) the high volatility of the tetroxides of group 8 elements ruthenium (Ru) and osmium (Os) indicates that an isolation ofHs as volatile HsO4 is currently the most promising approach. The atomic formation enthalpies of oxides of group 8 elements Ru and Os were calculated on the basis of known thermodynamical properties and extrapolations for Hs and its oxides were performed. The trends of stability and the enthalpy of sublimation were evaluated from these extrapolations and the adsorption enthalpies evaluated using an empirical correlation which holds for several oxides. 2500 ; 1 INTRODUCTION MeO4(8) Well-known volatile compounds of group 8 elements | 2000 === ruthenium (Ru) and osmium (Os) are their tetroxides, RUO4 _ •— MeO3(g) 9 MeO2 (S) and OSO4, respectively. Due to the coordinative saturation 1 1500 B—" j = of the metal ions in symmetrical molecular geometries such o • MeO2(g) as the tetrahedral RUO4 and OSO4, the molecule - surface !. 1000 interaction of these compounds is dominated by % i : • MeO (a) *? 500 ; • physisorptive forces. The high volatility of RuO4 and OsO4 is related to this effect and makes these molecules suitable Ru OsHsl Hsll for gaschromatography experiments. The transactinide 0 ^ , , , element hassium (Hs, Z=108) is expected to be 600 650 700 750 800 850 9C homologuous to Ru and Os and should therefore also form AH°298(M(g)) [kJ/mol] a very volatile tetroxide, HsO . It is important to have a 4 Fig. 1: Atomic formation enthalpies of the gaseous and notion about the volatility of this compound in order to plan solid oxides of group 8 elements as a function of an experimental set-up for the chemical separation and the standard enthalpy of the gaseous metals. The investigation of Hs as tetroxide. We have therefore straight lines are linear regressions. calculated the sublimation enthalpy AHsuW on the basis of an extrapolation along the memebers of group 8 and Values of (52±8) kJ/mol (RuO4 [3]) and 56.6 kJ/mol (OsO4 evaluated the adsorption enthalpy AHads on quartz surface. [4]) are taken from the literature. 57 kJ/mol are calculated for Hs I and 58 kJ/mol for Hs II. Comparison between the 2 CALCULATIONS / RESULTS standard sublimation enthalpy of macroscopic amounts and As reference for the extrapolation, the standard enthalpies the adsorption enthalpy of carrier-free oxides showed that there exists a good linear correlation between these two of the gaseous monoatomic elements AH°298(Me(g)) were used. Since an estimation of the error of this value is quantities. An updated correlation taking into account also difficult, a realistic range limited by two values for more recent experiments [5] resulted in AH°(Hs(g)), denoted by Hs I (790 kJ/mol [1]) and Hs II (842 -AHads=(6.271±7.780)+(0.680±0.028)-AHsubl kJ/mol [2]) was chosen. Then, the atomic formation Adorption enthalpies of (-41±9) kJ/mol for RuO4, (-45±9) enthalpies of the gaseous and solid oxides MeOx(&S) were kJ/mol for OsO4, (-45±9) kJ/mol for Hs I and (46±9) kJ/mol determined with for Hs II, respectively, are calculated with this correlation. 0 0 0 AH*(MeOx(g))=AH 298(MeOx(g))-AH 298(Me(g))-x-AH 298(O(g)) Comparison of these values clearly shows that the 0 adsorption behavior of HsO4 on quartz is expected to be the AH*(MeOx(s))=AH 298(MeOx(s))-AH°298(Me(g))-x-AH°298(O(g)) same as the one of OsO4 and therefore HsO4 is considered and are shown in Fig. 1 as a function of the standard to be suitable for a first ever chemical investigation of Hs. enthalpy of the gaseous metals. In a correlation of AH*(MeOX(gS)) against AH°298(Me(g)) for elements of a given REFERENCES group, the stability of the compound MeOx increases with increasing atomic number if the slope of the correlation line [1] B. Eichler, Kernenergie 19 (10), 307 (1976). is greater than 1. That is because the AH° (Me ) values 298 (g) [2] B. Fricke, Structure and Bonding, Springer-Verlag, are already included in the quantities of AH (MeO ( )). The x gS Berlin, Heidelberg, New York, 1975, Vol. 21, p. 92. slope of the linear regression of the values of the gaseous tetroxides is 2.06, indicating increasing stability from RuO4 [3] J.A. Rard, Chem. Rev. 85, 1 (1985). to OsO4. Consequently, HsO4 is expected to be thermodynamically even more stable. [4] H. Oppermann et al., Z.Naturforsch. 53b, 1352(1998). In a next step, the standard sublimation enthalpies were [5] R. Eichler et al., Radiochim. Acta 87, 151 (1999). calculated from the atomic formation enthalpies according to AH°subl=AH*(MeOx(g))-AH*(MeOx(s)). 124 EVALUATION OF THE ENTHALPY OF ADSORPTION OF OsO4 ON QUARTZ Ch.E. Dullmann, R. Eichler, H.W. Gdggeler, A. Tttrler (Univ. Bern & PSI), B. Eichler, D.T. Jost, D. Piguet (PSI) Short-lived Os-isotopes were produced in heavy ion reactions at the PHILIPS Cyclotron at PSI. Highly volatile Os- tetroxide was synthesized directly in the recoil chamber and transported to a quartz chromatography column kept at an isothermal but variable temperature. By measuring the yield at different temperatures, the retention time of the compund in the column was evaluated. Thus, an enthalpy of adsorption of AHJOsO4)=(-38.0±1.5) kJ/mol was determined using two different approaches. 1 INTRODUCTION Osmium (Os) is a member of group 8 of the periodic table of the elements and thus serves as a model for the transactinide element hassium (Hs, Z=108) which is expected to be also a member of group 8 and should therefore exhibit similar chemical properties. The highly o9 volatile tetroxide of Os (OsO4) is one of the best known compounds of this element and is extensively used as an oxidizing agent in organic chemistry. Due to its high 0) volatility (boiling point: 135 °C) it is suitable for adsorption Experimental Data - Monte-Carlo Simulation AHa(te=-38.0 kJ/mol gaschromatographic investigations. We have determined -•±1.5 kJ/mol the enthalpy of adsorption of OSO4 on quartz surface using short-lived carrier-free Os-isotopes. -100 -80 -60 -40 -20 0 Isothermal temperature [°C] 2 EXPERIMENTAL Short-lived Os isotopes were produced at the PHILIPS Cyclotron in the reaction 162Er(18O, 6-7n)173174Os at a beam energy of 116 MeV in the middle of the target and beam intensities of 100 particle-nA. The apparatus for In-situ Fig. 1: Relative yield vs. isothermal temperature curve for Volatilization and On-line detection (IVO) which is 173OsO4 (T =22.4 s). described in detail elsewhere [1,2] was used to synthesize OsO4 in-situ in the recoil chamber and to separate it from interfering by-products which were produced in transfer 3 RESULTS reactions or in reactions of the beam with impurities in the Fig. 1 shows the relative yield vs. isothermal temperature target, backing or target assembly. As carrier gas, 500 173 curve for Os (Ti/2=22.4 s). The solid line is the result of a ml/min helium and 50 ml/min oxygen were used. OSO4 was Monte-Carlo simulation of the experiment [5] assuming an transported from IVO via a 5 m long PFA teflon capillary enthalpy of adsorption AHads of -38.0 kJ/mol. The dashed (i.d.=2 mm) to a quartz chromatography column lines indicate the la-error range of ±1.5 kJ/mol. Analysis of (length=1.5 m, i.d.=2 mm) kept at a variable isothermal the experimental data using the model of mobile adsorption temperature. After passing through this column, the [6] yielded AH (OsO )=(-37±l) kJ/mol. molecules were transported through a 2 m long PFA teflon a 4 capillary (i.d. 2 mm) to the cluster chamber. For further transport, an aerosol was produced from molten REFERENCES lead (Pb) in argon (500 ml/min), since earlier experiments [1] Ch.E. Dullmann et al., Nucl. Instrum. Meth. A, in at FLNR in Dubna [3] and at PSI [1] have shown that a lead press. surface strongly adsorbs OsO4, presumably via its reducing surface to form less volatile Os compounds. Optimum [2] Ch.E. Dullmann et al., Ann. Rep. Univ.Bern & PSI transport yields of OsO4 were found if the molten Pb was 1999, p. 13 kept at 820 °C and then passed through a container of 3 1 [3] B. L. Zhuikov, et al., Report JINR Dubna, USSR, volume in order to allow the formation of agglomerates of P7-86-322 (1986). appropriate size. The aerosol was fed into the cluster chamber and the adsorbed Os compounds were transported [4] K. Siimmerer et al., to ROMA [4] for final counting. The isothermal GSI Ann. Rep. 1983/84-1, 246 (1984). temperature of the chromatography (IC) column was varied between ambient temperature and -80 °C to evaluate the [5] I. Zvara, Radiochim. Acta 38, 95 (1985). retention time of OsO on quartz. 4 [6] B. Eichler et al., Radiochim. Acta 30, 233 (1982). 125 THE INTERACTION OF ELEMENT 112 WITH METAL SURFACES B. Eichler (PSI) The enthalpies of solution, of net adsorption, and of segregation have been calculated for the interaction of element 112 with selected metal surfaces. The effect of these thermochemical values are discussed. INTRODUCTION 350- ± The net adsorption enthalpy and the enthalpy of segregation 300- A A Fe V w are thermochemical values, which characterize the 250- A o o °n W D w Nb Mo behaviour of a metal element at the surface of another 200- o Re D A A A metal. The partial molar net adsorption enthalpy at zero 150- S D surface coverage is a measure for the interaction of single Cu f D D 100- N1T Ir Ta atoms of metal A with the surface of metal B. The sum of 1 J 50- Cd the partial molar net adsorption enthalpy and the subli- 1 0 - i Pb ~~~Ag*~ f~•~ mation enthalpy of A yields the enthalpy of adsorption of Pd -50- the gaseous metal A on B. The probabilities, both of the 1000 1500 2000 2500 3000 3500 4000 surface enrichment in the case of implantation of A into the T (K) a) bulk phase of B and vice versa of the penetration of A into the bulk phase of B from the surface are characterized by 20- Cd D n „ 0- the enthalpy of segregation. A surface enrichment is Ag "° Pb Fe -20- o possible if the enthalpy of segregation is large and negative S Mo (<-50 kJ/mol). A dissolution of A in B can be assumed at -40- I -L - D small absolute and at positive values of the segregation -60- -: enthalpy in the case of no diffusion hindrance. The enthalpy -80- Ir a a -100- of solution and the enthalpy of segregation are both of Ta exceptional importance for the selection of adsorbens -120- Ti * a materials in order to prepare thin and stable samples, which -140- are required for high resolution a- and SF- decay 500 1000 1500 2000 2500 3000 3500 4000 measurements. Tm(K) b) CALCULATION 0- Cd, Ag The partial molar enthalpy of solution, the net adsorption -50- Au Pd enthalpy and the enthalpy of segregation have been -100- TiPt calculated using [1] and applying extrapolated values of -150- | Ni «S electron density at the Wigner-Seitz cell boundaries, of the Ir -200- Cu S Nb electronegativity parameter [2]. The extrapolations [2] 7Q D B Ta -250- ** & JMO D 1A* A<^ yielded six consistent data sets for the calculations. The R 6 results for the corresponding enthalpies of element 112 as a -300- Fe I A 0 W function of melting points of the adsorbens metals B are -350- * x s shown in figure 1 a-c. -400- -450- DISCUSSION 500 1000 1500 2000 2500 3000 3500 4000 The behaviour of element 112 at the selected metal surfaces T (K) C) is determined by contrary acting effects. Therefore, a continuous linear function can not be expected. Two Fig. 1: Enthalpies of solution (a), net adsorption (b) and observed dependencies are remarkable: For high melting segregation (c) as function of Tm of adsorbens metals B a low solubility, a high surface enrichment, and metals. thus, a high adsorption, and for low melting metals B a high solubility, a low surface enrichment and a low adsorption REFERENCES interaction can be expected. This sequence is a well known [1] B. Eichler, H. Rossbach: empirical rule for adsorption phenomena on metal surfaces. Radiochim. Acta 33,12 (1983). The influence of the enthalpy of solution is partially overruling this sequence. This influence is for example [2] B. Eichler, Metallchemie der Transaktinoide, visible at the Pd surface. It is well known that Pd forms PSI Bericht Nr. 00-09 (2000). very stable compounds with s- and p- metals. For element 112 in contrast to other d-metals small enthalpy of solution in Pd has been calculated. A limited solubility of element 112 in the solid phase of Pd can therefore be expected. The calculated data can be used for the selection of optimal materials in experimental studies of the chemical behaviour of element 112. 126 A FIRST ATTEMPT TO CHEMICALLY IDENTIFY ELEMENT 112 A.B. Yakushev, G.V. Buklanov, M.L. Chelnokov, V.l. Chepigin, S.N. Dmitriev, V.A. Gorshkov, V.Ya. Lebedev, O.N. Malyshev, Yu.Ts. Oganessian, A.G. Popeko, E.A. Sokol, S.N. Timokhin, V.M. Vasko, A.V. Yeremin, I. Zvara (FLNR Dubna), S. Hübener (FZ Rossendorf), A. Türler (PSI & Univ. Bern) A first experiment to chemically identify a previously discovered long-lived superheavy isotope of element 112 was conducted at the U-400 cyclotron of Flerov Laboratory of Nuclear Reactions, Dubna. Eventhough the experiment reached a sensitivity of a few picobarns, no decay that could be attributed to an isotope of elment 112 was observed. 1 INTRODUCTION A first attempt to chemically identify El 12 was performed at the Dubna U-400 cyclotron in January 2000. A 2-mg/cm The relatively long half-lives of isotopes of super-heavy 238 48 U3O8 target containing 100 ug of natural Nd on a 2 ¡^m elements obtained in Ca induced reactions, allow for the HAV AR foil (which served also as vacuum window) was first time to study their chemical properties. The chemical 17 48 irradiated with 6.85xl0 Ca ions (Elab=230-244 MeV). identification of the proton number is very important, since Recoils were thermalized in pure He at atmospheric none of the members of the observed decay chains are 283 pressure and transported through a 25 m long PTFE known. The nuclide 112 (Ti/2 = 3 min) can be produced 238 48 capillary to the detection apparatus. The transport time was in the reaction U( Ca, 3n) with a cross section of about 5 25 s at a gas flow rate of 500 ml/min. Eight detection pb [1]. Element 112 (El 12) should belong to group 12 of chambers were connected in series. Detectors 1 through 6 the periodic table like Zn, Cd, and Hg and exhibit some were coated with Au, the last two chambers contained Pd unique chemical properties. Some theoretical works predict, coated detectors. The chambers were positioned inside an that El 12 is very volatile and chemically inert and assemblage of 84 He-filled detectors (in a moderator) to resembles thus more Rn than Hg [2]. Two different register neutrons form spontaneous fission decays. The approaches are thus necessary. In a first step we developed detection efficiency for a single neutron was about 50%. a separation and detection method for Hg, expecting El 12 Decay events in the fission fragment energy range triggered to behave similarly and thus to strongly adsorb on some the measurement of prompt neutrons, which lasted 128 ¡O.S. metal surfaces due to intermetailic bonds. Neutrons were detected in this period with a time resolution of 1 \\s. The a-decay count rate in a single detector 2 EXPERIMENTAL 1 (Ea > 6 MeV) was 4.5 min" . All peaks in the spectra were 211 220 Tests with both long- and short-lived Hg isotopes showed, identified and attributed to the decay of ' Rn and its that an almost quantitative transport through a 30 m long descendants. teflon capillary is possible at room temperature. Next, the chemisorption of Hg on various metal surfaces in pure He 3 RESULTS AND DISCUSSION was studied at room temperature or slightly below it, in order to deposit El 12 directly on metal coated Si detector In our experiment no SF events were observed. If the surfaces. Adsorption of Hg was quantitative on Au, Pt or efficiencies measured for Hg held for El 12, we could have Pd. The rate of chemisorption was highest on Au. Only 1 expected detection of some 3 events based on a 5 pb cm2 of Au or Pd surface sufficed for quantitative production cross section. This experiment undoubtedly chemisorption of Hg from He at room temperature and flow showed the possibility of chemical identification of nuclei rates up to 1 1/min. The adsorption yield of Hg on Au at - produced with picobarn cross sections. The experiment 30°C decreased to 50%. For the experiments with short- does not give an unambiguous answer about physical and lived Hg isotopes at the U-400 cyclotron a flow-through chemical properties of element 112. In a next step, we plan detection chamber was constructed with a pair of square to increase the beam dose by at least a factor of two and to (2x2 cm) PIPS (passivated ion-implanted planar silicon) upgrade our detector system to measure a-decays and SF detectors, which were coated with about 40 |J,g/cm of Au events in the gas exiting the chambers with the PIPS or Pd. The distance between the detectors was 1 mm, which detectors using a special ionization chamber. resulted in a detection efficiency of 80% at a resolution of about 100 keV for 6 MeV a-particles. The residence time REFERENCES of the gas in each detector chamber was only a fraction of a [1] Yu.Ts. Oganessian et al., EPJ A5, 63 (1999). second. Several chambers were connected in series with [2] K. S. Pitzer, Chem. Phys. 63, 1032 (1975). short PTFE capillaries. 127 ON-LINE THERMOCHROMATOGRAPHIC STUDIES OF RADON AS A PRESUMABLE PSEUDOHOMOLOGUE OF THE ELEMENTS 112 AND 114 R. Eichler (Univ. Bern & PSI), B. Eichler (PSI) Thermochromatographic low temperature separations of 220Rn have been carried out using various metals, polar, and nonpolar materials as stationary phase. The expected dependence of the adsorption interaction of radon on the different polarizabilities of the stationary phase materials was approved experimentally. 1 INTRODUCTION temperature gradient was determined measuring its decay From theoretical relativistic calculations of atomic product 2l2Bi after each experiment of 1 h duration using a properties of the heaviest elements noble gas behaviour of Geiger-Muller counter and a 1 cm lead collimator. the elements 112, 114, and 118 can be expected [1]. 3 RESULTS AND DISCUSSION According to [2] for the fictitious noble gas elements 112 220 and 114 a high volatility and a less adsorption interaction The thermochromatogram of Rn on Ni is shown in Figure with metal surfaces can be expected. The scientific goal of 2. Typically, in all metal columns two deposition peaks or a experimental approvals of either metallic or non-metallic pronounced tailing to higher deposition temperatures have properties of elements 112 and 114 will be the confirmation been observed. This effect can be explained by an of established rules manifested in the periodic table or the adsorption of Rn first on a clean metal surface, which led to observation of deviations of chemical properties of a deposition at higher temperatures (Tl), and after some elements 112 and 114 due to relativistic effects in their time the metal surface is covered by ice. The Rn adsorption electron orbitals. In order to approve the model described in on ice is weak (-20 kJ/mol) [3] and led in our experiments [2], we studied in this work the adsorption of Rn as an to a deposition at lower temperatures (T2). The adsorption element with a nearly homologous behaviour compared to enthalpies AHaexp(l,2) have been calculated from the the possible noble gas elements 112 and 114 on various measured deposition temperatures using the mobile polar, nonpolar materials, and metals as stationary phase in adsorption model [4]. The estimated adsorption enthalpies on-line thermochromatography experiments. from T2 agree very well with data obtained in [3]. The AHam(xl calculated with the model from [2] seem to agree 2 EXPERIMENTAL well with the results of our experiments. V~7 II 40 50 Fig. 1: On-line low temperature thermochromatography Fig. 2: Thermochromatogram of 220Rn on Ni. setup with: 1 50 ml/min He carrier gas flow; 2 oven with Table 1: Deposition temperatures and deduced adsorption 232 U3O8 at 400°C; 3 drying unit (SICAPENT®); 4 enthalpies in (kJ/mol) together with adsorption enthalpies getter oven at 1000°C with Ta metal; 5 column; 6 AHam(xl calculated using the model in [2]. temperature gradient setup from 50 - -193°C with Surface T1°C AHa^l T2°C AHa,Tr2 AHa_ Pd -110 -37 -163 -25 33.5 Heating the source to 400°C supports the emanation of 220 232 Pt -149 -29 -186 -20 34.9 Rn from the U3O8 source. The carrier gas He Cu -73 -46 -181 -21 32.1 (50 ml/min) was loaded with 220Rn. Subsequently, in order Ag -147 -29 -191 -19 31.7 to remove traces of O and H O, the gas mixture was passed 2 2 Au -115 -36 -188 -19 35.4 through a gas drying unit, filled with Sicapent®, and through Ni -130 -33 -176 -23 31.9 a Ta metal getter (at 1000°C). The getter was placed directly into the thermochromatography column. The W -157 -27 -181 -21 32.7 materials used as stationary phase in the columns are listed SiO, -181 -21 A1A -172 -24 in table 1. The metal columns have been prepared using 81 metal foils, which were applied into a quartz tube Teflon -183 -20 (0, = 3 mm) and covered the entire inner surface of the REFERENCES quartz column. The surfaces of these "metal" columns were [1] K.S. Pitzer, J. Chem. Phys. 63, 1032 (1975). reduced and cleaned in a separate oven at 800°C in a [2] B. Eichler et al., this Annual Report. flowing gas mixture of He/H2 (Vol%-94/6). The possible H2 coverage was removed at the same temperature of 800°C in [3] B. Eichler et al., J. Phys. Chem. A 104, 3126 (2000). a gas flow of Ar. The deposition position of 220Rn along the [4] B. Eichler, I.Zvara, Radiochimica Acta 30, 233 (1982). 128 VAN DER WAALS INTERACTION OF ATOMS OF ELEMENTS 112,114, AND 118 WITH SOLID SURFACES B. Eichler (PSI), R. Eichler, H.W. Gaggeler (Univ. Bern & PSI) The interaction of the "fictitious" noble gases 112, 114, and 118 with metal surfaces has been estimated as a function of polarizability, ionization energy, and the distance to the surface. METHOD adsorption enthalpies of elements 112, 114, and 118 on For gaseous atoms and nonpolar symmetrical molecules the selected metal surfaces can be calculated. The results are Van der Waals interaction E with a solid surface nearly shown in Figure 2. equals the adsorption enthalpy. The Van der Waals interac- tion can be calculated as a function of the polarizability a 50-. (A3), of the distance between the atom or molecule and the • • 45- 118 m surface r (A), and of the characteristic energies of the atoms • • • or molecules EA and the surface material EB using eq. 1 [1] : 40- o 114 D • E= oc g EA EB (8r (EA+EB)) (1) 35- a • o o "—' • a O • For metals is g = 1. We used for EAB the average dipole o o o 30- o transition energy and substituted EAB with eq. 2 [2]: -A H 112 25- EAB = 1.57* IPAB (IPAB ionization potentials [1,7]) (2) With the predicted extremely high promotion energies for element 118 and also for elements 112 and 114 a noble gas Cu Pd Pt Au like behaviour can be expected [3]. Therefore, their interac- tion with solid surfaces should be exclusively of Van der Fig. 2: Adsorption enthalpies of elements 112, 114 and Waals nature. The correlation of the polarizabilities [1,4,5] 118 on different metal surfaces. with the radii of largest orbital which can be found for the lighter noble gases from He to Rn (eq. 3) is supposed to be DISCUSSION valid for these elements too: Evidently, these results are approximated values. Neverthe- 3 a = f(rmax ) (3) less they give a real picture of a possible adsorption be- As rmai we used the the maximum radial probability density haviour of the "fictitious" noble gas elements 112, 114, and of the electrons in the outer orbitals in the ground state 118 is given. However, only the experiment can prove if configuration of elements 112, 114, and 118, obtained from these elements are supposed to form colourless non con- relativistic calculations [6]. ducting solids in a fictitious condensed phase as would be This correlation is shown in Figure 1 for the noble gases expected for noble gas-like elements. For elements 112 and and element 112, 114, and 118. 114 this would be a distinct break of the rules manifested in the periodic table. Experimentally this break could be ob- served in gas adsorption chromatographic investigations with metallic stationary phases. If this elements do not form intermetallic bonds, a noble gas behaviuor can be assumed. REFERENCES [1] Handbook of Chemistry and Physics, ed. 79, CRC Press (1998). [2] L. Pauling, Sience 134, 3471 (1961). [3] K.S. Pitzer, J. Chem. Phys. 63, 1032 (1975). 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 [4] C.K. Jorgensen in Structure and Bonding, Springer Verlag, Berlin 1966, 243. [5] B. Eichler, H. P. Zimmermann, H. W. Gaggeler, Fig. 1: Correlation of polarizabilities with rmax for noble J. Phys. Chem. A 104, 3126 (2000). [6] J. P. Desclaux, gases, and extrapolation of rmax for elements 112, 114, and 118. Atomic and Nuclear Data Tables 12, 311 (1973). [7] O. L. Keller, G. T. Seaborg, The analysis of the distances of the lighter noble gases to Ann. Rev. Nucl. Sci. 27, 139 (1977). different solid surfaces, calculated with eq. 1 on the basis of [8] A. R. Miedema, B. E. Nieuwenhuys, literature data of adsorption enthalpies [8] yielded a sur- Surface Science 104, 491 (1981). prising result: a nearly constant distance (r) of 2.47 A has been calculated independent from the noble gas and from the nature of the solid surface. Applying this distance the 129 SEMI-EMPIRICAL CALCULATION OF ADSORPTION ENTROPIES S. Taut, S. Hubener (FZRossendorf), B. Eichler (PSI) Adsorption entropies can be calculated using statistical thermodynamics model, an empirical correlation between force constants and adsorption enthalpies, and the long known compensation effect between To and the adsorption en- thalpy. SYMBOLS Qllmns.adsmoh A molar standard surface area of adsorbed substance Jhindr ~ d inner column diameter f force constant It can be calculated from the frequency factor t0 of the Jhindr hindrance factor FRENKEL equation [2] g temperature gradient along the chromatography column h Planck constant h-v J electron system magnetic quantum number kT-\l- exp - k Boltzmann constant m mass of adsorpt atom and from experimental adsorption entropies with the equa- To ambient temperature sorption data of lanthanoids and actinoids on bcc metals: Tad! adsorption temperature T ua carrier gas speed at ambient temperature To V molar standard volume of substance to be adsorbed V adsorpt vibration frequency normal to surface CALCULATIONS OF ADSORPTION ENTHALPIES *o frequency factor in the FRENKEL equation Adsorption enthalpies can be calculated from thermochro- differential molar standard adsorption enthalpy matographic data [5]: AS", differential molar standard adsorption entropy T T, T o • f --ex1 p —— • or CALCULATION OF ADSORPTION ENTROPIES / T I RT Applying statistical partition functions for both gaseous and adsorbed state [1] and considering the non-ideal behaviour As has been shown, the adsorption entropy is not a simple of the two-dimensional adsorpt gas [2], an expression for parameter, but a function of the adsorption enthalpy. The the entropy of mobile adsorption was derived: program TECRAD [6] was modified such that its iteration loop for the enthalpy calculation considers the dependence of the adsorption entropy on the adsorption enthalpy. 2Jads+l 2/ ..+1 ACKNOWLEDGMENTS (kT-ln-i h-v V- l-exp - We gratefully acknowledge the support by BMBF, contract kT 06 DR 824. In [3] was shown that experimental adsorpt stretching fre- REFERENCES quencies follow the oscillation equation: [1] P.W.Atkins, "Physikalische Chemie"; 2nd edition, L Weinheim 1996, p. 640. [2] J. H. De Boer, Advances in Catalysis 8, 17 (1956). An empirical correlation between force constants and ad- [3] C. Astaldi, et. al., sorption enthalpies was derived from literature data: Solid State Commun. 75, 847 (1990). lo = -1.78 - 0.0036 • AH^ [U /moll [4] E. Bauer, "Chemisorption Systems", eds. Woodruff, D. P., King, D. A.; Elsevier 1984, p. 51. The stretching frequency can now be calculated. The hin- drance factor considers the non-ideal and ideal translation of [5] B. Eichler, I. Zvara, Radiochim. Acta 30, 233 (1982). the two-dimensional gas on the surface: [6] H. Funke, et. al., Report FZR-43, 53 (1994). 130 SELECTIVE GAS-PHASE TRANSPORT OF SHORT-LIVED, CARRIER-FREE IODINE ISOTOPES FROM A 252CF FISSION SOURCE S. Soverna (Univ. Bern), Ch.E. Dullmann, H.W. Gdggeler, A. Tilrler (Univ. Bern & PSI), M.Ammann (PSI) A selective gas-phase transport of carrier-free iodine nuclides from a 2S2Cf fission source was accomplished by using a moist (H2O) carrier gas (He/N2) (free of aerosol particles). The transported volatile iodine compound is tentatively identified as hypoiodous acid HOI. 1 INTRODUCTION decomposition of O2. It seems as if just a few ppm of O2 are needed in the carrier gas to form sufficient amounts of O3. Iodine containing compounds play an important role in the IO is a relatively unstable compound and rapidly reacts halogen activation and the ozone loss in the marine boun- with other radicals or compounds. One of the reaction dary layer [1]. To investigate the iodine compounds and partners of IO is the peroxyradical HO : their reactions in the atmosphere in model experiments at 2 the naturally occurring low concentration levels, the use of IO + HO 2 -» HOI + O2 radioactively labelled iodine reservoir species is very HO2 is produced by the radiative chemical decomposition 252 advantageous. The Cf fission source called Miss Piggy of H2O and O2. With this reaction HOI is formed, which is a [2] provides among other fission products [3] short-lived relatively stable compound and is transported to the iodine nuclides as primary fission fragments. To use these detection system. iodine isotopes as tracers a rapid selective chemical 10> isolation of the iodine isotopes is necessary. Nb,'°Tc, ""Nb, ""Mo, 16000 • 1<4Ba • '"Rh, l4sCe 4000 • 2 EXPERIMENTAL 12000 • / ""Rh The transport of the fission products was accomplished Counts / 0000- with a gasjet system [4]. Since it is expected that iodine 8000 • 10 min llr "Mi IO' + O 3 2 [3] Ch. E. Dullmann et al., PSI-Ann. Rep. 1998, 3 (1999). The iodine radical I is generated in the fission process, O3 is produced in the recoil chamber by the radiative chemical [4] R. J. Silva et al., Nucl. Inst. Meth. 147, 371 (1977). 131 oc-PEAK SHIFT IN COOLED PIN-DIODE DETECTORS D. T. Jost, D. Piguet (PS) This study shows the influence of temperature on the pulse height of small PIN-diodes used as a-particle detectors. 1 INTRODUCTION comparing the pulse height of the 5.806MeV a-line of MCm with the value at 20°C. The amplifier chain consisted It is planned to use inexpensive PIN-diodes to construct a of a Canberra 2001 preamplifier and an Ortec 855 dual thermochromatographic device for the investigation of chemical properties of superheavy elements. In the amplifier. One main amplifier was set to 0.5|J,s shaping time traditional approach to thermochromatography the chemical and the other to 3.0(Xs. species was passed through a quartz column at a constant temperature and a detection system at the exit of the 3 RESULTS column. Repeating this experiment at various temperatures Fig. 2 shows the temperature dependence of the pulse lead to a so-called breakthrough curve. Given the very low height. The most striking feature is the very large shift at - production yields for the super heavy elements (Element 160°C with 0.5(0.s shaping time while with a 3.0|^s setting 108: 1 atom per day), it is necessary to improve the overall we did not observe this dramatic change. Observing the efficiency of the system. Our approach is to combine the preamplifier output pulse with an oscilloscope showed a chromatographic retention part with the detection system. In the case of element 108 it is expected that the 108- significantly slower rise time at -160°C than at 20°C. This tetroxyde will be adsorbed on a quartz surface at about - effect can be explained by either the slower charge 80°C. We are planning to build a system with a temperature collection or with a change in the electrical capacity of the gradient from -10°C to -120°C. Two times 36 detectors of detector/preamplifier input stage due condensation or small 10mm length will be used to form this system giving a changes in the geometry caused by the different thermal temperature difference of about 3K per detector. This study expansion coefficients of the involved materials. With the was conducted in order to test functioning of the PIN- 3.0(0.s shaping time the shift is about -0.4 keV/K at diodes at the low temperatures and evaluate the influence 5.8MeV. Within three adjacent detectors the temperature on the energy resolution if three adjacent detectors are changes about 10K giving rise to a decrease in energy coupled to a common amplifier chain. resolution of approximately 4keV at 5.8 MeV. 10.0 9.5 - CO 1111111111111111111111111111111111111111111 11 -160 -140 -120 -100 -80 -60 -40 -20 0 20 Temperature [°C] Fig. 1: PIN-diode test setup. A) PIN-diode, B) Peltier element, C) Copper coldfinger, D) Copper braid, E) detector support, F) a-source, G) vacuum Fig. 2: Temperature dependence of the pulse height of a enclosure. Hamamatsu PIN-diode used as a-particle detector. 2 SETUP 4 CONCLUSION A lOxlOmm PIN-Diode (Hamamatsu S3590-2) was The decrease in energy resolution due to a 10K difference coupled with the cold side of a Peltier element (Melcor CP in detector temperature is acceptable for our purposes. Even 1,4-35-045 L) and this assembly was in turn mounted in an for 9MeV a-particles the decrease is less than lOkeV and old y-detector cryostat. The detector temperature was comparable to the effects caused by electrically coupling measured with a thermocouple in contact with the ceramics three detectors. support of the PIN-diode. The Peltier element was used to vary the detector temperature and gain some experience with relatively high currents close to the detector. Fig. 1 shows the schematic setup of the detector assembly. A 3- nuclide source (239Pu, 241Am, 248Cm) was used as calibration standard. The temperature dependence was determined by 132 TRANSPORT YIELDS OF SELENIUM NUCLIDES AT THE SINQ GAS-JET FACILITY M. Wachsmuth, B. Eichler, M. Ammann (PSI), F.L. Hdnssler, H.W. Gdggeler (Univ. Bern & PSI) The chemical interaction of different reactive gases (O2, H2, CO, C3H$ and only He) with short-lived selenium nuclides and the transport properties of the resulting products have been investigated using the SINQ gas-jet facility. INTRODUCTION RESULTS The use of short-lived bromine nuclides as tracers in Fig. 1 compares saturation activity of 84Se for the different laboratory studies of heterogeneous reactions of bromine gas mixtures, and Table 1 lists the decomposition compounds such as hypobromous acid (HOBr) enables temperature obtained for each system. The highest yield experiments under atmospherically relevant conditions. As was obtained in the case of C3H6. H2 and CO led to a five bromine nuclides, though produced with high efficiency in times smaller yield, while for O2 and He, a saturating thermal neutron induced fission of 235U, are not efficiently activity of only around 300 Bq was obtained. The resulting transported in the gas-jet facility at the Spallation neutron 84Br activity from the (3-decay of 84Se was around two source (SINQ) under a variety of gas conditions, the times higher. No difference in the Se transport yield selective transport of its precursor selenium is of interest. It between pure helium and 5 % O2 in He is apparent. has already been shown that by adding CO to the inert However, after decomposition, bromine could only be carrier gas (He), selenium nuclides can be transported to the separated in carrier free form in presence of oxygen (Fig. laboratory, where the daughter bromine nuclides could be 2). From the ability of the bromine compound to be separated under Br carrier addition [1]. However, it turned 2 absorbed on basic surfaces, to pass over solid CBr4 and to out that the presence of CO had a negative impact on the react with solid sodium bromide, it was tentatively photochemical conversion of the product molecules identified as HO84Br. (labelled Br2) to HOBr. Therefore, other gas mixtures were tested with respect to transport efficiency of Se nuclides 6000 which depends on the volatility and stability against reaction with wall materials of the molecules formed between the recoil atom and the added gas. In addition, the suitability of these gas mixtures for separation of Br nuclides in a useful chemical form was tested. EXPERIMENTAL 390 400 410 420 The experimental set-up was the same as described in [1]. Energy [keV] Activated charcoal was used to trap all gaseous nuclides in the laboratory and to compare the transport yields of the Se Fig. 2: Comparison of a direct catch (dotted line) and a nuclides. Carbon monoxide (750 ppm CO in He), propene decomposition/separation experiment (solid line) (650 ppm C3H6 in He), oxygen (5 % O2 in He), hydrogen (1 using 5 % O2 in He as transport gas. % H2 in He) and pure helium (99.9999%) were used. To get further information about the chemical identity and stability Table 1: Results of decomposition experiments. of the transport species, the decomposition temperatures were determined by cracking the transport molecules in the Gas Transport Td After separation tube furnace described in [1]. molecule [°C] He 700 -- 6000 n H2 (1 % in He) H2 Se 900 -- n 5000- O2 (5 % in He) H2 SeO3 750 HO°Br CO (650 ppm in He) OC"Se 800 nBr-Br * —•— Se-84He C3H6 (650 ppm in He) C3H6"Se 1050 -- —§§— Se-84 02 .1" 3000- Se-84H2 Td: Decomposition temperature; n: 83, 84, 85, 86; H Se-84 CO "* 2000- —*—Se-84 C3H6 —: daughter bromine nuclide could not be mobilised from the tube furnace; *: could only be mobilised after addition 1000- of 500 ppb Br2 as carrier. ACKNOWLEDGEMENT 5000 10000 15000 20000 This project is funded by the Swiss National Science Time [s] Foundation (No. 20-58775.99). 84 Fig. 1: Saturation activities of Se (Ti/2= 3.1 min), col- lected on a activated charcoal trap and measured REFERENCES with a HPGe detector, as a function of time. [1] M. Wachsmuth et al., Radiochim. Acta, in press (2000). 133 REACTION OF HO86Br WITH SODIUM BROMIDE AEROSOL M. Wachsmuth, M. Ammann (PSI), H W. Gdggeler (Univ. Bern & PSI) The reaction of gaseous hypobromous acid (HO mBr), available via the SINQ gasjet facility, with deliquescent sodium bromide (NaBr) aerosol particles has been investigated in an aerosol flow tube study. The reaction is fast, and at these low concentrations, the product, gaseous Br2 remains aerosol bound on the short time-scale. INTRODUCTION RESULTS The heterogeneous reaction of bromine compounds, and In Fig. 2, the partitioning of the 86Br activity between the particularly of hypobromous acid (HOBr), with sea-salt TBAH denuder and the particle filter is shown as a function bromide belongs to the key processes sustaining near of reaction time. With a long enough reaction time, surface ozone depletion events in the arctic at polar sunrise complete uptake onto the aerosol was observed, and no [1]. Only in one previous study, uptake of HOBr to release of a gas-phase product occurs. If a CBr4 denuder suspended aerosol particles have been measured in the was mounted behind the particle filter only a very small 86 laboratory [2]. The aim of the present work is to investigate fraction of Br from release of Br2 was found on this the HOBr(g) - aerosol bromide interaction at extremely low denuder. The desorption life-time from the deliquescent concentrations using the short-lived isotope 86Br of bromine bromide solution seems to be longer than the half-life of 86 available from the gas-jet facility at SINQ. Br, 55s, probably due to the significant solubility of Br2. However, when the NaBr particles were not humidified EXPERIMENTAL above the deliquescence point, i.e. when the NaBr only 86 contained adsorbed water at about 10% relative humidity, HO Br was produced from thermal decomposition of a 86 86 all HO Br taken up on the aerosol was immediately Se compound available from the SINQ gas-jet facility [3]. 86 NaBr aerosol particles were produced by nebulising an converted to and released as BrBr and observed in the aqueous sodium bromide solution (-0.2 M) and drying the CBr4 denuder in front of the TBAH denuder (data not resulting droplets in a diffusion dryer. The particles were shown). For the case of deliquescent NaBr particles, as then humidified to well above the deliquescence point shown in Fig.2, the increase of particulate bromine and the (85%). The size distribution was obtained from a decrease of HOBr(g) are consistent with very fast uptake. Differential Mobility Analyser (DMA) coupled to a According to mass transfer calculations, including diffusion Condensation Nucleus Counter (CNC). in the gas-phase, the uptake coefficient, i.e., the probability that a collision of HOBr(g) with the surface results in uptake, is larger than 0.5. go 2E+11 - 2,a •- 100 M U 1E+11 - 80 I 3 nti n £ "I 5E+1O - O u 60 u Is o 40 1 10 100 1000 B Midpoint diameter [nm] =3 20 Fig. 1: The size distribution of deliquescent NaBr aerosol Par t 0 at 50% relative humidity after it had been 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 humidified to 85%. Reaction time [s] HO86Br and the aerosol was mixed in a PFA flow tube Fig. 2: The reaction of gaseous HOBr with NaBr aerosols (perfluoroalkoxy copolymer). The reaction time was varied 86 as a function of time shown as partitioning of the by changing the position at which the HO Br is mixed with 86 86 Br activity between the TBAH denuder and the the aerosol. The total concentration of HO Br is on the 3 particle filter after the flow tube. order of 1000 cm" . After the flow tube, HOBr(g) was absorbed onto the walls of a denuder coated with Tetrabutylammonium hydroxide (TBAH), whereas the ACKNOWLEDGEMENT particles passed the denuder and were retained in a particle filter behind. From the measurement of the activity due to This project is funded by the Swiss National Science the decay of 86Br at the denuder and the filter with a y- Foundation (No. 20-58775.99). detector, the partitioning between HOBr(g) and paniculate bromine was derived. To distinguish between HOBr(g) and REFERENCES Br2(g), the expected product of the reaction, an additional [1] R. Vogt et al., Nature 383, 327 (1996). denuder coated with CBr4, was mounted in front of the TBAH denuder, or after the particle filter, to absorb Br2 in [2] J. P. D. Abbatt, G. C. G. Waschewsky, J. Phys. Chem. some experiments. A 102, 3719 (1998). 134 THE ADSORPTION OF NO, NO2 AND HONO ON ICE M. Ammann, T. Bartels, B. Eichler, P. Zimmermann (PSI) andH. W. Gdggeler (Uni. Bern & PSI) The adsorption of NO, NO2 and HONO on ice was investigated by means of thermo-chromatography and labelling with the short-lived radioactive tracer I3N. All species undergo a reversible adsorption process during migration through packed ice columns. Adsorption enthalpies were estimated for all three species. INTRODUCTION adsorption entropy, which can be estimated from statistical thermodynamics [4]. Based on the assumption that the Nitrogen oxides largely determine the budget of ozone in molecules do not lose rotational degrees of freedom during the atmosphere. As ice is a significant surface interacting the adsorption process, for NO, NO2, and HONO the with air masses containing nitrogen oxides in the upper adsorption enthalpies were -22, -28 and -40kJ/mol, troposphere, alpine, arctic and polar regions, the adsorption respectively. properties of nitrogen oxides on ice are of considerable interest for the chemistry in ice clouds and snow packs [1]. EXPERIMENTAL To investigate the interaction of nitrogen oxides with ice, its chromatographic retention in a column packed with ice spheres was observed using "N labelled molecules. I3NO was produced through 160(p,oc)l3N in a gas target at the Philips cyclotron of the Paul Scherrer Institute [2]. Passing 13 13 13 humidified NO over solid CrO3 resulted in NO2. HO NO 13 was produced by passing NO2 over solid n-1- 0 20 40 Naphtyldiethylenediamine. Rapidly freezing water droplets Position [cm] in liquid nitrogen and crystallizing them at 253 K resulted in ice spheres with a specific surface of about 0.01 lm2g', 13 Fig. 1: Deposition of N labelled NO2 at 110K after a which where packed into a column. The column was placed thermo-chromatography experiment on ice. NO2 into a thermo-chromatograph, a device in which a negative was fed to the column from the warm end at 0cm. temperature gradient from 253 K to 80 K was maintained [3]. From the warm end, the carrier gas containing the 13N labelled molecules passed the column for 30 minutes, the 280 3 1 flow rates were between 1.7 and 5.0cm s" . After the 260 experiment, the column was removed from the thermo- 8000 1 240 chromatograph and submersed into liquid nitrogen. The 220 „ 6000 \ deposition zones of the different 13N-species were recorded & 4000 • by scanning the column with a gamma detector. \ , • 160 • 140 "* 2000 • \ r \ • 120 • 100 RESULTS 0 — Each experiment resulted in a chromatogram as shown in 0 20 40 Fig. 1, for NO2, and in Fig. 2, for HONO and NO. In all cases, distinct peaks were observed for all species, which Position [cm] indicates that reversible adsorption is the process governing 13 migration of each species along the column. Under Fig. 2: Deposition of N labelled HONO at 155K and NO otherwise identical experimental conditions, the deposition at 80K after a thermo-chromatography experiment temperature did not depend on whether any of the species on ice. The carrier gas was fed to the column from was present alone or in a mixture. Therefore, no the warm end at 0cm. competitive adsorption process seems to be relevant. Also, no indications for decomposition or oxidation reactions over ice were evident. The absolute concentration of each REFERENCES species was usually below 3ppb. No shift in the deposition [1] A. E. Jones et al., temperature was observed at concentrations up to lOOppb. Geophys. Res. Lett. 27, 345-348 (2000). At the deposition zone, where the molecules accumulated, [2] M. Ammann et al., Nature 395,157 (1998). the surface coverage on ice was at maximum about 1 % of a [3] B. Eichler et al., J. Phys. Chem. A 104, 3126 (2000). formal monolayer. Nevertheless, it can not be completely [4] B. Eichler et al., Radiochim. Acta 68, 41 (1995). ruled out that in the case of NO2 the adsorbed species was N2O4. Based on the assumptions of ideal linear chromatography and adsorption equilibrium, the adsorption enthalpies can be derived from the experimental parameters and the 135 THE ADSORPTION OF PEROXYACETYL NITRATE ON ICE T. Bartels, M. Ammann (PSI), H. W. Gaggeler (Univ. Bern & PSI) The adsorption of PAN on ice was investigated by means of thermo-chromatography of PAN labelled with the short- lived radioactive tracer nN {W2 = 10 min). First results show no decomposition of PAN on ice and an adsorption enthalpy of - 36 kJ/mol. Peroxyacetyl nitrate (PAN) is an atmospheric reservoir and ASU -AHU transport species of NO (NO and NO ). As NO largely a a x 2 x R R T determines the budget of ozone in the upper troposphere, it t-au. R T •p. a is important to understand the chemistry of PAN. Besides S'l -AHL thermal decomposition, heterogeneous processes may play an important role. A substrate for heterogeneous processing with t: duration of the experiment, a: temperature gradient, of PAN in the upper troposphere may be ice crystals in u0: linear gas velocity, s: column surface, To: starting cirrus clouds. temperature, R: gas constant, Ta: adsorption temperature, Currently, it is not known to what degree PAN partitions AH°a: standard adsorption enthalpy, AS°a: standard between the ice and gas phase through reversible adsorption adsorption entropy. and whether PAN decomposes to NOx on the ice phase. To investigate the interaction of PAN with ice, its chromatographic retention in a column packed with ice spheres was observed using radioactively labelled molecules. Rapidly freezing water droplets in liquid nitrogen and crystallizing them at 253 K resulted in ice spheres, which where packed into a column. The column was placed into a thermo-chromatograph, a device in which a negative temperature gradient from 253 K to 80 K was maintained [1]. From the warm end an N2-carrier gas containing 13N-PAN passed the column for 30 minutes. The 13N-PAN was synthesised by photolysis of acetone vapour I3 at 254 nm in presence of NO and O2 The "NO was Column Length [cm] produced through 160(p,oc)l3N in a gas target at the Philips cyclotron of the Paul Scherrer Institute [2]. Fig. 2: Chromatogram and temperature gradient (dots). The gas enters from the warm end at 50 cm. PAN deposited at 25 cm / 185 K and NO at 19 cm / 140 Excess 2 K. Thus, based on the experimentally determined deposition temperature, the adsorption enthalpy can be calculated. Obviously, the result depends on the choice of entropy Acetone (-160°C) change associated with adsorption. The entropy change can easily be calculated based on statistical thermo dynamical considerations for a symmetrical molecule. For PAN the Fig. 1: Experimental set-up of the flow system. adsorption entropy at the deposition temperature was TC: Thermo Chromatograph, CLD: NOx Analysis, estimated to be -171 J/K. hv: photolysis cell A typical experiment with a gas flow through the column of 95 ml/min, a geometrical diameter of the ice spheres of I3 1515 |xm, and experimental time of 30 minutes yields an After the experiment, the deposition zone of various N- adsorption enthalpy of -36 kJ/mol. species was deduced using a very sensitive gamma detector yielding a chromatogram as can be seen in Fig. 2. As the temperature gradient along the column is known, the ACKNOWLEDGEMENT deposition temperature of 13N-PAN could be determined. This work forms part of the EU project CUT-ICE (EVK2- CT-1999-00005) funded by the Swiss Federal Office for Based on ideal linear chromatography and the adsorption Education and Science. equilibrium, the following relation between experimental factors - on the left hand side of the equation -, and REFERENCES thermodynamic functions as well as the deposition temperature on the right hand side, holds [3]: [1] B. Eichler et al., J. Phys. Chem. A 104, 3126 (2000). [2] M. Ammann et al., Nature 395, 157 (1998). [3] B. Eichler et al., Radiochim. Acta 68,41 (1995). 136 THE REACTION OF HNO3 WITH SEA-SALT AEROSOL PARTICLES M. Ammann, F. Arens, L. Gutzwiller, E. Rossler (PSI), H.W. Gaggeler (Univ. Bern & PSI) U N labelled HNO3 was reacted with sea-salt aerosol particles, and formation of particulate nitrate was measured as a function of reaction time, HNO^ concentration. The reaction probability derived from the results is about 0.07. INTRODUCTION Fig. 1 shows a typical on-line record of HNO3 and particulate nitrate during an experiment. Each experiment Nitrogen oxides control the ozone abundance over large as shown there leads to one data point in Fig. 2 displaying areas of the troposphere. The oxidation to HNO3, and the number of labelled particulate nitrate leaving the flow uptake of the latter to aerosol particles or cloud droplets tube as a function of the interaction time. The solid line constitutes their main removal pathway. Only in one displays a best fit of a model describing mass transfer to the previous study, uptake to suspended aerosol particles have aerosol particles including diffusion yielding a preliminary been measured in the laboratory [1]. Using sea salt aerosol value of 0.07 for the uptake coefficient. This is higher than particles as an example, first results for the reaction with on pure bulk NaCl [3], but lower than Abbatt and HNO at very low concentrations are shown here. 3 Waschewsky [1] observed on deliquescent NaCl aerosol. In our system, the aerosol was dried to below 10% relative EXPERIMENTAL humidity and rehumidified to 30% probably not leading to Similar to our previous aerosol studies [2] we used 13N deliquescent particles. labelled NO2, humidified to 8% relative humidity at 20°C. The measurements presented here show the power of the The mixture was irradiated with 172nm UV radiation for methodology to determine the uptake kinetics of HNO3 to OH production, which rapidly converted 80% of the NO2 to aerosol particles under atmospheric conditions with respect HN03. Sea salt aerosol was produced by nebulising a to concentration and humidity. solution of commercially available synthetic sea salt. The total aerosol surface to volume ratio varied from 10"4 to 10~3 cmVcm3, as measured by a scanning mobility particle sizer. The aerosol and HNO3 flows were mixed in a small aerosol flow tube. By changing the length of the flow tube the interaction time between the aerosol and HN03 was varied. Immediately after, the resulting flow passed a narrow parallel plate diffusion denuder with selectively coated walls absorbing HNO3(g) and NO2(g), respectively, followed by a particle filter collecting the particles with HN03 or its product on them. The amount of labelled molecules absorbed in each of these traps is measured using a scanning coincident counting system consisting of two opposite y-detectors. 0 0.5 1 1.5 2 Residence time in flow reactor (s) Fig. 2: Amount of 13N labelled molecules leaving the aerosol flow tube attached to the particles, presumably in the form of nitrate, as a function of the residence time in the flow tube. The relative humidity was 30%, the temperature 300 K, and the HN03 concentration 3ppb. REFERENCES Time (min) [1] J. P. D. Abbatt and G. C. G. Waschewsky, J. Phys. Chem. A 102, 3719 (1998). Fig. 1: On-line record of HNO3(g), NO2(g), and HNO3 [2] M. Kalberer et al., Journal of Geophysical Research attached to the aerosol particles leaving the flow 104, 13825 (1999). tube for a typical experiment at 5 ppb HNO3. The [3] J. A. Davies and R. A. Cox, number of "N-labelled molecules of each species J. Phys. Chem. A 102, 7631 (1998). absorbed in its respective trap is plotted. After lOmin, the UV lamp is switched on to convert NO2 to HNO3, the aerosol is switched on and off at 15 and 25 min, respectively. 137 MODELLING THE HETEROGENEOUS REACTION OF NO2 ON DIESEL SOOT F. Arens, M. Ammann, L. Gutzwiller, U. Baltensperger (PSI), H.W. Gdggeler (Univ. Bern & PSI) Nitrous acid (HONO) may be formed via a reaction between nitrogen dioxide (NO2) and soot particles. Based on n results obtained earlier using N labelled NO2, a surface chemical model was developed to calculate atmospheric HONO formation rates. Nitrous acid (HONO) may be important because of its potential role in initiating daytime photochemistry by its rapid photolysis yielding OH radicals. The source of 5e+10 HONO in the atmosphere has not yet been conclusively identified. Several studies have recently identified soot as possible reactive surface for reaction with NO2 leading to HONO [1,2]. Sampling, characterisation and exposure of diesel soot samples to "N labelled NO2 is described in detail elsewhere [3]. In these experiments, the formation of HONO as a 10 15 20 25 30 35 40 function of NO2 concentration and relative humidity was NO2(ppb) followed over time. Fig. 1: Initial HONO formation rate on diesel soot particles The reaction rates of HONO increased with increasing NO2 as a function of the NO2 mixing ratio (r.h. = 30%) concentration (Fig. 1) and did not depend on relative and the corresponding inverse data (insert). humidity. HONO formation decreased with time (Fig. 2), indicating consumption of reactive surface species. Due to other experiments, here not explained in detail, we assume that HONO formation is caused by reduced organic species (RnH) on the soot surface oxydisable by NO2. On the basis of the results, HONO formation was interpreted in terms of a Langmuir-Hinshelwood model involving two overall surface reactions in parallel (reactions 1-3). 8 ppb NO2 9 ppb NO2 NO2(g)+S(S) NO2»S (S) (1) (H O) k, 2 (2) 18 ppb NO2 (S) '(S) (H20) k2 NO2'S(S)+R2H l(S)~ >S(s)+HONO(g)+R2(S) (3) For a noncompetitive Langmuir adsorption the equilibrium coverage of NO2 molecules on the soot surface is given by [NO2»S] KxX NO2 with K = f (4) e = (l + KxX ) 0 10 20 30 40 0 10 20 30 40 50 N02 des tim e (m in) where [NO2»S] denotes a physisorbed precursor state, XN02 Fig. 2: HONO formation rates as a function of time for denotes NO2 in the gas phase and Ns is the maximum different NO2 mixing ratios (r.h. = 30%). number of sites S available. The resulting HONO formation rate involving two surface reactions can be written as ACKNOWLEDGEMENT d\HONO] r l 1 This work forms part of the Eurotrac-2 project CMD +k2x[R2H\(t)y xN x0 (5) s (Chemical Mechanism Development) and has been supported by the 'Komission fur Technologie und with =\RIH] Innovation (KTI)'. (f) (t=0) REFERENCES [R2H\ =[R2H] (f = 0) [1] M. Ammann et al., Nature 395,157 (1998). Applying these equations to the experimental data, values [2] M. Kalberer et al., JGR 104, 13.825 (1999). for the unknown constants K, [RjH]^, [/?//](t=0), (Nsx kj) and (N x k ) were determined. This parameterisation [3] F. Arens et al., submitted to s 2 Environ. Sci. Technol. (2001). derived allows to predict the atmospheric HONO formation on diesel soot particles for a time scale up to several hours. 138 MEASUREMENT OF THE HONO EMISSION FROM A DIESEL ENGINE J. Kleffmann, J. Heland, R. Kurtenbach, J. C. Lorzer, P. Wiesen (Universitdt Wuppertal), M. Ammann, L. Gutzwiller (PSI), M. Rodenas Garcia, M. Pons, K. Wirtz(CEAM, Valencia), V. ScheerandR. Vogt (Ford, Aachen) HONO emission indices of a commercial diesel engine were measured under varying operating conditions and using differently formulated fuel. The four different measuring methods applied show good agreement. Nitrous acid (HONO) is formed during night time and • stand. Diesel photolysed to OH and NO at sunrise, thus initiating • Biodiesel photooxidation processes early in the morning. However, H < 5% aromatics M < 15% aromatics the mechanism of HONO formation is badly understood in E < 25% aromatics spite of intensive research in this field. Direct emissions from vehicles are contributing to atmospheric HONO o levels. Emission measurements were performed in the European Photoreactor EUPHORE in Valencia, Spain. A commercial 1.8 1 Diesel engine (44 kW, indirect fuel injection) was used for exhaust generation. About one tenth of the exhaust gas was transferred to the chamber through a heated transfer line and rapidly diluted in the chamber (dilution ratio -1:1000). This set-up prevented ONm 30 Nm 70 Nm ONm 30 Nm 70Noi 70Noi accel. accel. agglomeration of particles and the condensation of water hot) and semi-volatile organic hydrocarbons on the particles engine condition similar to "real world" conditions of driving a vehicle on a road. Fig. 1: HONO emission indices for different engine conditions using different diesel fuels. Five differently formulated fuels were used in the study: European standard Diesel, Biodiesel (RME) and three Diesel fuels with different content of aromatic The corresponding HONO/NOx ratio of HONO/NOx = hydrocarbons and low sulphur content (aromatics < 25%, < (7±2)xl0~3 is in agreement with [5] but still does not explain 15% and < 5%). While the European standard Diesel the observed ratios before sunrise. Therefore, in the contained significant amounts of di- and poly-aromatics and atmosphere, HONO is not formed through emission from 425ppm sulfur, the diesel fuels with < 5%, < 15% and < diesel engines, but rather by secondary processes on 25% aromatics were formulated almost only with mono- surfaces. aromatics and 45ppm sulfur. ACKNOWLEDGEMENT HONO measurements were performed with different well established techniques and a newly developed instrument: This study formed part of the EU project DIFUSO (ENV4- CT97-0390) supported by the Swiss Federal Office for (1) A wett effluent diffusion denuder (WEDD) [1]; Education and Science. (2) A DO AS spectrometer [2]; REFERENCES (3) HPLC technique [3]; [1] C. Zellweger, M. Ammann, P. Hofer, (4) Additional HONO measurements were performed with U. Baltensperger, Atmos. Environ. 33, 1131 (1999). a long path absorption photometer (LOPAP) [4]. [2] T. Etzkorn, R. Volkamer and U. Platt in: Emission indices (El: g HONO per kg fuel burnt) were Becker. K. H. (ed.): Final Report of the EC-Project derived from the ratio of the weighted mean HONO EUPHORE, 65 (1996). increase measured by all instruments per CO2 increase after exhaust gas injection. It was observed that the HONO [3] X. Zhou, H. Qiao, G. Deng and K. Civerolo, emission indices are almost independent of fuel formulation Environ. Sci. Technol. 33, 3672 (1999). and engine load, although the sulphur and aromatic hydrocarbon content of the fuel varied significantly. [4] J. Heland, J. Kleffmann, R. Kurtenbach, P. Wiesen, Accordingly, from all emission data obtained a mean value Environ. Sci. Techno/, in preparation (2001). of EIH0N0 = (0.11±0.04) g/kg was derived. This value is in [5] K.H. Becker, J.A.G. Gomes, J. Kleffmann, good agreement with the value of -0.1 g/kg for Diesel R. Kurtenbach, J. C. Lorzer, M. Spittler, P. Wiesen, engines from a recent tunnel study (Becker et ah, 2000). R. Ackermann, A. Geyer and U. Platt, Atmos. Environ, in preparation (2001). 139 SIGNIFICANT NITRITE FORMATION IN DIESEL EXHAUST L. Gutzwiller, F. Arens, M. Ammann (PSI) The aqueous reduction of NO, by species contained in diesel exhaust is quantified and may account for hitherto unexplained HONO to NOx levels in the atmosphere before sunrise. Nitrous acid (HONO) is formed during night time and diesel exhaust (above 120°C) was injected into the flow photolysed to OH and NO at sunrise, thus initiating tube so that the first cold surface seen by the exhaust gas photooxidation processes early in the morning. According was the water film itself. The NO2 concentration was varied to a model study, HONO accounts for a five fold increase in order to determine the total amount of nitrite forming in OH concentration at 06:00h and a 16% increase in net species. The contribution of reactions (1) and (2) were photochemical ozone formation [1]. subtracted from the total nitrite signal in order to obtain the amount of nitrite attributed to reaction (3) involving In a recent study, Arens et al. [2] showed that about 1017 additional species. HONO molecules are formed per mg diesel soot. This is the highest conversion ratio cited in the literature for the NOx/soot system so far, although the soot particles were collected after stripping gas phase components from the 16000 exhaust. Instead of examining the role played by soot 14000 • particles, we focus in the present study on possible HONO 12000 formation by (semi volatile) species contained in the gas g 10000 phase of hot exhaust; once dissolved in water, these species O 8000 • may react with NO2. The following reactions are implicated X 6000 in the aqueous phase formation of nitrite, i.e. dissolved 4000 • HONO: 2000 0 • 2 NO2 (aq) => 2 H+ + NO3" + NO2" (1) NO2 (ppb) 2 • 2 NO2 (aq) + HSO3- (aq) => 2 NO2" + 3 H+ + SO4 " (2) Fig. 2: Equivalent gas phase HONO formation from the reaction of an organic species contained in the • NO2 (aq) + ArO" (aq) + H+ => NO2" + ArO + H+ (3) exhaust with NO2. Squares and diamonds Reactions (1) and (2) are well known but account only correspond to 1 and 3kW load, respectively. partially for the observed nitrite formation in the interaction of diesel exhaust with wet surfaces. Our hypothesis is that Under atmospheric conditions, these species contained in reactions analogous to (3) involving phenols (ArOH) or the exhaust may also be adsorbed on wet surfaces and react similar reducing agents may form additional nitrite. with NO2 to nitrite and hence HONO as atmospheric aqueous phases tend to be acidic. Thus, volatile organic species in the exhaust may account for higher HONO to NOX ratios at night than expected from the reaction of NO2 on soot or HONO emissions, only. synthetic air &NO2 ACKNOWLEDGEMENT This work was supported by the Swiss Federal Office for Education and Science (contribution to the EU-project NITROCAT, EVK2-CT-1999-00025). REFERENCES [1] M. E. Jenkin, R. A.Cox, and D. J. Williams, Atmos. Environ. 22, 487 (1988). Fig. 1: Schematic design of the experimental set-up. [2] F. Arens, L. Gutzwiller, U. Baltensperger, The principle of the wetted wall flow tube (WWFT) H. W. Gaggeler, M. Ammann, corresponds to the one described in detail by Zellweger et submitted to Environ. Sci. Technol. (2001). 1 al. [3]. In short, a constant air flow of 0.48 1 min was [3] C. Zellweger, M. Ammann, P. Hofer, drawn through a parallel plate diffusion denuder and fed U. Baltensperger, Atmos. Environ. 33, 1131 (1999). into a NOX analyser. The denuder effluent (0.56 ml/min, residence time 20sec) was preconcentrated on ion exchange columns and analyzed by ion chromatography. The duration of the preconcentration was 7 min. The rate constant of reaction (1) was confirmed with our set-up. This means that the water film of our WWFT is well mixed, thus allowing aqueous phase kinetic measurements. Hot 140 AN ALPINE ICE-CORE RECORD OF ANTHROPOGENIC HF AND HCl EMISSIONS A. Eichler (Univ. Bern & PS1), M. Schwikowski (PS1), H.W. Gaggeler (Univ. Bern & PS1) Ice-core records of an Alpine glacier from the southern Swiss Alps were used to reconstruct sources of inorganic F and Cl' in precipitation. Our results suggest that on average 16% of the Cl' deposition and most of the F deposition in the period 1937-94 were due to HCl and HF emissions from anthropogenic sources. Concentrations of F and Cl" were analysed in an Alpine ice In contrast to other western European countries waste core from Grenzgletscher in order to investigate emission incineration is the largest national source of anthropogenic sources of both species and the anthropogenic influence on HCl emissions in Switzerland, because most domestic precipitation chemistry in the Alpine region. The ice core waste is burned. Estimates of historical HCl emissions in covers the time period 1937-94 [1]. Switzerland show a strong increase compared to the coal F and Cl concentration records consist of a total of 2320 burning level in the period 1960-85 due to rising waste samples. The observed strong correlation between [Cl~] and incineration and the large amounts of PVC in waste ([4], [Na+] on the one hand and between [Cl~] and [Ca2+] on the Fig. 1A). Because of the installation of flue gas scrubbers other hand revealed that the main source of Cl in the sou- as a consequence of air pollution control measures a decline thern Swiss Alps is sea salt originally transported together in emissions has occurred since 1985. The good agreement with mineral dust from the Saharan area. The non-sea-salt in the trend between estimated Swiss HCl emissions and fraction of Cl (nssCl) was calculated using a C17Na+ molar our data (Fig. 1A) indicates that the nssCl" concentration concentration ratio of 1, which is assumed to represent the record at the drilling site is mainly determined by local HCl sea-salt ratio at this glacier site [2]. The record of nssCl emissions. concentrations (5-year averages) is shown in Figure 1A, Regarding the F record no significant correlation with any revealing a strong increase between 1960 and 1985, fol- other major ionic species was observed, suggesting that a lowed by a steep decrease. The contribution of nssCi to the different source was responsible for the major contribution total Cl" amounts to 50% at the most with a mean value of to the F budget over the last 60 years at this site. The 16% for the entire time period. development of the F concentrations (5-year averages) over the period 1937-94 is shown in Figure IB. The profile 1-12 exhibits a steep increase until 1965, followed by a steady -10 decrease. F measurements in a Greenland ice core indicate that coal burning is the most important source of anthropogenic F at this site [5]. However, historical HF emission estimates for Switzerland [4] reveal that the con- tribution of HF emissions from coal burning is less than O 17% over the last 60 years (Fig. IB). Increasing HF emis- I sions up to 1970 are due to increasing aluminum production in nearby plants at Chippis and Martigny in the Rhone valley, which are about 40 km distant from the drilling site. As a consequence of the installation of waste-air purification systems a steep decrease in HF emissions -800 occurred after 1970. By comparing our data with the trend in historical emission estimates (see Fig. IB) we conclude -600 c- that similar to nssCl the major part of F originated from a nearby local source. This is in agreement with the expected short lifetimes of HCl and HF in the atmosphere due to -400 | their high water solubility, leading to a complete uptake by cloud droplets and subsequent wet deposition close to -200 sources. Our results indicate a strong impact of emissions of short- 0.00- lived atmospheric species such as HCl and HF on local and 1930 1940 1950 1960 1970 1980 1990 regional precipitation chemistry. Year Fig. 1: 5-year average concentration records of nssCl" (A) REFERENCES and F (B) (lines) together with historical emission estimations of HCl and HF for Switzerland in the [1] A. Eichler et al., J. Glaciol., in press. period 1935-1990 (dashed lines). Diamonds repre- [2] A. Eichler et al., Geophys. Res. Lett. 27, 3225 (2000). sent emissions from coal burning, while stars indi- [3] Lightowlers et al., Atmos. Environ. 22, 7 (1988). cate total emissions, derived from [4]. [4] BUWAL, Schriftenreihe Umweltschutz 256 (1995). Sources of nssCl" could be direct HCl emissions from industrial sources. The largest sources of anthropogenic [5] de Angelis et al., J. Geophys. Res. 99, 1157 (1994). HCl emissions in western Europe are estimated to be coal combustion (about 75% in 1983) and waste incineration [3]. 141 NORTH-SOUTH DEPOSITION GRADIENTS OF TRACE SPECIES IN THE ALPS A. Eichler (Univ. Bern & PSI), M. Schwikowski, M. Furger (PSI), H.W. Gaggeler (Univ. Bern & PSI) North-South deposition gradients of trace species in the Alps were investigated based on the seasonally resolved analysis of ice cores from two sites in the Alps. No gradients were found for species of anthropogenic origin, while dust- and sea-salt-related species show a different behaviour at the two sites due to the different transport patterns to the Alps. Due to their extent the Alps act as a barrier for air mass Concentrations of species of anthropogenic origin show an flow, and therefore a north to south gradient of the air pol- accordant seasonal cycle with two to three times higher lution impact on the high-alpine environment is expected. summer- than winter concentrations. This can be explained In order to assess the geographical and seasonal trends of by precipitation from the same air masses at both sites. the deposition of trace components, glaciochemical records These are convective precipitation in summer from aerosol from two Alpine glaciers (Fieschergletscher, northern Alps rich air, when trace species from the planetary boundary and Grenzgletscher, southern Alps) were used. layer can reach the Alps and advective precipitation in win- + ter from aerosol poor air, representing conditions of the free Ice-core records of the main aerosol-related species (NH4 , 2 2+ 2+ + troposphere. On the other hand species of dust- and sea- NO3", SO4 ", Ca , Mg , Na\ K , Cl") were compared for the salt-origin show a completely different seasonal behaviour time period 1945-83, which is covered by both ice cores at both sites. While the concentrations of these species [1], [2]. Correlation analyses performed for the logarithmic exhibit a pronounced seasonal pattern at the southern concentrations revealed the main sources for the trace Alpine chain, concentrations are constant throughout the species: year for the northern Alps. The different seasonality of 2 (1) NH/, NO3, SO4 : Anthropogen, dust-related species is due to the different seasonal (2) Ca2+, Mg2+: Dust, behaviour of the transport of Saharan dust to the sites (Fig. (3) Na\ K\ Cl: Sea-salt. 2). This becomes obvious by comparing the Ca2+ In contrary to the Fieschergletscher concentrations of dust- concentrations at Fiescher- and Grenzgletscher with the and sea-salt-related species are well correlated for the number of filters with visible Saharan dust deposit at the Grenzgletscher [1], [2]. Thus, the transport of Saharan dust, nearby stations Jungfraujoch and Plan Rosa, respectively. which is the main source of mineral dust at the Grenzgletscher [1], to the southern Alpine chain is coupled 10- JFJ GG FG to the transport of sea-salt. 8- -10- 12- en ^ 6- Q_ -12- •12 ;r 10- in -14- O _ -16- 4 s ° CO -18- -20- -12 Wi Fr So He Wi Wi Fr So He Wi -22- 2+ Wi Fr So He Wi Wi Fr So He Wi Fig. 2: Annual cycle of the Ca concentrations (dashed li- nes) at Grenzgletscher (GG) and Fieschergletscher 2.0- (FG) along with the number of filters with Saharan dust (lines) observed at nearby stations Plan Rosa (PR, 1968-77, [3]) and Jungfraujoch (JFJ, 1995- 99, [4]). O 8- 0.8- The similar annual cycle of the concentrations of dust- related and sea-salt species at the Grenzgletscher is explained by their coupled transport to the southern Alps Wi Fr So He Wi Wi Fr So He Wi (see above). The constant concentrations of sea-salt species 18 + 2+ Fig. 1: Annual cycle of the 8 O-values, NH4 -, Ca -, and throughout the year at the Fieschergletscher, however, can Na+-concentrations for Fieschergletscher (circles) be explained by the transport of sea-salt with westerly and Grenzgletscher (triangles) in the period 1974- winds from the Atlantic Ocean to the northern Alps. These 83. 818O values are shown in comparison to the conditions are uniformly distributed throughout the year. temperature at Col du Gd. St. Bernard (2480m asl). REFERENCES Concentration records of trace species were compared on a [1] A. Eichler, Ph. D. Thesis, University Bern (2000). seasonal time scale for the period 1974-83 (Fig. 1). Based on the temperature dependent parameter S18O samples were [2] M. Schwikowski et al., classified in winter-, spring-, summer- and autumn samples J. Geophys. Res. 104, 13709 (1999). [1]. The good agreement between the seasonal cycle of the [3] Prodi and Fea, 818O-values at both places and of the air temperature at the Veroff. Schweiz. Meteorol. Anstalt 40, 179 (1978). Col du Gd. St. Bernard (2480 m asl, Fig. 1) indicates that [4] C. Zellweger-Fasi, private communication (2000). the different classes indeed represent the actual seasons. 142 ELECTRICAL CONDUCTIVITY MEASUREMENT ON AN ICE CORE FROM THE ILLIMANI (6430 m, 16°39'S, 67°47'W), BOLIVIA St. Knttsel (Univ. Bern & PSI), J.-D. Taupin (IRD, Montpellier), J.-R. Petit (LGGE, Grenoble), U. Schotterer (Univ. Bern), M. Schwikowski (PSI), H.W. Gaggeler (Univ. Bern & PSI) For a first dating, the electrical conductivity was measured on an ice core from Illimani. By this fast method, a continuous signal over the whole ice core is received, from which maxima in conductivity can be assigned to volcanic events and annual layers can be counted. The preliminary dating obtained by annual layer counting and ice flow modelling agreed well, indicating that several hundred years of palaeoclimate information are preserved by this glacier. INTRODUCTION to the Pinatubo eruption in 1992) an average accumulation rate of 0.67 m weq. y"1 was derived. This accumulation rate In June 1999, two ice cores were drilled down to bedrock at and an ice thickness of 111.2 m weq. was used to model the 138 and 136 m, respectively, on Illimani, Bolivia, by a joint ice flow with a one-dimensional model [3]. PSI/IRD expedition [1]. To perform a first dating and to interrelate the two ice cores, the electrical conductivity was 2000 . St.' Hdens 1980 or H Chichon 1982 measured [see e.g. 2]. TritiumPeakl96t Agung 190*$%!? Tritium Peak 1959 The non-destructive electrical conductivity method (ECM) 1950- ffldal94' Ice flow model gives an indication about acidity in the ice, and is applied Annual layers 1900- before cutting the ice. It serves as a screening for a counting Santa Maria 19 preliminary detection of seasonal layers as well as for a first Krakatau 1883 dating by identifying volcanic events. This allows Jf 1850- determining a suitable depth resolution for the subsequent Extrapolation of the Ice flow model analysis. 1800- laid (^ Cctopaxil768C*k EXPERIMENTAL PART 1750- Tatumail739(^ The electrical conductivity measurements were performed Iceflowmodel:t = [3] at the Laboratoire de Glaciologie et Geophysique de 1700 l'Environnement (LGGE) in Grenoble, France. 20 40 60 The electrical conductivity was measured after cutting off a Depth |niwq] 8 mm section in longitudinal direction of the core. After Fig. 2: Age-depth relationship for an Illimani ice core polishing, two electrodes slide over the ice core and the obtained by annual layer counting, ice flow current is measured in dependence of the depth. modelling, and identification of volcanic events. RESULTS AND DISCUSSION The obtained age-depth relationship is shown in Fig. 2, The raw ECM data were averaged over 1 cm and the along with the result of annual layer counting, the location averaged data versus depth are shown in Fig. 1. Seasonal of the two maxima in tritium activity (attributed to the years layers were identified by their characteristic two minima, 1959 and 1964), and ECM peaks assigned to volcanic possibly corresponding to the dry seasons. Annual layer events [4]. The different dating methods agree well and counting was performed down to a depth of 40 m indicate that the ice core from Illimani covers a time period waterequivalent (m weq.). From the accumulation of the of several hundred years. In future, 210Pb activity will be measured and trace elements with stronger seasonal cycles will be analysed to confirm this first dating. REFERENCES [1] B. Zweifel et al., Ann. Rep. Univ. Bern & PSI 1999, p.39. [2] K. Taylor et al., J. Glaciology 38, 325 (1992). [3] J.F. Nye, J. of Glaciology 4 (36), 785-789 (1963). [4] T. Simkin et al., Volcanoes of the world, Smithsonian Institution, 1983. 40 60 Depth [mweq] first six years (confirmed by a maximum conductivity due Fig. 1: 1-cm average ECM data versus depth. 143 SEASONAL RECORD OF GLACIOCHEMICAL AND ISOTOPIC SIGNALS IN A SHALLOW ICE CORE FROM CHIMBORAZO, ECUADOR. P. Ginot (Univ. Bern & PSI), U Schotterer (Univ. Bern), W. Stickler (GSF-Inst. for Hydrology, Neuherberg), B. Francou (IRD, Quito), R. Gallaire (IRD, La Paz), M. Schwikowski (PSI), H.W. Gaggeler (Univ. Bern & PSI). First results from a shallow ice core drilled at the summit of Chimborazo indicate the possibility to reconstruct normal seasonal climate conditions as well as the ENSO influenced variability from this region for several decades. In December 1999, a 16-meter ice core was recovered from averaged isotope values. The bimodal shape of some major the summit of Chimborazo (6310 m a.s.l., 1°28'S, ions (i.e. calcium, magnesium, nitrate, sulphate, 78°50'W, Ecuador, fig. 1) to explore the suitability of this ammonium) is intensified by enrichment due to glacier as palaeoatmosphere and climate archive. The sublimation, dry deposition, and riming during the less Chimborazo is located at a borderline influenced by two humid periods of the year [3]. Sodium and chloride are different source regions of atmospheric moisture, the highly correlated (r2=0.9), but sea salt concentration Pacific, and the Amazon basin. The meteorological difference don't show the "distance from the coast" effect conditions in this region are also affected by the at the drilling site (Pacific/Atlantic is 200km/4000km) as displacement of the Intertropical Convergence Zone source indicator for atmospheric moisture. (ITCZ), and by El Nino/La Nina events which may influence the interannual variability. The displacement of Nevertheless, methanesulfonate (MSA) with a short life the ITCZ results in a bimodal precipitation regime, time in the atmosphere and produced by the oceanic characterized by two wet periods in the year. Stable biosphere shows higher concentrations during the February isotopes in monthly composites of precipitation in Ecuador to May period which could indicate a major Pacific clearly showed this shape. Similar results were obtained by moisture source. Formate on the other hand originates event-based precipitation sampling in the frame of the mainly from vegetation cover and shows a different ISOHYC project which aims at following the isotopic behaviour which is not in phase with MSA. This again may fingerprints of ENSO in a transect over the Andes. Up to point to a predominant source from the Amazon basin now, the ENSO modulated variability could only be (fig-2). checked by the long-term isotope record of Izobamba, (°/J MSA (ppb) (ppb) where it is less pronounced as in coastal regions [1; 2]. -20-18-16-14-12 o 10 20 0 100 200 300 3600 Dly2 3900 1 Dry] Wet) 4200 : 4500 • D,y2 CM Wai 2 4800 • 1 Dlyt • 5100 • Well , <4V ^ *C"*'. 5400 • Dly 2 5700 Wet 2 Yea 1 Dly \ 6000 Calcium Well 6300 Nitrate 0 200 400 600 Formiate (ppb) Fig. 2: Seasonal variations of 818O and chemical species Fig. 1: Chimborazo: Peak Whymper (6310 m) seen from from a section of the 1999 Chimborazo ice core. Peak Ventimilla (6250 m), the drilling site. These encouraging results finally led to the decision to In fact, not only the stable isotope record shows large sea- perform a bedrock drilling on Chimborazo. In Nov./Dec. sonal variations along the Chimborazo core, but also the 2000 in total 140 m of ice cores were recovered. The chemical constituents. The bimodal shape is clearly longest reached at a depth of 55 meters. More information observable in most of the years. We averaged the individual is available under: www.inamhi.gov.ee/Chimborazo2000 values according to more wet and dry periods, identified on the basis of 8I8O seasonality for three consecutive years modulated by the displacement of the ITCZ to examine the REFERENCES: behaviour of atmospheric constituents (fig.2). [1] M. Garcia, Villalba, F., Araguas-Araguas, L., and 18 Rozanski, K., Proc. Symp. IAEA, Vienna 1998. The most depleted 8 O values are associated with the [2] U. Schotterer et al., in preparation. maximum of precipitation during the southward movement [3] P. Ginot et al., submitted to J. Geophys. Res. of ITCZ from February to May, the second maximum during "veranillo" (Oct. to Jan) is less pronounced in the 144 GLACIOLOGICAL AND CHEMICAL SURVEY AT GLACIAR ESMERALDA, CHILE M. Schwikowski, S. Briltsch (PSI), G. Casassa, M.A. Godoi (Univ. de Magallanes), A. Giannini, A. Rivera (Geografi'a, Univ. de Chile), E. Vera, R. Adaros (Geofi'sica, Univ. de Chile), St. Kniisel (Univ. Bern & PSI), Ch. Kull (Univ. Bern) On 11th December 2000, snow samples were collected and a glaciological survey was performed at the upper part of glaciar Esmeralda on Cerro del Plomo in the Central Chilean Andes in order to explore the suitability of this glacier as palaeoatmosphere and climate archive. Glaciochemical results and the observed maximum ice thickness of about 100 m indicate that this glacier is a potential archive. 1 INTRODUCTION 3 GLACIOLOGICAL SURVEY The Cerro del Plomo (33°14'S, 70°13'W, 5424 m asl) is The radar system used is a portable HF impulse-type, located in an area influenced by the Westerlies circulation developed at Universidad de Magallanes and used system and is therefore assumed to receive precipitation successfully in glaciers of north-central Chile [2], Patagonia formed by humidity from the Pacific. Thus, its glaciers are [3] and Antarctica [4]. The transmitter was a Narod model potential archives for the reconstruction of the climate [5], powered by a 12 V battery, which generates a pulse of phenomenon El Nino. In addition, also the history of air 1100 V, a rise time < 2 ns and a pulse repetition rate of 512 pollution from Santiago might be accessible from pulses/s. Two 8 m-long dipole antennas loaded with palaeorecords, since the distance between Cerro del Plomo resistors were connected to the transmitter, generating an and Santiago is only 40 km. electromagnetic wave with a central frequency of about 6 MHz. Wires were inserted inside webbing tape, thus 2 GLACIOCHEMICAL STUDY protecting the antennas and allowing to use them as regular Eight surface snow samples and six snow pit samples of 2 mountain ropes [6]. The receiver consisted of a Tektronics cm thickness were collected from the upper, flat part of THS-720 digital storage oscilloscope, connected to glaciar Esmeralda at an elevation of about 5300 m. The receiving antennas (of the same characteristics as the samples were transported back to the laboratory in pre- transmitting ones) by means of a balun. Data were stored in cleaned polyethylene tubes, and concentrations of major the field with a Husky MP 2500 portable PC connected to ionic species were analysed by ion chromatography. the oscilloscope through the RS-232 port. Averaging of 16 Table 1 shows median ionic concentrations of the snow pit traces was performed using the oscilloscope, storing one samples in comparison to results of an analogous snow pit averaged trace every 4 s. from Cerro Tapado, which is located about 500 km further Surface coordinates were recorded every 1 sec with a single to the North [1]. For calculating the medians, the surface GPS receiver Trimble Geoexoplorer II, with single- layer affected by post-depositional processes such as frequency C/A code, which gave an accuracy of about +10 sublimation and dry deposition [1] was not considered. m in horizontal coordinates, and ± 20 m in elevation. Concentrations at glaciar Esmeralda are significantly lower Two profiles were measured at the upper part of glacier for all species except F, Mg2+, and Ca2+. This difference Esmeralda (Fig. 1), at an elevation of ca. 5330 m. The might be due to a larger amount of snow precipitation at the "transverse" profile started at the right (southeast) margin southern site, leading to a dilution of atmospheric species of the glacier and ended at the left margin (northwest), with scavenged by snow. a length of 390 m. The "diagonal" profile with a length of The crusty snow surface present indicated that sublimation 290 m started ca. 100 m from the left margin, ended at the influences glaciar Esmeralda. However, this effect seems upstream margin of the glacier, about 20 m from the rock less strong compared to Cerro Tapado, since the glacier ridge of Cerro del Plomo. Both profiles intersected near the surface was flat and no penitents were formed. As already central point of the upper dome of glaciar Esmeralda. described for the Cerro Tapado glacier [1], post- Surface gradient is small in this section of the glacier, with depositional effects such as sublimation and dry deposition an average slope of 3 % for the diagonal profile, and 5 % result in a strong enrichment of most ionic species in the for the transverse profile. A raster display of the radar data topmost snow layer. This is also observed at glaciar is shown in Fig. 2, corresponding to the transverse profile. Esmeralda as indicated by the enrichment ratios (ER) in The glacier bed is shown as a V-shaped valley with a Table 1, which are defined as ratios of the surface snow and maximum ice thickness near the centre of the profile. Due the snow pit median concentrations. In agreement with to the shallow ice thickness, bed echoes are strong, but in results from Cerro Tapado, hydronium (H+) as well as the part masked by the direct airwave. Radar data were processed to attenuate the direct airwave, and then migrated organic acids acetate (H3CO2) and formate (HCO2) were lost from the surface due to sublimation, as indicated by to correct for the geometric effect due to the strong bed low ER values. Chloride (Cl), calcium (Ca2+), sodium slope of the glacier. As expected, the bed appears as a U- + + shape valley in the migrated profiles, with two-way travel (Na ), and ammonium (NH4 ) were most strongly enriched, caused by sublimation as well as dry deposition, whereas times which are about 18 % larger than the non-migrated + travel times, and migrated ice thickness values about 8 % potassium (K ), fluoride (F), nitrate (NO3), magnesium 2+ 2 larger than the non-migrated values. (Mg ), and sulphate (SO4 ) showed an intermediate behaviour. Considering the migrated results, and 170 m/|^s for the electromagnetic wave speed in ice, maximum ice thickness in the transverse profile was 98 m, corresponding to a two- 145 way travel time of 1.17 |J.s. In the diagonal profile, ACKNOWLEDGEMENTS maximum ice thickness was 106 m, corresponding to a two- The work was supported by the Swiss National Science way travel time of 1.26 [is. From these results, a deep basin Foundation, Project 2100-050854.97. Part of the radar work with ice thickness of about 100 m is found in the central was funded through project FONDECYT 1980293. We part of the upper section of glaciar Esmeralda. Steep bed thank Cesar Acufia who drew the map and Carlos Cardenas slopes exist within this basin, with maximum values of 47% and Jose Araos for their help with the radar figures. (transverse profile) and 59% (diagonal profile). Precision of the radar results can be assessed by comparing the migrated ice thickness at the intersection of both REFERENCES profiles. According to the transverse profile, the ice [1] P. Ginot et al., submitted to J. Geophys. Res. thickness at the intersection is 90 m, and according to the [2] A. Rivera et al., Ann. Rep. Univ. Bern & PSI 1999, diagonal profile it is 114 m. The average value at the p. 38. intersection is therefore 102 ± 12 m (± 13%). This error [3] G. Casassa, A. Rivera, Anales Instituto Patagonia, value is considered to be an adequate estimate of the ice Serie Cs. Nat. (Chile) 26, 129 (1998). thickness error. The relatively large error value of 13 % is [4] G. Casassa et al., FRISP Report 12, 7 (1998). due to the steep bed slopes present in the study area. A [5] B. B. Narod, G. K. Clarke, more complex 3D migration could reduce substantially this J. Glaciology 40, 190 (1994). error, but to achieve that, a complete gridded set of radar [6] A. Gades, PhD thesis, University of Washington, data would be needed. (1998), p. 192. Table 1: Median concentrations in |a.eq 1' of ionic species in snow pits from glaciar Esmeralda and Cerro Tapado. Enrichment ratios (ER, ratio between medians of surface snow and snow pit samples) al glaciar Esmeralda are also shown. H+ H,CO, HCO, K" F NO, Mg- SO," a Ca3* Na" NH; Esmeralda 2.5 0.04 0.11 0.09 0.0J 1.30 0.25 2.10 0.37 1.29 0.25 0.05 Tapado 7.9 0.73 0.70 0.25 0.02 6.16 0.34 5.90 1.62 L63 o.sa 0.47 ER 1.7 1.39 2.09 3.77 4.40 4.86 7.05 7.32 10.7 UA 15,1 22,] TOPOGRAPHY OF CERRO DEL PLOMO GLACIER TRANSVERS E WITH THE LOCATION OF THE RADAR PROFILES in in HI z ii o X H I-00 luu 2UU 3UO DISTANCE (m) Fig. 2: Non-migrated raster image of radar data corresponding to the transverse profile. The glacier surface (time zero) appears flat because it has not been corrected using the GPS elevation data. The glacier bed is the V-shaped reflection which appears dark on the image, with a maximum migrated depth of 107 m. Time represents non- migrated two-way travel time. Thickness is calculated from the migrated travel time. Fig. 1: Map showing the transverse and diagonal radar profiles. Glacier extensions are taken from the 1:50.000 scale map of Instituto Geografico Militar, and include some areas of rock covered by snow. Glaciar Esmeralda and glaciar el Plomo are separated by a rocky ridge at ca. 5350 m. The upstream end of glaciar Esmeralda is indicated by the broken line "ice limit". 146 THE INFLUENCE OF SUBLIMATION ON STABLE ISOTOPE RECORDS RECOVERED FROM HIGH ALTITUDE GLACIERS IN THE TROPICAL ANDES U. Schotterer (Univ.Bern), W. Stickler (Institute for Hydrology, Neuherberg), K. Frohlich (Vienna), P. Ginot (Univ.Bern & PSI), Ch. Kull (Univ.Bern), H.W. Gdggeler (Univ.Bern & PSI), B. Pouyaud, (IRD, Lima). Sublimation dominates the ablation process on cold, high-altitude glaciers in the tropical Andes. By altering the isotopic composition of the surface snow layers this process may disturb the climatic information. On Cerro Tapado (Chile) it could be demonstrated that in general the isotopically enriched surface layers are constantly sublimated and the downward flux of enriched isotope species is blocked by re-condensation of moisture during night. To reveal information about past physical and chemical The main features of the model include the description of changes in the atmosphere from glaciers in the tropical the isotopic enrichment at the surface by a net diffusive flux Andes the influence of sublimation has to be ruled out first. of 82H and 818O into the interior of the firn profile. Transport of water vapour through the firn and exchange Moreover, a time-dependent co-ordinate system (its origin with ambient humidity alter the stable isotope composition is defined by the firn surface) accounts for the firn loss at (and the chemistry) of the surface layers. As an example, the surface in terms of an apparent advective movement of seasonal changes in evaporation of snow may remarkably the firn layers towards the surface. The velocity of this amplify seasonal changes in S18O (1). To assess post-depo- movement, equal to the sublimation rate, reproduced the sitional influences on ice cores from arid environments like experimental data of the latter in the same order of on Cerro Tapado (5536 m, 30°08' S, 69°55' W) a magnitude. (Mass loss obtained by sublimation pans does sublimation experiment was carried out [Stickler et ah, not include the re-condensation of water vapour from submitted]. deeper layers). li-'i-n Fi'< •-. • i Ivai Fig. 2: Measured and calculated change in 8 O and Fig. 1: For uniform conditions the uppermost 7cm from deuterium excess at the firn surface versus time. the pit were removed for the experiment. The results of this study suggest that under comparable The measurements of a newly created surface at 7cm depth environmental conditions the influence of sublimation on the isotope record of ice cores is rather limited and of minor (sampled twice a day for 31/2 days) showed the same 2 2 18 importance. In any case simultaneous measurements of S H strong enrichment in 8 H and 8 O as the original surface I8 layers down to that depth. Concerning the deuterium excess and 8 O (change in slope) may help to identify suspicious d, the strong decrease occurred at daytime while during the layers deeper in a core which remained influenced due to night the values remained comparatively constant. At different environmental conditions. However, major daytime the sublimation is enhanced due to the higher consequences are to be expected for the interpretation of the moisture deficit of the ambient air accompanied by variability of chemical species. The large differences relatively high firn surface temperatures. Low surface between volatile, soluble, and insoluble components caused temperatures at night cause condensation of water vapour in by sublimation and obtained by the same experiment are the firn pores near the surface and thus inhibit penetration discussed in detail elsewhere [Ginot et al., submitted]. of the isotopically enriched surface front into deeper firn layers. This explanation was not only supported by the REFERENCE isotope profile obtained from the little snow pit through detailed sampling down to 38cm; the modification of the [1] P. M. Grootes, M. Stuiver, L. G. Thompson, and isotopic composition at the surface could be described E. Mosley-Thompson, Oxygen Isotope Changes in quantitatively by a model too. Tropical Ice, Quelccaya, Peru, J. Geophys. Res. 94, No. Dl, 1187(1989). 147 ANALYSIS OF DUST LAYERS IN AN ICE CORE FROM CERRO TAPADO, CHILE S. Olivier (Univ. Bern), H.W. Gaggeler, P. Ginot (Univ. Bern & PSI), M. Schwikowski (PSI) The concentrations of insoluble particles in an ice core from Cerro Tapado were measured with a Coulter Counter. In order to determine the occurrence of certain mineral dust tracers (aluminium (Al), calcium (Ca), iron (Fe), magnesium (Mg), and mangan (Mn)), the ice samples were additionally analysed with ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry). The precipitation regime at the Cerro Tapado (5536 m, A good correlation between the particle number and the 30°08'S, 69°55'W, Chile) is discontinuous: wet season concentrations of the insoluble mineral dust tracers Al and during the austral winter, and a long dry season from Fe (but also Mg, Mn, and Ca) is observed. Assuming that September to April. As a consequence, mineral dust layers the dust layers are due to the dry seasons, a mean annual are formed on the glacier surface during austral summer as accumulation of water over the analysed ice section of 0.41 a result of post-depositional processes like dry deposition of ± 0.21 m w.eq. results, which is in agreement with the 0.31 dust or ice sublimation [1]. Using these horizons it should m w.eq. determined for the upper 10.5 m w.eq. of the ice therefore be possible to identify annual layers for dating core [2]. purposes. The record of insoluble particles was compared with the In order to detect the dust layers, the suitability of the two record of soluble Ca [3] determined by ion chromatography following methods was tested: (IC), which has already been used as a tracer for the dry period. Ca is assumed to be irreversibly deposited and First, the number of insoluble particles (1-30 Jim) in the ice enriched due to ice sublimation and dry deposition during core section from 13.7 to 16.6 m water equivalent (w.eq.) the austral summer [1] (Figure 2). was determined with a Coulter Counter Z2. The Coulter method of counting and sizing is based on the detection and measurement of changes in electrical resistance produced by a particle suspended in a conductive liquid passing through a small aperture. soluble Ca insoluble Al Second, the melted and acidified samples of the same section were analysed with ICP-OES. The concentrations of insoluble Al, Ca, Fe, Mg, and Mn were used as mineral dust tracers. In order to determine the insoluble fractions, the soluble fractions were subtracted from the overall concentrations. For the measurement of the soluble fractions, a part of each ice sample was filtered through a 14.8 15.3 15.7 0.2 |J,m membrane. Al and Fe were found almost Cbre-depth [mw.eq.] exclusively in the insoluble fractions (all filtrate Fig. 2: Records of the concentration of soluble calcium concentrations were below the detection limit, which is 20 (bold line) determined by IC and of insoluble ppb for Al and 10 ppb for Fe). On the other hand, soluble aluminium (continuous line) determined with ICP- Ca, Mg, and Mn contributed up to 95% to the total OES. Weighted running means over approx. 0.1 m concentration of these elements. (3 samples) are shown. The records of the particle number concentration (PN) and of the concentrations of insoluble Al and Fe are shown in Figure 1. Contrary to the signature of the dust tracers (e.g. insoluble aluminium or particle number), soluble calcium shows only one significant peak at 14.1 m w.eq. and a smaller one at 15.2 m w. eq.. In conclusion, the selected mineral dust tracers can be used for dating purposes even in core sections with a missing seasonal stratigraphy of soluble Ca. Thus, the application of these tracers opens up the possibility of dating by annual layer counting of ice cores from glaciers with a discontinuous precipitation regime. REFERENCES [ 1 ] P. Ginot et al., submitted to Fig. 1: Records of the concentrations of insoluble Fe J. ofGeophys. (2000). (dashed line) and Al (continuous line) and of the [2] U. Schotterer, personal communication. particle number PN (bold line). Weighted running means over approx. 0.1 m (3 samples) are shown. [3] P. Ginot, personal communication. The arrows indicate assigned dust layers. 148 FIRST GLACIO-CHEMICAL INVESTIGATION OF BELUKHA GLACIER IN THE SIBERIAN ALTAI M. Schwikowski, A. Schmitz, S. Brütsch, F. Stampfli (PSI), H.W. Gäggeler (Univ. Bern & PSI), M.Funk (VAW), U. Schotterer (Univ. Bern), T. Papina, St. Eyrik, S. Temerev (IWEP, Barnaul), A. Saprykin, O. Shuvaeva (IIC, Novosibirsk), V. Galakhov (Altai State University) In an exploratory study a shallow firn core was recovered and a glaciological survey was undertaken at Belukha glacier in the Siberian Altai. Chemical records along with a sufficient ice thickness indicate the suitability of this glacier as palaeoatmospheric archive. Thus, a deep drilling is planned for summer 20001. The Central Eurasian Altai mountain range is located on precipitation. In summer, atmospheric transport to high- the boundary between East Kazakhstan, Southwest Siberia, mountain sites is enhanced and the non-vegetated areas Northwest China, and Mongolia. It forms a natural barrier surrounding the glacier are snow-free, both facilitating for trans-boundary transport of air pollutants emitted mineral dust deposition. Because only one summer especially from heavy metal mining and metallurgically maximum is observed in the record, we assume that the 6 used areas of East Kazakhstan and Southwest Siberia as m of firn represent approximately the precipitation of one well as of radionuclides released into the atmosphere by the year. Semipalatinsk nuclear test site. The maximum ice thickness measured was 150 m, and the For the reconstruction of air pollution levels in the Altai firn temperature at 6 m depth was -1.4°C. With this region, glacier ice cores are among the privileged paleo relatively high temperature, the occurrence of meltwater archives. Although the Altai mountain range is formation can't be excluded. However, as discussed above, considerably glaciated, most of the glaciers are located at the stratigraphy of chemical species seems to be essentially elevations significantly below 4000 m asi and are therefore unaffected by melting processes. assumed to be affected by meltwater percolation. The aim 35- of this study was therefore the search of a suitable, i.e. cold Ammonium glacier and the drilling of an exploratory shallow firn core 30- Sulphate at the selected site. The main purpose of analysing this shallow core was the identification of possible melt features and of seasonal layers. The Belukha is the highest mountain in the Altai (4506 m asi) and a glacier located immediately west of Belukha (49°48'49"N, 86°32'29"E, 3895 m asi) was selected for the first glacio-chemical investigation. On 12 July 2000, a 6 m firn core was drilled and snow samples were collected from a 1.5 m deep snow pit. Radio echosounding was performed to determine glacier thickness and the temperature in the borehole at 6 m depth was measured. 120 •4E+05 Firn core and snow pit samples were transported in frozen condition to the Institute of Inorganic Chemistry in Insoluble particles Novosibirsk, where the firn core was cut into 3.5 cm -3E+05 segments and packed in pre-cleaned containers. From Novosibirsk to PSI samples were also transported in frozen condition, cooled with dry ice. CO In firn core and snow pit samples concentrations of major CL ionic species and of insoluble particles were analysed by -1E+05 ion chromatography and by the Coulter Counter technique. The stable isotope ratios 818O and 8D were determined by isotope-mass spectrometry, pH and conductivity by pH- + 12 3 4 5 electrode and conductivity cell. Concentrations of NH4 and 2 Depth below snow surface (m) SO4 " in the 6 m firn core fluctuated largly, but both were highly correlated (Fig. 1). Since a study on an Alpine ice core showed that meltwater percolation influenced the + 2 2 Fig. 1: Concentrations of NH4 and SO4 (upper panel) as concentration of SO4 ~ significantly, whereas the 2+ + well as of Ca and insoluble particles (lower stratigraphy of NH4 remained undisturbed [1], we assume that melting processes were of minor importance in the top- panel) along the 6 m firn core. most 6 m firn layer. Especially the concentrations of Ca2+ and insoluble particles show a pronounced maximum between 0.5 and 2.5 m depth (Fig. 1). Both species are REFERENCE normally associated with mineral dust and we therefore [1] A. Eichler et al., Tellus, in press. assume that the maximum is related to summer 149 CONTINUOUS MELTING AND ION CHROMATOGRAPHIC ANALYSES OF ICE CORES T. M. Huber, H.W. Gaggeler (Univ. Bern & PSI), A. Gaschen, M. Schwikowski (PSI) With the continuous melting and ion chromatographic analyses, a new method was developed which combines the advantages of the continuous flow analysis with ion chromatography as a multi-component analysis technique. The new method is well suited to quantify the overall amounts of ionic impurities in ice and to resolve their concentration patterns. The common way of analyzing ice cores is to remove the 200 possibly contaminated outer parts, cut the inner cores in 15 pieces, melt them and analyze each piece separately (see e.g 'M ° [1, 2]). This procedure is time-consuming and prone to contamination. By continuously melting and analyzing the % 100 ice cores, these two effects can be reduced. This so called continuous flow analysis (CFA) [3] was successfully U applied for recording concentration profiles of different 0 tracers in Greenland and Antarctica [4, 5]. However, the Coitveittsonal Analysis CFA technique requires a separate detector for every spe- i- 210 Continuous Melting cies analyzed. Not for every species of interest a detection DXI and Analysis reaction sensitive enough exists. Thus, the number of possible analytes is limited. Udisti et al. [6] used a melting ^ 140 device coupled with an ion chromatograph in order to de- termine chloride, nitrate and sulfate. However, only semi- I 70 continuous data sets could be achieved. ^ 0 "I- 400 Our approach is to take advantage of the full potential of M ion chromatography as a multicomponent analytical method " 300 and to couple it to a melting device in order to determine continuously organic anions (acetate, formate, oxalate and •a 200 e methanesulfonate) as well as inorganic anions (fluoride, S loo chloride, nitrate and sulfate) and cations (sodium, ammo- nium, potassium, magnesium and calcium). A detailed < 0 description of the setup can be found in [7]. 20 40 60 80 100 In order to verify the new continuous melting and analysis Depth [cm] method, a 95.5 cm long section of an ice core (density 0.87 g cm"1) from Grenzgletscher (Swiss Alps, Monte Rosa Massif, 4200 m asl.) was analyzed and the results compared Fig. 1: Concentration profiles of chloride, formate and to those obtained by the conventional technique. The reso- ammonium determined by continuous melting and lution for the continuous melting at a melting head tem- analysis (black curve) and conventional analysis perature of 35 °C was 3 cm, while the resolution for the (gray curve). conventional analysis was 5 cm. The concentration profiles of chloride, formate and ammo- nium obtained with the two different methods are shown in REFERENCES Fig. 1 as examples. The profiles for chloride and ammo- [1] M. Legrand et al., J. Chromatogr., 640, 251 (1993). nium agree well, i. e. both the absolute values and the spa- tial patterns are reproduced by the two methods. The con- [2] M. Schwikowski, Chimia, 51, 786 (1997). centrations of formate determined by the new method tend to be lower, particularly for concentrations below 20 (Xg I"1. [3] K. Fuhrer et al., Atmos. Enivron., 27A, 1873 (1993). This is attributed to a higher blank value of the conven- [4] A. Sigg et al., Environ. Sci. Technol., 28, 204 (1994). tional technique, indicating contamination during sample preparation and contact with laboratory air. [5] R. Rothlisberger et al., In order to compare the performance of the two methods for Environ. Sci. Technol., 34, 338 (2000). all species analyzed, the total amounts of ions in a hypo- [6] Udisti et al., Annals of Glaciology 30, 20 (2000). thetical sub-core of 1 cm2 cross-section and 95.5 cm length were calculated. The amounts calculated for both methods [7] T. Huber et al., submitted to J. Chromatogr. (2000). agree well (linear regression: correlation coefficient 0.991, slope 0.991, intercept -0.575). Thus, the newly developed method is well suited for the analysis of ice cores. 150 PRELIMINARY RESULTS OF TRACE ELEMENT ANALYSIS IN ICE CORES BY CONTINUOUS ICE MELTING (CIM) ICP-MS St. Knusel, T. Huber (Univ. Bern & PSI), M. Schwikowski (PSI) and H.W. Gaggeler (Univ. Bern & PSI) In order to analyse a set of trace elements in ice cores, a new method, continuous ice melting inductively coupled plasma mass spectrometry (CIM-ICP-MS) has been developed. The main advantages are a less time-consuming sample preparation, a reduced risk of contamination, and the possibility to obtain a higher spatial and therefore temporal resolution of the trace element records. INTRODUCTION The melting head separates the melt water in an inner, un- contaminated flow and in an outer, possibly contaminated Aerosol related chemical trace species deposited with snow flow. As illustrated in Fig. 1, the inner melt water is, after are the key parameters to identify air mass origin. Using passing a degaser, acidified (0.1 M HNO3) and an internal typical chemical signatures, marine, volcanic, arid or vege- standard (103Rh) for the analysis by ICP-MS is added. tated terrestrial, biomass burning, and anthropogenic Afterwards, the melt water is introduced in the ICP-MS by sources of air masses can be identified and temporal an HPLC pump. changes of the contributions of the various sources can be investigated. In order to reconstruct historical El Nino and La Nina periods using an ice core from Illimani, Bolivia FIRST RESULTS (6430 m, 16°39'S, 67°47'W) [1], one approach is to char- The CIM-ICP-MS method was tested by analysing a 60 cm acterise air mass origins related to precipitation formation ice core from the Alps, and comparing the results with during this periods. For this purpose, a set of trace elements those from conventional analyses. Although the concentra- will be analysed in the ice samples by ICP-MS. tion patterns could be reproduced by the new method for a part of elements, as illustrated in Fig. 2 for 79Br, the abso- The conventional procedure of preparing ice samples for lute concentrations obtained by CIM-ICP-MS were signifi- trace element analyses is a mechanical decontamination cantly lower. Possible reasons are adsorption processes on under clean room conditions at -20°C [2]. The outer layers the walls of the capillaries, connecting the melting-head are removed by chiselling, which is a time-consuming with the nebulizer of the ICP-MS, differently filtered sam- process with a high risk of contamination. An additional ples, insufficient acidification, and contamination of con- disadvantage of this procedure is the limitation in spatial ventionally prepared samples. and subsequently temporal resolution. Therefore, a new method has been developed: the coupling of a melting de- 4TO0 - vice [3] with an ICP-MS (ELEMENT, Finnigan MAT), which allows a continuous decontamination and melting as 3500 - well as analysis of the ice core. 3 3TO0 - & 2'500 - THE PRINCIPLE OF THE MELTING g The continuous ice melting (CIM) ICP-MS consists of an | 21300 - ice-melting device, which was developed for continuous S 1500 - melting and ion chromatographic analyses of ice cores [3, U 1TO0 - 4], and which has now been coupled to the ICP-MS. Br-79, CIM -»-Br-79, conventional 500 - 0 0 10 20 30 40 50 60 . Deep TTIXVLT. -20"C Depth [cm] Fig. 2: Depth profile of Br in an ice core from the Alps, Infusion pump ICP- comparison CIM-ICP-MS with conventional NO MS analysis. In future, the dead volume will be significantly reduced in order to minimise adsorption processes. In addition, the Degaser Mixing Tee Nebulizer contamination will be controlled and the acid strength, if necessary, adapted.REFERENCES [1] St. Knusel et al., this Annual Report. [2] L. Tobler et al., Ann. Rep. Univ. Bern & PSI 1999, p. 42. Fig. 1: Schematic of CIM-ICP-MS. [3] T.M. Huber et al.,submitted to J. Chromatography A. [4] T.M. Huber et al., this Annual Report. 151 FIRST APPROACH TO DETERMINE CONCENTRATIONS OF MERCURY IN ICE CORES BY COLD VAPOUR ICP-MS S. Eyrikh (IWEP), L. Tobler, M. Schwikowski (PSI), H.W. Gaggeler (Univ. Bern & PSI) The very low concentrations of Hg expected in snow and ice samples require an extremely sensitive and accurate analytical technique as well as a contamination-free methodology. The potential of Cold Vapour ICP-MS for Hg determination was tested and first experiments on standard and sample handling were conducted. 1 INTRODUCTION concentration was observed, as shown in Fig. 1. The intensity of the Hg signal increased steadily until the acid One of the major questions connected with the present concentration reached 0.5 to 1 N HNO , where it became environmental mercury problem is the historical trend. 3 sufficiently stable. Thus, we consider 0.7 N HNO as Some attempts to estimate global "pre-industrial" emissions 3 optimal acid concentration. to the atmosphere have been made from Greenland ice core data. High mercury concentrations (10-230 ppt) reported in The reproducibility for 200Hg and 202Hg in the same sample earlier studies of ice cores and snow from polar region are (10 determinations) was RSD=3.0 and 2.7%, and in 20 likely incorrect [1]. During recent years new analytical different blank samples RSD=3.1 and 3.4%, respectively. techniques have become available, these include ultra- sensitive and specific analytical equipment and In a solution of 100 ppt Hg, a loss of Hg after 17 days of contamination-free methodologies. Concentrations of Hg as storage at 4°C was observed as shown in Fig. 2. The loss low as 0.19-2.21 ppt were reported from a Greenland ice was most pronounced for Hg solutions with low acid core [2], whereas higher values were found in snow concentrations. Thus, the most important process seems to samples collected on the ice cover and on the hill be the loss of Hg onto the walls of the sample tubes, and surrounding the Lake Baikal, Siberia (8.6-60 ppt) [3]. In not contamination. both studies, sampling was carried out following 250000 -| recommendations of a protocol for ultra-clean work. Hg ^*^20pptHg, —^^100 ppt Hg Q. 200000 concentrations in our snow samples, which were collected o j-i-a- °— • at Belukha glacier in the Siberian Altai [4], should be in the above-mentioned range (as low as few ppt). isit y AV , 2 ANALYTICAL TECHNIQUE 0 0.5 1 1.5 2 2.5 Inductively coupled plasma mass spectrometry (ICP-MS) is Concentration of nitric acid, N valued for its multi-element capability and its excellent detection limits for many elements. However, in case of Hg 2 2 Fig. 1: Dependence of Hg signal on HN03 concentra- it suffers from bad transport and ionisation efficiencies, tion. which can be greatly improved by using cold vapour generation. There, Hg gas is separated from the liquid sample, and is effectively transferred into the plasma, where ionisation takes place under very dry conditions not loaded with aerosol. In this study we equipped our ICP-MS (ELEMENT, Finnigan MAT) with a Hydrogen Generator having a membrane gas-liquid separator design [5] and optimised the analysis parameters such as pump speed and wash time for Hg determination. 0.1 0.15 0.3 3 METHODOLOGY SET-UP Concentration of nitric acid, N Both contamination and loss of Hg are possible during 202 storage. The instability of Hg solutions is explained by the Fig. 2: Loss of Hg from standard solution after 17 days specific Hg properties: high volatility of Hg°; ability of of storage at 4°C. dissolved Hg2+ to be reduced to Hg°; adsorption of dissolved Hg on suspended particles and vessel walls; contamination REFERENCES from vessel, reagents, and from air diffusing through the [1] H. Appelqvist et al., Nature 273, 657 (1978). plastic vessels. Normally, Hg solutions are stabilised by [2] J.M. Vandal et al., Nature 362, 621 (1993). acidification with HNO3. Therefore, the influence of acid concentration on the intensity of the Hg signal was tested. [3] M. Leemakers et al., in: Global and regional mercury In addition, the stability of Hg solution kept at 4°C in a cycles, W. Baeyens, R. Ebinghaus, O. Vasiliev (eds.), refrigerator was studied. Kluwer Academic Publishers, p. 307 (1996). 4 RESULTS [4] M. Schwikowski et al., this Annual Report. [5] B. Klaue, J.D. Blum, Anal. Chem., 71, 1408 (1999). Various HNO3 concentrations were applied on a blank, and on standards with concentrations of 20 ppt and 100 ppt Hg. A strong dependence of the obtained Hg signal on acid 152 DETERMINATION OF TOTAL DISSOLVED SILICON FOR3 Si DATING OF GLACIER ICE U. Morgenstern (GNS, New Zealand), L. Tobler, M. Schwikowski (PSI), H.W. Gdggeler (Univ. Bern & PSI) Cosmogenic J2Si has potential for dating ice cores in the time range of 50-1000 years. Accelerator mass spectrometry (AMS) is used for measurement of the 31Si/Si ratio, and to derive 32Si concentrations, independent analysis of stable silicon is necessary. Results of Si determination in NZ glacier snow and ice by high resolution ICP-MS are presented. 1 INTRODUCTION concentrations. After a washout time of 3 h of the ICP-MS an overall blank of 14 ppb Si was obtained, with a detection Ice cores provide a wealth of palaeoclimate information, limit of 5 ppb (3a criterion). and low- to mid-latitude glaciers offer a unique opportunity Additional to silicon, the sulphur concentration was to study regional patterns of climate change over recent determined in the ice samples. Sulphur recovery in the ion millennia. However, most stratigraphies of mountain exchange process was not calibrated at the time of glaciers are incomplete, and dating techniques based on extraction, but we assume it to be similar to Si. Because counting annual layers are limited. sulphur is the main interference for 32Si AMS measurement, Cosmogenic 32Si, with half-life of ca. 140 years, is ideally an estimate of the sulphur concentration in the sample can suited to provide the necessary time information. However, indicate the demands on chemical purification of the AMS only accelerator mass spectrometry (AMS) is able to samples. provide the required high sensitivity for ice core analysis. Recently this technique became available for measurement 3 RESULTS of 32Si/Si in natural samples [1]. 32Si/Si ratios above the AMS detection limit are found only in snow and ice In Fig.l the concentrations for Si and S in the ice samples samples with low total Si. For 32Si dating, one difficulty is are presented. For many samples Si cone, is below 2 ppb. the AMS measurement of the 32Si/Si ratio. The other These were the samples with no visible dust in the challenge is to determine accurately such low Si meltwater. All the samples with Si > 5 ppb had visible dust concentrations. in the meltwater. We assume, therefore, that the increased Si concentrations are due to dissolution of Si from dust. 2 EXPERIMENTAL 60 We analysed snow and ice samples from the Franz Josef glacier, New Zealand (43°S, 170°E, ca. 2,200 m a.s.l.), for 50 total dissolved Si. NZ's glaciers contain very little dust in the region of snow accumulation. Si concentrations were • Si 40 therefore expected to be below 10 ppb, too low to be a. determined directly with any method. Thus, Si was pre- concentrated by ion exchange [1] to shift the Si 30 concentration into a range were it can be analysed with at § least 5% accuracy. To keep the initial amount of sample for 20 Si analysis small (< 100 g), an analytical method with high sensitivity is necessary such as high resolution ICP-MS. 10 The analysis of silicon (three stable isotopes with 28 29 30 abundances Si 92.23%, Si 4.67%, Si 3.10%) by a 0 • •••••» • • quadrupole ICP-MS is not possible due to interference Fig. 1: Si and S concentration (dissolved) in snow and ice mainly from N2 and CO2 on all three Si-masses. Table 1 lists the possible interferences of the 3 Si-isotopes and the samples from Franz Josef Glacier (NZ). resolution needed to resolve them. The concentration of sulphur in the ice and snow samples is typically 5-10 times that of silicon. Therefore, total sulphur Table 1: Interferences of the 3 stable Si isotopes suppression in the sample material (containing only a few ug Si) of > 1016 is necessary for AMS analysis. Suppression Isotope Interferences Resolution of ca. 10" can be achieved within AMS systems with a gas- !8 I2 16 + 14 + filled magnet. Therefore, sulphur concentration in the target Si C O , N2 1556, 958 material must be reduced by a factor > 105 prior to AMS !9Si I2C16OH+, 15N14N+ 1104,1086 measurement, which might be achieved by heating the )0 14 16 + 12 18 + 13 16 + Si N O , C O , C OH 1238, 1181,927 sample material to more than 1000°C in hydrogen A double focussing ICP-MS (Elementl, Finnigan MAT) atmosphere. was used to determine silicon in medium resolution (R = REFERENCE m/Am = 3500). Silicon from the glass material (spraychamber, torch etc), [1] U. Morgenstern, L. K. Fifield , A. Zondervan, the ultrapure water and acids, used to dilute standards and Nucl. Instrum. Meth. B 172, 605 (2000). to wash sample containers, and from the sample containers present a blank problem in the determination of ultra low Si 153 APPLICABILITY OF TXRF FOR TRACE ELEMENT ANALYSIS IN ICE SAMPLES N.L. Misra, L. Tobler, M. Schwikowski (PSI) Total Reflection X-ray Fluorescence (TXRF) Spectrometry has been used to analyse trace elements in ice sample. The results were compared with the results of ICP-MS. For some samples and elements agreements in results of ICP-MS and TXRF are satisfactory but for others the difference is significant, probably due to heterogenity of the samples because of presence of insoluble matter. Ice samples from glacier ice cores contain elements in a were earlier analysed by ICP-MS a comparison between wide range of concentrations. As an illustration, Ca in ice these analysis results was made. The agreement between samples analysed in this laboratory varied from 1.5 to 6400 TXRF and ICP-MS results was in many cases not ppb whereas U varied from 0.2-30 ppt. Though ICP-MS is satisfactory. For the elements Ca, Mn, Zn, Pb, Rb and Sr a technique, which has excellent detection limits, and is generally the ratio of their amounts determined by TXRF being used for ice sample analysis, there are some problems (W Tube) and ICP-MS varied between 0.30-3.00. For the when samples contain insoluble particles. In recent years elements Sc, V, Cr, Ni, Th and U this ratio was far away TXRF has been used in trace elements analysis of various from unity. A scatter plot of concentrations of Ca environmental samples and has been proven to be capable determined by ICP-MS and by TXRF (W tube) is shown in to analyse solutions as well as suspensions up to a certain Figure 1. extent [1,2]. In the present work the possibility of using TXRF for trace element analysis in ice samples was 1400 1:1 explored. 1200 jr 1000 A TXRF spectrometer developed at PSI [3] was used. Two modes of element excitation, Mo tube having mainly Mo •i 800 S 600 Ka (55 kV, 10 mA) and W tube with mainly continuum (40 kV, 10 mA) were used. Relative sensitivities for elements P •f 400 (Z=15) - Y (Z=39), Pb, U and Th were determined using 200 suitable multielement standards (MES). Detection limits of the elements were determined using these data. They varied 0 200 400 600 800 1000 1200 1400 from 2.3 ppm to 10 ppb and 1 ppm to 56 ppb for S (Z=16) - Ca (ppb) by W Tube Y (Z=39) using Mo and W excitations, respectively. A multielement standard with concentrations of 20 ppm of the Fig. 1: Comparison of results of Ca analysis in eight ice elements P, K, Ca, V, Cr, Mn, Fe, Co, Ni, Zn, Ga, Ge, Rb samples by TXRF (W Tube) and ICP-MS and Sr was analysed using Y as internal standard. The results were within 15% of the expected values except for Although the agreement between TXRF results using W or K, Fe and Zn. Similarly with the W tube MES containing Mo tube is satisfactory, the discrepancy between TXRF and the elements P, S, K, Ca, Sc, V, Cr, Mn, Fe, Cu, Zn, Ga, ICP-MS results is obvious. This discrepancy might be As, Se, Y, Zr, Nb, Hg and U were analysed using Y and Co explained by a non-uniformity of the ice samples, possibly as internal standards. The results were within 20% of the due to insoluble particles present in the ice, or by problems expected values. in the preconcentration step. Thus, future work is needed to be able to explain the disagreement between TXRF and TXRF spectra of ice samples show very weak intensities of ICP-MS. X-ray lines indicating that pre-concentration is necessary before analysis. Preconcentration studies were made under ACKNOWLEDGEMENT class 100 clean room conditions on a multielement standard containing S, Ca, Cr, Co, Ge, Hg, Rb and Nb with Financial support for the work from ICSC-World Labora- concentration of 0.74 ppb for each element. The solution tory is kindly acknowledged. We thank F. Hegediis for his was subjected to evaporation under an IR lamp. The help in operating the TXRF spectrometer. recovery for the elements varied up to 20% from the expected values, except for Hg with a variation above 30%. REFERENCES Preconcentration studies on ice samples showed a variation of 15% in recovery for elements present in higher [1] R. Klockenkamper, concentrations (e.g. Ca). However, the recovery for low Total Reflection X-ray Fluorescence Analysis, atomic number elements or elements present in very low John Wiley & Sons, Inc. New York (1997). concentrations showed large differences from the expected [2] L. M. Muia, F. Lahatra Razafindramisa, and R.E.Van values. Four ice samples from Colle Gnifetti glacier (Swiss Grieken, Spectrochim. Acta 46 B, 1421 (1991). Alps) were analysed for the elements P, S, K, Ca, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Pb, Th and U using Mo tube. [3] F. Hegediis, Chimia 46, 477 (1992). Similarly, eight samples were analysed using W tube. Out of these eight ice samples, four were the same as measured with Mo tube, but the specimens were freshly prepared. The results obtained by Mo and W tube showed in general a good agreement. As some of the elements in these samples 154 7Be AND 10Be CONCENTRATIONS AT THE HIGH-ALPINE SITE JUNGFRAUJOCH L. Tobler, P.W. Kubik, M. Schwikowski (PSI), H.W. Gaggeler (Univ. Bern & PSI), C. Schnabel (Univ. Bern & ETHZ) The atmospheric concentrations of the cosmogenic radionuclides 7Be and 10Be have been measured at Jungfraujoch (3580 m a.s.l) within the EU project STACCATO (Influence of Stratosphere-Troposphere Exchange in a Changing Climate on Atmospheric Transport and Oxidation Capacity). The isotopic ratio wBe / 7Be is used as a probe for the intrusion of relatively old stratospheric air masses into the troposphere. Stratospheric-tropospheric exchange (STE) is one of the intrusions of relatively old stratospheric air into the factors controlling the budgets of ozone, water vapour and troposphere. other substances in the lower stratosphere and the Within the STACCATO project, 10Be has been measured troposphere. Cosmogenic radionuclides, which are using accelerator mass spectrometry at the PSI/ETH produced by cosmic ray particles in the atmosphere, could facility. 10Be/7Be ratios on filter samples collected at the provide valuable information on STE. In the framework of Jungfraujoch between 19/2 and 4/4/00 are shown in Fig. 2. the EU project STACCATO, particle bound 7Be and l0Be are collected on glass fibre filters (using a HIVOL air 25 T sampler) at the Jungfraujoch with a time resolution of 48 h _ 20 by the NABEL network [1]. 7 S, 15 Half of the filters are used to measure the Be activity (Tl/2 = 53.12 d) through its characteristic y-radiation (Ey: 478 keV, Iy: 10.52 %) in a well-type Ge-detector. J° Fig. 1 shows monthly arithmetic mean values of the atmospheric concentration of 7Be at the Jungfraujoch. The values of the year 2000 are in general lower by a factor of about 1.2 compared to the values for 1996 and 1997. These q q lower values may be explained by a maximum of solar d d activity in 2000, due to the 11-year solar cycle, which Date decreases the production rate of 7Be. The value of July 2000 Fig. 2: Particle bound 10Be/7Be ratios from air filter is very low, which might be due to bad weather conditions samples from the Jungfraujoch. with frequent precipitation leading to strong wet scavenging l0 7 of particles during this time period. The very high Be/ Be ratios at the end of February 2000 indicate a stratospheric intrusion confirmed by ozone data and relative humidity. Luder [5] also measured a high monthly mean isotopic ratio in precipitation at the Jungfraujoch in March 1984. However, he attributed this ratio to dust contamination rather than to an intrusion of very old stratospheric air masses. That we tend to exclude, since Ca concentrations, measured as a dust parameter during this time, did not show enhanced concentrations [6]. The slow decrease of the very high 10Be/7Be ratios is due to additional intrusion events during March 2000, which were observed by other groups, measuring high ozone and 7Be concentrations, and low relative humidity at other Alpine Aug Sep Oct sites. ACKNOWLEDGMENT Fig. 1: Comparison of monthly arithmetic mean activity 7 This study is part of the EU research project STACCATO concentrations for Be at the Jungfraujoch for the (EVK2-CT1999-00050) and is funded by the Bundesamt time period January to October 2000 fur Bildung und Wissenschaft (BBW) of Switzerland. The (STACCATO), respectively for April 1996 to sampling and the surrender of the filters by the EMPA October 1997(previous project VOTALP [2]). (operator of the NABEL network) are highly appreciated. Whereas wet scavenging can affect 7Be and l0Be concentrations, the ratio 10Be / 7Be is unaffected by such REFERENCES processes. Consequently, Raisbeck et al. [3] proposed to [1] NABEL Luftbelastung 1999, BUWAL SRU-316 (2000). use this isotopic ratio as a probe for atmospheric transport [2] S. Hubener et al., Ann. Rep. Univ. Bern & PSI (1999), processes. Raisbeck et al. [3] and Dibb et al. [4] both found p. 16. higher 10Be/7Be ratios in the lower stratosphere than in the [3] G.M. Raisbeck etal., upper one. They explained this by a relatively slow Geophys. Res. Lett. 8,1015 (1981). downward transport of air masses from the upper [4] J.E. Dibb et al., J. Geophys. Res. 99, 12855 (1994). stratosphere (7Be decays faster than l0Be). These higher [5] R. Luder, Lizentiatsarbeit, Universitat Bern (1986). 10Be/7Be ratios in the lower stratosphere, which clearly [6] S. Henning, personal communication. exceed 10Be/7Be ratios of approx. 2.2 measured by Dibb et al. [4] for tropospheric air masses, can be used to determine 155 A NEW INDUCTIVELY COUPLED PLASMA OPTICAL EMISSION SPECTROMETER (ICP-OES) FOR TRACE ELEMENT ANALYSES R. Keil, M. Schwikowski (PSI) Our sequential ICP-OES (3410, ARL) was replaced by a new simultaneous ICP spectrometer (Varian Vista). Main advantages of the new instrument are lower detection limits for most of the elements, shorter analysis times, and higher precision. Since 1988 Inductively Coupled Plasma Optical Emission Table 1: Results of trace element analyses in ultra-pure Spectrometry (ICP-OES) has been extensively used in the water (samples SI and S2) using the Varian Vista ICP- analytical chemistry group of our laboratory for analyses of OES. "<" means that the concentration is below detection trace elements in a wide range of different samples from limit. For comparison detections limits (DL, defined as 3o customers representing nearly all PSI units [1, 2]. The in- of background) obtained by the two ICP-OES using ultra- strument used for more than twelve years (3410, Applied sonic nebulizers (ARL AA81467 and CETAC U5000AT+) Research Laboratory) was replaced in November 2000 by a are given, along with the factor of improvement (F). new generation device (Varian Vista). Characteristics of this new ICP-OES are: • A simultaneous spectrometer using an echelle Element SI S2 DL DL F polychromator (Mgl"') 0-igi"1) (3410, (Varian • A Charged Coupled Device (CCD) detector ARL) Vista) 1 1 • An axially viewed plasma Oigi ) Oigi ) • A compact design, bench-mounted. Al 0.7 < 0.5 0.1 5 The benefits of the new spectrometer include better detec- Ba 1.05 0.049 0.05 0.002 25 tion limits due to the axial viewing as well as higher preci- sion and shorter analysis time due to simultaneous meas- Ca 2.51 2.53 0.002 0.02 10 urements of all element wavelengths. The improvement Co < < 0.8 0.1 8 resulting from better detection limits is demonstrated for the case of trace element analysis in ultra-pure water used Cr 0.12 < 0.3 0.05 6 in an autoclave. In Table 1 results of analysis of 15 trace Cu 1.71 0.41 0.4 0.05 8 elements in two ultra-pure water samples (SI and S2) are shown, along with the detection limits, defined as 3a of Fe 4.85 1.01 0.3 0.05 6 background. For comparison, detection limits obtained with the former ICP-OES are also given, and the factor of im- Mg 0.560 0.334 0.005 0.05 10 provement is shown. Detection limits with the new ICP- Mn 0.034 0.050 0.05 0.005 10 OES are lower by factors of 1-40, depending on the ele- ment. Mo 0.13 < 2.0 0.05 40 With the new ICP-OES, pure analysis times (without Na 0.91 1.71 0.3 0.02 15 evaluation of the results) could be reduced to about 1 S 5.0 5.0 2.0 2.0 1 minute, including wash-time, for manual sample introduc- tion. The use of an autosampler increases the analysis time, Si 6.0 4.0 2.0 2.0 1 since a longer wash and sample transport time is required. For comparison, the analysis time with the sequential ICP- Sr 0.051 0.011 0.02 0.002 10 OES was dependent on the number of elements, e.g., an Zn 0.99 0.11 0.3 0.05 6 analysis of 15 elements took about 5 minutes. REFERENCES [1] R. Keil, Ann. Rep. Univ. Bern & PSI 1994, p. 36. [2] R. Keil, M. Schwikowski, Ann. Rep. Univ. Bern & PSI 1996, p. 23. 156 CEMENT CHEMISTRY: QUALITY CONTROL AND DEVELOPMENTS 2000 H.P. Zimmermann, M. Patorski, L. Dohring, M. Egloff(PSI) This report gives a short summary of the projects and developments in our group during 2000. This year was mostly dedicated to product control and Routine product control was the main activity for the finishing already running projects. We received or nuclear power plants. At last we could finish some work for produced 25 radioactive and 6 inactive sample-sets. The KKG or at least bring it close to the end like some amount of samples to be tested depends strongly on the considerations concerning sedimentation processes in production schedules in the power plants and on bitumen matrices or leaching experiments in dependence of modifications of recipes etc. Therefore, we had a somewhat the salt contents of the matrix. In 2001 we will have to lower number of compressive strength (about 245) and y- optimise the recipe for solidification of the dirt collected in spectrometric measurements (about 700 including glass a now dismantled oil separator of KKB. samples, see below) [1]. Also the dismantling of the former research reactor During the last cementation campaign of incinerator ashes DIORIT is still in progress. It is planned for 2001 to at PSI sample sets for product control have been taken prepare the graphite for solidification with cement. overcoming the difficulties caused by lumps bigger than 4 mm in diameter. These would hamper the compressive strength measurements using our usual sample cylinders of 20 mm diameter and 40 mm height. A simple gadget composed of a vibrated sieve with 4 mm mesh and a funnel allowed to take representative samples with out the bigger particles. We made some progress in our endeavour to set up quality control procedures for the products of the ZWILAG plasma incinerator. The y-spectrometric measurements of the liquids from the leaching tests of activated slag samples were finished. A preliminary data evaluation showed that the order of magnitude of the leaching rates at room temperature can be determined by our 'normal standard leaching procedure' but the following y-spectrometric Infrastructure measurements will be very time consuming (3-5 days at least, even with an acceptable detector efficiency and a low NAGRA background). The leaching rates of this first tested sample were well below the limits required by the guideline HSK- R-14 of the Swiss Federal Nuclear Safety Inspectorate. PSI We also tried a perhaps unusual approach to determine the Fig. 1: Distribution of working capacity between our surface area of a piece of slag with an irregular surface customers. (KKW: all Swiss nuclear power plants). geometry. S. Baechler and his colleagues of the Department of Physics of the University of Fribourg performed a neutron tomography of a piece of slag at SINQ (spallation ACKNOWLEDGEMENTS induced neutron source) and produced a 3D image of it. But at the moment we still have to search for an easy method to We want to thank S. Baechler and his colleagues of the calculate the surface area itself using the data of the image. Department of Physics of the University of Fribourg for their spontaneous help and H.-U. Aebersold for the Meanwhile, during the commissioning of the incinerator at irradiations at SINQ/PSI. ZWILAG some other inactive slag samples with a different composition and other surface properties were produced on site. A successful test was performed to obtain samples by REFERENCE core drilling without a cooling liquid and cutting the 'core' with a diamond equipped blade in pieces of a define regular [1] H.P. Zimmermann et al., Ann. Rep. Univ. Bern & PSI geometry. It was decided to repeat the neutron activation 1999, p. 51. with the pneumatic tube transport system of the SINQ (spallation induced neutron source) isotope production and the leaching tests with these samples but the work is still at the beginning. 157 DETERMINATION OF THE RADIONUCLIDE INVENTORY IN ACCELERATOR WASTE R. Weinreich, M. Argentini, S. Stallone (PSI) As an essential part of waste management the nuclide inventories of radioactive waste which has been generated in the PSI facilities must be determined. Chemical separation methods leading to pure solutions of long-lived radionuclides useful for accelerator mass spectrometry have been developed and tested on waste of dismantled targets BX2 and BMA and the beam dumps of the targets E, BX 2 and BMA. Conditions for separation of cations by ion chromatography were optimized. According to the irradiation of materials with accelerators, For separation of mono- and divalent elements, an universal radioactivity is induced. By the primary beam, the targets, cation exchange column (100x4.6 mm) was used. The their beam dumps and beam lining elements are activated. isocratic elution was performed with 2.0 mM tartaric acid / By the induced secondary radiation, mostly by high-energy 0.9 mM oxalic acid, at a flow of 1.5 ml/min. Under these neutrons, the surroundings of the target equipment are conditions, the sequence of the eluted cations was: Li+, Na+, activated, including its shielding. Thus, when accelerator K+, Cs+, Zn2+, Be2+, Mn2+, Ca2+, Sr2+, Ba2+; all peaks were facilities are decommissioned or when an accelerator completely separated. The three-valent cations were equipment or its elements are changed technically, separated on a Waters Spherisorb 5 SCX column (150x4.6 dismounted activated parts must be disposed, and an mm). The isocratic elution war performed with 3.0 mM oc- appropriated concept should be developed before. HIBA / 4.0 mM glycolic acid; the solution was adjusted to pH 4.0 with HN0 . The sequence of the eluted cations were At Paul Scherrer Institute, smaller activated parts of the 3 then Lu3+, Yb3+, Tm3+, Er3+, Ho3+, Dy3+, Tb3+, Gd3+, Eu3+, accelerators were cast in concrete troughs which were used Sm3+, Nd3+, Pr3+, Ce3+, La3+. All elements are separated for shielding walls. Such pieces proved to be a safe interim completely, only the peaks of Gd and Eu show a small disposal. Recently, however, highly activated targets and overlapping. beam dumps were dismantled. In detail, these elements refer to the beam dump and construction materials of Target By this ionic chromatographic procedure, the following E (16 years in use), the biomedical 7t-meson target BMA (8 long-lived radionuclides should be separated: 1.6-106-a years) and its beam dump and the 72 MeV target equipment 10Be, 2.6-a 22Na, 7.2-105-a 26A1, 1.3-109-a 40K, 1.0-105-a BX2 (15 years in use). Moreover, several graphite 41Ca, 3.7-106-a 53Mn, 10.5-a 133Ba, 6-104-a 137La, 13.3-a degraders were dismounted which should contain 3H and 152Eu, 150-a 157Tb and 1.37-a 173Lu/3.31-a 174Lu. 14C, and some activated aluminum parts are also to be analyzed. Last but not least, samples of activated parts of SINQ-targets were taken consisting of zirkalloy and lead, respectively. Formally, all radionuclides with a sufficient long half-life are interesting for disposal problems or for handling before disposal. The analytical separation steps of the samples should lead to pure solutions of long-lived cations useful for accelerator mass spectrometry (AMS). In the progress of this work, the isocratic separation of the most useful cations in mono-, di- and three-valent states by high performance ionic chromatography was investigated. 158 HIGH AND INTERMEDIATE ENERGY NUCLEAR DATA FOR ACCELERATOR- DRIVEN SYSTEMS (HINDAS) R. Michel (Univ. Hannover), R. Weinreich (PSI), HA. Synal (ETH-PSI), N. Olsson (Univ. Uppsala), H. Schuhmacher (PTB Braunschweig), U. Herpers (Univ. Koln) The joint EU-project should deliver data useful for the treatment of nuclear waste produced by power reactors. In the frame of this project, the group is measuring cross sections for residual nuclide production induced by neutrons and protons in the energy region of 20-200 MeV. An accelerator-driven system (ADS) consists of the cou- The intention to describe these reactions by appropriate pling of a high energy intense proton beam (~1 GeV) with a models and to validate the model data by radioanalytical spallation target and a subcritical core. The spallation mod- measurements is equivalent to the handling of the PSI rad- ule, the window between the target and the accelerator, and waste; the chemical problems are nearly identical. The main the surrounding materials are subject to a wide variety of emphasis in both projects is to develop high-efficient nuclear reactions induced by particles with energies much chemical separation methods for long-lived radionuclides higher than in conventional fission reactors, and even fu- which should be measured mainly by accelerator mass sion reactors. The detailed engineering design of an ADS spectrometry. The routine determination of long-lived nu- will require that the performance of the spallation target and clides 10Be, 26A1 and 36C1 should be supplemented by heav- all the problems related to the existence of high-energy ier nuclei like 32Si, 53Mn and/or 60Fe. particles can de predicted with sufficient accuracy. In year 2000, many irradiations of lead and uranium targets The 1-2 GeV proton beam that is incident on the ADS tar- and target stacks have been performed by 72 MeV protons get (e.g. lead or lead-bismuth eutectics) will create a large at the PSI Philips Cyclotron, by 200 MeV protons at Uni- amount of spallation products, mainly neutrons and protons, versity of Uppsala and with neutrons of different energies at with energies covering the full range up to the GeV region. both Uppsala and the University of Louvain-la-Neuve. The At present, there are still a lot of missing data in the 20-200 y-Spectra of the irradiated targets have been measured. The MeV region, especially for the neutron induced reactions chemical treatment will be performed in the next years. and above 800 MeV, where data are scarce and fragmen- tary. Since measuring of all these reactions would be time- consuming and expensive, it is necessary to use computa- tional tools and models, which properly describe all the nuclear reactions that take place in the spallation module of an ADS. 159 MEASUREMENT OF RADIONUCLIDE CONTENTS IN ACTIVATED GRAPHITE M. Argentini, R. Weinreich (PSI) The radionuclide content of a graphite target irradiated for 3 years was measured. After a appropriate cooling time, this type of waste should not pose problems in waste management. Target E consisted of graphite, the investigated copy be- In this solution, tritium activity was measured directly by came operational on June 1991 and was dismounted on low-level counting between 0.0 and 18.6 keV (Hionic-Fluor June 1994, after 10D73 hours of operation, with an inte- cocktail, Packard). Since it could be shown that 3H was grated beam current of 3.98 Ah. After a cooling time of yielded in great access compared with 14C, special attention more than 5 years, the samples were prepared on September must be paid to avoid tritium contamination of14 C: 1999. In a round flask, the aqueous solution was carefully evapo- The following radionuclides were measured: 12.3-a 3H, rated to dryness and further dried for some hours in vacuo. 53.3-d 7Be, 5730-a 14C, 2.6-a 22Na and 312.2-d 54Mn. The The flask was then connected to a distillation apparatus first four radionuclides are produced in the target itself, which was kept continuously under dry nitrogen, free from while 54Mn probably is produced from copper contamina- carbon dioxide. The dried substance was dissolved in di- tions which might accumulate during the operation time. luted sulfuric acid by careful dropwise addition. The re- 7Be, 22Na and 54Mn were measured by y-spectroscopy with- leased gases were passed through two traps filled with out chemical treatment, 3H and 14C, however, were sepa- cone, sulfuric acid and collected in a calibrated amount of rated before measuring by classical chemical procedures.- IN sodium hydroxide as described above. Finally, the 14C activity was measured in this solution by (3-counting in the The graphite sample was oxidized at 900°C in a furnace energy range between 2 and 265 keV. under a flow of dried oxygen which is free from carbon dioxide. The oxidation process was generally completed Although the main amount of tritium has been evaporated within 3 hours. The released gas mixture passed three flasks during cyclotron operation, the handling of the target is containing calibrated amounts of bi-distilled water and defined by the tritium content. After an appropriate cooling sodium hydroxide (6.68 g per 1 g graphite to be oxidized). time, the other nuclides are not of importance for handling. 55 % of the tritium activity were collected in the first flask The irradiated graphite targets might be a source of 7Be and and 40 % in the second. 14C was collected quantitatively in (not yet measured) 10Be. the first flask (94-97 %). Table 1: Results (Bq/g) (EOB = End of Bombardment, June 1994) Nuclide Sample 1 Sample 2 Sample 3 EOB Dec.31,1999 EOB Dec. 31,1999 EOB Dec. 31,1999 3H 7.99 • 106 5.81 • 106 1.17 • 107 8.55 • 106 4.20 • 105 3.45 • 105 7Be* 8.54 • 10" 2730 9.25 • 1014 2960 3.47 • 1013 111 >4C 7.84 7.83 10.2 10.2 <1 <1 22Na 253 57.3 262 59.4 8.58 1.95 54Mn 76 + 28 0.82 + 0.30 31 + 16 0.34 + 0.17 27+12 0.30 + 0.13 * due to low counting rate, measurement must be repeated 161 Laboratory for Ion Beam Physics 162 LABORATORY FOR ION BEAM PHYSICS M. Suter (ETHZ &PSI) Our main research interests are related to ion beam In order to be competitive and to play a leading role in the techniques, which are used to determine elemental field of AMS, continuously upgrading the equipment is compositions of materials and for the analysis of trace necessary and innovative developments are essential. elements and rare long-lived radionuclides. For these During the last few years, we concentrated our efforts on activities, we have now available two electrostatic tandem the development of very small and compact AMS systems. accelerators, both located in our laboratory at ETH Based on a new concept for the elimination of molecular Honggerberg interferences, it was possible to design a small radiocarbon dating facility operating at a terminal voltage of only a few About 80 % of our research are related to accelerator mass hundred kV. Presently, the potential of this new technique spectrometry (AMS). With this very sensitive detection for other radionuclides such as 26A1, 4lCa and I29I is being technique we can measure isotopic ratios or trace element studied intensively. Promising results have been obtained, concentrations at very low levels. Typical isotopic ratios indicating a potential much larger than originally found in the natural environment are in the range of 10l0 to envisioned. Several improvement and modification of our 10l5. Presently, we routinely use AMS for the detection small system are still needed for optimized operating long-lived radionuclides l0Be, I4C,26 A1, 36C1, 4lCa and l2% condition and to minimize background problems. which are primarily produced by cosmic rays. Under special conditions these radionuclides can be used for In the materials sciences part of our research, our activities dating, but they also play an important role as natural were mainly concentrated on new applications of the tracers in environmental research to study exchange micro-focused AMS ion source, the development of new processes in atmosphere and the oceans of the present and types of point ion sources and the investigation of fluorine the past. diffusion as an indicator of exposure age. The number of measurements performed in collaborations and partly as a We recognizes the following trends in our applications service for industrial research laboratories has again grown. program: In order to increase the throughput we installed a new 1) The demand for radiocarbon dating in archeology and automated irradiation station, increased the capacity of our the arts is still increasing. ion beam analysis chamber and developed software for 2) Exposure dating of surface rocks starts to play an batch processing. essential role in the fields of geology and glaciology. There is clearly a growing demand among most users of 3) The application of AMS to biomedical research, in our facilities for precision analysis of light element contents which long-lived radionuclides are used as tracers, is (H, C, N, O) in materials. We therefore concentrate on being recognized. further development of nuclear methods capable of 4) Increasing interest in the monitoring of the release and satisfying these requests. distribution of I29I from nuclear fuel reprocessing plants is shown. 5000i • 14C a 4000- • 10Be dl 3000 • 26AI,36CI,41 Ca and 1291 [ i 2000- — 1 11 1 000 - I 06 6 **• -i s - 1 0 -J CM OO CO 98 0 k 98 8 | 99 2 | f 99 4 | 99 6 i 99 8 i oo o i f O5 C35 e , 98 Fig. 1: Development of the number of AMS measurements at the PSI/ETH AMS facility during the last 20 years. 163 THE PSI/ETH TANDEM ACCELERATOR FACILITY H.-A Synal, M. Döbeli, H. Fuhrmann, P.W. Kubik (PSI), G. Bonani, M. Grajear, I. Hajdas, S. Ivy-Ochs, S. Jacob, C. Maden, R. Mühle, J. Santos, J. Scheer, C. Schnabel, M. Suter, S. Tschudi (ETHZ) The year 2000 operation of the PSI/ETH tandem accelerator at ETH Hönggerberg is summarised in a detailed com- pilation consisting of beamtime allocation and the number of measured AMS samples for the various radionuclides and the major fields of research. Hours % Samples 1998 1999 2000 1998 1999 2000 1998 1999 2000 AMS Be-10 475 373 503 17.1 13.7 17.0 1098 1187 1664 C-14 881 842 1039 31.7 30.9 35.1 1755 1768 2055 Al-26 103 48 129 3.7 1.8 4.4 231 83 259 Cl-36 161 313 127 5.8 11.5 4.3 401 623 275 1-129 111 103 169 4.0 3.8 5.7 291 327 415 Heavy Elements 81 99 49 2.9 3.6 1.7 2 12 23 Subtotal 1812 1778 2016 65.3 65.2 68.1 Materials Sciences 416 357 265 15.0 13.1 8.9 Accelerator SIMS 171 193 400 6.2 7.1 13.5 Tests 119 57 90 4.3 2.1 3.0 Conditioning 257 344 191 9.3 12.6 6.4 Total 2775 2729 2962 100 100 100 3778 4000 4691 Beamtime statistics 1998-2000 Research Field Be-10 C-14 Al-26 Cl-36 1-129 Total Oceanography 290 102 392 8% Ice Core Samples 396 140 20 556 12% Limnology 61 13 74 2% Atmosphere 63 54 34 131 282 6% Environmental Monitoring 49 49 1% Exposure Age Dating, Others 219 149 84 28 47 527 11% Earth Sciences (Total) 1029 318 84 202 247 1880 40% Meteorite/Cross Sections 33 24 8 65 1% Archaeology 670 670 14% Others, Tests 240 654 106 32 63 1095 23% Subtotal 273 1324 130 32 71 1830 39% Standards 229 296 34 28 74 661 14% Blanks 133 117 11 13 23 297 6% Total 1664 2055 259 275 415 4668 100% Compilation of measured AMS samples at the PSI/ETH AMS facility in 2000 The PSI/ETH tandem accelerator operated last year for related to analyses of polar and Alpine ice cores. For 129I, 2962 hours, an increase of approximately 10% over 1999. environmental monitoring and studies related to atmos- Also the total number of analysed AMS samples increased pheric transport phenomena continued. The microbeam ion again. With 4691 samples, the year 2000 was the most suc- source was used in connection with experiments to evaluate cessful year since we began routine AMS measurements in detection limits of platinum group elements and of 10Be 1982. Of the total beamtime, 68 % was devoted to AMS, samples prepared without any carrier addition. 9% to the material sciences and 13 % was used to measure The new small AMS system for radiocarbon dating was stable trace elements in connection with the focused ion used for 14C dating measurements as well as for studies of beam sputter source. For tests and accelerator conditioning fundamental processes in AMS at low beam energies. The only 10 % of the total beamtime was needed. detection of radionuclides heavier than 14C has been inves- For 10Be, the number of samples measured has increased by tigated. For the first time, 26A1/A1 and 41Ca/Ca isotopic ratio as much as 40 % mainly due to several new projects con- measurements have successfully been performed at beam nected to exposure age studies. For the first time, more than energies below 1 MeV. The overall efficiencies are compa- 2000 individual 14C samples were analysed in one year. rable to those at large accelerators. Again, a large number of 10Be and j6Cl measurements were 164 INVESTIGATION OF NATURAL °Be/Be RATIOS WITH ACCELERATOR MASS SPECTROMETRY (AMS) C. Maden, M. Frank, M. Suter (ETHZ), P.W. Kubik, M. Dobeli (PSI) An AMS method for measuring natural 10Be/Be ratios has been developed at the PSI/ETH AMS facility. Because no 9Be carrier is added during sample preparation, samples of the order of 100 ng are obtained. They can be analysed using a finely focussed Cs+ primary ion beam. Standard samples have been measured, and it has been shown that the method can compete with techniques such as SIMS and the combination of conventional 10Be AMS and ICP-MS. For some applications in the geological sciences, such as as a function of measuring time. The nominal 10Be/Be ratio dating of manganese crusts, it is the natural 10Be/Be ratio of of the sample is 1.08109. The measured mean l0Be/l6O ratio a sample that is of interest. Conventional 10Be AMS is a is 0.82-10' with a statistical error of 5.3%. standard method for measuring 10Be/Be ratios. However, so far only the absolute concentration of 10Be in the original sample can be determined, because several hundred micro- gramms of "Be carrier are added during sample preparation. Using a preparation method that does not add 9Be carrier [1], samples of a few hundred nanogramms in size and with 10Be concentrations orders of magnitude higher than for conventional 10Be AMS are obtained. These can be ana- lyzed with the finely focussed Cs+ primary ion beam pro- duced by the Atomika Cs431 source of the PSI/ETH AMS facility. The Cs beam has a spot size of about 100 jxm and is operated with beam currents of around 600 nA. The sec- ondary BeO ions are extracted into the main beamline of 0 200 400 600 800 1000 1200 1400 1600 the AMS facility and are analysed the identical way as in Time (s) conventional l0Be AMS measurements. For standard samples, the Be is in a 1000 ppm solution ei- Fig. 2: Measurement of a standard sample with a nominal 10 ther as BeNO, or as BeSO4. By pipetting some tenths of a Be/Be ratio of 1.0810". microliter of the solution onto a silicon wafer, evaporating the solvent at 70 °C and baking the silicon wafer at a tem- With repeated measurement on different spots of the sam- perature of 800 °C for two hours, the nitrate or the sulfate is ple it has been demonstrated that a sufficient analysing cur- reduced to an oxide and a spot of a few hundred rent can be extracted from a 200 ng sample for longer than nanogramms of BeO is left on the silicon wafer. To avoid two hours. Transmission, ion source yield and total effi- 10 mass fractionation due to the geometrical shape of the BeO ciency are almost identical to values of conventional Be 9 3+ 16 5+ grain sitting on the silicon the BeO grain is pressed into a AMS (Transmission: 16.5% and 7.0% for Be and O re- highly pure sheet of aluminium and then coated with about spectively; ion source yield: 1%; total efficiency: 0.1%). 20 nm of Gold to reduce electrical charging of the sample The suppression of interferences is the same for both meth- by the Cs beam. Figure 1 shows a schematic cross section ods which would theoretically allow one to measure natural 12 through a prepared sample. ratios of lower than 10" . But demanding that a measure- Au ment with statistical error of 10% should be performed in 1 hour the detection limit rises to 1-10l0. In summary, it can be said that the new AMS method for measuring natural l0Be/Be ratios is able to compete with al- ready existing methods in sensitivity as well as precision [3] and will be tested on samples from manganese crusts in the near future. 500 |im Fig. 1: Schematic cross section through a sample prepared REFERENCES for measurement. [1] F. v. Blankenburg et al., l0 Chem. Geol., 129,93 (1996). So far, BeSO4 standard solutions with known Be/Be ratios ranging from 10"6 down to 10l0 [2] have been analysed with [2] H.J. Hofman et al., the new method. Reproducible measurements of the iso- Nucl. Instrum. Meth. B 29, 32 (1987). topic ratios have been performed. An example of a meas- [3] N.S. Belshaw et al., Int. J. of Mass Spectrometry and urement is shown in Fig. 2. Both the I6O5+ current coming Ion Processes, 142, 55 (1995). from the break-up of the 9Bel6O molecule in the tandem ac- celerator as well as the measured l0Be/l6O ratio are plotted 165 DENDROCHRONOLOGICAL AND RADIOCARBON DATING OF THE SCYTHEN BURIAL PLACE IN THE PAZYRYK VALLEY IN THE ALTAI MOUNTAINS, SOUTH SIBERIA G. Bonani, I. Hajdas (ETHZ), U. Rouff (Bilro fur Archdologie, Zurich), M. Seifert (Archaologischer Dienst Graubilnden, Haldenstein), V. Molodinand I. Sljusarenko (Institute of Archaeology and Ethnology, Nowosibirsk) Fourteen kurgans (burial mounds) have been found in the Pazyryk valley, 1600 meters above sea level in the Altai region in the heart of the Eurasian landmass. The first kur- gan was excavated in 1929 by a Russian specialist in Sibe- rian archaeology. A further seven burial mounds were opened in the 1940s. Five of the excavated tombs are of very large size and have distinct constructions. In the youngest kurgan (no. 5), the world's most famous and old- est pile rug was discovered. The contents of the barrows CALIBRATION CURVE were preserved because the water inside the burial pit had • KURGAN ULANDRVK 4 frozen, as a result both of local climatic conditions and of O KURGAN PAZYRIK 2 the construction of the tombs itself. The time of origin of -700 -650 -600 -550 -500 -450 -400 -350 -300 the Pazyryk carpet as well as the dating of the whole CALBC Pazyryk culture were uncertain up to now. The kurgans Fig. 2: 14C profiles of two different mounds, kurgan were thought to have been built in the 5th-4th centuries BC, ULANDRYK 4 (18 dates) and kurgan PAZYRIK but the culture of their builders and users, given the name 2 (12 dates), synchronized with the radiocarbon 'Pazyryk', has been identified as early nomadic, of Scythen master calibration curve. type with many local peculiarities. Between 1996 and 1998 more than 250 samples from The world's most famous and oldest pile rug, the so-called tombs of different regions in the Altai Mountains were in- Pazyryk carpet (Fig. 3) is exhibited in the Hermitage Mu- vestigated. The tree ring patterns of wood samples from seum of St. Petersburg (Russia). It was also dated at the more than 20 kurgans of different burial places could be ETH/PSI accelerator facility, yielding a calibrated calendar synchronized (Fig. 1). As no dendrochronological master age (95 % confidence limit) of BC 383 - 332 (25.4 %) or curve is available for this region, the I4C profiles of two BC 328 - 200 (74.6 %). In combination with the tree ring timbers from two different mounds were measured. Every studies of wood samples from the different kurgans, an ab- other set of 10 tree rings was selected for the measure- solute age of BC 260 - 250 could be determined. ments. The two profiles obtained from 18 respectively 12 dates (weighted means of two, respectively four independ- ent measurements) were then synchronized with the radio- carbon master calibration curve of the last 10'000 years [1] (Fig. 2). The synchronization allows the absolute dating of the tombs between BC 350±5 and BC 240±5. Fig. 3: Pazyryk carpet: wool, 200 x 183 cm (Hermit- age Museum of St. Petersburg) Lab. No.: ETH-18906; Radiocarbon age: 2245±35 y BP; Calibrated age ranges at BC 383 - 332 (25.4 %) 95 % confidence limit: BC 328 - 200 (74.6 %) Absolute age: BC 260 - 250 Fig. 1: Examples of synchronization of tree ring patterns REFERENCE of wood samples from three different burial fields. [1] M. Stuiver et al., Radiocarbon 35 No. 1, 35 (1993). 166 BIOSPHERE 2 OCEAN RADIOCARBON EXPERIMENT W.S. Broecker, C. Longdon, A. Sanyal (LDEO, Columbia Univ.), I.Hajdas, G. Bonani (ETHZ) The results of a radiocarbon spike experiment are summarised in this report. We have evidence for a roughly five- fold enhancement of the rate of CO2 gas exchange over that expected from a O, and SF6 gas exchange experiment. This suggests that catalysis of HCO} to CO2 must be occurring as the result of the release of carbonic anhydrase from biota. With its high ratio of biota to water volume, Biosphere 2's ocean is the ideal place to study this effect. On January 12th, 2000 several microcuries of radiocarbon mol/m2 or 0.13g/cm2. As shown in Figure 1, the halving I4 (in HCO3 form) were added to the Biosphere 2 ocean. This time for the C excess steadily increased. This surely re- I4 addition raised the I4C to C ratio in the dissolved inorganic flects the respiration of C -tagged organics. As stated carbon from 0.56 to 4.56 of the pre-industrial ratio in the above, based on the dark hour O, drawdown rate, the initial Earth's atmosphere. Then, over the period of half a year, halving time would be expected to be 30 days (as opposed the I4C to C ratio drifted back down to 0.85 of the pre- to the observed 17 days). This leads us to suspect that car- industrial ratio (see Table 1 and Figure 1 for summary). bonic anhydrase-driven enhancement of CO2 exchange is taking place. Table 1: Summary of radiocarbon measurements on dis- 14 Our next step will be to make a simple air-water-biota 3- solved inorganic carbon. (* T.I.A.: Time after input of C; 14 14 box model in attempt to confirm the seeming anomaly be- +: ( C/C)/( C/C)1850-0.56; **: Average of 5 measurements) I4 tween the nighttime O2 data and the initial C decline rate. We will also determine what spectrum of residence times 14 Date T.A.I.* c/c Excess+ (i.e., time between production of organic matter and its de- 14 struction by respiration) would fit the decline of the I4C to Days c/c C ratio. If, as we suspect, the O2 data explains only part of 19 July 99 WM850.54 0 - the decline, then we have to find means to estimate the role 10 January 00 0.56 - of catalysis by carbonic anhydrase. The obvious way to go 12 January 00 0 4.56 4.00 about this will be to measure the rate of I4C build-up in air I4 21 January 00 9 3.25 2.69 space over the ocean. As the residual excess of C is now 17 February 00 36 1.68 1.12 quite small, this will be done when we add a second spike I4 09 March 00 57 1.30 0.74 of C to the ocean. One thing should be kept in mind. If the I4 17 April 00 96 0.95 0.39 storage of C in the biota is assumed to explain the entire I4 I4 15 June 00 155 0.85** 0.29 C drawdown, then the residence time of the excess C in the ocean-biota reservoir will be closer to 2500 days. This Two ways exist for this reduction. One is the exchange of opens the possibility of using the ocean as a steady source CO, between the ocean and the overlying atmosphere. The of I4C for terrestrial experiments in the mangrove and sa- other is via respiration carbon stored in the organic matter vanna of Biosphere 2. making up the organisms inhabiting the ocean bottom. We have carried out gas exchange experiments using SF6 and O2 which yield gas residence time of about 2 days. Because the ratio of total dissolved carbon (LCO2) to CO2 in the ocean is about 100 (i.e., 2000 umol/L ZCO2 to 20 umol/L I4 CO2), the C residence time would be expected to be about 200 days. Thus, it is clear that the rapid reduction in I4C can be due to CO2 exchange with the overlying air only, if there is a very large enhancement of CO2 exchange through the catalysis of the HCO 3 to CO, reaction by carbonic anhy- drase leaked from biota. Based on the O2 consumption rate 3 50 100 150 200 during dark periods (mean 1.810 mol/L/hr), the rate of in- DAYS AFTER ADDITION 3 put of respiration CO2 can be estimated (-40-10" mol/L/day). This rate is high enough to explain only about I4 half of the decline of the initial ratio of 14C to C. An upper Fig. 1: Decline of excess C in the dissolved inorganic limit on the amount of active biomass can be obtained by carbon of Biosphere 2's ocean addition of tracer 14 assuming that the entire is the result of the addition of res- C. As can be seen, the first halving was accom- plished in 17 days and the second in 23 days. piration CO2. In this case the ratio of biomass carbon to dis- solved inorganic carbon would be 4.00 divided by 0.29 or 13.8. The amount of carbon in the ocean is 2 mol/m3 or 8 mol/m2. Hence, the amount of biota carbon would be 110 167 VARIATIONS IN ATMOSPHERIC 14C CONTENT 40,000 AGO AND RADIOCARBON AGE OF HEINRICH EVENT 4 /. Hajdas, G. Bonani (ETHZ), J. McManus (WHO1), M. Mendelson, S. Hemming (LDEO, Columbia Univ.) Distinct layers of ice rafted debris observed in deep sea sediments from the North Atlantic have been correlated with climatic events in this region. Here, we present results of AMS 14C dating of one of the layers in ODP 984 core re- covered south of Iceland. To reconstruct variations in atmospheric I4C content, a second independent record of the lacustrine section from Wilson Creek (CA) was dated. The atmospheric content of 14C changes due to variations in crease in 14C content. Based on the North Atlantic record the 14C production rate and the exchange between the car- we can say that the excursion precedes HE4 and, as already bon reservoirs of ocean, atmosphere and biosphere. The ra- discussed, might add to the problems of dating that event. diocarbon calibration curve reconstructs the relationship between radiocarbon age and calendar age of the last 11,600 calendar years. However, the application of the ra- diocarbon method in dating climate records extends back to 40 kyr BP. Beyond the range of the calibration curve (>11,600) and Cariaco chronology (>14,500 cal BP) [1], the INTCAL98 data set [2] is available but the resolution of this data is low. Therefore, fast changes in 14C content simi- lar to the one observed during the Younger Dryas cannot be reproduced and taken into account in data analysis. In 1988, Heinrich [3] observed 6 massive layers of ice rafted debris in North Atlantic sediments which were de- posited during the last glaciation. He suggested that the de- bris were brought by armadas of icebergs, which surged from the ice sheets. New studies at various locations in the North Atlantic region as well as correlation with climate re- 820 cords of Greenland ice cores were published in the early 25000 30000 35000 40000 45000 50000 14/ 1990's [4]. An important aspect for the correlation between 'CageBP records is chronology. Most deep-sea sediments are dated using AMS 14C dating of foraminifera shells. Although the Fig. 1: Radiocarbon chronologies of ODP 984 core and radiocarbon ages of the Heinrich Events HE1 (14.3 kyr Wilson Creek are plotted on the same radiocarbon BP), HE2 (21 kyr BP), HE3 (27 kyr BP) and HE4 (ca. 35 time scale. The data sets are shifted because of dif- kyr BP) are established [4], discrepancies in chronologies ferent sedimentation rates, but the interesting fea- have been reported [5]. ture of the I4C excursion is visible in both records Our results of dating the HE4 layer in high sedimentation as a decrease in radiocarbon age from ca. 35,000 ODP 984 core, which was recovered south of Iceland, show to 31,000 and an increase of ages back to 34,000- that the age of this event can be difficult to assess for vari- 35,000 BP. ous reasons. First of all, records typically studied are deep- sea sediments with low sedimentation rates on an order of a few cm/kyr. Because of that, it might be difficult to collect REFERENCES sufficient amount of material (foraminifera shells) needed [1] K. Hughen et al., Science 290,1952 (2000) for an AMS sample. Secondly, sediment layers of Heinrich events are known to be poor in foraminifera. This fact is [2] M. Stuiver et al., Radiocarbon 40,1041 (1998) making the dating even more difficult. The third complica- [3] H. Heinrich., Quat. Res. 29,143 (1988) tion is characteristic for HE4. The age of 35 kyr BP is close to the limit of the radiocarbon dating method. Therefore [4] G. Bond et al., Nature 365,143 (1993) any contamination with modern or younger carbon (secon- [5] L. Vidal et al., dary calcite) can result in ages which are too young. More- over, dramatic changes in atmospheric 14C might add to Earth and Planet. Sci. Lett. 146,13 (1997) those problems. Recently, an increased atmospheric 14C/12C ratio at ca. 40 kyr BP has been observed in U/Th dated spaleothems and deep-sea cores. The timing of this excursion is close to HE4 and can influence the radiocarbon chronology of stud- ied records. In order to reproduce the reported excursion, ostracode shells from the Wilson Creek exposure north of Mono Lake (CA) were dated. Both records show an in- 168 LATE PLEISTOCENE SEQUENCES OF THE BLACK SEA SHELF: CALIBRATION BY AMS 14C DATING C. O. Major, W. B. F. Ryan (LDEO, Columbia Univ.), I. Hajdas, G. Bonani (ETHZ) Radiocarbon dates of mollusk shells and bulk organic carbon can be used to reconstruct the rate and amplitude of Black Sea sea level changes from the Last Glacial Maximum (18,000 BP) to the present. The Black Sea is a large, semi-enclosed brackish to marine result of increased freshwater input from melting glaciers water body, whose water budget has varied dramatically or the reflection of early marine leakage into the Black on glacial-interglacial time scales. During glacial stages, Sea, which would necessitate a synchronous rise of Black lower world sea levels results in the loss of marine water Sea and world sea levels. input via the shallow Bosporus and Dardanelles sills. Con- tinued fresh water input via large Eurasian and Anatolian Table 1: Summary of dating results from Black Sea cores rivers transformed the Black Sea to a fresh to brackish wa- 14 ter body during these times. The transition from the last Depth (cm) Dated material C Age (uncor- freshwater stage (Neoeuxine) to the modern marine stage rected) BP is marked by a change in the benthic faunal assemblages 2 Dreissena 8275 ± 70 and the onset of sapropel formation in the deep basin. 3 Dreissena 10430 ± 80 Our study seeks to determine the rate and amplitude of 11 Dreissena 10260 ± 95 Black Sea sea level changes from the Last Glacial Maxi- 14 Dreissena 10560 ± 75 mum (-18 ky BP) to the present, and the degree to which 14 Dreissena 10090 ± 130 the sea level is controlled by varying river input, climate 15 Dreissena 12310 ± 95 change, and connection with the world oceans. Forty-one 22 Dreissena 8305 ± 80 samples, including shells and bulk organic material, were submitted to ETH for radiocarbon dating. The ages of mol- 33 Mytilus 6750 ± 70 lusk shells from the base of the upper Neoeuxine unit con- 33 Dreissena 7940 ± 75 firmed a transgression of Black Sea sea level between -20 34 Dreissena 8660 ± 75 and 7.6 ky BP (all reported ages are unconnected for reser- 38 Dreissena 20490 ± 150 voir effect). This transgressive unit onlaps an interbedded 39 Dreissena 8360 ± 75 barren unit, which is dated by bulk organic carbon to ap- 41 Dreissena 8300 ± 70 proximately 23 to 27 ky BP. This basal unit, which is seen 45 Dreissena 10250 ± 90 in seismic profiles to have a seaward dipping geometry 52 Bulk organic material 23630 ± 180 and a truncated upper surface, is interpreted as a low stand 60 Bulk organic material 24980 ±200 delta of the Danube River. Mollusk shells from the mid- shelf region, between 60 and 80 m, were reworked into 93 Monodacna 7655 ± 75 large dune-like bedforms between 7.65 and 7.1 ky BP, 94.5 Turricaspia 10640 ± 80 suggesting a brief regression of Black Sea sea level in the 110.5 Monodacna 7865 ± 70 early Holocene or intensive submarine sediment transport. 114 Bulk organic material 26630 ±230 In addition, we have found that glacial-interglacial transi- 115 Dreissena 14010 ± 100 tion, marked by a change in sediment composition to more 118.5 Dreissena 11410 ±110 calcium carbonate and smectite-rich sediments as well as a 18 127 Dreissena 24160 ± 190 positive shift in the 8 O of mollusk shells, appears be- 130 Monodacna 9580 ± 80 tween -13 and 7 ky BP. The preceding period in our re- 154.5 Dreissena 12790 ±110 cord appears to have been characterized by high sedimen- tation rates in the deep basin and continental slope and wi- 161 Dreissena 8345 ± 70 despread erosion of the Black Sea shelf. 176.5 Dreissena 8360 ± 70 A remaining question is the degree to which the Black Sea 186.5 Dreissena 12820 ± 100 sea level rose and fell independently of world sea level 215 Dreissena 14950 ± 100 during its isolated phase. The Caspian Sea, another en- 704 Dreissena 17760 ± 130 closed brackish water body, experienced base level 840 Dreissena 20580 ± 150 changes of up to 80 m over the last glacial cycle [1]. These changes are ascribed to changes in the river/precipitation input versus water loss by evaporation and periodic over- REFERENCE flow to the Black Sea. We seek to resolve whether the [1] A.A. Svitoch, Oceanology 39, 94 (1999). Black Sea transgression during the late Pleistocene was the 169 A LATE-GLACIAL AND EARLY HOLOCENE ENVIRONMENT AND CLIMATE HISTORY FOR THE NEUCHATEL REGION (SWITZERLAND) N. Thew, P. Hadorn, (Service cantonal d'archeologie, Neuchdtel), G. R. Coope (Univ. of London), G. Lemdahl (Vaxjo Univ.), I. Hajdas, G. Bonani (ETHZ) Radiocarbon chronology of the site Hauterive/Rouges-Terres was established using AMS dating of terrestrial plant macrofossils. This chronology provides a basis for absolute dating of climatic events of the last deglaciation and be- ginning of Holocene (14,000 to 8,000 yr BP). Environmental changes such as fluctuations of lake level, response of flora (pollen) and fauna (insects and molluscs) to the climatic change were studied. The site of Hauterive/Rouges-Terres, situated near the coincided with a change in sedimentation (alternating silts northwestern part of Lake Neuchatel (Switzerland), was and sands gave way to organic silts) which seems to indi- discovered in 1992 in the deep construction trench for the cate a rise in lake level. The plant remains show subsequent A5 motorway. Field investigations were carried out during colonization by tree birches, willows and poplars. The the summers of 1992 and 1993. Fifteen profiles covering Betula phase of the B0lling was marked by the deposition 130 m of horizontal stratigraphy have been drawn, de- of silty marls. A significant lowering of the lake level dur- scribed and sampled for sediment, pollen, plant macrofos- ing the Youngest Dryas biozone (leading to the formation sil, insect and mollusk analyses. Careful cleaning of the of pebble beaches and sand layers) caused the erosion of all whole section allowed layers to be followed and correlated sediments dating from the Aller0d biozone, and the forma- between the 15 profiles permitting lithostratigraphic units tion of loading structures. The insects indicate a return to to be established for all of the documented sediments. colder climatic conditions. At the start of the Preboreal an These deposits formed in an embayment at the margin of abrupt climatic warming coincided with a major rise in lake Lake Neuchatel, with lake sediments predominating to- level and the subsequent deposition of silty marls, silts and wards the deeper part of the depression, passing laterally fine sands. The Boreal and Atlantic biozones were marked into lake margin and supra-littoral marsh and colluvial de- by sediments rich in oncoliths. posits. Pollen analysis on four of the profiles have con- firmed field hypotheses that these deposits represent a Table 1: Radiocarbon chronology of the Rouges-Terres complex sequence of Late Glacial to middle Holocene climatic record sediments. These sediments are reflecting changing condi- tions in the local environment (linked to lake level varia- Regional Inferred vegetation Radiocarbon tions, and phases of stability and instability of the adjoining pollen age terrestrial land surface) determined by regional scale pat- zones terns of climate change. Despite the variable nature of these sediments, the pollen sequence fits very well with the re- Boreal Deciduous forest, hazel, ca. 8000 BP gional pollen zones published for the Swiss Plateau [1]. An elm, oak, lime absolute chronology has also been established for these four profiles, based on more than 60 AMS dates ranging Preboreal Pine and birch forest, ar- 9200-10,000 from 14,200 to 8,000 BP. Sediments of the Oldest Dryas rival hazel, elm, oak BP biozone were dominated towards the edge of the depression by colluvial gravels with alternating layers of silts and Younger Hiatus, erosion of the Al- <10,000- sands. The gravel contained many frost-shattered pebbles. Dryas ler0d, open pine forest 11,000 BP Notable deformation structures (several phases) could be with birch observed, resulting from solifluction and possibly cryotur- bation. Low pollen concentrations show rapid sedimenta- B0lling Reforestation by juniper, <12,000- tion during the Oldest Dryas biozone but, despite this, the buckthorn, birch, willow 12,500 BP finer sediments were found to contain remarkable concen- trations of plant macro-remains, insects and molluscs. The Oldest Meadows with arctic and 12,500-14,500 plant material consists of leaves, fruits, seeds, bud-scales Dryas alpine herbs, treeless BP and twigs that reflect an arctic and alpine Oldest Dryas flora [2]. Among the identified remains are aquatic species, plants typical of lake shore marshes, alpine meadows and loose rocks, as well as dwarf shrubs (Betula nana, Dryas REFERENCES octopetala, Salix retusa). Insect analyses indicate extremely cold conditions throughout the Oldest Dryas biozone. The [1] B. Ammann et al., Boreas 18,109 (1989). molluscs include alpine, arctic and Siberian species [3]. [2] G. R. Coope et al., J. Quat. Sci. 15,157 (2000). The insects clearly show a sudden and intense temperature warming at the very end of the Betula nana phase just be- [3] G. Lang, Quartare Vegetationsgeschichte Europas. fore the reforestation by juniper and tree birch, which Fischer, Jena, Stuttgart, New York, p. 462 (1994). marks the beginning of the B0lling biozone. This warming 170 THE APPLICATION OF IN SITU COSMOGENIC NUCLIDE EXPOSURE DATING (10Be, 26A1), TO GLACIAL DEPOSITS OF THE LAST DEGLACIATION IN THE SOUTHERN ANDES OF CHILE C. Fogwill, W.M.Phillips (Univ. of Edinburgh), P.W. Kubik(PSI) This report presents preliminary results from AMS measurement of the in situ produced nuclides 10Be and 26Al in gla- cial landforms in Fuego, Patagonia. This data provides some of the first reliable independent chronological controls of the glaciation of this region during the last glacial transition. The timing of high frequency - low amplitude climatic variations during the last glacial/interglacial transition is important to our understanding of the nature of interhemi- spheric leads and lags in global climate signalling. To this end, the measurement of in situ produced cosmogenic nu- clides by AMS provides geomorphologists with an indis- pensable tool for dating the emplacement of geographical features. These are related to the advance and retreat of gla- ciers in response to climate [1]. Fuego Patagonia is one of the only large landmasses to ex- tend beyond 55° south (see Figure 1). It has been suggested that glacial dynamics in this region are controlled by the lo- cation, moisture content and intensity of the westerlies [2, 3], which are themselves controlled by global pressure sys- tems. Knowledge of the timing of glaciation therefore indi- cates both precipitation and temperature regimes at varying latitudes throughout Patagonia. By constructing an accurate chronology, the nature of interhemispheric climate change during the last glacial termination can be elucidated. This is currently a contentious topic, which continues to be widely debated [4, 5, 6]. This project applies cosmogenic exposure dating to a vari- ety of glacial landforms. These landforms are a product of advancing glaciers during the last glacial cycle. Two sites were selected in southernmost South America; Paine and Magellan (Fig. 1) based on the findings of geomorphologi- cal field studies in this region [7]. These previous studies Fig. 1: Map of southern-most South America, with pre- have identified a series of glacial limits. Attempts to pro- sent day ice fields (shaded areas), and sampling duce a reliable radiocarbon chronology for the Paine and areas in boxes. Magellan regions have yielded few useful bracketing dates due to the lack of preserved organic material. A prelimi- nary radiocarbon chronology has been developed from this REFERENCES work. This provides an ideal testing ground for cosmogenic [1] S. Ivy-Ochs, dating. Ph.D. thesis #11763, ETH Zurich (1996). Initial results with 10Be have dated a number of large errat- ics in the Magellan Region. The dates are 21- 24,000 yrs [2] A. Hubbard, BP using a production rate of 5.1 ± 0.2 10Be atoms g"1 y"1 at Earth and Planet. Sci. Lett. 22, 79 (1997). sea level [8]. These dates are from a giant rockfall deposit, [3] G.H. Dentonefa/., which occurred on to the advancing ice sheet and which Geog. Ann. 81 A (2), 107 (1999). was then transported supraglacially before final deposition on the eventual limit of the terminal position of the ice [4] T. Blunier et al, Nature 394,739 (1998). sheet at this time. [5] T.V. Lowell et al., Science 269,1541 (1995). [6] R.M. McCulloch et al., This data provides the first evidence of glaciation in this J. Quaternary Sci. 15,409 (2000). region contemporaneous with the Last Glacial Maximum. [7] CM. Clapperton et al., A total of thirty samples have been taken in all, in an at- Quat. Res. 44,133 (1995). tempt to produce a reliable chronology of this region. [8] J. Stone, J. Geophys. Res. 10, 23753 (2000). 171 SLIP RATES OF ACTIVE THRUSTS AT THE NORTHEASTERN MARGIN OF TIBET (CHINA) AS REVEALED BY 21Ne AND 10Be EXPOSURE AGES OF LATE PLEISTOCENE ALLUVIAL FANS R. Hetzel, S. Niedermann (GFZPotsdam), P.W. Kubik (PSI), S. Ivy-Ochs (ETHZ), M. Tao (CAS, China) Late Pleistocene 10Be and 21Ne exposure ages obtained from an alluvial fan located at the NE margin of Tibet con- strain the vertical slip rate of an active thrust fault at 0.3-0.5 mm/yr. Our results demonstrate that previous slip rate estimates, which were based on the assumption that tectonically offset surfaces have formed during early Holocene warming, are doubtful. Slip rate determinations should include rigorous dating of the surfaces affected by faulting. This ongoing project aims to quantify slip rates of active sites. Since cosmogenic nuclides are not only produced in- thrusts at the front of the Qilian Shan, in order to better situ, but also prior to the deposition of the clasts during ex- constrain the Late Pleistocene/Holocene deformation his- humation and transport, this inherited component (also re- tory at the northeastern margin of the Tibetan Plateau. ferred to as "geological blank"; [3]) must be taken into ac- Seismically active thrusts and strike-slip faults demonstrate count. Therefore, we also collected clasts from intermittent that the 5500 m high Qilian Shan is an actively growing streams that cross the fault scarp line (see Fig. 1). As indi- NE-vergent thrust-and-fold belt [1]. There exist only few vidual clasts contain different amounts of the inherited slip rate estimates of active thrusts in the Qilian Shan. component, we followed the amalgamation approach of These estimates are based on the assumption that surfaces, Anderson et al. [4] and include 30-40 individual clasts into tectonically offset by faults, have formed during early one sample. Holocene warming and deglaciation as a result of increased At site 1 (40 m vertical uplift), a surface sample yields a surface runoff. Ages of 10±2 ka and 11±3 ka have been as- 21Ne age of 132±17 ka and a 10Be age of 118+18 ka (2a), signed to alluvial fan surfaces offset by thrust faults [1,2]. both ages being in excellent agreement. At site 2 (57 m ver- In contrast to this assumption, our first 10Be and 21Ne expo- tical uplift), a surface sample gave a 21Ne age of 320±22 ka sure ages demonstrate that surfaces considerably older than that is considerably older than the 10Be age of 188±25 ka. Holocene are preserved in the Qilian Shan. This discrepancy is interpreted to be caused by a neon com- The studied Yumen thrust is a NNE-dipping thrust fault lo- ponent that deviates from the neon composition of air. This cated -10 km north of the steep mountain front of the Qil- non-atmospheric component is most likely present in fluid ian Shan at an elevation of 2000 m (97°45'E, 39°50'N). It inclusions and results in an anomalously old Ne age. There- has displaced the surface of an alluvial fan and forms a fore, only the Be age is interpreted as geologically 30 km long south-facing fault scarp (Fig. 1). At two study meaningful at site 2. The ages mentioned so far have not sites, topographic profiles demonstrate that the thrust has a yet been corrected for a "geological blank". A 10Be and a vertical displacement of 40 m and 57 m, respectively. As- 21Ne analysis of two different samples from active streams suming an early Holocene age of -10 ka for the fan surface suggest that the inherited cosmogenic component is only a would translate into a vertical slip rate of 4-6 mm/a. relatively small fraction of the total cosmogenic component (less then a quarter). A detailed consideration of the inher- ited component must await further analyses. However, the ages that have already been obtained demonstrate that the average rate of vertical tectonic uplift along the Yumen thrust is at both sites only some 0.3-0.5mm/a. This is an or- der of magnitude smaller than the rate that would be ob- tained assuming an early Holocene age of the alluvial fan surface. Thus, rigorous dating of tectonically offset sur- faces is a prerequisite for determining reliable rates of tec- tonic faulting. REFERENCES [1] B. Meyer et al., Geophys. J. Int. 135, 1 (1998). [2] P. Tapponnier et al., Fig. 1: Corona-image of the western part of the Yumen Earth Planet. Sci. Lett. 97, 382 (1990). thrust. Intermittent streams flowing north have in- cised into the uplifted hanging wall of the thrust. [3] E.T. Brown et al., Quartz clasts were collected from the surface of Geol. Soc. Am. Bull. 110, 377 (1998). the fan. [4] R.S. Anderson, et al., Geology. 24, 47 (1996). To constrain the age of the tectonically uplifted fan surface we sampled quartz clasts from the surface of the fan at both 172 COSMOGENIC NUCLIDE EROSION ASSESSMENT OF TROPICAL HIGHLANDS (SRI LANKA) A.L. T. Hewawasam, F. von Blanckenburg, M. Schaller (Univ. Bern), P. W. Kubik (PSI) Present-day soil erosion rates have been compared to cosmogenic erosion rates for the Upper Mahaweli catchment, Sri Lanka. Our study reveals that cosmogenic erosion rates solely represent the rates of natural erosion. More im- portantly, the technique can be used to infer the influence of deforestation on soil erosion, when used in conjunction with present-day erosion rates. To date, these man-made changes have remained difficult to quantify. In szYw-produced cosmogenic nuclides are generated in • Six Small Catchments (RG) minerals at the earth's surface mainly due to neutron spalla- o Sediments from Six Small Catchments (CN) "" A Very Small Forest Catchments (CN) '' tion and muon capture reactions. Their concentration is a o Very Small Agricultural Catchments (CN) function of time and of the surface lowering rate. In an en- I \ tire landscape, large-scale erosion rates can be determined 1 from quartz in river sediment if the rate of nuclide produc- 100- i 1 tion equals that of nuclide loss through sediment transport in a river. We employed this concept to quantify large-scale erosion rates for an integrated time period in a tropical A ° ? ?-S highland. o 10Be and 26A1 concentrations were measured in pure quartz 10- oo from river sediments of six small tributaries of the Ma- A A haweli river, Sri Lanka. The tributaries are draining a mountain range of 600-2500 m altitude which is underlain 100 1000 by crystalline rocks. The catchment areas had been covered Drainage Area [km ] with thick forest until the 19* century. Later, the forest cover had been removed on a large scale, principally Fig. 1: Erosion rates derived from sediments from six through two phases of agricultural plantation. Only a few Mahaweli River tributaries, small forest catch- isolated patches of the original rain forest remain. Conse- ments, and small agricultural catchments (RG: quently, the area is experiencing severe soil erosion today. river gauging, CN: cosmogenic nuclides) At present, the spatially averaged soil erosion rates for the six catchments can be calculated from suspended and dis- The difference between the low cosmogenic nuclide de- solved load data. The present-day soil erosion is severe rived erosion rates (10-30 mm/ky) and those from present- and ranges from 100 mm/ky to 500 mm/ky. day river-load gauging (100 mm/ky to 500 mm/ky) sug- In contrast, erosion rates for the six catchments based on gests that deforestation and plantation agriculture has in- measured 10Be concentrations range from 10 mm/ky to 30 creased the present-day soil erosion by a factor of 10 to 20 mm/ky. Measured erosion rates based on 26A1 concentra- over the island's natural erosion. tions for five randomly selected samples are consistent with those of calculated by 10Be concentrations. Moreover, sev- eral very small catchments (both agricultural and original forest) were also sampled in the Upper Mahaweli catch- ment for the erosion study. The measured erosion rates for sediment and surface soil from both original forests and ag- riculturally utilised area are similar to the large-scale ero- sion from the six catchments of Mahaweli. This suggests that the cosmogenic technique is not sensitive to recent human effects (Figure 1). This is because the cosmogenic nuclide-derived erosion rates average over a period of 10 to 50 kys. Therefore, this novel technique can be used as an effective tool to quantify natural erosion, which is essen- tially controlled by climate and tectonics. 173 CAN WE USE COSMOGENIC NUCLIDES TO DATE STONE ARTIFACTS? S. Ivy-Ochs (ETHZ), R. Wiist (Univ. Vancouver), P.W. Kubik (PSI), H. Mttller-Beck (Univ. Tubingen), C. Schluchter (Univ. Bern) Two chert artifacts from the Thebes Mountains near Luxor, Egypt, have yielded concentrations of cosmogenie 10Be that allow calculation of nominal exposure ages of around 300,000 years. Tools associated with the flakes can be attributed to the Late Acheulean or early Middle Paleolithic. These exposure ages represent composite ages, comprised of exposures both before and after working. Lithic artifacts can be dated by determining absolute ages 3. the time after the flake was chipped from a cobble. on associated geological materials (using 14C, U-series, The crucial question is what proportion of the exposure was electron spin resonance, 40Ar/j9Ar, luminescence) or directly acquired before the cobbles were worked? Had the cobbles dated with luminescence techniques. We present here first been exposed for a few thousand years, for tens of results of an attempt to use surface exposure dating with thousands of years or for longer? One approach that may cosmogenic nuclides to date siliceous artifacts [1]. The help to narrow down the time range is to analyze chert restricting caveats are that the artifacts must have been nodules located close to collected worked pieces but still continuously exposed since fabrication but must not have embedded in the limestone bedrock. From this we should been exposed earlier. Otherwise, earlier exposure must be be able to estimate the erosion rate affecting the removal of determinable independently. overlying bedrock. This should provide a further step Both artifacts were collected atop limestone benches of the towards deconvolution of the three time periods of the Eocene Thebes Formation which form cliffs along the west composite exposure. side of the Nile. The site is at elevation 240 m (150 m Is it possible that the calculated composite exposure ages above the present elevation of the Nile and about 15 km are the actual exposure ages for these artifacts? Is such an away from it). This area, where abundant chert nodules age reasonable for the typology exhibited by the flakes and have weathered out, has been a collection, extraction and associated tools? The two dated pieces belong to the more fabrication site since the Early Paleolithic (since at least heavily varnished artifacts known from the Luxor area 400,000 years ago [2]. The two artifacts we have analyzed collections. They are connected with more archaic Later thus far are flakes made during the knapping process; they Acheulean inventories, before more refined Middle are not themselves tools. Both artifacts were severely wind- Paleolithic sites with less varnished tools appear. The polished and bore a well-developed mottled dark brown to 'dates' measured are well in accordance with the older black patina of desert varnish. range of the estimated time window for the Early to Middle Paleolithic transition. Acheulean artifacts from middle Egypt are known to date from at least 400,000 years ago, with the Final Acheulean at 350,000-400,000 years ago [2]. The Early Middle Paleolithic is centered on 150,000 to 200,000 [2]. It is the transition of the Early to Middle Paleolithic which is difficult to pinpoint. For example, 2 McBrearty and Brooks [5] quote the introduction of Middle •••• " •" «- "m Stone Age technology at 250,000 to 300,000 years ago. K These preliminary results are intriguing and highlight the exciting potential of surface exposure dating of siliceous artifacts. REFERENCES Fig. 1: Sampling site on resistant benches of Thebes limestone. [1] S. Ivy-Ochs et al., submitted to Radiocarbon s (2001). [2] P.M. Vermeersch, Paleolithic Living Sites in Upper Our first results are for two different artifacts. The l0Be and Middle Egypt. concentrations allow calculation of nominal exposure ages Leuven University Press, Leuven, Belgium (2000). of around 300,000 years (using the production rate of Kubik et al. [3] and the scaling factors of Lai [4]). These [3] P.W. Kubik etal., exposure ages are composite ages made up of: Earth and Planet. Sci. Lett. 161, 231 (1998). 1. the time the chert nodule was enclosed in the limestone [4] Lai, Earth and Planet. Sci. Lett. 104, 424 (1991). bed rock and gradually getting closer to the surface as the limestone around it eroded away, plus [5] S. McBrearty and A.S. Brooks, J. Human, 2. the time that the eroded out chert cobble was lying on Evolution 39 (5), 453 (2000). the plateau surface prior to being worked on, plus 174 A 30,000 YEAR EROSION RATE RECORD FROM COSMOGENIC NUCLIDES IN RIVER TERRACE SEDIMENTS IN THE MASSIF CENTRAL, FRANCE M. Schaller, F. von Blanckenburg (Univ. Bern), A. Veldkamp (Wageningen Univ.), P.W. Kubik (PSI), N. Hovius (Univ. of Cambridge) The concentration of cosmogenic nuclides in sediment of terraces with known age can be used to calculate time- integrated paleo-erosion rates for entire river catchments. The erosion rates obtained for Late Pleistocene to Holocene terraces of the Allier river in the Massif Central, France, range from 33-55 mm/ky. These rates agree well with rates inferred from sediment accumulation in Lac Chambon situated within the upper Allier basin. The quantification of past continental erosion is a challenge These results present a plausible explanation for the excess of principal importance to studies of tectonics and cosmogenic erosion rates measured in recent river sediment environmental change. Existing techniques are 1) with respect to estimates based upon river load gauging in thermobarometry of metamorphic belts; 2) fission track the same streams: recent river-borne quartz contains a analysis; and 3) sediment accumulation budgets of natural memory of the Late Pleistocene to Holocene erosion basins. We have used a new technique, exploiting history. Importantly, the cosmogenic nuclide approach cosmogenic nuclides in dated river terraces, to quantify makes it possible to determine changes in time-integrated catchment-wide rates of "paleo erosion". Quartz sand in erosion rates from previous climate cycles, or in river terraces can be used to determine the time-integrated tectonically active regions. erosion rates concomitant with terrace formation. Measured cosmogenic 10Be concentrations in quartz are corrected for 200-| post-depositional irradiation using the known terrace age. The remaining nuclide inventory is attributed to irradiation 175- in the source area of the sediments. Erosion rates can then 150- be calculated using the steady-state assumption of Lai [1] 125- and making use production rates scaled for the mean altitude and latitude of the upstream area. 100- This approach has been tested on the Late Pleistocene and 75- Holocene terraces of the Allier and Dore rivers in the 50- Massif Central, France. These terraces have been 25- extensively studied, dated, and modelled [2]. In addition, very precise estimates of Late Pleistocene to Holocene 0 5000 10000 15000 20000 25000 30000 35000 erosion rates exist for Lac Chambon, based upon sediment Time Before Present (y) accumulation in the basin [3]. Erosion rates based on 10Be concentrations have been calculated with the production rate of Kubik et al. [4] and the altitude/latitude scaling of Fig. 1: Cosmogenic nuclide-derived erosion rates Lai [1], both modified for the muon production rate values measured in terrace sediments of the Allier and of Heisinger [5]. The erosion rates are all between 33 and Dore basin (squares). Erosion rates measured by 55 mm/ky for the Late Pleistocene to Holocene terrace sediment accumulation in the basin of Lac samples. These rates are very similar to those measured Chambon back to 12,600 years ([3], solid line). A with 10Be in sands from the active Allier and Dore channels model simulation represents the cosmogenic (31-59 mm/ky). They are also in agreement with the long- nuclide-derived erosion rates expected from river term estimates based on sediment accumulation in Lac sediment at any point back through time based Chambon (50-160 mm/ky). A quantitative model is used to upon integration through time of the Lac Chambon calculate apparent erosion rates expected from cosmogenic erosion history (dashed line). nuclides using as input erosion rates derived from sediment accumulation rates in the basin of Lac Chambon. The REFERENCES model demonstrates that strong, short-term fluctuations in [1] D. Lai, Earth Planet. Sci. Lett. 104,424 (1991) "real" erosion are damped in the cosmogenic record due to the considerable lag time (ca. 20 ky) required for the [2] A. Veldkamp and S.B. Kroonenberg, cosmogenic nuclide budget to settle back into steady-state Geologie en Mijnbouw 72,179 (1993). after a change in erosion rate. Erosion rates of 50-160 [3] JJ Macaire et al., Earth Surface Processes and mm/ky from the sediment accumulation in the basin of Lac Landforms 22,473 (1997). Chambon are damped to values of 50-70 mm/ky in this P.W. Kubik etal., model calculation. Model results are in good agreement [4] Earth Planet. Sci. Lett. 161, 231 (1998). with the erosion rates derived from the 10Be concentration in the river terraces. [5] B.P. Heisinger, Ph.D. Thesis,. TU Munchen (1998) 175 LAST MAJOR ADVANCE OF TAYLOR GLACIER INTO CENTRAL BEACON VALLEY, ANTARCTICA, AT LEAST 4 MA AGO S. Tschudi, C. Schluchter (Univ. Bern), S. Ivy-Ochs, J.M. Schafer (ETHZ), P.W. Kubik(PSI), N. Potter (Dickinson College), G.H. Denton (Univ. of Maine), D. R. Marchant (Boston Univ.) Surface exposure dating with cosmogenic nuclides provides absolute chronological information for Granite drift, a glacigenic sediment deposited by a Taylor Glacier advance into central Beacon Valley, Antarctica. Our analysis yields a minimum exposure age of ~ 4.0 Ma indicating a simple exposure history. It supports the contention that buried remnant ice underlying the floor of central Beacon Valley is at least mid Pliocene, maybe Miocene in age. Beacon Valley, Antarctica, is a crucial site for the strictly minimum ages, as no erosion or coverage has been reconstruction of Antarctic paleoglaciations and landscape taken into account. l0Be, 26A1 and 2lNe results being in evolution. The valley acts like an "overflow basin" of the agreement argue for a simple history of exposure. East Antarctic Ice Sheet (EAIS), which makes glacial Therefore, Taylor Glacier deposited the Granite drift into sediments in Beacon Valley an important archive for past central Beacon Valley sometime prior to 4.0 Ma. This is fluctuations of Taylor Glacier and hence Taylor Dome. consistent with the correlation of Granite drift with Although a relative stratigraphy of surficial glacial Quartermain I and II drifts in Arena Valley as suggested by sediments in Beacon Valley is well defined [e.g. 1, 2], an Marchant et al. [2]. This age also suggests an early Pliocene absolute chronology is lacking. Underlying the valley floor, or older age for the Sirius Group deposits at Mt. Feather, a remnant body of ice is buried, which is suggested to be which is in accord with [9, 10]. From our multi-nuclide Miocene in age [3]. This age determination has been analysis one can conclude that Taylor Glacier never questioned [4] and is presently under further discussion [5]. reached this part of Beacon Valley again and Granite drift therefore represents the last major advance. This The goal of this study was to date Granite drift, a glacial contradicts an overriding of high-altitude sites by the EAIS sediment deposited by a major advance of Taylor Glacier within the Dry Valleys at 3.1 Ma ago, as proposed by into central Beacon Valley [1], by means of surface Webb et al. [11]. Moreover, our data strongly support the exposure dating with cosmogenic l0Be, 26A1 and 2lNe. contention that ash deposits on top of Granite drift are in Dating this drift also provides a minimum age for situ and that the underlying remnant ice is indeed several deposition of the stratigraphically older deposits of the million years in age [3]. Sirius Group at Mt. Feather [e.g. 2], and it would shed light on the discussion of the age of the buried body of ice. This work was partly funded by Swiss National Science Foundation grants 21-043469.95/1 and 21-053942.98 and by the United States Division of Polar Programs of the National Science Foundation. REFERENCES [I] G. H. Denton et al., Geogr. Ann. 75 A, 155 (1993). [2] D. R. Marchant et al., Geogr. Ann. 75 A, 269 (1993). [3] D. E. Sugden et al., Nature 376, 412 (1995). [4] R.C.A. Hindmarsh et al., Geogr. Ann. 80 A, 209 (1998). [5] J. M. Schafer etal., Earth and Planet. Sci. Lett. 179, 91 (2000). 10' [6] P.W. Kubik etal., Be [atoms / g] Earth and Planet. Sci. Lett. 161, 231 (1998). Fig. 1: Two-nuclide plot of all measured samples. The [7] S. Tschudi et al., submitted to Geology, (2001). concentrations are normalized to sea level and [8] D. Lai, Earth and Planet. high latitude using the production rates of Kubik et Sci. Lett. 104, 424-439 (1991). al. [6] (for details see [7]. [9] S. Ivy-Ochs et al., in: The Antarctic Region: Geological Evolution and Proceses, ed. C.A. Ricci, Six granitic clasts on the valley floor from the surface of Terra Antarctica Publication, Siena, Italy, 1153 Granite drift near its outer margin were sampled and (1997). l0 26 2l analyzed for Be, A1 and partly also for Ne. The [10] J.M. Schaferetal., minimum exposure ages for these clasts range from 0.9 ± Earth and Planet. Sci. Lett. 167, 215 (1999). 0.1 Ma to 4.0 ± 0.2 Ma [7], calculated with the production rates of Kubik et al. [6] scaled after Lai [8]. These ages are [II] P. N. Webb et al., Geology 12, 287 (1984). 176 CONSTRAINTS FOR THE LATEST GLACIAL ADVANCE ON WRANGEL ISLAND FROM SURFACE EXPOSURE DATING S. Tschudi, C. Schluchter (Univ. Bern), P.W. Kubik (PSI), J. Karhu, M. Saarnisto (Geol. Survey of Finland) From Wrangel Island, bedrock and loose rock samples were collected for surface exposure dating. Especially the bedrock surface samples were expected to provide new constraints for the chronology of glaciations on the island. Minimum exposure ages based on 10Be suggest that no major glaciations have affected Wrangel Island or the adjacent shelf area after about 65 ka, which seems to rule out a major glaciation during the Last Glacial Maximum. Wrangel Island is well known for the abundance of with repeated periods of exposure and shielding during the mammoth skeletal remains. A number of bones, teeth and past. Bedrock samples reflect the deglaciation time of the tusks have been radiocarbon dated and the ages seem to last glacial event only, if the advancing glacier eroded cover the whole period from about 30'000 to 4'000 years enough material from the bedrock surface to reset the BP [1, 2] with some data coincident with the Last Glacial cosmogenic "chronometer". Sample Wra 2 bears a Maximum (LGM). These results suggest that during the relatively young exposure age (about 12 ka, [6]), which LGM this part of the continental shelf was ice-free, could indicate that the sampled boulder has suffered although globally the period is characterized by the disintegration and possibly rotation due to frost action. maximum ice volume of the last glacial cycle [3]. Sample Wra 4 has a minimum exposure age estimate of However, Grosswald [4, 5] proposed an extensive East about 26 ka [6]. Here, field evidence excludes a former Siberian ice sheet, which covered most of the northeastern coverage by valley glaciers. Thus, any major advances of Russian shelf during the LGM, including Wrangel Island. glacial ice sheets should have occurred before this date. To determine a glacial chronology, rock samples for These minimum exposure age estimates indicate that, surface exposure dating were collected (see Fig. 1) from excluding local valley glaciers, no major growth of glacial exposed bedrock (samples Wra 1 and Wra 4) and loose ice occurred on Wrangel Island during the Late boulders (sample Wra 2) to be analyzed for 10Be [6]. Weichselian glaciation and possibly even during the Middle Weichselian. This work was partly funded by the Swiss National Science Foundation grant 21-043469.95/1. The Geological Survey of Finland and the Academy of Finland funded the expedition to Wrangel Island by J. Karhu and M. Saarnisto (1997). WraL'2 V REFERENCES [1] S. L. Vartanyan et al., Radiocarbon 37, 1 (1995). [2] L. D. Sulerzhitsky and F. A. Romanenko, Wra1 Ambio28, 251 (1999). [3] N. J. Shackleton, Quaternary Sci. Reviews 6, 183 (1987). Fig. 1: The Bering Strait region and a sketch map of [4] M. G. Grosswald, Wrangel Island (W) with sample localities. Polar Geography and Geology 12, 239 (1988). The calculation of exposure ages follows the formalism of [5] M. G. Grosswald, in: World Atlas of Snow and Ice Lai [7]. For the production rates of in-situ 10Be, we have Resources, ed. V.M. Kotlyakov, Russian Acadamy of chosen the value of Kubik et al. [8]. All our calculations are Sciences, Moscow, Russia, 385-386 (1997). based on the production rate depth dependency of Masarik [6] J. A. Karhu et al., and Reedy [9]. Geometric shielding of surrounding hills, as Global and Planetary Changes, in press (2001). well as Quaternary uplift of Wrangel Island due to tectonics [7] D. Lai, or isostatic rebound (e.g. [10]) influences the production Earth and Planet. Sci. Lett. 104, 424 (1991). rate on the order of < 1% and have therefore been not taken [8] P.W. Kubik etal., into account here. Similarly, the influence of vegetation and Earth and Planet. Sci. Lett. 161, 231 (1998). snow coverage can be neglected. [9] J. Masarik and R. C. Reedy, The minimum exposure age estimate for the bedrock Earth and Planet. Sci. Lett. 136, 381 (1995). surface sample Wra 1 would suggest no major glacial [10] D. A. McManus and J. S. Creager, advances in this area later than about 65 ka [6]. This age, Quaternary Research 21, 317 (1984). however, could also reflect a complex exposure history 177 COSMOGENIC ISOTOPE CONSTRAINTS ON EROSION RATES IN THE HIMALAYA D. Vance (Univ. of London), M. Bickle (Univ. of Cambridge), S. Ivy-Ochs (ETHZ), P.W. Kubik (PSI) 10Be and 26Al concentrations have been measured in quartz separated from river sediment sampled along the upper reaches of the Ganges catchment in the Himalaya. The data, along with Nd isotopic data, demonstrate that the approach provides a reliable estimate of erosion rates in a mountain catchment, even when erosion rates are extremely rapid (several mm per year). Erosion is a critical process for the structural and thermal sub-catchment draining the Tibetan plateau, 4.1 mm/yr in a evolution of continental crust involved in collisional sub-catchment which drains the steepest topography in the orogens and is probably a prime control on chemical main part of the Himalayan range, and 1.3 mm/yr in a weathering rates. Quantification of time-integrated, lower altitude sub-catchment which drains vegetated spatially-averaged riverine particulate loads has foothills. These data imply that the single most important traditionally proved difficult, however [1, 2]. Present-day factor affecting erosion rates in these areas is the slope. The erosion rates can be derived by direct measurement of average erosion rate for the entire catchment of a second sediment fluxes but only provide an instantaneous snapshot tributary, the Bagirathi, is 1.4 mm/yr. that may be biased by short-term fluctuations and For the Alaknanda, the relative inputs calculated from the anthropogenic activity. Time-integrated erosion rates can 10Be analyses (62% from the plateau and mountain belt, be estimated from the volumes of sediments in molasse 38% from the foothills) are close to the estimates of relative basins but these do not provide information on spatial fluxes from Nd isotope compositions (54% from the variations of rates within mountain belts. Cosmogenic plateau and mountain belt and 46% from the foothills). The isotope concentrations of river sediment provide a sediment balance between the Alaknanda and Bagirathi measurement of the integrated erosive flux from a sub-catchments derived from the 10Be measurements (22% catchment above the sampling point [e.g. 1]. Here, we Bagirathi and 78% Alaknanda) is broadly consistent with report estimates of 10Be and 26A1 measurements on quartz in the fact that the Bagirathi drains 36% of the total area. The river bed sediments from the headwaters of the Ganges. 10Be estimates are also consistent with the balance The estimation of erosion rates from the cosmogenic suggested by the Nd isotopic composition of the two isotope inventory of river sediments depends on several tributaries and that of the river sediment beneath the assumptions that have been detailed elsewhere [2]. The confluence. The results from the lowest point sampled in most serious potential problem for this study is that of the Ganges, at Rishikesh where the river leaves the foothills contamination of 10Be analyses by rain-water derived Be and enters the Ganges plain, are more complex. The erosive because the high erosion rates in the Himalaya result in low flux at Rishikesh is less than the combined sum for the cosmogenic isotope concentrations (1 to 2 x 104 atoms Bagirathi and the Alaknanda at the confluence of the two 10Be/g). As a result samples of quartz greater than 100 g tributaries. These discrepancies may result from sediment need to be rigorously cleaned. Samples in this study have storage in the region just above Rishikesh or be due to been cleaned by a combination of repeated magnetic and anthropogenic disturbances. Calculations suggest that heavy liquid mineral separation alternating with etching in storage times of the order of 100 years would be required. cold HF until Al concentrations are less than 100 ppm. Our data display 26Al/10Be ratios that are within error of the REFERENCES production ratio [3]. In addition, duplicate samples in two localities have 10Be concentrations within analytical error. [1] D.E. Granger et al., J. Geology 104, 249 (1996). We are fortunate in that different geological units within [2] P. Bierman and E.J. Steig, Earth Surface Proc. and the Himalaya have different Nd isotopic compositions and Landforms 21,125 (1996). that the boundaries of these geological units also correspond to major topographic boundaries within the [3] P.W. Kubik etal., mountain belt. These differences in Nd isotopic Earth Planet. Sci. Lett. 161, 231 (1998). composition are mirrored in the sediment and allow the calculation of relative sediment yields from different parts of the mountain belt that can be compared with estimates derived from cosmogenic isotope-derived estimates of erosive fluxes. The 10Be concentration in the sediment allows calculation of two different erosion rates: 1) an average erosion rate for the whole catchment above that point; 2) average erosion rates for sub-catchments from subtraction of the fluxes from upstream sub-catchments. In one tributary, the Alaknanda, the calculated erosion rates are 1.5 mm/yr in a 178 DETECTION OF THE 205 YEAR SOLAR CYCLE DURING THE LAST ICE AGE /. Beer, G. Wagner, R. Muscheler (EAWAG), P.W. Kubik (PSI) A cycle of 205 years has been found in the l0Be record from the GRIP ice core (Greenland) for the glacial period 25'000 to 50'000 years before present. There are clear indications that this cycle is due to solar modulation of the galactic cosmic radiation. Cosmogenic radionuclides in ice cores offer the unique How do we know whether this cycle is of solar or climatic opportunity to detect solar cycles over time scales of origin? Assuming that the l0Be flux reflects the mean global millennia. Solar physicists are interested in the long-term l0Be production rate [7] and using published behaviour of the length and the amplitude of the cycles in paleogeomagnetic field variations [6] the geomagnetic order to understand the underlying mechanisms that drive modulation effect on the 205 yr cycle can be investigated. the solar dynamo [1]. Climatologists on the other hand The main trends of the geomagnetic field intensity during compare climate records with long records of solar the last ice age are fairly well known. In the lower panel of variability in order to investigate what role solar variability Figure 1 the paleogeomagnetic field intensity is presented plays in climate change [2]. The well known 11-yr relative to the level of today. This curve is based on Schwabe cycle was found in l0Be ice core records [3] and remanence measurements from six sediment cores from the could be extended considerably compared to the North Atlantic [6]. The figure shows in the upper panel the observational sunspot record that covers about 400 years. bandpass-filtered l0Be flux with a frequency range between (215 yr)' and (195 yr)"1. During the minimum of the The l0Be concentration data from the GRIP ice core is magnetic field at about 38.5 kyr BP the amplitude of the based on ice samples of 55 cm length. In the time interval 205 yr cycle is significantly higher than during time from 25 to 50 kyr BP, this corresponds to a mean time periods, when the geomagnetic field intensity was similar resolution of about 45 yr. to today's. Taking into account that the amplitude of solar The analysis of the l0Be flux record using various spectral activity cycles changes with time (e.g. sunspot cycle) [2], analysis techniques reveals a dominant period of 205 ± 5 yr the agreement between the envelope of the filter output [4]. The same periodicity was previously found in 14C data (upper panel) and the geomagnetic field intensity (lower measured in tree rings covering the past 10'000 years [5]. panel) is good. This geomagnetic modulation of the amplitude strongly points to a solar origin of the periodicity of approximately 205 yr in the l0Be flux. sz REFERENCES B! ZJ 9- [1] J. Beer et al., Solar Physics 181, 237 (1998). [2] J. Beeretal., a Quaternary Science Reviews 19, 403 (2000). 3 [3] J. Beer et al., Nature 347, 164 (1990). [4] G. Wagner et al., Geophys. Res. Let. 28 (2), 303 (2001). [5] M. Stuiver et al., Radiocarbon 40,1041 (1998). [6] C. Laj et al., Philos. Trans. R. Soc. London, 35 40 45 50 Ser. A 358, 1009 (2000). Age [kyrBP] [7] G. Wagner etal., 10 1 Nucl. Instr. and Meth. B172, 597 (2000). Fig. 1: Upper panel: Bandpass-filtered Be flux [(215 yr)" < x < (195 yr)"1] over the time period of 25 to 50 kyr BP in relative units. Lower panel: paleomagnetic field intensities during the last ice age based on remanence measurements of several North Atlantic sediment cores [6]. The record is low pass filtered (cutoff frequency = 1/3 kyr"1) to obtain a time resolution comparable to the envelope of the bandpass- filtered 10Be flux. 179 AIR-FIRN-TRANSFER OF 10Be ON POLAR ICE SHEETS A. Stanzick, M. Huke, D. Wagenbach (Univ. Heidelberg), P.W. Kubik (PSI), S. Kipfstuhl (AWI, Bremerhaven) Recent spatial trends of10Be have been investigated infirnfrom central Greenland and Antarctica. We found that the geographical variations of mBe in Greenland are controlled by the spatial distribution of the mean snow accumulation rate. In Antarctica, first measurements indicate a comparable mechanism. Thus, the higher 10Be concentrations there compared to Greenland seem to be the result of the higher dry deposition fraction relative to the total deposition flux. Polar ice sheets constitute important archives for aerosol related species allowing ice core based reconstruction of We expect that ongoing studies focusing on 10Be in firn and paleoclimatic and paleoenvironmental conditions. In this air of central Antarctica will confirm these results and will context, the cosmogenic radioisotope 10Be (half-life 1.5 Ma) also give new and more detailed insights into the air-firn is an important tool for the reconstruction of solar activity relationship at deep ice-core drill sites. and geomagnetic field variations. However, ice core records of 10Be are also influenced by changes of the atmospheric transfer from the source regions (stratosphere and upper troposphere) and by locally varying deposition conditions. Therefore, we investigated the second influence, the air-firn transfer of sub-micron aerosol species by utilizing the spatial variations of 10Be firn concentrations in large areas of Greenland and Antarctica to simulate the temporally varying deposition conditions. s o In central Greenland, 18 shallow firn cores comprising the years 1950-1995 were analyzed for their 10Be a concentrations along two traverses, the North Greenland © A NGT East Traverse (NGT) [1, 2] and the EGIG (Expedition • NGT West Glaciologique Internationale Groenland) Traverse [3]. V EGIG East • Others Supplemented by earlier measurements [4, 5] adjusted to -Linear fit the above period, a factor of 2-3 for the spatial variation of the central Greenland ice sheet was found. As illustrated in 0.0 Figure 1, the 10Be concentrations in firn show a clear 2.5 5.0 7.5 10.0 dependence on the inverse accumulation rate. This could be explained by a simple macroscopic deposition model [1] 1 / Accumulation Rate [a / m.w.e.] taking into account different deposition mechanisms (dry and wet) leading to nearly constant means for the dry l0 deposition 10Be flux and the 10Be concentration in fresh Fig. 1: Be average firn concentrations versus inverse snow for the entire central Greenland ice sheet. As a result, average snow accumulation rates for NGT, EGIG the dry deposition fraction of 10Be amounts to ca. 50 % for and earlier measurements [4, 5] for central the low accumulation area (-10 cm water equivalent / yr) Greenland, (m.w.e. = meter water equivalent) in the northeast of Greenland and to 35 % for Summit. REFERENCES To date, in Antarctica, only few 10Be concentrations in the [1] H. Fischer et al., J. Geophys. Res. 103 D17, 21,927- surrounding areas of the deep drilling locations of Dome C (74°S, 124°E) and DML [6] and at the German Antarctic 21,934 (1997). research station Neumayer [7] have been measured. Recent [2] H. Fischer et al., Geophys. Res. Lett. 25, 1749-1752 10Be concentrations in firn lie between 1.2 and 5.2104at/g (1998). 10 and indicate also a linear correlation between Be [3] H. Fischer et al., J. Glaciol. 41, 515-527 (1995). concentrations in firn and the inverse accumulation rate. Long-term 10Be observations at the German Antarctic [4] J. Beer et al., Nature 347, 164-166 (1990). station Neumayer [7] show similar mean 10Be [5] J. Beer et al.: Proc. 18th Int. Cosmic Ray Conf., concentrations in air relative to Summit, Greenland Bangalore, India, 9, 317-320, Tata Institute of (performed during the winter campaign 1997/1998) and Fundamental Research, Bombay (1983). similar scavenging ratios. We therefore propose that the [6] H. Oerter et al., Ann. Glaciol. 30, 27-34 (2000). higher concentrations in Antarctic firn are mainly the result of lower accumulation rates compared to Greenland leading [7] D. Wagenbach et al., J. Geophys. Res. 103 D9, to much higher dry deposition fractions in Antarctica. 11,007-11,020(1998). 180 ICE CORE RECOVERY FROM THE SOUTH INILCHEK GLACIER (KYRGHYZSTAN) H.-A. Synal (PSI), D. Cecil, J. Green, D. Naftz (US Geological Survey), J. Santos (Univ. Sevilla), J. Beer (EAWAG), K. Kreutz (Univ. Maine), C. Wake (Univ. New Hampshire), Vladimir B. Aizen (Univ. Santa Barbara) An expedition to the South Inilchek Glacier in the Tien Shan Mountains has been successfully completed. Two deep ice cores, 167 m and 162 m in length, could be recovered. At the PSI/ETH AMS facility the concentration of the long-lived radionuclides 10Be, 36Cl and 129I are now being measured in the first 100 m of one core. To recover information on climate changes the cores are being analyzed both for important trace elements and for their isotopic composition. Ice cores are unique archives preserving precipitation over records, was shipped to Zurich and is now being processed long periods of time. In the recent past, such archives have for the analysis with AMS. been exploited to obtain information on past climate changes. Most important are the deep polar ice core The radionuclide records will be used to records, which can cover time periods of several hundred thousand years. However, information derived from polar • establish time markers of fallout events from the regions cannot necessarily be taken as being representative nuclear weapons tests in the 1950's and 1960's, for changes that have taken place at mid-latitudes. In order • reconstruct the fallout distribution of 36C1 at mid- to better understand the link between observations made at polar sites and the information derived from regions at mid- latitudes, latitudes Alpine glacier archives play a key role. • evaluate ice accumulation rates, • establish a time scale in combination with stable isotope and major trace element data, • reconstruct the anthropogenic increase of ml in central Asia. To achieve these tasks the following procedure is applied. For the radionuclides 36C1 and I29I the first 100 meters will be analyzed with a resolution of 1 m per sample using accelerator mass spectrometry. This should correspond to a roughly annual time resolution. It is planned to obtain complete information on the past 60 years, reaching back well into pre-nuclear times. A suite of samples is planned to recover the pre-nuclear concentration of 36C1. In parallel to the AMS analysis, the samples will be measured with gamma spectrometry to obtain information on the l37Cs Fig. 1: Drill site at an elevation of 5085 m on the South fallout, which peaked in 1953 and 1963. Inilchek Glacier in the Tien Shan Mountains (42°N, 80°E). At this location an ice core of 167 m PRESENT STATUS length was recovered. Since a large number of different nuclides will be The U.S. Geological Survey is conducting a collaborative measured, a complex chemical sample preparation protocol isotopic research program on mid-latitude glaciers around has to be followed. It has been decided to test this protocol the world. Three of the glaciers being studied are the with a first set of samples. For this test, 20 samples have Inilchek Glacier located in the Tien Shan Mountains on the been prepared. Starting at a core depth of 10 m, the samples rd I29 borders of Kyrghyzstan, Kazakzstan, and China, the are taken from every 3 m. Preparation of the I samples Nangpai Gosum Glacier located in the Himalayan was completed and the measurements took place in Mountains of Nepal, and the Upper Fremont Glacier December 2000. A preliminary ml profile shows the rise located in the Wind River Mountain Range of Wyoming, and fall of anthropogenic I29I produced during the nuclear U.S.A. weapons tests. The preparation of the 36C1 samples will be finished by January 2001 and the measurements are During the field campaign 2000 on the South Inilchek scheduled for February 2001. The l37Cs measurements are Glacier, two deep ice cores were recovered. The first core in progress. Based on the results of the first set of samples, (167 m) has in part (100 m) been prepared in the field for 10 j6 129 lj7 the chemical separation protocol will be optimized. Sample the analysis of the radionuclides Be, Cl, I and Cs. preparation, AMS and gamma measurements will then The ice of the core, allocated to recover the radionuclide proceed. 181 PALEOMAGNETIC FIELD RECONSTRUCTION BASED ON COSMOGENIC 36C1 IN THE GRIP ICE CORE G. Wagner, J. Beer, R. Muscheler (EAWAG), C. Laj, C. Kissel (CEA/CNRS), H.-A. Synal (PSI) A distinct peak has been discovered in the 36Cl data from the GRIP ice core between the Dansgaard Oeschger events 6 and 7 at approximately 32 kyr BP. This peak can be attributed to a minimum in the geomagnetic field associated with the Mono Lake event. Furthermore the 36Cl peak provides an additional time marker similar to a peak found earlier corresponding to the Laschamp event at about 40 kyr BP. The cosmogenic radionuclide 36C1 is produced in reconstruction of the geomagnetic field using the interactions of cosmic ray particles with the Ar atoms of the continuous 36C1 record in the GRIP ice core of Greenland atmosphere [1,2]. The production varies inversely with the for the time period between 30 and 43 kyr BP [4]. The Earth's geomagnetic field intensity, which modulates the upper panel of Figure 1 shows the 36C1 concentrations (grey cosmic ray flux entering the atmosphere, and it is sensitive line with circles) from the GRIP ice core. In the same panel mainly to the geomagnetic dipole field and not the non- the 8ISO data (black line, inversely plotted) are shown [5]. dipolar components. The radionuclide production rate is In the lower panel the solid black line shows the especially sensitive to low geomagnetic fields because it geomagnetic field reconstruction derived from the 36C1 flux increases non-linearly for a decreasing geomagnetic field. data which are low pass filtered with a cutoff frequency of (2000 years)'. The dotted line shows the recently published Mono Lake Laschamp paleomagnetic field data from deep-sea sediments in the event event North Atlantic [4, 6]. The shaded area around the dotted line depicts the uncertainties (± 2 o). Overall, the two completely independent geomagnetic field reconstructions agree very well. Two prominent minima of the geomagnetic field intensity, the Mono Lake event and the Lachamp event, are present in both data sets. The fact that the Mono Lake event can be detected in the 36C1 data shows that this event is a global phenomenon due to changes in the geomagnetic dipole field. Furthermore the 36C1 peak between Dansgaard Oeschger events 6 & 7 has several important implications. I4C dating of the last ice age has to be discussed in terms of this newly discovered 36C1 peak, because the 36Cldata is a direct measure of the I4C production rate_[l, 2]. Finally, the Mono Lake event visible in geomagnetic field intensity and 36C1 records provides an additional time marker to synchronise different climate archives such as ice and sediment cores. REFERENCES CO E [1] J. Masarik and J. Beer, J. Geophys. Res. 104, 12099 - o 12111 (1999). CD 30 32 34 36 38 40 42 CD Age BP [kyr] [2] G. Wagner et al., Nucl. Instr. Meth. B 172, 597 - 604 (2000). Fig. 1: Upper panel: %C1 concentrations [4] (grey line [3] S. Baumgartner et al., Science 279, 1330 -1332 with circles) as a function of the time scale of (1998). IS Johnsen et al. [5]. In the same panel the 8 O data [4] G. Wagner et al., Earth and Planet. Sci. Lett. 181, 1 - is shown with the usual numbering scheme for the 6 (2000). Dansgaard-Oeschger events [7]. Lower panel: two paleomagnetic field [5] S. J. Johnsen et al., Tellus 47B, 624 - 629 (1995). reconstructions based on 36C1 (solid line) and on [6] C. Laj et al., Phil. Trans. Royal Soc. Lond. A 358, ocean sediments of the North Atlantic [4, 6] 1009 - 1025 (2000). (dotted line). [7] P. M. Grootes and M. Stuiver, J. Geophys. Res. 102, Polar ice sheets represent the most direct archive for the 26455 - 26470 (1997). production of %C1 [e.g. 2, 3]. Here, we present the 182 COMPOSITION-DEPENDENT SCAVENGING OF °Be BY MARINE PARTICLES R. F. Anderson, Z. Chase, M. Q. Fleisher, (LDEO, Columbia Univ.), P.W. Kubik (PSI), M. Suter (ETHZ) Many elements are removed from ocean water by scavenging onto particles. The affinity of particles for each dissolved species depends on particle composition. Fractionation during scavenging of10Be and230Th varies with the J0 30 opal/CaCO3 ratio of particles. Be/ Th ratios in marine sediments may therefore serve as a geochemical proxy to help assess the role of climate-related changes in ocean ecology as an agent regulating atmospheric CO2. Ice core records demonstrate a striking correlation between as a partition coefficient, K(N) = (atoms/g the CO2 content of the atmosphere and Earth's climate over particles)/(atoms/ g the past 400,000 years [1]. The efficacy of the ocean's seawater). Fractionation among nuclides is expressed as the biological pump as an agent partitioning CO2 between the ratio of their K values; F(Th/Be) = K(Th)/K(Be). We find atmosphere and the deep sea depends in large part on the that F(Th/Be) depends strongly on the opal/CaCO3 ratio of relative abundance of calcareous and siliceous (primarily particles (Figure 1). The composition dependence of this diatoms) plankton [2]. Consequently, there is a widespread fractionation during scavenging is so strong that it interest in reconstructing the structure of planktonic overwhelms much smaller effects due to spatial variability ecosystems under past climate regimes to establish the role in dissolved loBe/230Th ratios. Consequently, the annual l0 23O 234 of ocean biogeochemistry in regulating atmospheric CO2. average paniculate Be/ Thxs ("xs" = unsupported by U) Microfossil remains of planktonic organisms are poorly ratio delivered to sediments is a strong function of the preserved in marine sediments. Furthermore, preservation paniculate opal/CaCO, ratio (Figure 2). We are still is highly variable in time and space, and it cannot be exploring this newly-discovered relationship to determine, lo 230 evaluated a priori. It is desirable, therefore, to develop a if Be/ Thxs ratios, which are preserved during early simple geochemical proxy with which to reconstruct the diagenesis when biogenic materials are regenerated, can be initial opal/CaCO, ratio of planktonic material sinking into used as a tool to reconstruct past changes in the structure of the deep sea, prior to any modification by dissolution. planktonic ecosystems. 10' E Q. o o AESOPS TS n a EqPac 05 1 o =°o10 o U o- 10' 1 CD o ( 5 DQ *10° o • • NE Pacific O o O O AESOPS • • EqPac LL o oo '•c - 10" 10 10" 10u 10u 10' 10' opakcarbonate (%:%) opahcarbonate (%:%) lo 230 Fig. 2: Annual average Be/ Thxs ratio in marine particles Fig. 1: Relative affinity of marine particles for scavenging 230 l0 collected by sediment traps related to opal/CaCO3 of dissolved Th and Be, expressed as the ratio ratio. Individual samples depicted in Fig. 1 have of their partition coefficients (F), related to particle been combined to create annual averages. composition. EqPac = equatorial Pacific at 140°W; Additional northeastern (NE) Pacific Ocean results AESOPS = Southern Ocean at 170°W. are from Lao et al. [3]. By comparing the nuclide content of particles collected in time-series sediment traps with the dissolved concentration REFERENCES of each nuclide in the overlying water column, we have [1] J. R. Petit et al., Nature 399,429-436 (1999). established that the affinity of particles for scavenging of Th (Be) decreases (increases) with increasing opal content [2] D.M. Sigman and E.A. Boyle, Nature 407, 859-869 of particles, whereas the affinity of particles for Th (Be) (2000). increases (decreases) with increasing CaCO3 content. The [3] Y. Lao et al., Geochim. Cosmochim. Acta. 57, 205- affinity of particles for each nuclide (N) can be expressed 210(1993). 183 10Be SEDIMENTATION AND TRANSPORT PROCESSES IN THE SOUTH ATLANTIC M. Christl, C. Strobl, S. Siegle, A. Mangini (Heidelberg Academy of Science), P.W. Kubik (PSI) The production of 10Be is controlled by the flux of galactic cosmic rays which are (on a millenial timescale) modulated by the shielding of the Earth's magnetic field. If all factors influencing the depositional flux of'°Be into deep sea sediments can be quantified or estimated by model calculations, it will be possible to obtain an individual record of the Earth's magnetic field from 10Be fluxes. Deep sea sediments were suggested as archives for the reconstruction of the changes of the Earth's magnetic field in the past by measuring profiles of the cosmogenic radionuclide10Be[l,2]. Fa/Fp(Pa) / Fa/Fp(Th) Fa/Fp(Be) / Fa/Fp(Th) The aim of our study is to quantify the factors influencing - - - Fa/Fp(Th) the depositional flux of 10Be in the deep sea such as: (i) sediment redistribution (focussing and winnowing), (ii) changes of biological productivity at ocean boundaries, and (iii) glacial to interglacial changes of ocean circulation. Whereas focussing and winnowing can be corrected for by 230 normalizing to Thex, points (ii) and (iii) require model calculations. We use a two-box model [3] and are OPEN OCEAN MarginRR= 15 developing a simple multi-box model to investigate the 1.00 • 10 OpenRR- 1.5 sensitivity of Be to changes in water circulation and 0.95 - • bioproductivity in the South Atlantic. 0.90 - - - Fa/Fp(Th) , / _^._ " 0.85 First results obtained by modelling the Pacific Ocean show Fa/Fp(Pa) / Fa/Fp(Th) 10 0.80 - that the measured Be depositional flux (even if normalized Fa/Fp(Be) / Fa/Fp(Th) 2j to °Thex) can be up to 3.5 times higher than the production value, if the sediment core is located at an ocean margin 0.70 • area. On the other hand, the flux in the central Pacific may 0.65 - • V ——^^"— 230 •' v —-" amount to 2/3 ( Thex normalized) of the production value. 0.60 - Figure 1 shows the calculated depositional fluxes of 10Be, 231Pa and 230Th in the Pacific Ocean as a function of water residence time T using the model of [3]. The vertical rain res Fig. 1: Model calculations applied to the Pacific Ocean. rates (RR) in the open Pacific Ocean are taken from The following parameters were used: sediment core data [4], the values for the margin box were volumes: (margin / open ocean) = 0.1 estimated to be tenfold the open ocean value. In the central bioproductivity: vertical rain rate [g/cm2 kyr] in Pacific Ocean the residence time of water is more than 500 margin box =15 years. In this case, the 10Be flux is not very sensitive to open ocean box =1.5 changes in water circulation. The model derived X-Axis: water residence time in open ocean box scavenging factors can be used to correct the (^Th^ 10 Y-Axis: calculated depositional flux / production: normalized) Be depositional flux. Our results applied to 230 for Th: Fa/Fp(Th) the Holocene data of [4] match within the uncertainty the lc 6 2 for ke:Fa/Fp(Be)/Fa/Fp(Th) production value of 1.2-10 Atoms/cm yr [5]. 231 for Pa:Fa/Fp(Pa)/Fa/Fp(Th) In the present study we selected core 1089B to investigate l0Be sedimentation and transport processes on a high resolution time scale in the Southern Ocean. During Ocean REFERENCES Drilling Program Leg 177 sediments in the southeast Atlantic sector of the Southern Ocean were sampled to [1] L. Lao et al., EPSL 113,173 (1992). study the paleoceanographic history of the Antarctic region [2] M. Frank et al., EPSL 149, 121 (1997). on short (millennial) to long (Cenozoic) time scales. Seven sites were drilled along a north-south transect across the [3] T. Asmus et al., Marine Geology 159, 63 (1999). Antarctic Circumpolar Current [6]. Site 1089 is located [4] B. Schwarz, PhD thesis Univ. Heidelberg (1996). north of the Agulhas Ridge at a water depth of 4620 m. The average sedimentation rate over the last 450 thousand years [5] M. Monaghan et al., is about 15 cm/ka providing a high temporal resolution. In Earth Planet. Sci.Lett 76, 279 (1985/86). the future we will apply our models to the South Atlantic [6] Proc. of the Ocean Drilling Program 177, (1999). Ocean with its even more complex hydrography. 184 °Be AND Pb-TIME-SERIES OF A Fe-Mn CRUST FROM THE TASMAN BASIN, SOUTH-WESTERN PACIFIC T. van de Flierdt, M. Frank, A.N. Halliday (ETHZ), P.W. Kubik (PSI) So36 63 KD, a ferromanganese crust from the southwestern Pacific Ocean, was analyzed for 10Be by AMS and for lead isotopes by MC-ICPMS. The preliminary 10Be derived growth rate of the crust is 1.8 mm/Ma. The Pb isotope time series reflects an isotopic variations of the ambient deep water caused by changes of the sources of weathering input and ocean circulation over the past ~ 22 Ma. The isotopic composition of Pb in the ocean is influenced general increase in the 207Pb/206Pb ratios from -19 Ma to the by continental weathering, hydrothermal inputs and present. This general increase has not been continuous. circulation of water masses. It varies within and between Two steps where the Pb isotope ratios increased abruptly the oceans, consistent with its short residence time in are observed at 7.1 Ma and 2.9 Ma. seawater (50 years in the Atlantic and up to 200-400 years 0.839 in the Pacific [1]). Ferromanganese crusts, which have 0.838 grown by direct precipitation of Mn and Fe hydroxides from ambient deep water, incorporate its Pb isotopic 0.837 composition and record variations over millions of years. 0.836 H Fe-Mn crust 63 KD was recovered during cruise Sonne 36 -0.835 from the Tasman Basin in the southwestern Pacific Ocean £ 0.834 (28°34.0'S, 163°00'E) in a water depth of 1700 m. A - 0.833 profile of this 35 mm thick crust was taken to obtain a 0.832- chronology based on the decay profile of cosmogenic 10Be (tl/2= 1.5 Ma). A growth rate of 1.8 mm/Ma is derived from -0.831 10 the Be data of the uppermost 16.5 mm of the crust. Below 0.830 10 16.5 mm depth, the Be data do not show an exponential 0 20 decay which points to rapid growth. This needs to be 9 verified by normalization to stable Be for the same 207 206 Fig. 2: Pb/ Pb time series of crust 63 KD measured by samples. These measurements will be made in the near MC-ICPMS (data points are shown as filled future. diamonds). For comparison 3 profiles of crusts from the central Pacific are shown, which were measured by LA-MC-ICPMS [3] and by MC- ICPMS [4]. 1.00 o The 207Pb/206Pb ratios of crust 63 KD are generally lower than for crusts in the equatorial Pacific. This is due to the stronger influence of Circum Antarctic water masses, 207 206 0.10- which have a Pb/ Pb ratio of ~ 0.828 before entering the Pacific Basin. During the past ~ 6 Ma the Pb isotope time series shows trends comparable with the equatorial Pacific data sets, which points to similar input sources. Prior to 6 Ma the difference between crust 63 KD and the equatorial 0.01 4 8 12 16 20 24 28 32 36 Pacific was much larger. This gives evidence for the depth [mm] dominance of local input sources at these locations and suggests a weaker water mass exchange and mixing Fig. 1: 10Be data for Fe-Mn crust 63 KD from the Tasman between 19 and 6 Ma. To validate these interpretations a Basin, southwestern Pacific. For the time series time series of Nd isotopes will be measured. Nd has a (Fig. 2) the growth rate of 1.8 mm/Ma has been longer residence time in the ocean and is therefore less extrapolated to the base of the crust. influenced by local sources. A higher resolution record was sampled and analyzed for REFERENCES variations in Pb isotope composition by MC-ICPMS (Figure 2). The external reproducibility was obtained by [1] B. K. Schaule and C. C. Patterson, repeated measurements of the NBS 981 standard. All Earth Planet. Sci. Lett. 54, 97 (1981). measured sample ratios were normalized to the accepted [2] W. Todt et al., Gephys. Monogr. 95, 429 (1996). value for the standard [2]. Figure 2 shows the time series of [3] J.N. Christensen et al., Science 277, 913 (1997). the 207Pb/206Pb ratio in comparison to other crusts from the [4] K. David et al., Chem. Geol. (2001), in press. Pacific Ocean. The time series of crust 63 KD shows a 185 10Be / 7Be RATIOS AT THE HIGH-ALPINE SITE JUNGFRAUJOCH C. Schnabel (Univ. Bern & ETHZ), L. Tobler, P. W. Kubik, M. Schwikowski (PSI), H. W. Gdggeler (Univ. Bern & PS1) The particle bound atmospheric concentrations of the cosmogenic radionuclides 7Be and 10Be have been measured at the Jungfraujoch (3580 m a.s.l). The isotopic ratio l0Be /1 Be can be used as a probe for the intrusion of relatively old stratospheric air masses into the troposphere. Stratospheric-tropospheric exchange (STE) is one of the The very high 10Be/7Be ratios at the end of February 2000 factors controlling the budgets of ozone, water vapour and indicate a stratospheric intrusion, which has been other substances in the lower stratosphere and the confirmed by ozone and relative humidity data. Luder [4] troposphere. Cosmogenic radionuclides, which are also measured a high monthly mean isotopic ratio in produced by cosmic ray particles in the atmosphere, could precipitation at the Jungfraujoch in March 1984. However, provide valuable information on STE. A stratospheric in that case the uncertainty of the isotopic ratio was very intrusion into the troposphere gives rise to an increase of large and a minimum in 7Be concentration suggested dust 7Be and ozone concentrations as well as to a decrease of contamination as explanation. We tend to exclude this relative humidity in the affected tropospheric area. explanation for our case, since Ca concentrations, measured However, a maximum in 7Be can also result from other as a dust indicator, did not show enhanced concentrations meteorological processes. If such a process takes place, [5] and since a maximum in 7Be concentration was found. 10Be will be affected to the same extent as 7Be. The slow decrease of the very high 10Be/7Be ratios should Consequently, Raisbeck et al. [1] proposed to use the be due to additional intrusion events during March 2000, isotopic ratio 10Be/7Be as a probe for atmospheric transport which were reported by other groups taking part in the processes. Raisbeck et al. [1] and Dibb et al. [2] both found STACCATO project measuring high ozone and 7Be higher 10Be/7Be ratios in the lower stratosphere than in the concentrations and low relative humidity at the Zugspitze upper one. They explained this by a relatively slow (Germany) [6], the Sonnblick (Austria) [7] and Monte downward transport of air masses from the upper Cimone (Italy) [8]. However, for this period several stratosphere (7Be decays faster than 10Be). These higher samples were combined obscuring the temporal fine 10Be/7Be ratios in the lower stratosphere, which clearly structure. In terms of ozone concentrations alone, an exceed 10Be/7Be ratios of approx. 2.2 measured by Dibb et intrusion event that took place from March 20 to March 22, al. [2] for tropospheric air masses, can be used to determine 2000 was more pronounced at least at the Zugspitze [6] and intrusions of relatively old stratospheric air into the at Monte Cimone [8] than that one at end of February. troposphere. Therefore, the period from March 19 to March 26, 2000 has been chosen for a detailed case study. Both Be isotopes In the framework of the EU project STACCATO (Influence will be measured with the same time resolution as the filter of Stratosphere-Troposphere Exchange in a Changing collection (2 days). Climate on Atmospheric Transport and Oxidation Capacity), particle bound 7Be and 10Be are collected on glass fibre filters (using a HIVOL air sampler) at the ACKNOWLEDGMENT Jungfraujoch with a time resolution of 48 h by the NABEL This study is part of the EU research project STACCATO 7 network [3]. Half of the filters are used to measure the Be (EVK2-CT1999-00050) and is funded by the Bundesamt activity (T1/2 = 53.12 d) through its characteristic y- fur Bildung und Wissenschaft (BBW) of Switzerland. The 10 radiation in a well-type Ge-detector and the Be sampling and the delivery of the filters by the EMPA concentration using accelerator mass spectrometry at the (operator of the NABEL network) are highly appreciated. PSI/ETH facility. 10Be/7Be ratios measured on filter samples collected at the REFERENCES Jungfraujoch between Feb. 19 and April 4, 2000 are shown in Fig. 1. [1] G.M. Raisbeck etal., Geophys. Res. Lett. 8, 1015 (1981). [2] J.E. Dibb et al., J. Geophys. Res. 99, 12855 (1994). [3] NABEL Luftbelastung 1999, BUWAL SRU-316 (2000). [4] R. Luder, Lizentiatsarbeit, Universitat Bern (1986). [5] S. Henning, pers. comm. [6] T. Trickl and E. Scheel, pers. comm. Date [7] M. Mandl, pers. comm. Fig. 1: Particle bound 10Be/7Be ratios in air filter samples [8] P. Cristofanelli, pers. comm. from the Jungfraujoch (3580 m a.s.l.). 186 129I IN RAIN WATER NEAR ZURICH C. Schnabel (ETHZ & Univ. Bern), S. Szidat (Univ. Hannover & Univ. Bern & PSI), H.-A. Synal (PSI), J.M. Lopez- Gutierrez (Univ. Sevilla), J. Beer (EAWAG) I291 concentrations in precipitation at Diibendorf/Ziirich have been determined with monthly resolution during almost three years in the mid 1990s. The results confirm that annual mean I29I concentrations in precipitation in central Europe have remained about constant since the late 1980s. Some evidence for a substantial contribution of the gaseous emissions from nuclear fuel reprocessing plants to 129I in the precipitation in central Europe is presented. 129 I is a long-lived (T1/2=15.7 Ma) radionuclide whose concentrations in the environment have been elevated by Liquid emissions (1988=1) several orders of magnitude due to human activities, mainly Gaseous emissions (1988=1) by emissions from nuclear fuel reprocessing plants. After a A Bachhuber & Bunzl, Bavaria [5] 129 nearly continuous increase of I concentrations from 1950 o Dijbendorf / Zurich [This work] to the mid 1980s, which is reflected in an ice core from the 129 ~O~ Krupp & Aumann, South. Germany Swiss Alps [1], the environmental I concentrations in [3] -O- Szidat et al., Lower saxony, inland central Europe seemed to have remained stable in the 1990s [6] [2]. One of the main goals of the present work is to verify this observation using precipitation samples from Switzerland. Our data show a large month-to-month variability of a factor of about 100 between the lowest and the highest 1988 1990 1998 2000 monthly 129I atom concentration. A similar variation was observed by Krupp and Aumann in rainfall in Germany [3]. 129 A comparison of our annual mean I concentrations with Fig. 1: Liquid and gaseous 129I emissions from La Hague literature data for central Europe from the late 1980s to the and Sellafield normalized to their 1988 values (for late 1990s is shown in Fig. 1. It confirms the statement of references see [4]). One scale unit corresponds to 129 Szidat et al. [2] that I concentrations in precipitation in 50.5 kg 129I liquid and to 6.89 kg gaseous central Europe have not increased further since the late emissions. 129I concentrations in precipitation are 1980s. normalized to the 1988 value of Bachhuber and Bunzl [5]. One scale unit equals 3.75-109 atoms The question, whether gaseous or liquid emissions from the 129 two major European nuclear fuel reprocessing plants, La I/kg. A vertical line indicates a range of annual Hague and Sellafield, dominate 129I in precipitation, is means from different locations. addressed in detail by Schnabel et al. [4]. Here, just a few aspects of this question are briefly discussed. Although the ACKNOWLEDGMENT liquid emissions exceeded the gaseous ones by a factor of The preparation of some of the samples by S. Bollhalder- 30 from 1991-1996, an upper limit of only 1.37 kg is Liick (EAWAG) is gratefully acknowledged. estimated for the mass of 129I that is transferred annually from the sea to the atmosphere due to a low iodine evaporation from the marine into the atmospheric REFERENCES compartment. This upper limit can preliminarily be [1] M.J.M. Wagner etal., compared to the 6.5 kg 129I emitted per year directly into Nucl. Instrum. Meth. B 113, 490 (1996). the atmosphere during the same period [4]. [2] S. Szidat et al., Another approach to address the question is to compare the Nucl. Instrum. Meth. Phys. Res. B172, 699 (2000). time dependence of 129I concentration in precipitation with those of the gaseous and liquid releases from the two [3] G. Krupp, D. C. Aumann, plants. The respective data are also shown in Fig. 1. The J. Environ. Radioactivity 46, 287 (1999). fact that the gaseous releases correlate much better with the 129I concentrations in central Europe suggests a substantial [4] C. Schnabel et al., subm. to Radiochim. Acta, (2001). 129 contribution of gaseous releases to I in the precipitation. [5] H. Bachhuber and K. Bunzl, However, we were not yet able to explain quantitatively the J. Environ. Radioactivity 16, 77 (1992). large month-to-month scatter in the concentrations and can [6] S. Szidat, Ph.D. thesis, University Hannover (2000). therefore not definitely answer the question about the dominant 129I source. 187 PROSPECTS OF 129I AS AN ENVIRONMETAL TRACER S. Szidat (Univ. Hannover & Univ. Bern & PSI), T. Ernst, R. Michel (Univ. Hannover), C. Schnabel (Univ. Bern & ETHZ), H.-A. Synal (PSI), J.M. Lopez-Gutierrez (Univ. Sevilla) In a systematic study, the distribution of the long-lived radionuclide ]29I together with the only stable iodine isotope, 127I, was investigated in precipitation, surface and shallow groundwaters in Lower Saxony, Germany. Estimated residence times of iodine in the surface soil zone surpass water residence times by one to three orders of magnitude. The natural abundances of I have changed by several residence times in the surface soil. In this model, mean orders of magnitude as a consequence of civil and military transition times rare calculated according to use of nuclear fission. The anthropogenic signal of 129I can t be used to study environmental processes [1-3]. Due to the T = - biophilic character of iodine, l29yl21\ isotopic ratios may In (1 -Hit)) show the significance of organic matter in the surface soil zone for the iodine transport [3]. with the time t of constant input and the fraction H(t) of the input signal that is observed in the investigated In a systematic study, we analyzed 127I and 129I in open- compartment, t characterizes the time span between the field precipitation, surface and shallow groundwaters in sampling time of a sample and 1986, the interpolated Lower Saxony, Northern Germany (Tab. 1). The area was beginning of the constant input; H(t) is given as the ratio of divided into four regions, namely I (NW): North Sea 129I/127I in the examined sample and the mean precipitation coastal area, II (SW): Northern German lowlands, III (SE): value of 6.5-10"7. ris calculated for every single sample Harz Mountains area, and IV (NE): Valley of the river and geometric means are given in Tab. 2 with standard 127 Elbe. I was measured with ICP-MS at University of uncertainties of the mean. Hannover, 129I with accelerator mass spectrometry (AMS) at the PSI/ETH tandem facility. For details of sample Table 2: Mean iodine residence times in surface soil zones preparation, measurements and quality assurance see [2-4]. and characteristic time constants of water transfer into groundwater with standard uncertainties. Table 1: 129i/127I in several Lower Saxonian natural waters from 1997-1999 as geometric means with standard deviations of the observed values. Sample Region ^iodine tritium [a] [a] 12 27 I biased by sea water — V i Sample Region 50 [1010] Surface II 360 ! 50 — 210 1600 water III 1290 ! 180 — I 10 8300 1400 160 2100 IV 670 ! 130 - Precipitation II 9 6200 1600 210 3800 I 830 ! 170 7 ± 5 (open-field) III 4600 2100 80 2200 Ground II 360 ! 70 12 ± 1 IV 3700 1400 1000 water III 2700 ! 700 9 ± 4 490 46000 I 12 460 ! 240 IV 40000 ! 21000 19 ± 2 130 Surface II 12 220 ! 80 This modelling suggests a horizontal and vertical iodine 40 water III 11 60 ! 30 transport delayed by one to three orders of magnitude 120 compared to water movements. Surface and ground water IV 12 120 ! 60 residence times agree within their expanded uncertainties 50 I 3 ioo ! 30 (95 %) except for region IV where an impermeable zone at 120 the ground water sampling site is assumed. Ground II 4 220 ! 80 28 water III 4 30 ! 15 + 10 REFERENCES IV 5 2 2 The deposition of atmospherical " I is the most important [1] A. Schmidt et al., Sci. Total Environ. 223, 131 (1998). source in the upper terrestrial environment in central [2] S. Szidat et al., Europe. A survey of central European precipitation of the last 20 years [2-4] indicated a dramatic increase of 129I/127I Nucl. Instrum. Meth. B 172, 699 (2000). ratios until the middle 1980s, followed by a nearly constant [3] S. Szidat, Ph.D. Thesis, Univ. Hannover (2000). value of about 6.5-10"7 until now. [4] S. Szidat et al., Kerntechnik 65,160 (2000). When using these precipitation values as an input function in a simple exponential model [5] for the transfer of iodine [5] A. Zuber in: ed P. Fritz, J. C. Fontes, Handbook of in the surface of a catchment, one can estimate mean iodine environmental istope geochemistry, Vol. 2B, p. 1 Elsevier, Amsterdam (1986). 188 BERYLLIUM LIQUID ALLOY ION SOURCES FOR FOCUSED ION BEAM IMPLANTATION R. Mtihle (ETHZ, PSI), M. Dobeli (PSI) AuBe and AuBeSi liquid alloy ion sources have been developed for focused ion beam implantation. The alloys were produced by melting in an evacuated quartz ampoule followed by quenching in water. The melting property of the alloys were investigated by pyrometric temperature measurements. We have investigated the source current stability, the current-voltage characteristics, and the mass spectrum as a function of the source current. Liquid metal ion sources (LMIS) and especially liquid alloy given in Tab. 1. The fraction of Be ions is lower than ion sources (LAIS) have found extensive use as ion sources expected. Nevertheless, the source is suitable for ion of high brightness in focused ion beam (FIB) systems with implantation purposes because of the low operation a wide range of applications such as microfabrication by temperature and its high stability. A small percentage of Si micromachining and deposition, focused ion beam ions was found in the mass spectrum of the AuBe LAIS lithography and ion implantation as well as microanalysis due to reactions between beryllium and the quartz ampoule. of materials [1]. The development of LAIS for Be and Si The AuBeSi LAIS could be operated in a stable way at a are important for the implantation in compound source current as low as 1 LIA at a heating current of 2.4 A semiconductors, as for example GaAs and GaP. and a temperature of 630 °C. The mass spectrum for a The alloys were prepared by melting the constituents in source current of 5 \xA is shown in Fig. 1 and the evacuated quartz ampoules, followed by a water quench at corresponding ion flux fractions for this source current are room temperature. The aim was to prepare eutectic given in Tab. 1. The summation over all peaks in the mass compositions, namely Au795Be2l5 with a liquidus spectrum gives the following ion flux fractions in atom-% temperature of 580 °C [2] and Au70Bel5Sil5 with a liquidus for Au/Be/Si: 93.1/6.8/0.1 for the AuBe LAIS and temperature of 610 °C [3]. The indices stand for atomic 86.6/6.5/6.9 for the AuBeSi LAIS. percent. An ion source consists of a tungsten needle 1.E+06 emitter, which is wetted with the alloy, and an extraction electrode with a hole diameter of 1 mm at a distance of 0.6 mm from the needle tip. Both sources were investigated in 1.E+05 - a time-of-flight spectrometer [4]. Their characteristics were determined as a function of the temperature, which was measured from outside of the vacuum chamber with an c 1.E+04 - optical two-colour pyrometer. Table 1: Ion flux fractions (IFF) in % of the AuBe and 1.E+03 - AuBeSi LAIS at a source current of 5 |iA. 1.E+02 Ion IFF / % IFF / % AuBe AuBeSi 1.E+01 500 2500 3000 Be++ 2.0 1.9 Be+ 0.6 1.6 Fig. 1: Mass spectrum of the AuBeSi liquid alloy ion source for a source current of 5 |iA, obtained with sr 1.5E-2 4.6 a time-of-flight spectrometer [4]. sr 3.0E-3 1.7 REFERENCES Au++ 17.6 2.9 [1] J. Melngailis, J. Vac. Sci. Technol. B 5,469 (1987). + Au 66.1 72.1 [2] Phase Diagrams of Binary Gold Alloys, ed. H. Okamoto and T. B. Massalski (ASM, Au + 7.1 5.3 2 Metals Park, OH, USA) (1987). + Au3 3.1 1.1 [3] D. F. Reich et al., Microelectron. Eng. 5, 171 (1986). The AuBe LAIS could be operated in a stable way at a [4] R. Miihle et al., source current as low as 0.54 uA for a heating current of J. Phys. D: Appl. Phys. 32,161 (1999). 2.8 A and a temperature of 610 °C. The measured ion flux fractions of the main peaks at a source current of 5 |JA are 189 A GePd LIQUID ALLOY ION SOURCE FOR FOCUSED ION BEAM IMPLANTATION R. Muhle (ETHZ, PSI), A. Spiegel (EPFL), M. Dobeli (PSI) A GePd liquid alloy ion source has been developed for selective surface activation by focused ion beam implantation. The alloy was produced by melting in an evacuated quartz ampoule followed by quenching in water. The melting property of the alloy was investigated by pyrometric temperature measurements. We have investigated the source current stability, the current-voltage characteristics, and the mass spectrum as a function of the source current. New pathways are now explored to sensitize single crystal 1.E+05 surfaces for selective chemical or electrochemical nanogrowth or nanostructuring by focused ion beam implantation [1]. This necessitates the development of ion 1.E+04 - sources for the required ion species. Our first experiments have been made with Ga ions from a Ga liquid metal ion source (LMIS) and Au ions from a AuSi liquid alloy ion 1.E+03 source (LAIS). For the implantation of Pd ions a GePd LAIS was developed using a eutectic alloy with 36 atomic percent palladium and a liquidus temperature of 725 °C [2]. 1.E+02 The alloy was prepared by melting the constituents in an evacuated quartz ampoule followed by a water quench at 1.E+01 room temperature. This procedure ensures that the alloy 500 1000 1500 2000 2500 solidifies congruently and is therefore nearly homogeneous. channel The ion source consists of a tungsten-needle emitter, which is wetted with the alloy, and an extraction electrode with a Fig. 1: Mass spectrum of the GePd liquid alloy ion source hole diameter of 1 mm at a distance of 0.6 mm from the for a source current of 5 |iA, obtained with the needle tip. The source was investigated in a time-of-flight time-of-flight spectrometer. spectrometer [3]. Its characteristics were determined as a function of the temperature, which was measured with an optical two-colour pyrometer. The GePd LAIS could be operated in a stable way at a source current as low as 0.86 iiA for a heating current of 2.7 A and a temperature of 750 °C. The mass spectrum is shown in Fig.l. Flux fractions of selected ions are listed in Tab.l for a source current of 5 |iA. Tab. 1: Ion flux fractions (IFF) of the first peaks in Fig. 1. Ion Pd+ Pd++ Ge+ Ge++ GePd+ GePd++ IFF / % 28. 1.0 14. 19. 14.5 9.3 9 4 9 200 400 600 800 1000 1200 Each peak in the mass spectrum is composed from several channel sub-peaks due to the many isotopes of Ge and Pd. ++ Germanium has 5 isotopes and palladium 6. This results in Fig. 2: Mass spectrum of the GePd molecules from the 13 peaks for the GePd+ and GePd++ molecular ions (see GePd liquid alloy ion source for a source current Fig. 2 for the GePd++ molecules). As for the case of AuGe of 2.5 jxA, obtained with the time-of-flight and CoGe LAIS, Ge, ions could not be observed. The spectrometer. summation over all peaks in the mass spectrum yields 51.4 at-% Ge and 48.6 at-% Pd. This composition and the ion flux fractions change with source temperature and source REFERENCES current. The energy width of the different peaks was also [1] A. Spiegel et al., This annual report. determined as a function of source current. [2] H. Okamoto, J. of Phase Equilibria 13, 410 (1992). At a source current of 5 \iA the Pd+ peak has an relative intensity of nearly 30 %. In conclusion, the developed [3] R. Miihle et al., GePd liquid alloy ion source is well suited for the J. Phys. D: Appl. Phys. 32,161 (1999). implantation of Pd with the focused ion beam. 190 NANOSTRUCTURED MATERIALS BY SELECTIVE SURFACE ACTIVATION USING FOCUSED ION BEAM IMPLANTATION A. Spiegel (EPFL), R. Miihle (ETHZ, PSI), M. Dobeli (PSI), P. Schmuki (Univ. ofErlangen-Nurnberg, Germany) Ion beam induced surface damage on semiconductors may promote local electrochemical reactions which can be used to deposit material selectively at the damaged sites. Cu and Au have been elctrochemically deposited on focused ion beam written patterns on Si wafers with a spatial resolution of <300 nm. The sub-100 nm range is within reach. The aim of this work is to explore new pathways to achieve Different electrolytes were used (0.1 M CuSO4 + 0.05 M selective chemical or electrochemical nanogrowth or H2SO4 and 0.01 M CuSO4 + 0.05 M H2SO4 for Cu nanostructuring of materials on locally sensitized single deposition and 0.01 M KAu(CN)2 + 1 M KCN for Au crystal silicon surfaces. In earlier work [1,2] this effect has deposits) under varying electrochemical conditions been used to locally dissolve and porosify the substrate by (potentiostatic with varying exposure times and potentials oxidation. Sensitization is carried out by a direct writing and potentiodynamic with varying scanning velocity and process using the focused ion beam (FIB) system installed start as well as end potentials). at the Laboratory for Micro- and Nanotechnology (PSI). At activated surface locations a subsequent chemical or RESULTS AND CONCLUSION electrochemical reaction will be triggered selectively leading to the nanosize material or functionality. Fig. 1 We have been able to selectively deposit both gold and shows current-voltage curves of an intact and a damaged copper in the sub-micrometer range on FIB-induced surface silicon surface in a Cu containing electrolyte. The onset of damage patterns. Cu deposition causes a current increase (electrons have to get from the Si surface to the Cu2+ ions in the electrolyte in order to reduce it to metallic Cu, which will then precipitate). The point where the current increase begins is called 'deposit formation potential' (DFP;). It can be seen easily that the DFP is shifted to higher potentials E for the FIB-damaged surface; we call this shifted DFP for defect surfaces DFPd. We assume that this shift is due to a facilitated Schottky barrier breakdown at the defect sites. EXPERIMENTAL DETAILS For ion implantation we used the FIB system installed in the LMN cleanroom at PSI. .'.(: III Fig. 2: Au deposited on FIB-written damage template ^ i (optical micrograph). s j > i Fig. 2 shows the sample surface after electrochemical 10 treatment. It can be seen clearly that Au deposition has 10"" Selective occurred. Subsequent analysis by electron microscopy and intact Deposition k atomic force microscopy showed that the Au crystallites 7 d efect DFP 10" have an average size of roughly 100 nm and that the D 10"8 i , , , i , , , i smallest structures were in the 300 nm range. In the near -8000 -6000 -4000 -2000 future we will further optimize the process in order to E vs SCE [mV] achieve higher resolution (<100 nm) as well as more Fig. 1: Current-voltage behavior of intact and damaged Si homogeneously distributed particles (especially when using (idealized). Cu electrolytes). 2+ We have been working with Au-Si (for Au ions) and Ga REFERENCES ion sources built inhouse. Different acceleration voltages (23 and 30 keV) as well as implant doses (1011 - 1017 [1] P. Schmuki et al., Phys. Rev. Lett. 80, 4060 (1998). 2 ions/cm ) have been used. These parameters were varied in [2] A. Spiegel et al., order to determine their influence on the electrochemical J. Electrochem. Soc. 147, 2993 (2000). behavior. All electrochemical experiments were carried out using a standard three-electrode setup (sample as working electrode, Pt counter electrode, standard calomel reference electrode SCE) under potentiostatic or -dynamic conditions. 191 LIST OF PUBLICATIONS LABORATORY FOR PARTICLE PHYSICS R-87-12 J. Arnold, B. van den Brandt, M. Daum, Ph. Demierre, M. Finger, M. Finger,Jr., J. Franz, N. Goujon-Naef, P. Hautle, R. Hess, A. Janata, J. A. Konter, H. Lacker, C. Lechanoine-Leluc, F. Lehar, S. Mango, D. Rapin, E.'Rossle, P. A. Schmelzbach, H. Schmitt, P. Sereni, M. Slunecka, A. Teglia, B. Vuaridel Measurement of spin observables in neutron-proton elastic scattering Part I: Correlation parameters Eur. Phys. J. C 17, 67 (2000). J. Arnold, B. van den Brandt, M. Daum, Ph. Demierre, M. Finger, M. Fingerjr., J. Franz, N. Goujon-Naef, P. Hautle, R. Hess, A. Janata, J. A. Konter, H. Lacker, C. Lechanoine-Leluc, F. Lehar, S. Mango, D. Rapin, E.'Rossle, P. A. Schmelzbach, H. Schmitt, P. Sereni, M. Slunecka, A. Teglia, B. Vuaridel Measurement of spin observables in neutron-proton elastic scattering Part II: Rescattering parameters Eur. Phys. J. C 17, 83 (2000). R-87-13 M. Planinic, D. Androic, G. Backenstoss, D. Bosnar, T. Dooling, M. Furic, P. A. M. Gram, N. K. Gregory, A. Hoffart, C. H. Q. Ingram, A. Klein, K. Koch, J. Khler, B. Kotlinski, M. Kroedel, G. Kyle, A. Lehmann, A. O. Mateos, K. Michaelian, T. Petkovi, R. P. Redwine, D. Rowntree, N. Simicevic, R. Trezeciak, H. Ullrich, H. J. Weyer, M. Wildi, and K. E. Wilson Pion absorption on 4-He into the ppdfinal state. Phys. Rev. C 61 054604,1 (2000). R-96-05 M. Daum, M. Janousch, P.-R. Kettle, J. Koglin, D. Pocanic, J. Schottmuller, C. Wigger, Z. G. Zhao KARMEN Time Anomaly: Search for a neutral particle of mass 33.9 MeV in pion decay Phys. Rev. Lett. 85, 1815 (2000). R-97-02 D. F. Anagnostopoulos, G. Borchert, D. Chatellard, J.-P. Egger, D. Gotta, M. Hennebach, P. Indelicate, Y.W. Liu, B. Manil, N. Nelms and L. M. Simons Mass of the charged pion Acta Phys. Pol. B 31, 2219 (2000). T. Siems, D. F. Anagnostopoulos, G. Borchert, D. Gotta, P. Hauser, K. Kirch, L. M. Simons, P. El-Khoury, P. Indelicate, M. Augsburger, D. Chatellard, J.-P. Egger First direct observation of Coulomb explosion during the formation of exotic atoms Phys. Rev. Lett. 84, 4573 (2000). R-97-03 Ch. Brian§on, V. B. Brudanin, J. Deutsch, V. Egorov, T. Filipova, M. Kudoyarov, V. Lobanov, T. Mamedov, A. Pasternak, R. Prieels, A. Salamatin, Yu. Shitov, Ts. Vylov, I. A. Yutlandov, Sh. Zaparov. The spin-neutrino correlation revisited in 28Si muon-capture : A new determination of the induced pseudosaclar coupling gp/ga Nucl. Phys. A671, 647 (2000). R-97-05 P. Kammel, A. Adamczak, V. A. Andreev, D. V. Balin, T. Case, K. M. Crowe, J. Deutsch, P. U. Dick, A. Dijksman, J. Egger, A. A. Fetisov, V. A. Ganzha, J. Govaerts, F. J. Hartmann, W. D. Herold, V. I. Jatsoura, A. G. Krivshich, E. M. Maev, O. E. Maev, V. E. Markushin, J. Martino, C. Petitjean, G. E. Petrov, R. Prieels, S. M. Sadetsky, G. N. Schapkin, R. Schmidt, W. Schoeps, W. Schott, G. G. Semenchuk, A. A. Vorobyov, N. I. Voropaev, Precision measurement of /ip capture in a hydrogen TPC Nucl. Phys. A 663/664,911c (2000). 192 R-98-02 B. Gartner, P. Ackerbauer, W.H. Breunlich, M. Cargnelli, P. Kammel, R. King, B. Lauss, J. Marton, W. Prymas, J. Zmeskal, C. Petitjean, M. Augsburger, D. Chatellard, J.-P. Egger, T. von Egidy, F. J. Hartmann, A. Kosak, M. Mühlbauer, F. Mulhauser, L.A. Schaller, L. Schellenberg, H. Schneuwly, Y.-A. Thalmann, S. Tresch, A. Werthmüller Ground state muon transfer from deuterium to 3He and 4He Phys. Rev. A 62, 012501 (2000). R-98-03 R. Pohl, F. Biraben, C.A.N. Conde, C. Donche-Gay, T. W. Haensch, F. J. Hartmann, P. Häuser, V. W. Hughes, O. Huot, P. Indelicate, P. Knowles, F. Kottmann, Y.-W. Liu, F. Mulhauser, F. Nez, C. Petitjean, P. Rabinowitz, J.M.F. dos Santos, L.A. Schaller, H. Schneuwly, W. Schott, L. M. Simons, D. Taqqu, F. Trehin, J. 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Schenck Magnetic and structural instabilities in the stripe-phase region of La\^^BaQ.r25-ySryCu0i (0< y< 0.1) J. Phys.: Condens. Matter 12, 3401 (2000). RA-93-02 C. J. Rhodes Duplicity ofthiyl radicals in toxicology: Protector and Foe in: Toxicology of the Human Environment - the Critical Role of Free Radicals C. J. Rhodes, ed., Taylor and Francis, London, 2000, p285. C. J. Rhodes, T. C. Dintinger, C. A. Scott Dynamics of cyclohexadienyl radicals in zeolite X, by longitudinal field muon relaxation Magn. Reson. Chem. 38, 62 (2000). C. J. Rhodes, T. C Dintinger, C. A. Scott Sorption of benzene in cation-exchanged zeolite X, as measured by muon spin relaxation (LF-MuSRx) Magn. Reson. Chem. 38,729 (2000). P. F. Kelly, A. Soriano-Rama, P. T. Wood, I. D. Reid, T. A. Claxton, C. J. Rhodes,U. A. Jayasooriya Muonium addition to sulfur-nitrogen chains Magn. Reson. Chem. 38, S65 (2000). C. J. Rhodes Radiotracer studies of free radicals using muonium (the Second Hydrogen Radioisotope) Prog. 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Fischer ßSR spectroscopy on superconducting Chevrel phase compounds Physica B 289-290, 381 (2000). RA-94-03 G. J. Nieuwenhuys, N. G. Patil, H. Noijons, D. G. Tomuta, D. E. MacLaughlin, R. H. Heffner, A. Amato Determination of the muon site in URh^Ge-i Physica B 289-290, 228 (2000). RA-94-04 F Y. Ogrin, S. L. Lee, C. Ager, C. M. Aegerter, E. M. Forgan, S. H. Lloyd, P. G. Kealey, T. Riseman, R. Cubitt, G. Wirth Vortex studies in heavy-ion irradiated BÍ2.i§SrittCaCu2O%+$ probed by ßSR and small-angle neutron scattering Physica B 289-290, 355 (2000). RA-94-07 Eve M. Martin, E. Schreier, G. M. Kalvius, A. Kratzer, O. Hartmann, R. Wäppling, D. R. Noakes, K. Kröp, R. Ballou, J. Deportes Magnetic properties ofGdMn^from ßSR Physica B 289-290,265 (2000). RA-94-08 F J. Burghart, W Potzel, G. M. Kalvius, E. Schreier, G. Grosse, D. R. Noakes, W Schäfer, W. Kockelmann, S. J. Campbell, W. A. Kaczmarek, A. Martin, M. K. Krause Magnetism of crystalline and nanostructured ZnFe^O^ Physica B 289-290,286 (2000). 202 RA-94-14 G. Solt, C. Baines, V. S. Egorov, D. Herlach, U. Zimmermann Observation ofdia- and paramagnetic domains in beryllium and white tin by muon spin rotation spectroscopy J. Appl. Phys. 87, 7144 (2000). G. Solt, V. S. Egorov, C. Baines, D. Herlach, U. Zimmermann Evidence for Condon domains in white tin with two de Haas-van Alphen periods Phys. Rev. B 62, R11933 (2000). RA-95-03 M. Pinkpank, A. Amato, D. Andreica, F. N. Gygax, H. R. Ott, A. Schenck Dynamic magnetic properties of GdBaiCuzO^x as function of the oxygen content Physica B 289-290,295 (2000). M. Pinkpank, A. Amato, D. Andreica, F. N. Gygax, H. R. Ott, A. Schenck Time effects induced by the muon point charge in the antiferromagnetically ordered phase of HoBa^Cu^Oi Physica B 289-290,316 (2000). RA-95-10 V. Yu. Pomjakushin, A. M. Balagurov, A. A. Zakharov, F. N. Gygax, A. Schenck, A. Amato, D. Herlach Concomitance of magnetic ordering and superconductivity in low oxygen mobility La^CuO^+x single crystal Physica C 341-348,2153 (2000). RA-95-15 A. Yaouanc, P. Dalmas de Reotier, F. N. Gygax, A. Schenck, A. Amato, C. Baines, P. C. M. Gubbens, C. T. Kaiser, A. de Visser, R. J. Keizer, A. Huxley, A. A. Menovsky Evidence for a two component magnetic response in UPt^ Phys. Rev. Lett. 84, 2702 (2000). P. Dalmas de Reotier, A. Yaouanc, P. C. M. Gubbens, C. T. Kaiser, A. M. Mulders, F. N. Gygax, A. Schenck, A. Amato, C. Baines, A. de Visser, R. J. Keizer, P. Bonville, P. J. C. King, A. Huxley, A. A. Menovsky Magnetism and superconductivity of UPt% by muon spin techniques Physica B 289-290,10 (2000). RA-95-17 D. Herlach, T. Albrecht, C. Biihrer, D. M. Herlach, D. Platzek, J. Reske, K. Maier [iSR on Coi-xPdx, an alloy exhibiting ferromagnetism in the liquid phase Physica B 289-290,232 (2000). D. Herlach, C. Kottler, T. Wider, K. Maier Hydrogen embrittlement of metals Physica B 289-290,443 (2000). RA-95-18 A. Schenck, R. J. Keizer, A. de Visser, A. Amato, D. Andreica, F. N. Gygax, M. Pinkpank, P. Estrela, M. J. Graf, A. A. Menovsky, J. J. M. Franse Muon localization site in U(Pt,Pd)z Physica B 289-290,455 (2000). A. de Visser, M. J. Graf, P. Estrela, A. Amato, C. Baines, D. Andreica, F. N. Gygax, A. Schenck Magnetic quantum critical point and superconductivity in UPt^ doped with Pd Phys. Rev. Lett. 85, 3005 (2000). RA-96-07 T. Blasius, Ch. Niedermayer, D. M. Pooke, D. R. Noakes, C. E. Stronach, E. J. Ansaldo, A. Golnik, C. Bernhard Low-temperature vortex structures of the mixed state in Physica B 289-290,365 (2000). 203 RA-96-09 C. J. Rhodes, T. C. Dintinger, H. A. Moynihan, I. D. Reid Spin-labelling with the Second Hydrogen Radioisotope: Radicals formed from squalene by muonium addition Free Radical Research 33, 75 (2000). C. J. Rhodes, T. C. Dintinger, H. A. Moynihan, I. D. Reid Radiolabelling studies of free radical reactions using muonium (the Second Hydrogen Radioisotope): Evidence of a direct antioxidant role for vitamin K in repair of oxidative damage to lipids Magn. Reson. Chem. 38, 646 (2000). M. C. R. Symons, C. J. Rhodes, I. D. Reid Evidence for the solvation of hydrogen atoms by water Magn. Reson. Chem. 38, 823 (2000). C. J. Rhodes, T. C. Dintinger, C. S. Hinds, H. Morris, I. D. Reid Hydrogen radioisotopic labelling studies using muonium: Properties ofthiyl radicals potentially relevant to cellular membrane damage Magn. Reson. Chem. 38, S49 (2000). RA-96-10 D. Andreica, N. Cavadini, H. U. Giidel, F. N. Gygax, K. Kramer, M. Pinkpank, A. Schenck Muon-induced break-up of spin-singlet pairs in the double-chain compound KCuClz Physica B 289-290,176 (2000). RA-96-11 P. Schobinger-Papamantellos, N. P. Duong, K. H. J. Buschow, D. Andreica, F. N. Gygax, M. Pinkpank, A. Schenck Comparative study of the magnetic properties ofTbFe^Alg, and YFe^Als compounds Physica B 289-290,277 (2000). RA-97-01 B. Heisel, R. Hempelmann, O. Hartmann, R. Wappling [iSR-experiments on proton-conducting oxides Physica B 289-290,487 (2000). RA-97-03 E. V. Raspopina, A. M. Balagurov, V. Yu. Pomjakushin, V. V. Sikolenko, A. V. Gribanov, A. Amato, A. Schenck Magnetic structure ofU{Pd\-xFex)-2Ge-2 studied by muSR: comparison with neutron diffraction data Physica B 289-290,282 (2000). V. Yu. Pomjakushin, A. M. Balagurov, E. V. Raspopina, V. V. Sikolenko, A. V. Gribanov, A. Schenck, A. Amato, U. Zimmermann, I. S. Lyubitin Modulated magnetic structure of U(Pd\-xFex)2Ge2 studiedby /iSR J. Phys.: Condensed Matter 12, 7969 (2000). RA-97-04 V. N. Duginov, K. I. Gritsaj, A. Amato, C. Baines, D. Herlach, V. Yu. Pomjakushin, U. Zimmermann, A. N. Ponomarev, I. A. Krivosheev, A. A. Nezhivoy, A. V. Gribanov, V. N. Nikiforov, Yu. D. Seropegin Study of the magnetic properties of CezPd2oSie compound Physica B 289-290,43 (2000). RA-97-06 Z. Salman, A. Keren, P. Mendels, A. Scuiller, M. Verdaguer Quantum fluctuations of the magnetization in high spin molecules - a [iSR study Physica B 289-290,106 (2000). RA-97-12 K. W. Klamut, B. Dabrowski, R. Dybzinski, Z. Bukowski, A. Shengelaya, R. Khasanov, S. Dottinger, H. Keller Muon-spin rotation study of the magnetic correlations in La2-xCai+xCu2Oe+s superconductors J. Appl. Phys. 87, 5558 (2000). 204 RA-97-15 R. M. Macrae, I. D. Reid, J. U. von-Schütz, K. Nagamine Order-disorder transition in anthracene/tetracyanobenzene probed by muonium-substituted radicals Physica B 289-290,616 (2000). RA-97-17 F. N. Gygax, P. Vajda, D. Andreica, M. Pinkpank, A. Schenck Positive muons in rare-earth dideuterides Physica B 289-290, 273 (2000). RA-97-19 I. M. Marshall, S. J. Blundell, A. Husmann, Th. Jestädt, B. W. Lovett, F. L. Pratt, J. Lago, P. D. Battle, M. J. Rosseinsky Spin dynamics in high oxidation state iron oxides displaying colossal magnetoresistance Physica B 289-290, 89 (2000). A. Husmann, S. J. Blundell, Th. Jestädt, B. W. Lovett, I. M. Marshall, F. L. Pratt, L. E. Spring, P. D. Battle, M. J. Rosseinsky Effect of dimensionality on the magnetic properties of Ruddlesden-Popper manganites Physica B 289-290, 69 (2000). A. I. Coldea, L. D. Noailles, I. M. Marshall, S. J. Blundell, J. Singleton, P. D. Battle, M. J. Rosseinsky Enhancement of the magnetoresistance at the Curie temperature of the ferromagnetic insulator Lai.^Sr Phys. Rev. B 62, R6077 (2000). RA-97-22 B. W. Lovett, J. S. Stießberger, S. J. Blundell, Th. Jestädt, A. Ardavan, I. M. Marshall, F. L. Pratt, I. D. Reid Director fluctuations in a nematic liquid crystal probed using ALC spectroscopy Physica B 289-290, 612 (2000). RA-97-23 J. M. Gil, H. V. Alberto, R. C. Viläo, J. Piroto Duarte, P. J. Mendes, N. Ayres de Campos, A. Weidinger, J. Krauser, Ch. Niedermayer, S. F. J. Cox Shallow-level muonium centre in CdS Physica B 289-290,563 (2000). RA-97-24 I. Z. Machi, S. H. Connell, J. P. F. Sellschop, K. Bharuth-Ram, B. P. Doyle, R. D. Maclear, J. Major and R. Scheuermann Quantum diffusion of tetrahedral interstitial muonium in diamond Physica B 289-290,468 (2000). RA-97-25 T. N. Mamedov, D. G. Andrianov, D. Herlach, K. I. Gritsaj, V. N. Gorelkin, O. Kormann, J. Major, A. V. Stoikov, M. Schefzik, U. Zimmermann ¡i-spin rotation study of the temperature dependent relaxation rate of acceptor centers in silicon JETP Lett. 71, 438 (2000). T. N. Mamedov, K. I. Gritsaj, A. V. Stoikov, D. G. Andrianov, D. Herlach, U. Zimmermann, V. N. Gorelkin, O. Kormann, J. Major, M. Schefzik ß~SR investigations in silicon Physica B 289-290, 574 (2000). RA-97-26 O. Kormann, J. Major, I. D. Reid, A. Rock, M. Schefzik, L. Schimmele, A. Seeger, D. Herlach Radio-frequency ßSR investigations on paramagnetic muonium centres in crystalline silicon Physica B 289-290, 530 (2000). 205 R. Scheuermann, J. Major, A. Seeger, L. Schimmele, J. Schmidl, D. Herlach The interaction of positive muons with photogenerated charge carriers in crystalline silicon Physica B 289-290, 534 (2000). J. Major, I. D. Reid, A. Rock, M. Schefzik, R. Scheuermann, J. Schmidl, U. Zimmermann, D. Herlach, O. Kormann A novel time-differential /JSR data-acquisition system Physica B 289-290,702 (2000). RA-97-28 I. D. Reid, S. F. J. Cox Muons in sulphur Physica B 289-290,620 (2000). I. D. Reid, S. F. J. Cox, U. A. Jayasooriya, G. A. Hopkins Muon-spin spectroscopy in selenium Magn. Reson. Chem. 38, S3 (2000). RA-98-01 A. N. Ponomarev, I. G. Ivanter, I. A. Krivosheev, A. A. Nezhivoy, B. A. Nikolsky, V. N. Duginov, K. I. Gritsaj, V. G. Olshevsky, D. Herlach, V. Yu. Pomjakushin, U. Zimmermann Magnetic fields acting on muons in textured and single crystalline holmium Physica B 289-290,236 (2000). RA-98-03 G. Wiesinger, Ch. Reichl, E. Gratz, P. Mietniowski, H. Figiel Muon diffusion and relaxation in YC02 Physica B 289-290,307 (2000). RA-98-04 R. H. Heffner, J. E. Sonier, D. E. MacLaughlin, G. J. Nieuwenhuys, G. Ehlers, F. Mezei, S.-W Cheong, J. Gardner, H. Roder Observation of two time scales in the ferromagnetic manganite Lai_xCaxMn03, x ~ 0.3 Phys. Rev. Lett. 85, 3285 (2000). R. H. Heffner, J. Sonier, D. E. MacLaughlin, G. J. Nieuwenhuys, Y. J. Uemura, G. M. Luke, S.-W Cheong Evidence for a distributed ferromagnetic transition in (La, Ca)MnO3 Physica B 289-290,61 (2000). R. H. Heffner Muon spin relaxation studies of Small-Moment Heavy Fermion Systems, in: Magnetism in Heavy Fermion Systems, (Ed. Harry Radousky, World Scientific, Nov. 2000). RA-98-06 A. Schenck, D. Andreica, F. N. Gygax, M. Pinkpank, K. A. McEwen, A. Amato Anomalous temperature dependence of the n+-Knight shift and the phase diagram of UPd^ Physica B 289-290, 311 (2000). RA-98-07 D. Andreica, A. Amato, F. N. Gygax, M. Pinkpank, A. Schenck Chemical pressure effects in the Yb(Cui-xNix)2Si2 system Physica B 289-290, 24 (2000). RA-98-16 W. A. MacFarlane, P. Mendels, J. Bobroff, A.V. Dooglav, A.V. Egorov, H. Alloul, N. Blanchard, G. Collin, P. G. Picard, A. Keren, P. J. C. King, J. Lord Antiferromagnetism in water doped YBa2CuzOe+x for x 6.5) Physica B 289-290, 291 (2000). 206 RA-98-18 H. Dilger, E. Roduner, R. Scheuermann, J. Major, M. Schefzik, R. Stösser, M. Päch, D. G. Fleming Mass and temperature effects on the hyperfine coupling of atomic hydrogen isotopes in cages Physica B 289-290,482 (2000). R. Scheuermann, H. Dilger, E. Roduner, J. Major, M. Schefzik, A. Amato, D. Herlach, A. Raselli, I. D. Reid A novel set-up for fast muon-spin-rotation experiments Physica B 289-290, 698 (2000). RA-98-20 U. Staub, B. Roessli, A. Amato Magnetic ordering in LÍ2CUO2 studied by muSR technique Physica B 289-290,299 (2000). RA-99-03 G. M. Kalvius, A. Kratzer, G. Grosse, D. R. Noakes, R. Wäppling, H. v. Löhneysen, T. Takabatake, Y. Echizen TJie onset of magnetism in CeNi\-xTxSn(T=Cu,Pt) Physica B 289-290, 256 (2000). RA-99-05 D. Andreica, F. N. Gygax, M. Pinkpank, A. Schenck, T. Chatterji, R. Suryanarayanan, G. Dhalenne, A. Revcolevschi Charge / orbital and antiferromagnetic ordering in LaSr^Mn^ O7 Physica B 289-290,65 (2000). RA-99-06 R. De Renzi, G. Allodi, M. C. Guidi, G. Guidi, M. Hennion, L. Pinsard, A. Amato Magnetic order in pure LaMnO-¡ and in Ca-doped single crystals Physica B 289-290, 52 (2000). R. De Renzi, G. Allodi, G. Amoretti, M. C. Guidi, S. Fanesi, G. Guidi, F. Licci, A. Caneiro, F. Prado, R. Sanchez, S. Oseroff, A. Amato Phase diagram of low doping manganites Physica B 289-290, 85 (2000). RA-99-09 V. S. Egorov, G. Solt, C. Baines, D. Herlach, U. Zimmermann Superconducting intermediate state in white tin near Hc: new results by ¡iSR Physica B 289-290, 393 (2000). RA-99-15 C. J. Rhodes, T. C. Dintinger, I. D. Reid, C. A. Scott Mobility of dichloroethyl radicals sorbed in kaolin and silica: Models of heterogeneous environmental processes Magn. Reson. Chem. 38, 281 (2000). C. J. Rhodes, T. C. Dintinger, I. D. Reid, C. A. Scott Spin-labelling studies of benzene sorbed in carbon particles using muonium: A molecular view of sorption by environmental carbon Magn. Reson. Chem. 38, S58 (2000). 207 LOW ENERGY MUONS T. J. Jackson, C. Binns, E. M. Forgan, E. Morenzoni, Ch. Niedermayer, H. Glückler, A. Hofer, H. Luetkens, T. Prokscha, T. M. Riseman, A. Schatz, M. Birke, J. Litterst, G. Schatz, H. P. Weber Superparamagnetic relaxation in iron nanoclusters measured by low energy muons J. Phys.: Condensed Matter 12,1399 (2000). T. J. Jackson, T. M. Riseman, E. M. Forgan, H. Glückler, T. Prokscha, E. Morenzoni, M. Pleines, Ch. Niedermayer, G. Schatz, H. Luetkens, J. Litterst Depth resolved profile of the magnetic field beneath the surface of a superconductor with a few nm resolution Phys. Rev. Lett. 84, 4958 (2000). See also Phys. Rev. Focus 5, Story 22, 15 May (2000). E. M. Forgan, T. J. Jackson, T. M. Riseman, H. Glückler, E. Morenzoni, T. Prokscha, H. P. Weber, A. Hofer, Ch. Niedermayer, G. Schatz, M. Birke, H. Luetkens, J. Litterst, A. Schatz, C. Binns A low-energy muon study of thermal activation in single-domain iron particles Physica B 289-290,137 (2000). H. Glückler, E. Morenzoni, T. Prokscha, M. Birke, E. M. Forgan, A. Hofer, T. J. Jackson, J. Litterst, H. Luetkens, Ch. Niedermayer, M. Pleines, T. M. Riseman, G. Schatz Range studies of low-energy muons in a thin Al film Physica B 289-290,658 (2000). H. Luetkens, J. Korecki, H. Glückler, E. Morenzoni, T. Prokscha, A. Schatz, M. Birke, E. M. Forgan, B. Handke, A. Hofer, T. J. Jackson, M. Kubik, F. J. Litterst, Ch. Niedermayer, M. Pleines, T. M. Riseman, G. Schatz, T. Slezak, H. P. Weber Magnetism of thin chromium films studied with low-energy muon spin rotation Physica B 289-290,326 (2000). E. Morenzoni, H. Glückler, T. Prokscha, H. P. Weber, E. M. Forgan, T. J. Jackson, H. Luetkens, Ch. Niedermayer, M. Pleines, M. Birke, A. Hofer, J. Litterst, T. Riseman, G. Schatz Low-energy ßSR at PSI: present and future Physica B 289-290,653 (2000). M. Pleines, E. M. Forgan, H. Glückler, A. Hofer, E. Morenzoni, Ch. Niedermayer, T. Prokscha, T. M. Riseman, M. Birke, T. J. Jackson, J. Litterst, H. Luetkens, A. Schatz, G. Schatz Temperature dependence of the magnetic penetration depth in an YBa^Cu^Oi-ifilm Physica B 289-290,369 (2000). T. M. Riseman, T. J. Jackson, M. W. Long, E. M. Forgan, E. Morenzoni, H. Glückler, T. Prokscha, H. P. Weber, Ch. Niedermayer, A. Hofer, M. Pleines, G. Schatz, J. Litterst, H. Luetkens, A. Schatz Measurements of the penetration depth of an YBÜ2CU-¡OT-S thin film with low-energy muons Physica B 289-290, 334 (2000). A. Schenck, F. N. Gygax, D. Andreica, M. Pinkpank, G. J. Nieuwenhuys, J. Aarts, S. Freisem, M. Hesselberth, J. A. Mydosh, E. Morenzoni, H. Glückler, Th. Prokscha, A. 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Ackens, et al., - R-97-02 Collaboration A high-rate X-ray detector for exotic-atom spectroscopy DPG Spring meeting, Dresden (Germany), March 20 - 24, 2000. D Anagnostopoulos, et al., - R-97-02 Collaboration Charged Pion Mass Determination and Energy-Calibration Standards based on Pionic X-ray Transitions Hydrogen Atomll: Precise physics of simple atomic systems (PSAS 2000), Castiglione della Pescaia (Italy), June 1 - 3, 2000. D. Anagnostopoulos et al., - R-98-01 Collaboration Pionic Hydrogen: Status and Outlook Hydrogen Atom II: Precise physics of simple atomic systems, PSAS 2000, Casiglione della Pescaia (Italy), June 1-3, 2000. R. Baur - CMS Collaboration Readout of the CMS Pixel Detector International Workshop on Semiconductor Pixel Detectors for Particles and X-rays PIXEL2000, Genova (Italy), June 5-8, 2000. M. 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Gotta Pionic Hydrogen VIII. International Oberjoch meeting on Broken Symmetries and Meson Nuclear Physics, Oberjoch (Germany), September 4 - 9, 2000. R. Horisberger - CMS Collaboration Readout architectures for pixel detectors International Workshop on Semiconductor Pixel Detectors for Particles and X-rays PIXEL2000, Genova (Italy), June 5-8, 2000. 217 P. Indelicato and L.M. Simons Crystal Spectroscopy and Exotic Atoms QED 2000 2nd Workshop on frontier tests of Quantum Electrodynamics and Physics of the Vacuum, Trieste (Italy), October 6 - 10, 2000. C.H.Q.Ingram. Pion Absorption Results from the Meson Factories. Invited (plenary) talk at 16th International Conference on Few-Body Problems in Physics, Taipei (Taiwan), March 6 - 10, 2000. T.S. Jensen Stark Mixing and Elastic Scattering in Pionic and Muonic Hydrogen The XVII European Conference on Few-Body Problems in Physics, Few Body 2000, Evora (Portugal), September 11-16, 2000. M. Kavcic, et al., - Z-97-02 - collaboration L-shell ionization in near-central collisions of heavy ions with low Z targets 16th International Conference on the Application of Accelerators in Research and Industry (CAARI 2000), Denton, 76203-1427 TX (USA), November 1 - 4, 2000. P.-R. Kettle - NewHeavns Collaboration The KARMEN Time Anomaly, Search for a Neutral Particle of Mass 33.9 MeV in Pion Decay ICHEP2000, XXXth International Conference on High Energy Physics, Osaka (Japan), July 27 - August 2, 2000. B. Kotlinski - CMS Collaboration The CMS Pixel Detector International Workshop on Semiconductor Pixel Detectors for Particles and X-rays PIXEL2000, Genova (Italy), June 5 - 8, 2000. B. Kotlinski, R. Baur, K. Gabathuler, R. Horisberger, R. Schnyder, W Erdmann. - CMS Collaboration Readout of the CMS Pixel Detector 6th Workshop on Electronics for LHC Experiments, Cracow (Poland), September 11-15, 2000. F. Kottmann Laser spectroscopy of the Lamb shift in muonic hydrogen Status report at the PSI Users Meeting, PSI, Villigen (Switzerland), January 17, 2000. F. Kottmann Towards a Lamb shift measurement in muonic hydrogen Second workshop on frontier tests of QED and physics of the vacuum, Trieste (Italy), October 6 - 10, 2000. Y.-W. Liu Laser spectroscopy of exotic atoms The Fourth Asian International Seminar on Atomic and Molecular Physics, Taipei (Taiwan), October 13 - 18, 2000. Y.-W. Liu The laser system for the muonic hydrogen Lamb shift measurement XVII International Conference on Atomic Physics, ICAP 2000, Florence (Italy), June 4 - 9, 2000. V.E. Markushin and T.S. Jensen Atomic Cascade and X-ray Yields in light exotic Atoms 7th International Conference on Hypernuclear and Low Energy Kaon Physics, Torino (Italy), October 23 - 27, 2000. 218 X. Morelle et al., - R-97-06 Collaboration Measuring the Michel Parameter Xi" in Polarized Muon Decay Spin Physics Symposium, SPIN2000, Osaka (Japan), Oktober 16 - 21, 2000. M. Pajek et al., - Z-99-05 Collaboration High-resolution measurements ofTh and U L-y x-rays induced by energetic O ions 10th International Conference on the Physics of Highly Charged Ions (HCI 2000), Berkeley, CA 94710 (USA), July 30 - August 3, 2000. R. Pohl Towards a measurement of the Lamb shift in muonic hydrogen International conference "Hydrogen Atom II", Castiglione (Italy), June 1-3, 2000. R. Prieels et al., - R-97-06 Collaboration A Precision Measurement of the Michel parameter x" Proceedings of the 7th Conference on the Intersections of Particles and Nuclear Physics, CIPANP 2000, Quebec (Canada), May 22 - 28, 2000. L.M. Simons Muonic Hydrogen VIII. International Oberjoch meeting on Broken Symmetries and Meson Nuclear Physics, Oberjoch (Germany), September 4 - 9, 2000. C. Wigger - New Heavns Collaboration (PSI-Virginia-Beijing) The KARMEN Time Anomaly: Search for a Neutral Particle of Mass 33.9 MeV in Pion Decay Tagung der Schweizerischen Physikalischen Gesellschaft, Montreux (Switzerland), March 16 - 17, 2000. THEORY GROUP C. Alexandrou, P. de Forcrand and M. D'Elia The relevance of center vortices Contribution to the 17th International Symposium on Lattice Field Theory (LATTICE 99), Pisa (Italy), June 29 - July 3, 1999; Nucl. Phys. (Proc.Suppl.) 83, 437 (2000). C. Alexandrou, P. de Forcrand and M. D'Elia The role of center vortices in QCD Contribution to the 15th International Conference on Particle and Nuclei (PANIC 99), Uppsala (Sweden), June 10 -16, 1999; Nucl. Phys. A 663/664,1031c (2000). C. Alexandrou, P. de Forcrand and M. D'Elia Improved multiboson algorithm Contribution to the 17th International Symposium on Lattice Field Theory (LATTICE 99), Pisa (Italy), June 29 - July 3, 1999; Nucl. Phys. (Proc.Suppl.) 83, 765 (2000). A. Bori§i Truncated overlap fermions Contribution to 17th International Symposium on Lattice Field Theory (LATTICE 99), Pisa (Italy), June 29 - July 3, 1999; Nucl. Phys. (Proc. Suppl.) 83, 771 (2000). A. Denner, S. Dittmaier, M. Roth, D. Wackeroth Precise predictions for W-pair production at LEP-2 with RACOON WW Contribution to the 35th Rencontres de Moriond: Electroweak Interactions and Unified Theories, Les Arcs (France), March 11-18, 2000; hep-ph/0005074 A. Denner, S. Dittmaier, M. Roth, D. Wackeroth Radiative corrections to e+e~ —> WW —> 4 fermions with RACOONWW Contribution to the Zeuthen Workshop on Elementary Particle Theory: Loops and Legs in Quantum Field Theory, Konigstein-Weissig (Germany), April 9 - 14, 2000; hep-ph/9912447, Nucl. Phys. (Proc. Suppl.) 89, 100 (2000). 219 A. Denner, S. Dittmaier, M. Roth, D. Wackeroth Electroweak precision physics at e+e~ colliders with RACOONWW Contribution to the 22nd Annual MRST (Montreal-Rochester-Syracuse-Toronto) Meeting: Conference on Theoretical High Energy Physics, Rochester, New York (USA), May 8 - 9, 2000; hep-ph/0007245; in: 'Theoretical High Energy Physics, MRST2000', ed. C.R. Hagen, (American Institue of Physics, Melville, New York (USA), 2000), p. 40. A. Denner, S. Dittmaier, M. Roth, D. Wackeroth Electroweak radiative corrections to off-shell W-pair production Contribution to DPF 2000: The Meeting of the Division of Particles and Fields of the American Physical Society, Columbus, Ohio (USA), August 9 - 12, 2000; hep-ph/0011119 S. Diirr The phase transition in the multiflavor Schwinger model Contribution to the International Conference on Quantization, Gauge Theory, and Strings: Conference Dedicated to the Memory of Professor Efim Fradkin, Moscow (Russia), June 5 - 10, 2000; hep-th/0009094 S. Diirr Testing the Leutwyler-Smilga prediction regarding the global topological charge distribution on the lattice Contribution to the International Euroconference in Quantum Chromodynamics: 15 Years of the QCD - Montpellier Conference (QCD 00), Montpellier (France), July 6 - 13, 2000; hep-ph/0009139 S. Diirr Study of the Leutwyler-Smilga regimes: lessons for full QCD simulations Contribution to the 18th International Symposium on Lattice Field Theory (Lattice 2000), Bangalore (India), August, 17 - 22, 2000; hep-lat/0010037 M. W. Griinewald et al.7 E. Accomando, A. Denner Fourfermion production in electron-positron collisions Report of the four-fermion working group of the LEP2-MC workshop, held at CERN from 1999 to 2000; hep-ph/0005309 S. Hay wood et al, A. Denner Electroweak physics Proceedings of the Workshop on Standard Model Physics (and more) at the LHC, Geneva (Switzerland), October 14 -15,1999; eds. G. Altarelli and M.L. Mangano, 117 (2000); hep-ph/0003275 V. A. Kuz'min, T. V. Tetereva, K. Junker On the strength of spin-isospin transitions in A = 28 nuclei Contribution to the BLTP International Conference on Nuclear Structure and Related Topics (NSRT 2000), Dubna (Russia), June 6 - 10, 2000; nucl-th/0009061 V. A. Kuz'min, T. A. Tetereva, K. Junker and A. A. Ovchinnikova The Total Rates of Ordinary Muon Capture - Microscopic Calculations for Heavy Nuclei Contribution to the Annual Conference on Nuclear Spectroskopy and Nuclear Structure, St. Petersburg (Russia), June 2000; Dubna preprint E4-2000-202 M. P. Locher, V. E. Markushin, S. von Rotz Antiproton-nucleon annihilation, multistep processes and the OZI rule Contribution to the 16th IUPAP International Conference on Few-Body Problems in Physics, Taipei (Taiwan), March 6 - 10, 2000. V. E. Markushin The structure of the light scalar mesons and QCD sum rules Proceedings of the Workshop on Production, Properties, and Interaction of Mesons, (MESON'2000), Cracow (Poland), May 19 - 23, 2000; Acta Physica Polonica B 31, 2665 (2000); hep-ph/0008096. V. E. Markushin and T. S. Jensen Atomic Cascade and X-ray yields in light exotic atoms Contribution to the 7th International Conference on Hypernuclear and Low Energy Kaon Physics, Torino (Italy), October 23 - 27, 2000. 220 M. Melles Precision Higgs physics at a 77 collider Contribution to the International Workshop on High-Energy Photon Colliders (GG 2000), Hamburg (Germany), June 14 - 17, 2000; hep-ph/0008125 M. Melles Two loop mass effects in the static position space QCD potential Contribution to the International Euroconference in Quantum Chromodynamics: 15 Years of the QCD Montpellier Conference (QCD 00), Montpellier (France), July 6 - 13, 2000; hep-ph/0009085 M. Melles Electroweak Sudakov corrections Contribution to the 5th International Linear Collider Workshop (LCWS 2000), Fermilab, Batavia, Illinois (USA), October 24 - 28, 2000; hep-ph/0012196 M. Melles The Standard Model Higgs in 77 collisions Contribution to the 5th International Linear Collider Workshop (LCWS 2000), Fermilab, Batavia, Illinois (USA), October 24 - 28, 2000; hep-ph/0012195 R. Rosenfelder Coulomb Corrections to Elastic Electron-Proton Scattering and the Proton Charge Radius Contribution to Hydrogen II - Precise Physics of Simple Atomic Systems, Castiglione della Pescaia, Tuscany (Italy), June 1 - 3, 2000. A. W. Schreiber, R. Rosenfelder, C. Alexandrou What Can We Learn from QED at Large Couplings ? Proceedings of the 3rd International Symposium on Symmetries in Subatomic Physics, Adelaide (Australia), March 13 -17, 2000; hep-th/0007182 A. W. Schreiber, R. Rosenfelder The Feynman Variational Approach to Relativistic Quantum Field Theory Contribution to the 14th National Congress of the Australian Institute of Physics, Adelaide (Australia), December 10 -15, 2000. LABORATORY FOR MUON SPIN SPECTROSCOPY D. Andreica, A. Amato et al., RA-98-07 Collaboration liSR under pressure, first results on CeRh2Sh ESF Conference on Non Fermi Liquid Effects in Metallic Systems with Strong Electronic Correlation, Newton Institute, Cambridge (UK), January 5 - 8, 2000. D. Andreica, A. Amato et al., RA-98-07 Collaboration liSR under pressure, first results on CeRh^Sh 18th General Conference of the CONDENSED MATTER DIVISION of the European Physical Society, Montreux (Switzerland), March 14-18, 2000. E. Morenzoni et al., PSI-Birmingham-Leicester-Braunschweig-Konstanz Collaboration Use of polarized muons for investigations on the scale of nm 18th General Conference of the CONDENSED MATTER DIVISION of the European Physical Society, Montreux (Switzerland), March 14-18, 2000. G. Solt et al., RA-94-14 Collaboration Magnetic (Condon) domains in s-p metals: beryllium and white tin 18th General Conference of the CONDENSED MATTER DIVISION of the European Physical Society, Montreux (Switzerland), March 14-18, 2000. 221 W. B. Waeber Electron hyper-state representation of strongly correlated systems 18th General Conference of the CONDENSED MATTER DIVISION of the European Physical Society, Montreux (Switzerland), March 14-18, 2000. H. Luetkens et al, PSI-Braunschweig-Cracow-Birmingham-Konstanz Collaboration Magnetism of thin Chromium films Nuclear Methods in Magnetism, NMM 2000, Rio de Janeiro (Brasil), August 2 - 4, 2000. E. Morenzoni (invited) Muon spin rotation and relaxation experiments on thin films Nuclear Methods in Magnetism, NMM 2000, Rio de Janeiro (Brasil), August 2 - 4, 2000. D. Andreica, F. N. Gygax, A. Schenck, A. Amato et al., RA-98-07 Collaboration [iSR studies of the nonmagnetic-magnetic transition in highly correlated electron systems International Conference on Magnetism, ICM 2000, Recife (Brasil), August 6-11, 2000. H. Luetkens et al., PSI-Braunschweig-Cracow-Birmingham-Konstanz Collaboration Magnetism of thin chromium films International Conference on Magnetism, ICM 2000, Recife (Brasil), August 6-11, 2000. E. Morenzoni et al., PSI-Birmingham-Leicester-Braunschweig-Konstanz Collaboration Superparamagnetic relaxation in Fe clusters measured by low energy muon spin rotation International Conference on Magnetism, ICM 2000, Recife (Brasil), August 6-11, 2000. E. Morenzoni et al., PSI-Leiden-Braunschweig-Konstanz-Ziirich Collaboration Finite size effects in single layers spin-glass films studied by LE-muon spin relaxation International Conference on Magnetism, ICM 2000, Recife (Brasil), August 6-11, 2000. A. Schenck, D. Andreica, F. N. Gygax, A. Amato et al., RA-98-06 Collaboration Unusual static and dynamical magnetic features in PrCu^ as observed by /iSR spectroscopy International Conference on Magnetism, ICM 2000, Recife (Brasil), August 6-11, 2000. H. Luetkens Magnetism of thin chromium films studied with low energy muon spin rotation DPG Friihjahrstagung, Regensburg (Germany), March 27-31, 2000. M. Pleines Measurements of the Penetration Depth in both the Meissner and the Mixed States of a YBaiCu^O-j-^, Thin Film with Low Energy Muons DPG Friihjahrstagung, Regensburg (Germany), March 27-31, 2000. D. Andreica, F. N. Gygax, A. Schenck, A. Amato et al., RA-98-07 Collaboration /iSR studies of the nonmagnetic-magnetic transition in YbCu^-xAlx FERLIN Workshop, II Ciocco (Italiy), October 5 - 7, 2000. V. N. Duginov et al., A. Amato, C. Baines, D. Herlach, U. Zimmermann, RA-97-04 Collaboration Study of the magnetic properties of CesPd2oSie 34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science, Repino (Russia), February 14 - 20, 2000. V. S. Egorov, G. Solt, C. Baines, D. Herlach, U. Zimmermann, RA-99-09 Collaboration SR investigation of the topological phase transition in the type-I superconductor white tin 34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science, Repino (Russia), February 14 - 20, 2000. 222 T. N. Mamedov et al., D. Herlach, U. Zimmermann, RA-97-25 Collaboration The /iSR method and acceptor centers in Si 34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science, Repino (Russia), February 14 - 20, 2000. T. N. Mamedov et al., D. Herlach, U. Zimmermann, RA-97-25 Collaboration The magnetic moment of the negative muon in IS states of different atoms 34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science, Repino (Russia), February 14 - 20, 2000. A. N. Ponomarev et al., D. Herlach, U. Zimmermann, RA-98-01 Collaboration Magnetic fields acting on muons in textured and single crystalline holmium 34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science, Repino (Russia), February 14 - 20, 2000. T. Prokscha Experiments with low-energy muons at PSI 34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science, Repino (Russia), February 14 - 20, 2000. G. Solt, V. S. Egorov, C. Baines, D. Herlach, U. Zimmermann, RA-94-14 Collaboration Diamagnetic domains in Sn? 34th Winter School of the St. Petersburg Nuclear Physics Institute and the Russian Academy of Science, Repino (Russia), February 14 - 20, 2000. H. Gliickler Reichweite niederenergetischer Myonen in Metallen Workshop Energiereiche Atomare Stosse, Riezlern (Austria), January 30, 2000. H. Gliickler liSR an Oberfldchen und diinnen Schichten ,3-NMR und /J,SR Treffen, Braunschweig (Germany), April 2000. H. Luetkens Experimente mit niederenergetischen Myonen BMBF-Verbundtreffen Wasserstoff und Myonen in niederdimensionalen Systemen, Bochum (Germany), May 26-27, 2000. M. Pleines Experimente mit niederenergetischen Myonen: Bestimmung der Londonschen Eindringtiefe in diinnen supraleitenden Filmen BMBF-Verbundtreffen Wasserstoff und Myonen in niederdimensionalen Systemen, Bochum (Germany), May 26-27, 2000. H. Gliickler LE-fiSR: eine neue Methode zur Erforschung von Magnetismus an Oberfldchen und diinnen Schichten BESSY, Berlin (Germany), 2000. R. Khasanov Oxygen isotope effect on in-plane penetration depth in underdoped Y\-xPrxBa-2CuzO~!-?, LMU Seminar, PSI, Villigen (Switzerland), November 21, 2000. E. Morenzoni Thin film studies with polarized low energy muons Physikalisches Kolloquium, Zurich (Switzerland), June 14, 2000. E. Morenzoni Myonen als Sonden im Oberfldchenbereich Seminarreihe Industrienahe Entwicklungen und Methoden, PSI, Villigen (Switzerland), November 3, 2000. 223 LABORATORY FOR ASTROPHYSICS D. Amato, D. Pankow, K. Thomsen, Force limited vibration test test ofHESII imager, International Institute of Acousitcs and Vibration's 7th International Congress on Sound and Vibration, V-2527, Gramisch-Partenkirchen (Germany), July 4-7, 2000. M. Audard, M. Giidel, A. J. den Boggende, A. C. Brinkman, J. W. den Herder, J. S. Kaastra, R. Mewe, A. J. J. Raassen, C. de Vries, E. Behar, J. Cottam, S. M. Kahn, F. B. S. Paerels, J. R. Peterson, A. P. Rasmussen, M. Sako, G. Branduardi-Raymont, I. Sakelliou, C. Erd, Stellar coronae with XMM-Newton RGS. II, X-Ray Variability X-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000. M. Audard, M. Giidel, R. Mewe, A. J. J. Raassen, E. Behar, Stellar coronae with XMM-Newton RGS Toulouse X-Ray Astronomy Workshop, Toulouse (France), September 2000. Proceedings of the workshop : Sept. 2000, Toulouse. E. Behar, A. P. Rasmussen, J. Cottam, S. M. Kahn, F. B. S. Paerels, J. R. Peterson, M. Sako, A. C. Brinkman, A. J. den Boggende, J. W. den Herder, C. P. de Vries, C. Ferrigno, J. S. Kaastra, R. Mewe, T. Tamura, K. J. van der Heyden, G. Branduardi-Raymont, I. Sakelliou, M. Audard, M. Giidel, C. Erd, Modeling ofNon Equilibrium Ionizing Plasmas: Applications and Comparison with Supernova Remnant Observations by the RGS Spectrometer 2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000. J. J. Bochanski J. M. DePasquale, L. E. DeWarf, P. V. DiTuro, E. f. Guinan, G. P. McCook, M. Giidel, J. Hargis, I. Ribas The Sun in Time: Starspots and Luminosity Variations of the Solar-type Stars of Different Ages 196th Meeting of the AAS, Rochester, NY (USA), June 5 - 8, 2000. Bull. Am. Astron. Soc. 196, 46.07. G. Branduardi-Raymont, M. J. Page, I. Sakelliou, S. Zane, A. J. den Boggende, A. C. Brinkman, J. W. den Herder, J. S. Kaastra, R. Mewe, C. de Vries, E. Behar, J. Cottam, S. M. Kahn, F. B. S. Paerels, J. R. Peterson, A. P. Rasmussen, M. Sako, M. Audard, M. Giidel, M. Kuster, J. Wilms, C. Erd XMM-Newton RGS Observations ofMCG -6-30-15 andMrk 766: Evidence for emission lines from a relativistic accretion disk X-Ray Astronomy 2000, Palermo (Italy), September 4 - 8 2000. J. C. Brown, S. Krucker, M. Giidel, A. O. Benz, Mechanisms for Coronal Mass Supply by Evaporative Micro-Events. Recent Insights into the Physics of the Sun and Heliosphere, Highlights from SOHO and other Space Missions. IAU General Assembly, Manchester (UK), August 7-11, 2000. J. Cottam, A. J. den Boggende, G. Branduardi-Raymont, A. C. Brinkman, C. Erd, M. Giidel, S. M. Kahn R. Mewe, F. B. S. Paerels, A. P. Rasmussen, I. Sakelliou, M. Sako, C.P. de Vries, High Resolution Spectroscopy ofEXO 0748-67 with the RGS on XMM 196th Meeting of the AAS, Rochester, NY (USA), June 5 - 8, 2000. Bull. Am. Astron. Soc. 196, 34.18. J. J. Drake, V L. Kashyap, M. Audard, M. Giidel, Active Stellar Coronae: Lots of Little Flares? 196th Meeting of the AAS, Rochester, NY (USA), June 5 - 8, 2000. Bull. Am. Astron. Soc. 196,54.07. S. A. Drake, N. E. White, M. Giidel, J. S. Kaastra, R. Mewe, T. Simon, K. P. Singh, A Chandra HETG Observation of the Active Binary Algol: Flaring and Quiescent Spectra 2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000. AAS Bulletin 32 (3), 42.08. 224 L. Grenacher, Ph. Jetzer, R. Piffaretti, D. Puy, M. Signore, Shape and geometry of galaxy clusters and the SZ effect Proceedings of the SZ in Toulouse workshop Toulouse (France), 29-30 June 2000. e-proceedings Toulouse observatory, astro-ph/0010512 L. Grenacher, Ph. Jetzer, D. Puy, Cold clouds in cooling flows Proceedings of the Workshop on Large Scale Structure in the X-ray Universe, Santorini (Greece), September 20 - 22,1999. Atlantiscience Eds., 371 (2000). L. Grenacher, Ph. Jetzer, D. Puy, Molecular Clouds in Cooling Flow Cluster of Galaxies Proceedings of the Clustering at high redshift conference, Marseille (France), June 29 - July 2, 1999. ASP Conference Series vol. 200,415 (2000). L. Grenacher, Microlensing and the galactic mass functions IX Marcel Grossmann Meeting, Rome (Italy), July 4, 2000. L. Grenacher, P. Jetzer, D. Puy, Thermal Equilibrium of Cold Clouds in PKS 0745-191 Proceedings of the Workshop on Large Scale Structure in the X-ray Universe, Santorini (Greece), September 20 - 22, 1999. Atlantiscience Eds., 373 (2000). M. Giidel, Characteristics of the RGS data and calibrations XMM-Newton Science Advisory Group (SAG) Meeting, Leicester (UK), May 10, 2000. M. Giidel, First Results from XMM/RGS XMM-Newton Science Survey Centre Consortium Meeting, Leicester (UK), May 11, 2000. M. Giidel, X-ray Spectroscopy of Stellar Coronae A New Decade of Cosmic X-Ray Spectroscopy, Utrecht (Netherlands), July 7, 2000. M. Giidel, X-Ray Spectroscopic Studies of Stars - Invited Review, New Vistas from X-Ray Observatories, Warsaw (Poland), July 16 - 23, 2000. M. Giidel, M. Audard, E. F. Guinan, J. J. Drake, V. L. Kashyap, R. Mewe, I. Y. Alekseev, AD Leo from X-Rays to Radio: Are Flares Responsible for the Heating of Stellar Coronae? X-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000. M. Giidel, M. Audard, A. J. den Boggende, A. C. Brinkman, J. W. den Herder, J. S. Kaastra, R. Mewe, A. J. J. Raassen, C. P. de Vries, E. Behar, J. Cottam, S. M. Kahn, F. B. S. Paerels, J. R. Peterson, A. P. Rasmussen, M. Sako, G. Branduardi-Raymont, I. Sakelliou, C. Erd, Stellar Coronae with XMM-Newton RGS. I, Coronal Structure X-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000. 225 M. Güdel, M. Audard, E. Behar, J. Cottam, S. M. Kahn, F. B. S. Paerels, J. R. Peterson, A. P. Rasmussen, G. Branduardi-Raymont, I. Sakelliou, A. J. den Boggende, A. C. Brinkman, J. W. den Herder, J. Kaastra, R. Mewe, T. Tamura, C. P. de Vries, C. Erd and the XMM Collaboration, Stellar Coronal Spectroscopy with the XMM-Newton RGS 2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000. AAS Bulletin 32 (3), 45.03. M. Güdel, Roentgenastronomie mit XMM-Newton: Erste Resultate Physikalischen Kolloqium, Universität Gießen (Germany), December 18, 2000. W. Hajdas, Proton Irradiation Facility at PSI1999-2000 ESA/ESTEC Final Presentation Day, Noordwijk (Netherlands), January 26, 2000. W. Hajdas, N. Frey, O. Morath, K. Thomsen, A. Zehnder and W. Wittwer, Experimental Study of Space Proton Environment Effects on HESSI Detector Background Nuclear and Space Radiation Effects Conference NSREC, Reno (USA), 2000. W. Hajdas, P. Buehler, A. Zehnder, R. Harboe-Sorensen, Proton Irradiation Facility and Space Radiation Monitoring 1st International Workshop on Space Radiation Research and 11th annual NASA Radiation Health Investigators Meeting, Arona (Italy), May 28-31, 2000. R. Henneck, Die High Energy Solar Spectmscopic Imager (HESSI) Mission, Frühjahrstagung "Extraterrestrische Physik" der DPG, Bremen (Germany), March 21 - 24, 2000. Verhandlungen der DPG, ISSN 0420-0195,2/2000, p.94. J. W. den Herder, G. Branduardi-Raymont, A. C. Brinkman, J. Cottam, A. J. den Boggende, L. Dubbeldam, C. Erd, M. Güdel, J. S. Kaastra, S. M. Kahn, R. Mewe, F. B. Paerels, I. Sakelliou, A. P. Rasmussen, J. Spodek, K. Thomsen, C. P. de Vries, Description and Performance of the Reflection Grating Spectrometer on board of XMM-Newton SPIE Conference, Munich (Germany), Spring 2000. SPIE Proceedings, vol. 4012, 102 (2000). Ph. Jetzer, Dunkle Materie in der Milchstrasse Physikalische Chemie, Universität Zürich (Switzerland), January 20, 2000. Ph. Jetzer, Gravitational lensing SIGRAV Graduate School in Contemporary Relativity and Gravitational Physics, Villa Olmo, Como (Italy), May 8 - 13, 2000. Ph. Jetzer, Gravitationslinseneffekt und dunkle Materie in der Milchstrasse University of Köln (Germany), July 11, 2000. Ph. Jetzer, Dark matter and microlensing CAPP 2000 Meeting, Verbier (Switzerland), July 18, 2000. J. S. Kaastra, M. Audard, M. Güdel, A. J. den Boggende, A. C. Brinkman, J. W. den Herder, R. Mewe, A. J. J. Raassen, C. P. de Vries, E. Behar, J. Cottam, S. M. Kahn, F. B. S. Paerels, J. R. Peterson, A. P. Rasmussen, M. Sako, G. Branduardi-Raymont, I. Sakelliou, C. Erd, X-ray Spectroscopy ofClusters of Galaxies with XMM X-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000. 226 V. L. Kashyap, J. J. Drake, M. Audard, M. Giidel, Flare Distributions and Coronal Heating on FKAqr 196th Meeting of the AAS, Rochester, NY (USA), June 5 - 8, 2000. Bull. Am. Astron. Soc. 196, 13.05 E. C. Kirk, J. Olsen, E. Miiller, A. Al Mazouzi, Ph. Lerch, A. Zehnder, H.R. Ott, Micro structural examination ofTES multilayers Trends in Condensed Matter Physics, Monte Verita (Italy), September 3-8, 2000. Ph. Lerch, E.C. Kirk, J. Olsen, A. Zehnder, H.R. Ott, Energy and time resolved imaging with cryogenic detectors 18th General Conference of the Condensed Matter Division of the European Physical Society, Montreux (Switzerland), March 13-17, 2000. Ph. Lerch, E. C. Kirk, J. Olsen, A. Zehnder, Readout issues with 1D/2D arrays ofSTJ Proc. Int. Workshop on Superconducting Detectors and Bolometers, Napoli (Italy), October (2000). M. A. Leutenegger, M. Audard, E. Behar, A. J. den Boggende, A. C. Brinkman, G. Branduardi-Raymont, J. Cottam, C. Erd, C. Ferrigno, M. Giidel, J. W. den Herder, J. S. Kaastra, S. M. Kahn, H. Magee, R. Mewe, F. B. S. Paerels, R. Pallavicini, J. R. Peterson, A. P. Rasmussen, G. Rauw, M. Sako, T. Tamura, I. Sakelliou, K. Thomsen, C. de Vries, High-Resolution X-Ray Spectroscopy ofZeta Puppis and Eta Carinae with the RGS on XMM 2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000. AAS Bulletin bf 32 (3), 42.01. J. Olsen, E. C. Kirk, Ph. Lerch, A. Zehnder, H. R. Ott, Mo/Au Microcalorimeters for the detection of radiation and particles Trends in Condensed Matter Physics, Monte Verita (Italy), September 3-8, 2000. F. B. S. Paerels, M. Audard, E. Behar, G. Branduardi-Raymont, A. C. Brinkman, J. Cottam, A. J. F. den Boggende, J. W. den Herder, C. P. de Vries, C. Erd, C. Ferrigno, M. Giidel, H. W. Hartmann, J. S. Kaastra, S. M. Kahn, R. Mewe, J. R. Peterson, A. P. Rasmussen, I. Sakelliou, M. Sako, T. Tamura, K. J. van der Heyden, High Resolution Spectroscopy of the Stellar Photosphere ofCal 83 with XMM-Newton/RGS X-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000. F. B. S. Paerels, M. Audard, E. Behar, G. Branduardi-Raymont, A. C. Brinkman, J. Cottam, A. J. den Boggende, J. W. den Herder, C. de Vries, C. Ferrigno, M. Giidel, J. S. Kaastra, S. M. Kahn, R. Mewe, J. R. Peterson, A. P. Rasmussen, I. Sakelliou, M. Sako, T. Tamura, K. van der Heyden, High Resolution Spectroscopy of the Nuclear Region ofNGC1068 with XMM-Newton/RGS 2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5-10, 2000. AAS Bulletin 32 (3), 1.05. G. Paesold and A. O. Benz, Electron Firehose Instability and Acceleration of Electrons in Solar Flares XXV EGS General Assembly, Nice (France), April 2000. G. Paesold, A. O. Benz, K.-L. Klein, N. Vilmer, Spatial Analysis of Solar Type III Events Associated with Narrowband Spikes at Metric Wavelength AGU Fall Meeting, San Francisco (USA), December 2000. F. De Paolis, G. Ingrosso, Ph. Jetzer, M. Roncadelli, A gamma ray halo around the Milky Way Proceedings of the meeting The Chaotic Universe, Rome and Pescara (Italy), February 1-5,1999. World Scientific (Singapore), 414 (2000). 227 J. R. Peterson, M. Audard, E. Behar, A. J. den Boggende, A. C. Brinkman, G. Branduardi-Raymont, J. Cottam, C. Erd, C. Ferrigno, M. Giidel, J. W. den Herder, J. G. Jernigan, J. S. Kaastra, S. M. Kahn, R. Mewe, F. B. S. Paerels, A. P. Rasmussen, M. Sako, T. Tamura, I. Sakelliou, K. Thomsen, C. P. de Vries, X-ray Spectroscopy of Clusters of Galaxies with XMM-Newton 2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000. AAS Bulletin 32 (3), 13.22. D. Puy, The Sunyaev-Zel'dovich effect Paul Scherrer Institut-LAP, Villigen (Switzerland), March 23, 2000. D. Puy, The Sunyaev-Zel'dovich effect for cluster of galaxies, implications for cosmology University of Bern (Switzerland), May 10, 2000. D. Puy, Cosmológica! Thermal decoupling and primordial molecules JENAM 2000 meeting, Moscow (Russia), May 31, 2000. D. Puy, Shape and geometry of galaxy clusters and the SZ effect Observatory of Toulouse (France), June 29, 2000. D. Puy, Cosmochemistry in the early Universe ICTP conference 2000, Trieste (Italy), September 22, 2000. A. P. Rasmussen, M. Audard, E. Behar, J. A. M. Bleeker, A. J. den Boggende, G. Branduardi-Raymont, A. C. Brinkman, J. Cottam, L. Dubbeldam, C. Erd, M. Güdel, J. W. den Herder, J. S. Kaastra, S. M. Kahn, R. Mewe, F. B. S. Paerels, J. R. Peterson, C. P. de Vries, I. Sakelliou, K. Thomsen, A. Zehnder, XMM/RGS High Resolution Spectroscopy of the Magellanic Cloud Supernova Remnant Sample: 1E0102-72.3 and the Others X-Ray Astronomy 2000, Palermo (Italy), September 4 - 8, 2000. A. P. Rasmussen, E. Behar, J. Cottam, S. M. Kahn, F. B. S. Paerels, J. R. Peterson, M. Sako, J. A. M. Bleeker, A. J. den Boggende, A. C. Brinkman, J. W. den Herder, K. J. van der Heyden, J. Kaastra, R. Mewe, T. Tamura, C. P. de Vries, G. Branduardi-Raymont, I. Sakelliou, M. Audard, M. Güdel, C. Erd, The Magellanic Cloud Supernova Remnant Sample as Observed by XMM/Newton RGS 2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000. AAS Bulletin 32 (3), 40.03. M. Sako, M. Audard, E. Behar, A. J. den Boggende, Th. Boiler, G. Branduardi-Raymont, A. C. Brinkman, J. Cottam, C. Erd, C. Ferrigno, M. Güdel, J. W. den Herder, J. S. Kaastra, S. M. Kahn, A. Lagostina, R. Mewe, F. B. S. Paerels, J. R. Peterson, M. Pierre, E. M. Puchnarewicz, A. P. Rasmussen, T. Tamura, I. Sakelliou, K. Thomsen, C. P. de Vries, XMM-Newton Observation of the Complex Absorbing Medium in IRAS 13349+2438 2000 Meeting of the AAS High Energy Astrophysics Division, Honolulu (USA), November 5 - 10, 2000. AAS Bulletin 32 (3), 2.03. K. W. Smith, I. A. Bonnell, J. P. Emerson, T. Jenness, SCUBA Observations of NGC1333/IRAS4 Colloquium at Onsala Space Observatory (Sweden), June 2000. K. W. Smith, I. A. Bonnell, Free Floating Planets in Stellar Cluster Presentation at the Asgård Users Day, December 2000. 228 LABORATORY FOR MICRO AND NANO TECHNOLOGY J. A. Anna Selvan, D. Griitzmacher, E. Miiller and J. Gobrecht Comparison of growth of Si thin films on low temperature amophous substrates by MBE and PECVD Materials Research Society Spring meeting., San Fransisco (USA), May 2000. J. A. Anna Selvan, D. Grutzmacher, M. Kummer, H von Kanel, M. Rebien, E. Miiller, E. Ortelli and J. Gobrecht Development of Si films by new methods of DC PECVD techniques for thin film solar cell applications 16th E.C. Photovoltaic Solar Energy Conf., Glasgow (UK), Mai 2000. J. A. Anna Selvan, D. Grutzmacher, M. Hadorn, B. Bitnar, W. Durisch, S. Stutz, T. Neiger and J. Gobrecht Tuneable plasma filters for TPV systems using transparent conducting oxides of tin doped indium oxide and Al doped Zinc Oxide 16* E.C. Photovoltaic Solar Energy Conf., Glasgow (UK), Mai 2000. B. Baumeister, T.A. Jung and L. Scandella Fracture Mechanics and Erosive Wear of Microfabricated SiO2-Nanotowers on Si: SPM Studies and New Experimental Modes 4* International Conference on the Development and Technological Application of Scanning Probe Methods (SXM4), Minister (Germany), September 25 - 27, 2000. S. Berner, M. Brunner, H. Suzuki, T.A. Jung and H.-J. Guentherodt Deposition System for Single Molecule STM Experiments 4th Hasliberg Workshop on Nanoscience, Hasliberg (Switzerland), October 16 - 20, 2000. S. Berner, M. Brunner, H. Suzuki, T.A. Jung and H.-J. Guentherodt Single Molecule Physics, Molecular Epitaxy and Layering: The Experimental Approach 4th International Conference on the Development and Technological Application of Scanning Probe Methods (SXM4), Minister (Germany), September 25 - 27, 2000. S. Berner, M. Brunner, H. Suzuki, T.A. Jung and H.-J. Guentherodt Molecular Patterning in UHV: From Deposition to STM Experiments Workshop on Scanning Probe Microscopies and Organic Materials IX, Hannover (Germany), October 9-11, 2000. J.H.H. Bongaerts, C. David, G. H. Wegdam, M. A. de Vries and J. F. van der Veen Focusing an x-ray beam onto a planar waveguide using a Fresnel zone plate SLS Workshop, Les Diablerets (Switzerland), October 16 - 20, (2000). M. Brunner, S. Berner, H. Suzuki, T.A. Jung and H.-J. Guentherodt Structure and Confirmation of Single Molecules from UHV-STM Workshop on Scanning Probe Microscopies and Organic Materials IX, Hannover (Germany), October 9-11, 2000. A. Beyer, O. Leifeld, S. Stutz, E. Miiller and D. Griitzmacher In-situ STM analysis andphotoluminescence of C-induced Ge dots International Symposium on "Nanostructures: Physics and Technology", St. Petersburg (Russia), June 19 -23, 2000. A. Beyer, O. Leifeld, G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, E. Mtiller, S. Stutz and D. Grutzmacher Luminescence enhancement from Si using SiGe and SiGeC quantum confinement structures Seminar: Centre de recherche sur les mechanismes de la croissance cristalline, CRNS, Marseille (France), July 28, 2000. A. Beyer, O. Leifeld, O. Kirfel, G. Dehlinger, L. Diehl, U. Gennser, H. Sigg, E. Mtiller, S. Stutz and D. Grutzmacher Si-Ge-(C) Nanostrukturen - Moglichkeiten der Lichtemission aus Si Seminar: Walter-Schottky-Institute, Technical University Miinchen (Germany), November 7, 2000. A. Beyer, O. Leifeld, O. Kirfel, G. Dehlinger, U. Gennser, H. Sigg, E. Miiller, S. Stutz and D. Griitzmacher Si technology off the beaten path: Molecular beam epitaxy of low dimensional Si/SiGeC structures Seminar: Institute for Semiconductor Physics, Johannes Keppler Universitat Linz (Austria), December7, 2000. C. David Nanofabrication of diffractive optical elements by low voltage electron beam lithography Institute of Microtechnology, University of Neuchatel (Switzerland), January 26, 2000. 229 C. David, D. Wiesmann, R. Germann, F. Horst, B. J. Offrein, R. Beyeler, H.W.M. Salemink and G. L. Bona Apodised Bragg gratings in planar waveguides for add-drop filters Micro and Nanoengineering MNE 2000, Jena (Germany), September 19, 2000. C. David, L. Heyderman, B. Ketterer, E. Deckardt, U. Dötsch and B. Nöhammer The LION at PSI ELBUM Meeting, Jena (Germany), September 22, 2000. C. David Nano fabrication of diffractive x-ray optics SLS Workshop, Les Diablerets (Switzerland), October 18, 2000. C. David X-ray lenses Gray Laboratories, Northwood (UK), November 15, 2000. C. David, J. Wei, T. Lippert and A. Wokaun Diffractive grey tone masks for laser ablation lithography Micro and Nanoengineering MNE 2000, Jena (Germany), September 19, 2000. J.-H. Fabian, L. Scandella, R. Berger, J. Gobrecht, Ph. Lerch and E. Meyer A Micromechanical Device for Thermal Analysis ofNanogram Sample Quantities 12* International Congress on Thermal Analysis and Calorimetry, International Confederation for Thermal Analysis and Calorimetry ICTAC, Copenhagen (Danemark), August 14 - 18, 2000. J.-H. Fabian, L. Scandella, H. Fuhrmann, J. Gobrecht, E. Meyer and Ph. Lerch Finite Element Calculations of Micromechanical Cantilever Sensor-Arrays for Nanoscale Thermal Analysis 18th CAD-FEM Users' Meeting, International Congress on FEM Technology, Friedrichshafen (Germany), September 20 - 22, 2000, J. Gobrecht, H. Schift, C. David, W. Kaiser, A. D'Amore, D. Simoneta and L. Scandella Injection molded plastic chip for calibration of scanning probe microscopes Invited talk, 4th Seminar on Quantitative Microscopy QM 2000, Semmering (Austria), January 12 - 14, 2000. J. Gobrecht and H. Schift Functional Nanostructures on Surfaces: from „ Manufacture " to Mass Production " Invited talk, 16th meeting Schweiz. Gesellschaft für Oberflächentechnik, Fribourg (Switzerland), January 27, 2000. J. Gobrecht Nanotechnology - Between Science Fiction and Real World Applications Invited talk, Unisys Users Association 2000 Conference, The Hague (NL), May 15 - 18, 2000. J. Gobrecht Micro- and nanostructuring of Surfaces for non-electronic applications Invited talk, 6th Annual Meeting of the Swiss Society of Biomaterials, Davos (Switzerland), June 8-9, 2000. J. Gobrecht Nanotechnologie Invited seminar talk, Zentralinstitut für Biomedizinische Technik, Friedrich-Alexander Universität, Erlangen-Nürnberg (Germany), July 20, 2000. J. Gobrecht Kristallines Silizium: Fortschritte und Zukunft beim Arbeitspferd der Photovoltaik Nationale Photovoltaik-Tagung, Neuchatel (Switzerland), November 7-8, 2000. Proc.(ed. S. Novak, BfE), 56 (2000). J. Gobrecht Nanotechnologie - Perspektiven für neue Werkstoffe und Methoden in der biomedizinischen Technik 34. Jahrestagung der Deutschen, Österreichischen und Schweizerischen Gesellschaft für Biomedizinische Technik, Lübeck (Germany), September 28 - 30, 2000. 230 J. Gobrecht, L. Heyderman and H. Schift Submicron- and Nanostructuring of Surfaces for Non-Electronic Applications Swiss-Japanese Workshop on Nanoscience, Riken (Japan), October 27 - 28, 2000. J. Gobrecht Mikro- und Nanostrukturtechnikfür Oberflächen: Beschichten - strukturieren - charakterisieren PSI-Seminarreihe „Industrienahe Entwicklungen", Seminar „Oberflächentechnologie", Vilügen (Switzerland), November 3, 2000. A. Grubelnik, C. Padeste and L. Tiefenauer Amperometric immunosensor for penicillin in milk Biosensors 2000, San Diego (USA), May 24 - 26, 2000. D.Grützmacher Strukturierung im nm-Bereich Seminar: Fakultät für Elektrotechnik, Technische Universität Ilmenau (Germany), July 20, 2000. D. Grützmacher Nanostrukturen: Neue Wege für die Lichtemission aus Silizium Seminar: Fakultät für Elektrotechnik, Technische Universität Ilmenau (Germany), July 20, 2000. L. J. Heyderman, H. Schift and J. Gobrecht Micro- and Nanorheological Aspects of Thin Thermoplastic Films during Hot Embossing 6* MELARI /NID Workshop on Printing, Univ. of Twente (Netherlands), June 25 - 28, 2000. L. J. Heyderman, H. Schift and J. Gobrecht Nanoreplication at the Paul Scherrer Institute MESA-Insitute, Univ. of Twente (Netherlands), June 28, 2000. L. J. Heyderman, H. Schift, C. David, B. Ketterer, M. Auf der Maur and J. Gobrecht Nano fabrication using hot embossing lithography and electroforming MNE'2000, Jena (Germany), September 20 - 22, 2000. L. J. Heyderman, H. Schift and J. Gobrecht Micro- and nanorheological aspects of thin thermoplastic films during hot embossing EPS-CMD Montreux (Switzerland), March 13 - 17, 2000. L. J. Heyderman, H. Schift, C. David and J. Gobrecht Micro- and nanorheological study of thin thermoplastic films during hot embossing Hasliberg workshop on Nanoscience, Hasliberg (Switzerland), October 16 - 20, 2000. T. A. Jung Single molecules at surfaces: Will there be molecular devices after microelectronics? Invited Seminar, University of Nijmegen (Netherlands), September 12, 2000. T. A. Jung, H. Yanagi and H. Suzuki Molecular Nanoscience: The Science for future Technologies Japanese Swiss Workshop on Nanoscience, Riken (Japan), October 26 - 29, 2000. T. A. Jung, S. Berner, M. Brunner, B. Baumeister and H. Suzuki The Physics and Chemistry of Molecules at Interfaces: Where is the single molecular device? Invited presentation, University of Ulm (Germany), November 24, 2000. T. A. Jung, S. Berner, M. Brunner and H. Suzuki Molecular Nanoscience at Surfaces and Interfaces: What's different from Molecular Biology and what's needed for Molecular Devices? Invited Seminar, University of Neuchatel (Switzerland), December 4, 2000. T. A. Jung The Role of Physics for the Future of our Global Society Invited Presentation at the World Conference of Physical Societies, held in Conjunction with the Max Planck Centennial Week, Berlin (Germany), December 15 - 16, 2000. 231 O. Leifeld, A. Beyer, E. Miiller, D. Griitzmacher and K. Kern Nucleation ofGe dots on the C-alloyed Si(OOl) surface European Materials Research Society Spring Meeting, Strasbourg (France), May 5 - June 2, 2000. C. Padeste Molekulare Architektur fur die elektrochemische Biosensorik DFG-Workshop ,,Reaktion und Stabilitat von Nanopartikeln", Dresden (Germany), April 2 - 4, 2000. C. Padeste, A. Grubelnik and L. Tiefenauer Molecular architecture for electrochemical biosensors Biosensors 2000, San Diego (USA), May 24 - 26, 2000. F. Pfeiffer, T. Salditt, C. David and P. H0gh0j X-Ray Waveguides SLS Workshop, Les Diablerets (Switzerland), October 16 - 20, (2000). F. Pfeiffer, T. Salditt, P. Hoghoj and C. David Newly designed x-ray waveguides 45th SPIE Annual Meeting, San Diego (USA), August 3, 2000. R. Ros, F. Schwesinger, T. Stranz, A. Pliickthun, H-J. Giintherodt and L. Tiefenauer Characterization of antibody-antigen complexes using force spectroscopy 44th Ann. Meet. Biophys., New Orleans (USA), February 12 - 16, 2000. H. Schift Replication of micro- and nanostructures using molding techniques Lecture given at the CSEM Colloquium Series on Applications on Nanosciences, Neuchatel (Switzerland), April 28, 2000. H. Schift, A. D'Amore, C. David, M. Gabriel, J. Gobrecht, W. Kaiser and D. Simoneta Quantitative analysis of the molding of nanostructures EIPBN'2000, Palm Springs (USA), May 30 - June 2, 2000. H. Schift, L J. Heyderman, M. Auf der Maur and J. Gobrecht Pattern formation in hot embossing of thin polymer films TNT'2000, Toledo (Spain), Octoberl6 - 20, 2000. H. Schift The nano replication toolbox: from mastering to mass fabrication TOP Nano 21 meeting, Bern (Switzerland), October 24, 2000. H. Schift, A. D'Amore, M. Gabriel, J. Gobrecht, L. J. Heyderman, W. Kaiser and D. Simoneta Replication of micro- and nanostructures using molding techniques US-Swiss Forum on Nano Bio Sciences, Princeton (USA), December 14 - 15, 2000. H. Schift, L J. Heyderman and J. Gobrecht Nanoreplication in polymers using hot embossing and injection molding NFP36 closing meeting, Bern (Switzerland), November 13 - 14, 2000. H. Sigg, S. Gehrsitz and F-K Reinhart Vegards law in the AlGaAs system Group seminar IBM Forschungslabor, Riischlikon (Switzerland), June 20, 2000 H. Sigg, G. Dehlinger, L. Diehl, U. Gennser, J. Faist, K. Ensslin, D. Griitzmacher and E. Miiller Possibilities of a Si-based quantum cascade laser ? Seminar at Physik Institut Universitat Linz (Austria), December 12, 2000 H. Sorribas, D. Braun, C. Padeste, P. Sonderegger and L. Tiefenauer Neurite outgrowth on surfaces treated with neural adhesion molecules 2nd MEA Conference, Reutlingen (Germany), July 22 - 23, 2000. 232 H. Sorribas, C.Padeste, P. Sonderegger and L. Tiefenauer Patterns of adhesion molecules for cell guidance Ann. Meet. Swiss Soc. Biomaterials, Davos (Switzerland), June 8-9, 2000. H. Sorribas Neurons on microstructured biofunctionalised surfaces AO Research Institut, Davos (Switzerland), January 28, 2000. H. Suzuki, S. Berner, M. Brunner, H. Yanagi, D. Schlettwein, T. A. Jung and H.-J. Giintherodt Rotational behaviour in orientation of sub-phtalocyanine overlayer on Ag suface First International Conference on Molecular Electronics and Bioelectronics (M&BE1), Awaji Yumebutai International Conference Center (Japan), March 5 - 7, 2000. H. Suzuki, S. Berner, M. Brunner, H. Yanagi, D. Schlettwein, T. A. Jung and H.-J. Giintherodt Characterization of molecular overlayers on metal surface in dynamic equilibrium by scanning tunneling microscope International Conference on Nanomolecular Electronics, Kobe (Japan), December 5-7, 2000. H. Suzuki, S. Berner, M. Brunner, H. Yanagi, D. Schlettwein, H. Rauscher, F. J. Himpsel, K. Muellen, T. A. Jung and H.-J. Guentherodt Single Molecule Mechanics and Electronics of Individual Molecules at Contacting Interfaces Invited Presentation at Molelecular Electronics 2000, Organizer: United Engineering Foundation, Inc. Kailua - Kona (USA), December 10 - 14,. 2000. H. Suzuki, S. Berner, M. Brunner, H. Yanagi, D. Schlettwein, T. A. Jung and H.-J. Giintherodt Comparative Analysis of Various Porphyrin Compounds from Scanning Tunneling Microscopy and Spectroscopy with Sub-Molecular Resolution Second International Conference on Scanning Probe Spectroscopy, Hamburg (Germany), July 19 - 22, 2000. L. Tiefenauer, A. Grubelnik, R. Ros, H. Sorribas and C. Padeste Microstructuring and functionalization of surfaces for biosensors and related applications CHI-Conference on ,,Lab-chips and microarrays", Zurich (Switzerland), January 17 -19, 2000. L. Tiefenauer Molecular Nanotechnology: Functional molecules on structured surfaces Seminar Inorg. Chemistry, ETH Zurich (Switzerland), April 28, 2000. L. Tiefenauer Force spectroscopy for investigating biorecognition US-Swiss Forum on Nano Bio Science, Princeton University NJ (USA), December 13 -16, 2000. L. Tiefenauer, A. Grubelnik and C. Padeste Prevention of protein adsorption to active gold electrodes World Biomaterials Congress, Kamuela (USA), May 15 - 20, 2000. LABORATORY FOR RADIO- AND ENVIRONMENTAL CHEMISTRY HEAVY ELEMENTS Ch.E. Dullmann IVO - ein neuer Separator fur In-Situ Verfluchtigung und On-line Detektion Seminar Radio- und Umweltchemie, Universitat Bern (Switzerland), April 14, 2000. Ch.E. Dullmann, A. Tiirler, D.T. Jost, D. Piguet, H. Blumer, B. Eichler, R. Eichler, H.W. Gaggeler IVO - new apparatus for In-situ Volatilization and On-line detection of transactinide elements 5th International Conference on Nuclear and Radiochemistry (NRC5), Pontresina (Switzerland), September 3-8, 2000. B. Eichler Interaction of transactinides Z=104-116 with metal surfaces 5th International Conference on Nuclear and Radiochemistry (NRC5), Pontresina (Switzerland), September 3-8, 2000. 233 R. Eichler, H. Gaggeler, A. Tiirler, K.E. Gregorich, D.C. Hoffman, H. Nitsche, C.A. Laue, M. Schadel, A.B. Yakushev First chemical characterization ofbohrium (element 107) 220th ACS meeting, Division of Nuclear Chemistry & Technology, Washington D.C. (USA), August 20 - 24, 2000. R. Eichler Gasphase chemistry ofbohrium (element 107) 5th International Conference on Nuclear and Radiochemistry (NRC5), Pontresina (Switzerland), September 3-8, 2000. H.W. Gaggeler Chemistry ofTransactinide Elements Workshop on "Sciences with low energy radioactive beams", IPNS/KEK, Tokyo (Japan), March 10, 2000. H.W. Gaggeler Gas Phase Chemistry of the Transactinide Elements JAERI, Tokai (Japan), Macrh 12, 2000. H.W. Gaggeler Status of the Spoliation Neutron Source SINQ JAERI, Tokai (Japan), March 12, 2000. H.W. Gaggeler Das Wettrennen am obersten Ende des Periodensystems: Chemie versus Physik Physikalisches Kolloquium, ETHZ/Univ. Zurich (Switzerland), April 5, 2000. H.W. Gaggeler Gas Phase Chemistry of Transactinides Chemical and Nuclear Properties of the Heaviest Elements - A Symposium in Memory of Glenn T. Seaborg ACS Meeting, Washington (USA), August 20 - 24, 2000. H.W. Gaggeler 5th Nuclear and Radiochemistry Conference (NRC5) Pontresina (Switzerland), September 3-8, 2000 (organizer). H.W. Gaggeler Radioactivity measurements at Jungfraujoch NDSC steering committee meeting, Hotel Seepark, Thun (Switzerland), September 12 - 14, 2000. H.W. Gaggeler 1st das Ende des Periodensy stems erreicht? Tagung der Schweiz. Gymnasiallehrer, Baden (Switzerland), September 26, 2000. H.W. Gaggeler New Results from Heavy Element Research Seminar Section TEM, Paul Scherrer Institut, Villigen (Switzerland), November 10, 2000. A. Tiirler Heavy Element Research at the Paul Scherrer Institute Nuclear Physics Forum, 88" Cyclotron, Lawrence Berkeley National Laboratory, Berkeley (USA), April 27, 2000. A. Tiirler Chemistry and Physics of Heavy and Superheavy Elements Cyclotron Institute Colloquium, Cyclotron Institute, Texas A&M University, College Station (USA), May 16, 2000. A. Tiirler Heavy Element Research at the Paul Scherrer Institute Nuclear Chemistry Division Seminar, Nuclear Chemistry Division, Lawrence Livermore National Laboratory, Livermore (USA), May 25, 2000. A. Tiirler Anwendungen kurzlebiger Radionuklide Seminar fiir Kern- und Radiochemie, Institut fur Kernchemie, Universitat Mainz (Germany), June 26, 2000. 234 A. Türler, P. A. Wilk, R. Eichler, K. E. Gregorich, D. T. Jost, C. A. Laue, V. Ninov, J. L. Adams, W. Brüchle, R. Dressier, Ch. E. Diillmann, B. Eichler, H.W. Gäggeler, D. C. Hoffman, S. Hübener, U. W. Kirbach, M. R. Lane, V.M.H. Lavanchy, D. M. Lee, H. Nitsche, J. B. Patin, M. Schädel, D. A. Shaugnessy, D. A. Strellis, S. Taut, L. Tobler, Yu. Tsyganov, A. Vahle, A. B. Yakushev Two new isotopes of element 107:266Bh and 267Bh 7th International Conference on Nucleus Nucleus Collisions, Strasbourg (France), July 3-7, 2000. A. Tiirler Nuclear Chemistry Studies of Superheavy Elements Symposium on Future Physics with Exotic Nuclei, GSI Darmstadt (Germany), July 10 - 11, 2000. A. Türler Halides and Oxyhalides of the Transactinide Elements Rf Db, and S g 5th International Conference on Nuclear and Radiochemistry (NRC5), Pontresina (Switzerland), September 3-8, 2000. A. Türler Chemie mit kurzlebigen Radionukliden Institut für Radiochemie, TU München, Garching (Germany), November 21, 2000. SURFACE CHEMISTRY M. Ammann, F. Arens, L. Gutzwiller, U. Baltensperger, H.W. Gäggeler The reaction ofNO2 with diesel soot: a significant source ofHONO? European Geophysical Society, XXV General Assembly, Nice (France), April 25 - 29, 2000. M. Ammann, L. Gutzwiller, U. Baltensperger, H.W. Gäggeler Measurement ofHONO with a wett effluent diffusion dénuder and possible implications for nitrite formation in aqueous solution in presence of diesel exhaust Final Meeting of the EU-project DIFUSO, CEAM, Valencia (Spain), July 24, 2000. M. Ammann, L. Gutzwiller The heterogeneous reaction ofNO2 with organic compounds representative of VOC photooxidation products Kick-off Meeting of the EU Project NITROCAT, Wuppertal (Germany), May 5, 2000. M. Ammann Short-lived radiotracers for surface chemical studies. Invited lecture 5th Nuclear and Radiochemistry Conference (NRC5) Pontresina (Switzerland), September 3-8, 2000. M. Ammann, T. Bartels, M. Wachsmuth, H.W. Gäggeler Adsorption of nitrogen oxides on ice American Geophysical Union Fall, Meeting, San Francisco (USA), December 15 - 19, 2000. M. Ammann, T. Bartels, P. Zimmermann, B. Eichler, H.W. Gäggeler The adsorption of NO and NO2 on ice European Geophysical Society, XXV General Assembly EGS2000, Nizza (France), April 25 - 29, 2000. M. Ammann, T. Bartels Adsorption of trace gas species on ice Kick-off meeting of the EU Project Cut-ice, Mainz (Germany), March 13 -14, 2000. F. Arens, M. Ammann, L. Gutzwiller, U. Baltensperger, H.W. Gäggeler Formation of HONO from the reaction ofNO2 with diesel soot European Aerosol Conference, Dublin (Ireland), September 3 - 8, 2000. J. Aerosol Sei. 31, S1035 (2000). F. Arens, L. Gutzwiller, T. Bartels, M. Wachsmuth, H.W. Gäggeler, M. Ammann The reaction ofHNO3 with sea salt aerosol particles Chemical Mechanism Development, EC/Eurotrac-2 Joint Workshop, Lausanne (Switzerland), September 11 - 13, 2000. F. Arens, M. Ammann, L. Gutzwiller, U. Baltensperger, H.W. Gäggeler The reactivity of NO, with diesel soot and OH substituted PAHs Eurotrac-2 Symposium 2000, Garmisch-Partenkirchen (Germany), March 27-31, 2000. 235 T. Bartels Adsorption von Peroxyacetylnitrat aufEis Seminar Radio- und Umweltchemie, Universitat Bern (Switzerland), December 8, 2000. T. Bartels, H.W. Gaggeler, M. Ammann Adsorption of PAN on ice 5th Nuclear and Radiochemistry Conference (NRC5) Pontresina (Switzerland), September 3-8, 2000. T. Bartels, H.W. Gaggeler, M. Ammann Adsorption of PAN on ice Chemical Mechanism Development, EC/Eurotrac-2 Joint Workshop, Lausanne (Switzerland), September 11 - 13, 2000. J. N. Crowley, R. A. Cox, M. Ammann, G. Poulet, A. Horn, R. Zellner, M. J. Rossi, P. Mirabel, F. Domine Chemistry of the upper troposphere: laboratory studies of heterogeneous processes on ice Aviation, Aerosols, Contrails and Cirrus clouds, Seeheim (Germany), July 10 - 12, 2000. L. Gutzwiller Impact of diesel exhaust on atmospheric processes Department of Chemistry, Universidad Nacional Autonoma de Mexico (Mexico), March 3, 2000. L. Gutzwiller HONO Bildung an Dieselruss in einer Smogkammer im Rahmen des Projekts DIFUSO Seminar Radio- und Umweltchemie, Universitat Bern (Switzerland), April 14, 2000. L. Gutzwiller, U. Baltensperger, M. Ammann Aqueous reduction of nitrogen dioxide to nitrite at gas phase concentrations below lppm NO2 European Geophysical Society, XXV General Assembly EGS2000, Nizza (France), April 25 - 29, 2000. L. Gutzwiller, F. Arens, M. Ammann The HONO formation capacity of diesel exhaust Chemical Mechanism Development, EC/Eurotrac-2 Joint Workshop, Lausanne (Switzerland), September 11 - 13, 2000. L. Gutzwiller, F. Arens, M. Ammann The HONO formation capacity of diesel exhaust Energy Technologies for a Sustainable Future, Paul Scherrer Institute, Villigen (Switzerland), November 23 - 24, 2000. L. Gutzwiller Why should we measure HONO in Mexico City? Centro de Ciencias de la Atmosfera, Universidad Nacional Autonoma de Mexico (Mexico), March 3, 2000. M. Wachsmuth, B. Eichler, L. Tobler, D.T. Jost, H.W. Gaggeler, M. Ammann On-line gas-phase separation of short-lived bromine nuclides from precursor selenium 5th Nuclear and Radiochemistry Conference (NRC5) Pontresina (Switzerland), September 3-8, 2000. ANALYTICAL CHEMISTRY A. Eichler, M. Schwikowski, H.W. Gaggeler, U. Schotterer, M. Ammann Reconstruction of historical aerosol concentrations in Europe from Alpine ice cores EUROTRAC-2 Symposium 2000, Garmisch-Partenkirchen (Germany), March 27-31, 2000. A. Eichler Interpretation chemischer Signale in einem Eisbohrkern vom Grenzgletscher (Walliser Alpen) Seminar Radio- und Umweltchemie, Universitat Bern (Switzerland), April 14, 2000. A. Eichler, M. Schwikowski, H.W. Gaggeler, U. Schotterer High resolution paleo atmospheric records from ice cores of the northern and southern Alps European Geophysical Society, XXV General Assembly, Nice (France), April 25 - 29, 2000. A. Eichler, M. Schwikowski, H.W. Gaggeler, V. Furrer, H.-A. Synal, J. Beer Historical deposition records of radioactive isotopes from an Alpine Ice Core 5th International Conference on Nuclear and Radiochemistry (NRC5), Pontresina (Switzerland), September 3-8, 2000. 236 H.W. Gaggeler Snow and ice from the Alps as environmental archives Observatoire de Geneve, Geneva (Switzerland), January 11, 2000. H.W. Gaggeler Glaziologische Naturgefahren Workshop, Glaziologische Kommission und Naturforschende Gesellschaft Oberwallis der Schweiz. Akademie der Naturwissenschaften (SANW), H.W. Gaggeler and H. Schmidt (Organizers), Brig (Switzerland), January 13, 2000. H.W. Gaggeler Alpengletscher als Umweltarchive Naturforschende Gesellschaft Solothurn, Solothurn (Switzerland), February 21, 2000. P. Ginot, U. Schotterer, M. Schwikowski, W. Stichler, H.W. Gaggeler Glaciochemical evidence of past El Nino events in an ice core from Cerro Tapado, Chile European Geophysical Society, XXV General Assembly, Nice (France), April 25 - 29, 2000. P. Ginot Cerro Tapado Ice Core: El Nino record and importance of post deposition effects Seminar Radio- und Umweltchemie, Universitat Bern (Switzerland), June 16,2000. P. Ginot, C. Kull, U. Schotterer, M. Schwikowski, H.W. Gaggeler Effects of post depositional processes on glaciochemical records derived from Andean Cerro Tapado glacier 17. Geowissenschaftliches Lateinamerika-Kolloquium, Stuttgart (Germany), October 11-13, 2000. T. M. Huber Kontinuierliches Schmelzen und Analysieren von Eisbohrkernen im Vergleich mit konventioneller Analysentechnik Seminar Radio- und Umweltchemie, Paul Scherrer Institut, Villigen (Switzerland), May 12, 2000. T. M. Huber Kontinuierliche Analyse von Eisbohrkernen mittels lonenchromatographie Anwendertreffen Ionenchromatographie, Dionex, Olten (Switzerland), May 23, 2000. T. M. Huber, M. Schwikowski, H.W. Gaggeler Continuous Melting and Ion Chromatographic Analyses of Ice Cores International Ion Chromatography Symposium, Nice (France), September 11-14, 2000. S. Kniisel, T. M. Huber, M. Schwikowski, H.W. Gaggeler Analyse von Schwermetallen im Gletschereis mit kontinuierlicher Schmelzmethode und doppelfokussierendem ICP-MS 5. Symposium: Massenspektrometrische Verfahren der Elementspurenanalyse, Jiilich (Germany), September 18 - 21,2000. S. Kniisel Analysis of trace elements in ice cores by CIM-ICP-MS Seminar Radio- und Umweltchemie, Paul Scherrer Institut, Villigen (Switzerland), November 10, 2000. V.H.M. Lavanchy, U. Baltensperger, G. Bonani, U. Schotterer, M. Schwikowski, M. Suter, H.W. Gaggeler Historical record of carbonaceous particles from an ice core from the Alps and a first attempt for their 14C dating European Geophysical Society, XXV General Assembly, Nice (France), April 25 - 29, 2000. N.L. Misra Some studies on the applicability of Total Reflection X-ray Fluorescence (TXRF)for trace element analysis in ice samples Seminar des Kompetenzzentrums Analytische Chemie der ETH Zurich, Zurich (Switzerland), November 30, 2000. U. Schotterer Isotopen im Wasserkreislauf als Klimaindikator: Bedeutung des Messnetzes der Landeshydrologie und -geologie fur Grundwasseruntersuchungen Jahrestagung der Gesellschaft fur Hydrogeologie: Isotopen im Grundwasser, ETH Zurich (Switzerland), April 14, 2000. 237 U. Schotterer The isotopic fingerprint of El Nino in precipitation and ice cores from the tropical Andes Seminar Lab. des Sciences du Climat et de l'Environnement, C.E. Saclay, Gif-sur-Yvette (France), April 27, 2000. U. Schotterer Isotopic fingerprints for detecting El Nino in ice cores Seminar Radio- und Umweltchemie, Universitat Bern (Switzerland), June 16, 2000. M. Schwikowski, P. Ginot, H.W. Gaggeler, U. Schotterer, M. Funk, R. Gallaire, B. Pouyaud, A. Rivera, F. Stampfli, W. Stichler Palaeo atmospheric chemistry and climate records from Cerro Tapado glacier, Norte Chico, Chile, Ice Fields Scientific Task Force, March 24 - 28, 2000, sailing on board the "Aquiles" to the Ice Fields, CECS Valdivia (Chile), March 29, 2000. M. Schwikowski, B. Tenberken-Potzsch, M. Ammann Sampling and Separation of ice crystals and supercooled cloud droplets EUROTRAC-2 Symposium 2000, Garmisch-Partenkirchen (Germany), March 27-31, 2000. M. Schwikowski, H.W. Gaggeler, U. Schotterer, A. Dallenbach 1000 year palaeo record of the European atmosphere from an alpine ice core (Colle Gnifetti, Swiss Alps), European Geophysical Society, XXV General Assembly, Nice (France), April 25 - 29, 2000. M. Schwikowski, H.W. Gaggeler, U. Schotterer Ecological studies in the Alps and Andes Int. Conf. on social-oriented environmental problems of contiguous territories of Altai-Sayany Region, Polyex Hotel, Aya Gorni Altai (Russia), July 3 - 7, 2000. M. Schwikowski Hochalpine Gletscher als Archive fiir Klima- und Atmospharenforschung ASE-Seminar, Paul Scherrer Institut, Villigen (Switzerland), November 7, 2000. M. Schwikowski First glacio-chemical investigation of Belukha glacier in the Siberian Altai Seminar Radio- und Umweltchemie, Paul Scherrer Institut, Villigen (Switzerland), November 10, 2000. M. Schwikowski Analyse von chemischen Spurenstoffen in Eis zur Rekonstruktion der Luftverschmutzung Universitat Hamburg, Institut fur Anorganische und Angewandte Chemie, Hamburg (Germany), November 24, 2000. W. Stichler, U. Schotterer Climate Variability in Europe as derived from the GNIP data base Workshop ,,In Momoriam Hans Oeschger: Towards an Isotope Climatology", Max Planck Institut fur Meteorologie, Hamburg (Germany), September 4-6, 2000. N. Streit, E. Weingartner, M. Schwikowski, F. Hegediis, H.W. Gaggeler, U. Baltensperger Total reflection X-ray fluorescence (TXRF) as a method of ambient aerosol analysis Applica 2000, Zurich (Switzerland), September 26 - 28, 2000. L. Tobler, E. Lehmann, H.W. Gaggeler The Irradiation Facility for Neutron Activation at the Spoliation Neutron Source SINQ 5th International Conference on Nuclear and Radiochemistry (NRC5), Pontresina (Switzerland), September 3-8, 2000. L. Tobler, M. Schwikowski, H.W. Gaggeler Historische Entwicklung von Bleikonzentrationen und Blei-Isotopenverhdltnissen in einem alpinen Eisbohrkern 5. Symposium: Massenspektrometrische Verfahren der Elementspurenanalyse, Julich (Germany), September 18 - 21,2000. L. Tobler MeasuremMeasurement of7Be and 2l0Pb activity concentrations at the Jungfraujoch Meeting EU STACCATO-Project, Thessaloniki (Greece), October 30-31, 2000. 238 PROJECT RAD WASTE M. Argentini, R. Weinreich Measurement of Radionuclide contents in activated graphite 5th International Conference on Nuclear and Radiochemistry (NRC5), Pontresina (Switzerland), September 3-8, 2000. R. Weinreich Bestimmung des Radionuklid-Inventars in Beschleunigerabfalien Seminar der Abteilung ASE/96 des PSI, Villigen (Switzerland), March 15, 2000. R. Weinreich, M. Argentini Determination of the Radionuclide inventories in Accelerator Waste 5th International Conference on Nuclear and Radiochemistry (NRC5), Pontresina (Switzerland), 3-8 September 2000. LABORATORY FOR ION BEAM PHYSICS G. Bonani, I. Hajdas, U. Rouff, M. Seifert, V. Molodin and I. Sljusarenko Dendrochronological and radiocarbon dating of the scythen burial place in the Pazyrik vally in the Altai montains, South Siberia 17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000. M. Dobeli Hochauflosende Flugzeitspektrometrie Seminar, Max Planck Institut fur Plasmaphysik, Garching (Germany), February 17, 2000. M. Dobeli Thermal Stability of Implanted Fission Product Elements in Yttria Stabilized Zirconia Spring Meeting of the European Materials Research Society, Strasbourg (France), May 30, 2000. H. Haas, G. Bonani, Z. Hawass, M. Lehner, S. Nakhla, J. Nolan, R. Wenke and W. Wolfli Radiocarbon dating of Egyptian old kingdom monuments 17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000. I. Hajdas, G. Bonani, J. Beer, G. Bonino and G.C. Castagnoli An anomalous rise in the I4C activity 40 kyr ago 17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000. I. Hajdas, G. Bonani, D. Aritztegui and P. Moreno Radiocarbon chronologies of the late glacial cold reversal in Huelemo, Chile and Mascardi, Argentina 17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000. S. Ivy-Ochs Surface exposure dating of boulders on moraines with 10Be,26 Al and 36Cl: the Last Glacial Maximum to the Preboreal Seminar, Universitat Wien, Vienna (Austria), October 19, 2000. S. Ivy-Ochs, R. Wiist, P.W. Kubik, C. Schliichter Dating of stone tools from the Luxor region, Egypt, using 10Be 17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000. S.W.A. Jacob Beschleunigermassenspektrometrie bei tiefen Energien:Innovation, Probleme, Losungen Kernphysikseminar, ETH Zurich (Switzerland), May 9, 2000. S.W.A. Jacob Beschleunigermassenspektrometrie bei tiefen Energien Seminar, Universitat Wien, Vienna (Austria), November 23, 2000. 239 P.W. Kubik Langlebige kosmogene Nuklide an der Erdoberfläche: Werkzeuge zur Charakterisierung von Landschaftsentwicklungen Seminar, Universität Wien, Vienna (Austria), June 15, 2000. C. Maden, M. Döbeli, M. Suter Analyse von '0Be/'Be-Verhältnissen mit AMS Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Bonn (Germany), April 3-7, 2000. C. Maden, M. Döbeli, M. Suter Investigation of natural '0Be/'Be-ratios with Accelerator Mass Spectrometry Doktorandenseminar, ETHZ / Universität Zürich (Switzerland), October 3-5, 2000. C. Maden, M. Döbeli, P.W. Kubik, M. Suter, M. Frank Investigation of natural '0Be/'Be-ratios with Accelerator Mass Spectrometry Conference on the Application of Accelerators in Research and Industry CAARI 2000, Dentón (USA), November 1 - 4, 2000. C. Maden, M. Döbeli, P.W. Kubik, M. Suter, M. Frank Analyse von natürlichen '"BefBe-Verhältnissen mit AMS Seminar, Universität Wien, Vienna (Austria), December 7, 2000. R. Muscheler, J. Beer, G. Wagner, P.W. Kubik, C. Laj, J. Masarik 14 C and wBe - System and Production Effects 17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000. M. Schaller, F. von Blanckenburg, N. Hovius and P. W. Kubik Large-scale, long-term erosion rates determined from wBe in European river sediments Goldschmidt 2000 Conference, Oxford (UK), September 3 - 8, 2000. J.A. Scheer, S.W.A. Jacob, M. Suter, H.-A. Synal Messung von 26Al bei tiefen Energien Frühjahrstagung der Deutschen Physikalischen Gesellschaft, Bonn (Germany), April 3-7, 2000. C. Schnabel Iod-129 im Niederschlag in Mitteleuropa - woher kommt es? Seminar, Zentrum für Strahlenschutz und Radioökologie, Universität Hannover, Hannover (Germany), June 15, 2000. C. Schnabel, S. Xue, P. Ma, G.F. Herzog, K. Fifield, R.G. Cresswell, M.L. di Tada, P. Hausladen, and R.C. Reedy, Nickel-59 in surface layers of lunar basalt 74275: implications for the solar alpha particle flux Lunar and Planetary Science Conference, Houston (USA), March 13 -17, 2000. C. Schnabel, J.M. Lopez-Gutierrez, H.-A. Synal, M. Gloris, R. Michel, J. Kuhnhenn, and U. Herpers, Determination of production cross sections and production rates of iodine-129 in order to model its production from tellurium 63rd Annual Meeting of the Meteoritical Society, Chicago (USA), August 28 - September 1, 2000. C. Schnabel, J.M. Lopez-Gutierrez, S. Szidat, J. Beer, and H.-A. Synal I29I in rain water near Zurich 5th International Conference on Nuclear and Radiochemistry, Pontresina (Switzerland), September 3-8, 2000. C. Schnabel, L. Tobler, P.W.Kubik, H.W. Gäggeler 7Be, wBe and 2l0Pb activity concentrations at the Jungfraujoch Meeting of the EU project STACCATO, Thessaloniki (Greece), October 30-31, 2000. M. Suter New developments in accelerator mass spectrometry and their impacts on biomédical studies Seminar, Nestle Research Center, Lausanne (Switzerland), February 15, 2000. 240 M. Suter Altersbestimmungen mit Teilchenbeschleunigern Astronomische Gesellschaft, Luzern (Switzerland), May 8, 2000. M. Suter Status and Prospects of Accelerator Mass Spectrometry 17th International Radiocarbon Conference, Judean Hills (Israel), June 18 - 23, 2000. M. Suter Beschleunigermassenspektrometrie - Neue Techniken und Anwendungen Seminar, Universitat Basel, Basel (Switzerland), December 7, 2000. H.-A. Synal Moglichkeiten und Anwendungen von AMS Messungen mit36 Cl Seminar, Universitat Hannover, Hannover (Germany), January 5, 2000. H.-A. Synal Nachweis langlebiger Radionuklide mit Beschleunigermassenspektrometrie Seminar, Universitat Bern, Berne (Switzerland), January 21, 2000. H.-A. Synal Langlebige Radionuklide: Ultrasensitive Nachweismethoden und Anwendungen Seminar, Bergakademie Freiberg, Freiberg (Germany), February 8, 2000. H.-A. Synal Ca measurements @ the Zurich AMS System OSTEODIET-Meeting, Cork (Ireland), February 18, 2000. H.-A. Synal Moglichkeiten und Anwendungen von AMS Messungen mit36 Cl Friihjahrstagung der Deutschen Physikalischen Gesellschaft, Bonn (Germany), April 4, 2000. H.-A. Synal New Directions in Accelerator Mass Spectrometry Seminar, Purdue University, West Lafayette (USA), April 17, 2000. H.-A. Synal, S. Jacob and M. Suter Status of Radiocarbon Detection at Low Energies 17th International Radiocarbonconference, Judean Hills (Israel), June 18-23, 2000. H.-A. Synal, S. Jacob and M. Suter The PSI/ETH Small AMS System: New Results 15th Conference on Applications of Accelerators in Research and Industry, Denton Texas (USA), November 3, 2000. H.-A. Synal AMS of long-lived Radionuclides: New Developments and Applications Seminar, US Geological Survey, Idaho Falls (USA), November 7, 2000. S. Szidat, R. Michel, T. Ernst, J. Handl, D. Jakob, H.-A. Synal, C. Schnabel Status and trends of iodine-129 abundances in the European environment 5th International Conference on Nuclear and Radiochemistry, Pontresina (Switzerland), September 3-8, 2000. S. Tschudi AnwendungAnwendungsmoeglichkeiten von kosmogenen Nukliden ('"Be, 26Al und 2lNe) in der Eiszeitgeologie Kernphysikseminar, ETH Zurich, Zurich (Switzerland), November 28, 2000. S. Tschudi Expositionsaltersbestimmung in Finnland und Russland: Schwierigkeiten-Resultate-Zukunft Berner Quartargesprache, University of Berne, Berne (Switzerland), March 29, 2000. 241 F. von Blanckenburg, M. Schaller and P.W. Kubik A new geochemical method for the determination of large-scale erosion rates, and its comparison to conventional river load gauging Annual Meeting of the Deutsche Geologische Vereinigung, Vienna (Austria), April 14 -17, 2000. F. von Blanckenburg, M. Schaller, T. Veldkamp, N. Hovius and P. W. Kubik Late Pleistocene to Holocene erosion rate variations from cosmogenie nuclides in river terrace sediments Goldschmidt 2000 Conference, Oxford (UK), September 3 - 8, 2000. D. Vance, M. Bickle. S. Ivy-Ochs and P. Kubik Cosmo genie isotope measurements of erosion rates in the Himalaya Goldschmidt 2000 Conference, Oxford (UK), September 3 - 8, 2000. G. Wagner, J. Beer, C. Laj, C. Kissel, R. Muscheler, J. Masarik, H.-A. Synal Detection of the Mono Lake event in the Cl-36 flux in the GRIP ice core, European Geophysical Society XXV General Assembly, Nice (France), April 25 - 29, 2000. G. Wagner, J. Beer, R. Muscheler, J. Masarik, H.-A. Synal Detection of solar cycles in the Cl-36 record from the GRIP ice core, European Geophysical Society XXV General Assembly, Nice (France), April 25 - 29, 2000. G. Wagner, J. Beer, C. Laj, C. Kissel, J. Masarik, R. Muscheler, H.-A. Synal Paleomagnetic field reconstruction based on cosmogenic isotopes of the GRIP ice core, Workshop at the GeoForschungsZentrum, Potsdam (Germany), November 9-11, 2000. G. Wagner, J. Beer, R. Muscheler C. Laj, C. Kissel, J. Masarik, H.-A. Synal Reconstruction of the snow accumulation rate of central Greenland during the last ice age using the cosmogenic radionuclides Cl-36 & Be-10 and geomagnetic field intensity data American Geophysical Union Conference, December 2000. 242 PUBLICATIONS AND LECTURES FOR GENERAL PUBLIC R. Eichler Forschung am Paul Scherrer Institut Rotary Club Zurich, PSI-Forum, 6. Marz 2000 R. Eichler Forschung am Paul Scherrer Institut Regionalplanungsgruppe Brugg, PSI19. April 2000. R. Eichler Physikvorlesung fur Kinder PSI-Brunch, PSI-Forum, 14. Mai 2000. M. Giidel XMM-Newton Measures the Hot Universe Cern Courier 40 (7), 17-20 2000. Ph. Jetzer Materia oscura e lenti gravitazionali Liceo Cantonale di Lugano, PSI-Forum, 2. Marz 2000. A. Zehnder Rontgenastronomie Physikdepartement Tagung, ETH-Zurich, 16. Juni 2000. A. Zehnder HESSI Physik. Gesellschaft Zurich, ETH-Zurich, September 2000. A. Zehnder Sonne und Sterne im Rontgenlich PSI Pensioniertenvereinigung, PSI, 5. Dezember 2000. 243 LECTURES AND COURSES Prof. Dr. R. Eichler ETH Zurich, SSOO: • Physikpraktikum fur Vorgeriickte • Particle Physics Seminar (with others) • Physikalisches Kolloquium (with others) • Teilchenphysikpraktium am PSI ETH Zurich, WS00/01: • Physik I fur Mathematiker und Physiker • Physikpraktikum fur Vorgeriickte • Particle Physics Seminar (with others) • Physikalisches Kolloquium (with others) LABORATORY FOR ASTROPHYSICS Dr. M. Gtidel ETH Zurich und Universitat Zurich, WS00/01: • Hochenergie-Astrophysik (with Prof. A. Benz) PD Dr. Ph. Jetzer Universitat Zurich, SSOO: • Einfiihrung in die Astro-Teilchenphysik Universitat Zurich, WS00/01: • Mitwirkung an der Organisation des Theorie-Seminars (gemeinsam mit der ETH) ETH Zurich, WS00/01 • Mitwirkung am Proseminar in Theoret. Physik LABORATORY FOR MICRO AND NANO TECHNOLOGY Dr. J. Gobrecht ETH Zurich, WS00/01: • Vorlesung und Ubungen ,,Grundlagen der Mikro- und Nanotechnik" Dr. D. Grutzmacher Universitat Konstanz, WS00/01: • Vorlesung "Optik" (Main lecturer: Prof. P. Leiderer) Dr. T.A. Jung Universitat Basel, WS00/01: • Vorlesung "Einfiihrung in die Nanowissenschaften" (with others) Dr. H. Sigg Universitat Zurich, SSOO: • "VP Halbleiterpraktikum" (together with Prof. B. Patterson) LABORATORY FOR RADIO- AND ENVIRONMENTAL CHEMISTRY Prof. Dr. H.W. Gaggeler Universitat Bern, SSOO: • Physikalische Chemie IV • Instrumentalanalytik II • Seminar in anorganischer und physikalischer Chemie (with others) • Seminar in Radio- und Umweltchemie (with Dr. M. Ammann), in collaboration with Paul Scherrer Institut 244 Universitat Bern, WSOO/01: • Anwendung von Radioisotopen • Radiochemiepraktikum (with PD Dr. A. Tiirler) • Seminar in anorganischer und physikalischer Chemie (with others) • Seminar in Radio- und Umweltchemie (with Dr. M. Ammann), in collaboration with Paul Scherrer Institut Dr. M. Schwikowski Universitat Bern, SSOO: • Instrumentalanalytik II (with Prof. H.W. Gaggeler) PD Dr. A. Turler Universitat Bern, WSOO/01: • Eigenschaften schwerster Elemente LABORATORY FOR ION BEAM PHYSICS Prof. Dr. M. Suter ETH Zurich, SSOO: • Seminar Kernphysik mit Anwendungen (with others) • Doktorierendenseminar iiber Kern- und Teilchenphysik (with others) ETH Zurich, WSOO/01: • Kernphysik II, Wahlfachvorlesung • Seminar Kernphysik mit Anwendungen (with others) LABORATORY FOR PARTICLE PHYSICS THEORY GROUP PD Dr. A. Denner ETH Zurich, SSOO: • Proseminar Theoretische Physik (with others) • Das Standardmodell der elektroschwachen Wechselwirkung und dessen Erweiterungen PD Dr. D. Graudenz ETH Zurich, SSOO: • Einfiihrung in die Quantenchromodynamik PD Dr. K. Junker Technische Universitat Wien, SSOO: • Einfiihrung in die theoretische Mittelenergiephysik Dr. M. Melles ETH Zurich, SSOO and WSOO/01: • Seminar iiber Physik der Elementarteilchen (with A. Denner) PD Dr. R. Rosenfelder ETH Zurich, WSOO/01: • Solitonen, Instantonen und Monopole 245 AWARDS Titels: C. David Award for second best poster Diffractive grey tone masks for laser ablation lithography Micro and Nanoengineering MNE 2000, Jena, 19. Sept. 2000 Ph. Jetzer Titularprofessor at Universitat Zurich K. Thomsen ES A personal award to Knud Thomsen "in recognition of his outstanding contribution to the XMM-Newton programme" HESSI / PSI Team NASA Award to HESSI PSI Team: "Goddard space flight center group achievement award" for oustanding teamwork Habilitation: E. Morenzoni: Title of thesis: Generation and applications of polarized low energy muons PSI and ETH Zurich Doctoral Thesis: B. Artur: Title of thesis: Measurement of WW Production Cross Section and Mass of the W boson PSI Thesis advisors: Prof. Dr. H. Hofer / Dr. M. Pohl (ETH Zurich) Dr. M. Fabre (PSI) Y. Bonetti: Title of thesis: Laserinterferenz-Lithographie zur Herstellung von Modell-Katalysatoren PSI Thesis advisors: Prof. Dr. R. Prins (ETH Zurich) Dr. J. Gobrecht (PSI) A. Eichler: Title of thesis: Deposition von Spurenstojfen in Firn und Eis alpiner Gletscher, Untersuchung von Nord-Sudgradienten PSI/Universitat Bern Thesis advisors: Prof. Dr. H.W. Gaggeler (Universitat Bern & PSI) Dr. M. Schwikowski (PSI) 246 R. Eichler: Title of thesis: Die chemische Charakterisierung des Transactinoids Bohrium (Bh, Element 107) Universitat Bern/PSI Thesis advisors: Prof. Dr. H.W. Gaggeler (Universitat Bern & PSI) Prof. Dr. B. Eichler (PSI) H. A. Fuhrmann: Title of thesis: Herstellung von sub-jim CoSi2-Strukturen mit dem fokussierten Ionenstrahl ETH Zurich Thesis advisors: Prof. Dr. H. R. Ott (ETH Zurich) Dr. M. Dobeli (PSI) S. Graf: Title of thesis: Photon drag spectroscopy of the two-dimensional electron gas in GaAs/AlGaAs quantum well systems PSI Thesis advisors: Prof. Dr. W. Bachthold (ETH Zurich) Dr. H. Sigg (PSI) L. Grenacher: Title of thesis: Baryonic Dark Matter in Clusters and Spiral Galaxies PSI/Universitat Zurich Thesis advisors: Prof. Dr. N. Straumann (Universitat Zurich) Prof. Dr. Ph. Jetzer (PSI & Universitat Zurich) J. Koglin: Title of thesis: The KARMEN Time Anomaly: Search for a Neutral Particle of Mass 33,9 MeV in Pion Decay PSI Thesis advisors: Prof. Dr. D. Pocanic (Universitat Virginia) Dr. M. Daum (PSI) M. Pinkpank: Title of thesis: Rare Earth Magnetism in Cuprates PSI Thesis advisors: Prof. Dr. H. R. Ott (ETH Zurich) PD Dr. A. Schenk (ETH Zurich) 247 R. Ros: Title of thesis: Kraftmessungen an einzelnen Antikorpermolekulen PSI Thesis advisors: Prof. Dr. H.-J. Giintherodt (Universitat Basel) Dr. L. Tiefenauer (PSI) N. Streit: Title of thesis: Chemical and Physical Characterization of Ambient Aerosols in Source and Sink PSI Thesis advisors: Prof. Dr. H.W. Gaggeler (Universitat Bern & PSI) PD Dr. U. Baltensperger (PSI) M. Strassle: Title of thesis: Contributions to the Electrodynamics of Compact Objects and the Dark Matter Search in the Universe PSI Thesis advisors: Prof. Dr. N. Straumann (Universitat Zurich) PD Dr. Ph. Jetzer (PSI) S. Tschudi: Title of thesis: Surface exposure dating: a geologist's view with examples from both hemispheres Universitat Bern / PSI Thesis advisors: Prof. Dr. C. Schliichter (Universitat Bern) Dr. P. W. Kubik (PSI)