INIS-mf—12692

Paul Scherrer Institut

DEPARTMENT F3 Condensend Matter Research and Materials Sciences

Progress Report 1989

Paul Scherrer Institut Telefon 056 / 99 2111 WQrenllngen und Vllllgen Telex 82 7414 psi ch CH-5232 Vllllgen PSI Telefax 056 / 98 23 27 FOREWORD

Looking back on the activities of one year, one 1989 was also a year of intense activities in view of the most obvious questions is always: "have of exploring new directions of research for F3. we reached our goals that we set out in the be- The defect physics group was involved in eval- ginning?" For the period of 1989 and the De- uating the possibilities for installing an intense partment F3 ( and ma- e+-source at PSI. Apart from the challenge of terials sciences) the answer in most cases is yes. developing a new kind of scientific tool, appli- + + We aimed at enforcing the general concept of cations like e -microscopy and e -spectroscopy applying nuclear methods in condensed mat- at a yet unknown level seem attractive. Another ter physics and materials science research. As new installation, namely an electron planned, a new PSI group for /iSR was created, resonance (ECR) source for heavy ions at one and its main first task is the planning of //SR ar- of the injector was mainly pushed by eas at the beam lines for the time after the our chemists, who foresee new possibilities in accelerator shut down and the construction of the field of chemistry with very small quantities new and up-to-date general-purpose /JSR spec- of matter. trometers that will be available to the growing While these new projects are supported by inter- /iSR community. Construction of the ested groups at Swiss Universities ( and source SINQ is proceeding as planned, Fribourg), our laboratory for technical physics and various crucial new positions in particular sought an industrial collaboration in view of de- areas of this project were filled. Activities rely- veloping and constructing a superconducting en- ing on application of the heavy-ion Tandem van ergy storage system . Progress in these endeav- de Graaff accelerator in materials science have ours is less fast than we hoped for. Another been initiated and are supported by additional ambitious project of some international prestige new positions and doctoral-theses projects. was brought up by the PIREX group, namely the Within the SINQ project a new program for installation of an intense 14 MeV the development and construction of improved for defect studies in relation with fusion reactor neutron mirrors has been started with the final containers. Although we believe that PSI could goal of providing enhanced neutron fluxes at the deliver an original solution to the problem, we spectrometers. Another surface-science related had to abandon the idea at an early stage, mainly program was initiated in relation with the de- because of obvious lack of manpower and fi- velopment of superconducting detector systems. nances. Anticipating future activities in applications of These remarks and the following scientific re- these detectors, we joined a number of inter- ports demonstrate clearly that F3 is sailing with national collaborations involved in space-based full strength although the winds are not always missions for astrophysical investigations. This favourable. We certainly have more ideas for an- may develop into a program related to space chor places than we can cope with and we need technology and parts of astrophysics, an enter- to make some decisions about our routing in the prise which does not exist in in this future. We are grateful to all external users and form and would contribute to fulfilling the task partners for their interest, support and help in of PSI as being a national laboratory. These setting the pace. plans seem to find support among interested groups at Swiss Universities. i

H.R^Ott He Department F3 Paul Schener Institut WUrenUngen and Villigen CH-S232VilligenPSI Switzerland

Telephone (Exchange) 056/ 99 21 Ilor056/993111

Telefax and Telex:

Telefax: Telex: 3000 Head of Department 0567993294 827419 3101 Myon Spectioscopy 056V99 3294 827419 3102 0567992327 82 7417 3800 Spallation Neutron Source 0567993294 827419 3104 Cryogenic Detectors 0567993294 827419

3110 Accelerator Mass Spectroscopy 01/3712665 -

3200 to Chemistry Division 05679823 27 82 74 17 3216

3301 Defect Physics 056/982327 827417 3302 PIREX 05679823 27 827417

3400 to Technical Physics Division 056799 3294 827419 3432

Editing: H.W. Gaggeler, R. Lorenzen

4.90 2000 51245/4 TABLE OF CONTENTS

Condensed Matter Research (3100) Myon Spectroscopy /iSR (3101)

MAGNETIC FLUX DISTRIBUTION IN THE HIGH-T,. SUPERCONDUCTOR YBasClfeO, STUD- IED BY /iSR (RA-72-05) STRUCTURES OF MUONATED FREE RADICALS (RA-74-04)

MAGNETIC CORRELATIONS IN SUPERCONDUCTING YBa2Cu30r (RA-76-03) FIELD DEPENDENT MUON KNIGHT SHIFT AND RELAXATION IN A Bi SINGLE CRYSTAL (RA-76-05)

STUDY OF THE SYSTEM U2_rSrrCuO4 BY STROBOSCOPIC pSR (RA-76-05) LOW-TEMPERATURE p+SR EXPERIMENTS ON a-IRON SINGLE CRYSTALS (RA-78-02, RA- 85-06) 7T+ / p+ CHANNELLING STUDIES ON GOLD (RA-79-02) TEMPERATURE-DEPENDENCE OF POSITIVE MUON-DECAY CHANNELLING IN SEMICON- DUCTORS (RA-79-10) A /iSR STUDY OF THE 1K PHASE TRANSITION IN THE HEAVY ELECTRON COMPOUND UCus (RA-85-12)

MAGNETIC ORDERING INDUCED BY DOPING OF YBa2Cu3O7 (RA-85-17) jiSR INVESTIGATION OF LOCALIZED AND ITINERANT MAGNETS (RA-8S-18(A)) /ISR STUDIES OF RARE EARTH MAGNETS (RA-85-18(B)) RADICAL REORIENTATION IN SOLIDS AND ON SURFACES (RA-86-07(A)) /i+SR IN CHEVREL PHASE SUPERCONDUCTORS CRA-«7-O2) /i-SR IN SEMICONDUCTORS (RA-88-04)

Neutron Scattering (3102)

THE CRYSTALLINE ELECTRIC FIELD OF Pr2CuO4 (ETHZ - PSI - U.K. - USA)

HIGH-TC POWDER SAMPLE PRODUCTION (ETHZ - PSI)

PHONON DISPERSION IN Li2S (ETHZ - GENF - OAK RIDGE) SEARCH FOR LIGHT-INDUCED STRUCTURE CHANGES IN SODIUM- NITROPRUSSIDE ON POLYCRYSTALLINE SAMPLES (ETHZ - PSI - BERN) SEARCH FOR LIGHT-INDUCED STRUCTURE CHANGES IN SODIUM-NTTROPRUSSIDE ON SINGLE CRYSTALS (ETHZ - PSI - LLB - ILL - KOLN - BERN) MAGNETIC PROPERTIES AND ANTIFERROMAGNETIC Cu ORDERING IN Pr2Cu04 (ETHZ - USA - ETH - PSI) OSCILLATING RADIAL COLLIMATOR OF DMC DIFFRACTOMETER (ETHZ • PSI) LONG-RANGE F.C.C. ANTIFERROMAGNETIC ORDERING OF TYPE ID IN YbAs (ETHZ - GRENOBLE)

MAGNETIC ORDERING OF REPd3 (RE = Nd, Er, Tm, Yb) (ETHZ - MUNSTER) NUCLEAR AND MAGNETIC STRUCTURE OF THE PERMANENT MAGNET MATERIAL Lu3Fei4C (ETHZ - PSI - Philips) NUCLEAR STRUCTURE OF Na8(AlSiO4)6(OH)2- 2(H2O) (8:2:2-SODALITHE) AT 175 AND 10 K (PSI - Universitflt Konsianz - ETHZ) CRITICAL DYNAMICS IN NICKEL NEAR Tc (PSI - GRENOBLE - BERLIN - Gif sur Yveue)

LONGITUDINAL SPIN FLUCTUATIONS IN Ni BELOW Tc (PSI - GRENOBLE - NEW YORK)

LONGITUDINAL SPIN FLUCTUATIONS IN THE DIPOLAR FERROMAGNET EuS ABOVE Tc (PSI - HAMBURG - GRENOBLE) LOW TEMPERATURE STATE OF UCu5 (PSI - ETHZ) Cryogenic Detectors (3104) PHONON DETECTION IN SINGLE CRYSTALLINE SILICON WITH SUPERCONDUCTING TUN- SS NEUNO JUNCTIONS (Paul Schorcr Institut) HIGH-Tc? SUPERCONDUCTING FILMS FOR PARTICLE DETECTORS (PSI - Liechtenstein - 59 ETHZ)

Accelerator Mass Spectrcmetry AMS (3110) THE ACCELERATOR MASS SPECTROMBTRY FACfcrTY PSI -ETH (PSI -ETHZ) 61 DETERMINATION OP CROSS SECTIONS FOR THE PRODUCTION OF "Be BY HIGH-ENERGY 63 PROTONS (KOLN - HANNOVER - ETHZ) ATMOSPHERIC TRANSPORT OF BOMB-PRODUCED MC1 (PSI -ETHZ -BERN) 65 DETERMINATION OF AVERAGE PARTICLE-SETTLING VELOCITIES USING THE 10Be/7Be 67 RATIO (EAWAG - ETHZ - PSI) ISOTOPIC COMPOSITION OF ATMOSPHERIC (Heidelberg - ETHZ - PSI) 68 THIN LAYER ACTIVATION OF HIP JOINT PROSTHESES FOR TRIBOLOOICM. TESTS 70 (SULZBR - ETHZ) AMS MC MEASUREMENT OF SMALL VOLUME OCEANIC WATER SAMPLES: BXPERIMBN- 72 TAL PROCEDURE AND COMPARISON WITH LOW-LEVEL COUNTING TECHNIQUE (Heidel- berg-ETHZ)

Chemistry (3200) Geochemistry (3211)

DATING GROUND WATER WITH RADON-222: LABORATORY EXPERIMENTS (PSI - BERN - 75 ETHZ) SORPTION OF BARIUM ON A <32-pm GRAIN SKB FRACTION OF GLACIOFLUVIAL DE- 77 POSITS (Paul Schemr Institut)

Trace Elements (3212)

DEPENDENCE OF SOME ELEMENT CONTENTS IN NEEDLES OF NORWAY SPRUCE ON 79 SOIL PARAMETERS (Paul Scherrcr Institut)

Aerosol Chemistry (3213)

MASS TRANSFER TO DIFFUSION GROWN AGGLOMERATES AND THEIR FRACTAL DIMEN- 81 SION (PSI - ETHZ - DUISBURG) CONTINUOUS BACKGROUND AEROSOL MONITORING WITH THE EPIPHANIOMETER (PSI 83 - PASADENA) FOG CHEMISTRY AT LAEGEREN (WSL • BERN - PSI) 86 ATMOSPHERIC STUDIES AT JUNGFRAUJOCH (PSI - BERN) 88

Heavy Elements (3214)

COLD FUSION REACTIONS WITH «Ca (PSI - BERN - GSI - MAINZ - HELSINKI) 91 GASPHASE CHEMISTRY EXPERIMENTS WITH ELEMENT 105 (PSI - BERN - LBL - GSI - 93 MAINZ) GASCHEMICAL SEPARATIONS BY SELECTIVE DESORPTION FROM SMALL KC1 PARTI- 95 CUES (LBL-PSI-GSI-MAINZ) Cement Products (3216) ACTIVITIES OF THE CEMENT CHEMISTRY GROUP (Paul Schener Institut) 97 DETERMINATION OF 36C1 IN COOLING WATER AND IN RESINS FROM KKG USING AMS 98 AND LSC (PSI - NAGRA • ETHZ)

Materials Sciences (3300) Defect Physics (3301) POSITRON PHYSICS AT PSI 99 HIGH EFFICIENCY POSITRON MODERATION (Paul Schentr Iiuttait) 101 EVIDENCE FOR OFF-SYMMETRY POSITION OF INTERSTITIAL IMPLANTED IN 103 CRYSTALLINE BISMUTH (PSI • ) COHESIVE PROPERTIES OF SMALL CLUSTERS WITH IRON AND COPPER FOR A STUDY 105 OF PHASE SEPARATION IN ALLOYS IRRADIATION FACILITY WITH VARIABLE TEMPERATURE, NEUTRON ENVIRONMENT 107 AND IN-SITU STRAINING (Paul Schener Institut) MATHEMATICAL ANALYSIS OF GRAIN BOUNDARY MISORIENTATION (PSI - GRENOBLE 109 - ORSAY - NEW HAVEN) THE ROLE OF CHEMICAL COMPOSITION IN THE NEUTRON IRRADIATION EMBRITTLE- 110 MENT SENSITIVITY OF FE-BASED ALLOYS (Paul Schener Institut)

PIREX, Irradiation Damages, Fusion (3302) THE GROWTH OF HELIUM BUBBLES IN 600 MeV PROTON IRRADIATED ALUMINUM DUR- 113 ING POSTIRRADIATION ANNEALING (PSI - EPFL) THE TENSILE AND FATIGUE PROPERTIES OF THE 1.4914 MARTENSITIC STEEL (PSI - 115 PEKING)

Technical Physics (3400) STUDY PROJECTS (Paul Schener Institut) 119 CURRENT LEAD TEST (Paul Schemer Institut) 121 OPERATION OF A 50 kA SUPERCONDUCTING TRANSFORMER FOR THE SULTAN TEST 123 FACILITY (Paul Schemer Institut) INVESTIGATION OF HYSTERETIC INTERORAIN CRITICAL CURRENT DENSnTTIES IN 125 POLYCRYSTALUNE HIGH Ic-SUPERCONDUCTORS (Paul Schener Institut)

List of Publications 127

Contributions to Conferences and Workshops 134

Lectures and Courses 139 Condensed Matter Research (3100)

Myon Spectroscopy /iSR (3101)

MAGNETIC FLUX DISTRIBUTION IN THE HIGH-TC SUPERCONDUCTOR YBa2Cu302 STUDIED BY /*SR

RA-72-05, ZÜRICH - ETHZ • BIRMINGHAM - IBM

E.M. Foigan1, E. Kaldis', H. Keller', W. Kündig'5, Y. Maeno1. B. Pümpin', C. Rössel*. S. Rusiecki', I.M. SavW, J.W. Schneider*. H. Simmler", P. Zimmermann*

* Physik-Instilul der Universität Zürich, CH-8001 Zürich t Laboratorium für Festkörperphysik ETH Zürich, CH-8093 Zürich t School of Physics and Space Research, University of Birmingham, GB-Birmingham BIS 2TT § IBM Research Division, Zurich Research Laboratory, CH-8803 Rüschlikon

Since the muon spin rotation (pSR) technique offers an —•-•-•-. elegant way to probe the local magnetic field distribution 3.0 YBOJCUJO, p(B) in a superconductor, it is often applied to investi- 2.5 x = 6.970(1) sintered sample gate the behavior of the London penetration depth A. The 2.0 temperature dependence of A contains crucial information 350mT (FC) on the involved pairing mechanism (s- or p-wave, strong- 1.5 or weak-coupling). In addition, the zero-temperature value 1.0 A(0) sets a scale for the screening of an external field Bext 0.5 and is one of the characteristic lengths of a superconductor. 0.0 If a perfect triangular vortex lattice is formed in a supercon- ductor, it is possible to calculate the magnetic penetration -O.5L 20 40 60 80 100 depth A by means of [1,2] 120 300 TEMPERATURE (K) 4 2 A = 0.0371*o/(AB ), (1) Figure 1: Depolarization rate a as a function of temperature 2 where (AB ) is the second moment of p(B). This equation for a high quality, sintered YBa2Cu30l; sample in a field is only valid for high magnetic fields, where of 350 mT (FC). The line is a fit to the data using the 3 (AB ) is independent of BM( [1]. For conventional s- temperature dependence given by the two-fluid model. wave pairing, the temperature dependence of the penetra- tion depth is generally described by the empirical expres- sion \{T) = A(0)(l - (T/Ti)4]"1'2 (two-fluid model). In this tetter, we present an accurate measurement of 6.970(1)1 prepared at the ETHZ was used to determine the the temperature dependence of the effective penetration temperature dependence of KJJ. Magnetization measure- depth \tlj (powder average) in a high quality sintered ments exhibit a very sharp transition at Tc = 89.5(5) K with YBa2CuaOx sample. The anisotropy of this uniaxial super- a width of 8 K (10-90%) and a Meissner fraction of approx- conductor was studied by performing /iSR experiments on imately 60% in a field of 14.2 mT. In a first step, a field scan a mosaic of YBa2Cu3O.r single crystals for different angles was performed on the sample [3]. Every point of this scan 0 between the external field Bczt and the crystallographic was obtained after field-cooling (FC) the sample from above c-axis. In order to learn more about the flux line structure in Te to 10 K. The fiSR spectra were analysed by assuming a a sintered specimen, the influence of a dc-current on p(B) Gaussian distribution p{B). Under this assumption, the sec- ond moment of p(B) is given by (AB2) = 2<72/72, where

A high quality sintered YBa2Cu3OI sample [x = a is the /iSR depolarization rate and y,, the gyromagnetic ratio of the muon. Above 150 mT,

RA-74-04, ZURICH - LONDON - GLASGOW

T. Azuma', D. Bultar*, H. Fischer-S, R.M. Macrae', I.D. Reid', CJ. Rhodes', E. Roduner"5, B.C. Webster4

* Physikalisch-Chemisches Institui .Univcrsitat Zurich, CH-8057 Ziirich t Department of Chemistry, Queen Mary College, GB-London, El 4NS t Chemistry Department, The University, GB-Glasgow G12 8QQ

Introduction The positive muon allows the study of the formation, Nucleus i A' R' structure, and dynamics of organic free radicals, using the (MHz) experimental technique of muon spin rotation (/iSR) in 1 -2.82 transverse magnetic fields [1,2]. In the past year we con- CHMu muon pc 2 128.71 -1.69 centrated on investigations of the effect of crystal fields, 3 4.51 substituents, and solvent effects on the radical hyperfine 1 -3.11 coupling constants. CHMu muon 0'c 2 143.54 -1.27 3 4.38 The influence of a crystal field 1 -2.61 The study of muonated free radicals in a single crystal CHMu muon 0d 2 138.90 -1.75 of naphthalene has been brought to a successful conclusion 3 4.36 [3]. The project was designed to compare results obtained 1 -2.86 for muonated radicals with those for hydrogen-containing CHMu muon 0'd 2 136.56 -1.73 radicals [4], to investigate the effect of isotopic substitution 3 4.59 within a crystalline environment. Fig. 1 shows the a- and /3-radical signals observed in a naphthalene solution; in the crystal each signal splits into eight [3]. Table 1: Principal values of the reduced hyperfine coupling tensors of Mu-substituted /3-radicals in single-crystal naph- 10 thalene; A'u = A'iao + B'i{. Each radical gives rise to two a signals due to the different orientations of the two molecules 06 per unit cell.

H others in the principal planes of the molecular co-ordinate ' (Xf system. This allowed us to assign the radicals to pairs I arising from addition at the same . Further ar- 0- guments based on the direction of the tensors relative to the molecule and (for the /^-radicals) the crystalline envi- ronment led to an absolute identification for each radical. 0 The assignments are given in Table 2 while Fig. 2 shows 100 150 200 250 300 the position of the I3C and P'c muons within the crystal. Frequency (MHz) A comparison with the EN DOR data [4] is hampered Figure 1: The /iSR Fourier power spectrum from a solution somewhat by the fact that those data were obtained at 4.2 K of naphthalene in acetone. Assignment of the lines to a- whereas our experiments were conducted at room temper- and ^-radicals is shown. The feature c is an artefact from ature. However, we found that the direction cosines of the the digital clock. hyperfine tensors at carbon B (radicals <*„ and a'a) aver- aged less than eight degrees different from those reported The crystal (25 mm x 30 mm long) was oriented for CH2 protons in the ENDOR work. We find with the help of X-ray diffraction photographs taken at the effects of around +20% in the reduced isotropic hyperfine Institute for Crystallography and Petrography, ETH Zurich. couplings for the a-radicals compared to the ENDOR re- With this information and knowledge of the relationship sults, which is typical for cyclohexadienyl radicals; we es- between the orientation of identical radicals at the two dif- timate that experiments at comparable temperatures would ferent molecular positions in the crystal we were then able add another 4-5% due to the usual negative temperature to identify not only the eight a-radicals, but also all the dependence of the couplings. The isotope effect for the weaker /^-radical signals. Table 1 gives the reduced hyper- anisotropies, on the other hand, is about -10%, which is in fine tensors for the ^-radicals, which should be compared line with expectations due to the lengthened C-Mu bond. to the reduced coupling /1J, of 137.14 MHz obtained in It is noticeable in Table 1 that the two /3-radical addi- solution. tion positions give rise to significantly different pairings of The hyperfine tensors show a high degree of symmetry, the hyperfine couplings. We ascribe this to the fact that with each of the tensors for both species reflecting into the the environments of the muons in the (3* and 0'd radicals Catom above below Acetone:water o A 010:1 • 0 ft a 15:1 • B Ota < 25 0 40:1 - D < E • Pure • o ac a Table 2: Absolute assignment of the addition positions and O directions of all Mu-substituted radicals at the unit cell's • D reference molecule in naphthalene. See Fig. 2 for atom plin g (h P 3 labelling, "above" and "below" the molecule refer to the O positive a direction. o S • a

K15 o X •

• Q 10 a i 200 250 300 Temperature (K) Figure 3: Temperature dependence of the muon hypcrfine coupling constant in the 2-muoxyprop-2-yl radical in solu- tions of propan-2-one (acetone) and water.

The lowering of the coupling constants with increasing water concentration is thought to be due to the greater hy- drogen bonding within the mixtures. Associated with this hydrogen bonding is a hindering of the internal rotation of the O-Mu group. Fitting the measured couplings to the- ory using a quantum mechanical averaging technique gave values of the barrier height to internal rotation for the 2- Figure 2: The crystal environment of the radicals formed by muoxyprop-2-yl radical which increase from 3828 J mol"1 addition at the E' C atom. In the ft radical, the muon has in pure propan-2-one to 4572 J mol"1 for a 100:1 (V/V) two very close neighbours (solid lines - the lightly shaded propan-2-one:water mixture and 8816 J mol"1 in a 15:1 atom is a H atom in the next unit cell); in the j3[ radical mixture. These barriers are lower than those of the corre- the neighbours are more distant sponding hydroxy radical extracted from ESR studies. This is attributed to the smaller moment of inertia of the O-Mu group relative to the O-H group, which results in a greater are quite similar, but for the j3c radical the muon has two amplitude of Iteration for the muon. closely neighbouring H 2.32 and 2.39 A distant while the proton has four neighbours all further away than 2.9 A (see Fig. 2). This would lead to a rotation of the CHMu References: group, moving the muon towards the molecular plane and [1] E. Roduner et al., Chem. Phys. 54 (1981) 261. lowering its hypcrfine coupling; similarly the 0'c radical will have an increased muon coupling [3]. [2] E. Roduner, Lecture Notes in Chemistry, Vol. 49. Springer Heidelberg (1988). Effects of hydrogen bonding on 2-muoxyprop-2-yl radical dynamics [3] I.D. Reid and E. Roduncr, submitted to Structural Chemistry. The temperature dependence of the muon hyperfine cou- pling constant was measured for the 2-muoxyprop-2-yl rad- [4] U.R. Bbhme and H.C. Wolf, Chem. Phys. Lett. 17 ical in several aqueous solutions of propan-2-one. The cou- (1972) 582. plings are small and show positive temperature coefficients. Addition of only a small amount of water into propan-2- one causes a lowering of the coupling at all temperatures but the change in the coupling from that in pure propan-2- one is not invariant with temperature, being less at lower temperatures for all the mixtures studied. MAGNETIC CORRELATIONS IN SUPERCONDUCTING YBa2Cu3Ox

RA-76-03, KONSTANZ - CONNECTICUT - BERLIN

Ch. Niedermayer, H. Glückler", A. GolnikH, G. Nowitzke', E. Recknagers, J. I. Badnick', W. Paulus«, R. SchöUhoml, A. Weidinger8s

• Universität Konstanz, Fakultät für Physik, D-7750 Konstanz t University of Connecticut, Physics Department, CT 06268 Storrs, USA Î Technische Universität Berlin, Inst. f. Anorganische und Analytische Chemie, D-1000 Berlin 12 § Hahn-Meitner-Institut Berlin, Bereich Kern- und Strahlenphysik, D-1000 Berlin 39 f University of Warsaw, Inst, of Experimental Physics, PL-00681 Warsaw

Antiferromagnetism in strongly oxygen deficient YBa3Cu3Or was discovered by Nishida et al. [1] and sub- sequently by Brewer et al. [2] in /iSR studies. studies [3] proved the existence of long range antiferromagnetic order in samples with an oxygen con- tent in the range 6 to 6.4. In the present experiment we looked for magnetic correlations in YBa2Cu3Or samples with oxygen concentrations above z=6.4, i.e. in the region where the samples are superconducting. Investigations in this direction are particularly interesting for a better un- derstanding of the relationship between antiferromagnetism and superconductivity and the suggestions that antiferro- magnetic correlations are responsible for the pairing of the superconducting charge carriers [4,5]. The oxygen-deficient samples were prepared by quenching fully oxygenated ma- terial from elevated temperatures (where the equilibrium oxygen content is reduced) to liquid nitrogen temperature 0.0 0.2 0.4 0.8 0.8 1.0 [6]. The samples were cooled down in zero magnetic field and no magnetic field was applied during the measurement. Fig. 1 shows /JSR spectra for YBa Cu O .6 at 900 mK and 2 3 6 Figure 1: /iSR spectra for YBa2Cu3O6.6 at 900mK and 10 K, respectively. The muon decay asymmetry in the 10 K 10 K. The solid lines are theoretical fit curves. spectrum with a spin depolarization rate A as O.l/is'1 is due to nuclear moments in the YBaCuO structure, whereas the fast decay in the 900 mK spectrum with A ss 3.5/JS"1 defi- (mT) nitely requires magnetic fields of electronic origin. Thus, 2 4 6 8 10 12 the fast relaxation in the 900 m K spectrum is a clear indi- cation for the existence of internal magnetic fields due to electronic moments. The internal fields disappear at around 3 K. Similar results were obtained for all samples with su- perconducting transition temperatures Tc below S0K but no internal fields were found for samples with Tc > S0K. The magnitude of the internal magnetic field {\Bß\) which is roughly given by

= 7«- i with ?„ = 851.4 MHz/T (1)

is strongly dependent on the superconducting transition 2 4 6 8 10 12 1 temperature Tc. This is shown in Figure 2 together with Depol.Rate ((is ) earlier results for the LaSrCuO-system [7]. It is interesting

to note that the distance between the two lines in Figure 2 Figure 2: The superconducting transition temperature Tc as corresponds roughly to the ratio of the highest Neel temper- a function of the muon-spin depolarization rate, which is a ature in the YBaCuO and LaSrCuO systems (TN=450K measure of the internal magnetic field (|ßp|>, as measured and TW = 315K), respectively. This is a further indication in La2_xSrrCu04 and YBa2Cu3Or. that magnetism and superconductivity are intimately related in these systems. References

[1] N. Nishida et al., Japn. J. Appl. Phys. 26 (1987) L1856. [2] J. H. Brewer et al., Phys. Rev. Lea. 60 (1988) 1073. [3] J. M. Tranquada et al., Phys. Rev. Lett 60 (1988) 1S6. [4] V. I. Emery, Phys. Rev. Lett. 58 (1987) 2794. [S] J. R. Schrieffer et al.. Phys. Rev. Lett. 60 (1988) 944. [6] H. Eickenbusch et al., Angew. Chem. Int. Ed. Engl. 26(1987)1188. [7] A. Weidinger et al., Phys. Rev. Lett 62 (1989) 102. FIELD DEPENDENT MUON KNIGHT SHIFT AND RELAXATION IN A Bi SINGLE CRYSTAL

RA-76-0S, ETHZ

B. Birrer, F.N. Gygax, B. Hitli, E. Lippelt, A. Schencks, M. Weber

Institul fur Mittclcnergiephysik der ETH Ziirich, CH-S232 Villigen PSI

The muon Knight shift, K,,, and the relaxation rate,

Figures la, b and c display the second moment M2 of the field distribution at the muon site, which for a Gaussian 2 distribution is given by A/2 = 2c . The dashed-dotted lines represent fits of the expression \U = M-, i, + A • 0 80 100 120 140 lr.0 130 PS(cose) (zero field) or M2 = M2|lso + A • P%(cosO) + B • >*nlalion Id^g :'}[cos$) + C • P$(cos9) (transverse fields). These angular dependencies of the second moment follow from symmetry considerations in zero or transverse external fields [1]. The

agreement with the data is excellent. StC. MOM. The solid and dashed lines show the calculated second M 0.013T "». moment of the dipolar field at the muon site produced by the PHI-0 Bi nuclear magnetic moments which are subject to both the Zecman and the quadrupole interaction. The rigid lattice values were assumed; the muon was located either at site 1 -e e- (solid line) or at site 2 (dashed line) cf the two possible interstitial sites [2] in the Bi lattice. Compared to the experimental results, the calculated second moments are too small by at least a factor of 2. In transverse fields the shapes of the experimental and of the calculated curves differ drastically. Obviously, ihe rigid lattice situation is not given around the muon site. The analysis points to two possible ways to better de- scribe the data: SIC. MOM. 0.07 —.—. - -. — •--.—•—-•—•—.- -.—•—•—•—*—*—*—•— O.7t7T . -• i) A lattice relaxation (in fact, a lattice contraction(l) PHI-0 0 06 around the muon has to be introduced [2]). UK O.OS

0 01 ii) An off-center position of the muon (cluster calcula- tions are indicating this [3]). 0.0)

0.0? In both cases a radial electric field gradient (EFG) has to be assumed in contrast to the axial EFG observed in the 0.01 rigid Bi lattice [4]. C 1,0 m so mo i.'o no v-o i? Despite these additional assumptions, the pronounced fln.sr.Ml ion (df?.jt •(»>-, 1 field dependence of the second moment - see Figure 2, where data in additional magnetic fields are shown - cannot be explained yet. Figures la,b,c: Angular dependence of the second moment The angular dependence of the muon Knight shift is in zero field, 0.013 T, and 0.747 T at 11 K. See text for displayed in Figure 3. In all fields measured, K^ shows a details.

8 complicated structure involving P$(cos6) and P$(cosO) terms. In view of the fact that the muon Knight shift should somehow reflect the electronic spin susceptibility [S] this is O.IS 074! PHI-W surprising, since a susceptibility depending on fourth order 1IK -780 terms in the direction cosine has never been observed.

Sit. MUM. 0.0/0

0.150.AI 0.0

0 055

0 050 0 ?[) tO 60 SO 100 1?0 HO UU 180 0 045 ORILNTATION (dofjreesl

0 0(0 Figure 3: Angular dependence of the muon Knight shift 0 035 measured at 11 K in external magnetic fields of 0.249 T (o), 0.374 (-), 0.498 T (A), and 0.747 T (D). (I 010 60 80 100 120 140 160 ORI[NTATIC1N (dogreesl

Figure 2: Angular dependence of the second moment at References 11 K in 0.249 T (o). 0.374 T (-), 0.498 T (A) and 0.747 T (a). [1] F.N. Gygax et al., Phys. Rev. Lett. 56 (1986) 2842. [2] F.N. Gygax et al., Z. Phys. B71 (1988) 473. The shape of the data remains more or less unchanged in different fields whereas the absolute height of the curves is [3] G. Solt, B. Delley, E. Lippelt, to be published. field dependent. This may be attributed to the de Haas-van AlpJien effect for which Bi is well known [6]. [4] R. Vianden et al., Hyperfine Interact. 15/16 (1983) 1081. [S] A. Schenck, Muon Spin Rotation Spectroscopy (Adam Hilger, Bristol, 1985). [6] O. Shoenberg, Proc. Roy. Soc. A170 (1939) 341. STUDY OF THE SYSTEM La2-ISrrCu04 BY STROBOSCOPIC

RA-76-05, MOSCOW - ETHZ

P. Birrer', F.N. Gygaxt, B. Hitti', E. KrasnoperoV, E. Lippell', A. Ponomarev", A. Schenck'5, M. Weber*

• Kurchatov Institute of Atomic Energy, USSR-123 182 Moscow t Instilut fiir Mittelenergiephysik der ETH Zurich, CH-5232 Villigen PSI

The superconducting properties of the high Tc mate- from one-component fits to the data taken by stroboscopic rials must be closely related to their electronic structure. /iSR. The temperature range extends from room tempera- In this respect any information on the correlation of elec- ture down to just below Tc. We do not discuss the data tronic properties and the phase diagram of the high Tc su- below Tc since the shift here is dominated by the diamag- perconductors may provide important clues about which netism of the superconducting samples. parameters are involved in the occurance of superconduc- tivity. In the present study we report on measurements of + the /i Knight shift in the system La2_iSrICu04 with i=5%, 10%, 15% and 25%, where each x implies a differ- ent hole carrier concentration. The polycrystalline sintered samples of spherical shape were prepared and character- ized at the Kurchatov Institute. Figure 1 displays the tran- sition temperatures and their width. The /i+ Knight shift A'=(B,, - Hcxl)/Hext is a measure of the local spin den- sity which is related to the Pauli spin susceptibility and - via exchange effects - also to local moments, perhaps at the Cu-sites. The amount of the shift depends in addi- tion on the overall charge distribution and in particular on the distribution and density of mobile charge carriers This concerns both the Pauli related part of the Knight shift as well as exchange contributions (i.e. RKKK mediated or superexchange). Thus monitoring the /i+ Knight shift as a function of temperature and carrier (hole) concentration one may perhaps be able to follow corresponding changes in certain aspects of the electronic structure. Such stud- ies will be complementary to related NMR-measurements. The results presented below are not yet in a state where far reaching conclusions can be drawn, but the data cer- tainly show that the /i+ Knight shift is indeed sensitive to temperature and hole doping.

Temperature (K) Figure 2: Temperature dependence of Knight shift and sig- nal amplitude (asymmetry) in the samples with x=0.05 and i=0.10.

The asymmetries for the 10% and 15% samples show no temperature dependence which implies that a one-com- ponent description of the data is well justified. The Knight shift of the 10% sample shows also no temperature depen- dence. The average value of about -20 ppm could indicate 0.000 0.100 0.200 0.300 0.400 that only a chemical shift is measured, which for protons Si concentration in metals as well as for hydrogen atoms is of the order of -20 ppm. The 15% sample shows a slight temperature Figure 1: Superconducting transition temperatures and dependence. On the whole the shift is somewhat more pos- width of transitions (indicated by the bars) of the inves- itive. The Knight shift K of the 5% sample (not supercon- tigated samples. ducting) decreases markedly from room temperature down to 200 K where the trend is reversed. Also at 200 K the Figure 2 and Figure 3 display results for the /*+ Knight asymmetry of the signal starts to drop. This is an indication shift and the asymmetry of the /JSR signal as obtained that the signal consists in fact of two components. Below

10 200 K one component seems to become invisible to the fit, probably because of a drastically increased line width and shift in position. At lower temperatures only the narrow component remains. Its Knight shift then is comparable to the one of the 10% sample. The drastic decrease of K be- low 60 K is quite interesting. It probably is related to the onset of magnetic order which in this sample should occur at around 20 K. The appearance of a second component with a large temperature dependent line width and pronounced shift at higher temperatures is less expected since it implies the presence of some sort of magnetic order already far above ~20K. Even more surprising in this respect are the results from the superconducting 25% sample, which also shows a drop in asymmetry below 160 K, although in this case no magnetic ordering phenomena are known to exist Here the Knight shift has a relatively large negative value at room temperature which drops to 25 ppm below ~100K. In summary the n+ Knight shift and its variation with temperature show a dependence on hole concentration, par- ticularly pointed out by the component which is lost in the one-component fits at lower temperatures. The meaning of these results will be investigated in future studies. 100 200 300 Temperature (K)

Figure 3: Temperature dependence of Knight shift and asymmetry in the samples with x=0.15 and z-0.25.

11 LOW-TEMPERATURE /i+SR EXPERIMENTS ON a-IRON SINGLE CRYSTALS

RA-78-02, RA-85-06, STUTTGART - PSI

C. Baines', A. Fritzschet, M. Hampele", R. Henes', D. Herlach*, M. Krenke", K. Maier', J. Major's L Schimmele' A. Seeger* *s, W. Staiger', W. Tempi'

• Universiiat StuUgan, Instiiul fiir Theoretische und Angewandle Physik, Pfaffenwaldring 57 D-7000 Stullgart 80 t Max-Planck-Institut fur Metallforschung, Institut TUr Physik, Postfach 800665, D-7000 Stuttgart 80 t Paul-Schcrrer-Institul, CH-5232 Villigen PSI

The spin precession frequencies u^ = 7^ B^ (7^ = 8 l IO'I— 8.516-10 T"'s" \Bli= magnetic fields at the //+ sites) as well as longitudinal (A) and transverse (fa) spin relaxation rales of positive muons (/i+) in a-iron single crystals have been measured at PSI on four different samples down to 20 mK in applied magnetic fields Bappi up to 3 T. We recall that in ferromagnets we may write

J3/J = -Bappl + Bdemag + fiLorenlz + Bdip + Bpermj.

Bdemag denotes the demagnetization field, BLmatI the Lorentz field, Bdip the dipolar field, and BFermi the /*+- electron contact field. A spherical crystal (diameter 9mm) was investigated in the PSI low-temperature facility between 20 mK and 2K and in a helium evaporation cryostat at T > 2.7 K. The dependence of the spin precession frequencies on transverse magnetic fields is shown in Fig. 1. At elevated temperatures the Bdip contributions to ui^ are averaged out due to the + rapid diffusion of the /x . Since for spheres Bdemag + BLorenu = 0, we have W(i = 7(1. |Bappi + BFermil- From the zero of the frequency (Fig. 1) we deduce (at 2.7 K and at 5.0K)BFermi = -(1.06 ± 0.01) T in agreement with earlier results [1]. Within experimental error B^rmi was independent of the crystallographic direction of Bappl. Fig. 2 shows the longitudinal relaxation rates for r[K] Bappi||(lll) that were obtained by fitting the raw data by either one (Fig. 2a) or two (Fig. 2b) exponentials. From Figure 2: Longitudinal ^+ spin relaxation rates versus Fig. 2a we see that the results are in agreement with those temperature. Sample: spherical single crystal, orientation: (lll)||Bappl. Applied magnetic fields: Bappi =2.0T(O), 2.5T (o), 3.0T (A), a) Results from a one component fit. Earlier results [2] measured on a different spherical a-iron single crystal are shown as well: Bappi = 2.0 T (x), Bappi = 4.5 T (+). b) Results of a two component fit.

on a less pure sample investigated in a different spectrom- eter [2]. Below 1K the two-component fit is clearly su- perior. Whereas the asymmetry a of the slow compo- nent (a » 0.03 - 0.05) is nearly T-independent, that of the fast component decreases with decreasing temperature [a(lK) ss 0.16, a(20mK) « 0.05]. In agreement with our earlier suggestion [2] we believe that the fast relaxation rate is associated with the occupation of metastablc sites by the + Figure 1: Transverse /i spin precession frequencies versus muons. applied magnetic field. Sample: spherical a-iron single In a bec crystal magnetically saturated in (111) the dipo- crystal; orientations: (100)||B,ppi, [2.7 K (D), 5.0 K (o)j, lar fields at interstitial sites of tetragonal point symmetry (Hl)l|Bappl[2.7K(A),5.0K(O)]. arc parallel to the (211) directions perpendicular to (HI).

12 80 o O 60 o 40 o 20 A A 1= a D > O A 0 a A A -20 a -40 -60 D a a D

T[K]

Figure 3: Transverse muon spin precession frequencies ver- Figure S: Transverse muon spin precession frequencies ver- sus temperature at zero applied magnetic field. Samples: sus temperature at applied magnetic field Bappi = 2.2 T. Fe-W-Fe (o), Fe-Al-Fe(D), Fe unstrained (A). Samples: Fe-W-Fe (o), Fe-Al-Fe (D), Fe unstrained (A).

Hence, the local fields B,, at the various sites are inclined Figs. 3 and 4 give w,, and Ta for Bapp, = 0. The with respect to (111). For small /i+ jump rates and not too strained samples show a minimum of w,, at T ss 30 K. large |Bappi + BFermi\ "wiggles" superimposed on the lon- (Fig. 3). Particularly interesting features are that in spite of gitudinal relaxation discussed above should appear. Such rather pronounced differences near the u,, minimum, below "wiggles" have indeed been observed between 50mK and 5 K the two strained samples give the same w,, but differ 300 mK up to flappi = 2T. radically from the unstrained sample both in uJT) and In the usual interpretation of /J+SR in a-Fe [15] the ^+ r,(T). energies are assumed to be unaffected by variations in the Examples of w,,{T) and A(T) in finite Bappi(< 3T) magnetic fields. At very low temperatures this assumption are shown in Figs. 5 and 6 for flappl = 2.2 T. From Fig. 6 is certainly inadmissible since the spontaneous magnetiza- we see that in the strained samples A(X) passes through a tion of a-iron is accompanied by magnetostrictive strains maximum at about 40 K. of the order of magnitude 10"5, which interact with the As expected the results show a definitive dependence tetragonal elastic distorsions surrounding the /<+. In or- on strain. A surprising feature is that the effects make der to investigate the effects of elastic strains and of the themselves felt already at rather high temperatures. destruction of cubic symmetries associated with them inde- This work was funded by the Bundesministerium fur pendently of changes in the magnetization we prepared at Forschung und Technologic, Bonn, Federal Republic of room temperature sandwich samples in which the difference Germany, under contract no. 03-SE2STU-0. in the thermal expansion of a-Fe and Al (W) was used to subject monocrystalline Fe platelets to compressional (ten- sile) planar stresses at low temperatures. An Al (W) plaie 10' was covered on both sides with thin monocrystalline a-Fe n plates fixed by a two-component epoxy adhesive. In these samples as well as in an unstrained a-Fe reference crys- $ DO tal (100) planes were parallel to the plates. The magnetic to7 8 8 o field (0T< Bapp, < 3T) and the direction of the transverse polarized muon beam were perpendicular to the plates.

10' T[K] nt" Figure 6: Transverse muon spin relaxation rates versus tem- perature at applied magnetic field flappi = 2.2 T. Samples: Fe-W-Fe (o), Fe-Al-Fe (•), Fe unstrained (A).

Id" References

[1] A.B.Denison, H.Graf, W.Kundig, and P.F.Meier, inuo inn T\K\ Helvetica Physica Acta 52 (1979) 460 [2] E. Yagi, G. Flik, K. Fttrderer, N. Haas, D. Hcrlach, Figure 4: Transverse muon spin relaxation rates versus tem- J. Major, A. Seeger, W. Jacobs, M. Krause, M. Krauth, perature at zero applied magnetic field. Samples: Fe-W-Fe H.-J. Mundinger, and H. Orth, Phys. Rev. B30 (1984) (o), Fe-Al-Fe(D), Fe unstrained (A). 44

13 ir+ / n+ CHANNELLING STUDIES ON GOLD

RA-79-02, STUTTGART

S. Connell", G. Fabritius', M. Krenke', K. Maier*s, A. Seeger**, W. Staiger*. E. Widmann'

* Max-Planck-Insdtui fflr Metallforschung, InsUtut fUr Physik, Postfach 800665, D-7000 Stuttgart 80 t Institut fiir Theoretische und Angewandte Physik, University Stuttgart, D-7000 Stuttgart 80

In earlier ir+/n+ channelling experiments on copper [crystallizing in the face-centred cubic (fee) structure] we found that the implanted do not exclusively oc- cupy octahedral interstitial sites [1,2,3], as is indicated by changes in the muon flux pattern in the (100) direction at elevated temperatures. At temperatures above 300 K the 7T+ may also occupy metastable letrahcdral interstices [3]. As has been shown elsewhere r4], the conclusions drawn from the T+/V+ channelling .xperiments are compatible with the /i+SR data on copper [5], Because of the very I o small hydrogen solubility in Au, Ag and Cu, very little is known about the sites of hydrogen or its from stan- dard methods. The interesting behaviour of ir+ and possi- bly of p+ in Cu was the motivation for performing further ir+//i+ channelling experiments on Au, which possesses an fee structure, too.

O-site T-site

-15 -10 -5

Figure 1: Projection of T-sites and O-sites in the fee struc- 15 ture along (100) and (110) directions.

10 A look at the projections of tetrahedral and octahedral sites in the (100) direction (Fig. 1) shows that a distinction XKNKK

between these two types of sites is possible by means of 5 a ir+/fi+ channelling experiment: The O-sites are blocked •a A U • by the atom rows whereas the T-sites are situated in the ::..::x '^kjj^H centre of the (100) channels and should give rise to muon I o _ flux enhancement. M t + + Therefore we performed JT //I measurements in the 8 •••••••••:•:•:•:• temperature range 10 K < T < 300 K on high-purity -3 *!' (6N) Au single crystals of sufficiently low mosaic spread 1s: (< 0.1°) orientated in a (100) or in a (110) direction. The It results indicate that in the low-temperature region around -10 HKSHBS 15 K only O-sites were occupied because we observed a blocking dip in the (100) direction (Fig. 2) and a rather strong muon flux enhancement along the (110) channel, -13 accompanied by planar channelling along the {111} planes - 15 - in 3 0 3 10 IS (Fig. 3). if [mnd) In contrast to our Cu measurements a transition from blocking to channelling could not be detected. Figure 3: Muon flux density measured at 10 K on Au ori- When we went to higher temperatures, the blocking ef- entated along (110).

14 (2) Owing to the interaction with the thermal vibrations of the lattice atoms, at elevated temperatures the 7 channelled muons are scattered out of the channel. This effect, which is known as "thermal dechan- a nelling", occurs mainly for muons with large trans- verse energies since their trajectories run close to the 4 atom rows. \ Thermal dechannelling leads to a reduction and a narrowing S of the channelling profiles which are in agreement with our —' 3 observations. A quantitative study on the temperature de- pendence of dechannelling yields the following expression *" a a) for the increase of transverse energy £j.[6,7]:

1 dEx{T) 4ir 0 dz m \ 9aTF •)"

1 + 9CXP ( P ) ' \l - 9CXP I ~T J 0) ca L * VfiXmax/J L 2 V £u.rmM/J The thermal displacement p,h is given by ^^ I 1/2 1 2 9 \ Ah = 12.1 A • K ' f (^ + \) I (M • 0o) (2)

&5 e where {x) denotes the Debye function, and x = &o/T the b) ratio of the Debye temperature @o to the absolute temper- ^ 7 ature T. Zi,m,v denote the nuclear charge, the mass, and the velocity of the channelled particle, Zi% M, N the nu- clear charge, the mass, and the number density of the crystal

atoms, and

5 TEMPERATURE-DEPENDENCE OF POSITIVE MUON-DECAY CHANNELLING IN SEMICONDUCTORS

RA-79-10, ZURICH - PSI

P. Eschle*. H. Keller*, W. Kttndig', B. Patterson*, B. PUmpin*, J. Schneider', I. Savie*. H. Simmler*5, U. Straumann' P. Truer

* Physikinstitut der Universitft Zurich, CH-8001 Zurich t PSI c/o Laboratories RCA Ltd., CH-8048 Zurich

A number of channelling experiments have been per- Fig. 2). On the other hand, no muonium states could be formed in order to determine the position of hydrogen-like observed by /iSR. impurities in semiconductors and metals. In intrinsic ma- terials, several parameters turned out to affect the impurity site(s): In Czochralski grown silicon, muons are trapped at the T-site by oxygen impurities [1]. The jr-site in ger- manium is influenced by the free carrier density [2]. Tem- perature dependent channelling patterns were observed in FZ-SUicon < 110>, T = 300 K 7r//j-channelling experiments on Ge as well as in He beam- experiments on D-irradiated silicon [2,3]. :Afn¥V. uwVt^ In order to investigate such temperature effects, we have performed /i/e-channelling experiments using new equip- ment at temperatures ranging from 95 K to 400 K. Although the critical angle for the 37MeV positrons is very small, the advantage of the /j/e-decay technique compared to other lattice steering techniques is that detailed spectroscopic data FZ-Slllcon < 110>. T = 250 K on different p-states are available from /JSR measurements. First results were reported in 1988 [4]. A temperature de- pendent /i-site in float-zone silicon was observed. The two beam periods in 1989 were used to complete the silicon data and to extend the measurements on other semiconductors such as gallium arsenide and indium phos- phide. Results for float-zone silicon are shown in Fig. 1. It is clearly seen that a muon site transition takes place be- tween 200 K and room temperature. As identified by means of planar simulations, the site is T(tetrahedral)-like at low temperature and BC(bond-center)-like at high temperature. Below 200 K, no changes in the pattern were observed. In comparison to /JSR data, the coincidence with the disap- pearance of the isotropic muonium (Mu) is striking [5]. The low temperature anisotropic muonium (Mu*) does not exhibit a site transition, slough the transverse /iSR sig- nal is lost already around 120 K, probably due to spin-spin interaction of the bound electron and free carriers [6]. In conclusion, we relate the observed site change to the Mu slate which is therefore metastable. The anisotropic BC- like site (where at low temperatures Mu* is observed by //SR), is more stable and acts as a trapping center for Mu. DISTANCE |mm] The results for gallium arsenide are quite analogous. Again we observe a site transition from a T- to a BC-like site, with a transition temperature range shifted to 300 to Figure 1: channelling patterns of ji-decay positrons in 37S K. The population of the different states investigated float-zone silicon at various temperatures, recorded with by /iSR is similar to silicon, that is, the transition is again an x-y multiwire proportional chamber (dark and light fea- related to the Mu state. The temperature "delay" in the tures correspond, respectively, to enhanced and diminished site change is explained by impurity trapping at the T-site positron detection probability). On the right hand side, pro- as observed in Czochralski silicon. The indium phosphide jections of the histograms along a (11 l)-plane are shown. A pattern is not changed by varying the sample temperature. site transition of the decaying muons occurs between 200 K It corresponds to the BC-like /*-site at all temperatures (see and room temperature.

16 In summary, the measurements strongly indicate a meia- stable Mu state at a T-like site and a Mu — Mu' transition InP<110>, T= 100 K in float-zone silicon. A similar transition is observed in gallium arsenide. In all measurements the BC-like site was found to be the most stable ji-site. Recalling Hie observation of the analogous transition in diamond [7], we suggest that the metastability of Mu and the transition to a more stable BC-like anisotropic site is universal for a wide class of zincblende structure materials.

References

[1] B. Patterson et al., Phys. Rev. Lett 52 (1984) 938. [2] G. Flik et al., Phys. Rev. Leu. 57 (1986) 563. [3] B. Bech Nielsen., in Oxygen. Carbon, Hydrogen and Nitrogen in Crystalline Silicon, MSR Proceedings, Vol. 59, 1986 p. 487. [4] P. Eschle et al., PSI Progress Report 1988, Departc- ment F3, p. 14. [5] B. Patterson, Rev. Mod. Phys. 60 (1988) 127. GaAs < 110>, T = 300 K [6] E. Albert el al., Hyperfine Interact 17-19 (1984) 759. [7] W. Odermatl et al., Hyperfine Interact. 32 (1986) 583.

Figure 2: (lll)-blocking in indium phosphide at low tem- perature (top) and (lll)-channelling in gallium arsenide at room temperature (bottom).

17 A /xSR STUDY OF THE IK PHASE TRANSITION IN THE HEAVY ELECTRON COMPOUND UCu5

RA-8S-12, ETHZ

P. Birrer', F.N. Gygax", B. Hiui", E. Lippelf, H.R. Ott»s, A. Schenck'5, M. Weber'

* Insiitut fur Mittelenergiephysik der ETH Zurich, CH-S232 Villigen PSI t Laboraiorium fur Festkorperphysik der ETH Zurich, CH-8093 Zurich

Low temperature specific heat measurements character- ize the intermeiallic compound UCu5 as a heavy electron system whose Fermi liquid state, curiously, develops at tem- peratures well below the onset of antiferromagnetic order which is observed at TN=l5 K [1]. Specific heat measure- ments have further shown that a second phase transition occurs at ~1 K displaying hysteretic behavior but no la- tent heat [1]. The nature of this phase transition has not been determined yet. Neutron diffraction results seem to suggest that this phase transition is not associated with a change in magnetic order [2]. Similar features in the spe- cific heat data as those mentioned are observed in transitions between commensurate and incommensurate charge density wave states [3].

0.4 0.6 0A 1J0 \2 ^A Tenperahre (K)

Figure 2: Temperature dependence of the muon spin re- laxation rates a in UCu5: a) the component v\, (similar 0.4 0.6 0.8 1.0 1.2 1.4 1.6 behaviour for the i/2-component); b) the additional compo- nent, related to v\\ c) the non-oscillating component (i/4=0). Temperature (K)

Figure 1: Temperature dependence of the muon spin pre- component occured with a certain amplitude which also cession frequencies i/t and i/2 in UCu5. turned out to be temperature independent. In the new sample both similarities and interesting dif- We have performed zero field /iSR measurements on a ferences are observed. We see again the 13.65 MHz-, the new polycrystalline UCu5 sample which was shown before 19.75 MHz- and the nonoscillating component. The tem- to undergo the transition at ~1 K. A previously investigated perature dependence of vx and i/2 is displayed in Fig. 1. sample did not show the transition probably due to the pres- No suspicious features show up around 1 K, i.e. the av- + ence of impurities. In these previous measurements [4] in erage field at the /J sites is not affected by the phase zero field for T < 15 K, two spontaneous p+ precession fre- transition. However, if we look at the relaxation rates, quencies were observed with values of i/!=19.75 MHz and new features show up as can be seen in Figs. 2a,c. Below i/2=13.65 MHz for T —»0 K and a very smooth behavior ~1.2 K the relaxation rates of the oscillating and the non around 1 K. Both components and a third non-oscillating oscillating components rise dramatically as the temperature one (i/=0) displayed an essentially temperature independent is further lowered, i.e. the width of the field distribution at + relaxation rate of ~0.4 /M"1 from 30 mK up to 10 K. Each the fj sites starts to rise at the phase transition. To render

18 things even more complicated there is a third oscillating Our tentative explanation for what we observe is that component (1/3) close in frequency to the fl=19.75 MHz the U-sublattice and its magnetic ordering are not involved component but with a very different relaxation behavior, in the phase transition, but that the Cu-sublattice suffers shown in Fig. 2b. This component is in fact related to the some change. This change must lead to a distribution of + 19.75 MHz component. While below 1.2 K the amplitudes /i sites centered at the original rigid lattice position in the of both components are equal and temperature independent, undisturbed case. Concurrent with the emerging fuzziness above 1.2 K the amplitude of the 19.75 MHz component of the ji+ site is an increased width in field distribution + starts to rise by the same proportion as the amplitude of the experienced by the /i . The change of the Cu-sublatlicc other component decreases. The sum remains temperature could be related to a charge density wave phenomenon as independent This is shown in Fig. 3. already mentioned above. The implication of some kind of disorder below —1.2 K may flr.o be consistent with the observation of an increased uectrical resistivity below that temperature [1]. a-— References 5 Ai = A3"llx. t [1] H.R. Ott et al., Phys. Rev. Lett. 55 (1985) 1595.

A4 = (i». \ +%+ * • [2] P. BOni et al., this volume. - 000 ooooooooam< ^°~- _. A3 IOCOO Q - A A2° fix. [3] W.L. McMillan, Phys. Rev. B14 (1976) 1496. [4] S. Barth et al., i. Magn. Magn. Mai. 76+77 (1988) O.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 455. Temperature (K)

Figure 3: Temperature dependence of asymmetries. The

asymmetries A\+A3, A2, A4 corresponding to the compo-

nents v\, 1/3,i/2,1/4 are basically temperature independent. The values shown are average values which were fixed in a final round of fitting the other parameters. MAGNETIC ORDERING INDUCED BY HYDROGEN DOPING OF YBa2Cu307

RA-85-17, KONSTANZ-CONNECTICUT-BERLIN

H. Glückler, Ch. Ntedemnayer\ G. Nowitzke", R. Simon', E. Recknagel'5, J. I. Budnick', A. Golnik» W Paulus5 R. SchollhomS, A. Weidinger's

* Universität Konstanz, Fakultät für Physik, D-7750 Konstanz t University of Connecticut, Physics Department, CT 06268 Storrs, USA t University of Warsaw, Inst, of Exp. Physics, PL-00681 Warsaw § Technische Universität Berlin, Inst. f. Anorganische und Analytische Chemie, D-1000 Berlin 12 H Hahn-Meitner-Institut Berlin, Bereich Kern- und Strahlenphysik, D-1000 Berlin 39

The physical properties of YBaXuaO,, change from pies with x < 1.17 remain orthorhombic with almost no metallic and superconducting for y = 7.0 to semiconduct- change in the lattice parameters within experimental errors. ing and antiferromagnetic for y = 6.0, the transition be- Fig. 1 shows the /JSR spectra and their Fourier trans-

tween the two regimes occuring around y = 6.4 [1,2]. In forms of uncharged and hydrogen charged YBa2Cu307 a /iSR-experiment we found that a similar change can be samples. The main feature of the hydrogen charged sample achieved by adding hydrogen to the system but leaving the is an oscillation of approximately 2 MHz superimposed on oxygen stoichiometry unchanged. Our data suggest that hy- an exponentially decaying asymmetry. In addition, a weak drogen acts as an electron donor filling the hole slates in but clearly visible oscillation of approximately 4 MHz is YBa3Cu3O7. present. In the uncharged sample, the oscillations are ab- The sample preparation started from well characterized sent and the asymmetry is essentially constant in the time

YHanCu3O7 materials with superconducting transition tem- range shown; the slight decay of the asymmetry is due to

peratures Tc above 90 K. The hydrogen intercalation was nuclear moments. done from the gase phase at hydrogen pressures of several bars and at a temperature of 168°C. The hydrogen uptake took several hours to days depending on the desired hydro- gen concentration in the sample. As expected the uptake was faster in the powders than in the pellets but choosing the appropriate charging time the same charging state and also the same /iSR results were obtained for both types of material. The hydrogen concentration in the sample was calculated from the pressure difference in the charging cell before and after hydrogen uptake. X-ray powder diffrac- tion measurements have shown that YB32CU3O7H,; sam-

50 100 150 200 250 300 350 400 Temperature (K)

Figure 2: Temperature dependence of the //SR frequencies

in a hydrogen charged YBa2Cu3O7 sample. The solid line represents a fit to the data with the prediction of the S = 1/2 molecular field model. The Neel temperature of the sample is approximately 320 K.

The temperature dependence of the two frequencies is shown in Fig. 2. The data follow a Brillouin function with a 0.5 1.0 1.5 5 10 15 Ncel temperature of approximately 320 K. Very similar data Time (/is) Frequency (MHz) were obtained for all samples with H-concentrations above x = 0.5. For lower hydrogen concentrations no oscillations Figure 1: /iSR spectra and their Fourier transforms of an were found in the /JSR spectra. The fraction of muons ex-

uncharged and a hydrogen charged YBa2Cu3O7 sample in periencing either one of the two frequencies is plotted in zero external field. The oscillation in the lower spectrum Fig. 3. A continuous increase of this fraction with increas- is a clear indication of magnetic ordering in the sample. ing H-concentration and a possible saturation is visible. In the uncharged sample (upper spectrum) the oscillation is absent Summarizing the experimental data we come to the fol- lowing conclusion: Hydrogen doping of YBasCu3O7 cre- ates a well defined magnetic state which is characterized in the /JSR experiment by a strong 2 MHz and a weaker 4 MHz signal. The values of the observed frequencies indicate that the magnetic structure in YBa2Cu3O7Hr is the same as in YBa2Cu3O6, i.e., that the Cu moments order antiferromag- netically in the Cu-O planes. A check of this assignment by neutron diffraction would be desirable. The formation of the magnetic state starts at a hydrogen concentration of x = 0.S and reaches a saturation at around x « 1.2 (see Fig. 3). Adding the fraction in the exponentially decaying part, the data indicate that the sample is fully magnetic if the hydrogen concentration exceeds approximately i = 1.2. The present data are in qualitative agreement with the assumption that each hydrogen atom donates one electron into the conduction band, thereby compensating 1/2 Oxy- gen atom. In this simple model the doping of YBa2Cu3O7 with x = 1.2 hydrogen is equivalent to the removal of 0.6 oxygens. Therefore, YBa2Cu3O7Hi 2 and YBa2Cu3064 0.5 1.0 1.5 2.0 2.5 should be equivalent. The magnetic structures of these two Hydrogen concentration systems are indeed very similar.

Figure 3: Fraction of muons which contribute to the 2 MHz and 4 MHz signal as a function of the hydrogen concentra- References tion in YBa Cu O H . The fraction of the exponentially 2 3 7 r U] J.H. Brewer et al., Phys. Rev. Lett 60 (1988) 1073 decaying signal, which is less well determined, is not in- cluded here. For x > 1.2 the total fraction (2 MHz, 4 MHz [2] J.M. Tranquada el al., Phys. Rev. Lett. 60 (1988) 1S6 and exponentially decaying part) is approximately 1.

21 INVESTIGATION OF LOCALIZED AND ITINERANT MAGNETS

RA-85-18(A), MUNICH - PSI - ZURICH - BEER-SHEVA - GRENOBLE

G.M. Kalvius's, FJ. Linersf, L. AscM, A. Kratzer', K.H. Munch", K. Aggarwal", M. Weber", A. Schenckl, B. Hitti1, F.N. Gygaxi, K. MattenbergerS, O. Vogt*, J. Gal', S. Fredo", R. Ballou", R. Lemaire-,

* Physik Department, Technische Universität München, D-8046 Garching. t Sektion Physik, Universität München, D-8000 München. j Paul Scherrer Institut, CH-5232 Villigen-PSI. § Labor für Festkörperphysik, ETH Zürich, CH-8093 Zürich. Ü Department of Nucl. Engineering, Ben-Gurion University, IL-84190 Beer-Sheva. a Laboratoire Louis Néel, CNRS, F-38042 Grenoble.

We report some selected (and in part still preliminary) (the spin fluctuation rate is 1/r = 0.17 MHz), meaning that results on the static and dynamic magnetic properties of spin excitations are absent. The spectral shape remains the the compounds UAs, USb, NpAl2, and YMn2 [1,2]. UAs same over the whole range of the type I, Ik structure. The and USb have the NaCI structure. They are fairly localized absence of spin excitations is true throughout the ordered and strongly anisoiropic magnets, but some delocalization regime and in particular holds right below 7V It can be can occur on account of hybridization with the ligands. In taken as evidence for some degree of delocalization of the UAs the magnetic transitions are first order and coupled Sf electrons. to lattice distortions and volume changes. NpAl2 belongs to the cubic Laves phases (CIS-structure). In the actinides this series shows various degrees of 5f-5f overlap. The itinerant 3d transition metal compound YMn3 exhibits an extreme volume change at its Néel temperature TN which leads, among other, to a strong thermal hysteresis. The origin is magnetic frustration due to the typical triangular arrangement of magnetic ions in the CIS structure. UAs and USb UAs undergoes simple collinear (type I, Ik) anliferro- magnen'c order at Tjv = 123 K. At 62 K a transition into a more complex non-collinear (type IA, 2k) occurs. USb has only one magnetic transition (at TN = 214 K) into a non-collinear antiferromagnetic structure (Type I, 3k) [3]. It is of second order.

1.0 1.5 20 2.5 3.0 35 Time [ßs]

Figure 2: Zero and longitudinal field spectra of USb slightly below the Néel temperature and at 4 K. The fit procedure was the same as for Fig. 1. 0.0 0.5 1.0 l.S 2.0 2.5 3.0 3.5 Time [fis] The situation is in part different in USb (see Fig. 2). Figure 1 : Zero and longitudinal field spectra of UAs slightly Common with UAs is the absence of spontaneous spin ro- below the Néel temperature. The spectra were globally fit- tation and the Lorentzian field distribution. Its width, how- ted to a dynamic Lorentzian Kubo-Toyabe function with the ever, is about four times wider. Most significant is the fields restrained to the set values and using the same nor- change in dynamics between the spectrum just below TN malization factor, initial asymmetry, and field distribution (1/r sa 1 MHz in zero field) and the one at low temperatures width. (1/r sa 0.5 MHz in zero field). Weak spin excitations are present which freeze out for T — 0. Also, a small decrease Fig. 1 presents zero and longitudinal field spectra of of width is found between 200 K and 4 K. A broadening of UAs slightly below Tu- They show firstly that all field field coupled to a speed up of fluctuations is in contrast to contributions (dipolar as well as contact) from neighboring common expectation. The fit to the 4 K spectrum shown U atoms cancel. Secondly, the spectra arc essentially static in Fig. 2 assumes a field independent width. This is clearly not correct. In fact, the width decreases by about 15% be- tween zero and 10 mT longitudinal field. In addition, the relaxation rate is slightly field dependent: the spectrum be- comes more static with higher fields. All these effects are still under investigation. More details on UAs can be found in [1].

Figure 3: Zero field spectrum of ferromagnetic NpAl2. 50 100 ISO 200 Temperature [K] NpAl, NpAlo is a ferromagnet with T as 56 K. MOssbauer high c Figure 4: Top: Relative intensity of the paramagnetic /JSR pressure spectroscopy [4] has proven that NpAl2 is not a fully localized magnet A zero field /iSR spectrum is shown signal (see text) in YMn2. T$ and TJy are the Neel tem- in Fig. 3. One notices the presence of a spin rotation pattern peratures on warming and cooling, respectively. Bottom: (containing more than one frequency) riding on a strongly Transverse field relaxation rate of the paramagnetic /iSR damped smooth signal. The rotating pattern appears only signal. The regime between TjSJ' and T£ is only accessible on cooling. below Tc and the frequencies roughly follow sample mag- netization. Hence it is clearly connected to magnetic order in NpAlj. It is too early to say whether the rotating signal fraction" in Fig. 4 (top) for both, warming and cooling se- arises from all or only a part of the muons stopped in the quences. The plot reproduces well the thermal hysteresis NpAl sample. The spin rotation frequency corresponds to 2 seen earlier in dilatometric measurements [5] which, inci- a field at the muon site on the order of only 10 mT. This is dentally also shows an irregularity near 140 K. The strongly difficult to understand for the bulk of a ferromagnet. Most damped signal is tentatively assigned to a phase with ex- important at this stage is. that it has been proven that /iSR treme short range order. spectroscopy can be performed on Np compounds, despite Even well above 7\ the damping of the paramagnetic the fact that only small samples are available and that heavy signal is not affected by longitudinal fields (measured up encapsulation is required because of the radioactivity of the to 0.1 T), meaning that depolarization must arise from the sample. This will make possible comparisons with (he large fluctuating atomic moments on manganese. Fig. 4 (bottom) amount of hypcrfine data available from 237Np MOssbauer shows the temperature dependence of the damping rate over spectroscopy [4]. the whole temperature range where a paramagnetic signal is YMn, present. A weak maximum is seen at T\ which thus looks Measurements were performed on a sample containing like a phase transition. Most significant is the strong rise 10% Tb which was added because it changes the spin struc- in A on approaching Tfi. It suggests that YMn2 wishes to ture from the helical modulation in pure YMn2 to simple undergo a second order phase transition. This is, however, aniiferromagnetic order. It was hoped that this would en- hindered (by frustration) and the system makes the large able us to observe spontaneous spin rotation in the ordered volume change and hence a first order transition. state. The data proved otherwise. Zero field spectra of anti- ferromagnetic YMn, (i.e. for T < T^ in the warming and T < T£ in the cooling sequence) consisted only of a weak References signal with a high damping rate (A > 5/is~'). Obviously the majority of muons siand under the influence of broadly [1] L. Asch et al., Europhys. Lett. 10 (1989) 673. distributed fields and depolarize too rapidly to contribute to [2] L. Asch, Physica B161 (1989) 299 a /iSR spectrum. Above Tff or T£, respectively, an addi- 1 tional new signal with a low damping rate (~ 0.2/JS' ) ap- [3] J. Rossat-Mignod et al., in Hdbk. Phys. Chem. Ac- pears. The strongly damped pattern remains unchanged, its tinides, (A.J. Freeman, G. Lander, eds.) Vol.1, p.4I5 intensity relative to the weakly damped signal being ~40%. Rising the temperature further this subspectrum decreases [4] B.D. Dunlap and G.M. Kalvius, ibid., Vol.2, p.329 in intensity and vanishes around Tt = 150 K altogether. The remaining (weakly damped) spectrum is the signal of para- [5] H. Wada el al., J. Magn. Magn. Mat. 70(1987) 134 magnetic YMn2. Its intensity (normalized lo T=225K) as a function of temperature is plotted as "paramagnetic STUDIES OF RARE EARTH MAGNETS

RA-85-18(B), UPPSALA - MUNICH - GRENOBLE - PSI

O. Hartmann*. E. Karlsson*. R. Wappling', L. Asch", K. Aggarwal*. A. Kratzer', G.M. Kalvius*5. FJ. Litterst'. A. Yaouanc8, P. Dalmas de Reotier8, B. Barbara1, F.N. Gygax", B. Hitti", E. Lippelt0, A. Schenck"

* Institute of Physics, University of Uppsala, S-7S121 Uppsala t Sektion Physik, Universitiit MUnchen, D-8000 MUnchen t Physik Department, Technische Universitfll MUnchen, D-8046 Garching § DRF/SPh, CENG, F-38041 Grenoble-Cedex 1 Lab. Louis Neel, F-38041 Grenoble-Cedex a Paul Schemer Institut, CH-5232 Villigen PSI

We report here on some of our recent results on two rate A remains almost constant. From the magnitude of A rare earth (RE) magnetic materials: (a) the cubic Laves one concludes that the contribution of fluctuating Ce spins phase CcAl2, (b) hexagonal Gd metal. Both samples were to the muon spin depolarization (seen as damping of the available as single crystal spheres. The measurements were /iSR signal) is small and that the dominant effect arises carried out for different crystalline directions between 300 K from the quasistatic nuclear dipole fields of the Al atoms. and 2 K with ss 90 MeV/c muons at the /iE4 . The decrease in A above 80 K could then be attributed to an onset of slow diffusive motion of the muon. In Gael, CeAI2 there is an indication of a second step in X(T) near 120 K. Thus far it has not been possible to observe sponta- A possible explanation is that the muon diffuses freely only neous rotation of the muon spin in the magnetically ordered above 120 K, while its motion in the range from 120 K - regime of the REA12 intermetallic compounds. Hence, the 200 K is hindered by some trapping mechanism. interpretation of /iSR data on these materials [1] obtained in the paramagnetic region had to be carried out without a defi- nite knowledge of the interstitial site occupied by the muon. Similarly, there where uncertainties concerning muon mo- bility and its possible influence on the data [2]. CeAl2 is particularly well suited for a study of the paramagnetic .20 T= 69 K • . regime since a transition into an antiferromagnetically or- . • * . •• * •_ . 15 dered state occurs only at very low temperatures (Tw = 3.6 K) [3]. . 10 T= 136 K .05 ''''•• 'I ' '

• /*"••. « .30

1 ! Rat e A [ , B .25 \ •' " / ft "BI • h « .20 "V 1" 2-2 . 15 • I•I ".10 *» * * • . 10 ° .05 3-1 .05 i «—i- • 10 100 Temperature [K] Rotation Angle [°] Figure 1: Temperature dependence of the transverse muon spin relaxation rate in CeAl2. At 3.6 K a transition into an Figure 2: Measured and calculated angular dependence of antiferromagnetic state occurs. the muon spin relaxation rate in CeAl2. The crystal is rotated around the [110] direction. Zero degree corresponds The temperature dependence of the /iSR relaxation rate to the field applied along [110], 90 degree along [100]. For measured in a transverse field of 0.15 T is depicted in Figure more details see text. 1. Near the transition point the usual rapid increase of the damping rate A is seen. It is caused by the slowing down Our measurement of the angular dependence of the re- of spin fluctuations due to the formation of paramagnetic laxation rate at low and high temperatures gave concluding spin correlations [1]. Between 10K and 80K the damping evidence that the onset of muon mobility is responsible for the variation of X(T) seen in Figure 1. Furthermore, if the damping rate of the /iSR signal is observed most clearly in action of static nuclear dipolc fields on a stationary muon this range (see Figure 3). is the primary cause of muon spin depolarization, then the Unusual is the temperature variation of the (zero field) location of the muon can be determined from the shape of damping rate in the paramagnetic regime just above the the oricntational dependence of damping rate [4]. Curie point. As can be seen from Figure 4, the depolariza- As discussed in reference [1], there are three possible tion (which originate from fluctuating Gd spins) is notice- interstitial sites in the cubic Laves phase (CIS) structure. ably different for muons with their spins oriented parallel They are the center of tetrahedrons formed by either 2 Al or perpendicular the the c-axis (i.e. the direction of mag- and 2 RE atoms, 3 Al and 1 RE atom, or 4 Al atoms netization just below Tc), meaning that spin fluctuations and called the 2-2, 3-1, 4-0 sites, respectively. The mea- possess a pronounced anisotropy even in the paramagnetic sured angular variation of damping rate at 69 K and 136 K is regime. Furthermore, the typical slowing down of param- shown in Figure 2 together with the calculated dependence agnetic spin fluctuations on approach to the (second order) for the pure static situation. At low temperatures (69 K) magnetic phase transition [1] is seen here only when the the data are fully compatible with the theoretical prediction implanted muons are spin polarized perpendicular to the for the 2-2 site. At high temperatures (136 K) all angular direction of the c-axis. dependence of A is lost due to the averaging effect of a mobile muon. A quite similar behavior of \(T) as shown in Figure 1 1.0- Gd-Metal (except, of course, the behavior near the transition point) zero field damping has been observed in polycrystalline samples of diamag- Jo.9- nctic LaAlj, of paramagnetic UAI2 and PrAl2. UA13 is a 0B strong spin fluctuator and does not undergo magnetic or- 1 dering. PrAl2 has a Curie point at 30 K. Our finding that the muon looses its static character around 80 K can thus be \ cl beon extended to the rare earth and actinide di-aluminides (cubic \ * Laves phases) in general. The same extension can proba- I 0.6 I ell beam bly be made for the location of the muon at the 2-2 site at low temperatures. These results must be taken into ac- 0.5 count when interpreting /iSR data with respect to magnetic, 0 12 3 4 especially spin dynamical properties. Temperature (above Tc) [K]

Figure 4: Zero field ftSR relaxation rate in Gd metal slightly above the Curie temperature for two orientations.

Similar effects have recently been seen with /JSR on a single crystal sample of Erbium metal [6]. It should be noted, however, that Er, in contrast to Gd (which is an S-state ion) possesses a strong ionic anisotropy due to its large orbital angular momentum.

References

100 200 [1] O. Hartmann el al., J. Phys. F: Metal Phys. 16 (1986) Temperature [K] 1493.

[2] B.A. Gradwohl et al., Hypcrfine Interact. 31 (1986) Figure 3: /iSR relaxation rate in ferromagnetic Gd metal (• = c||beam, • = clbcam). 319. [3] B. Barbara el al., Solid State Commun. 24 (1977) 481. Gd-melal Gadolinium orders fcrromagnctically at Tc = 293 K. [4] O. Hartmann, Phys. Rev. Letters 39 (1977) 832. The spontaneous muon spin rotation frequency below Tc [5] A.B. Denison ct al., Helvetica Physica Acta 52 (1979) has been observed previously in polycrystalline material 460. (e.g. [5]). Its temperature dependence is complicated due to the fact, thai the magnetization starts to turn out of the [6] O. Hartmann et al., (unpublished). hexagonal c-axis near 230 K. The maximum turning angle of 0 = 60° is reached at 200 K. the magnetization then slowly turns back to & = 30" between 200 K and 50 K. Our single crystal data verified the general picture of the /JSR frequency variation with temperature in the ferromag- netic regime as reported in Reference [5], We could, how- ever, resolve finer details in the temperature range between 230 K and 200 K where the rapid turning of magnetization direction occurs. In particular, a pronounced maximum in RADICAL REORIENTATION IN SOLIDS AND ON SURFACES

RA-86-07(A), ZURICH - PARMA - GLASGOW

T. Azuma*. D. Buttart, T. HotiT, I.D. Reid', G. Cristopholini', R. De Renzit, M. Ricc6', E. Roduner's, B.C. Webster'

* Physikalisch-Chemisches Institul der Universitat Zurich, CH-8057 Zurich t Dipartimento di Fisica, Universita di Parma, 1-43100 Parma t Chemistry Department, The University, GB-Glasgow G12 8QQ

Spin polarised energetic positive muons injected in mat- o.oo- ter are used routinely to sense magnetic interaction phenom- 381 K ena in various environments. As they thermalise in the tar- get a certain fraction form muonium atoms (Mu = /n+e~) by electron capture near thermal energy. Mu behaves as -0.02 a very light isotope of hydrogen (mum » imH) and un- o.oo-i dergoes similar chemical reactions. In particular, it adds to unsaturated bonds to form muonated free radicals with 363 K the muon substituted as a spin polarised hydrogen nucleus. This has been used in the past to probe the radiolytical for- mation process and the structure of radicals in liquids, and -0.02 also to determine accurate absolute rate constants of fast 0.00 radical reactions which are not easily accessible by con- 343 K ventional means [1]. The experimental technique monitors changes in decay-positron anisotropy as a longitudinal magnetic field -0.02 is scanned through a region where states with different muon spin quantisations become near-degenerate (Avoided 15500 16000 16500 17000 Level Crossing, ALC). Prominent resonances correspond Field (Gauss) to the magnetic selection rule A(m,, + mt)=0 and repre- sent the exchange of spin polarisation between the muon Figure 1: Amu = 1 ALC resonance observed with poly- and a magnetic nucleus. A second type with AmM=l, Arai=Am, = 0 is considered as muon precession in the crystalline hexamethylbenzene in its plastic phase. remnant transverse component of the local field when the external field cancels the longitudinal component. Here, the crossing of levels is avoided via the dipolar part of the such chemical transformations are short-lived and escape hyperfine interaction. Under isotropic conditions the res- direct detection. It is conceivable that various free radicals onance is lost This is the case when a radical averages are among these transients. Structure, adsorption and sur- dynamically over all orientations, where the critical time is face dynamics of diamagnetic potential intermediates have set by the hyperfine anisotropy, i.e. typically 10-30 MHz. been well studied by thermodynamic or spectroscopic meth- ods, whereas paramagnetic species terminate at catalytically The latter type of resonance is an ideal indicator of relevant temperatures so that they are not present in suffi- small anisotropies. This was demonstrated recently for the ciently high concentration to allow their observation. The rcoricntational motion of muonated radicals in polycrys- otherwise powerful laser techniques are hampered by the talline norbornene in its plastic phase [2]. Norborncne is a non-transparent nature of the systems. Here, we demon- molecule of near globular shape, and previous NMR as well strate for the model case of cyclohexadienyl radicals on as Raman experiments gave no evidence for anisotropic re- silica that a novel technique involving energetic positive orientation. muons as spin probes is sufficiently sensitive to allow the Hexamethylbenzene, a disk-like molecule, also forms a study of radicals under such constrained conditions. plastic phase with a residual rotational degree of freedom. Fig. 1 shows ALC-pSR spectra of its Mu-adduct radical Our experiments were carried out in a SiO2 powder sample of Cab-O-Sil grade EH-5 with an average grain di- at different temperatures. The solid line is a fit based on 2 the assumption of fast uniaxial rotation. Obviously, it re- ameter of 7 nm and a surface area of 380 m /g. The sam- produces the experimental points well at 7'=381 K and at ple was baked out under vacuum for 48 hours to remove 363 K, but considerable deviations arc apparent at 343 K. adsorbed water. This treatment leaves about 4 hydroxyl groups/nm2 at the surface. Then, sufficient degassed ben- The fitted value for axial anisotropy, Dzl = -5.8 MHz, proves rotation about the normal to the molecular plane. At zene to form a monolayer coverage was admitted to the cell the lowest temperature, motion is too slow, and the hyper- before the vacuum connection was sealed. fine Hamiltonian is no longer uniaxial. At 334 K we observed a strong resonance at 2.070 T and Heterogeneously catalyzed reactions usually proceed at two weaker ones at 2.885 T and 2.945 T. They are all of outer or inner interfaces or large surface area materials the A( m,, + m*)=0 type and identify the muonated cyclo- which are often not homogeneous. Many intermediates of hexadienyl radical, CeHeMu, which has A,, = 513 MHz and

26 At = 126MHz (methylene proton), -25 MHz (ortho pro- thus appears to be the only type of motion which can ex- tons) and -36 MHz (para proton) [1]. The strongest sig- plain the observed effects. Models for quantitative analysis nal was measured at twelve temperatures in the range 139- of line broadening exist so far only for chemical reactions 334 K. Representative curves are shown in Fig. 2. Their and spin exchange effects [4] but will have to be developed Lorentzian shape indicates isotropic conditions at all tem- for reorientational motion. Qualitatively, the present obser- peratures. In this context it is important to note that the vations show that complete randomisation of orientation is Am,, = 1 resonance which is expected around 1.9 T was not achieved in £10 ns. detected at any temperature. In bulk benzene this transition It is interesting to note that over the temperature range sets in extremely strongly below the freezing point [3], and studied there is no evidence of a phase transition in the it is the strongest signal also in norbornene and in hexam- adsorbed benzene monolayer such as, for example, two- ethylbenzene (Fig. 1). dimensional melting. However, a clear transition was ob- served when the equivalent of five monolayers was con- densed on the powder. This opens the promising perspec- tive to study the phase behaviour of very thin films.

References

[1] E. Roduner, The Positive Muon as a Probe in Free Radical Chemistry; Lecture Notes in Chemistry 49; Springer-Verlag: Berlin, 1988. [2] E. Roduner, I.D. Reid, M. Ricc6 and R. De Renzi, Ber. Bunsenges. Phys. Chem. 93 (1989) 1194-1197. [3] E. Roduner, Chimia 43 (1989) 86-97. [4] M. Heming, et al. Chem. Phys. 129 (1989) 335-350.

2.0 2.1 2.2 Field (Tula)

Figure 2: A(m,, + mt)=0 ALC resonances obtained from the methylene proton in muonaied cyclohexadienyl radi- cals in a monolayer of benzene on 7 run SiO2 grains. The data were fitted to a Lorentzian resonance on a cubic back- ground, which has been removed in these displays; the solid curves give the fitted resonances.

The line-width increases continuously with decreasing temperature, in total by a factor of five over the whole range. This shows that the fluctuation of the hypertine interaction becomes slower due to decreased mobility of the radical. It is expected that a non-spherical adsorbed species has a preferred orientation with respect to the sur- face. Three types of motion could be responsible for line width effects. The first is rotation about an axis perpendic- ular to the surface. This leads to a cylindrical Hamiltonian by partial averaging of the hyperfine anisotropy. As we have seen the AmM = 1 resonance is a sensitive indicator of small anisotropies [2]. The absence of this signal at all tem- peratures shows that there is no residual anisotropy in the C6H6Mu/Cab-O-Sil system down to 139K, and that motion is not simply uniaxial. The second type of motion is rota- tion about an axis parallel to the surface. For a flat species like C6H6Mu this is more likely a flip, i.e. a jump between two orientations with identical hyperfine interactions, which would not lead to the disappearance of the Am, = 1 res- onance. The third motion to be considered is translation. On a flat surface this would not affect the orientation of the radical with respect to the magnetic field. For a more or less spherical grain with non-uniform surface, however, this leads very quickly to an averaging over all orientations and thus to the disappearance of the Am,, = 1 signal. The observed resonance obviously shows line width effects be- cause it has a different dependence on hyperfine couplings and senses motion on a different time scale. Translation

27 /*+SR IN CHEVREL PHASE SUPERCONDUCTORS

RA-87-02, ETHZ - GENEVA

P. Birrer", D. Cattani', j. Core', M. Decroux's, 0. Fischer', F.N. Gygax', B. Hiui', E. Lippelf, A. Schenck'5, M. Weber*

• Institut fur Mittelenergiephysik der ETH ZQrich, CH-5232 Villigen PSI t Dcpartement de Physique de la Maiiere Condensee, University de Geneve, CH-1211 Geneve 4

The chevrel phase compound Eui_ISnxMo6Ss,Se8_v displays different features depending on the value of x. lable 1: Compilation of extracted values of

A = Ao (1)

Fined values for a(T=0 K) and Tc for different samples as well as the calculated penetration length Ao are listed in lable 1.

10 15 20 Temperature [K|

Figure 1: Relaxation rate

28 3 correlation between I/A

0 50 100 150 200 250 300 BM [mTJ

Figure 3:

29 //SR IN SEMICONDUCTORS

RA-88-04, STUTTGART - PSI

R. Abela', V. Claust, M. Hampele», D. Herlach*, M. Ko:»*, K. Maier'5, J. Major», A. Seeger't, W. Sigle*, W. Staiger*. W. Tempi*, E. Widmann '

* Max-Planck-Institul für Metallforschung, Instil dt für Physik, Postfach 800665, D-7000 Stuttgart 80 t Institut für Theoretische und Angewandte Physik, Universität Stuttgart, Pfaffenwaldring 57, D-7000 Stuttgart 80 t Paul-Scherrer-Insitut, CH-S232 VUUgen PE.I

The behaviour of negative muons (yr) in condensed B,,u,,\ are the asymmetry, the damping rate, 640 MHz, which we attribute to the hyperfine interaction at the circular frequency, and the phase of the signal. The the quasi-Al nuclei (Fig. 2). Fig. 3 gives an Arrhenius plot subscript 2 refers to the muons stopped in the moderator. for the temperature dependence of the asymmetry Ai for all experiments performed in an external field of 0.04 T. The kind of doping seems to be unimportant for the decrease of Ai at temperatures below 25 K. The behaviour of A\ cannot be explained by the occu- pation probability of the quasi-Al acceptors. This is obvious in the case of n-doped silicon where the Fermi level is al- ways above the aluminium acceptor level. A fit of the data of Fig. 3 leads to a very low activation enthalpy of about 1 meV. Such a small value might find its explanation in the formation of interstitial quasi-Al2+ at low temperatures during muon capture. When the muon cascades down to the ground state, a 411keV ^-quantum is emitted [2]. Un- der normal conditions the recoil energy of 3.1 eV would not be sufficient to displace Si atoms from their lattice sites but when the muon is captured most of the outer electrons are removed because of Auger processes at the start of the cascade. The threshold energy for displacement is presum- ably lowered to such an extent that quasi-Al interstitials Time ( [ pi ] are produced by the y~ capture. From the experiments we deduce that only below 20 K are the Frenkel-pair config- Figure 1: y~SR signal of n-doped silicon in an applied urations produced sufficiently long-lived to give rise to a magnetic field of 0.04 T at room temperature after the sub- detectable y~ signal. traction of backgrounds and correction for the finite muon lifetime.

30 Temperature [ K ] In order to exploit the full potential of the present tech- nique further experiments are necessary, e.g. measurements on more heavily doped Si-crystals. Particularly promis- 3120 sa 25 12 10 5 8 7 ing appear to be the experiments with pairs of aligned 7- detectors in order to investigate the anisotropy of the dis- 68 igg - Slol 55 " 9 o Slnl placement process. sa o Sin2 The authors are indebted to F.N. Cygax, A. Schenck (ETH Zurich), and E. Roduner (Unversity of Zurich) for the us { 9 ta ! use of their JISR apparatus. The work was supported by the i Bundesministerium filr Forschung und Technologie, Bonn, 35 | Fed. Rep. of Germany, under contract no. 03-SE2STU-O. S f 3a TH 25 References a J 28 [1] CD. Watkins, in: Radiation Damage in Semiconduc- tors, edited by P. Baruch, Dunod, Paris, 196S 9 is [2] R.C. Barrett, in: Muon Physics I, edited by V.W. 3.3 2« 83.3 iae in 125 ms Hughes and C.S. Wu, Acad. Press, New York, 1975 i/r [10-3

Figure 3: Anhenius plot of the asymmetries At of all sam- ples measured in an external magnetic field of 0.04 T. Neutron Scattering (3102)

The neutron scattering technique is an indispensible tool In 1989 the research program covered areas such as in the study of the static and dynamic properties of con- high- temperature superconductors, magnetism, materials densed matter. It is used in various scientific disciplines research, molecular systems, phase transitions, etc. The such as biology, chemistry, solid state physics, crystallo- results of some typical experiments are described on the fol- graphy and materials research. In 1989 scientists from more lowing pages. A complete account of the scientific activities than 40 different research groups used the facilities of the was published in a separate "Progress Report" (LNS-150) Laboratory for Neutron Scattering (LNS, ETH Zurich) at which is available on request. the reactor Saphir. The experiments are usually carried out on a collaborative scientific basis. Details of the available instruments and sample environment equipments are sum- marized in the brochure "Guide-Lines for Using the Neu- tron Scattering Facilities of the LNS" which is available on request

33 THE CRYSTALLINE ELECTRIC FIELD OF Pr2Cu04

ETHZ - PSI - U.K. - USA,

P. AUenspactr, A. Furrer, H.R. Ottn, R. Osborn?, A.D. TaylorS, S.-W. Cheong11, Z. Fisk*

* Labor fur Neutronenstreuung, ETH Zurich, CH- S232 ViUigen PSI t Laboratorium fiir Festkorperphysik, ETH Honggerberg, CH - 8093 Zurich t Paul Scherrer Institut, CH - 5232 Villigen PSI § Rutherford Appleton Laboratory, Chilton, Didcot, U.K. K Los Alamos National Laboratory, Los Alamos, USA

Compounds of the type R2Cu04 (R = Pr, Nd) crys- higher than 90 meV as predicted in a recent study of the tallizing in the T'-type structure recently gained consider- magnetic properties of Pr2Cu04 [1]. The date analysis is able interest due to claimed n-type (electron carrier) super- in progress. conductivity with Tc >20 K in substituted systems such as R-Ce-Sr-Cu-O. We have made a neutron spectroscopic study of the parent compound Pr2CuO4 in order to derive the crystal field (CEF) level scheme. Characteristic energy spectra are shown in Fig. 1. The scattering is dominated by an intense inelastic line (peak A) at 18 meV whose in- tensity decreases upon raising the temperature; so it can immediately be interpreted as a ground-state crystal-field transition. The same is true for the much weaker line (peak

Figure 2: Energy spectra of scattered from poly- crystalline Pr2Cu04 measured on HET. Figure 1: Energy spectra of neutrons scattered from poly- crystalline Pr2CuO4 measured on a triple-axis spectrometer at the reactor Saphir. A tentative CEF level scheme is in- dicated on top of the Figure [1]. References [1] P. Allenspach, S.-W. Cheong, A. Dommann, P. Fischer, B) at about 88 meV. Excited crystal-field transitions show Z. Fisk, A. Furrer, H.R. Ott, B. Rupp, Z. Phys. B77 up at about 68 meV (peaks C and D). We have confirmed (1989) 185. the magnetic origin of all these lines by studying the peak intensities versus modulus of the scattering vector Q which exhibit the expected form factor behaviour. Additional neu- tron spectroscopic measurements have been performed at the spallation neutron source ISIS with use of the high- energy time-of-flight spectrometer HET. Typical data are shown in Fig. 2, which are in fair agreement with Fig. 1. It is important to notice that there are no CEF transitions

34 HIGH-TC POWDER SAMPLE PRODUCTION

ETHZ • PSI,

P. Allenspach', M. Koch', B. Rupp', A. Isacson', R. Thuf, U. Staub*. J. Mesof, M. Webert, R. HSfeli*, JJ. MUnchJ, U. Zimmermann1

* Labor filr Neutronenstreuung ETH Zurich, CH-5232 Villigen PSI t Institut fur Mittelenergiephysik ETH Zurich, CH-5232 ViUigen PSI t Paul Scherrer Institut, CH-5232 Villigen PSI

The aim of our sample production is to obtain series References of single phase ceramic material with different rare earth ions and different oxygen contents. The procedure devel- [1] P. Meuffels, B. Rupp, E. Porschke, Physica C 156 oped in Jiilich (FRG) is described elsewhere [1]. In order (1988) 441. to obtain sufficient material for neutron scattering and /iSR measurements we enlarged the devices: the capacity of our sintering and oxygen loading furnace is 300g and 30g, re- spectively. These furnaces are shown in Fig. 1 and Fig. 2, and the improvement of structure after each sintering process, measured with X-ray diffraction, in Figs. 3a-c. u 3

7

Figure 1: Sintering furnace. 1. oxygen 99.9 %, 2. SiO2-tube, 3. registration thermocouple, 4. Al203-boals, 5. sample pressed to pellets, 6. furnace control thermocou- ple, 7. tube furnace, 8. paraffin bottle.

Figure 2: Oxygen loading furnace. 1. tube furnace, 2. SiOj-tube, 3. Pt-boat, 4. registration thermocouple, 5. pressure cells (different ranges), 6. turbopump pressure control, 7. turbopump, 8. UHV-valves, 9. prevolume, 10. oxygen 99.999%, 11. helium, 12. furnace control thermo- couple, 13. prevolume thermocouple.

35 uti muu i ta •>

a si

31. a 31. a 4t.ii 51. g l^ai '••»» ••» «• UH • LI *•

*UI ii. ai a. a <«. a «. ai

! c A s a

- JL A3 an fta fta «?sa M fr.a TKO - ThET* /O - SPACING

Figure 3: X-ray powder diffraction pattern of NdBa3Cu307_j after first (a), second (b) and third (c) sintering process.

36 PHONON DISPERSION IN Li2S

ETHZ • GENF - OAK RIDGE,

W. Biihrer*, J. Mesof, H. Bill', H.G. Smith'

* Labor fiir Neutronenstreuung ETH Zurich, CH-S232 Villigen PSI t Dept. de Chimie Physique, University de Geneve, CH-1211 Genf i Solid State Division, Oak Ridge National Laboratory, 37831 Oak Ridge

Lithium sulphide crystallizes in the anti-fluorite struc- Using a simple shell model with polarisation of the S ture. It shows at temperatures above 500 K (Tm = 1660 K) ions, we succeeded in a first approach to reconstruct the a high increase of the ionic conductivity, associated with a measured curves (Fig. 1). This model allows us to predict specific heat anomaly probably due to Frenkel defects. As some properties of the crystal. For example the measured the creation of such defects is closely related to the thermal and calculated elastic constants are in good agreement to motion of the ions, (consequently to the lattice vibrations) each other (Table 1). Interesting is the strong difference it was interesting to determine the phonon dispersions of between C(l,2) and C(4,4) indicating that the crystal tends this crystal. to build covalent liaisons (forces have non-central contri- 7 Experiments on a Bridgeman-grown single Li2S crys- butions). This fact is corroborated by the predominance of tal have been performed on the triple-axis-spectrometer at the parameter Al and by the deviation of the lithium charge 15 K. Results are shown in Fig. 1. Except the upper optic Z(Li) from unity (Table 2). modes, the complete dispersion relation was determined. In After having calculated the vibration spectrum it was comparison with the Na2S crystal [1], the acoustic modes at possible to predict, within the harmonic approximation, the the zone boundary are shifted to higher frequencies and the temperature dependence of the specific heat (Fig. 2) and order of the Raman and infrared modes has been reversed. of the mean square displacements (Fig. 3). On the Fig. 3 This is essentially due to the small mass of the Lithium ion. we see clearly a deviation from experimental values (elastic neutron scattering) above 900 K revealing the strong anhar- monic behaviour of a superionic crystal. Further measure- ments are in progress.

DELTA SIGMA

• lJ

In plan Ull-I I 1* |))Kn ( IDU)

Figure 1: Phonon dispersion of Li2S at 15 K. Lines: best fit shell model. Figure 2: Calculated specific heat Figure 3: Mean Square Displacements.

Table 1: Measured and calculated elastic constants. References c;; .1) i c:• .-) i o::.J! 9. 36 i .20 i i. 3: ! [1] W. BUhrer, H. Bill, J. Phys. C 13 (1980) 5495. ! calculi: 3.

lable 2: Adjusted parameters of the simple shell model.

I S I S I I A3 I B2 I A3 I 13 I u I 4 I k I t 1 i>,a> iQ.mil.3m-o.i;<.u.i7; ;-o,mi o.ati i.t I-Q.039I3>;Q iu.701

38 SEARCH FOR LIGHT-INDUCED STRUCTURE CHANGES IN SODIUM- NITROPRUSSIDE ON POLYCRYSTALLINE SAMPLES

ETHZ • PSI - BERN,

MJUidlinger*, J. Schefert. H.U. Gildell

* Labor fiir Neulronenstreuung ETH Zurich, CH - 5232 Villigen PSI t Paul Scherrer Institut, CH-S232 Villigen PSI { Institut for anorganische Chemie, Universita't Bern, CH-3000 Bern

At temperatures below 190 K, crystalline Na2[Fe(CN)5- NO]. 2D2O and most of its derivatives can be transformed into an extremely longliving metastable state (r > 107 sec) by polarized light with 3S0 nm < A < 540 nm [1]. Data collection on a deuterated powder sample at 80 K was performed for the ground state and the two metastable states, using the DMC powder diffractometer in the high resolution mode (24 hours per slate) in order to search for small differences between groundsiate and metastable slates. Due to absorption and random orientation of the micro- crystals with respect to the polarization of the light, it is impossible to excite more than 15-20 % of a powder sam- ple. The expected structural changes, known from Raman specuoscopy, are in the range of 0.1 A, and the bonding angles should not change by more than 3°. These restric- tions show why we only could measure rather small changes Figure 1: One of the additional reflections found in between the different states: Changes which are hardly big- metaslable slate I: a) groundstate at 295 K, b) metastable ger than the standard deviations. In the metastable stale we state I at 80 K. found several additional reflections which are forbidden in the spacegroup Pnnm (No. 58) [2] and even are not in correspondence with the orthorhombic cell dimensions (a = 6.128 A, b = 11.82 A, c = 15.55 A) (c.f.fig.l). References We will try to verify these observations on single crys- tals. It has not been shown yet whether there are any coup- [1] Th. Woike et al., to be publ. in Chem. Cryst. ling forces between the excited molecules, which possibly could lead to a long-range order or whether here is any do- [2] F. Bouomley, P.S. White, Acta Cryst. B 35 (1979) main structure built of zones with population of 100 % and 2193-2195. 0 %, respectively.

39 SEARCH FOR LIGHT-INDUCED STRUCTURE CHANGES IN SODIUM-NITROPRUSSIDE ON SINGLE CRYSTALS

ETHZ - PSI - LLB - ILL - KOLN • BERN,

M. Rudlinger*. J. Schefer', O. Heger'. P. Schweiss*. G. Chevrier', T. Vogt*, G. Maclmyre8, S. HaussUhl*. H.U. GUdel°

* Labor fiir Neutronenstreuung ETH Zurich, CH-S232 Villigen PSI t Paul Scheirer lnstitut, CH-S232 Villigen PSI X LLB, CENS, F-91191 Gif sur Yvelle § lnsiitut Lauc-Langevin, F-38042 Grenoble i Institut filr Kristallographie. Uni Koln, D-5000 Koln a Institut fur anorganische Chemie, Uni Bern, CH-3000 Bern

At temperatures below 190 K, crystalline Na3[Fe(CN)s- Table 1: NO] • 2D2O and most of its derivatives can be transformed Structural parameters of Na2[Fe(CN)5NO] • 2D2O at 80 K 7 into an extremely longliving metastable state (r > 10 sec) (groundstate). Spacegroup Pnnm, RF = 3.61 %, based on by polarized light with 350 nm < A < S40 nm [1]. 4529 observed reflections (3923 > 3

Detailed investigations with different indirect methods Atom Po». X V z a such as Raman spectroscopy, Mossbauer- and transmission Ol 48 0.8863(1! 0.40509(7) 0.5 '• 1 measurements, etc. have been performed within the last Nl 46 0.09948(9) 0.12372(4) 0.5 '-. X2 ah 0.66697(61 0.11954(3) 0.64193(2) 1. ten years. Several authors made contradictory suggestions X3 45 0.25031(6) 0.40523(3) 0.35554(2) 1. about the nature of this effect and the consequences on the N4 4S 0.72730(8) 0.35798(4) 0.5 1. crystal structures [1,2]. Nal 4f 05 0.0 0.24591(7) I- N»2 4e 0.0 0.0 0.37820(7) 1. Fe 4g 0.50053(7) 0.28015(3) 0.5 1. 1 Cl 48 0.2499(1) 0 18278(51 0.5 1- We first measured the structure of the groundstate at 80 Sh 0.60742(3) 0.17961(4) 0.58790(3) 1. ! Co 3h 0.34591181 0.36167(4) 0 41086(3) 1. K at the reactor Orphee, Saclay/Paris to exclude a phase o: Sh 0.171611) 0.12239(5) 0.26854(4) 1. transition between 80 and 295 K. The refined parameters 31 3h 0.1357(21 0.19384(6) 0.28618(5) 0.89611' are listed in lab. 1. The crystal was cut into a perfect 33 8h 0.0631(11 0.12392(7) 0.22457(5) 0.86111 cube of 3 mm size with faces parallel to the orthorhombic axes. We observed "forbidden" reflections such as hOO, Table 2: OkO, etc., with intensities of about 3 or 4 times a. This Structural parameters of Na2[Fe(CN)5NO] • 2D2O at 80 K problem is also present at 295 K as published by Navaza (metastable state). Spacegroup Pnnm, RF = 7.0 %, based et al. [3]. t/)-scans made on various of these reflections on 3320 observed reflections, measured at D9/ILL. exclude Renninger effects. One of the difficulties in the refinement was anisotropy in V. probably due to highly i Atom • Pos. fB I anisotropic extinction of the crystal. 01 1 4B 0.8865(5) 0.4054(3) 05 1. 0.50 | Nl I 4* 0.0977(41 0.1239(2) 1 0.5 1. : "° 1 N2 ah 0.6665(2) 0.1193(1) 1 0.6424(1) 1. .n 1 N3 ! 4, 0.2495(3) 04055(1) 1 0.3553(1) - 27 44 Subsequently we measured the metastable states of so- N4 ! •* 0.7263(3) 0.3575(21 , 0.5 1. ; Nil 1 4f 0.5 0.0 ! 0.2461(3) 79 dium nitroprusside at 80 K at D9/ILL, Grenoble. The D9 N»2 4e 0.0 0.0 1 0.3781(3) 1. 0 74 3 1 1 0 measurement was performed on a 2 x 2 x 0.6 mm crystal, Ft . 4R 0.4992(3) 0.2793(2) 0.5 I. 22 illuminated in a modified closed-cycle Helium refrigerator Cl ! 4, 0.2436(5) 0.1829(4) • 0.5 i. 0 70 C2 | 8h 0.6067(31 0.1796(2) I O.iaS3(l] 1 0 30 at 80 K with laser light of 488 nm for about 90 hours. cs : *h 0.3455(31 0.3611(2) . 0.4108111 1. 0 50 02 j 0.171714) I 0.1224(21 | 0.2680(1) i The population was periodically checked by transmission ah 1 '• i '•'• 1 measurements during the 10 day experiment. No change of Dl ; ah 0.1381(7) 0.2002(3) 0.2355(3) ! 0.62 1 ih ! 0.0630(7) 1 0.123614) , 0.2234(21 1 0 66 ; 2.33 the photocurreni has been observed. i D' References First treatment of the dataset, using the same structure model as for the refinement of our low temperature ground- [i] Th. Woike, KFA-Report Jul-1922, JUlich, Germany, state data showed, that there occured structural changes, e.g. 1984 the N4-01 -bonding length has changed from 1.12 to 1.13 A, the Fe-N4 one from 1.667 to 1.671 A. Refinement is mostly [2] D. Gross, Dissertation Uni Heidelberg (1984). limited by the water molecules, the occupancies of the two [3] A. Navaza et al., Acta Cryst. (1989) C45, 839-841. D-sites lend to be asymmetric. The refined parameters are listed in Tab. 2. These results seem to be contradictory lo the additional reflections found in powder sample.

40 MAGNETIC PROPERTIES AND ANTIFERROMAGNETIC Cu ORDERING IN Pr2CuO4

ETHZ - USA - ETH • PSI,

P. Allenspach\ P. Fischer', A. Furrer*. S.-W. Cheongt, Z. Fisk*. A. Dommann*, H.R. Oti», B. RuppS

* Labor fUr Neuironensireuung, ETH Zurich, CH-5232 Villingen PSI t Los Alamos National Laboratory, Los Alamos, USA t Laboralorium fur Festkorperphysik, ETH Honggerberg, CH-8093 Zurich § Paul Scherrer Institut, CH - 5232 Villigen PSI

Bulk magnetisation measurements and neutron-scattering experiments were performed both on a polycrystalline sam- ple and on a single- crystal of Pr2CuO4 in temperature 1 range from 1.5 to 300 K. Pr2Cu04 crystallizes with the T V (Nd2Cu04)-type structure (Fig. 1). We observed antifer- romagnetic ordering with peculiar temperature dependence (Fig. 2) of the Cu moments below T* = (190 ± 2) K in a single crystal and below T = (250 ± 10) K in pow- N X . r.-C!»0 = ilK der material. The magnetic unit cell dimensions are am = 0.5 2a0, cm = c0; the Cu moments are oriented in the basal plane with a magnetic saturation moment of pcu = (0.45 3 •d \ | P-rCuO. (Vk.1) I ± 0.12)/ifl. pr * does not order magnetically above 1.5 K due to its crystal-field induced singlet ground state as ver- 220 K r • 1" ified by inelastic neutron scattering. More detailed results are published in [1]. 0 0.5 u> IS

Reduced Temperature T/TM

Figure 2: Temperature dependence of the reduced sublauice 2+ magnetisation of Cu in Pr2Cu04 as determined from neu- tron intensities of the single-crystal (1/2,1/2,1) reflection. The dotted line represents a mean-field (MF) model for S = 1/2, the solid line is a critical exponent fit (C(l-T/Tw)") yielding /? = 0.34(4), TN = 190(2) K. The inset shows the intensities of the (1/2,1/2,1) reflection above and below TN.

References

[1] P. AUenspach, S.-W. Cheong, A. Dommann, P. Fischer, Z. Fisk, A. Furrer, H.R. Olt, B. Rupp, Z. Phys. B77 (1989) 185.

€ Cu O O O Pr

Figure 1: V (Nd2Cu04)-type crystal structure of Pr2Cu04.

41 OSCILLATING RADIAL COLLIMATOR OF DMC DIFFRACTOMETER

ETHZ - PSI,

M. Koch', R. Thut", A. Isacson*. P. Fischer*, J. Schefer'

* Labor fur Neutronenstreuung ETH Zurich, CH • S232 Villigen PSI t Paul Scherrer Institut, CH - 5232 Villigen PSI

An oscillating radial collimalor has been recently in- stalled between sample and detector on the DMC diffrac- tometer to avoid Bragg scattering from cryostats and fur- naces, such as our Al/Ta high-temperature radiation oven (maximum 1500 K). Compared to the also available V fur- nance the peak-to-background ratio is thus essentially im- proved. The collimator (cf. Fig. 1) has an inner radius of 2S.S cm and an outer radius of 4S.0 cm. The angular distance between the 73 cadmium coated steel plates (19.4 cm long and 6.4 cm high) of 0.02 thickness is 1.2° (both sides are coated with 0.008 cm of cadmium). The principle of the system is similar to the one described in [1] and similar to radial collimators used at HMI, Berlin. The collimator is moved on three steel spheres in 2000 microsteps accord- ing to variable speed (< 240 steps s"1) within 2 x 1.2°. The end positions are defined by accurate microswitches (adjustable positions). To obtain a uniform distribution of the blade positions, the end positions are measured twice and set exactly to the position of a blade. The collima- tor moves independently of the measurement, except for occasional adjustment of the speed. Fig. 2 shows the dif- ference between a measurement of a UCu5 sample in a dilution cryostat with and without this collimator system. It absorbs about 21 % of the neutrons, but yields also a cor- responding background reduction by a factor of 2.7S. The oscillating background in Fig. 2 is caused by the cadmium coated blades of the nonscillating collimator. 80

Figure 2: Diffraction pattern of UCu5 at 4 K in a dilution cryostat without (a) and with (frequency = 240 steps s"1 (b) and 0 steps s"1 (c) oscillating collimator. Maximum peak intensity is 8.4 x 104 (measurement time: 1 h, A = 1.703 A, collimation ali2,3 = 40", -, 18') (P. B6ni, unpublished).

References

[1] A.F. Wright, M. Berneron, S.P. Heatman, Nucl. Instr. and Meth. 180 (1981) 6SS.

Figure 1: Oscillating radial collimator of DMC diffractome- ter.

42 LONG-RANGE F.C.C. ANTIFERROMAGNETIC ORDERING OF TYPE III IN YbAs

ETHZ - GRENOBLE,

A. DOnni', P. Fischer', A. Furrer', F. Hulligert, S. Haydent

* Labor fur Neutronenstreuung, ETH Zurich, CH - 5232 Villigen PSI t Labor filr FestkOrperphysik, ETH Zurich, CH - 8093 Zurich t Institut Laue-Langevin, F - 38042 Grenoble

Specific heat measurements below 1 K in the ytterbium monopnictides YbX (X = N, P, As) revealed the existence of low temperature phase transitions [1]. Neutron diffrac- 71 tion investigations performed on a single crystal of the rare J •- earth compound YbAs proved the existence of long-range f.c.c. antiferromagnetic ordering of type III (Fig. 1), below Tw = 0.7 K, corresponding to it [1,0,0.5] [2]. The ordered I* magnetic saturation moments of magnitude /iy4 = 0.86 (3) 1 /jfl, orientated perpendicular to [0,0,1] (Table 1), are re- ,' i duced due to Kondo hybridization. The temperature depen- a | dence of the staggered magnetization exhibits a most un- 7 usual critical behaviour (Fig. 3), in striking agreement with - — • m %•

Mossbauer results [3]. The crystalline-electric-field (CEF) • | splitting was measured for the same single-crystalline sam- ple yielding the level sequence r6 • r8 (18 meV) - r7 (40 2 y^ meV) with the CEF parameters B4 = -2.05 • 10 ~ meV and 5 B6 = 7.33 • 10- meV. 1 1 On spectrometer IN 12 at ILL Grenoble the magnetic 7 exitation spectrum of YbAs in the ordered state was inves- tigated. Discrete spinwave excitations were found below Figure 1: F.c.c. antiferromagnetic structure of type III of 0.5 meV (Fig. 2); they are split into to transverse modes, YbAs corresponding iok = [1,0,1/2] and ferromagnetic cou- as in CeAs [4]. Due to the large separation of the excited pling between the two sublauices • and • crystal-field states from the CEF r6 doublet ground state YbAs can be considered as an effective S = 1/2 system. The detailed data analysis within the randon-phase approx- imation is in progress. Table 1:

Observed and calculated Integrated aagnetic (H) and nuclear (H) neutron Intensities of TbAa at 1-7 aJC (rtfarrtnf to Z domain, Lorentz factor corrected and Intensity averaged over I,T,2 domains, A I - I obs " Xcalc'- ^bs

43 1.0 cooling haatlng cooling heating 1*S li— '"V \ % • % 1 t ) .0,0.0 • * a Temperature [K] Temperature [K] ) b) YbAs (0.5,0.0,1.0 s (1.5,1 a) YbA

0.0 0.2 0.4 0.6 0.8 10 6 0.8 0.0 0.2 0.4 0.

Interactions 40 (1988) 381. e J6hanno. J.M. Marimom da Cunha, H.R. Ott, Hyperfin 0.0 0.0

Commun. 71 (1989) 365. mun. 55(1985)113.

0.2 0.4 1.0- 0.6 0.8

n n

0.2 0.4

0.6

o.a

n Mag

t Magne . [4] B. HiUg, A. Furrer, Phys. Rev. B 34 (1986) 6258 , G. [3] P. BonviUe, J.A. Hodges, F. Hulliger, P. Imbert d State [2] A. DOnni, P. Fischer, A. Furrer, F. Hulliger, Soli

e Com- [1] H.R. Ott, H. Rudigier, F. Hulliger, Solid Stat References a) (1.5,1.0,0.0) and b) (0.5,0.0,1.0). s zation fiy j, based on magnetic peak intensities of reflection

e magneti- Figure 3: Temperature dependences of sublattic 1 Til ,1 F J9UIOUI 0 MAGNETIC ORDERING OF REPd3 (RE = Nd, Er, Tm, Yb)

ETHZ - MÜNSTER,

O. Elsenhans', P. Fischer", H.-G. Purwinst

• Labor für Neutronenstreuung ETH Zurich, CH - 5232 Villigen PSI t Westfälische Wilhelms Universität Münster, D - 4400 Münster

In the series of the (Rare Earth)-Pd3 compounds, which thermodynamic experiments [2,5], which suggested antifer- crystallize in the cubic AuCu3 structure, bulk magnetic romagnetic ordering with Tjv < 0.2 K. Our results, obtained measurements [1,2,3] indicate long-range antiferromagnetic by neutron diffraction, yield the same magnetic structure as ordering for most Rare Earth elements, except for the inter- for TmPd3, but with TN = 3 K and nEr = 6 jiB at T = 8 mediate-valence regime comprising the elements Ce, Tm mK (Fig. 2). and Yb. However recently an increasing number of mag- As shown in Fig. 2, the observed temperature depen- netically ordering intermeiallic compounds has been found dence of the magnetic peak intensity, which is proportional and identified as intermediate valent in the ordered state. In to the square of the ordered magnetic moment of the Er contrast to the case of Ce, where one of the 4f" fluctuating ions, shows an unusual behaviour with an apparent crit- configurations is non- magnetic, the Tm ions may fluctu- ical exponent ß > 1. Also NdPd seems to exhibit an 13 12 3 ate between two magnetic configurations 4f and 4f , i.e. unexpected temperature dependence of the magnetic peak yielding the possibility of magnetically ordered interme- intensity below T = 0.2 K (Fig. 3). The corresponding con- diate valent compounds. Indeed, we observed by means clusions from macroscopic measurements [1,2] suggested of neutron diffraction antiferromagnetic ordering in TmPd3 an antiferromagnetic ordering below T = 0.2 K. On the with a Néel-temperature TN = 0.8 K (Fig. 1). The mag- other hand, our neutron scattering experiments revealed an netic structure may be described by a propagation vector k incommensurate antiferromagnetic ordering at much higher = (1/2,1/2,0), and the magnetic moments of the Tm ions are temperatures, namely with a Néel-temperature in the range oriented parallel to [001]. The magnitude of the magnetic of 1 K. For 0.7 K < T < 1 K, the development of long- moment was found to be /irm = 1 /JB at T = 8 mK. range magnetic ordering seems to be suppressed.

ErPd,

= 7.1

Figure 2: Temperature dependence of the (1/2,1/2,0) and Figure 1: Temperature dependence of the (1/2,1/2,0) peak of the (1/2,3/2,0) peak intensities of polycrystalline ErPd3, 3 4 intensity of polycrystalline TmPd3, measured by neutron measured by neutron diffraction in a He/ He-dilution cryo- diffraction in a 3He/4He-dilution cryostat. stat. The lines are guides to the eye.

Also in the case of YbPd3 we found evidence for long- In TbPd3 [6,7], which orders according to an incom- range magnetic ordering. However, this compound is the mensurate antiferromagnetic structure, we have evidences only example in the REPd3 series, where no antiferromag- for induced magnetic moments of the Pd ions. It is not netic ordering were found. Neutron diffraction experiments yet clear, if this effect yields the unusual temperature de- showed ferromagnetic ordering below Tc = 0.37 K, with pendence of the magnetization of ErPd3 and of NdPd3. In an ordered magnetic moment of the Yb ions of \iy t =1.7 NdPd3, nuclear spin polarization due to the hyperfine field /iß at T = 8 mK. This result is in contradiction to recent of the ordered election spins of the Nd ions may cause therniodynamic measurements [4], where antiferromagnelic the increase of the magnetic peak intensity for T < 0.2 K. ordering below Tjv = 0.18 K was proposed. Also for ErPd3, Further calculations are in progress in order to clarify the we found different results compared to the corresponding situation.

45 Figure 3: Temperature dependence of a dominant anliferro- magnetic peak intensity of polycrysialline NdPda measuied by neutron diffraction in a 3He/4He-dilution cryostat. The line is a guide to the eye.

References

[1] W.E. Gardner. J. Penfold, T.F. Smith, I.R. Harris, J. Phys. F2 (1972) 133. [2] W. Drewes, Ph. D. Thesis, Westf&lische Wilhelms Uni- versiiat MUnster, FRO (1986). [3] I. Flouquet, P. Haen, C. Vettier, J. Magn. Magn. Mat. 29 (1982) 159. [4] F. Oster, B. Polit, E. Braun, H. Schmidt, J. Langen. N. Lossau, J. Magn. Magn. Mat. 63,64, (1987) 629. [5] J.M. Machado da Silva, J. Phys. CS (1979) 152 [6] O. Elsenhans, P. Fischer, K.N. Clausen, H.-G. Purwins, F. Hulliger, J. Phys. 49, C8 (1988) 42S. [7] O. Elsenhans, P. Fischer, H.-G. Purwins, "Magnetic Ordering of TbPd", this reporL

46 NUCLEAR AND MAGNETIC STRUCTURE OF THE PERMANENT MAGNET MATERIAL Lu2Fe14C

ETHZ • PSI - Philips,

Ch. Hellwig', K. Girgis', J. Sehefer', K.HJ. Buschow'

* Institut fur Krisiallographie und Petrographie, ETH Zurich, CH-8092 Zurich t Solid Slate Physics (F3), , CH-S232 Villigen PSI J Philips Research Laboratories, 5600 Ja Eindhoven, The Netherlands

In the course of investigations of new cobalt free perma- nent magnet materials Lu2Fei4C has been studied melallo- graphically, by microprobe analysis. X-ray and by neutron diffraction methods. Lu2Fe14C crystallizes in the tetrag- onal space group P42/mnm (No. 136) with 68 atoms per unit cell. The T,. determined from macroscopic measure- ments is 495 K [1] These materials are of technical interest. Neutron diffraction measurements were carried out at 295 K and 23 K. The measurements were performed on the DMC- spectrometer [2] at the reactor SAPHIR (PSI). Nuclear and magnetic parameters of the Rietveld refinement (c.f. figure 1) are summarized in table 1 (23 K only). Structure param- eters are comparable to Nd2Fe14C [3]. The sample contains traces of Fe, therefore a two phase Rietveld calculation has been applied.

Table 1: Figure 1: Observed and calculated neutron diffraction Structural and magnetic parameters of Lu Fe C 2 14 pattern of Lu Fci C at 23 K. Neutron wavelength A = Magnetic moments are fixed parallel c 2 4 1.7028(2) A . Measurement dme: 12 hours/point (simul- Al Po» X ¥ z fi. IHS) B[V) Lul 4T" .2592(5) .2592(5) .0 .44(7) tanous measurement of 400 points). Refinement parame- Lu2 4« .1442(5) -.1442(5) .0 44(7) ters are summarized in table 1. Additional peaks are due Fel 16k .22560) .5632(3) .1201(2) 2.5(1) 51(2) Fc2 16k .03490) .35810) .1748(2) 2.8(1) 51(2) to traces of iron. ra »i .0971(3) .09710) .2006(3) 3.1(2) 51(2) Fo4 »i .3161(2) 3161(2) .24560) 39(2) .51(2) Fe5 4e .0 .0 .6072(4) 1.7(2) •51(2) Fo6 4c .0 .5 .0 2.4(1) •51(2) C 4g .3694(5) -.3694(5) .0 5(1) References i,b. 8.697(5) X, ell.689(7) X -4.1ft, Rm.. - 3.7*. R.ro, . 6.2%, R... -2.1% [1] F.R. de Boer et al., J. Magn. Magn. Mat 72 (1988) 167 This work has been supported by 'Swiss National Sci- ence Foundation, Nationalfonds zur FOrdcrung der wis- [2] J. Schefer et al, Nucl. Instruments Methods A , senschaftlichen Forschung'. to be published (1990) [3] R.B. Helmholdt and K.H.J. Buschow, J. Less.-Comm. MeL 144 (1988) L33

47 NUCLEAR STRUCTURE OF Na8(AlSiO4)6(OH)2 2(H2O) (8:2:2-SODALITHE) AT 175 AND 10 K

PSI - Universitat Konstanz - ETHZ,

J. Schefer'J. Felsche',P. Siegcrt and M. Wiebcke'

* Solid Stale Physics (F3), Paul Scherrer Insiiiut, CH-S232 Villigen PSI t Universilat Konslanz, Fakultat filr Chemie, D-77S0 Konslanz, R.F.A.

The nuclear structure of 8:2:2 sodalithe has been in- vestigated by means of neutron and X-Ray diffraction at Tlblcl:

295 K and 10 K. A phase transition has been observed StmctuiB pmmacn of Nia(AlSiO()6(OH)j 2(H3O) it 1T5 K. at ISO K (c.f. figure 2) from cubic disordered room tem- Wavelength A-1.7O3(l)A. perature structure to orthorhombic low temperature struc- ture. First assumption of a central hydrogen atom (2a) Spgr. P-43n Cell 1-8.87(5) X has been rejected due to high temperature factors. The Rr.d R^.-.022,R.ro, .-0,016, R ..-.014 model presented in figure 1 and tables 1 and 2 shows K y z n B,.o Al 1/4 0 \H 1 o.8(» a highly disordered structure, yielding e.g. OH-distances «

H2 8(e) .373(1) 373(1) .373(1) 29(2) SI S between the two 02-atoms ('bonding' angle 172(3)°, 02- Tible 2: 02 distance 2.43(4)A, O2-H1 distance 1.19(2)A). Positions Interatomic disuncea and bond inglca. of heavy atoms are in agreement with [1], Observed and Legl Center Leg2 Bond 1 [A] Anglo [") Bond 2 [A] calculated profile intensities are shown in figure 3. The 02 111 O2 1.15(J) 172(3) 1.19(4) HI O2 H2 1.19(2) 107(3) 0.99(4) low temperature measurement shows an orthorhombic dis- HI 02 H2 0.86(3) 145(3) 0.99(4) tortion. Observed neutron diffraction patterns may be ex- AL 1 At 2 Interatomic distince [A] plained on a P222 based model as given in [2]. Due to the O2 O2 0.88(4), 1.33(8), UHp), 2.02(6), 2.311(4) 02 HI 0.86(3), 1.19(2), 1.57(3) high number of refinement parameters, the powder results O2 H2 0.99(4), 2.32(4). 2.880) on the protonated sample cannot locate the hydrogen atoms N« 02 2J6(4), 3.07(2) N. HI 2.42(1), 3.050) accurately enough. The refinement yields lattice constants Na H2 2.78(1), 2.95(1) of 8.908(2)A, b=8.912(2)A and c=8.8020(7)A. In contra- diction to [2] this does finally not exclude a tetragonal unit cell (a=b).

. N«i(AlSiO,MOH), 2

sou

GM

O * 2(10

5(1 HKI 11.(1 Ml '.'Ml

T<-ni|i,.ratiu |K|

Figure 2: Phase transition of the 8:2:2 sodalithe (Na8(AlSiO4)6(OH)2 2(H2O)) at 150 K measured on the 330-reflection with A = 2.34(2)A. Figure 1: Model of complex built by the OH~- and H20-molecules. The frame work atoms are not included.

48 References

[1] I. Hassan and H.D. Grundy, Acta. CrysL C 39 (1983) 3 [2] O.S. Bondareva and Y.U.A. Malinovskii, Sov. Phys. CrysL 28 (1983) 273

Figure 3: Observed and calculated neutron diffraction in- tensities of Na8(AlSiO4)6(OH)2. 2(H2O) at 175 K. CRITICAL DYNAMICS IN NICKEL NEAR Tc

PSI - GRENOBLE - BERLIN - Gif sur Yvette,

P. Boni', B. Faragof, F. Mezei1, and R. PapoularS

* Paul Scheirer Institut, CH-5232 Villigen PSI t Institut Laue-Langevin, 38042 Grenoble Cedex, France j Hahn-Meitner Institut, D-1000 Berlin. Germany § Laboratoire Léon Brillouin, CEN Saclay, F-91191 Gif sur Yvette, France

Although Fe and the europium calcogenides EuO and —i— EuS were believed to be some of the most ideal realisations i i i • -i •- of an isotropic ferromagnet, it became appearent that the • 100073 o dynamics of the spin fluctuations was more complicated ~ ¥ 1.0015 Ni than expected. The linewidth r of the quasielastic neutron o 10031 scattering at Tc is proportional to q" with z = 2.5 over "~ D 10063 more than four decades in energy in Fe [1] and EuO [2] Û 1.013 and the expected crossover to z = 2 at small q, where the ~ O 1.025 dipolar interactions become important, is not observed. The 0 o A non-univcrsial behaviour of the measured linewidth in Fe o made the experimental situation even more confusing. In a recent mode-mode coupling calculation for an iso- fi ___—-~ tropic Heisenberg ferromagnet by Frey and Schwabl [3] I i „_.i... .III. the deviations of the critical dynamics in Fe from the pure isotropic behaviour near Tc was convincingly traced back to the influence of dipolar interactions at small q. More- over their theory explains correctly that z = 2.5 even for Figure 1: Dynamical scaling function for Ni above Tc. 1 « ID for the transverse fluctuations. Later Aberger The solid lines are the theoretical predictions based on the and Folk [4] predicted a shape crossover in the inelas- mode-mode coupling calculations of [3]. The numbers in- tic paramagnetic scattering caused by dipolar interactions dicate the temperature in units of Tc. and explained apparent inconsistencies [2] between neutron scattering data as measured at small q and large q. theory and experiment In order to make a fair comparison Because of the weakness of the dipolar interactions in with theory a more detailed data analysis is required. Ni (çg( ~ ^ïg"s) it is possible to study the isotropic critical behaviour of the Heisenberg Hamiltonian at much smaller q than in the above systems. Therefore we have References used the TOF spectrometer INS and the spin echo spectrom- eter IN 11 to investigate the spin diffusion in Ni at very small [1] F. Mezei, Phys. Rev. Lett. 49, 1096 (1982). q in a forward scattering configuration. The linewidth of the diffuse magnetic scattering was measured at several temper- [2] P. Boni, M. E. Chen, and G. Shirane, Phys. Rev. B 33, atures Tc

versus x — KX/q, where /q is the inverse correlation length. Because of a lack of resolution programs that take into ac- count the strong dispersion of the magnetic scattering the plotted data can only be considered as being preliminary. Obviously f(x) is not a universial function of z alone, be- cause the data points deviate from the Résibois-Piette like behaviour in a systematic way, similar as in Fe. Astonish- ingly the theoretical prediction based on the mode-mode coupling calculations by Frey and Schwabl (solid lines) does not reproduce our experimental Ni data either. At present we do not understand the discrepancies between

50 LONGITUDINAL SPIN FLUCTUATIONS IN Ni BELOW Tc

PSI • GRENOBLE - NEW YORK,

P. Boni", J. L. Martinez', J. M. Tranquada'

* Paul Scherrer Institut, CH-5232 ViUigen PSI t Institut Laue-Langevin, 38042 Grenoble Cfidex, France \ Brookhaven National Laboratory, Upton, New York 11973, USA

Despite of a great deal of theoretical and experimental are proportional to

14.7meV 30'-40'-40'-40'-Ni0.97Tc(1.03 1.03 1.03) 600

longitudinal transverse

a-') Figure 2: Inverse integrated neutron intensity versus q2. The data for the transverse fluctuations is directly propor- tional to q2 and is shifted by /"' = 0.04.

At the smallest momentum transfers investigated we cannot rule out the occurence of inelastic peaks in the lon- gitudinal spectra. Therefore we plan to extend the mea- surements to smaller q and lower T in order to explore the spectral shape and the l/q divergence with high resolution.

0 2 4 References ENERGY (meV) [1] V. G. Vaks, A. I. Larkin, and S. A. Pikin, Soviet Phys. Figure 1: Longitudinal (flipper off) and transverse scatter- JETP 26, 647 (1968). ing (flipper on) at T = 0.97Tc and H = 1.1 kOe. No corrections have been applied to the data. LA is the longi- [2] J. Villain, in Critical Phenomena in Alloys, Magnets tudinal acoustic phonon. and Superconductors, ed. Mills et al., p. 423 (McGraw Hill, New York, 1971). In order to shed more light on the dynamics of the [3] P. W. Mitchell, R. A. Cowley, and R. Pynn, J. Phys. longitudinal fluctuations in isotropic ferromagnets we have C17, L875 (1984). investigated the inelastic neutron scattering from G0Ni at medium wave vector transfers 0.06 < q < 0.18 A"1 be- low Tc • The raw data in Fig. 1 demonstrates that the non-spin flip scattering (flipper off) , i. e. the longitu- dinal scattering, is indeed quasielastic, in contrast to the transverse fluctuations (flipper on). The spin wave energies

51 LONGITUDINAL SPIN FLUCTUATIONS IN THE DIPOLAR

FERROMAGNET EuS ABOVE Tc

PSI - HAMBURG - GRENOBLE,

P. Boni",, D. Gorlitzt, J. Router', J. L. Martinez'

* Paul Scherrer Institut, CH-S232 VUligen PSI t InsUtut fiir Angewandte Physik, Universita't Hamburg, D-2000 Hamburg, Deutschland \ Institut Lauc-Langcvin, 38042 Grenoble Cddex, France

According to dynamical scaling theory of the critical fluctuations in isotropic ferromagneis the relaxation rate is given by

T = */(«,/«)«", longitudinal where

52 LOW TEMPERATURE STATE OF UCu5

PSI - ETHZ,

P. B6ni", P. Fischer', H. R. Oil1

* Paul Scherrer Institut, CH-5232 Villigen PSI t Labor fiir Neutronenstreuung ETHZ, CH-5232 Villigen PSI X Laboratorium for Festkorperphysik ETH, CH-8093 Zurich

orders antiferromagnetically at 15 K and under- lion. In particular the antiferromagnetic order persists down goes another phase transition near 1 K, The latter phase to the lowest temperatures and the magnetic moment does transition opens gaps in the excitation spectrum of the heavy not change. The Cu(200) and the UCuB (333)/(511) peaks electrons and is not understood yet [1]. Therefore we have seem to increase slightly, possibly because of nuclear ef- investigated the nuclear and magnetic structure of UCu5 by fects. Since the pure Cu peak increases loo, the increase in means of neutron diffraction at the DMC spectrometer at the UCu5 (333)/(511) peak with decreasing temperature is the reactor Saphir. not related to a phase transition. All Cu and UCus peaks are observable, with the exception of the very weak (442)/(600) and the (640) reflections of UCus. A detailed analysis of *)000 the magnetic peaks should yield the magnetic form factor ofU.

3)000 10000 References 13000 [1] H. R. Ott, H. Rudigier, E. Felder, Z. Fisk, and B. Bat- 10000 Uogg, Phys. Rev. Lett. 55.1595 (1985). [2] A. Murasik, S. Ligenza, and A. Zygmunt, phys. staL sol. (a) 23, K163 (1974).

Figure 1: Diffraction spectrum near 10 mK

TO. 00 60.00

Figure 2: Difference spectrum 1(10 mK) -1(1.34 K)

The UCu5 sample was mounted on the cold finger of a dilution refrigerator. First we have measured diffraction patterns at 1.34 K over an angular range 3° < IB < 140° and confirmed the known crystal structure and the oc- curence of antiferromagnetic ordering below 15 K [2]. Then we cooled the sample to approximately 10 mK and repeated the measurements (Fig. 1). In Fig. 2 we show a differ- ence scan over an angular range of 80°. There is wether an indication for a structural nor a magnetic phase trans i- Cryogenic Detectors (3104)

PHONON DETECTION IN SINGLE CRYSTALLINE SILICON WITH SUPERCONDUCTING TUNNELING JUNCTIONS

Paul Scherrer Institut, CH - 5232 Villigen PSI

W. Roihmund, C.W. Hagen, A. Zchnder

ABSTRACT irradiated at the front or the back side. The operating tem- perature was between 0.4 K and 1.0 K. The measurements Recent experimental results on phonon detection with SnA were carried out in vacuum, unless stated otherwise. The SnOz/Sn superconducting tunneling junctions (STJ) are re- signals of each junction were measured independently with ported. Phonons are generated in a single-crystalline Si sub- two charge-sensitive preamplifiers. Only correlated signals strate by means of a-radiau'on. Two STJ's, evaporated on within a time window of 5/JS between the two junctions top of the substrate, are used as detectors. At low tempera- were accepted. Pulse height and rise time of each signal tures (T < 0.9K) a strong correlation is found between the were measured as well as the time difference between the energies deposited in both junctions. Marked differences two correlated pulses. Furthermore, the rate of correlated are observed between frontside and backside irradiation of events was determined and compared to the total rate of the substrates. Phonon focusing, due to the anisotropic elas- correlated and uncorrelated events. Calibration was done tic constants of Si, is held responsible for the observed en- by applying a test pulse to each preamplifier, which could ergy correlations. be varied in amplitude and rise time. More than 20 runs with 13 different STJ pairs were performed.

INTRODUCTION RESULTS AND DISCUSSION

Superconducting tunneling junctions (STJ) are powerful de- A typical energy correlation spectrum, measured at a tem- tectors for particles and ionizing radiation. The quasiparti- perature of 0.S K, is shown in fig. 2a. The energies are cle excitations of a superconductor are separated from the calculated conservatively, assuming that a phonon energy superconducting ground state by an energy gap of the order of 2A=1.2 meV is needed for each Cooper pair to break up. of 1 meV, which is three orders of magnitude smaller than From fig. 2a it is seen that for each event detected in STJ 1 the gap of a semiconductor. As the Debye energy is consid- coincidental events of four distinct energies are detected in erably larger than the superconducting energy gap, phonons STJ 2, and vice versa. The number of events detected by of energy larger than 2A are capable of breaking Cooper STJ1 are plotted versus energy in fig. 2b. At low energies pairs and, due to their fast pair breaking time1), produce a a threshold is seen which is above the electronic threshold. signal in a STJ detector. Good energy resolution for X-rays This can be ascribed to phonons which are thermalized be- from a 55Fe source has already been achieved with this kind low 2A before hitting the junctions. For some substrates of detectors 2i3'4). We present here a study of the propa- a strong temperature dependence of the threshold energy gation of phonons, generated by a-particle absorption, in was observed. Fig. 2c shows an energy correlation plot at single crystalline Si substrates. a temperature of 0.9 K for the sample of fig.2a. The low energy pulses corresponding to a location of absorption far away from the junctions are now absent, as can be seen EXPERIMENTAL SETUP more clearly in fig.2d. The coincidence rate for 0.S K and 0.9 K was 370 s"1 and 20 s"1, respectively. As the coin- Figure 1 shows the experimental setup for our measure- cidence rates are small the contribution of uncorrelated co- 5) ments. Two Sn/SnOz/Sn STJ's were evaporated 100 /jin incidental events can be safely neglected. Within ~ 1 ns apart onto the polished (100) surface of a silicon substrate the energy of an a-particle is converted into longitudinal (thickness 330 /im). The backside of the substrate was un- and transverse acoustic phonons. These are assumed to be polished. The junctions were aligned with one of the main isotropically distributed in momentum space. In an elasti- crystal axes. The whole substrate (lOx 13 mm3) was irradi- cally isotropic solid the group velocity of the phonons is ated with 5.5MeV o-particles from a 2/*Ci 24lAm-source. parallel to the phase velocity, which means that in veloc- The average penetration depth of the a-particles in Si is 12 ity space the phonons are isotropically distributed as well. /im . Three different substrate purities (20 ficm, 500 (tan In that case one would not expect any correlation between and 5000 ficm) were investigated and the substrates were the energies Et and E2 detected in the STJ's. In the ab-

55 sence of scattering, an energy scatter plot like fig. 2 would 9) that scattered phonons, too, can retain a highly directed simply show a wedge shape with boundaries E2=a Ej and flux. This means thai the focusing pattern will be largely E:,=Ei/a, 0, surface phonons in Ge are focused in other directions than bulk phonons. 4) W. Rothmund and A. Zehnder, in Low Temperature Using the computer codes of Camley et al. 8), the focusing Detectors for Neutrinos and Dark Matter, ed. by directions for surface waves on Si were calculated, but did L. Gonzales-Mestres and D. Perret-Gallix, Editions not lead to a satisfactory agreement with the experiments. Frontieres, France, 217(1988) To investigate surface effects three STJ's were evaporated 5) L.V. Keldysh and N.N. Sibeldin, in Non Equilibrium on a single substrate. A scratch (SO /an wide, S /im deep) in the substrate between STJ1 and STJ2 was expected to Phonons in Nonmetallic Crystals, edited by W. Eisen- suppress signals from surface phonons and bulk phonons menger and A.A. Kaplyanskii, Elseviers Science Pub- impinging directly on both junctions. The coincidental sig- lishers B.V., 508(1986) nals in STJ1 and STJ2 were compared to those of STJ2 6) B. Taylor, HJ. Maris and C. Elbaum, Phys. Rev. and STJ3, for frontside irradiation. No marked differences Lett. 23,416(1969) were observed, neither in the energy correlation plots, nor in the coincidence rates (~ 350 s"1). This result rules out 7) G.A. Northrop and J.P.Wolfe, Phys. Rev. §22,6196 the possible involvement of surface phonons, but it strongly (1980) suggests the occurrence of boundary reflections. Additional support for this suggestion is obtained from measurements 8) R.E. Camley and A.A. Maradudin, Phys. Rev. B27, on substrates covered with a superfluid 4He film (~ 10A 1959 (1983) thickness). This results in a drastic decrease of the signal 9) J.A. Shields, J.P. Wolfe and S. Tamura, Z. Phys. amplitude and the coincidence rate (~ 10 s"1). Figure 4 B76.295 (1989) shows the effect of helium film coverage on the substrate of fig. 3, for front- (fig. 4a) and backside (fig. 4b) irra- diation. As superfluid helium is known to act as a phonon sink, a fair amount of phonons will leave the substrate in- stead of being reflected at the surface. This leads to the observed decrease of the signal amplitudes and accordingly to a down-scaling of the detected energies, as is clearly seen in fig. 4. Recently it was shown by Shields el al.

56 :ioo>

Figure 1: Schematic drawing of the two superconducting tunneling junctions evaporated on top of a Si substrate. The shaded areas are the contact pads.

a) b) 1

400

\ 1 £200 A u

fc o d) rr

y £0< NUM B

20

? • i • • 0 0 1 2 0 1 2 ENERGY STJ1 (keV) ENERGY STJKkeV)

Figure 2: Typical energy correlation plots at a) T=0.5 K and c) T=0.9 K. A clear temperature dependent threshold is observed which is better seen in the 'Number of counts' vs. 'Energy STJl' plots: b) T-0.5 K and d) T=0.9 K.

0 2 4 6 8 0 1 2 ENERGY STJ1 (keV) ENERGY STJl (keV)

Figure 3: Typical energy correlation plots for frontside (3a) and backside (3b) irradiation. i. a) b) _. 8 - •#•

12 f - i' CM —> to >- A 1 -

2 -1 ENERG Y «

• i i i i i i i . ***. i i 0 2 A 6 8 (3 1 2 ENERGY STJ1 (kcV) ENERGY STJKkcV)

Figure 4: Energy correlation plots obtained on the substrate of Fig. 3, covered with a superfluid helium film for frontside (4a) and backside (4b) irradiation. HIGH-Tc SUPERCONDUCTING FILMS FOR PARTICLE DETECTORS

PSI - Liechtenstein - ETHZ,

C.W. Hagen", M. Scherschel1, A. Zehnder*, S. Zhao*

* Paul Scherrer Institut, CH-5232 ViUigen PSI t Balzers Lid., FL-9496 Balzers, Liechtenstein t Laboratorium fiir FestkOiperphysik, ETH-HOnggerberg, CH-8093 Zurich, Switzerland

We report on the deposition of high-Tc superconducting thin films of YBa2Cu3O7_ x by means of laser ablation. The films were patterned using conventional photolithographic techniques. The long term aim of the present study is the development of superconducting strip detectors for panicle identification. INTRODUCTION '— 0,-Mut In the fields of astrophysics and high-energy physics there is a still growing need for high-resolution detection of ra- diation and particles. Superconductors are very promising candidates for the use as detector materials because of their smaller energy gap (~ 1 meV) compared to the gap in semi- conductors ( ~ 1 eV). Conventional superconductors have been used successfully for X-ray and a-particle detection IbHl [1], either in the form of superconducting tunneling junc- tions or in the form of superconducting thin strips. Common Figure 1: Schematic setup of the laser deposition system. requirement for the proper operation of these detectors is the very low operating temperature ( < 1 K ). The discov- ery of high-Tc superconductivity offers the possibility of epitaxial growth of the films. The temperature was mon- developing detectors which operate at higher temperatures itored by a thermocouple mounted inside the heater. At (e.g. 77 K). The purpose of the present study is to develop the maximum attainable temperature of 1050°C the sub- high-Tc superconducting deteciors. This requires first the strate temperature was measured to be 3OO-35O°C lower manufacturing of high-Tc superconducting films, granular than the temperature of the heater. The distance between ones as well as epitaxial ones depending on the application the target and the substrate was 3 cm. During the depo- of the detector. The subject of this paper is the preparation sition process a flowing oxygen stream was directed onto of high-T,. films by means of laser ablation. the substrate. As the oxygen pressure was measured at a distance of 30 cm from the oxygen nozzle (see fig. 1) the FILM DEPOSITION real pressure at the substrate is estimated to be one order of magnitude higher. After the deposition the oxygen pressure Several techniques like electron beam evaporation, sputter- in the chamber was increased to 80 mbar and subsequently ing or laser ablation, have been used to grow high-Tc super- the heater power was switched off. The substrates cooled conducting films. The first report on high-Tc films made by down to 200°C in about 7 min. At this temperature the means of excimer laser ablation was by Inametal. [2]. This chamber was vented with air assuming that oxygen diffu- relatively low-cost and fast technique yields highly textured sion at this temperature is negligible. Then the substrates films with sharp resistive transitions and high critical cur- were removed from the chamber without any postannealing rent densities. We used laser ablation for the deposition of process. The resistance was determined by standard four YBa2Cu3O7_r on substrates of single crystalline SrTiO3. probe measurements. The electrical contacts were made The schematic diagram of the laser deposition system is with silver paint. The thickness of the films was measured shown in fig. 1 The beam of a high-power, pulsed excimer by means of a mechanical stylus. laser was focused on a YBa2Cu3O7_z target which was mounted on a rotary feedthrough in a high vacuum cham- ber. The output power of the laser was 100 mj/pulse at a RESULTS wavelength of 308 nm (XeCl gasfilling). Repetition rates Of all constituents in the laser-generated plume oxygen has between 5Hz and 50 Hz ware used and the laser tluence 2 the lowest sticking probability to the substrate. To obtain on the target was 3.5 J/cm . Each laser shot creates a for- the right composition of the film it is therefore necessary ward oriented jet of evaporated material (the plume) which to introduce oxygen in the vacuum chamber during depo- condenses on the substrate that was mounted on a heater sition. Furthermore the oxygen atmosphere contributes to just opposite the target The substrates used in our exper- collisional cooling of the atoms and molecules in the plume. iments were (lOO)-oriented SrTiOa plates. The substrates Actually the brightness of the plume is influenced signif- have to be heated during the deposition process to ensure icantly by the oxygen pressure, as was also observed by

59 tional photolithographic processing and etching in a di- lute acetic acid solution. This patterning method has been

successful in producing YBa2Cu3O7_r strips with widths down to 3fim [6]. The films were spincoated with Ship- ley AZ-135OJ positive resist (spin velocity 6000 rpm) and baked out for 15 min at 80°C. After exposure (typically „ 0.4 - 15 sec) the photoresist was developed in Shipley Micro- posit developer. Subsequently the films were etched in a solution of 1 part acetic acid in 120 parts water. The re- maining photoresist was removed in acetone. The strips obtained in this way showed well-defined edges and no de-

crease of Tc compared to the original films. For both strips and films critical current densities of ~ 103 A/cm2 at 77 K and ~ 10s A/cm3 at 4.2 K were obtained from preliminary transport current measurements. An applied magnetic field of 30 mT, perpendicular to the film, had almost no effect 0.0 on the critical current density. This indicates that the films 80 90 100 are topologically closed and that the current is not limited TEMPERATURE [K] by weak links between grains.

Figure 2: Normalized resistance versus temperature ob- SUMMARY tained on a 500 nm thick film of YBa2Cu3O7_I, deposited Superconducting films and thin strips of YBa2Cu3O7_j. on a single crystalline substrate of SrTiO by means of laser 3 have been made by means of laser ablation. Although the ablation. films have a high Tc of 90 K the resistive transitions are still rather broad. The critical current densility is two or- Zheng et al. [3]. In the pressure range 5.10"3- 5.10"2 ders of magnitude lower than the best reported values for mbar the bright part of the plume was observed to have epitaxial films. More work has to be done to optimize the a length of 3.S cm, although the total plume extended to deposition parameters and to produce strips which can be 7.S cm. Outside of this pressure range the plume length used for particle detection. decreased rapidly. The substrate was mounted at a distance of 3 cm from the target, i.e. in the bright, high-density, ACKNOWLEDGEMENT part of the plume. The direction of the plume was found We are very grateful to Dr. F. Kottmann and Dr. T. Gerber to be always perpendicular to the target, independent of the for making their lasers available to us. angle of incidence of the laser beam. Continuous rotation of the target during the deposition is imperative in order to prevent the laser beam of burning holes in the target, out of References which almost no material can escape. In the range of 1-4 J/crrr the laser fluence did not affect the length of the bright [1] A. Zehnder, Proceedings of the International Sympo- region of the plume. However, as was shown by Roas et al. sium on Fundamental Symmetries in Nuclei and Par- [4], the composition of (he deposited film does depend on ticles, 1989, to be published by World Scientific Pub- the laser fluence. In all our experiments the laser fluence lishing Co. 2 was 3.5 J/cm , for which the right composition should be [2] A. Inam, M.S. Hegde, X.D. Wu, T. Venkatesan, P. Eng- obtained. The quality of the deposited films depends rather land, P.F. Miceli, E.W. Chase, C.C. Chang, J.M. Teras- strongly on the oxygen pressure after deposition and during con and J.B. Wachtman, Appl. Phys. Lett. 53 (1988) the cooling of the film. At an estimated substrate tempera- 908 ture of 670°C and oxygen pressure of 5.10"3 mbar during [3] J.P. Zheng, Q.Y. Ying, S. Watanachchi, Z.Q. Huang, the deposition it was found that low oxygen pressures (e.g. D.T. Shaw and H.S. Kwok, Appl. Phys. Lett. 54 (1989) 8 mbar) during the cooldown resulted in a low onset temper- 954 ature TC]0 (80 K) and a rather large transition width (20 K). At pressures of several tens of millibars (typically 80 mbar) [4] B. Roas, L.Schultz and G. Endues, J. Less-Common Metals 151 (1989) 413 7; 0 was 90 K with a transition width of 8 K. In fig. 2 a typical resistive transition is shown. The large width of the [5] J. FrOhlingsdorf, W. Zander and B. Stritzker, 1. Less- transition is probably due to the low substrate temperature. Common Metals 151 (1989) 407 Frohlingsdorf ct al. [5] showed that the transition width [6] I. Shih and C.X. Qiu, Appl. Phys. Lett. 52 (1988) 1523 depends strongly on the substrate temperature. Lower sub- strate temperatures resulted in non-superconducting films, i.e. al these temperatures the transition from the tetragonal to the orlhorhombic phase did not occur. The preparation of films at higher temperatures is now in progress.

FILMPATTERNING The best films were used for patterning. Snips of widths ranging from 5/jm to 40/imwere made by using conven-

60 Accelerator Mass Spectrometry ÂMS (3110)

THE ACCELERATOR MASS SPECTROMETRY FACILITY PSI - ETH

PSI - ETHZ,

G. Bonani", R. Finkel", U. Fischer', HJ. Hofmann*. W. Neumann*, T. Niklaus*, M. Suter', H.A. SynaT, W. Wölfli\ U. Zoppi"

* Institut fur Mittelenergiephysik, ETH-Hönggerberg, CH - 8093 Zürich t Paul Seltener Institut, c/o ETH-Hönggerberg, CH - 8093 Zürich t on leave from Lawrence Livermore National Laboratory, 94SS0 Livermore, CA, USA

The 6 MV tandem accelerator at the ETH-Hönggerberg, capability of monitoring vacuum conditions and of control- which is operated by PSI in collaboration with the ETH in ling pump operation. The pumping system and associated Zurich has mainly been used for Accelerator Mass Spcc- equipment was installed during the shut-down and mainte- uometry (AMS), with additional applications in materials nance period in October 1989 and has been operating for science. A summary of the operation in 1989 is given in several months without any failures. Table I. The number of samples listed includes standard and The new stripper enables us to operate under conditions blank samples. which are optimum for production of carbon ions in the New Developments in AMS 4+ state, i.e. with sufficient Ar density in the gas strip- Keeping pace with the rapidly growing demands for per to reach charge-state equilibrium at energies between AMS data, and with the world wide effort to improve AMS S.2 to 6 MeV. Under these conditions the efficiency of techniques, requires a continuous effort to improve our Coproduction is more than 70%. In the first experiments AMS facility. We have, therefore, implemented an exten- an overall transmission (high energy Faraday cup relative sive long-term program to study systematically the funda- to low energy Faraday cup) of more than 50% was attained. mental physical processes involved in AMS measurements. For this is an improvement of almost a Based on the knowledge gained from this work, we are op- factor of two compared to the previous performance and al- timizing the individual components of our facility in order lows attaining a larger through-put or higher accuracy with 14 to increase the efficiency, sensitivity and precision of our the same beam time. For radioisotopes other than C, foil AMS measurements. Higher precision is required primar- strippers are used. With the new equipment and thinner C- ily by 14C studies, while the other long-lived radionuclides foils (3 /ig) the transmission for Be is enhanced by a factor primarily make demands on high sensitivity. of 3. For AI and CI and improvement of a factor of 2 has been reached. Based on detailed studies of the physics of the stripping process in MeV ions we designed a new stripper arrange- In many cases isobaric interferences limit the sensitivity ment for the terminal of the accelerator. The primary im- with which an isotope can be determined. Normally, dE/dx provements were to move the foil stripper behind the gas discrimination is used for separating isobars in the energy stripper (instead of in front of it) and to equip the terminal range accessed by our EN-tandem accelerator. Based on with a turbo-molecular pump for [«circulating the stripper knowledge of stopping power, the length of the AE elec- gas[l][2]. Rearranging the foil and gas strippers enabled trodes has been optimized, especially for the separation of us to reduce losses due to angular straggling produced in 36C1 from 36S. The sulfur rate can now be suppressed by the ion beam as it passes through the stripper foil. The about 4 orders of magnitude at an energy of 48 MeV. For turbo-molecular pump allows a higher gas density to be samples having less than 2 ppm S, a sensitivity of a few used in the stripper at the same time that vacuum condi- times 1O-15(36CI/C1) is possible. The limit is predomi- tions are improved in the acceleration tubes. This results nantly determined by the natural energy straggling which both in enhanced stripping efficiency and reduced losses is caused by charge-state fluctuations during the slopping due to charge exchange. process. In order to operate the turbo-molecular pump, which is A gas-filled-magnet has been tested as an alternative located in the high voltage terminal, we had to develop spe- isobar separation technique. In this technique the ions arc cial electronics for the 2-phase pump motor. The equipment deflected according to their average charge[3]. We have had to produce the appropriate frequency (600 Hz) from the measured the charge exchange cross sections for Si and Cl single phase generator (440 Hz) and be able to withstand and used these in ray-trace calculations in order to optimize the high pressure of the insulating gas present in the tandem the gas-filled-magnet performance. Test measurements with and the effects of occasional high voltage sparks. An opti- an existing magnet are in progress. Based on this informa- cal link and a microprocessor in the terminal gives us the tion a new magnet arrangement is being designed. This

61 TaWe I Operation of the Tkndera Facility in 1989

Project Hours % Samples AMS: luBe 275.0 13.5 910 »c 759.0 37.2 1228 26 Al 51.5 2.5 114 36Q 121.5 5.9 250 Tests 187.5 9.2 - Subtotal 1394.5 68.3 2492 Materials Science 297.5 14.5 Conditioning, Development 351.0 17.2 - Total 2043.0 100.0

gas filled magnet technique will be superior to the AE-E JUrg Beer of EAWAG we continue to extend the range of method at high count rates in which pulse pile-up effects, sample types for which we can prepare targets and to de- baseline shifts, and incomplete charge collection reduce the crease the amount of target material needed for analysis. resolution of the dE/dx counter below optimum. Such ef- Tests using small diameter sample holders have allowed us fects are important in measurements of 32Si, in which the to decrease the mount of carrier needed for Be analysis interfering isobar, 32S, is the most abundant isotope of sul- by a factor of 5. We have now developed techniques for fur. For the detection of 32Si in natural concentrations a preparing Be targets from meteorites and terrestrial silicates rejection of sulfur to 8 to 10 orders of magnitude is required in addition to the precipitation and ice core work which we even when best possible chemical separation is applied to have undertaken in the past. We have also implemented the targets. techniques for measuring 26A1 in terrestrial quartz and me- A new ion source and associated injection has been teorites. We have identified and remedied several potential built and will be operational soon. This additional injector sources of S contamination in our 36C1 target preparation will significantly enhance the duty cycle of the AMS sys- procedure. By diluting with AgBr, we are now able to tem, since the ion source has the highest failure rate of any analyze smaller 36C1 samples than before. component in the system and requires a significant amount A complete uC-target preparation line, with the capa- of maintenance time. In addition to improving reliability, bility of simultaneously handling 5 samples, has been in- the new injector will also improve performance, since it is stalled. This system uses the Vogel method of catalyzed equipped with an electrostatic 90° deflector, which acts as reduction of CO2. We continue to work on understanding a high resolution energy filter, thus increasing the mass res- the sources of residual 14C background in our system and olution of the following magnetic mass spectrometer. The on devising methods to reduce this background further. new 90° magnet, with a bending radius of 60 cm, will ex- tend the accessible mass range up to the heaviest elements and opens new fields of application with stable and radioac- References tive isotopes. In order to be able to analyze efficiently the data from [1] HJ. Hofmann, G. Bonani, M. Suter, and W. Wolfli, the large numbers of samples we measure, an appropri- Nucl.Instr.and Meth. B29 (1987) 110. ate data handling system was needed. It was decided to [2] M. Suter, J. Beer, D. Billeter, G. Bonani, HJ. Hof- use PC's on a Network with a commercially available data mann, H.A. Synal, and W. Wolfli, Nucl.Instr.and Meth base system. Software has been developed for processing B41 (1989) 734. all the analytical data in a consistent manner. The pro- gram contains procedures for subtracting background based [3] M. Paul, B.G. Glagola, W. Hennig. J.G. Keller, W. on the detector spectrum and/or from blank samples, for Kulschera, Z. Liu, K.E. Rehm, B. Schneck, and R.H. normalization to standards, and for calculation of weighted Siemssen, Nucl.Instr.and Meth. A277 (1989) 418 means of several measurements. For all these procedures it includes automatic error calculations and determination of standard deviations. For carbon, stable isotope ratios are also analyzed and the radiocarbon ages are determined. Sample preparation techniques have significant effects on the performance of AMS. In addition to the chemical reduction of isobaric interferences, which is a primary con- in many sample preparation techniques, other aspects of sample preparation are also important. Target purity and uniformity have important effects on ion current stability and intensity and thus on the accuracy of analyses. In ad- dition, for many applications it is important to be able to analyze the smallest sample possible. Sample preparation techniques, e.g. reducing the amount of carrier needed to prepare a target, can help in this. In collaboration with Dr.

62 DETERMINATION OF CROSS SECTIONS FOR THE PRODUCTION OF 10Be BY HIGH-ENERGY PROTONS

KÖLN - HANNOVER - ETHZ,

B. Dittrich*. U. Herpers*. M. Lupke», R. Michel*. H. J. Hofmann', W. Wölfli',

* AbleUung Nuklearchemie, Universität zu Köln, D - 5000 Köln 41 t Zentraleinrichtung für Strahlenschutz, Universität Hannover, D - 3000 Hannover 1 X Institut fur Miltelenetgiephysik, ETH-Hönggerberg, CH - 8093 Zürich

The knowledge of cross sections of nuclear reactions 10" is important for many fields of science. Particularly, they are needed in astrophysics and meteoritics to describe the interactions of cosmic rays with matter. Galactic and so- lar cosmic rays consist of about 90% protons and 10% -101» alpha-particles [1]. Stable and radioactive nuclides pro- duced by nuclear interactions of cosmic rays with terrestrial and extraterrestrial matter give information about various processes in the solar system. For the interpretation of pro- duction in extraterrestrial matter an exact model is necessary which can be only developed on the basis of accurate cross sections of the entire energy-region of the cosmic rays. For

the galactic protons energies between 500 MeV and lOGeV 3 10 • 10 " 10 ' 10 - are of interest. In cross sections are nec- ENERGY I MeV ) essary to understand nuclear reaction mechanisms and the Fig. 2 differences between spallalion and fragmentation processes. Excitation function for the reaction Fe(p,3pxn/°Be as Especially the production of 1DBe, a spalogenic nuclide in revealed by the cross sections from our work [4] and by meteorites, is of interest for the calculation of the irradiation earlier data (v = [3]; x = [7]; cxi = [8]). ages of extraterrestrial bodies.

V, Mn, Fe, Co, Ni, Cu, Nb, Rh, Zr, Au) were chosen to be of interest for both, for meteoritics and for nuclear physics. a Between the different elements there were high purity Al- B foils in order to avoid cross contamination and at the same time to serve as monitor foils. For each elements foil an in- dividual flux was determined from the nearest Al-monitor. The fluxes were determined on the basis of the cross sec- X tions for the reaction 2TAl(p,3p3n)22Na as recommended by Tobailem and de Lassus St Genies [2]. O(p, Spxn)10Be The 7-measuremenis were supported by automatic sam- ple changes controlled by a personal computer which accu- mulated the data, too. The detector efficiencies were cal- 10 •• 10 ibrated with radionuclide standards ,the accuracies of the ENERGY standards were given between 2 and 4.5%. A detailed dis- Fig. 1 cussion of the errors of cross section determination is given Excitation function for the reaction 0(p,5pxn)10Be as in [3]. revealed by the cross sections from our work [4] and by After cooling of the irradiated foils the chemical sepa- earlier data (y = [3]; x = [5]; » = [6]). rations and preparations of samples for the accelerator mass spectrometry were done. Thereby it was necessary to sepa- The aim of the irradiations carried out is the experi- rate several long-lived radionuclides from one foil. Besides mental determination of a large number of product nuclides the 10Be separation samples for the determination of 26A1, from target elements with masses between 16 and 196. The 41Ca and 53Mn were prepared, which still wait for AMS- study comprises the measurement of radionuclides by y- measurement. The chemical separations were done by us- spectrometry and accelerator mass spectromctry as well as ing ion exchange, precipitating hydroxides and in case of of stable rare gas isotopes by conventional mass spectrome- iron, extraction methods. At the end of the analysis the try. The irradiations were performed with 800 MeV protons Be-fraction is precipitated as hydroxide, washed with bi- at Los Alamos National Laboratory (LANL, USA) and with distilled water and glowed to BeO. The BcO powder was 1200 and 2600 MeV protons at Laboratoire Nationale Sat- mixed with high purity copper powder and pressed in sam- urne (LNS, F). The target elements (O, Mg, Al, Si, Ca, Ti, ple holders for the AMS measurement

63 So we could provide cross sections for the production of 10Be from the target elements oxygen, magnesium, silicon, aluminum and iron until now for proton energies of 800, 1200 and 2600 MeV. Several discrepancies in the shapes of the excitation functions could be clarified and gaps could be filled. The cross sections for the production of 10Be show in general the same trend as the excitation function for the production of 7Be. For the reactions investigated 10Be seems to be a pure fragmentation product, but an exact model for the production is not developed yet A detailed description and discussion is given in [4]. Some results of our work [4] are compared to the data of other authors in Fig. 1 and Fig. 2. This work was supported by the Deutsche Forschungs- gemeinschaft.

References

[1] Alsmiller Jr., R.G. et al.; ORNL-RSIC-35 (1972). [2] Tobailem, J., de Lassus SLGenies, C.H.; Ad- ditif No.2 a la CEA-N-1466(1)(1975),CEA-N- 1466(4)(1977),CEA-N-1466(5)(1981). [3] Michel, R. et al.; Analyst 114 (1989) 287-293. [4] Dittrich, B. et al.; Determination of Cross Sections for the Production of 7Be, l0Be and 22Na by High Energy Protons, Radiochim. Acta, accepted for publication. [5] Amin, B.S. et al.; NucLPhys. A195 (1972) 311-320. [6] Raisbeck, CM. et al.; 15th Intl. Cosmic Ray Conf., Plovdiv, vol. 2 (1977) 203-207. [7] Theis, St.; Thesis, UnivcrsiUU zu KOln (1986). [8] Honda, M., Lai, D.; NucLPhys. 51 (1964) 363-368.

64 ATMOSPHERIC TRANSPORT OF BOMB-PRODUCED 36C1

PSl - ETHZ - BERN,

H.-A. Synal*. J. Beer', G. Bonani", M. Suter', W. Wölfli"

* Institut für Miuelenergiephysik, ETH-Hönggerbcrg, CH - 8093 Zürich t Physics Institute, University of Bem, CH - 3012 Bern present address: EAWAG, CH - 8600 Dübendorf t Paul Scherrer Institut, e/o ETH-Hönggerberg, CH - 8093 Zürich

10 36 36 Radioisotopes, such as Be

*SI input functions Bl and B3. For the purpose of this model cosmogenic production in the troposphere was neglected. Moreover, a steady state system is assumed so that all air N4 troposphere transfers from one box to another must be compensated by a reverse air flow. It is assumed that there is no connection between local and global tropospheric boxes. This assump- tion is reasonable because of the long transport times from the test sites to Greenland and the short tropospheric res- idence times of 36C1. For this 4-box model a set of four apposition coupled linear differential equation can be derived. Due to the complex function Q(t) giving the bomb produced 36CI input to Nl, this system is solved numerically using Fig. 1 Runge-Kutta formalism. 4-box exchange model to describe atmospheric trans- 36 port of Ci. For the model calculation the ratio of the sizes of the

65 D D • measured fallout-data and 1974 at Mururoa. These tests also belong to class 2. simulated fallout-data All atmospheric test explosions over land surface belong to a atmospheric teats group three. During the time of high 36C1 release into the atmosphere in the fifties and early sixties the small con- tribution from land-based tests is not visible, despite the high total yield of test explosions over land surface. But in the late seventies, when atmospheric 36C1 content ap- proached natural levels, tests from this class gave a visible contribution. At least seven Chinese tests at Lop Nor have to be considered. All subsurface nuclear tests are grouped into the fourth class. No 36CI release to the atmosphere is expected from those tests. To reproduce the experimental data an assumption con- cerning the amount of 30Cl released from all known lest 1940 1950 1000 1970 1080 1980 explosions had to be made. Overall about 70 kg 36C1 have been considered, with maximum amounts of 15,18 and 20 36 Fig. 2 kg C1 in 1954, 1956 and 1958. With these input val- Comparison between measured fallout data and model ues, Q(t), model calculations were carried cut to obtain 36 calculations. C1 fallout rates. The results are shown in Fig. 2. To re- produce the clear structure on the descending edge of the measured fallout curve, only small 36C1 contribution (sslO stratospheric box to tropospheric box is set as 1 : 4, similar to 500 limes smaller than at peak maximum) are necessary. to the ratios of air masses actually contained in stratosphere This indicates that atmospheric tests carried out after the and troposphere. The ratio between local and global part of nuclear test ban treaty have to be considered in interpreting 5 the observed fallout pattern. The stratospheric residence the atmosphere is 1 : 10 . Model calculation show that the 36 system is not very sensitive to this parameter. In particular time derived for C1 of about 2 years seems reasonable, the exponential decay of fallout rates is unaffected. It is as- although the steep fluctuations in the observed fallout data sumed that stratospheric air is well mixed. For this reason cannot be reproduced. For that reason this time has to be the time constant which describes the mixing of air between regarded as an upper limit. the local and the global stratospheric box was set to two We would like to thank Prof. H. Oeschger and his co- months. The residence time for 36C1 in the troposphere is workers for providing the ice sample. In addition we are short. For calculation this time was set to two weeks. Since grateful to A. Blinov for his help with sample preparation. this lime is short compared to the stratospheric residence time the fallout pattern is nearly unaffected by changing this parameter. The most sensitive parameter is the strato- References spheric residence time. This parameter is derived from the [1] D. Lai, B. Peters, Handbuch der Physik, Springer Ver- experimental data between 1960 and 1964 which show an lag Berlin, (1967) 551-612. exponential decay of fallout rates. An estimate of 36C1 production in thermonuclear ex- [2] M. Suter, J. Beer, G. Bonani, D. Michel, H. Oeschger, plosions taking place over the ocean can be made, by as- H.-A. Synal, W. Wfilfli, Nucl.Instr.Meth. B29 (1987) suming a total production of 2xlO26 neutrons per mega- 211-215. ton yield[6]. Considering that 50% of these neutrons enter the water where the reaction 35Cl(n, 7)36C1 [3] D. Elmore, L.E. Tubbs, D. Newman, XZ. Ma, R.C. takes place with 32% probability, one gets a total produc- Finkel, K. Nishiizumi, J. Beer, H. Oeschger, M. An- tion of 2 kg 36C1 per megaton yield [3]. This estimate can dree, Nature Vol. 300, No. 5894, (1982) 735-737. 36 only give a rough idea of C1 production in nuclear test [4] H.-A. Synal, J. Beer, G. Bonani, HJ. Hofmann, M. explosions because neutron fluxes from each bomb may Suter, W. Wolfli, Nucl.Instr.Meth. B29 (1987) 146- vary over a wide range depending strongly on the type of 150. bomb. Moreover the abundance of the 35C1 target nuclei may differ by orders of magnitudes depending on whether [5] H.-A. Synal, ETH Thesis, (1989) Nr. 8987. explosions over land or at high altitudes arc considered. For this reason a classification of all known bomb tests into four [6] L. Machta, USAEC, (1963) 369-391. groups has been made. Information on nuclear test explo- [7] I. Zander, R. Araskog, Forsvaret Forskningsanstalt sions are taken from FOA report published by the Research Avdelning, (1973) Report 4. Institute of National Defense, Sweder.[7]. The first group consists of all tests taking place on ships. The highest 36C1 production is expected from those tests. Overall 34 tests of this class have been reported, mainly in 1954, 1956 and 1958. The second class contains all at- mospheric tests which were carried out on small islands. During the time between 1946 and 1962, 105 test explo- sions from the USA and Great Britain in this class are known. After the nuclear test ban treaty of 5.8.1963, about 40 French atmospheric tests were carried out between 1966

66 DETERMINATION OF AVERAGE PARTICLE-SETTLING VELOCITIES USING THE ^Be^Be RATIO

EAWAG - ETHZ - PSI,

J. Beer', E. Wieland", HJ. Hofmann*, M. Suter*. W. Wolflit

* Environmental Physics, Institute for Aquatic Sciences and Water Pollution Control, EAWAG. CH - 8600 Dubendorf t Institut fur Millelcncrgiephysik, ETH-Honggerberg, CH - 8093 Zurich } Paul Scherrer Institut, c/o ETH-Honggerberg, CH - 8093 Zurich

Particle transport plays an important role in the elimi- A significant advantage of Ihe use of the 10Be/7Be ratio nation of pollutants (organic compounds, heavy metals, ra- for the determination of settling velocities is that physical dioactive fallout) from aquatic ecosystems and and in the and chemical processes within the lake do not distinguish budget of nutrients in lakes. The determination of set- between the isotopes and iherefoie do not influence die tling velocities is difficult because they are relatively small i°Be/?Be ratio. (m/day) compared to horizontal flow rates (km/day). As part of a mulii-tracer study of radionuclides in Lake Zurich, the 10Be/7Be ratio has been used for the first time for the determination of settling velocities. Two sediment traps were placed at depths of SO and 130 m in the center of Lake Zurich. Samples were collected at 1 to 2 month intervals and were analyzed in the labora- tory. sloPb,137Cs, and 7Be were determined by gamma spectrometry. In addition, the samples from 1987 were an- alyzed for 1DBe using the ETH/PSI AMS facility. Both beryllium isotopes are continuously produced in the atmo- sphere by spoliation reactions induced by cosmic rays. Al- though the cosmic-ray intensity varies by up to 40%, the production ratio 10Be/7Be is practically constant and has a well-determined value of 0.3 to 0.5. Since the half-life of 7Be has the relatively short value of 53.2 days while that of 10Be is 1.5 x 106 years, the "Be^Be ratio increases continuously with time because of radioactive decay.

10 7 Be/ Be = Ao (e

10Be and 7Be attach rather quickly to atmospheric aerosols. They are carried to the earth's surface by pre- cipitation with a mean atmospheric residence time of about one year. The behavior of panicles in Lake Zurich is illustrated in the Figure 1. The particle flux, in g/m2/day, is shown for sediment trap A (50 m) and B (130 m). The generally higher flux in summer is Ihe result of a higher bioproduc- livity in summer. Trap B has on average a 20% higher particle flux than trap A. This is Ihe result of a density cur- rent which flows along the edge of the lake basin toward the deepest point in the lake. 7Be and 10Be show the same increased flux in the summer as does the particle flux (Fig. 200 300 400 2 and 3). In addition, the 10Be flux in trap B is higher than DaysIn1987 in trap A. Because of radioactive decay, 7Be on ihe other Fig. 1 to Fig. 3 hand is generally lower in trap B than in trap A. A compar- 7 10 ison of the 10Be/7Be ratio (Fig. 4) reveals a consistently Fluxes of particles, Be, and Be in Lake Zurich For the higher value in trap B. The interpretation of this ratio as year 1987. a settling velocity is shown in Fig. 5. The mean settling Fig. 4 and Fig. 5 velocity of particles in Lake Zurich is about 2 m/day. lofle/7Be ratio and corresponding apparent settling ve- locities. ISOTOPIC COMPOSITION OF ATMOSPHERIC METHANE

Heidelberg - ETHZ - PSI,

Rainer Bösinger*. Ingeborg Levin*, Georges Bonani*, Martin Suter*, Willy Wölfflt

* Institut für Umweltphysik, Universität Heidelberg, Im Neuenheimer Feld 366, D - 6900 Heidelberg t Institut für Mittelenergiephysik, ETH-Hönggerberg, CH - 8093 Zürich t Paul Scheuer Institut, c/o ETH-Hönggerberg, CH - 8093 Zürich

Methane is a strong infrared absorber that directly and 1 I ! I 1 T ' I indirectly affects atmospheric temperature. It also influ- ences tropospheric and stratospheric ozone [S], and is a major source of stratospheric water [3]. The atmospheric concentration of methane increased from about 0.7 ppmv to about 1.7 ppmv within the last ISO years with a recent increase of about 1% per year [4]. The atmospheric cycle of methane is still relatively poorly known, especially the £ magnitude and trend of individual sources. Atmospheric methane is produced by bacteria in wet environments (wet- 1 lands, tundra, rice fields), by ruminants, and from gas and coal mining ('fossil' methane). Destruction of methane occurs mainly through reaction with OH radicals in the 1987 1988 1089 troposphere. For the investigation of the global budget June 87 - June 89 Irnuntn^,] isotope analyses of methane supply additional independent information.The HC content of atmospheric methane is thus Fig. 2 14 C in atmospheric methane at Schauinsland (*) and particularly sensitive to the relative contribution of the fos- 14 sil methane. Jungfraujoch (0). The C level is significantly higher over the European continent than at the Atlantic site Izana (straight line from Fig.l) due to the reactor 14CH4 "° rrTT" 1TTTTTT7 "1 'VI 1 I ' source in Europe.

CO2 are removed by silica gel and molecular sieve. Un- der these conditions CH4 is quantitatively adsorbed on the charcoal while most of the air is pumped off. Desorption of CH4 from the charcoal is achieved by flushing with helium at 300 °C. After separation from remaining contaminants like CO, CO2, and hydrocarbons by gas chromatography with pure synthetic air as carrier gas, the methane frac- tion is trapped in the sampling loop of a combustion cy- cle. Here CH4 is oxidized over platinum at 600 °C resp. 1987 900 °C. The resulting CO2 and H2O are collected in cool- June 87 .lune B9 [months] ing traps at -78 °C and -196 °C. The overall yield for Fig. 1 atmospheric samples is (90 ± 9)%. The recovered H O is 14O

68 References [1] BOsinger R., Isotopenmessungen an almospharischem und quellnahem Methan, doctoral thesis, University of Heidelberg, 1990 A [2] Bonani G., Beer J., Hofmann H., Synal H., Suter M., WOlfli W., Pfleiderer C, Kromcr B., Junghans C, and Miinnich K.O., Fracn'onation, precision and accuracy in 14C and 13C measurements, Nucl. Instr. & Meth. 9 '"• I in Phys. Res., B29, 87-90,1987

[3] Ehhalt D., On the consequence of a tropospheric CH4 1988 1989 increase to the exosphcric density, J. Geophys. Res., 91, D2, 2843, 1986 Fig. 3 [4] Ehhalt D., How has the atmospheric concentration of 14C in atmospheric methane in Heidelberg. The level is CH changed?, in: The Changing Atmosphere, Row- generally higher than at the At/antic site /zana (straight 4 land F., and Isaksen 1. (eds.), pp. 25-32,1988 fine from Fig.l). ^CH* peaks up to 600 pM could be identified as direct contaminations from the nearby [5] Isaksen I., Is the oxidizing capacity of the atmosphere plants Biblis and Philippsburg, (The changing?, in: The Changing Atmosphere, Rowland crosses represent 24 hour samples and the histogram F., and Isaksen I. (eds.), pp. 141-157, 1988 are weekly averages.) [6] Kramer B., Pfleidercr C, Schlosser P., Levin I., Miin- nich K.O., Bonani G., Suter M., and Wolfli W., AMS 14C measurement of small volume oceanic water sam- ples: Experimental procedure and comparison with Forest (1205 m asl, 48°N 8°E) and Jungfraujoch, Swiss low-level counting technique, Nucl. Instr. & Meth. in Alps (3454 m asl, 47°N 8°E) are significantly influenced Phys. Res., B29, 302-305, 1987 by the predominantly continental methane sources (Fig. 1 [7] Kunz C, Carbon-14 discharge at three light water re- and Fig. 2). The data at these stations if compared to 'clean actors. Health Physics, 49, 1, 25-35,1985 air' at Izaila (2376 m asl, 28°N 16°W) show a mean con- centration offset in 1987-89 of (70± 10) ppbv caused by the continental CH4 sources (recent biogenic and fossil fuel). Although a considerable 14C depletion over the continent 14 due to C free fossil fuel CH4 sources had been expected 14 the CH4 level at Schauinsland and Jungfraujoch has been observed to be (4.5 ± 1.5) pM higher if compared to mar- itime 'clean air' over the Atlantic (Izaila). This has been 14 attributed to CH4 emissions from European pressurized water reactors (PWR).

14 The atmospheric CH4 data from Heidelberg (110 m 14 asl, 49°N 8°E, Fig.3) confirm this finding: CH4 con- centrations in Heidelberg reach up to more than 600 pM, 14 about six times the maritime CH4 level. The nearby nu- clear power plants Biblis (35 km north west of Heidelberg) and Philippsburg (25 km south west of Heidelberg) could be identified as the sources of this contamination. With an atmospheric dispersion estimate we could calculate a mean 14 11 CH4 emission rate of (4.0 ± 1.7) • 10 Bq/(GWe yr). This is in good agreement with direct measurements of the off-gas discharge of two PWR's in USA resulting in 3.5 10n Boy(GW(.yr) [7]. The sum of all European PWR emissions could be estimated to (2.3 ±1.0) 1013 Bq/yr 14 in 1988. This shows that the CH4 emissions of PWR's I4 are already an important CH4 source term not only in 14 Europe but also for the global CH4 budget. Due to this 'contamination' the identification of fossil methane sources, particularly in an industrialized area like the Upper Rhine 14 Valley, is no longer unambiguous by CH4 measurements. 14 However, the nuclear power plant CH4 source — up to now restricted only to the Northern Hemisphere — pro- 14 vides an unique tracer for the global CH4 modelling in the atmosphere.

69 THIN LAYER ACTIVATION OF HIP JOINT PROSTHESES FOR TRIBOLOGICAL TESTS

SULZER - ETHZ,

P. Heimgartner*. W. Neumannt, R.M. Streicher', W. Wolfflt

* Gebr. Sulzer AG, 0811, CH - 8401 Winterthur t Institut fiir Mittelenergiephysik, ETH-HOnggcrberg, CH - 8093 Zurich

Within a program to investigate the benefits of metal- ples were measured. The accuracy of the measured depth metal hip joint prostheses made from CoCrMo forged alloy profiles amounts to a very few percent Precise relative Protasul-21WF, thin layer activation (TLA) has been ap- excitation functions for the reactions 59Co(d,p)60Co and plied to a wear study of artificial hip joints. 100Mo(of,n)103Ru computed from these measurements are Hip joint prostheses consisting of balls and cups made given in ref. [3]. from CoCrMo cast alloy, which had been in use for up Two different prostheses made from Protasul-21WF to 20 years, showed extremely low average wear rates of with diameters of 28 and 32 mm, respectively, were investi- 1 to 10 pm per year when examined after re-operation[l]. gated. Prior to activation, the ball/cup couple was mounted Compared to the currently used couples of cast CoCrMo in the hip joint simulator Stanmore Mk III[4] in order to or AI2O3 balls and ultrahighmolecular weight polyethylene mark the main areas of wear by touching. Then within cups, this is a reduction in wear rate by a factor of 10 to these areas, spots of 7 - 8 mm in diameter were activated. 100. Therefore, the wear behaviour of CoCrMo forged Under clean room conditions, the activated prostheses were alloy Proiasul-21WF against itself, which is new in this ap- mounted in the simulator with a blood serum solution as plication, was to be investigated by means of a hip joint medium. With a frequency of 0.5 Hz, the joint was me- simulator. This device simulates human motions. Since chanically loaded with a force that varied in a cycle between low wear rates of a few /an in the course of months were 300 and 1550 N. In intervals of 250 000 or 500 000 cy- expected, thin layer activation, which provides submicron cles the run was interrupted, the joint dismantled, cleaned sensitivity in wear measurements (see e.g. ref.[2]), was em- to remove radioactive debris, and the residual 7-intensities ployed together with a conventional mechanical measuring were measured off-line. With a counting period of one day, method. a precision in wear measurement of about ± 0.03 /im stan- The austenitic CoCrMo alloy Protasul-21WF contains, dard deviation could be achieved. Each run was extended 6 besides the main constituent Co, 27 - 30% by weight Cr, to 2.5 • 10 cycles, which took about six months. 5-7% Mo, < 0.75% Fe, < 1% Mn, < l%Ni, < 1% Si, In addition, the dimensions of ball and cup were me- and 0.15 - 0.25% C. In order to measure the wear rates of chanically taken at 500 points by means of a numerically both components and to avoid errors due to mutual mate- controlled 3D-coordinate measuring device. Comparison rial transfer, ball and cup had to be labelled with distinct with the measurements made prior to testing gives the wear. radionuclides. The desired activation depth was 50 pm for The maximum difference is called "linear wear". Sensitiv- the ball and 70 jim for the cup. These requirements as ity and reproducibility of this method are 2 /im, compared well as those of yields and half-lives could be met in the to 0.1 nm with TLA. following way. The ball was activated with 18 MeV a- The wear results are summarized in Fig. 1. Obviously, particles (0.8 /iAh), and the cup with 7.5 MeV deuterons the wear couple of Fig. la is an unfavourable one, while 60 (0.35 /iA). Co is produced by the deuterons, but not by that of Fig. lb is a favourable one. When a newly manufac- 103 the a-particles, whereas Ru is produced by a-particles tured artificial hip joint starts to work, it shows a mnning-in: 58 only. Co is the most abundant product of the a-particles, the two components match to each other by plastic defor- while it occurs only weakly with the deuterons. The reac- mation and wear. After running-in has taken place, wear is 59 60 100 103 tions exploited are Co(d,p) Co, Mo(a,n) Ru. and markedly reduced and the cumulated wear proceeds linearly ss S8 Mn(a,n) Co. All irradiations were performed at the with working time. This regime starts at 2 • 106 and 106 6 MV tandem accelerator. The 7-peak intensity measure- cycles in Fig. la and Fig. lb, respectively; the wear rate in ments were performed by means of a Ge(HP) detector (24% Fig. lb becomes as low as 0.2 /im/106 cycles. The linear relative efficiency). The total detector pulse rates were wear figures given by the mechanical method exceed the 3 < 10 cps. TLA results by a factor of ~ 1.6. This can be explained In order to relate the measured loss in 7-activity to the in the following way: the mechanical value is the linear loss of surface material, the depth profiles of the specific ac- wear at the position of maximum wear, while with the TLA tivity of the radionuclides produced in Protasul-21WF were method averaging occurs over the activated area 8 mm in measured. Cylindrical samples of Protasul-21WF (20 mm diameter, further, the area of maximum wear imperfectly in diameter, 4 mm thick) with a plane surface were activated overlaps with the activated area, the position of which had with deuterons and a-particles, layers of about 3 jim were to be determined by touching before the joint started to worn one by one using manual lapping with diamond paste work. Thus, both methods supplement each other while of 3 and 1 /im granulation. For each step, the residual the position-sensitive mechanical method gives the position mass and the residual 7-intensities of the activated sam- of the area of maximum wear, the TLA method detects the cum. linear wear (urn) cum. linear wear (urn) a / r 10

0

million cycles million cycles Fig. 1: Simulator test of Protasul-21WF hip joints; cumulated measured wear vs number of simulator cycles. Mechanical measurement: * cup, o ball; TLA measurement: + cup, O bail, (a) Hip joint diameter 28 mm. (b) Hip joint diameter 32 mm. (by courtesy ofElsevier Science Publishers N.V.) wear occurring at the activated spot with a sensitivity of 0.1 fan. The mechanical measuring method detects both plastic deformation and wear, the TLA method detects the wear only, which alone is of interest. This effect seems to be present in the data of Fig. la below ~ 106 cycles. The TLA method would have been sensitive to material transfer bom one component to die other. No indication of this effect was detected in both experimental series. This report is a summary of ief.[3].

References [1] MJF. Semlitsch, R.M. Streicher and H. Weber, Or- thopade 18 (1989) 36. [2] T.W. Coition. Contemp. Phys. 26 (198S) 521. [3] W. Neumann, W. Wolfli, P. Heimgartner and R.M. Streicher, NuclJnstr.&Meth. B, in press. [4] K.WJ. Wright, in: Biocompabbility of Orthopaedic Implants, vol. I (CRC Press, 1982) p. 141.

71 AMS 14C MEASUREMENT OF SMALL VOLUME OCEANIC WATER SAMPLES: EXPERIMENTAL PROCEDURE AND COMPARISON WITH LOW-LEVEL COUNTING TECHNIQUE

Heidelberg - ETHZ,

B. Kramer', C. Pfleiderer', P. Schlosser', I. Levin', K.O. Miinnich', G. Bonani*. M. Suler*. W. Wolfli"

* Insutut fur Mittelenergiephysik, ETH-Honggerberg, CH - 8093 Ziirich t Insutut flir Umweltphysik der Universitai Heidelberg, Im Neuenheimer Feld 366, D - 6900 Heidelberg t Paul Schener Institut, c/o ETH-Honggerberg, CH - 8093 Zurich

1. Introduction (formerly SIN) AMS facility at Zurich. Details of the mea- surement are described elsewhere [3][4][5][6]. The large AMS 14C measurement of oceanic water samples has not volume samples were measured in the Heidelberg 14C lab- yet found wide application. The reason is that using radio- oratory by CO2 gas counUng[7]. carbon in oceanic circulation studies often requires ultimate precision (< 5%o) because radiocarbon concentration gra- dients are small due to the long half life of 14C and the AMS-LLC comparison typical time scales in the ocean being on the order of hun- -180 -160 -140 -120 -100 dreds of years or less. On the other hand it would be highly Or desirable to make use of the small sample size (< 0.5 1 of water) needed for AMS instead of the large volume samples (as 2501) required for the conventional low-level counting method. This holds especially for studies in polar regions 1000 • 1000 where large volume work may be impossible or. most ships but which are key regions for controlling the deep circula- tion of the oceans. 2000 St 317 LLC " 2000 14 Our fist AMS C measurements on samples from a st 317 AMS station in the northwestern Weddell Sea showed that it is 3000 3000 possible to obtain a precision well below ± 10%0 [1]. The i d-H purpose of this paper is to present another 14C profile taken in the southern Weddell Sea measured both by AMS and by low-level counting which demonstrates that a precision of the AMS measurement of about ± 5%o has been reached. The procedures followed on board and in the laboratory are outlined, and the overall precision is discussed. 6000 5000

-140 -120 -100 2. Techniques C-14 [%0] Fig. 1 All water samples have been taken on leg two of the fifth 14 C depth profile at station 317 located in the south- cruise of the German Polar Research Vessel "Polarstem" to ern Weddell Sea (geographical position: 6ff 25.8'S, 1° Antarctica (ANT V/2, Winter Weddell Sea Project, June- 0.2'W). Large volume (XV) samples measured by low- September 1986) using large volume (270 1) stainless steel level counting technique are marked by (+) and small Gerard-Ewing samplers. From these first the AMS samples volume (SV) AMS samples by (D). Total errors (la) are (0.5 1) were drawn into preevacuated glass bulbs fitted with indicated. glass valves (Lowers & Harpert). The samples were poi- soned with HgCl2 which had been put into the bulbs prior to evacuation. Then the remaining water was processed on board (CO2 extraction and absorption in NaOH) to obtain 3. Results the samples for conventional low-level counting. 14 In the laboratory the carbonate was extracted as CO2 The C data are presented in form of depth profiles in Fig. by acidifying the water sample with phosphoric acid [2]. A 1 and are listed additionally in Table I. The data are reported small amount of the gas sample was used to determine its as A14 C, i.e. as per mil deviations from the 1950 decay 13C content by conventional mass spectrometry. The re- corrected NBS oxalic acid standard. From hydrographic pa- maining CO2 was reduced to carbon catalytically by means rameters (temperature, salinity) and from our earlier work of an iron catalyst [3]. We modified the original setup to [1] a smooth 14C depth profile can be expected. From the speed up the reaction and to optimize reaction parameters. comparison of the AMS data with the large volume data The small volume samples were measured at ETH/PSI it is evident that within their accuracy of ±5%o the AMS

72 results are in good agreement with the large volume data We are grateful to C. Junghans for measurement of the (see Fig. 1). This gives confidence that no additional er- 13C samples and to H.G. Junghans for his help in the sam- rors are introduced by the sampling and target preparation pling of the large volume 14C samples. This work was procedures. The mean difference between the 10 data pairs funded by the Swiss National Science Foundation and by gives no indication for the existence of a statistically signif- the Deutsche ForschungsgemeinschafL icant offset between the two data sets. A Discussion of the A more detailed discussion is given elsewhere[8]. 14C data in the context of the Weddell Sea oceanography will be given elsewhere. References Table I l4C measurements of water samples taken on station [1] P. Schlosser, C. Pfleiderer, B. Kromer, I. Levin, K.O. 317 in the southern Weddell Sea. A14 CAM Somali vol- Munnich, G. Bonani, M. Sutcr, and W. Wolfli, Radio- ume samples measured at the ETH/PSI (formerly SIN) ca,bon29(3)(1987)347. facility; A14Cxcc-' large volume samples measured at 14 [2] H. Dorr, and K.O. Munnich, Radiocarbon, 22 (1980) tie Heidelberg C laboratory by low-level counting technique. 909. station 317.6811 25.8'S, T 0.2'E; Aug.8,1986 [3] J.S. Vogel, J.R. Southern, D.E. Nelson, and T.A. Brown, Nucl.Insu-.and Meth. B5 (1984) 289. 14 <•) A14C*' Depth A CLLC AM S (m) (%o) \ /OO/ [4] M. Suter, R. Balzer, G. Bonani, HJ. Hofmann, E. 8 -126 Morenzoni, M. Nessi, and W. Wolfli, Nucl.Instr.and 35 -123 -122 0.71 Meth. B5 (1984) 117. 192 -150 -150 0.33 387 -157 0.23 [5] G. Bonani, H.J. Hofmann, E. Morenzoni, M. Nessi, 584 -158 -160 0.27 M. Suter, and W. Wolfli, Radiocarbon 28 (1986) 246. 780 -159 0.26 [6] G. Bonani, J. Beer, H.J. Hofmann, H.A. Synal, M. 977 -162 -158 0.22 Suter, W. WOlfli, C. Pfleiderer, B. Kromer, C. Jung- 1273 -160 0.34 hans, and K.O. Munnich, Nucl.Instr. and Meth. B29 1567 -163 0.36 (1987) 87. 1942 -159 -157 0.49 2344 -160 [7] H. Schoch, and K.O. Munnich, in Methods of low- 2743 -158 -159 0.44 level counting and spectrometry (IAEA, Vienna, 1981) 3142 -154 -157 0.50 pp. 361-370. 3542 -157 -151 0.42 3944 -154 0.51 [8] B. Kromer, C. Pfleiderer,P. Schlosser, I. Levin, K.O. 4194 -157 -150 0.45 Munnich, G. Bonani, M. Suter, and W. Wofli, 4279 -157 -151 0.46 Nucl.Instr. and Meth. B29 (1987) 302.

"» 1

Geochemistry (3211)

DATING GROUND WATER WITH RADON-222: LABORATORY EXPERIMENTS

PSI - BERN - ETHZ,

E. Hochn*, HJl. von Gunten"', F. Stauffer1, Th. Dracos'

* Paul Scheuer Institut, CH-5232 Villigen PSI t Laboratorium für Radiochemie, Universität Bern, CH-3000 Bern 9 t Institut für Hydromechanik und Wasserwirtschaft, Eidg. Technische Hochschule, CH-8093 Zürich-Hönggerberg

Since 1985 we study the concentrations of Radon-222 in ure 1. A simultaneous salt-tracer injection indicated travel ground waters. In earlier work we estimated ground-water times for the water between inlet and of let of up to about flow velocities at three infiltration field sites in Northern 9 days and a flow velocity of the water of about 0.5 m d1. and Central Switzerland applying a method which has been Thus steady- state radon concentrations were not reached developed in our laboratory [1]. Radon concentrations in in the lank. While expecting an exponential ingrowth of the infiltrating water grow at the River Glatt site from es- radioactivity, we found too small radon concentrations in sentially zero in the river to a steady-state concentration of the first three probes near the inflow boundary and in the about 17 Bq L"1. The ingrowth follows a (1 - e~x')-law, last probe near the outflow boundary, see Figure 1. A = 0.18 d"1 being the decay constant of Radon-222 and In a second experiment, the water in the tank was left t the travel time in the ground. Assuming a homogeneous undisturbed, i.e. without flow, for about a month (about distribution of the progenitors of radon (Ra-222, U-238) 8 half lives) to allow for the build-up of the steady-state in the aquifer and no mixing with older ground water one radon concentration. Subsequent sampling (13 samples) re- obtains a flow velocity of about 4.6 m d"1 for the freshly vealed a value of 7.8 ± 0.6 Bq L"1. With this information, infiltrated water of this site. In the future we intend to es- travel times of the waters from the inlet boundary to the timate water travel times at sites of artificial ground-water respective probes were estimated with the radon method, recharge for the supply of drinking water. In this note we using the data of the first experiment The travel times briefly report about a test of the method in laboratory box compare reasonably well with those from the salt tracer experiments [2]: observations. We attribute the too low values near the in- flow boundary with a possibly inhomogeneous distribution For the experiments a sand box (4.8 x 1.4 x 0.05 m) was of the radium in the box. This may be due to a wash- out used which was filled with two horizontal layers of a well- of fine particles which exhibit a higher emanating power. sorted quartz sand of a technical grade (grain sizes, upper This wash-out could have occurred during earlier experi- layer: 0.1 - 0.7 mm, lower layer: 0.1 - 0.9 mm), see Figure ments which were performed in the box at much higher 1. The sand contains impurities and fine-grained particles flow rates. We attribute the loo low value near the outflow which are mainly responsible for radon emanation. In a first boundary to mixing with water from outside the box. This experiment, tap water of a low radon concentration (about mixing may be due to the drawdown produced during the 0.1 Bq L"1) flowed through the water-saturated box paral- sampling. The drawdown could have resulted in reverse lel to the bedding at a steady rate of about 9 L d"1. The flow from the constant-head vessel. The ingrowth of radon water entered the box at the narrow side from 4 inlets with as described here confirms the results of the field studies. separation devices, and left the box at the other end through a sieve which separated the sand from a water gauge and a constant-head vessel. Triplicate measurements at 7 probes, which are located along a flow line, showed the expected increase in radon concentration to about 6 Bq L~ ', see Fig-

75 i 1 I lo -- - • i 5 - } - i 0

0 j «l ur !

z '. 5 a \ 1 1 P j 'i i

•>*•.;•" Una III!

2.0 4.0 X [m|

Figure 1: Radon Activity (Bq/L)

References

[1] E. Hoehn. H.R. von Gunten, Water Resour. Res., 25(8) (1989) 1795- 1803. [2] E. Hoehn, HJR. von Gunten, F. Stauffer, Th. Dracos, XXII Congress of IAHR, Lausanne, Switzerland, 31.8 - 4.9.1987, Seminar on Transport of Contaminants in Ground Water.

76 SORPTION OF BARIUM ON A <32-/xm GRAIN SIZE FRACTION OF GLACIOFUJVIAL DEPOSITS

Paul Scherrer Institut, CH-5232 Villigen PSI

A. Griitter, H.R. von Gunten, E. Rossler

These investigations are performed in the framework of beginning of the sorption experiment exchangeable a research program dealing with the behaviour of radionu- barium is introduced into the system as well by the clides and heavy metal ions in Swiss aquifers consisting synthetic groundwater as by the solid material. The of glacioftuvial deposits. These aquifers are a major re- lowest concentration accessible is influenced by Ihe source for drinking water in Switzerland. The chemical amount of exchangeable barium introduced with Ihe behaviour of barium is similar to that of strontium and ra- solid material. Since the treated materials contained dium. We therefore expect the sorption mechanisms for much less exchangeable barium than the untreated these three elements to be similar. Strontium and radium material - the exchangeable barium was largely re- have radionuclides which can present a hazard to health. placed by other cations during the chemical treat- The materials used for these studies originate from ments -, lower concentrations could be reached in a glaciofluvial deposit near Glattfelden, 15 km north of the case of the treated materials. Zurich. The glaciofluvial deposits are very heterogenous with respect to grain size and mineralogical composition. • Otherwise, the isotherms of the treated and the un- The main constituents are quartz, calcite, dolomite, feldspars treated materials differ so little, that it is safe to and clay minerals (illite and chlorite). In earlier experiments say that neither the carbonates nor the free oxides we had investigated the sorption behaviour of barium on or the organic substances contribute considerably to different grain size fractions using synthetic ground waters the sorption of barium on the <32- yxa material from of different compositions. Based on these results we had Glattfelden. suggested that cation exchange mechanisms on clay miner- als were responsible for the sorption behaviour of barium. In order to corroborate this statement, we performed sorp- tion and desorption experiments with barium in synthetic groundwater on <32-/im materials, which had been chem- ically treated to remove

• the carbonates • the carbonates and free oxides and • the carbonates, free oxides and Ihe organic sub- stances.

The experiments were performed using the batch tech- nique and Ba- 133 as tracer. 100 mg of the chemically treated solids were agitated with 20 ml of synthetic ground- water for 14 days. The synthetic groundwater added at the start of the sorption experiments contained various con- centrations of barium (2.10-8 to 1.10-4 -M) and Ba-133 as tracer. The phases were separated by centrifugation at Figure 1: Sorption (full symbols) and desorption (empty about 20 000 g. Afterwards the desorption experiments symbols) results of barium in synthetic groundwater on a were started by adding 20 ml of synthetic groundwater to <32-^m grain size fraction of glaciofluvial deposits freed the solid material. from carbonates (»,o). from carbonates and free oxides The results of these investigations are shown in Figure 1 (•, A) and from carbonates, free oxides and organic sub- together with the curve for the untreated material. The data stances (^,v)- The behaviour of the untreated material are corrected for changes in the specific activity occuring is represented by the solid line. [Ba2+] and [Ba2+]s are during the experiment. The following conclusions can be the concentrations of barium in solution and in the solid, drawn: respectively; C is the cation exchange capacity of the solid.

- The isotherms for the 3 treated materials are indistin- guishable. - The isotherms of the treated materials could be in- vestigated at considerably lower concentrations of barium than the isotherm of the untreated material. This observation can be explained as follows: At the

77 , Trace Elements (3212)

DEPENDENCE OF SOME ELEMENT CONTENTS IN NEEDLES OF NORWAY SPRUCE ON SOIL PARAMETERS

Paul Scherrer Institut, CH-S232 Villigen PS1

A. Wyttenbach, L. Tobler, S. Bajo

This investigation was undertaken as part of the research and plant physiological behaviour of Co and Mn, these el- program dealing with the relationships between trace ele- ements show very strong inter-element-correlations in nee- ments in spruce needles, in the aerosol deposited on the dles: log(ng/g Co) = 0.414 + 0.472 log(/ig/g Mn) with needles, and in the soils of the individual sites. Investi- n=47, r=0.7690, P<0.001 (Fig. 3). However, the uptake of gated parameters are the inherent content of 23 elements Co seems to be repressed relative to that of Mn, as can be in spruce needles at 47 sites in the vicinity of Winterthur seen from the Mn/Co-ratios which are 80 for total contents [1], the mass and the composition of the aerosol retained in soils, 200 for extractable contents, 1500 for the concen- on the surface of the needles [2], and some soil parameters trations in the soil solution [7], but 2000, resp. 11000 for (total and EDTA-extractablc contents of elements, content the concentrations in needles at pH 7.5, resp. pH 3.5. of organic matter and pH at 3 different depths) [3]. When- ever feasible, determinations of concentrations were done by instrumental analysis, which has the Potassium, rubidium and cesium capabilities of determining major as well as trace elements While K, the concentration of which in needles is a few in the samples. Results on the interaction between different thousend /ig/g, is frequently determined, Rb and Cs gener- compartments have been [4] [S] [6] or will be published ally are not, what must be attributed to their small concen- shortly. In the following only some examples for relation- trations (Rb >240 ng/g, Cs >4 ng/g). Information'on these ships between soil parameters and needles will be given. elements is iherfore very scarce. We found no correlation for K contents in needles with soil pH, but highly signifi- cant negative correlations for Rb and Cs: Manganese and cobalt log(/ig/g Rb) = 1.07-0.130 pH (n=39, r=-0.4463), P<0.005) Mn is often determined in spruce needles, but information log(ng/g Cs) = 1.68-0.104 pH (n=32, r=-0.4273, P<0.025). on Co is almost completely lacking because of its small There is no similar information in the literature for stable Rb concentration (> 4 ng/g). Both elements show highly sig- and Cs, but it has been noted repeatedly [9] that soil acidity nificant negative correlations between their needle concen- is the principal factor for the varying uptake of 137Cs into tration and the soil pH (Fig. 1): plants from different soils. Both total and extractable Rb log(/ig/g Mn) = 4.29-0.406 pH (n=38, r=-0.8695, P<0.001) and Cs-contents in the soils of our sites are very constant log(ng/g Co) = 2.57-0.211 pH (n=37, r=-0.6684, P<0.001) (coefficient of variation ~ 10 % for total concentrations); Contrary to these negative correlations, both total and ex- this constancy has also been noted for other soils [10]. As tractable Mn-concentrations in soils have a positive cor- neither total nor extractable soil contents show a pH depen- relation with pH (Fig. 2), which is thought to be an in- dence similar to that of needle concentrations, they both can dication of the dissolution of Mn-oxihydroxides with sub- be dismissed as an important factor in determining the nee- sequent loss of Mn from the more acid soils. The be- dle concentrations of Rb and Cs. However it is supposed haviour of Co, which in soils is partially contained in the that the free ions of K, Rb and Cs are reversibly bound to Mn-oxihydroxides, is somewhat similar to that of Mn. In clay minerals, and that this equilibrium is shiftet in more view of the opposite pH-dependcnce of needle concentra- acid soils in the direction of higher concentrations in the tions and soil contents, it is evident that soil contents are soil solution, which therefore has the same dependence on not the major parameter governing needle concentrations of soil pH as is observed for the needle contents of Rl and Mn and Co. Instead it is suspected that the concentration Cs. of Mn and Co in the soil solution, which has been shown to increase exponentially wiih soil acidity [7], is the main factor determining needle concentrations, as both the con- centrations in the soil solution and in needles have the same negative dependence on soil pH. The pH dependence of soil solution concentrations can be interpreted as the result of the pH dependence of the solubility of Mn-hydroxides [8]. As a consequence of the similar chemical, pedological

79 As in the case of Mn and Co, the similar behaviour of Rb and Cs leads to very strong inter-element-correlations in needles: log(ng/g Cs) = 0.774 + 0.817 log(/jg/g Rb) with n=35, r=0.8669, P<0.001. The Rb/Cs ratios are 18 for total contents in soils, 23 for extracted contents, but 200 for the concentrations in needles; the higher ratio in needles is either due to a stronger adsorption on the clay particles or to a repressed uptake of Cs with respect to Rb. The insensitivity of K contents on soil pH leads to different distribution functions of the needle concentrations in the whole investigated population (Fig. 4); K- values are normally distributed, those of Rb and Cs lognormally, and there are no inter-elemem-correlaiions between K and Rb GO 100 orCs. Don r* n neodten

Figure 3; Concentration of Co and Mn in needles of Nor- way spruce (regression line and 95 % prediction value).

r-i i i

40- i • i i i i 30- i i • —' 1_ 20- i JI 10- K ! Rb |_^ Figure 1: Concentration of Mn in needles of Norway spruce i , as a function of the pH of the site (regression line and 95 % prediction range). 0 1.5 3 4.5 6 7.5 9 %. 0 1 2 3 4 S 6 7 8 pan Concentration in needles Figure 4: Frequency distribution of the concentration of K and of Rb in needles of Norway spruce at 47 sites.

References

[1] A. Wyttenbach, S. Bajo, L. Tobler, J. Biol. Trace Elem. Res., in press. [2] A. Wyttenbach, S. Bajo, L. Tobler, J. Radioanal. Nucl. Chem. 114(1987) 137. [3] S. Bajo, A. Wyttenbach, L. Tobler, H. Conradin, J. Radioanal. Nucl Chem. 134 (1989) 181.

pHofsoO [4] A. Wyuenbach, L. Tobler, S. Bajo, J. Aerosol Sci. 18 (1987) 609. Figure 2: Regression lines for the concentration of total Mn and of EDTA-extractable Mn in the soil (same sites as in [5] A. Wyttenbach, L. Tobler, S. Bajo, Tbxicol. Environ. Fig. 1) as a function of the soil pH; note linear left scale. Chem. 19 (1989) 25. The difference between the iwo lines represents the nonex- [6] A. Wyttenbach, L. Tbbler, S. Bajo, Forstwiss. Cbl. 109 tractable part of the Mn pool; as expected, it is independent (1989) 233 on pH. The Mn-conccntration in the soil solution (note log- arithmic right scale) is taken from [7] and does not refer to [7] J.R. Sanders, J. Soil Sci. 34 (1983) 315. our sites. [8] J.F. Longergan, in: Trace elements in Soil-Plant- Animal Systems, Academic Press, 1975,109-134. [9] R. Zach, J.L. Hawkins, K. Mayoh, J. Environ. Ra- dioact. 10 (1989) 19. [10] R.L. Jones, Soil Sci. Soc. Am. J. 53 (1989) 588. Aerosol Chemistry (3213)

MASS TRANSFER TO DIFFUSION GROWN AGGLOMERATES AND THEIR FRACTAL DIMENSION

PSI - ETHZ - DUISBURG,

U. Baltensperger"', H.W. Gflggeler', D.T. Josf, A. Schmidt- Otlt5

* Paul Schetrer Instilut, CH-5232 Villigen PSI t Presently at California Institute of Technology, Pasadena, CA 91125 USA t Labor fiir FestkOrperphysik, ETH HOnggerberg, CH-8093 Zurich § Presently at Process- and Aerosol Measurement Technology, University of Duisburg, D-4100 Duisburg

The chemical and dynamic behaviour of aerosol parti- tional to the "Fuchs surface" of the aerosol particles [S] it cles is to a large extent controlled by the mass transfer to was called epiphaniometer (Creek epiphania = surface of a the panicles. This mass transfer is related to that part of body). It could be shown [8] that the same is true in the the surface which is directly exposed to gas molecules. For case of agglomerates. It provides therefore a powerful tool spherical particles this exposed surface is identical to the for characterizing such agglomerates. geometrical surface. However, typical particles in the at- The relation mosphere or in industrial aerosols are agglomerates formed by diffusional coagulation of primary particles and exhibit (1) highly complicated structures. In order to describe dynam- ics, chemistry or optical behaviour of non-spherical parti- has been well established both by simulation [1] and exper- cles, approximations by special geometries like ellipsoids iment on populations of agglomerates liaving formed under or chains etc. fail to give satisfactory general descriptions. the same conditions [2]. Here, R, is the agglomerate's ra- It has been shown in simulations [1] and experiments [2] dius of gyration, N is the number of primary particles in that agglomerates grown by diffusion limited aggregation an agglomerate, and d; is the fractal dimension. Aerosol are fractal-like. In previous work by Schmidt-Otl [3,4] a particles are never fractal in a strict sense [9], since they technique was proposed to determine the fractal dimension are subject to size dependent restructuring. Hence, the ex- of gasborne agglomerates in situ by measuring their pho- ponent in eq.(2) can be set constant over a limited size toelectric activity. This method was restricted to the free range only. Here, the term "fractal-like dimension" has molecular regime. been proposed to distinguish from the purely mathematical Caggeler et al. have developed a device which is based definition. on the attachment of neutral radioactive mPb atoms to In can be shown [8] that in the free molecular regime aerosol particles [5]. It therefore provides a direct means (Knudsen number Kn = A/(2R) > 1, with A = molecule for determination of the mass transfer to these aerosol par- mean free path and R = agglomerate radius) ticles. The 2UPb atoms are produced at a constant rate by the decay of a short-lived radon isotope (219Rn) ema- P ~ R% (2) nating from a long-lived actinium source (227Ac). 211Pb Rz being the mobility equivalent radius of the aerosol par- atoms attached to aerosol particles are transported through ticle, and a capillary acting as a diffusion barrier for non-attached N ~ pt"2(d > 2), (3) lead atoms. At the end of the capillary, the aerosol parti- t cles and with them the attached lead atoms are deposited thus providing a correlation between the agglomerate mass on a filter. The resulting activity on the filter is measured and the attachment coefficient [8]. This result is restricted continuously by a surface barrier detector. Due to the rela- to fractal dimensions d/ > 2), since for d; < 2 the particles tively short half-life of 21 'Pb, the device allows continuous are transparent for diffusing molecules, and no difference is monitoring of aerosols, without changing or transporting found e.g. between linear strings (d/ = 1) and disc-shaped the filter. agglomerates (d/ = 2). The output signal Ep of the epiphaniometer is propor- tional to the auachement coefficient /?. Calibration ex- periments with spherical polystyrene latex aerosol parti- cles showed that the attachment coefficient of the 2UPb atoms can be described by the Fuchs coagulation theory [6,7]. Since the device delivers a signal which is propor-

81 This theoretical result for the free molecular regime was References coroborated by experiments with the epiphaniometer as well as by pholoemission [8], Silver agglomerates were pro- [1] T.A. Witten. L.M. Sander, Phys. Rev. Lett. 47 (1981) duced by evaporation of silver, with subsequent coagulation 1400. [4J. These agglomerates consisted out of spherical primary particles with a mean geometric panicle radius of 7.S nm. [2] S.R. Forrest, T.A. Wiuen, J. Phys. A12 (1979)L109. 63 This aerosol was then charged by a Ni /3-source and frac- [3] A. Schmidl-Ott, Appl. Phys. Lett. 52 (1988) 954 tionated with a differential mobility analyzer (DMA). The resulting monodisperse aerosol with a mobility equivalent [4] A. Schmidt-Ott, J. Aerosol Sci. 19 (1988) 5S3. radius between 10 and SO nm was then split for determina- tion of the number concentration by an aerosol electrometer, [5] H.W. Gaggclcr, U. Baltensperger, M. Emmenegger, the photoelectric activity t [41, and for the epiphaniomeier D.T. Jost, A. Schmidt-Ott, P. Haller, M. Hofmann, J. Ep measurement. Figure 1 shows the Ep signal as function Aerosol Sci. 20 (1989) 557. of the mobility equivalent radius on a logarithmic scale. A [6] N.A. Fuchs, Mechanics of Aerosols, Pergamon, New slope of 2 is obtained in agreement with eq. (2). York (1964). 10 [7] J.H. Seinfeld, Atmospheric Chemistry and Physics of Air Pollution, John Wiley, New York (1986). [8] A. Schmidt-Ott, U. Baltensperger, H.W. Gaggeler, D.T. Jost, submitted to J.Aerosol Sci. [9] RJ. Samson, G.W. Mulholland, J.W. Gentry, Langmuir 3 (1987) 272.

100 Rz(nm) Figure 1: Epiphaniometer signal as a function of the radius of silver agglomerates, with mobility equivalent radii Rz between 12 and 45.5 nm

The expected proportionality between 0 and the photo- electric activity e based on the above considerations could also be verified experimentally, with a correlation coeffi- cient of 0.99 [8]. By similar considerations, it can be shown [8] that in the continuum regime (Kn < 1):

(4) and N ~ /3d/ (5) Note that the limitation dj > 2 is not necessary here. Thus, we found different scaling laws for the determi- nation of the fractal dimension in the two different regimes. However, the behaviour of aerosol particles is governed by the mass transfer to the particles, which in both regimes can directly be determined by the attachment coefficient obtained from the epiphaniometer.

Acknowledgement We thank S.N. Rogak and R.C. Flagen. California Institute of Technology, Pasadena, CA, for their helpful comments.

82 CONTINUOUS BACKGROUND AEROSOL MONITORING WITH THE EPIPHANIOMETER

PSI - PASADENA,

U. Baltenspergef, H.W. GSggeler', D.T. Jost*. M. Emmenegger', W. NSgeli"

* Paul Scherrer Instilut, CH-S232 Villigen PSI t Presently at California Institute of Technology, Pasadena, CA 91125, USA

Ico core records from the polar ice sheets are commonly were placed lm below the snow surface, where the snow used in climatology to study environmental changes on a temperature is between -20 and -7 °[8]. The batteries were hemispheric or even global scale. On the other hand, mid- charged by means of two solar panels, mounted on a tri- latitude glaciers, e.g. from the Alps should be related more pod. The air inlet was mounted at the top of the tripod, directly to their local or regional environments and there- with a small cone to protect against snow drift. In order to fore provide more direct information about man's impact perform a vertical profile, two more epiphaniometers were on the atmosphere in the densley populated European area. installed in the region, one at the high-alpine research sta- Cold glaciers, where the record is not disturbed by melt wa- tion Gomergrat with its south observatory (3100 m a.s.l.) ter, are normally found in high-alpine regions presumably and one at Zermatt (1600 m a.s.l.), 14 km northwest of above the planetary boundary layer. However, only few Colle Gnifetti. aerosol data are available from such sites and the transport From data available from the NABEL network station mechanisms for polluted air masses to these sites are poorly on Jungfraujoch [9,10], the epiphaniometer signal could be investigated. Thus, data are needed to describe long-range compared with the mass of tutai suspended paniculate mat- transport over the Alps as well as regional transport by ter under background conditions. A correlation coefficient gravity generated winds. For this purpose, a recently de- of 0.78 (n=14) was found for the monthly means, which veloped device, the epiphaniometer [1,2], was installed on is reasonable bearing in mind that the correlation strongly one of the highest glaciers in the Alps, on Colle Gnifeui. depends on the aerosol size distribution. Large deviations Colle Gnifetti is a cold firn saddle on the Monte Rosa, at from this correlation were found during times with Saharan 44S0 m a.s.l. [4,5]. Due to the low temperatures, its stratig- dust events, with aerosol particles much larger than un- raphy is not disturbed by percolating melt water, and it is der normal conditions. According to this correlation, 1000 therefore an interesting place to investigate the atmospheric counts of the epiphaniometer signal correspond roughly to input during the last centuries [6]. The site is located at the 0.5 /ig/m3. watershed of the highest parts of the Swiss Alps, and it can A belter correlation was found (r=0.96 for 9 weekly be reached by air masses from north and south. samples), when only the sum of SO2,", NOJ and NHj Essentially, the epiphaniometer determines the surface in aerosol samples was compared with the epiphaniome- concentration of ambient aerosol particles by attachment of ter signal. These ions are found mostly in the so-called neutral radioactive 211Pb atoms emitted from a long-lived accumulation mode, which shows a much more constant actinium source (227Ac) [7], The aerosol particles and with size distribution, resulting in a better correlation with the them the attached 211Pb atoms are deposited on a filter. epiphaniometer. The resulting activity on the filters is measured continu- Figure 1 shows the epiphaniometer signal from Colle ously by a surface barrier detector. Due to the relatively Gnifetti for November 1988. The lowest value detected is short half-live of 2UPb (36.1 min), the device allows con- 4 counts per 30 minutes. Using the correlation obtained tinuous monitoring of aerosols, without changing or trans- from Jungfraujoch, these few counts correspond to only porting the filter. Due to the low flow rate of 1 1/min the 2 ng/m3. This demonstrates the unique sensitivity of the device consumes only 8 W including counting and data pro- device. On the other hand, half-hour values up to 66000 cessing. It is therefore suitable for battery operation. Its counts were found on Colle Gnifeui, which results in a excellent sensitivity allows measurements also at very low concentration range of more than four orders of magni- concentrations. Thus, the epiphaniomcter is well suited for tude. On 22 November, the signal changed by a factor aerosol investigations at remote places such as high-alpine of 40 within 5 hours (Fig. 1). This peak was also ob- sites. served on Jungfraujoch and could therefore be attributed to The ability of the epiphaniometer for measuring low long-range transport. Besides this peak, several more co- aerosol concentrations at high-alpine sites was first tested incidences between Colle Gnifetti and Jungfraujoch were at the high- alpine research station Jungfraujoch, (34S0 m found (1 to 5 every month). Thus, a combination of the a.s.l.). The epiphaniometer was connected to a modem, thus Jungfraujoch and Colic Gnifetti data is a powerful tool to allowing read-out of the data at any time from PSI. Con- recognize long-range transport events. tinuous epiphaniometer data at this site have been collected since January 1988. Since the tests on Jungfraujoch were successful, an cpi- phamomcter together with a solar panel was installed on Colle Gnifeui. The cpiphaniomctcr and the battery box

83 on a continuous basis [11). The data of this collaboration can be used to investigate short-range as well as long-range transport mechanisms and to verify corresponding models. Moreover, in the context of the programme Geophysical Monitoring for Climatic Change (GMCC), an epiphaniome- ter was installed at Mauna Loa Observatory, Hawaii, in De- cember 1989. Further participations in international aerosol measurement campaigns at remote places are planned.

Acknowledgements We thank Dr. R. Gehrig, EMPA, Dubendorf, for providing data of the NABEL station on Jungfraujoch. The possibil- ities to perform aerosol measurements including valuable technical support and surveillance of the epiphaniometer on IIBI« (Nowember IBBD) Jungfraujoch (K. and M. Kocher) are highly appreciated.

Figure 1: Epiphaniomcter signal from Colle Gnifelii, 44S0 m a.s.l., for November 1988. The peak on 21/22 November References is due to long-range transport. [13 H.W. Gflggeler, U. Baltensperger, D.T. Jost, patents: in order to investigate regional transport mechanisms, CH 3763/86- 4, pending: DE 3727903 A 1.2. the diurnal variations of the epiphaniometer signal were [2] H.W. Gaggeeler, U. Baltensperger, M. Emmenegger, determined as a function of the season. Figure 2 (top left) D.T. Jost, A. Srhmidt-Ott, P. Haller, M. Hofmann, J. shows the Colle Cnifetti data with a distinct diurnal pattern Aerosol Sci. 20 (1989) 557- 564. during autumn and spring, with a peak in late afternoon (all times are given in winter time). This pattern can be ex- [3] U. Baltensperger, H.W. GSggeler, D.T. Jost, M. plained by polluted air masses being transported upwards Emmenegger, W. N&geli, Atmos. Environ. (1990), in from lower regions by thermal convection. Therefore, the press. mixing height in the alps can be as high as 4450 m a.s.l. during the warmer seasons. On the other hand, in high win- [4] W. Haeberli, J. Alean, Annals of Glaciology 6 (1985) ter (e.g. December) the constant diurnal signal is a clear 161-163. indication that this site is not reached by lower air masses. Thus, during these months the air on Colle Gnifetti is very [5] U. Schouerer, H. Oeschger, D. Wagenbach, K.O. clean, with an average value for December corresponding Miinnich, Zeitschrift fur Gletscherkunde und Glazial- to about 1 /ig/m3, whereas mean values in September are geologie 21 (1985) 379- 388. higher by about a factor of five. However, peaks due to [6] D. Wagenbach, K.O. Munnich, U. Schouerer, H. long-range transport of polluted air masses are found at Oeschger, Annals of Glaciology 10 (1988) 183-187. any time. On the other hand, Zermalt shows a very differ- ent pattern (Fig. 2, bottom right). The values are about a [7] U. Baltensperger, H.W. Gaggeler, D.T. Jost, A. factor of 20 higher. The concentration range at this station Schmidl-Ott, this report (1990). is much smaller than on Colle Cnifetti, comprising only a factor of 40. Usually, two peaks are found in the diurnal [8] N. Beck, University of Heidelberg, personal commu- variation, one in the morning and one in the late evening. nication (1988). The morning peak shifts slightly with season. Winter val- [9] R. Gehrig, EMPA Dubendorf, personal communica- ues are lower than summer values, in contrast to places with tion (1988). high local anthropogenic emissions [10]. These peaks are therefore presumably due to mountain-valley winds trans- [10] BUS (1988) Luftbelaslung 1987, Messresuliate des porting the air masses from the relatively highly polluted Nationalen Beobachtungsneizes fiir Luftfremdstoffe Rhone valley to this mountain resort. However, more ex- (NABEL), Schriftenreihe Umweltschutz Nr. 94, Bun- periments have to be carried out to verify this statement. desamt filr Umweltschutz, Bern. The Gornergral station (Fig. 2, top right) which was [11] M.S. Lehmann, A. Neftel, B.E. Lehmann, U. Bal- chosen as an intermediate site between Colle Gnifetti and tensperger, H.W. Gaggelcr, D.T. Jost, IAMAP Sym- Zcrmatt, shows a pattern resembling more the Colle Gnifetti posium on Meteorological Aspects of Mesoscale and than the Zermatt pattern. Jungfraujoch (Fig. 2, bottom Long-range Pollution Transport, 1 to 2 August 1989, left) shows a very similar pattern to Colle Gnifetti, with Reading, UK. constant diurnal levels in high winter and an afternoon peak in autumn and spring, corroborating the findings on Colle Gnifctti. The results show that the epiphaniometer is well suited to continuous aerosol monitoring at extreme background sites. The measurements at Colle Gnifetti and Jungfrau- joch will be carried on, in order to collect further data at these unique background sites in the Alps. On Jungfrau- joch, the Physics Intitute of the has started to measure chemical constituents in the atmosphere

84 Cot. Qrilalti. 4450 m a 51 Gkwnerfpal, 3100 m asi

Sen as. -•- Ool 88 10 24 s -o- Nov. 88. .E -o- Jan 89. Juitfraiipch, 3450 m a.it Zermalt. 1800 masl -o— Feb 89. —•— Mai. 89. 69.

Figure 2: Diumal variations for Colle Gnifetti (4450 m a.sJ., top left), Gomergrat (3100 m asJ., top right), Zermann (1600 m a.s.l., bottom right), and Jungfraujoch (3450 m a,s.l., bottom left)

85 FOG CHEMISTRY AT LAEGEREN

WSL - BERN - PSI,

F. Joss"', U. Baltensperger'5

* Eidgenossisches Institut fur Wald, Schnee und Landschaft WSL, CH-8903 Birmensdorf t Presently at Physics Institute, University of Bern, Sidlerslrasse 5, CH-3012 Bern } Paul Scherrer Institut, CH-S232 Villigen PSI § Presently at California Institute of Technology, Pasadena, California 9112S, USA

In the Swiss central plateau fog occurs very frequently tributed to local sources. In these cases low pH's due to (50 to 80 days per year) [I]. Concentrations of major ions in HC1 input was found. fogs have been reported to be 10-50 times higher than those The aerosol concentrations at times without fog reach found commonly in acid rain, and extremely high acidities about the same values as the sum of the fog concentrations have been measured in fog water [2,3]. The high acidities and aerosol (with an aerodynamic diameter d<4/im) were and high concentrations of many other species in fog are lower than at times without fog. However, even during a potential risk for the vegetation. Selective evaporation fog conditions the interstitial aerosol (<4/im) contained a of water can produce highly concentrated solution of less substantial fraction of NHj, NOj and SO^". volatile species on leaf surfaces, enhancing cation leaching Higher concentrations were found with decreasing height and producing necrotic lesions on exposed leaves. within the fog layer, which is consistent with enhanced de- Therefore, fog chemistry investigation was included in position during fog conditions. This is especially true for the national research programme "Forest Decline and Air components that are predominantly present in the aerosol Pollution" (NFP-14+) of the Swiss National Foundation. phase without fog conditions [4]. We investigated fog water chemistry [4], whereas other Sulfur chemistry is complicated substantially by the for- groups (from SMA; Payeme, EMPA, Diibendorf, and PSI, mation of S(IV) complexes such as hydroxy methane sul- Villigen) were measuring meteorological parameters and fonate (HMS) from formaldehyde. HMS and other com- gaseous components of the air (horizontal and vertical wind plexes allow S(IV) to coexist with oxidants such as H2O2 velocities temperature and dew point temperature, radiation and O3 [7,8]. Under the chosen ion chromatographic condi- parameters, O3, NO, NOr and SO2, and PAN) [5,6]. tions, HMS was determined as sulfite, and the sum of sulfite Fog samples were collected with string collectors. Most and sulfate concentrations showed an excellent agreement sampling was performed either on the Ugern mountain, at with the total sulfur concentration as determined by ICP Zindelen (685 m a.s.l.) or at Hochwacht (848 m a.s.l.), (Fig. 1). This shows that all main sulfur containing species or at the floor of the Limmat valley below Zindelen (416 were determined. m a.s.l.). 97 samples were obtained between 1 Septem- ber, 1986 and 31 December, 1987. Simultaneous aerosol samples were obtained by filtering air through teflon filters after an impactor with a cutoff of 4 pm, and size fraction- ated aerosol samples were obtained on aluminium foils by a low pressure Bemer impactor with eight stages between 16 and 0.06 fim aerodynamic diameter.

In most of the fog samples, Cl", NOj, NO3, SO3~, SO,", oxalale, NHj (mostly by ion chromatography, IC), as well as the elements Al, B, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si and Zn (by inductively coupled plasma emission spectroscopy, ICP) and pH were determined. Af- ter extraction with H2O, Cl", NOJ, SOj", and NH+ were determined in the aerosol filter samples, and Cl", NO3, 0.6 0.8 1 1.2 + + 2 1 SOj", Na , NHj, and K in the impactor samples. ISO4 3 - (mmol r ) Means, medians, standard deviations in terms of con- centration in fog water as well as concentrations per m3 Figure 1: Comparison of the sum of the concentrations of of air were published elsewhere [4]. Concentration ranges sulfate and sulfite as determined by ion chromatography of up to two orders of magnitude were found. Even so, with the total sulfur concentration as determined by ICP highly correlated values of NHj, NO3, and SO^~ for the (R = 0.985, N=48). fog samples as well as for aerosol samples were found. NHj, NO,", SO;j~, and Cl~ represented 90 % of the ion Several scavenging processes are responsible for the sum. NHj often neutralized the strong acids, resulting in composition of fog water. First, aerosol particles (e.g. pH's at or slightly below 7, whereas also pH's down to 2.9 (NH4)2SO^) are scavenged by nuclealion scavenging (also were found. Evaporation processes caused increasing con- named activation) or impaction and interception. These centrations in the fog droplets. However, in certain cases, particles may be partially dissolved and thereby contribute increasing concentrations of fog constituents could be at- to the chemical composition of fog water. This process

86 could be exemplified by means or impactor measurements idation rate is low, the NOJ and NH+ fractions are higher wilh and without fog conditions. Aerosol concentrations due to continued gas phase scavenging of these species. without fog were slightly higher than with fog and showed a maximum at about 0.7 /im. With fog conditions, fog droplets were visible on the stages with larger diameters, Acknowledgements and ions were found also at these larger diameters [4]. We thank Dr. H. Turner, FSL Birmendorf for initiating this Second, water soluble gaseous species are scavenged project and his support Dr. P. Jeannet, SMA, Payeme, Dr. in the liquid phase and may then undergo fast acid-base R. Gehrig, EMPA Dubendorf, Dr. W. Graber, PSI Villigen, reactions. Due to higher effective Henry's law coefficients, and Dr. W. Landolt, FSL Birmensdorf provided the data concerning meteorological parameters and gaseous compo- this process is more important in the case of HNO3 or nents. Dr. J. Zobrist, EAWAG, Dubendorf, organized a NH3 than in the case of SO2 [9]. This is still true even if fog sampler intercomparison, and Dr. T. Schumann, ETH one takes into account that SO2 is oxidized to SOJj" (sec below). Thus, in relation to SO4" higher concentrations Zurich, provided the Berner impaclor. M. Guecheva, FSL of NO3 and NH+ were found in the fog water than in the Birmensdorf, A. Diara, FSL Birmensdorf, and M. Gloor, aerosol phase. PSI Villigen, performed the analysis, and A. KOllikcr, FSL Third, gaseous species are scavenged in the liquid phase Birmensdorf, constructed the sampling units. This work followed by oxidation reactions (e.g. SOj). The oxidation was supported by the Swiss National Science Foundation (No. 4.847.0.85.14). of S(IV) may be performed by various reactions. H2O2 is widely believed to be the most effective oxidant for sul- fite under atmospheric conditions. However, in an urban References atmosphere H3O2 is probably depicted very rapidly under fog conditions. Other possibilities for oxidation of S(IV) [1] H. Wanner, Geogr. Bcmensia G7 (1979) 41. to S(V1) are reactions of S(1V) with O3, NO3, PAN, O2 catalyzed by Fe(HI) or Mn(ll), and NOjT [10]. From the [2] J.W. Munger, DJ. Jacob, J.M. Waldman and M.R. measured gas phase concentrations of O3, NO2 (determined Hoffmann, J. Geophys. Res. 88 (1983) 5109. as difference between NO, and NO), PAN, and the aqueous phase concentrations of Fe and NOo the reaction rates of [3] C.A. Johnson, L. Sigg and J. Zobrisl, Atmos. Environ. these components with S(IV) were calculated for 64 sam- 21 (1987) 2365. ples. For samples with pH<6 oxidizable S(IV) was calcu- [4] F. Joos and U. Ballcnspcrger, submitted to Atmos. lated from the SO2 measurements in the gas phase, since the Environ. (1990). experimental data for S(IV)a, showed an apparent excess due to formation of complexes compared with thermody- [5] H. Turner, in Proc. Human Impacts and Management namical equilibrium calculations. Ozone was found to be of Mountain Forests, T. Fujimori and M. Kimura (Eds) the most important oxidant. However, oxidation by NO2 Ibaraki, Japan, (1987) 107. and O2 catalyzed by Fc(III) were slow [4]. [6] W. Natcr, Das aimosphiirenphysikalische Messsystcm des Projektes "Luftschadstoffe" (Waldschaden) an der LUgcm, EIR-Bericht No. 616, Paul Schcrrer Inslitul, Villigcn.

[7] W.J. Munger, C. Tiller and M.R. Hoffmann, Science 231 (1986)247.

[8] U. Baltenspcrger and S. Kcm, J. Chromatogr. 439 (1988) 121.

[9] J.H. Seinfeld, Atmospheric Chemistry and Physics of Air Pollution, John Wiley, New York (1986).

[10) S.N. Pandis and J.H. Seinfeld, J. Gcophys. Res. 94 (1989) 1105.

29 Dale(Ocl/Nov87)

Figure 2: Calculated oxidation rates of S(IV) and the SO?" fraction ([SO=-]/([NH+] + [CI"] + [NOJ] + [SO;"]), mol/mol) vs. time for the fog period from 26 October to 1 November 1987.

Figure 2 shows the calculated oxidation rates of S(1V) and the SO;;- fraction ([SO^]/([NH+] + [Cl" j + [NO3 ] + [SO? ])) during the fog period from 26 October to 1 November, 1987. The SO;;- fraction is following the S(IV) oxidation rate. High SO;" fractions arc found during times with high S(1V) oxidation rales. Thus, when the S(IV) ox-

87 ATMOSPHERIC STUDIES AT JUNGFRAUJOCH

PSI - BERN,

D.T. Josf, H.W. GSggeler", U. Baltenspergeft, B. Lehmann', M. Lehmann', A. Neftel*

* Paul Scherrer Institut, CH-5232 Villigen PSI t Presently at California Institute of Technology, Pasadena, USA { Physikalisches Institut, University Bern, CH-3000 Bern

The Jungfraujoch at 3450m a.s.l. is an unique location On May S, during still clear weather, the wind turned to study processes in the upper troposphere. The easy ac- from E to W. This was accompanied by a SO2 peak, missing cessibility and the good infrastructure of the high alpine in radon and the aerosols. About one day later, a front from research station enable continuous measurements of atmo- W crossed Jungfraujoch, causing snow-fall and a significant spheric parameters throughout the year even with instru- increase in humidity. The pattern of this situation was a ments of a certain complexity. Various organisations op- minor peak in radon and a large peak in aerosols. The erate long-term monitoring stations, such as SMA, KUER, beginning of a SO2 peak is also seen. However, due to and NABEL. In addition, research groups of several coun- fog the DOAS measurement was disabled. On May 8, a tries concentrate work on specific tracers in the air in or- minor front (leading only to partly clouded sky and a small der to understand their characteristic transport and transfor- increase in humidity) caused small but significant peaks mation mechanisms. In particular, the University of Bern both in radon and aerosols. No SO2 peak is seen. A very group has initiated a program for the continuous measure- pronounced change in weather occured on May 9. The wind ment of H2O2 (by flow injection analysis) and has installed changed to N bringing bad weather with snow-fall and fog a Differential Optical Absorption System (DOAS) for the for about four days. A huge radon peak marks the beginning simulaneous measurement of O3, SO2, NO2, and H2O with of this period. The radon concentration remained relatively high temperal resolution [3]. A group of the University of high over the whole period with winds from N to E. The Heidelberg continuously collects air for the measurement aerosols exhibited a pronounced peak at the beginning of 85 14 of Kr and CO2 and researchers from the University of this time period coinciding with the radon peak. No SO2 Liege use their high resolution spectra to determine atmo- structure is seen, since DOAS shut down for most of the spheric column concentrations of species such as e.g. CH4, time due to the low visibility. On May IS, the largest SO2 HC1, HF, CO, and others. The PSI group concentrates its peak of the time period depicted in Fig. 1 was observed. work on the measurement of aerosols and radon. It coincides with a clearing up and a change of the wind The epiphaniometer is an instrument developed at PSI direction from W to E marking the end of snowy weather. to continuously measure aerosol concentrations in the air [1] This large SO2 peak is accompanied by a minor peak in and can be used to detect polluted air-masses from long- radon and a medium large peak in aerosols. range events above the planetary boundry layer as well as In conclusion, clearly different patterns are observed for from vertical mixing by thermal convection [2]. the atmospheric components presented in Fig. 1. It is (he A modified version of the epiphaniometer which con- goal of our studies to characterize each distinguishable air tains no 237Ac source, measures the naturally occuring parcel which reaches the Jungfraujoch by its individual "fin- 2HPo activity from the decay of 214Pb (2MBi) again at- gerprint" of tracers and to combine this classification with tached to aerosol particles as a measure of the natural Rn- the continental and local weather situation. A collaboration concentration. In order to measure the rather low concen- with the Geographical Institute of the University of Bern trations of the naturally occurring activities a flow rate of has been initiated for a more detailed and systematic anal- 4 1/min and an integration time of 4 hours had to be used. ysis of the alpine meteorology. The radon concentration should give some information on the origin of the air-masses. In contrast to the monitoring stations operated e.g. in Acknowledgement the frame of the NABEL activities where daily and monthly We highly appreciate valuable technical support and surveil- averages and their trends are of primary interest the work lance of all installations on Jungfraujoch by K. and M. described in this contribution is mainly directed towards an Kocher. This work was partly supported by the Swiss Na- understanding of the short term dynamics of the observed tional Science Foundation and by COST. parameters and to the use of this information for under- standing the history of air parcels reaching the Jungfraujoch site. As can be seen in Figure 1 which is a plot of a) the SO2 concentration, b) the epiphaniometer signal (aerosol concentration), c) the natural Rn activity and d) meteo- rological parameters (temperature, rel. humidity, weather, wind direction and speed) [4] for the time period May 1st to 16th 1989. the tracer concentrations can vary by large fac- tor;; within hours. We shortly discuss the pattern observed ••:; May 1989 as presented in Figure 1: References

[1] H.W. GSggeler, U. Baltensperger, D.T. Jost, A. Schmidt-Ott, P. Haller, M. Hoffmann, J. Aerosol Sci. C 0000 • 0 3 O I M = » O 20 (1989) 557-564. 100 so r [2] U. Baltensperger, H.W. Gaggeler, D.T. Jost, M. 60 h j f K~ '^ 40 Emmenegger, W. NSgeli, Atmos. Environment, 24A, 20 in print (1990). 0 -20 [3] M.S. Lehmann, A. Neftel, B. Lehmann, U. Bal- tensperger, D.T. Jost, IAMAP Symp. on Meteorological Aspects of Mesoscale and Long-range Pollution Trans- port, 1-2 Aug. 1989, Reading, UK. [4] Wetterberichte der Schweizerischen Meteorologischen Anstalt Zurich, FOTOROTAR AG, Egg, Switzerland; 1-16 May 1989.

IB E

1 2 3 4 5 8 7 8 9 1011121314 IS 18 May 1989

Figure 1: Measured meteorological parameters together with radon-, aerosol-, (epiphaniometer) and SO2 - (DOAS) concentrations on Jungfraujoch.

89, Heavy Elements (3214)

COLD FUSION REACTIONS WITH 48Ca

PSI - BERN - GSI - MAINZ - HELSINKI,

H.W. Gaggelef, D.T. Josf, A. Tilrler', P. Armbrustert, W. Briichle*. H. Folger'. F.P. Hessberger*. S Hofmannl G. MUnzenbergl, V. Ninov', W. Reisdorf', M. SchSdelt, K. Summerer*. J.V. Kratz*. U. SchererS, M.E. Leino«

* Paul Scherrer Institut, CH-5232 Villigen PSI t Laboratorium fUr Radiochemie, Um'versitai Bern, CH-3000 Bern t Gesellschaft fUr Schwerionenforschung, GSI, D-61 Darmstadt § Institul fur Kernchemie, Universitat Mainz, D-65 Mainz f Department of Physics, University of Helsinki, Finland

Fusion reactions of 48Ca projectiles with 180Hf, 1S4W, 197Au, 208Pb and 2bJBi were studied. All experiments were performed at the SHIP velocity filter. As target 300 to 400 jjg/cnr thick metal.ic foils were used which were either mounted on a rotating target wheel (308Pb, M9Bi, 197Au) or used as single targets (180Hf, 184W). Evaporation residues were delected via their a-decay. In case of the reaction with 208Pb evaporation residues from the In and 2n channel were also detected via their grand-daughter nuclides using chemical techniques [1], All results are summarized in the Table 1 [2]. For the heavier systems 197Au, 108Pb and 209Bi the data can be well 0.60 0.70 reproduced with the code HIVAP assuming no (or only a Fiss.Ky *(a small) hindrance of fusion, i.e. Extra-Extra-push Bxx < 5 MeV. Fig. 1 summarizes (Exx) values from the literature Figure 1: Extra-extra push values from the literature (open and from this work. circles and crosses) and from this work (closed circles) as 180 184 Surprisingly, for the lighter systems ( Hf, W) the a function of the fissility parameter [2]. measured cross sections (3n-channel) were more than two orders of magnitude smaller than expected (HIVAP). At present we have no explanation for this discrepancy. Agree- ment between experimental and calculated values can only be obtained by reducing the macroscopic fission barrier of the compound nuclei by 30 to 40 %. Fig. 2 depicts a \ \\ schematic of how evaporation residue cross sections evolve \ <2n) for compound nuclei between Th and Lr. \ L(3n) ; f

go 100 Atomic Number of Compound Nucleus

Figure 2: Maximum cross sections for the main xn channels from 48Ca induced fusion reactions.

91 Table 1: Experimental cross sections

Incident Mosi Probable Cross section Energy Excilllion In 2n 3n [MeV/ul BneWlMeVl Inbl (nbl |nb|

4.34 13.2 5 27 5 27 4.42 16.3 212158 4.42" 16.7 260130 420150 4.44-1 17.4 7301150 4J0 19.3 23441S44 4J0» 19.7 180153 33851310 4.50" 19.7 31I014&0 4J7 21.9 18451433 4.65 212 41.1114 371JJ 4.74 28.8 39119 109133 «Cl*"»Bl 4.3S 13.7 54.5 4.46 17.6 61120 1217 4J3 19.6 20111 437196 4.61 22.7 S7.5 324175 4 69 25.9 38111 913 4.76 29.4 28111 "C«* 4.42 27.6 40115 4.48 30.0 42 H7 4j,3 33.6 36115 4.30 34.4 WO i?a + «

" In ihe middle or ihe mget {chemistry) or al 2/3 of ihe Utfgei (SHIP). Energy width within target ± 1.2 MeV (chem.) and ± i J MeV (SHIP). Additional energy uncertainly from UNILAC * as MeV. " Results from chemistry, all other data from SHIP. •' Sum or 2n and 3ri channel (sea tut].

References

[1] H. Gilggeler et al. GSI-scientific report, GS1-89-1 (1988) 18. f2] H. Gaggeler et al. Nucl. Phys. A5O2 (1989) 561c.

92 GASPHASE CHEMISTRY EXPERIMENTS WITH ELEMENT 105

PSI - BERN - LBL - GSI • MAINZ,

D.T. Jost-, H.W. Gäggelcr", U. Baltensperger", Nai-Qi Ya", A. Türlert, Ch. Lienertt, K.E. Gregorich', CM. Ganneu', H.L. Hall', R.A. Henderson*. D.M. Lee', J.D. Li', M.J. Nurmia', D.C. Hoffman', M.SchädelS, W. Briichle8, J.V. Kratz', H.P. Zimmermann', U.W. Scherer"

* Paul Scherrer Institut, CH-5232 ViUigen PSI t Institut für anorganische Chemie, Universität Bern, CH-3000 Bern 9 t Lawrence Berkeley Laboratory, Berkeley, CA § Gesellschaft für Schwerionenforschung, GSI, D-61 Darmstadt H Institut für Kernchemie, Universität Mainz, D-6S Mainz

Element 10S (hahnium (Ha) or nilsbohrium (Ns) de- According to Gregorich et al. [5] 2S2Ha has a 50% pending on the claim of its discovery) is so far the heaviest spontaneous fission branch. Taking the above sum of 160 clement whose chemical properties have been investigated. 262Ha events an equal number of sf-events decaying with a Early work on the gas-phase chemistry by Zvara [1] indi- 35 s half-live should have been seen. Comparing this with cated that it behaves similar to a group V element. We 19 events observed in the first 60 seconds we find that the have investigated the formation and volatility of the HaBr5 sf-branch is less than 25 %. compound using on-line gaschromatography. Figure 2 shows the decay analysis of the fission activ- The experiments were performed with 262Ha (T^ = ity of direct catch experiments (no chemistry). A new, so 35s), produced in the reaction 249Bk(l8O,5n) at the 88"- far not identified fission activity with a half live of 14 ± cyclotron at LBL. The gas-jet technique and a gaschromato- 4 s is clearly visible above the background from the spon- graphy set-up similar to the one used in previous experi- taneous fission activity of long lived actinides. This same ments [2,3] were employed. The LBL MG-wheel counting activity was also found in runs where HBr/BBr3 was used device with an 18 second stepping time was used to de- as bromating agent whereas in runs with HBr alone it was tect alpha- and fission- events. Pairs of CANBERRA PIPS not seen. This suggests an origin with a similar bromide (passivated ionimplanted planar silicon) detectors were in- chemistry as Ha. A fission activity with the 35 s half-live stalled in 6 counting positions giving a total counting time of 262Ha could not be identified. of 108 s after the end of the collection. These PIPS detec- tors proved to be very resistant to the corrosive gases used. Spectroscopic data was recorded event by event. An anal- ysis of all data accumulated in runs using HBr/BBr3 and temperatures from 300 to 500 ° give for the alpha events in the energy region of 262Ha and its daughter 258Lr (8.35 - 8.75 Mev) a half- live of 33 ± 6 s, in good agreement with the literature. Low energy tailing from the neighbor- ing SIlmPo at 8.88 Mev contributes less than 40% giving NucMe a lower limit of 160 262Ha events. The bromide complexes were formed by adding HBr or HBr which had passed over BBr3 to the carrier gas at the entrance of the gaschromatograph. Figure 1 shows the chemical yield curves for the Ha and its homologous ele- ments Nb and Ta as a function of temperature. From these curves we conclude that HaBr5 is more volatile than the cor- responding tantalum compound since the maximum yield is found at a lower temperature and that NbBr5 is more stable than HaBr5 since it can be formed without adding BBr3 to the HBr. These findings are in contrast to the volatility 100 200 300 400 500 600 700 BOO 900 sequence Nb>Ta>Ha recently published by Timochin el Temparatura ["CO al. [4] who used HBr/Br2, but in agreement with Kratz et al. [6] who showed that in aqueous solutions the hahnium Figure 1: Chemical yields for group V elements Nb, Ta halide complexes are more like the Nb complexes than the and Ha. Ta ones. References

[1] I. Zvara et al., Sov. Radiochem. 18, (1976) 328 [2] D.T. Jost el al., Inorg. Chim. Acla, 146 (1988) 255 [3] Nai-Qi Ya el al., Radiochim. AcU, 47 (1989) 1

401 [4] S.N. Timochin et al.. Abstract Int. School Seminar on Heavy Ion Physics, Dubna, Oct. 3-12 (1989) 20 20 hHai [S] K. Gregorich et al.. Radiochim. Acla, 43 (1988) 233 [6] J.V. Kratz et al., Radiochim. Acla, 48 (1989) 121. to & ô a 1 1 « ['I ] 3

2

i laaoi

Figure 2: Decay analysis of sf-events in a direct catch ex- periment with 36s stepping time.

94 GASCHEMICAL SEPARATIONS BY SELECTIVE DESORPTION FROM SMALL KC1 PARTICLES

LBL - PSI - GSI - MAINZ,

A. Türler', D.T. Joslt, H.W. Gäggeler', A. Kovacs', W. Briichle*. H. Folget4, M. Schädel», M. Gober«, J.V. Kratz5. P. Zimmermann9

* Lawrence Berkeley Laboratory, Berkeley, CA t Paul Scherrer Institut, CH-S232 ViUigen PSI i Gesellschafl für Schwerionenforschung, GSI, 0-61 Darmstadt § Institut für Kernchemie, Universität Mainz, D-65 Mainz

For chemical studies of heaviest elements on-line sepa- 1 l/min of carrier gas (He) and 100 ml/min of reactive gas rations in the gas-phase have proven to be very useful and which was added to the carrier gas at the position of the fast In recent years this technique was applied to search for wool plug. The temperature of the isothermal part of the superheavy elements [1] and to study chemical properties oven was kept at 500 ° and 600 °, respectively, for HBr of the heavy elements Lr [2] and 10S [3]. and HCI. After the column the products were thermalized, So far, the nuclides of interest were transported to the attached onto new KCI aerosols and transported along a gaschemistry set-up by a gas-jet device, mostly using KCI capillary to a collecting glass fibre filter, mounted on top as transporting species. In the chromatography column of a HPGe detector for 7-spectroscopy (for details see [2]). (usually quartz or metal) the particles containing the re- Fig. 1 shows the result with HBr as reactive gas. 100 action products were stopped on a wool plug which was % desorption yield represents the maximum value of the heated to a fixed temperature of about 1000 to 1100 °. chemical yield, which is dependent on the half-life on the Volatile species evaporating from this collecting plug were nuclide [4]. Typical values for the absolute chemical yields 170 1T2B then separated in a following isothermal section of the oven. are 70 % for W and 20 % for Re. Easiest desorption Depending on the temperature of this section species of a is obtained for Re, followed by W, Nb and Ta. This se- certain volatility were passing the chromatography column quence may be cxpalined by the maximum oxidation states and were then available for counting. For a detailed de- of the corresponding elements. In case of Nb and Ta, both scription of the entire chromatography apparatus see [2,4]. transition elements from group V, easier desorption is ob- The advantage of this technique is its speed and continuous served for Nb as compared to Ta, in agreement with results mode which allows chemical separations within a few sec- from isothermal chromatography [3]. onds [4]. The disadvantage, however, are the rather poor With HCI the desorption temperatures are higher than chemical separtion factors. Therefore, this technique was with HBr. This can be explained by a lower volatility of applied so far only for separations of groups of elements chlorides compared to bromides. Fig. 2 shows, as an exam- (as atoms or molecules) with distinctly different volatilities, ple, the data for 166Ta with HBr and HCI. Surprisingly, the e.g. in separations of highly volatile trans-actinide halides desorption curve measured with HCI has a local minimum from the much less volatile actinides halides [3]. at about 7S0 °. We attribute this minimum to a melting of In the following we have tried to perform chemical sepa- the KCI particles (melting point 760 °). rations using the same gaschromatography device but vary- ing the temperature of desorption of the products from the transporting KCI particles. References A 12.S mg/cm3 thick La target, mounted behind a dou- [1] P. Armbruster et al., Phys. Rev. Lett., 54,406 (1985) ble window system of 3.4 mg/cm2 Mo and 2 mg/cm2 Be, 40 was bombarded with Ar projectiles of an incident en- (2] D.T. Jost et al.. Inorg. Chim. Acia 146, 255 (1988) ergy of 9.2 MeV/u. This defines an energy range within the target of 8.10 to 6.26 MeV/u. According to a HIVAP [3] H. W. Gäggeler et al.. Report PSI-49 (1989) calculation for this energy range mainly nuclides from the channels 7n, p7n and a4n to o7n should be produced, all [4] Ya Nai-Qi et al., Radiochim. Acta, 47, 1 (1989) with cross sections above 10 mb. In the following we have analysed only such nuclides 172fl which are mainly produced directly, such as Re (Ti/2 = 15 s), 170W (2.4 min) or 166Ta (32 s). In addition, we also included into our chemical study 99mNb which was studied at PSI with the same set-up using its production via fission of 235U at the SAPHIR reactor [4], For all the above mentioned nuclides the desorption be- haviour from small (0 ss 40 nm) KCI particles was studied which were collected on a quartz wool plug. HBr and HCI were used as reactive gas. Typical gas-flow rates were

95 ZOO 300 400 500 600 300 400 SOO 600 700 800 900 Temperature CO Temperature (°C)

A 170W <2.4mln) V w8Ta(32s) M BllmNb<15s)

Figure 1: Relative desorption yields for some elements Figure 2: Relative desorption yields for 166Ta from KCI from KCI particles with HBr as reactive gas. with HBr (triangles) and HCI (crosses).

96 Cement Products (3216)

ACTIVITIES OF THE CEMENT CHEMISTRY GROUP

Paul Scherrer Institut, CH-S232 Villigen PSI

D. Laske, L. Dohring, M. Egloff, R. Ivankovic, M. Patorski, P. Schenk, Ch. Meier

Coordinated by NAGRA, the Swiss nuclear power plants delegate applied research and development (R + D) work in the field of solidification and conditioning of nuclear waste to the cement chemistry group at PSI. This work has to be performed in close contact with the corresponding KKW and usually results in internal reports delivered directly to NAGRA and the orderers. Scientists and technicians work- ing in this group require basic knowledge both in cement- and in radio-chemistry to handle the partly highly radioac- tive samples. The work covers mainly three different activities:

1. Recipes for cement-solidification of new types of ra- dioactive waste are being developed and tested. Con- ditioned final products, the waste-matrices, are then tested whether they fulfill the R-14 guidline of HSK, the Swiss safety authority for nuclear power plants. 2. New recipes developed at PSI on a lab-scale have to be introduced to the corresponding nuclear power plant at a 1:1 scale. This activity mainly requires practical help at the nuclear power plant when safety authorities test out the new processes. Usually it has to be shown that the R-14 guidline is also fulfilled for large- size samples.

3. For the KKW and the HSK we routinely test whether the final waste fulfills R-14. For that purpose from every 10th to 12th barrel of waste a random sample is taken. The curing time for hardening is three months, then the leaching properties of several radionuclides such as 60Co and 137Cs are measured over a lime pe- riod of ISO days as is described by the ISO-standard procedure. In addition, also mechanical properties of the matrix such as the compressive strength are de- termined but also the water- and sulfale- insistence is controlled.

All these procedures guarantee that final samples are con- ditioned in a safe way for intermediate and final storage in a repository.

97 DETERMINATION OF 36C1 IN COOLING WATER AND IN RESINS FROM KKG USING AMS AND LSC

PSI - NAGRA • ETHZ,

Liu Xinqi*. D. Laste*, H.W. Gäggeler\ K. Kurtzt, F. Brandt*, H. Synal8, W. WölfliS

« Paul Scherrer Institut, CH-5232 Villigen PSI t NAGRA, CH-5401 Baden } Kernkraftwerk Oösgen, CH-4658 Däniken jj Institut für Mittelenergiephysik, ETH-Hönggerberg, CH-8093 Zürich

a6 5 Cl is a long-lived cosmogenic nuclide (T1/2 = 3.0xl0 tween the two independent determinations are found. The y). Natural 36C1 is mainly produced by spoliation of cos- average final value is (1.1 ± O.l)xlOH 36C1 atoms per gram mic rays with 40Ar in the upper atmosphere. In nuclear dry resin. This corresponds to an activity of 8 Bq/g resin. power plants 36C1 is formed via neutron capture with 35C1 from Cl~ impurities in the primary reactor water. Even though Cl" concentrations in such water systems are low Sample Sample [CI"] N(JbCI/mr •"CI/Cl* (typically in the ppb level), the amount of 36C1 produced no. vol. is not negligible because of the high neutron capture cross ml ppb xlO10 xlO"4 section of 43 barns for the 35Cl(n,7)36Cl reaction and the I 1 10 6.23 3.66 high . Due to the long half-life of 36C1 and the 2 1 10 6.38 3.76 conservative geochemical behaviour of chloride it is highly 3 5 10 6.07 3.58 desirable to have available quantitative numbers on the 36C1 4 5 10 6.46 3.81 concentrations in nuclear waste. 5 10 10 5.74 3.39 36 In this work we determined the amount of C1 in fresh 36 primary reactor water from the PWR Gösgen and from ac- * number of C1 atoms per ml water. Table 1: tive ion exchange resins of this nuclear power plant. 36 The activity of 36C1 in reactor water is too low to C1 and total chloride concentrations in fresh primary re- be measured directly by conventional counting techniques. actor water from KKG. We therefore applied the so-called AMS (accelerator mass spectroscopy) technique to determine the 36C1 concentra- tion. The original sample contained 10 ppb Cl". To 1 to Sample no. N(abCl)/g- N(3bCl)/g" 10 ml of reactor water (see table 1) 3 ml Cl~ carrier (3.8 AMS LSC mg/ml) was added and a sample of AgCl was prepared as xlO14 xlO14 described elsewhere [1]. These samples were then intro- 1 0.94 1.21 duced into the ion source of the tandem accelerator at ETH 2 1.12 1.20 Honggerbcrg and the 36C1/35C1 ratio determined (for details 3 1.24 1.09 see [2]). 4 1.16 1.22 The results are summarized in table 1. From five deter- 36 minations we deduce an average concentration for CI of * number or 36C1 atoms per gram resin 10 (6.2 ± 0.2)xl0 atoms/ml water. This corresponds to an Table 2: activity for 36C1 of 4.4 Bq/1. The average ratio of 36CI/C|- 4 •""CI concentrations in active ion exchange resins from is about 3.6 x 10~ . KKG. As a next step the 36C1 content in loaded (active) ion exchange resins was measured. The resins (mixture of an- ion and cation resins) were first chemically processed: 2g of active resins were added to 15 ml of H2SO4 (cone) to References carbonate the resins and to distil Cl~ in form of HC1 at about 200 °. After some purification from SO2, HC1 was [1] Liu Xinqi cl al., to be published trapped in pure H O. This solution was processed, first as 2 [2] NJ. Conrad et al., Radiocarbon 28 (1986) 556. described above for an AMS measurement of 36CI and, second, also for liquid scintillation counting (LSC). In this case the solution was mixed with INSTA GEL scintilla- tor and counted with a TRI-CARB 1500 apparatus. LSC counting of the highly quenched samples was performed in the energy range 50 - 250 keV. Both the /7-spectrum and the long-time behaviour of the count-rate (no decay) was found to be in agreement with 36C1. Table 2 summarizes the results from both determinations. Good agreement be-

98 Materials Sciences (3300)

Defect Physics (3301)

POSITRON PHYSICS AT PSI

PSI - GENEVA

W.B. Waeber', U. Zimmermann', A.A. Manuel*. M. Peter*, H.R. Otl*

* Paul Scherrer lnslitul, CH-S232 Villigen PSI t Physique de la Matiere Condensed, University de Geneve

During the last 20 years, the various positron annihila- ment would also serve the universities of this country and tion techniques have contributed substantially 10 our knowl- other research groups from abroad to perform their own edge of vacancy type defects in pure metals. More recently, experiments above all in the domain of condensed matter the observed sensitivity of positrons to precipitates and in- physics and materials sciences. terfaces has opened new fields of applications such as the At a working seminar in July 1989 at PSI on 'Possible study of nucleation of u.^ial clusters and the growth and source techniques which could be implemented at PSI', the ripening of precipitates in alloys [1,2]. Positron trapping at idea of a new positron-modcrator-concept was born [5]. Cu-panicles in an Fe-matrix after both thermally and radi- It would be based on conventionally achievable ^-source ation induced precipitation has been observed [3,4]. Based strengths, and it anticipates to attain slow positron beam on these results which were obtained in a collaboration be- intensities of > 1010 e+/sec, whereas state of the an lab- tween ETH-Ziirich and PSI, it was decided to move the ex- oratory beams reach values of ~ 105 e+/sec [6]. Further- perimental equipment from Zurich to PSI. Two ID-ACAR more, in November an international workshop on 'Intense machines (long-slit angular correlation) are now installed slow positron beams and applications in condensed matter and in operation at PSI. physics and other scientific disciplines' was held at PSI. 38 One machine is a high resolution 1D-ACAR with two scientists from Japan, USA, USSR and Europe as well as scintillation counters (Nal(Tl) 50mm diameter, 250 mm 28 scientists from this country attended the meeting. The long) behind lead collimators (lmm slit width) at a dis- highlights of the workshop can be summarized into the fol- tance from the sample of 2.5m each (angular resolution lowing three issues: 0.4mrad FWHM). Cu-sheets, activated by thermal neutrons in the pool reactor Saphir to ICi 64Cu, are used as /?+- • The state of the art and worldwide situation of intense sources. The samples are placed in a vacuum chamber at slow positron beams p<10~6mbar. Measurements from ambient temperature to liquid N;, are possible. The second machine is an ACAR ap- • Reasons for the necessity of intense beams in the paratus with fixed detectors and a broad resolution (3mrad) domains of solid state physics, materials sciences and which measures ACAR at zero angle only, but with high atomic physics counting statistics (peak highi PH). Therefore, it becomes possible to measure the PH as a function of temperature in • Technical and scientific possibilities at PSI. a similar way as the S-parameier in the Dopplcr broadening technique. The samples can be heated up and cooled down The following proposition has found a deep consensus at fixed temperature rates, e.g. lK/min., between ambient among the participants: temperature and 800°C under HV conditions. "The scientists assisting the workshop on in- PSI is a national laboratory which offers infrastruc- tense beams of slow positrons and applications, tural possibilities for the installation of an intense positron realize that: source. This idea is being pursued seriously in a dedicated study with the aim to work out a project for the realization - The interest for positrons grows both in of an intense slow positron beam facility. Such an invest- research and industry

99 - present sources are far from attaining the- References oretical performance [1] K.Ghazi Wakili, U.Zimmermann, J.Brunner, Ph. Tip- - most interesting problems exist in metals, ping, W.B.Waeber and F. Heinrich, Phys. Status Solidi semiconductors, surfaces, which could A 102, 153 (1987). be studied with an intense beam - great efforts are undertaken in several in- [2] R.Krause et al., Proc. of the European Meeting stitutions, that the problem is timely and on Positron Studies of Defects, 23-27 March 1987, that coordination is possible, Wemigerode, GDR, Vol. 2, Part 1, Fl.F2.F5 and therefore recommend that PSI seriously [3] K.Ghazi Wakili, Diss. ETH Nr. 8722 (1988). considers the construction of an intense slow [4] K.Ghazi Wakili, Ph.Tipping, U.Zimmermann, and positron source. This would represent an es- sential contribution to contemporary research W.B.Waeber, Z.Phys. B, Condensed Matter (1990), in condensed matter physics". in press. [5] D. Taqqu, this volume. Both an issue of the proceedings of the workshop [7] and the formulation of a master proposal for the realization of [6] PJ. Schultz, K.G. Lynn, Rev. Modem Physics, 60 an intense slow positron beam facility project at PSI, will (1988) 701. underline the significance of positron physics activities at PSI. [7] Helvetica Physica Acta, Vol. 63, No. 4, (1990) in In view of potential interests on proposing user experi- press. ments for a possible future positron beam facility at PSI, a scientific questionnaire has been sent to the widest positron [8] J. Van House, A. Rich, Phys. Rev. Lett 60 (1988) community, encouraging research groups to submit specific 169. proposals. The result was a considerable response group- [9] J. Van House, A. Rich, Phys. Rev. Lett. 6J. (1988) ing mainly into the fields of solid slate physics and materi- 488. als science, concerning preferentially surfaces and defects. Most of the returned questionnaires expressed a willing- [10] G.R. Brandes, K.F. Canter, A.P. Mills Jr, Phys. Rev. ness to submit specific proposals and to participate in fu- Lett. 61 (1988) 492. ture positron user experiments at PSI. Among such user experiments positron microscopy [8,9,10] as a separate PSI project might open an exciting new field of applications, above all in surface and thin film physics and in defect physics.

100 HIGH EFFICIENCY POSITRON MODERATION

Paul Scherrer Institut, CH-5232 Villigen PSI

D. Taqqu

Various schemes have been proposed in the last years particles [4]. This is realized by inducing their multiple pas- for the achievement of intense slow positron beams. With sage through a thin foil, reducing thereby their energy as far the successful recent developments of the applications of as possible and extracting them just before stopping in the slow positrons in solid state physics and material research, foil takes place. Minimal blow-up of beam size during this the realisation of slow positron factories is being consid- operation is ensured by placing both source and slowing- ered seriously in many laboratories [1]. As there are some down foil on the axis of a high field solenoid (at field Bo) prospects that the PSI will enter this research field in the so that the positrons spiral around the magnetic field lines near future, it seemed appropriate to look for a production and remain transversally confined. Return toward the foil is scheme that makes optimal use of the available PSI infras- induced by introducing mirroring fields on both sides of the tructure. emitted high energy beam. A first mirror action is achieved The most standard slow positron beams arc based on by increasing the magnetic field to a maximal value Bm on /?+ radioactive sources. These can be converted into slow both sides of the source and foil assembly. This magnetic positrons when the last part of their slowing-down takes bottle field configuration is especially effective for the high place in the outer layer (so-called escape depth) of a well energy positrons which may pass hundreds of times through selected material (moderator). Since the escape depth (~ the foil before multiple scattering changes their angle to the 100 ftg/cm2) is much thinner than the average range of axis to value smaller than the cut-off angle of the mirror the /3's, the conversion efficiency is very low and the best field [5]. As this occurs predominantly at low energy a performance ever achieved (with solid neon as moderator second mirror actions is added: electrostatic columns with [2]) is about 1%. This fact, together with the limited activity positive terminal high voltage Vr are placed at both ends of standard laboratory /?+ sources, resulted in slow positron of the solenoidal field. These electrostatic mirrors return beam intensities of the order of 107-108 e+/sec. all positrons exiting the foil with energy less than eVr and ensure together with the magnetic mirrors a high overall The most straightforward approach to an increased beam confinement efficiency. intensity is to use stronger /?+ sources and at PSI the in- tense low energy proton beam available from the injector Figure 1 shows schematically the arrangement of the cyclotron is an optimal candidate for the production of var- main elements: the source is deposited on a thin foil sup- ious kind of muliicurie /?+ emitters. However, accelerator port and placed at the centre of the magnetic bottle. Most beam time and intensity are costly and it would be very high energy positrons are confined within it while those useful if a more optimal slow positron production scheme having slowed down to below eVr remain confined either could be achieved. within it or within the electrostatic mirrors. The extraction of the intermediate low-energy positron beam takes place in It is therefore interesting to re-examine the moderation a long solenoid of intermediate field strength where various efficiency limitation and try to overcome the barrier that transverse and longitudinal electric fields induce the sepa- limits this efficiency to about 1%. Increase of the escape ration of all positrons which have slowed-down to below depth and re-emission probability would be one way to a cut-off energy E (< 10 keV). This operation, explained achieve this goal, but extrapolation of the results of the c in detail in Ref. [3], leads to a beam of positrons of en- last decade of research in this field does not indicate any ergy between 0 and E that is directed towards an efficient significant improvement in moderator performance in the c moderator placed close to the source. The slow positrons near future. re-emitted by the moderator are extracted from the con- Another approach that has not yet exhausted its poten- fining fields by passing sideways of the right electrostatic tial is the optimization of the fraction of /?+ that stop within mirror. the escape depth. Some modest improvements in this direc- tion have been achieved by a careful design of the source The achievable moderation efficiency and beam inten- moderator geometry. sity depend on the kind of source and moderator used and on the strength of the mirror fields. The search for a more fundamental path have recently la [3] led to a particular design where the 0+ emitted by the For a F source prepared according to the state-of- li source are first transformed into a beam of less than 10 keV the-art technology [S] and deposited in the form of Li F 2 average energy. When such a beam is directed towards within a 4 mm diameter spot on a thin S ng/cm carbon 7 the moderator, it stops almost completely within the escape foil, a 3 Curies source with thickness of about 12 fig/cm depth and leads to a moderation efficiency close to the max- thickness is obtained.

imum ever achieved (70% in solid neon [2]). The overall Assuming flo=3 T, Bm/So=3 and Vr=200 kV, a con- moderation task is now accomplished in two separate steps finement efficiency in excess of 50% can be estimated. The and it is possible to optimize each of them independently of resulting beam is about 6 mm wide and, over such a diam- the other. The first operation, the production of the inter- eter, the average overall foil thickness amounts to about mediate beam is a compression in momentum phase space 12 ng/cm2. This is thin enough to keep the losses in the that requires a controlled slowing down of the high energy foil minimal at a cut-off energy Ec not exceeding 10 keV.

101 SOURCE —| INTERMEDIATE LOW ENERGY BEAM MOOERATOR-i - SLOWING DOWN BEAM

EL.' MAG. .MAG. SLOW 'POSITRON EL.V MIRROR MIRROR MIRROR BEAM MIRROR

Figure 1: Schematic arrangement of the main components and sketch of the various beams.

By using solid neon as moderator, about 50% of the con- References fined positrons will be converted into slow positrons. With an overall moderation efficiency exceeding 25% [1] See for example the various contribution of the PSl the resulting slow positron beam is equivalent to a stan- Workshop on slow positron beams and applications, dard beam of less than 1 cm1 emission area, and intensity November 21, 1989 to be published in Helv. Phys. exceeding 21010 e+/sec. It is relevant to point out that Acta. the source activity results from a target irradiation with a [2] A.P. Mills Jr. and E.M. Gullikson, Appl. Phys. Lett. cyclotron proton beam of not more than 20 nA current. 47 (1985) 239. Hence, as soon as improvements in target preparation tech- niques will allow higher irradiation currents, significant [3] D. Taqqu, contribution to the PSI Workshop on Slow increase in final slow positron beam intensity should be Positron Beams and Applications, to be published in achievable. Helv. Phys. Acta. [4] D. Taqqu, SIN Internal Report TM-30-25, 1984. [5] See for example J.D. Jackson, Classical Electrody- namics, Chapt. 12. [6] R. Iwata et al., Appl. Radiat. IsoL 38 (1987) 979.

102 EVIDENCE FOR OFF-SYMMETRY POSITION OF INTERSTITIAL MUONS IMPLANTED IN CRYSTALLINE BISMUTH

PSI • ZURICH,

G. Solt", E. Lippeltt, and B. Delley1

* Paul Schecier Institut, CH-5232 Villigen PSI t Instilui fur Miuelenetgiephysik der ETH Zurich, c/o PSI CH-5232 Villigen X PSI-RCA Laboratories, Badenerstrasse 569, CH-8048 Zurich

Recent muon spin rotation (pSR) experiments [1],[2] on a high purity Bi single crystal indicated a surprisingly broad distribution of magnetic fields at the muon position: > -17.5- the second moment M2 as a function of orientation was found to be 2-3 times larger than that expected for muons occupying one of the interstitial sites of symmetry V>3d in the rigid Bi-lattice. Now, if this broadening was entirely due to a lattice deformation around the muon, an unprece- dently large (~ 10%) displacement of Bi-atoms towards the interstitial centre would have to be invoked [1]. One re- alizes, however, that a substantial field broadening arises also if, instead of a strong lattice relaxation around a 'cen- tral* muon, the muon itself moves off-centre by 'relaxing' within the interstitial cage; such a displacement should re- sult, of course, from the particular position and shape of the potential that binds the muon at the interstice. This has motivated a theoretical study of the equilibrium positions 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 for both lattice atoms and muon in Bin00 clusters, the first distance from symmetry centre along c—axis [a.u.] results of which are presented here. Figure 1: Ground state energy of a Bia(/<) cluster modeling In determining the potential energy surface for the muon an interstice No.l [1] in rhombohedral bismuth at 78K. in various metals, pseudopotential and 'jellium' methods The electronic term {21e} (D), being the ground state for a [3]-[4] and cluster studies [5] were seen to give concor- muon in the symmetry centre, becomes the first excited state dant predictions. In view of the complex electronic and, in for a displacement beyond ~ 1.15 a.u.; the minimum for particular, lattice dynamical [6] properties of pure Bi, the the new ground state {16a} (o) determines the equilibrium cluster approach with a reasonably small number of atoms position along the c-axis. The dotted line indicates the total is perhaps more adequate here, even if a Bi-atom with its 83 energy with no muon in the cluster. electrons is not the simplest input for a molecular structure calculation.

We have calculated the cohesive energy of the Bin(/j) centre. The result is qualitatively similar for other sym- clusters by the method 'Dmol\ a local density functional metry directions, though with somewhat shallower minima, algorithm for polyatomic molecules and clusters [7]. Input and the potential wells are only deeper for interstice No.2 to Dmol are the nuclear coordinates, and specifications for (~ 0.8 eV along the c-axis) ; the results can be used to the quality of the numerical approximation. find the angular dependent potential in form of a series in symmetry harmonics. First, the total energy of a Bis(/i) molecule as a func- tion of muon coordinates was investigated. This 'mini- In Fig.2 the measured second moments of the dipolar mum' cluster is obviously the smallest reasonable unit rep- field [2] and also those calculated for a muon displaced resenting the distorted cubic 'cage' made up of the 2+6 first along the c-axis, with reference to Fig.l, are plotted for neighbours around an interstitial site in the rhombohedral three different muon positions. The overall qualitative im- Bi-lattice, in which two kinds (No. 1 and 2) of interstices provement on assuming a static, off-symmetry displaced alternate, differing slightly in shape but not in symmetry. muon is clear, although a discrepancy with too deep pre- The result for the muon potential energy in this 'minimum' dicted minima at 90° persists. cluster shows a local maximum at the interstice centre, and The above model for calculation has two main short- a minimum follows, for some displacement, in each direc- comings. First, the cluster Bi8(/i) is obviously too small tion studied so far. In Fig. 1 a cut of the energy surface is for allowing a conclusion on the solid: even if, purely geo- shown along the hexagonal c-axis. The Bi-coordinates for metrically, this unit is fairly well 'distinguished' in the lat- the interstice were fixed, at this stage, to the crystallographic tice, in our calculation of electronic structure all Bi atoms data. One notices the crossing of the two lowest electronic are actually at the 'surface', thus the ground state proper- levels as the muon moves along the c-axis, and the energy ties of this cluster may significantly differ from those of minimum is at a distance of ~ 0.8A from the symmetry the cage embedded in the crystal. Second, even if there

103 an off-symmetry minimum: a theoretical curve for Fig.2 on that case has to be calculated using a broad ground state 0.12 distribution of muon displacements. A detailed study of this cluster is still in progress. We only notice, that the temperature dependence of the measured second moments il],12] lends itself also to an interpretation with a weakly bound off-centre muon ground state. At the present stage one can conclude that the results for small clusters indicate an off-symmetry ground state position for the muon, which can explain some important features of the experiment. Whether this means a static

0.04 binding at a single deep minimum along the c-axis, muon motion along a torus joining radial minima for different direction!!, or one dimensional dynamics in a singularly flat o.c: potential box is subject of further studies. o.oo 0 20 60 80 100 120 140 160 180 References Orientation (degrees) [1] F.N. Gygax, B. Hitli, E. Lippclt, A. Schcnck and Figure 2: Second moments in zero external field for inter- S. Earth, Z.Phys.B 71, 473, 1988 stice No.l as a function of the angle between the c-axis and muon polarization, calculated for central and displaced |2] E. Lippclt, thesis, to be published muon positions, together with the experiment; the numbers ai the curves indicate the shift along the c-axis. 13) G. Soil, M. Mannincn and H. Beck, J.Phys.F:Met.Phys. 13, 1379, 1983

was a 'normally' deep radial minimum for each direction [4] S. Estreicher and P.F. Meier, Phys. Rev. B27,642,1983 in the potential energy, the surface along the locus of these [5] B. Lindgren, B. DeUey and D.E. Ellis. Hyperf. Interact. minima may be very flat and the muon wave function ac- 17-19, 393, 1984 cordingly extended. In other words, muon dynamics may have primary importance in interpreting the data. To deal 16] E.G. Brovman, Institute of Atomic Energy, Rept. IAE- with the first point, a preliminary calculation for the Bi3:_,(/j) 1456, Moscow 1967, transl. Los Alamos Rcpt. LA- cluster was carried out for the muon along the c-axis. With TR-68-33 1968, and R.E. MacFarlane, in Physics of a hardly noticeable local maximum at the centre ana a sim- Scmimeutls and Narrow-Gap Semiconductors, ed. D.L. ilarly shallow minimum beside, the energy surface is now Carter and R.T. Bate, Pergamon 1971 'singularly' flat until a displacement of ~ 0.7A, where it begins to rise. This implies a strong dclocalization along 17] B. Dclley, J. Chem. Phys. 92, 508, 1990. the c-axis, without a sufficiently deep well for binding at

104 COHESIVE PROPERTIES OF SMALL CLUSTERS WITH IRON AND COPPER FOR A STUDY OF PHASE SEPARATION IN ALLOYS

PSI - ZURICH

G. Solf and B. Delleyt

* Paul Scherrer Institut, CH-5232 Villigen PSI t PSI-RCA Laboratories, CH-8048 Zurich, Badenerstrasse 569

The recent interest for irradiation induced phase sepa- ration [I] and, in particular, precipitation of copper from supersaturated iron alloys under irradiation [2], [3] gives new actuality to questions on the stability, and cohesive properties in general, of small metal particles dispersed in a solvent metal. For irradiation induced copper particles with a diameter of 15-20A in iron the 'lattice' structure and properties of the interface are of primary interest, e.g. the recent observation of a nickel-rich interface for copper precipitates in Fe-Cu-Ni [4] is still waiting for explanation. To deal with these points, ab initio calculations of the elec- tronic structure for medium large (say, 50-100 atoms) metal clusters are of obvious help, since the intensive physical pa- rameters have been seen tc converge with increasing size and can reasonably be extrapolated to the case of the bulk solid [5]. The present calculations were done by the method 'Dmol' [6], an ab initio iterative, variational scheme with molecular orbitals determined in the frame of the local den- sity functional formalism; for our clusters with iron, spin 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7' 0.8 polarization was taken into account. The numerical basis consists of exact LDF wave functions for the neutral atoms and for ionic stales. Figure 1: Cohesive parameters for bec Fe^ clusters vs N"1/3, spin polarized calculation. The values for (l/N)=0 Here we report on results for the variation of cohesive (full circles) are the corresponding local density results [7] parameters for pure iron with increasing cluster size and on for the periodic solid; the experimental values for the en- the magnetization hole associated with a single, solute cop- ergy (x) and lattice parameter (*) are also shown. per atom. The calculated cohesive energy E/N and lattice constant a for FeN are plotted in Fig.l. For 'sufficiently' large clusters the dependence of both the energy, the relaxation of the lattice and spatial vari- 3 quantities on N~ " is expected to be linear, as found earlier ation of the spin density (magnetization) was calculated. for Cu/v [5]: this is a result of the interplay between the The structure of the 'hole' in magnetization around a non- cohesive 'bulk energy" and the opposing surface tension. magnetic precipitate determines, among others, the mag- Indeed, for cluster sizes where the simple macroscopical netic cross section for slow neutrons, the knowledge of relationship ec = e4 - sF/V is a reasonable approximation which is needed for the interpretation of small angle neu- (ec is the cohesive energy per unit volume, ej is that for the tron scattering data [2], [3]. The calculation for a cluster bulk, F and V are surface and volume of the cluster, V ~ of 59 Fe atoms takes typically 80 minutes on the CON- 3 Na ), this linearity follows. The maximum cluster size here VEX machine of the PSI. The result in Fig.2 shows the was N=59, that is 5 shells around a central atom in a bec spin density on the plane (110) with the Cu atom at the 3 lattice; the aim was to see the convergence with N ~' / , thus origin, giving a detailed picture of the spatial structure of a single structure was kept as fixed. Apart from the above the magnetic 'vacancy' being, in fact, a slightly polarized discussed general trend, small irregularities are expected unit cell. for particularly 'unsphericaT clusters: the relatively larger These first results show that the technique Dmol ade- surface for N=51 leads, for example, to an anomalously quately describes the equilibrium cohesive parameters for small volume and correspondingly less cohesive energy, iron and 'iron-based' clusters, the size of which can attain N well visible in Fig.l. In relation to the experiment, the ~ 100 or more at presently available computer capacity and prediction of a too small radius and thereby a too large speed, and that the cluster results can be used for a reason- calculated cohesive energy for iron is a known feature of ably accurate extrapolation of energies, optimum structure, the local density technique [7] and has little importance atomic distances or magnetization densities to the case of here. an infinite solvent. Next, a single Cu atom was put at the centre, and both

105 References

1 'J W [1] H. Wiedersich, in Physics of Radiation Effects in

•\ Crystals, ed. by R.A. Johnson and A.N. Orlov, North ;' %~ Holland, 1986

[2] P.A. Bcaven, F. Frisius, R. Kampmann and R. Wagner W /i\ ^ - in Atomic Transport and Defects in Metals by Neutron V Scattering, ed. by C. Janot et al. Springer 1986, p.228 [3] G. Soil, F. Frisius, W.B. Waeber and W. Biihrer in / i \ Effects of Radiation on Materials: 14th Int. Symp., / I \ ed. by N.H. Packan, R.E. Stoller and A.S. Kumar, .% V/ w. ASTM STP 1046, Philadelphia 1990, in press [4] MX Miller, D.T. Hoelzer, F. Ebrahimi, J.R. Hawthorne and M.G. Burke, Environmental Degra- A dation of Materials in Nuclear Power Systems-Water i' ^ Reactors, ed. by G J. Theus and J.R. Weeks, The Met- \ allurg.Society, Warrendale, 1988 \J / \ [51 B. Delley, D.E. Ellis, A.J. Freeman, E.J. Baerends and • ' » rr i M D. Post, Phys.Rev.B 27, 2132, 1983 Figure 2: Magnetization around a Cu atom in the bcc Fe [6] B. Delley, J. Chem. Phys. 92, 508, 1990 lattice: a plane (110) showing the 'hole' in spin density; the size of the map is 14x14 al.u., the distance between [7] V.L. Moruzzi, J.F. Janak and A.R. Williams, Calcu- 3 adjacent contour lines is 1 Bohr magnclon/A . lated Electronic Properties of Metals, Pergamon, 1978

106 IRRADIATION FACILITY WITH VARIABLE TEMPERATURE, NEUTRON ENVIRONMENT AND IN-SITU STRAINING

Paul Scherrer Inslitut, CH-5232 Villigen PSI

W.B. Waebcr, M. Caro, J. Stcpanek

Most of the conventional irradiation rigs used in ma- terials lest reactor irradiation experiments are set up for a fixed irradiation temperature, and a specific fission neutron spectrum determined by the chosen irradiation position. In most cases large volumes of specimens for fracture me- chanics have to be irradiated in a number of irradiation experiments in order to obtain conclusive results on the material's behaviour [1]. For each specific material such test programmes arc necessary procedures in engineering sciences for judging safety related questions, for example. In contrast, also for a research programme on the fun- damental questions of radiation induced phase separation in alloys, an irradiation facility is a prerequisit. However, such a facility has to meet conditions like high flexibility in performance, a wide range of irradiation parameters and small specimen sizes; these are the major requirements for studying radiation damage in a fundamental way by means of solid state physics and physical metallurgy approaches. These objectives are pursued and realized in a new ir- radiation facility project [2] at the pool reactor Saphir at PSI (Figure 1). In forthcomming neutron irradiation ex- periments, the variables on the specimen materials are the

irradiation temperature T,, a neutron spectrum parameter k

and an in-situ strain parameter

blocks, each at its own temperature (Tj ~ T£lWj,...,350°C)I

fission neutron spectrum ot ~ fE <^dE (Et = 0.5, 2.0, 5.0 15 2 1 MeV; ck ~ 10 ncm- sec-';dpa~ lOMO ) and in-situ uniaxial stress level (

107 Examples are [3]: References

• a detailed temperature dependent study of the thermal [1] W.B. Waeber and D.H. Njo in 'Radiation EmbritUe- relaxation of cascades into voids or dislocation loops ment of Nuclear Pressure Vessel Steels: An Inter- in pure iron national Review' (3rd volume), ed. by L.E. Sleele, ASTM STP 1011, Philadelphia 1989,48-69. • investigations of the precipitation kinetics in alloys, for example to determine critical temperatur- and [2] W.B. Waeber, presented at the IC-RDM (International concentration-dependent particle radii Group on Radiation Damage Mechanisms) Confer- ence. 7-11 November 1989, Helsinki. • low temperature internal friction experiments with the aim to study interaction mechanisms of dislocations [3] Current thesis work supported by the Schweizerischer with damage particles Nationalfonds zur Forderung der wissenschaftlichcn Forschung, in collaboration with EPFL. • measurements of the onset of annealing-recovery stages in precipitation kinetics [4]. [4] K. Ghazi-Wakili, P. Tipping, U. Zimmermann, W.B. Waeber, Z Phys. B: Cond. Matter, in press. For internal friction experiments and for certain nuclear solid state techniques [S] it is essential to work with highest [5] G. Solt, W.B. Waeber, U. Zimmermann, P. Tipping, F. purity specimen material and under UHV environmental Gygax, B. Hitti, A. Schenck and P. Beaven in 'Effects conditions in order to avoid impurity contamination before, of Radiation on Materials', 14th Intern. Symp., ASTM during and after irradiation. STP 1046 (1989) 180-198.

108 MATHEMATICAL ANALYSIS OF GRAIN BOUNDARY MISORIENTATION

PSI - GRENOBLE - ORSAY - NEW HAVEN,

H. Grimmer*, R. Bonnet', S. Lartiguc', L. Priester1, B.L. Adams5, J. Zhao5

* Paul Scherrer Institut, CH-S232 ViUigen PSI t Institut National Polytechnique de Grenoble, F-38402 Saint-Martin d'Heres j University Paris-Sud, F-9140S Orsay § Yale University, New Haven, Conn. 06520, USA

The physical properties of grain boundaries in polycrys- Measured orientation relationships between neighbour- talline materials form a rapidly growing area of research. ing grains are usually expressed in terms of the misorien- Relative orientations of neighbouring grains that are com- tation distribution function introduced by Bunge in 1982. patible with periodic grain boundaries play a major role The rotation describing the misorientation is usually given in numerical simulations of their properties as well as in in terms of Euler angles (,fi)> where 0 < \ < 2ir, the interpretation of experimental results [1]. The long ex- 0 < ft < 2JT and 0 < $ < IT; & is an in- perience of the first named author in developing rigorous variant measure on the rotation group. In the case of holo- methods of determining systematically such orientations has hedral cubic symmetry, misorieniations can be restricted to led to a number of international collaborations. an asymmetric domain 2 • 242 = 1152 smaller in measure Consider two congruent hexagonal, rhombohedral or than the set of all rotations. Such an asymmetric domain is tetragonal lattices related by a rotation R. Assume that usually chosen with as small as possible. It has the dis- the axial ratio c/a of the lattice and the angle 0 of the advantage that the Euler parametrizalion is highly discon- rotation are such that the two lattices have a large frac- tinuous at = 0. Zhao and Adams [6] therefore introduced tion of their symmetry translations in common. If c/a is an asymmetric domain with < ir/2 and as close to T/2 slightly changed, the common symmetry translations may as possible. This domain is compared in [7] with the asym- disappear and a small deformation of one of the lattices is metric domain in the space of unit quaternions introduced needed to restore them. This deformation can be found as by Grimmer in 1974 [8]. follows. Write A as a product of two rotations with axes perpendicular and parallel to the principal symmetry axis, R = RLR\\. Then the deformation is a pure shear in a References plane perpendicular to the axis of R± with tensor shear strain e = A sin 4, where A is the relative change of the [1] HJ. Fischmeister, J. Physique 46.C4 (1985) 3-23. axial ratio c/a and * is the angle of R± [2]. This result is [2] H. Grimmer, R. Bonnet, Acta Cryst. A (in print). important because it separates the parameter e, introduced by Bonnet and Durand, into a product of two factors, one [3] H. Grimmer, Helv. Phys. Acta 62 (1989) 231-234. depending on the lattice and the other on the misorientation. Systematic results on coincidence orientations of rhom- [4] H. Grimmer, Acta Cryst. A 45 (1989) 505-523. bohedral lattices [3,4] have been used to interprete transmis- [5] H. Grimmer, R. Bonnet, S. Lartigue, L. Priester, Phi- sion electron micrographs of grain boundaries in sintered a-alumina . Near-coincidence boundaries were found to los. Mag. A (in print). occur more frequently than would be the case for randomly [6] J. Zhao, B.L. Adams, Acta Cryst. A 44 (1988) 326-336. distributed orientations and in many cases to contain peri- odic networks of grain boundary dislocations. The analysis [7] BX. Adams, J. Zhao, H. Grimmer, Acta Cryst. A (in of such networks indicated that the coincidence descriptions print). with the lowest value of the multiplicity E best describes the boundary as long as e is less than 1 % [5]. This result [8] H. Grimmer, Acta Cryst. A 30 (1974) 685-688. needs confirmation by high resolution electron microscopy.

109 THE ROLE OF CHEMICAL COMPOSITION IN THE NEUTRON IRRADIATION EMBRITTLEMENT SENSITIVITY OF FE-BASED ALLOYS

Paul Scherrer Institut, CH-S232 Villigen PSI

P. Tipping. W.B. Waeber

A series of controlled composition steel alloys (ex- A contribution of P to radiation sensitivity was isolated perimental laboratory melts) originating from Japan and when B and C were compared; the mechanism for this is included in the IAEA Coordinated Research Programme, still subject to discussion though but indications are that were irradiated in the STILO facility in order to investi- it is associated with radiation-enhanced diffusion to matrix gate their propensity towards neutron irradiation embrittle- interfaces [1]. The P is likely to be in solid solution, and menL Using the change in microhardness as a measure is therefore free to interact with matrix defects or to form of the sensitivity to neutron damage, the effect of the ele- precipitates during 290C irradiation [2]. The precipitates ments copper, nickel and phosphorus were studied princi- are body-centered tetragonal Fe3P phase and these together pally. Two fluence levels were available namely O.S and with defect clusters could provide obstacles to glide dislo- 5.0 x 1019cm~2 E>lMeV and the irradiation temperature cation movement resulting in increased hardness sensitivity. was 290C. Nickel increased the neutron irradiation sensitivity for a given level of Cu and P (D, E and H and F and G). The behaviour was complex when the two different levels „ 120 Cu Nl Ni of P were taken into account. For instance, alloys F and G lay between E and H with respect to Ni, but they had approximately three times more P. However, they exhib- 100 — ited somewhat less sensitivity to irradiation, indicating a possible Ni-P interaction. An increase in Ni content causes CO 80 - grain boundary (temper) embrittlement in steels of this type in the temperature range 250 - 600C [1]. However, the o grain boundary effect will only influence toughness and not 60 — hardness [3]. Carbide forming elements (e.g. Cr, Mo, V, Zr and Ti) have a higher chemical interaction energy with P CO 40 — atoms (> 110kJ/mol.), than the latter with grain boundaries m (< 58kJ/moI.), and these elements tend to hold P in solid z solution, thus suppressing grain boundary segregation [4]. Q 20 — DC Nickel, on the other hand, has a low chemical interaction energy with P (?9kJ/mol.) and would exert little influence on retaining P in solid solution. In high Ni-P alloys (F and Cu 0-33 001 001 0-16 016 G), the P can come out of solid solution and segregate to P 0018 017 -007 0-006 002 the grain boundaries [2]. A consequence of this is that the amount of P available in solid solution for matrix interac- Ni 082 0-1 0 39 MB 0-62 0-82 0-82 tions is correspondingly less. This would lead to the lower increase in hardness (lessened sensitivity) observed. Figure 1: Copper, phosphorus and nickel influence on the Although the initial hardness values varied due to the sensitivity to fast neutron irradiation as indicated by micro- compositional differences, the increases in hardness were hardness increase. The top values of the bars correspond to more for higher Ni contents. The role of Ni is still not a fluence of 5.0xl019cm~2 and the top values of the non- 19 2 fully explained but it may influence the solubility of Cu in hatched portions to a fluence of 0.5xl0 cm" (E>lMeV). iron, [5] for example, by enabling higher degrees of super- Other elements present in the alloys were C 0.18, Si 0.27, saturation to be obtained, thus causing more precipitation Mn 1.45, S 0.001, Cr 0.15, Mo 0.54, V 0.01, Al 0.02 and Fe to occur for a given neutron fluence. - balance. All values are averages and are given in weight An interesting effect was noted for the case of a Fe- percent. 0.8 weight percent Cu model alloy [6]. This was solution treated by healing in vacuum to 840C and then quenching The effect of the steel's chemical compositions can be rapidly into saline solution at 18C, thus trapping virtually seen in Fig. 1. The sensitivity of the high Cu alloy A, was all of the Cu in solid solution. Effectively all of the hard- evident for both fluence levels investigated. The low Cu ness increase occurred during the first irradiation cycle [7] version of this alloy, B, did not even reach the low fluence afterwards, increasing the fluence by a factor of ten did level of hardness increase for A, even after ten times more little to alter the hardness. The isochronal behaviour of fluence. This indicates that the increase in hardness is at irradiated and unirradiated material is shown in Fig.2. least partly due to the amount of Cu available for precipi- tation or interaction with matrix defects due to irradiation.

110 The lower curve (unirradiated [7]) depicts classical pre- 220 cipitation hardening behaviour from a metastable age hard- ening alloy. As the temperature increases, nucleation, Os- wald ripening (precipitate growth = hardening) and finally resolution of the precipitates (= softening) occurs [8]. The upper curve indicates the way hardness is recovered for the irradiated case. That both curves finish below the value for the as-quenched super-saturated condition is probably a consequence of the removal of quenching stresses. Both conditions achieved the reference hardness value at 700C using 20min. isochronals.

References

[1] Hawthorne, J., and Former, E.Journal of Engineering for Industry Vol. 94, No.3, (1972), 807 [2] Little, E.A., ASTM STP 870 (1985), 1009 80 300 400 500 600 700 800 900 [3] Dieter, Q., in "Mechanical Metallurgy" McGraw- Hill TEMPERATURE [C] Book Co. Ed. (1961), 388 Figure 2: Isochronal recovery behaviour for a model Fe- [4] Ustinovshchikov, J.I., Acta metall. M, No.3, (1983) 0.8Cu alloy. The unirradiaied (U) state behaviour shows 355 age hardening and then softening whilst the neutron irradi- ated state (I) recovers in another way. The curves can be [5] Odette, G., and Lucas, G., ASTM STP 909 (1986), 206 interpreted in terms of the nucleation and growth of copper- [6] Origin of the sample material: P. Beaven, GKSS, rich particles and their subsequent resolution back into solid Geesthacht solution (U), and the annealing out of irradiation damage with subsequent copper-rich particle resolution (I). [7] K. Ghazi-Wakili, U. Zimmermann, J. Brunner, P. Tip- ping, W.B. Waeber and F. Heinrich, phys. stat. sol. (a) 102.153 (1987) [8] K. Ghazi-Wakili, P. Tipping, U. Zimmermann and W.B. Wacber, Z. Phys. B, Condensed Matter (1990), in press PIREX, Irradiation Damages, Fusion (3302)

THE GROWTH OF HELIUM BUBBLES IN 600 MeV PROTON IRRADIATED ALUMINUM DURING POSTIRRADIATION ANNEALING

PSI - EPFL,

F. Paschoud\ R. Gotthardt', M. Victoria"

* Paul Scherrer Inslitul, CH-S232 Villigen PSI t Institul dc Gdnic Alomique, EPFL, PH-Ecublens, 1015 Lausanne

Helium produced by spallalion reactions in 600 MeV Two main models apply to the growth of bubbles: in proton irradiated aluminium has been shown to be retained the so called Ostwald ripening, small bubbles dissolve at in the irradiated foil and to agglomerate in the form of bub- the expense of large ones. The other model considered is bles [1]. In the present experiment, the stability of such the migration and coalescence of bubbles. Ostwald ripening microstructures was tested in three irradiated specimens of has been proposed as the driving mechanism in the growth which the initial conditions arc given in Table 1. All the of bubbles at high temperatures in nickel [2] and steels specimens have a high density CB (5.1021 to 1022 m~3) of [3] while growth results in Al [4] and Nb [S] have been small bubbles (2-4 nm diameter). The annealing treatments explained by using the migration and growth model. The were performed in thinned electron microscopy discs under slope of the growth curve found in the present measure- vacuum at temperatures between 843 K (0.9 Tm) and 893 ments can be explained by the migration and coalescence K (0.96 Tm), where Tm is the melting temperature. After of facetted bubbles. In order to migrate, the bubbles must each annealing, the specimens were observed in the electron form new steps in the facets. The important parameter is in and the bubble distribution was recorded. An this case the line energy of the step formed, e. For spherical additional observation region was thinned down after each bubbles, the rate of change of the bubble radius, consider- annealing, to check for differences in growth between the ing that the equation of slate for a perfect gas applies, is thinned region (ISO nm) and that with the original thick- given by [5]: ness of the foil (10 ym). The study of the evolution of the dr _ 3mkT bubble distributions showed that there is more growth in the thick specimens, because of a loss of bubbles through where m is the total quantity of gas, 7 is the surface energy the surface in the pre-thinncd specimens. For the studies of of the bubble and D its diffusion coeficicnt. In the case of growth, only the information on the annealing of the thick b facetted bubbles, diffusion is limited by the nucleation of region was therefore taken into account. Furthermore, care- a step in the facet. A diffusion coeficient has been derived ful observations of the morphology of the bubbles shows for this case by Willertz et al [6]: that they are not perfectly spherical but rather facetted. Typ- ically, facets normal to <111> and <002> directions are rD, ( -2girreA found before annealing. Db = exp I kT J

g is the ratio of the size of a facet to the radius of the Table 1: bubble, a,, as is the mean jump distance of an atom in its Specimen Tir, Dose CB Diam. 1 anneil surface, e is the step line energy and Ds the surface diffusion No. [K| [dpal |m-3l |nm] [k] coeficienL The equation of state derived by Trinkaus [7] is SO 400 1,4 1 x 10" 2,1 873 now used for the comparison with the experimental results, 86 480 1,6 4.9 x 10" 3,9 843 since it is more realistic for the high pressure in the bubbles. 103 450 2.8 6.2 X 10" 4.8 893 An energy or 3.5 x 10"11 J/m is found for the line energy. Precise values of this energy have not been obtained in aluminium, but other studies of bubble growth in this metal The evolution of the mean diameter and the total con- indicate values of the order of 3.0 x lO"11 J/m [4]. centration of bubbles for different annealing times, is shown in Fig. 1. For two specimens, numbers SO and 103, the The results obtained in specimen 86, annealed at the growth is characterized by an increasing mean diameter and lowest temperature at which any growth could be observed a diminishing bubble density. Both variables saturate for in the thinned specimens, indicate a different behaviour in long annealing times. When the logarithm of the diameter as much as no growth is observed in the annealings between is plotted as a function of time, the two growth curves have 20 min and 5 hours, while the final bubble structure, after a gradual slope (About 1/22 in the case of specimen SO). 100 hours annealing, is in the expected range.

113 The information obtained from this specimen is insuffi- References cient to decide whether a different mechanism is active at the lower annealing temperature. [1] D. Gavillct, R. Golthardt, J.L. Martin, S. Green, W.V. Green and M. Victoria; ASTM STP 870, F.Gr -ner and J.S. perrin Eds.,1985, p. 394.

[2] M.L. Saltier and W.A. Jesser; J. Nucl. Maier. 122-123(1984)523.

[3] J. Rothaut, H. Schroeder and H. UUmaier; Phil. Mag. 47(1983)781.

[4] H. Shiraishi, H. Sakairi, E. Yagi. T. Karasawa, R.R. Hasiguti and R. Watanabe; Trans JIM 17(1976)749.

[5] PJ. Goodhew and S.K. Tyler; Proc. R. Soc. Lond. A3J7.(1981)151.

• 86 Tr. 84.3K [6] L.E. Willeru and P.G. Shewmon; Met. Trans.

O 50 Tr. 87 3K 1(1970)2217.

4 103 Trt B93K [7] H. Trinkaus; Rad. Effects 78(1983)189.

50 100 Time (hours]

Figure 1: Mean diameters and bubble number densities in the Ihick region of the specimen as a function of the annealing time. Specimens 86, SO and 103 annealed at 843, 873 and 893 K respectively.

114 THE TENSILE AND FATIGUE PROPERTIES OF THE 1.4914 MARTENSITIC STEEL

PSI - PEKING,

P. Manny", Yuzhen Ruan' and M. Victoria"

* Paul Schen-er Institut, CH-5232 Villigen PSI t Visiling Scientist from the Institute of Atomic Energy, Peking, China

Femtic/martensitic steels have usually a good resistance into equiaxed subgrains. The observed cell size is inversely to radiation induced void swelling. The 1.4914 is a steel proportional to the square of the saturation stress. of this class that has been selected in the European Fu- The results on the subsize PIREX specimens show that sion Technology Program as a candidate for the reactor first both their tensile [1] and low cycle fatigue [3,4] behaviour wall because it posseses in addition a number of attractive compares well to results obtained in bulk specimens. features, such as his high rupture strength at intermediate The strength of the steel is maintained up to 450°. The temperatures, good weldability and low thermal expansion sources of martensite strength are the lath structure, the [1]. high density of dislocations within the laths and the car- The preirradiated tensile and fatigue properties of the bide structure. Lattice distorsions in martensite tempered European MANET cast of this steel have been studied. The at temperatures as high as in the present case do not seem main elements shown by the chemical analysis of the cast to play an important role. In fact, Earthman et a! [5] point are (in wt.%): 0.13 C, 10.6 Cr, 0.87 Ni, 0.77 Mo, 0.22 V, out that in this case the structure is bec rather than bet, a 0.16 Nb, 0.82 Mn and 0.37 Si. The final structure, obtained fact confirmed by our X-ray investigations. Futhermore, the after 30 min austenitizing at 1075° and tempering for 2 TEM observations after deformation show the formation of hours at 750°, consists of very fine martensite laths of 1 - a dislocation cell structure already after room temperature 1.5 /jm with and a prior austenite grain size of 28 /im. Large deformation, leaving very little of (he original high dislo- Cr,3C6 are observed inside the laths and at lath boundaries. cation density in the martensite. The main hardening role The NbC are present as spheroids of 0.2 ^m, mostly in lath is then left to the carbides and the elements in solution in boundaries. Similar microstructures have been described in the martensite matrix. Of these, both Mo [6] and V [7] the same type of steels [2]. X- ray scattering measurements are expected to play a role, particularly in relation to the have shown a distorted bec structure, free of 6 - ferrite and ocurrence of dynamic strain ageing at intermediate temper- with very small amounts of retained austenite. atures. The sample geometry tested is that of the subsize speci- Finally, the enviromental influence in steels of this type mens used for irradiations in the PIREX facility. The tensile is documented [8] and is related to the observation that die specimens have a flat 9 mm gage length, 3 mm wide and microcrack density in air is over one order of magnitude 0.3 mm thick. The fatigue samples are thin walled tubes larger than in vacuum [5]. with a 9 mm gage length, 3.4 mm external diameter and a 0.35 mm wall thickness. One of the objectives of the present study is the comparison of the behaviour of these MPa subsize specimens to that of bulk ones. 1 700- v i - 2.6 x 10~* see In the tensile tests, the deformation takes place by the propagation of a deformation band. A minimun in total 600' / elongation is found for temperatures around 300°. This minimun coincides with the presence of serrations in the / S tensile curves due to dynamic strain ageing, as shown in ' "A — Fig. 1. \ Low cycle fatigue (LCF) endurance testing shows that fatigue life in air is shorter than in vacuum by a factor of 300 two, at room temperature and 1% total strain. The num- We so ber of cycles to failure for different total strains and testing •c •c temperatures are shown in Fig.2. Typical end of life val- ues vary from 1.3xl05 cycles for 0,5% total strain at room temperature to 7.5x10'' at the same strain and 450°. The introduction of hold times in the tensile part of the hystere- sis loop will futhermore decrease fatigue life but increase the time to failure. ENGINEERING STRAIN As can be seen in Fig 3, substantial softening is ob- served for all fatigue conditions. From the point of view of Figure 1: Tensile curves obtained with the subsize, fiat the microstmcture this softening is explained by the total PIREX specimens. Serrations are present at 250°. transformation during the fatigue test of the lath structure

115 References [1] K. Ehrlich; "Formulation of Initial Design Equa- tions for Type 1.4914 Manensitic Steel". Kf Karlsruhe Primarbericht, May 1986. [21 E.A. Little and L.P. Stoter, ASTM STP 782, H.R. Brager and J.S. Perrin Eds., p. 207. 1982. [3] Kf Karlsruhe Semi-annual Repon, KfK 4488, EUR 11392 EN, October 1988. [4] W.B. Jones in "Ferriiic Steels for High Temperature Applications", A.K. Khare. Ed. ASM 1983,p. 221. [S] J.C. Eanhman, G. Eggeler and B. Ilschner, Mater. Sc. and Eng. Al 10(1989)103. [6] B.B. Argent, M.N. VanNiekerk and G.A. Redfem; J.Iron and Steel Inst 208(1970)830. [7] W.B. Jones and J.A. Van den Avyle; Met. Trans. 11A(198O)1275. [8] K. Kanazawa, K. Yamaguchi and K. Kobayashi; Mater. Sc. and Eng. 40(1979)89.

116 °— —«"—••- '«

- ••- • 20 d ff c • • +• • ISO t,$C UO rtf c —0— 450

PlRCX •p«cim«n». acuum. 0.003 nc-1, 8 X/min

Figure 2: Low cycle fatigue endurance curves obtained with the tubular, PIREX type specimens.

1200- — IS 20 rflf C - - • O.SX 20 ill c • • I.I* ISO i*t C 1100' — O.*>% ISO d*g C

Ssss "" • - • • ^ >»^ "" — • t.S% 4S0 ill C

1000- OX 450 dtt C "—"—*-• ^'

i 000-

PlRCX ip.clm.ns. 0.001 iac-1. '8 X/mln (00- IS+2 10+1 10*4 CYCLE NUHBEH, HI

Figure 3: Dynamic softening, as obtained from the low cycle fatigue behaviour. Technical Physics (3400)

Superconductivity

STUDY PROJECTS

Paul Scherrer Institut, CH-S232 Villigen PSI

C. Marinucci

Magnetic separation processes, which for operational reasons should be kept as short as possible, are constrained by the cooling system, the A preliminary study on the feasibility of a superconduct- capacity of the refrigerator, and the mechanical integrity of ing magnetic separation project was started in March 1989. each component with respect to thermal stresses. The study Main goal is to identify potential applications of interest was performed with a pure thennal analysis and a de facto for a laboratory or industrial pilot unit, providing a base indirect heat conduction model to simulate the direct helium for a decision on such a development at PSI. The general flow, using the finite-element program MARC and the pre- principle of magnetic separation is the physical separation and post-processor PATRAN. Results have shown feasibil- and sorting of discrete panicles of common characteristics, ity and limitations of the cooldown and warmup modes achieved by the competing influence of magnetic forces, investigated. In particular, in the refrigerator-constrained forces of other physical origin and short-range interpani- mode (constant helium schedule of 0.7 K-hour"1) the com- cle forces. The attention has focused on separators in a plete system can be cooled down in as 13 days, and warmed continuous mode of operation, with high magnetic force up in as 18 days, with thennal gradients within acceptable densities generated by superconducting magnets (as lO8^" limits. These results have been presented at the Cryogenic Nnr3). In particular, High Gradient and Open Gradient Engineering Conf. in Los Angeles [2] and the Int. Symp. Magnetic Separators are investigated for applications in the on Numerical Methods in Engineering in Lausanne [3]. environmental (e.g. controlled removal of hardness, phos- phate and heavy metals from waste water system) and bio- technological (e.g. red blood cell extraction from whole blood, immobilized enzymes in food reactors) domain. Pre- liminary contacts with the University of Salford, a leading 300 center for separation science, have shown positive prospects for a future collaboration. A report on this study, including a review of the literature, the basic principles of magnetic separation and a list of potential interesting applications, is in preparation.

Computer aided analysis

The support for SULTAN-HI has continued with the en- ergy discharge analysis of the 50 kA superconducting trans- former [1], and the warmup-cooldown analysis of the com- plete system of split-coils and flanges. Main object of the latter was to investigate a number of procedures and to as- SO 100 150 200 250 300 350 sess their design requirements. Before the superconducting TIME [HRS] magnet system can start operation, it has to be cooled down from room to helium temperature. The system is warmed up Figure 1: Temperature time-history during cooldown of again to room temperature after being deenergized. These split-coils system

119 The computer activity in LTP was reviewed in an internal report which outlines the available general- and special- purpose software, and provides a user guide lo helium and material properties data bank [4].

References

[1] G. PASZTOR, E. AEBLI, B. JAKOB, P. MING, E. SIEGRIST, P. WEYMUTH -Operation of a 50kA Su- perconducting Transformer for the SULTAN Test Fa- cility - PSI-Newsletter (1990)

[2] C. MARINUCCI, P. WEYMUTH - Warmup analysis of the SULTAN-HI superconducting split coil system - Accepted for publication in the Proceedings of the Cryogenic Engineering Conference, Los Angeles (24- 28 July 1989)

[3] C. MARINUCCI, P. WEYMUTH - Thermal analysis of the SULTAN-Ill superconducting split coil system - Proceedings of the fifth International Symposium on Numerical Methods in Engineering, Springer-Verlag, Berlin (1989) 2:17-23 [4] C. MARINUCCI - Computer aided analysis in LTP - PS1 Internal Report LTP-89.07 (1989)

120 CURRENT LEAD TEST

Paul Scherrer Institut, CH-S232 Villigen PSI

E. Aebli I Horviilh M. Vogel D. TrajkoviC J.A. Zichy

The current leads of superconducting magnets are usu- passed through the heal exchanger HI and then it cooled ally mounted vertically and cooled by helium vapor. Since the superconducting cable, which shorted electrically the the leads must be accessible from the top of the magnet, two leads. Next the main stream was cooled down in the such an arrangement may pose restrictions on the magnet heat exchanger H2. In the negative current lead the He design. To draw off vapor for the leads a thermally iso- stream was split again. The valve V3 was used to regulate lated liquid helium bath is also needed. This bath is readily the amount of He cooling this lead. available for a pool boiling coil, however for forced flow After the main He stream crossed the heat exchanger H3 cooling a liquid helium cryosiat is needed in the vacuum it was finally expanded through the Joule-Thomson valve chamber of the magnet, increasing the costs and complicat- V4 into a He cryostat containing the neat exchangers. The ing the design further. To evaluate an alternative solution mass flow in the main He stream was measured in front the characteristic properties of horizontally mounted, forced of each current lead and behind the equipment. The water flow cooled current leads were investigated. The test was bath in front of the valves V2 and V3 was heated to fix the performed in the SULTAN facility with a pair of short cir- temperature of the return gas. The mass flow through both cuited 1 kA current leads. current leads was measured separately behind the valves. The design of the current lead is described elsewhere The position of the different sensors (temperature, pressure, [1], the experimental setup is shown in Fig. 1. differential pressure) and of the voltage taps is also given in Fig. 1. The reading of the different sensors was registered by the Data Aquisition System of the SULTAN facility. The voltages Ul = (£1 - E2), (72 = (£6 - El), the signals (P/T) Pressure and Temperature •i Valve of the quench detector and the temperatures of the current (OP) Dili-pressure I leads were plotted on a multichannel transient recorder. vj3 Temperature •©• Heatexchanger The cool down of the current leads was performed by CO Voltage lap Flowmeter passing about 4.S K cold helium directly through the main Heater cooling line, without any flow in the current leads. No spe- cial care was taken to reduce thermal stresses. After the helium temperature stabilized at about 4.5 K in the main stream, the temperature was less than S.S K at T2 and T3, however it remained at room temperature at Tl and T4. To reach stable starling conditions the mass flow was set by the valves V2 and V3 several hours before a run commenced. All experiments were performed in a similar manner; at first the current was increased in steps of 200 A until the maximum of 1 kA was reached and then, in some measure- ments, the mass flow rate through the current leads was 3 Flange altered. At each setting data were taken after stable condi- tions were reached. This was determined by checking on the recorder, whether the voltages Ul and U2 reached a stationary value. The stationary temperature at the warm end of the posi- tive lead versus current is shown in Fig. 2 for two different mass flow rates in the lead. At low current the temperature rise is small, however at design current the increase gets substantial. This nearly exponential temperature increase, reached in about 40 to 60 minutes at each data point, cor- responds to a similar rise of the voltage in each lead. As shown in Fig. 2, the change of mass flow rate in the main He H3 V* stream, does not effect much the temperature Tl and T4, respectively. This is explained by the fact, that the tem- Figure 1: Experimental set up to test the current leads perature at T2 and T3, respectively, was not influenced by cooled with supercritical helium. changing the flow rate in the main He stream. The cold end of the lead remained below 6.1 K during the experiments, The supercritical helium (He) entered the system at i.e. it was much less than the Tc of a NbTi superconductor valve VI. The He stream was split at first in the positive in zero magnetic field. current lead. A small amount, set by the valve V2, flow through the lead and wanned up thereby. The main stream

121 1 — 1 1

50-_ . i = 1000 (A) + POSITIVE LEAD * NEGATIVE LEAD

Q S40

LU \ 01 CC . \ \ O 30

3 < Ice free LU —*» ^20 I— Freezing

Ice coated

10 -

i 1 I 0.05 0.06 0.07 0.08 MASS FLOW IN CURRENT LEAD (g/s) 200 400 600 800 1000 Figure 3: Voltage rise in the current leads versus mass flow CURRENT (A) in them. Figure 2: Temperature on the warm end of the positive current lead versus mass flow in the lead for two settings of He mass flow in the main stream.

The stationary voltage in both current leads at lkA ver- sus He mass flow rate is plotted in Fig. 3. The range of mass flow rate, where water condensed and froze on the current leads is also indicated in this figure. To operate such current leads over longer periods of time it is necessary to protect them by setting an upper limit on the voltages Ul and U2. If active control of the current lead is permitted a tempera- ture signal could be used to regulate the mass flow through the lead, to operate it in the ice free region. No significant differences were detected between the two current leads. The measurement yielded that in the investigated pres- sure range up to 10 bar a mass flow rate of less than 0.06 g/s per 1000 A is needed to operate safely a hori- zontally mounted current lead. This mass flow rate is 25 % smaller Uian required for a vapor cooled lead of the same design. The results will be next compared with calculated heat loss through the current leads and an energy balance will be also attempted.

References

[1] H. Benz et. ai.; Cryogenics Vol.19 (1979) p.435

122 OPERATION OF A 50 kA SUPERCONDUCTING TRANSFORMER FOR THE SULTAN TEST FACILITY

Paul Scherrer Institut, CH-5232 Villigen PSI

G. Pasztor, E. Aebli, B. Jakob, P. Ming, E. Siegrist, P. Weymuth

1 Introduction 200 A current leads To meet the special requirements imposed by the NET fu- 4K helium inlet sion program, the magnet system of the SULTAN Test Fa- pumping tube. 90K helium inlet cility is being modified by replacing the NbTi middle coil by a pair of Nb3Sn split coils and by dividing the outer 6T 90K helium outlet coil into two halves. The resulted splitted magnet system SULTAN-1II, allows radial access of samples to the high 4K helium outlet field region and will provide the test capability of full size NET conductors. To supply the sample current a superconducting trans- vacuum tube former will be used instead of direct feeding of samples radiation shield from an external power supply. This solution eliminates cryoitat the problem of large heat losses produced by the current leads and does not need large and expensive power sup- secondary winding J-T valve plies. primary winding A superconducting transformer for secondary currents NWSOO up to SO kA was designed at PSI and subsequently manu- factured at ABB's Oerlikon works. The system consists of heat exchanger a layer wound indirectly cooled superconducting primary coil and ten secondary turns wound on primary coil. The helium supply primary is made of 3240 turns of NbTi multifilament wire and can be charged to 200 A. The secondary conductor is made of two parallel NbTi cables and can carry currents in excess of SO kA. current connection 2 Cooling and Instrumentation

The transformer coils are cooled by forced flow of super- critical helium. The coils and the cryostat are both mounted Figure 1: Top of sample holder with cryostat and super- on the same flange (see Figure 1). All components of this conducting transformer. compact unit are cooled in series having heat exchangers in between to cool the incoming helium back to 4.SK. A refrigerator schematic flow scheme is shown in Figure 2. The massflow in the cooling circuit can be regulated JT Valve with a JT valve located at the end of the cooling chain. HEX The liquid helium level in the cryostat which contains the Cu plate heat exchangers is kept constant by a heater. To measure (short) the temperature at different locations of the cooling cir- cuit CLTS- and CGRT sensors are installed. The massflow measurement is based on a differential pressure method, crymtat whereby an orifice is mounted in the cross sectional area I HEX of the cciiduit. In this way a pressure drop results between inlet and throttled cross section behind the orifice. Voltage taps with protective resistors were installed on the primary coil current connections and at the middle of the winding. In this way the coil is divided for quench primary second- protection into two equal parts. The energy stored in the coil ary coil coil needs to be removed in case of a quench in about Is to prevent excessive temperature increase. HEX To measure the current in the closed secondary circuit, Figure 2: Schematic flow scheme Rogowski coils were mounted on both secondary conduc-

123 tors. Previously they were calibrated at room temperature by replacing the secondary conductor by a copper bar of same dimensions and feeding it with a known current. Ad- ditionally to the Rogowski coils, the conductors were fit- ted with Hall-probes to measure their self field and con- sequently their current. The probes can be used for long period recordings like determination of the time constant of the secondary circuit.

3. Testing

For test purposes the current terminations of the secondary circuit were short circuited with a copper bar. In order to test the cooling characteristics of the system, pressure drop measurements were performed. The massflow was varied between 4 g/sec and 16 g/sec. The lowest massflow is given by the power dissipation of the system. The upper value was determined by the cooling power limitation of the refrigeration system. The whole transformer unit could be stably operated at any massflow within the mentioned range. As a second step of the test programme, the transformer M unit was charged and discharged for several times to de- termine the transformation ratio between primary and sec- ondary. For this measurement the signals of the two Ro- gowski coils, were used. The transformation ratio was de- termined to be 210. The system was energized with various current ramps in the range of 100-200 A/s in the secondary. During these runs the calibration of the Hall-probes was also done. The induced current in the secondary circuit decays with a time constant r = L/R where L is the total inductance of Figure 3: Electrical circuit with switch the loaded secondary and R the sum of the joint resistances in the circuit. R was determined by measuring the current in the secondary circuit as a function of time keeping the current in the primary coil constant. The time constant r 4. Conclusion was evaluated graphically and turned out to be 62 min- utes yielding a joint resistance in the secondary circuit of The first operation of the superconducting transformer with 3.510"9n. short circuited secondary demonstrated that the device meets the specifications and will allow the investigation of the In the SULTAN-in Facility the transformer unit will electrical properties of full size NET conductors in the SUL- be operated by a bipolar power supply. During the test TAN facility. period we simulated such an operation by a simple switch as shown in Figure 3. With such an array the operating range of the trans- former unit can be theoretically doubled, by driving the primary coil from -200A to +200A. In reality there are other parameters which are limiting the operation of the transformer to secondary currents in the range of 50 kA. However, the advantage of this operating mode is that the current in the secondary coil can be kept constant for a rather long time. The primary coil was first charged to -150A. This cur- rent was kept constant for several hours until the current in the secondary decayed to about 3kA. Subsequently, the secondary was energized again by sweeping the primary from -150A to +70A using the switch at the moment when the current of the primary coil was zero. As last step, the current ramp in the primary circuit was changed to a value which allows the compensation of the current decay in the secondary coil. A current of 50kA in the secondary could be kept constant during 25 minutes.

124 INVESTIGATION OF HYSTERETIC INTERGRAIN CRITICAL CURRENT DENSITITIES IN POLYCRYSTALLINE HIGH Tc-SUPERCONDUCTORS

Paul Scherrer Institut, CH-5232 Villigen PSI

K. Kwasnitza, Ch. Widmer

In sintered polycrystallinc samples of the high Tc super- The behaviour in figures 1 and 2 is very similar to the conductor YBa'jCuaO- the intergrain critical current density hysteresis of absorption energy at the grain in- jc shows irreversible behaviour as a function of cycling the terfaces [6]. Both effects have probably the field depen- applied magnetic field Ba, see for instance [1] - 15]. The dence of flux pinning as the same reason. We have mea- reason for this is the hysterctic contribution of the intragrain sured at 4.2K the intragrain magnetization and the mean persistent screening currents to the total B at the grain inter- grain size. From these values we determined the intra- face which determines the bulk jc, [2],[4]. This hysterelic grain jc and calculated for different arrays of crystal grains behaviour, as we have found out, is a basis for new data the contribution of the screening currents to the total mag- storage and programmable switching effects [2]. Last year netic field at the interface between two special neighbouring we have continued our investigations of these hysterctic ef- grains. If only a linear superposition of the B components fects. As figure I shows, is hysteretic i behaviour in some in the direction of applied Ba is assumed, it comes out that aspects analogous to hysterctic magnetization behaviour of mis contribution is too small to explain the hysterctic ef- usual type II superconductors with hysteresis area envelopes fects which occur at 4.2K even at an applied field of several and transients. In figure 2 our experimental buttcrflylike jc Tesla. Therefore we have developed a model with vectorial hysteresis curves for bipolar field cycling are displayed. superposition of the fields at the grain interfaces (see figure 3) taking also into account that in type II superconductors with flux pinning, jc strongly depends on the angle between the direction of the resulting magnetic field and the cirrenl direction. Further we have investigated the correlatu n be- tween the easily observable intragrain magnetization and the hysteresis of intergrain jc. It came out that for the same M value one can have different jc values at the same applied field Ba. Because different intragrain screening current con- figurations resulting from different field cycling may have the same magnetization value, as this is only an average value over the grain volume, but give different contribu- tions lo the magnetic field at the grain interface. Further we have experimentally determined in great detail the time relaxation behaviour of the intergrain jc. Usually in type II superconductors only persistent screening currents show "„ ( Trsli. ) a relaxation behaviour due to flux creep, while in our sin- tered polycrystallinc YBa2Cu307 samples also the critical Figure 1: Hysteretic critical transport current as function of transport current density changes in time. This jc relax- applied magnetic field cycling. ation behaviour is strongly hysteretic as figure 4 shows. When Ba had been increased from zero, je at a given Ba value increases in time, while when Ba had been reduced from larger values one measures now at the same Ba value a decrease of jc in time. We were able to explain this behaviour with the relaxation of the screening current con- figuration inside the grains, which lead also to the known logarithmic relaxation of the grain magnetization, see figure 5. Further for possible programmable switching and data storage applications of these hysteretic effects we have es- timated the energy necessary for writing information into the grains. Assuming a storage cell volume of 10~6cm3, which comprises a number of grains, we get the loss value of 510" " Jbit"'. As an other application aspect, we have investigated the dependence of intergrain jc at Ba=0 on the different remancni screening current configurations de- pending on prior field cycling. Finally we have started to study the short time switching- and response behaviour of Figure 2: Hysteretic jc curve when applied Ba is also cycled the bulk YBaCuO maierial. Using pulses of 1 ms duration to negative values. and a ramp lime of 25 /is, no time delay in the switching

125 behaviour could be detected. According to [7] the limiting 300, switching time in YBaCuO films will be < 1 ns.

Such possible switching- and data storage devices are cer- tainly inferior to the sensitivity of Josephson-devices, but are on the other side simpler, easier to fabricate and can be 3 loo used in larger magnetic fields.

a) lo Vector addition of magnetic 1o 100 1000 fields in grain interface limt (act

Figure 5: Relaxation of flux flow voltage for constant trans- a) port current I>I,. at Ba=l and 2 Tesla Increasing applied (a) after increasing Ba from 0 respectively field (b) after decreasing it from 3 Tesla. Increasing flux flow voltage U means that )e decreases and

decreasing U means jc increasing in lime. • groin

References

[1] K. KWASNITZA, B. JAKOB, G. VECSEY - Proc. of

the European Workshop on High Tc Superconductors b) and Potential Applications, Genova (1987) 389. Decreasing applied [2] K. KWASNITZA, CH. WIDMER-CRYOGENICS 29 field (1989) 1035

[3] K. MATSUZAKI, A. INUE, H. KIMURA, K. AOKI, T. MASUMOTO - Jap. Journal of Appl. Physics 26 (1987) 1310

[4] J.E. EVETTS, B.A. GLOWACKI - CRYOGENICS 28, (1988) 641

[5] K. WATANABE, K. NOTO, H. MARITA, H. FUJI- MORI, K, MIZUNO, T. AOMINE, B. Ni, T. MAT- SUSHITA, K. YAMAFUJI, Y. MUTO - CRYOGEN- Figure 3: Vectorial addition of magnetic fields at the grain ICS 29, (1989) 263 interface. [6] E.J. PAKULIS AND T. USADA - Phys. Rev 87 (1988) 5940

M (arb. units) [7] A. FRENKEL, T. VENKATESAN, CH. LIN, X.D. Wu, MS HEDGE AND A. INAM - Appl. Phys. Lett 53 (1988) 2704

Ba (Tesla)

Figure 4: Relaxation of intragrain magnetization when the field sweep is stopped.

126 LIST OF PUBLICATIONS

Myon Spectroscopy /

RA-72-0S: H. Keller, MUON-SPIN ROTATION EXPERIMENTS IN H1GH-Te SUPERCONDUCTORS AND RELATED MATERI- ALS. IBM J. Res. Develop. 33 (1989) 314.

B. PUmpin, H Keller, W. Kündig, W. Odermatt, I.M. Savifi, J.W. Schneider, H. Simmler, P. Zimmermann, J.G. Bednorz, Y. Maeno, K.A. Müller. C. Rössel, E. Kaldis, S. Rusiecki, W. Assmus, J. Kowalewski, MEASUREMENT OF THE LONDON PENETRATION DEPTHS IN YBajCifcO* BY MEANS OF MUON SPIN ROTATION (/iSR) EXPERIMENTS. Physica C 162-164 (1989) 151.

H. Keller, MUON-SPIN ROTATION EXPERIMENTS IN HIGH-T, SUPERCONDUCTORS. Proceedings of the 16lh Course: "Earlier and Recent Aspects of Superconductivity" of the International School of Materials Science and Technology, Erice (Italy), 1989, Springer Series in Solid State Sciences, Springer- Verlag, Heidelberg, J.G. Bednorz and K.A. Müller, editors, in press.

RA-74-04: E. Roduner, I.D. Reid, HYPERFINE AND STRUCTURAL ISOTOPE EFFECTS IN MUONATED CYCLOHEXADIENYL AND CY- CLOPENTYL RADICALS. Israel Journal of Chemistry 29 (1989) 3.

E. Roduner, Physikalisch-Chemisches Institut der Universität Zürich, CH-8057 Zürich. ANWENDUNGEN DES POSITIVEN MYONS ALS SONDE IN DER RADIKALCHEMIE AM BEISPIEL DES CYCLOHEXADŒNYL-RADIKALS. Chimia 43 (1989) 86.

RA-76-03: A. Weidinger, Ch. Niedermayer, A. Golnik, R. Simon, E. Recknagel, J. I. Budnick, B. Chamberland, Ch. Baines, OBSERVATION OF MAGNETIC ORDERING IN SUPERCONDUCTING La2-iSrICu04 BY MUON SPIN ROTATION. Phys. Rev. Lett. 62 (1989) 102.

RA-76-0S: P. Biner, F.N. O>gax, B. Hitti, E. Lippelt, A. Schenck, M. Weber, S. Barth, F. Hulliger, H.R. Ott, STRUCTURAL AND DYNAMIC PROPERTIES OF THE MAGNETIC ORDER IN THE 90 K SUPERCONDUCTOR HoBajCu3O7. Phys. Rev. B39 (1989) 11449.

127 H.R. Ott, S. Barth, F. Hulüger, P. Biner, EN. Gygax, B. Hitti, E. Lippelt, A. Sehende, M. Weber, P. Allenspach, Z. Fisk, B. Rupp, MAGNETIC INTERACTIONS IN HKJH-TC SUPERCONDUCTORS AND RELATED OXIDES. Springer Series in Solid-Stale Sei. 89 (1989) 329.

S. Barth, P. Biner, FJ4. Gygax, B. Hitti. E. Lippelt, A. Sehende, DIFFUSION, LATTICE SITES AND KNIGHT SHIFT OF THE POSITIVE MUON IN Bi AND Bn.j.Sb* SINGLE CRYSTALS. Z. Physik. Chemie NF 164 (1989) 1053.

P. Biner, F.N. Gygax, B. Hitti, E. Lippelt, A. Schenck, L. Schlapbach, fiSR INVESTIGATIONS OF CERIUM HYDRIDE. Z. Physik. Chemie NF IM (1989) 1047.

RA-78-02, RA-85-06: D. Herlach, V. Claus, K. FUrdrer, J. Major, A. Seeger, L. Schimmele, M. Schmolz, W. Staiger, W. Tempi, E. Yagi. POSITIVE MUONS AS LIGHT HYDROGEN ISOTOPES: LOCATION AND MOTION OF POSITIVE MUONS IN a-IRON STUDIED OVER FIVE TEMPERATURE DECADES Z. Phys. Chem. NF 164 (1989) 1041

D. Herlach, K. Maier, J. Major, A. Seeger, In: ERFORSCHUNG KONDENSIERTER MATERIE UND ATOMPHYSIK IM VERBUND MIT GROSSGERÄTEN Herausgegeben von den Komitees "Kemphysikalische Methoden in Festkörperphysik und Materialforschung ", "Forschung mit Synchrotronstrahlung", "Forschung mit Neutronen"; verantwortlicher Redakteur H. Ackermann Erschienen in: "Naturwissenschafliche Grundlagenforschung im Verbund mit Großgeräten" (Ausgabe 1989-1), Deutsches Elektronen- DESY, Hamburg 1989.

RA-78-02, RA-85-06, ctd.: L. Schimmele, A. Seeger, U. Wolf, K. Fttrderer. D. Herlach W. Tempi, THE EFFECTS OF MIXED OCCUPATION OF OCTAHEDRAL AND TETRAHEDRAL INTERSTICES ON THE SPIN RELAXATION OF POSITIVE MUONS IN FCC METALS Z. Phys. Chem. NF 164 (1989) 1035

RA-82-08: N. Kaplan, A. Grayevsky, P. Biner, F.N. Gygax, B. Hitti, E. Lippelt, A. Schenck. /i+ SPIN RESONANCE IN SINGLE-CRYSTAL PrNis: EVIDENCE FOR LOCAL MOMENTS AT Ni SITES. Phys. Rev. Lett. 62 (1989) 2732.

RA-85-12: S. Barth, H.R. Ott, F.N. Gygax, B. Hitti. E. Lippelt. A. Schenck, C. Baines, EVIDENCE OF FRUSTRATED MAGNETISM IN CeAl3 FROM MUON-SPIN-ROTATION SPECTROSCOPY. Phys. Rev. B39 (1989) 11695.

R.H. Heffner, J.O. Willis, J.L. Smith, P. Biner, C. Baines, F.N. Gygax, B. Hitti, E. Lippelt, H.R. Ott. A. Schenck, D.E. MacLaughlin, MUON-SPIN RELAXATION STUDIES OF WEAK MAGNETIC CORRELATIONS IN U,_rThrBe,3. Phys. Rev. B40 (1989) 806.

128 YJ. Uemura. WJ. Kossler, X.H. Yu, HE. Schone, J.R. Kempton, CE. Stronach, S. Barth, F.N. Cygax, B. Hitü, A. Schenck, C. Baines, W.F. Lankford, Y. Önuki, T. Komaisubara, COEXISTING STATIC MAGNETIC ORDER AND SUPERCONDUCTIVITY IN CeCu21Si2 FOUND BY MUON SPIN RELAXATION. Phys. Rev. B39 (1989) 4726.

RA-85-17: Ch. Niedermayer, H. Glückler, R. Simon, A. Golnik, E. Recknagel, A. Weidinger, J. I. Budnick, W. Paulus, R. Schöllhom. MAGNETIC ORDERING INDUCED BY HYDROGEN DOPING OF YBa2Cu3O7. Phys. Rev. B 40 (1989) 11386.

RA-85-18: L. Asch, G.M. Kalvius, FJ. Littéral, A. Schenck, B. Hitü, F.N. Gygax, Ch. Scon, K. Mauenberger, O. \fogt, STATIC AND DYNAMIC PROPERTIES OF UAs PROBED BY /iSR. Europhys. Lea. 10 (1989) 673.

L. Asch, FJ. Liltersl, A. Kratzer, K. Aggarwal, W. Potzel, G.M. Kalvius, F.N. Gygax, B. Hioi, A. Schenck, S. Bann, O. Vogt, K. Manenbeiger, /iSR STUDIES ON URANIUM- AND CERIUM MONOPNICTIDES. J. de Physique 49 (1988) C8-49S.

K. Aggarwal, G.M. Kalvius, A. Kratzer, FJ. Litterst, L. Asch, O. Harunann, FJ4. Gygax, A. Schenck, K. Mauenberger, O. Vtogt, A /iSR STUDY OF UP AND UTe. Hyperfine Interactions 51 (1989) 93S.

RA-85-18, ctd.: O. Hartmann, R. Wappling, A. Yaouanc, P. Datanas de Reotier, B. Barbara, K. Aggarwal, L. Asch, A. Kratzer, G.M. Kalvius, FJ. Litterst, F.N. Gygax, B. Hitti, E. Lippelt A. Schenck, /iSR STUDIES ON CeAlj. Hyperfine Interactions 51 (1989) 9SS.

L. Asch, /iSR ON ACTINIDE AND RELATED COMPOUNDS. Physica B 61 (1989) 299.

RA-86-07-A: M. Heming, E. Roduner. I.D. Reid, P.W.F. Louwrier, J.W. Schneider, H. Keller, W. Odemutt, B.D. Patterson, H. Simmler, B. Pilmpin, I.M. Savic", THE SEPARATION OF CHEMICAL REACTIVITY AND HEISENBERG SPIN EXCHANGE EFFECTS IN A RADICAL-RADICAL REACTION BY AVOIDED LEVEL CROSSING /iSR. Chem. Phys. 129 (1989) 33S.

129 E. Roduner, I.D. Reid, R. De Renzi, M. Ricc6, ANISOTROPY OF THE 2-NORBORNYL RADICAL REORIENTATIONAL DYNAMICS IN THE PLASTIC PHASE OF NORBORNENE AS DETERMINED BY ALC-/1SR. Ber. Bunsenges. Phys. Chem. 93 (1989) 1194.

RA-89-05: P. Biner. F.N. Cygax, B. Hitti, E. Lippelt, A. Schenck, M. Weber, B. Hettich, H. Malena, MAGNETIC PENETRATION DEPTH IN Bi2(Sr,Ca)2Cu08.j. Physica C158 (1989) 230.

Neutron Scattering

P. Allenspach, S.-W. Cheong, A. Dommann, P. Fischer, Z. Fisk, A. Furrer, H.R. Ott, B. Rupp MAGNETIC PROPERTIES AND ANTIFERROMAGNETIC Cu ORDERING IN Pr2Cu04 Z. Phys. B 77 (1989) 185-191.

P. Allenspach, A. Furrer, B. Rupp, H. Blank OXYGEN-VACANCY INDUCED CHANGES OF THE CRYSTEL-FIELD INTERACTION IN ErBa2CuaO, (6.1

I.S. Anderson, F. Atchison SINQ GUIDE CONCEPT IN ADVANCED NEUTRON SOURCES 1988 I.O.P. Conference Series No. 97 ISBN 0-85498-053-9.

I.S. Anderson, D.K. Ross, J£. Bonnet LONG RANGE DIFFUSION OF HYDROGEN IN YTTRIUM ZeiLphysikal. Chemie, Neue Folge 164 (1989) 923-928.

P. BOni, I.D. Axe, G. Shirane, RJ. Birgeneau, DA. Gabbe, HP. Jenssen, M.A. Kästner, PJ. Picone, T.R. Thurslon, M. Sato, S. Shamoto LATTICE INSTABILITY IN SINGLE-CRYSTAL La2Cu04 Physica B (1989) 902-905.

P. Boni, S.M. Shapiro MAGNETIC FIELD DEPENDENCE OF THE SPIN DYNAMICS IN THE REENTRANT SPIN GLASS

J. Phys.: Condens. matter 1 (1989) 6123-6129.

K. Conder, J. Schefer, E. Kaldis, R.X. Cai PROGRESS IN THE T-X PHASE-DIAGRAM OF THE SOLID SOLUTION CeH2CeH3; PART II: NEUTRON DIFFRACTION INVESTIGATIONS - TRIHYDRIDES Zeit. Physikal. Chem., Neue Folge 163 (1989) 125-134.

H.A. Graf, P. Boni, G. Shirane, M. Koghi, Y. Endoh, Y. Ishikawa PARAMAGNETIC NEUTRON SCATTERING FROM Pd2MnSn Phys. Rev. B 40 (1989) 4243-4248.

H.R. Ott, P. Biner, FJ4. Gygax, B. Hitti, E. Lippelt, A. Schenk, M. Weber, S. Barth, F. HuUiger. P. Allenspach, S.-W. Cheong, P. Fischer, Z. Fisk, A. Funer, B. Rupp MAGNETIC INTERACTIONS IN HIGH-T,; SUPERCONDUCTORS AND RELATED OXIDES Solid State Sciences, Vol. 89 (Springer. Berlin 1989) 329- 340.

130 B. Rupp, P. Allenspach, P. Fischer, A. Furrer ON THE CORRELATION OF SECONDARY STRUCUTRAL EFFECTS, SUPERCONDUCTIVITY AND CRYSTAL FIELD INTERACTION IN ErBajCuaO* - NEW EVIDENCE FOR A CHARGE TRANSFER MECHANISM? Physica C 162-164 (1989) 538-539.

B. Rupp, E. POrschke, P. Meuffels. P. Fischer, P. AUenspach NEUTRON-DIFFRACTION STUDY OF ErBa3Cu3Oz IN THE COMPOSITION RANGE 6.1

T.R. Thurston, RJ. Birgeneau, D.R. Gabbe, HP. Jenssen, M.A. Kastner, PJ. Picone, N.W. Preyer, J.D. Axe, P. Boni, G. Shinne. M. Sato, K. Fukuda, S. Shamoto NEUTRON SCATTERING STUDY OF SOFT OPTICAL PHONONS IN La2CuO4 Phys. Rev. B 39 (1989) 4327-4333

Accelerator Mass Spectrometry AMS

J. Arncsson. S. Gnepf, F.K. Kneubuhl. D. Billeter, W. Neumann, W. WOlfli. PROPOSAL FOR A DRIVEN BY A FAR-INFRARED FREE- ELECTRON LASER. Infrared Phys. Vol 29 No. 2-4 (1989) 607-630.

P.E. Damon, D.J. Donahue, B.H. Gore, A.L. Hatheway, AJ.T. Jull, T.W. Linick, P.J. Sercel, L.J. Toolin, C.R. Brank. E.T. Hall, R.E.M. Hedges, R. Housley, l.A. Uw, C. Perry, G. Bonani, S. Trumbore, W. WOlfli, J.C. Ambers, S.G.E. Bowman, M.N. Leese, M.S. Tile. RADIOCARBON DATING OF THE SHROUD OF TURIN. Nature, Vol. 337 No 6208 (1989) 611-615.

M. Suter, J. Beerm, D. Billeter, G. Bonani, HJ. Hofmann, H.A. Synal, W. WOlfli. ADVANCES IN AMS AT ZURICH. Nuclear Instr. and Methods in Phys. Research B 40/41 (1989) 734-740.

A. Schaelin, R. Loepfe, H. Mekhior, M. Suter, W. Wolfli. BERYLLIUM BOMBARDMENT FOR Ino.ssGao 4TAS AND InP PHOTOCONDUCTORS WITH PICOSEC- OND RESPONSE TIMES. Presented at 1st ECAART, 5.-9. Sept 1989 in Frankfurt a.M. (BRD), European Conf. on Accelerators in Applied Research and Technology (im Druck).

W. Neumann, W. Wolfli, P. Heimgaitner, R.M. Streicher. THIN LAYER ACTIVATION OF HIP JOINT PROSTHESES FOR TRIBOLOGICAL TESTS. Proc. 1st Europ. Conf. oon Accelerators in Applied Reserach and Technology, 5.-9. Sept. 1989 in Frankfurt a.M. (BRD) (im Druck in Nucl. Instr. & Meth. B).

W. Neumann, C. Stalder. THIN LAYER ACTIVATION APPLIED TO EROSIVF WEAR Proc. of the Ion Beam Analysis Conference, Kingston. Canada, 26.- 30. Juni 1989 (im Druck in Nucl. Instr. & Meth. B).

Chemistry

S. Bajo, A. Wyttenbach, L. Tobler, H. Conradin MULTIELEMENT DETERMINATION IN SOIL EXTRACTS BY INSTRUMENTAL NEUTRON ACTIVA- TION ANALYSIS J. Radioanal. Nucl. Chem. 134 (1989) 181-191.

131 W. Drost, E. Hoehn MACRODISPERSIVITY IN GRANULAR AQUIFERS DETERMINED WITH SINGLE-BOREHOLE TECH- NIQUES USING 82Br AS A TRACER Radiochim. Acta bf 47 (1989) 13-20.

G. Evans, H. Erten, S.N. Alavi, H.R. von Gunten, M. Elgin SUPERFICIAL DEEP-WATER SEDIMENTS OF THE EASTERN MARMARA BASIN Geo-Marine Letten 9 (1989) 27-36.

H.W. Gaggeler. D.T. Jost, U. Baltensperger, Ya Nai-Qi, K.E. Gregorich, CM. Gannett, H.L. Hall, R.A. Hen- derson, D.M. Lee, J.D. Li, MJ. Nurmia, D.C. Hoffman, A. Türler, Ch. Lienert, M. Schädel, W. Brüchle, J.V. Krau, HP. Zimmermann, U.W. Scherer FIRST RESULTS FROM GASCHEM1STRY EXPERIMENTS WITH HAHNIUM Report Paul Seltener Institute, ViUigen, PSI-49 (1989).

H.W. Gaggeler, U. Baltensperger, M. Emmenegger, D.T. Jost, A. Schmidt-Ott, P. Halter, M. Hofmann THE EPIPHANIOMETER, A NEW DEVICE FOR CONTINUOUS AEROSOL MONITORING J. Aerosol Science 20 (1989) SS7.

H.W. Gaggeler, D.T. Jost, A. Turler, P. Armbruster, W. Brüchle, H. Folger, F.P. Hessberger, S. Hofmann, G. Münzenberg, V. Ninov, W. Reisdorf, M. Schädel, K. Sümmerer, J.V. Kratz. U. Scherer, M.E. Leino COLD FUSION REACTIONS WITH «Ca Nucl. Phys. A 502 (1989) 561c.

F.P. Hessberger, H. Gaggeler, P. Armbruster, W. Brüchle, H. Folger, S. Hofmann, D. Jost, J.V. Kratz, M.E. Leino, G. Münzenberg, V. Ninov, M. Schädel, U. Scherer, K. Sümmerer, A. Türler, D. Ackermann THE NEW NUCLJDE M5U Z. Phys. A 333 (1989) 111.

E. Hoehn, H.R. von Gunten RADON IN GROUNDWATER: A TOOL TO ASSESS INFILTRATION FROM SURFACE WATERS TO AQUIFERS Water Resources Research 25 (8) (1989) 1795-1803.

J.V. Kratz, HP. Zimmermann, U.W. Scherrer, M. Schädel, W. Brüchle, K£. Gregorich, CM. Gannett. H.L. Hall, R.A. Henderson, D.M. Lee. J.D. Leyba, MJ. Nurmia, D.C. Hoffman. H. Gaggeler, DJost, U. Bal- tensperger, Ya Nai-Qi, A. Türler, Ch. Lienert CHEMICAL PROPERTIES OF ELEMENTS 105 IN AQUEOUS SOLUTION: HALIDE COMPLEX FORMA- TION AND ANION EXCHANGE INTO TRIISOOCTYL AMINE Radiochim. Acta 48 (1989) 121.

A. Wyttenbach, L. Tobler, S. Bajo Na, Cl AND Br 04 NEEDLES OF NORWAY SPRUCE (Pjibies) AND IN THE AEROSOL ADHERING TO THE NEEDLES Toxicol. Environmn. Chem. 19 (1989) 25-33.

A. Wyttenbach, L. Tobler, S. Bajo NADELINHALTSTOFFE UND ABLAGERUNGEN AUF NADELOBERFLÄCHEN VON FICHTEN Forstwi. Cbl. 108 (1989) 233-243.

Ya Nai Qi, D.T. Jost, U. Baltensperger. H.W. Gaggeler THE SAPHIR GAS-JET AND A FIRST APPLICATION TO AN ON-LINE SEPARATION OF NIOBIUM Radiochim. Acta 47 (1989) 1.

B. Zimmerli, A. Wyttenbach SELENIUM INTAKE IN THE SWISS POPULATION In: Selenium in Medicine and Biology (eds: J. Neve, A. Favier). Walter de Gruytes, New York (1989) 11-14.

132 Defect Physics H. Grimmer COMMENTS ON AN ASYMMETRIC DOMAIN FOR INTERCRYSTALUNE MISORIENTATION IN CUBIC MATERIALS IN THE SPACE OF EULER ANGLES Acta Cryst. A 45 (1989) FC1-PC2.

H. Grimmer A GEOMETRICAL MODEL OF SPECIAL GRAIN BOUNDARIES IN CORUNDUM Helv. Phys. Acta 62 (1989) 231-234.

H. Grimmer SYSTEMATIC DETERMINATION OF COINCIDENCE ORIENTATIONS FOR ALL HEXOGONAL LAT- TICES WITH AXIAL RATIO C/A IN A GIVEN INTERVAL Acia Cryst. A 45 (1989) 320-325.

H. Grimmer COINCIDENCE ORIENTATIONS OF GRAINS IN RHOMBOHEDRAL MATERIALS Acta Cryst. A 45 (1989) 505-523.

H. Grimmer TABLES OF ALL COINCIDENCE ORIENTATIONS WITH LOW MULTIPLICITY FOR ARBITRARY HEXAG- ONAL AND RHOMBOHEDRAL LATTICES Scripta Metall 23 (1989) 1407-1412.

PIREX

A. Allub, A. Caro and C. Wiecko A SIMPLE MODEL FOR THE SUPERCONDUCTING PHASE DIAGRAM NEAR THE METAL-INSULATOR TRANSITION J. Low. Temp. Phys. 75 (1989) 27.

A. Caro and M. Victoria QUANTUM CHEMICAL MOLECULAR DYNAMICS "Atomic Scale Calculations in Materials Science". MRS vol 141, p.19, J. Tersoff, D. VanderbiU and V. Vitek, Eds. (1989).

A. Caro and M. Victoria ION-ELECTRON INTERACTION IN MOLECULAR DYNAMICS CASCADES Phys. Rev. bf A40 (1989) 2287.

Q. Mate and A. Caro FRACTAL WAVE FUNCTIONS IN 1-D DISORDERED SYSTEMS WITH ELECTRIC FIELD J. Phys.: Condens. Matter 1 (1989) 901.

133 CONTRIBUTIONS TO CONFERENCES AND WORKSHOPS

(with PSI staff as participants only)

Myon Spectroscopy /zSR

RA-76-02 V. Claus, K. Förderer, D. Herlach, J. Major, A. Seeger, W. Staiger, W. Tempi SPINRELAXATION POSITIVER MUONEN IN CHROM: ANTIFERROMAGNE TISCHE SPINDICHTEWELLEN UND n+-DIFFUSION DPG-FrUhjahrstagung, Münster 1989

RA-76-05 H.R. OU, S. Barth, F. HuUiger, P. Biner. F.N. Gygax, B. Hitti, E. Lippelt, A. Schenck, M. Weber, P. Allenspach, Z. Fisk, B. Rupp MAGNETIC INTERACTIONS IN HIGH-TC SUPERCONDUCTORS AND RELATED OXIDES IBM-Symposium on Strong Correlations and Superconductivity, Japan, 22.-27.S.1989.

H.R. Ott, S. Barth. F. HuUiger, P. Biner, F.N. Gygax, B. Hitti, E. Lippelt, A. Schenck, M. Weber, P. Allenspach, Z. Fisk, B. Rupp MAGNETIC INTERACTIONS IN HIGH-TC SUPERCONDUCTORS Workshop on High-Te Superconductivity, Dubna, USSR, 26.6.-1.7.1989.

RA-78-02, RA-85-06 V. Claus, K. Förderer, D. Herlach, G. Majer, J. Major, L. Schimmele, M. Schmolz, A. Seeger, W. Staiger, W. Tempi, E. Yagi DIFFUSION DES "ELEMENTS EINS" (WASSERSTOFF) IN EISEN DPG-FrOhjahrsiagung, Monster 1989

RA-79-02 G. Fabritius, 1R. Feldmann, D. Herlach, M. Koch, K. Maier, M. Scherschel, A. Seeger, W. Staiger, E. Widmann GITTERPLÄTZE LEICHTER wASSERSTOFFISOTOPE IN HOCHREINEM EISEN UND GOLD DPG-FrOhjahrstagung, Münster 1989.

Neutron Scattering

P. Allenspach, A. Furier, and B. Rupp CHARGE REDISTRIBUTION IN THE CuOj PLANES OF ErBa2Cu3Oz (6

P. Boni, J.L. Martinez, and J.M. Tranquada LONGITUDINAL SPIN FLUCTUATIONS IN Ni BELOW Te 34th Annual Conference on Magnetism and Magnetic Materials, Boston, 28.11. - 1.12.89.

L. Rebelsky, S.M. Shapiro, P. Boni, H.G. Botin, and W. Zinn EuS ABOVE Tc: SPIN WAVE EXCITATIONS IN MAGNETIC FIELDS March Meeting of the American Physical Society, St Louis, MO, USA, 20. - 24.3.89.

134 B. Rupp, P. Allenspach, P. Fischer, and A. Funer ON THE CORRELATION OF SECONDARY STRUCTURAL EFFECTS, SUPERCONDUCTIVITY AND CRYSTAL FIELD INTERACTION IN ErBa2Cu3OI - NEW EVIDENCE FOR A CHARGE TRANSFER MECHANISM? Int. Conf. on Materials and Mechanisms of Superconductivity - High-Temperature Superconductors, Stanford, USA, 23. - 28.7.89.

Accelerator Mass Spectrometry AMS

M. Suter CHARGE STATE DISTRIBUTIONS OF Si AND Cl AFTER PASSING GAS OR FOIL STRIPPERS Inv. talk, 5th Int. Conf. on Electrostaic Accelerators, Strasbourg, 26.S.1989.

M. Suter LIMITS OF ISOLAR SEPARATION IN AMS WITH IONIZATION COUNTERS Inv. talk, IX: Ion Beam Analysis Conference, Kingston, Canada, 27.7.1989.

Geochemistry

H.R. von Gunten ZYKL1SCHE METALLMIGRATION IM GRUNDWASSER Workshop "Uferfiltration" der deutschen Forschungsgemeinschaft, Karlsruhe, 17.2.1989.

E. Hoehn, and H.R. von Gunten THE BEHAVIOR OF MANGANESE DURING INFILTRATION OF RIVER WATER TO GROUNDWATER in: H.E. Kobus, and W. Kinzelbach, eds.: "Contaminant transport in groundwater", Stuttgart, FRG, April 4-6,1989,73-74.

H.R. von Gunten MANGANESE CYCLES IN A RIVER INFILTRATION SYSTEM American Chemical Society Meeting, Environmental Division, Dallas, 12.4.1989.

H.R. von Gunten RADIONUCLIDE MIGRATION IN THE ENVIRONMENT (Invited papet) 2nd International Conf. on Analytical Chemistry in Nuclear Technology, Karlsruhe S.-9.6.1989.

H.R. von Gunten, E. Hoehn, G. Karametaxas, U. KrahenbUhl, M. Kuslys, Ch. Lienert, U. Waber PROCESSES AFFECTING THE MIGRATION OF HEAVY METALS IN INFILTRATING GROUNDWATER 7. Int. Conf. Heavy Metals in the Environment Genf, 12.-15.9.1989.

Trace Elements

A. Wyttenbach, S. Bajo, L. Tobler MAJOR AND TRACE ELEMENTS IN SPRUCE NEEDLES BY NAA Int. Conf. on "Nuclear Methods in the Life Sciences", GaithersburR, USA, 17.-21.4.1989.

L. Tobler, V. Funer, A. Wyttenbach ACTIVATION ANALYSIS OF HUMAN DIETARY SAMPLES WITH EPITHERMAL NEUTRONS Int Conf. on "Nuclear Methods in the Life Sciences", Gaithersburg, USA, 17.-21.4.1989.

L. Tobler, A. WyUenbach BESTIMMUNG VON Si IN PFLANZENMATERIALIEN DURCH EPITHERMISCHE NEUTRONENAK- TTVIERUNGSANSLYSE 14. Seminar "Aklivierungsanalyse". GDCh, Hannover, BRD, 10711.10.1989, und Schweiz. Chem. Ges., Bern, 20.10.1989.

13S A. Wyttenbach, S. Bajo, L. Tobler AEROSOLS ON NEEDLES OF NORWAY SPRUCE Int. Conf. on "Forest Decline Research", Friedrichshafen, BRD, 2.-6.10.1989.

S. Bajo, L. Tobler, A. Wyttenbach Fe, Mn, Co, Zn: RELATIONSHIPS BETWEEN THEIR CONCENTRATION IN NEEDLES OF NORWAY SPRUCE AND FOREST SOIL PARAMETERS Int. Conf. on "Heavy Metals in the Environment", Genf, 12.-15.9.1989.

Aerosol Chemistry

H.W. Gaggeler, U. Baltensperger, D.T. Jost CONTINUOUS HIGH ALPINE AEROSOL MEASUREMENTS WITH THE EPIPHANIOMETER IV. ALPTRAC Meeting, Grenoble, 12.1.1989.

U. Baltensperger PRELIMINARY RESULTS OF A TRANSFER STUDY ON WEISSFLUHJOCH DAVOS IV. ALPTRAC Meeting, Grenoble, 12.-13.1.1989.

H. Gaggeler, U. Baltensperger, D.T. Jost, A. Schmidt-Ott, P. HaUer, M. Hofmann THE EPIPHANIOMETER, A 311Pb GENERATOR FOR AEROSOL STUDIES 2nd Karlsruhe International Conference on Analytical Chemistry in Nuclear Technology, KfK Karlsruhe, 5.-9.6.1989.

U. Baltensperger CONTINUOUS BACKGROUND AEROSOL MONITORING WITH THE EPIPHANIOMETER Int. Conf. on Aerosols and Background Pollution, Galway, bland, 13.-15.6.1989.

H.W. Gaggeler, U. Baltensperger, D.T. Jost APPLICATIONS OF THE EPIPHANIOMETER TO ENVIRONMENTAL AEROSOL STUDIES European Aerosol Conference, Vienna, Austria, 18.-23.9.1989.

U. Baltensperger AEROSOL MEASUREMENTS WITH THE EPIPHANIOMETER Annual Meeting of the American Association for Aerosol Research, Reno. USA, 10.-13.10.1989.

H.W. Gaggeler ANLAGERUNG RADIOAKTTVER ISOTOPE ZUR CHARAKTERISIERUNG VON AEROSOLPARTIKELN Seminar liber Trends in der Aerosolforschung, Sonderforschungsbereich 209, Universitat Duisburg, 4.12.1989.

Heavy Elements

H. Gaggeler, D. Jost, A. TUrler, P. Armbruster, W. Bruchle, H. Folger, FP. Hessberger, S. Hofrnann, G. Munzenberg, V. Ninov, M. Schadel, K. Siimmerer, J.V. Kratz, U. Scherer, M. Leino COLD FUSION REACTIONS WITH ^Ca Fifty Years Research in Nuclear Fission, Berlin, 3.-7.4.1989.

D.T. Jost, U. Baltensperger, H.W. Gaggeler, Ya Nai-Qi ON-UNS GASCHROMATOGRAPHY FOR THE SEPARATION OF SHORT-LIVED NUCLIDES 2nd Karlsruhe International Conference on Analytical Chemistry in Nuclear Technology, KfK Karlsruhe, 5.- 9.6.1989.

H.W. Gaggeler, D.T. Jost, A. TUrler, P. Armbruster, W. Bruchle, H. Folger, FP. Hessberger, S. Hofmann, G. Munzenberg, V. Ninov, W. Reisdorf, M. SchSdel, K. Siimmerer, J.V. Kralz, U. Scherer, MM. Leino COLD FUSION REACTIONS WITH ""Ca Inv. talk. Int. School-Seminar on Heavy Ion Physics, Joint Institute for Nuclear Research JINR, Dubna, 3.-13.10.1989.

136 H.W. Gaggeler PRODUCTION OF ACT1NIDES AND TRANSACTINIDES IN HEAVY ION REACTIONS Inv. talk. Int. Chetn. Congress of Pacific Basin Societies, Honolulu, 17.-22.12.1989.

J.D. Leyba, D.C. Hoffman, A. Tiirler, H.R. von Gunten HEAVY ACTINIDE PRODUCTION FROM THE INTERACTIONS OF Ca-44 AND Ar-40 WITH Cm-248 Int Chem. Congress of Pacific Basin Societies, Honolulu, 17.-22.12.1989.

Defect Physics

W.B. Waeber, G. Solt, P. Tipping, F. Frisius, O. Merrier CORRELATION BETWEEN MEASURED MECHANICAL AND MICROPHYSICAL PARAMETERS FOR AN IRRADIATED PRESSURE VESSEL MATERIAL In: Transactions of the 10th International Conference on Structural Mechanics in Reactor Technology, Vol. S, Editor A.H. Hadjian, Los Angeles (1989) 149-154.

W.B. Waeber, U. Zimmermann, G. Solt, P. Tipping OPTIMISATION OF REACTOR PRESSURE VESSEL SURVEILLANCE. PROGRAM ANALYSIS Ibid. Vol. D, 161-166.

P. Tipping, W.B. Waeber IRRADIATION AND ANNEALING EFFECTS ON THE MECHANICAL PROPERTIES OF AN RPV STEEL AND ASSOCIATED PLEX CONSIDERATIONS Ibid, Vol. G, 239-244.

PIREX

A. Caro, and M. Victoria THE COMPUTER SIMULATION OF DEFECTS PRODUCED BY HIGH ENERGY PARTICLE IRRADIA- TION AND THE EVOLUTION OF THE MICROSTRUCTURE Italian-Swiss Physics Meeting, Como, Italy, May 1989.

A. Caro QUANTUM CHEMICAL MOLECULAR DYNAMICS APPLIED TO S-P MATALS Int. Conf. on Thermodynamics and Statistical Mechanics, Rio

A. Caro ION-ELECTRON INTERACTION IN MOLECULAR DYNAMICS CASCADES Int. Conf. on Thermodynamics and Statistical Mechanics, Rio de Janeiro, Brasil, August 1989.

A. Caro ION-ELECTRON INTERACTION IN MOLECULAR DYNAMICS CASCADES Embedded Atom Method Workshop, Sandia National Laboratory, California, USA, August 1989.

P. Marmy, Y. Ruan, and M. Victoria THE TENSILE AND FATIGUE PROPERTIES OF TYPE 1.4914 FERRITIC STEEL FOR FUSION REACTOR APPLICATIONS Fourth Int. Conf. on Fusion Reactor Materials, Kyoto, Japan, December 1989. To be published in J.Nucl.Mater.

A. Horsewell, B.N. Singh, S. Proennecke, WJ\ Sommer, and HX. Heinisch DEFECT STRUCTURES IN COPPER AND GOLD IRRADIATED WITH FAST NEUTRON, 14 MeV NEU- TRONS AND 600-800 MeV PROTONS Fourth Int Conf. on Fusion Reactor Materials, Kyoto, Japan, December 1989. To be published in J.Nucl.Mater.

137 Technical Physics

K. Kwasnitza, Ch. Widmer NEW PROGRAMMABLE SWITCHING AND STORAGE EFFECTS IN SUPERCONDUCTING POLYCRYS- TALLINE YBa2Cu3O7 DUE TO HYSTERETIC CRITICAL INTERGRAIN TRANSPORT CURRENT Paper presented at the Symposium on "Critical Current in High Tc Superconductors" - KfK-Karsruhe, October 1989. Cryogenics (1989) 29,1035.

G. Pasztor, E. Aebli, B. Jakob, P. Ming, E. Siegrist, P. Weymuth DESIGN, CONSTRUCTION AND TESTING OF A 50kA SUPERCONDUCTING TRANSFORMER Proc. of the 11th Int. Conf. on Magnet Technology, Japan, August-September 1989.

C. Marinucci, P. Weymuth WARMUP ANALYSIS OF THE SULTAN-m SUPERCONDUCTING SPLIT COIL SYSTEM Proc. Cryogenic Eng. Conference, Los Angeles, 1989.

138 LECTURES AND COURSES

(PSI staff only)

PD Dr. H.W. Gaggekr ETH-ZUrich, WS 89/90: - Radiochemie (Vorlesung und Praktikum)

PD Dr. H. Grimmer ETH-ZUrich und UniversiUU Zurich, WS 89/90: Krisiallographie I fur Physiker (gemeinsam mit U. Gramlich)

Prof. Dr. HJt. Ott ETH-ZUrich, SS 89: - Physik fllr Anfanger (Praktikum) - Physik fllr Lebensmiueling. (Praktikum) - Physik n (\brlesung und Uebungen) - Seminar FestkOrperphysik (gemeinsam mit anderen Dozenten)

WS 89/90: - Integr. Grundprakiikum in - Physik filr Anfanger (Praktikum) - FeslkOrperphysik I (Vbrlesung und Uebungen) - Seminar in FestkOrperphysik (gemeinsam mit anderen Dozenten)

Prof. Dr. Hit. von Gunten Universitfll Bern, SS 89: - Radiochemie (\forlesung und Praktikum) - Chemisches Seminar (gemeinsam mit anderen Dozenten) - Seminar in Radiochemie und Umwellchemie (gemeinsam mit anderen Dozenten)

Prof. Dr. A. Wyttenbach University Zurich, SS 89: - Bestimmung von Spurenelementen in umwellrelevanten Proben dutch Neuironenaktivierungsanalyse.

ETH-Zilrich, WS 89/90: - Physikalische Methoden der Mineral- und Gesteinsanalyse (gemeinsam mit anderen Dozenten).

139