NO0000041 UNIVERSITY OF DEPARTMENT OF PHYSICS
SECTION for NUCLEAR PHYSICS AND ENERGY PHYSICS
Annual Report January 1 - December 31 -1998
Department of Physics, University of Oslo P.O.Box 1048 Blindern N-0316 Oslo, Norway
UIO/PHYS/99-04 Received: 1999-08-27 ISSN-0332-5571 REPORT SERIES
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SECTION for NUCLEAR PHYSICS AND ENERGY PHYSICS
Annual Report January 1 - December 31 -1998
Department of Physics, University of Oslo P.O.Box 1048 Blindern N-0316 Oslo, Norway
UIO/PHYS/99-04 Received: 1999-08-27 ISSN-0332-5571 Contents
1 Introduction 7
2 Personnel 9 2.1 Research Staff 9 2.2 Technical Staff 10
3 Cyclotron operation and external user projects 11 3.1 Operation and Maintenance 11 3.2 External user projects 11 3.2.1 Production of 18F-fluorodeoxyglucose for medical PET-imaging ... 11 3.2.2 Basic Nuclear Chemistry Research 12 3.2.3 The application and study of 2UAt 13
4 Data Acquisition and Analysis 14 4.1 Introduction 14 4.2 Configuration 14 4.3 Acquisition and Data Analysis Software 17 4.4 Progress of the SIRI Data-Acquisition System Development 18
5 Nuclear Instrumentation 20 5.1 The CACTUS Detector 20 5.2 Properties of the CACTUS Detector Array 20 5.3 The SIRI Strip Detector Project 22 5.3.1 The Detectors 23 5.3.2 The Chip Read-Out System . 24 5.3.3 The Data Acquisition System 24 5.4 Background Radiation from Target Impurities 25
2 5.5 Liquid Nitrogen Filling System for Ge Detectors 26 5.6 The New Eventbuilder Single Board Computer 28
6 Experimental Nuclear Physics 30 6.1 Experiments at the Oslo Cyclotron 30 6.1.1 Introduction 30 6.1.2 Temperature and Heat Capacity of Rare-Earth Nuclei 31 6.1.3 The 162Dy(3He,a) and 162Dy(3He,3He') Reactions 34 6.1.4 Structure and Decay Properties of Heated 166Er 34 6.1.5 Direct 7-Feeding of the Ground State Band in Rare Earth Nuclei . . 37 6.1.6 Gamma-Ray Angular Correlation and Polarization Measurements of the 163Dy(3He,cry)162Dy Reaction 38 6.1.7 Back-Shifted Fermi Gas Model 40 6.1.8 Simultaneous Extraction of Level Density and 7-Ray Strength Function 41 6.1.9 Simulation of Statistical 7-Ray Spectra . . . 44 6.1.10 High-Resolution Measurements of Level Densities and 7-Ray Strength Functions 44 6.1.11 iif-Hindrance in Primary 7-Decay after Thermal and ARC Neutron Capture 46 6.1.12 Spectroscopy with Entry-State Selection: Nuclides Produced in the Reaction a+28Si 47 6.2 High Spin Properties of Nuclear States 50 6.2.1 Triaxial Superdeformed Bands in 164Lu and Enhanced El Decay-out Strength 50 6.2.2 Triaxial Superdeformed Bands in 163Lu 52 6.2.3 A Search for Exotic Rotational Structures in 167-169Hf by the Semi- Symmetric Cold Fusion Reaction 76Ge+96Zr 54 6.2.4 Octupole Structures in 226U 56 6.2.5 Shape coexistence in mIr 57 6.3 High and Intermediate Energy Nuclear Physics 59 6.3.1 Introduction 59 6.3.2 Strangeness Production in Ultrarelativistic Nucleus-Nucleus and Proton- Nucleus Collisions - The WA97 and NA57 Experiments 59 6.3.3 Hyperon production in Pb-Pb collisions at 158 A Gev/c 70 6.3.4 The BRAHMS - Broad RAnge Hadron Magnetic Spectrometer - Experiment at the RHIC Accelerator 71
3 6.3.5 Track recognition in BRAHMS using the Hough transform method . 74 6.3.6 A Large Ion Collider Experiment (ALICE) at the CERN LHC .... 76 6.3.7 The Spin of the Nucleons 77 6.4 Radiation physics and radiation protection 79 6.4.1 Radon and radon progeny in indoor air 79 6.4.2 Radon concentrations in groundwaters 81
7 Theoretical nuclear physics and nuclear astrophysics 83 7.1 Introduction 83 7.2 Nuclear structure research 84 7.2.1 Study of odd-mass N = 82 isotones with realistic effective interac- tions 84 7.2.2 Effective interactions and shell model studies of heavy tin isotopes . 84 7.2.3 Shell model studies of the proton drip line nucleus 106Sb 85 7.2.4 Ground state magnetic dipole moment of 135I 85 7.2.5 New island of ms isomers in neutron-rich nuclei around the Z = 28 and N = 40 shell closures 86 7.2.6 Shell model Monte Carlo studies of neutron-rich nuclei in the ls-Orf- lp-0/ shells 86 7.2.7 Towards the solution of the Cp/C\ anomaly in shell-model calcula- tions of muon capture 87 7.3 Hadron properties in the medium: Nuclear structure aspect 88 7.3.1 Hyperon properties in finite nuclei using realistic YN interactions . . 88 7.4 Nuclear astrophysics and dense matter studies 89 7.4.1 Phase transitions in rotating neutron stars 89 7.4.2 Phase transitions in neutron stars and maximum masses 90 7.4.3 Phases of dense matter in neutron stars 90 7.4.4 Structure of ^-stable neutron star matter with hyperons 90 7.4.5 Neutrino emissivities in neutron stars 90 7.4.6 Vortex lines in the crust superfluid of a neutron star 91 7.5 Superfluidity in infinite matter 92 7.5.1 Nucleon-nucleon phase shifts and pairing in neutron matter and nu- clear matter 92 7.5.2 Minimal relativity and 3Si-3Di pairing in symmetric nuclear matter 93
4 3 3 (•.5.3 P2- ^2 pairing in neutron matter with modern nucleon-nucleon po- tentials 93 7.6 Nucleon-nucleon interactions and nuclear many-body theory 94 7.6.1 Phaseshift equivalent NN potentials and the deuteron 94 7.6.2 Perturbative many-body approaches 94 7.7 Project: The Foundation of Quantum Physics 94 7.7.1 Description of vacuum in quantum field theory 94
8 Energy Physics 96 8.0.2 Solar heating and cooling systems at the Sun-Lab 96 8.0.3 Efficiency measurements of a solar thermal heating system 98 8.0.4 Calibration of the measuring equipment 101 8.0.5 Data acquisition system for a building integrated solar heating system 102 8.0.6 Simulation of active thermal solar collector systems 104 8.0.7 Transformation of the solar insolation values on sloped surfaces to horizontal surface values 104 8.0.8 A Combined Thermal and Photovoltaic Solar Energy Collector . . . 105 8.0.9 Stand alone solar system for domestic hot water heating 107 8.0.10 Regulation and Energy Monitoring in Low Temperature Heating Sys- tems 108 8.0.11 A study of heat distributors in wooden floor heating systems .... 109
9 Seminars 111
10 Committees, Conferences and Visits 112 10.1 Committees and Various Activities 112 10.2 Conferences 113
11 Theses, Publications and Talks 116 11.1 Theses 116 11.1.1 Cand. Scient. Theses 116 11.1.2 Dr. Scient. Theses 116 11.2 Scientific Publications and Proceedings 116 11.2.1 Nuclear Physics and Instrumentation 116 11.2.2 Energy 120
5 11.2.3 Radiation Research 120 11.2.4 Other Fields of Research 121 11.3 Reports and Abstracts 121 11.3.1 General 121 11.3.2 Nuclear Physics and Instrumentation 121 11.3.3 Energy 122 11.3.4 Radiation Research 122 11.4 Scientific Talks and Conference Reports 123 11.4.1 Nuclear Physics and Instrumentation 123 11.4.2 Energy 127 11.4.3 Radiation 127 11.5 Popular Science 128 11.5.1 Books 129 11.6 Pedagogical reports and talks 129 11.7 Science Policy and Science Philosophy 130 Chapter 1
Introduction
The present annual report from the Section for Nuclear- and Energy Physics is exclusively a research report. The scientific staff members are also strongly engaged in the university course teaching at all levels, and in various administrative duties, not reported here. The Nuclear- and Energy Physics section 1998 staff counted 10 members in permanent positions, two post. doc. fellows, one professor II (1/5 position for 5 years), 13 research fellows, and 2 engineers. Despite the very professional and persistent efforts of the technical staff, the comprehensive experimental activities are in strongly need for more technical support. The lack of technical positions is however a common university problem, of which Norwegian universities have more than their fair share. Experimental and theoretical nuclear physics is, and has always been, the main fields of research activity in the section. However, in the early seventies a growing research activity within solar energy was initiated, primarily based on the experimental and instrumentation expertise among the section members. This research, both fundamental and applied, has proven popular among students, and also among funding sources. The section has a long tradition in Radiation Research. In particular, fundamental pioneer work on Radon research has been done in this section through the years. This research is continued in close cooperation with the Norwegian Radiation Protection Authority. Furthermore, lately the demand for beamtime on the local cyclotron has increased consid- erably. In fact, at present the accelerator capacity is fully used, the capacity set by the availability of skilled operation staff and the necessary time for scheduled and unscheduled maintenance. The beamtime for external users now exceeds the beamtime allocated to nuclear physics experiments. In order to meet the urgent need for organizing and to give priority to the different accelerator based activities, a cyclotron board, with internal and external members, has now been established. The total beamtime used for experiments in 1998 was 1051 hours. 52 days were used by the Nuclear Physics section, 70 days by the University of Oslo Nuclear Chemistry section, and the Norwegian Cancer Hospital used the cyclotron for 12 days. 42 days were spent on maintenance. In experimental nuclear physics, the section members are engaged within three main fields of research: Nuclei at high temperature (the local cyclotron experiments), high spin nuclear structure (mainly within the EUROBALL collaboration), and high and intermediate energy nuclear physics (at CERN, Geneva and CELSIUS, Uppsala). The CERN-related activity and the Energy projects are almost exclusively financed from the National Research Council (NFR). For the remaining activities, the section gives, within the limits of funding, priority to the local accelerator facility. This is based on the philosophy that local experimental equipment is an important asset in a university institute. The SCANDITRONIX MC-35 cyclotron laboratory has been in operation since 1980. The main auxiliary equipments consists of a 28 Nal-detector system CACTUS, with a unique locally designed silicon strip E — AE detector array called SIRI. The basic running cost for the cyclotron laboratory is funded by the University of Oslo. The experimental activities, however, are completely dependent on the continued support from the Norwegian Research Council (NFR). Some of the section staff are engaged in two major international collaborations; the EU- ROBALL (former the NORDBALL) collaboration on the study of high spin nuclear states, and the CERN collaborations WA97 and NA57 studying ultra-relativistic heavy-ion colli- sions. The experiments in the high spin studies were formerly carried out mainly at NBI, Ris0, Denmark. In 1998 the staff members participated in experiments on EUROBALL at INFN, Legrano, Italy, and at Gamma-sphere, Argonne, 111. USA. The CERN project has a comparably high priority in the Research Council (i.e. in the program for sub-atomic physics). The main aim of this collaboration is the verification of the existence of quark-gluon plasma. The Norwegian participation in this project includes physicists from both Bergen University and from our section here in Oslo. The theoretical research covers several fields of nuclear physics and nuclear astrophysics, from nuclear structure studies to the structure of neutron stars. A common denominator in most of the problems studied is an underlying microscopic description within the framework of many-body theories of the interactions between the various hadrons. Furthermore, problems related to the foundations of quantum physics, such as the non-separability of systems in a pure quantum state and the completeness of quantum mechanics, are also studied. The solar energy research covers the study and development of solar heating and solar cooling systems. For this purpose, a small house, called the Sun-Lab, has been built. Sun.Lab has a thermal solar collector system, a cooling system, two heat stores and a floor heating system. Furthermore, both experimental and theoretical study of solar based hydrogen production is studied. The collaboration with the Norwegian Radiation Protection Authority on natural back- ground radiation research is continued. The study is focused on Radon in indoor air, which is the main source of exposure from ionizing radiation to the Norwegian population. A presentation of the section, the projects, staff and students can now be found on our new web-site: www.fys.uio.no/kjerne. Blindern, July 1999 Finn Ingebretsen Section leader. Chapter 2
Personnel
2.1 Research Staff
Lisbeth Bergholt Research fellow Fabio de Blasio Post doc. fellow (EU) Øystein Elgarøy Research fellow Torgeir Engeland Professor Lars E. Engvik Research fellow Kristoffer Gjötterud Assoc. professor Magne Guttormsen Professor Lisa. Henden Research fellow Morten Hjorth-Jensen Post doc. fellow Anne Holt Research fellow Finn Ingebretsen Professor (elected Section Leader) Gunnar Løvhøiden Professor Ole Martin Løvvik Research fellow (NFR)( until August) Michaela G. Meir Research fellow- Elin Melby Research fellow Svein Messelt Assoc. professor Roar A. Olsen Research fellow (on leave of absent) Eivind Osnes Professor John Rekstad Professor Andreas Schiller Research fellow Sunniva Siem Research Fellow (on leave of absent) Terje Strand Professor II Dunja Sultanovitc Research fellow (NFR) Per Olav Tjørn Professor Trine Spedstad Tveter Assoc. professor Stein W. Ødegård Research fellow Senior and retired staff
Sven L. Andersen Senior scientist emeritus Otto 0grim Senior scientist emeritus Ole H. Herbjornsen Senior scientist Trygve Holtebekk Professor emeritus Anders Storruste Senior scientist emeritus
2.2 Technical Staff
Eivind Atle Olsen Section chief engineer Jon VVikne Section engineer
10 Chapter 3
Cyclotron operation and external user projects
3.1 Operation and Maintenance
E.A. Olsen, J. Wikne and S. Messelt
The total beam time used in 1998 was 1051 hours. The beams used were 628 hours of 3He, 417 hours of 4He and 11 hours of protons. The Nuclear Chemistry Group occupied 70 days, of which 25 days were used for 211At production. 52 days were used for experiments in nuclear physics, and 12 days were used by The Norwegian Radium Hospital for18 F production. 30 days were use for scheduled and 12 days for unscheduled maintenance the latter mainly related to problems with the water cooling system.
3.2 External user projects
The user profile at the cyclotron has changed considerably during the last years. This is illustrated in figure 3.1. The main non-nuclear projects are described below.
3.2.1 Production of 18F-fluorodeoxyglucose for medical PET-imaging
Arne Skretting The Norwegian Radium Hospital The present project is a cooperation between OCL. Radium Hospital, The National Hos- pital of Norway and Institute of Energy Technology.
Positron emission tomography is a medical imaging technique that rests on radiopharma- ceuticals labeled with a positron emitter. We have constructed a target for the cyclotron that is used to produce 18F by proton activation of 18O-enriched water. The activity is then taken to the Institute of Energy Technology for preparation of 18F-fluorodeoxyglucose (FDG). Because of its higher uptake in cancer cells as compared to most normal tissues,
11 Days
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& pit . 0) 05 o 30 £ o SIC S •5 20 CO DC the i ph y lea r o CO 3 o 10 ^. JZ CD x: 5 O 0 J Nud e •fl n n 1995 1996 1997 1998
Figure 3.1: The Cyclotron user profile for the years 1996, 97 and 98. The demand for beamtime now exceeds the capacity.
FDG is being used in the Norwegian Radium Hospital to image the 3D distribution of FDG in the body, thereby visualizing primary and metastatic tumours. FDG may also be used for imaging of the brain and heart, as it will be in the National Hospital. The halflife of 18F is such (109 min) that it is practically impossible to import FDG from abroad. The activation is performed by irradiation for 1 hour in an activation target chamber with a 10 microampere, 16 MeV proton beam. The resulting quantity of approximately 20 GBq 18F is then transported by car to the Institute of Energy Technology, where production of FDG according to pharmaceutical good manufacturing practice (GMP) takes place. The distance of travel is considerable; if irradiation starts at 9 hours a.m., the first patient is injected at 2 hours p. m. The !>ospitals would like to produce 18F at least twice a week, but due to limited capacity, lack of personnel, nuclear physics experiments etc. this has not been possible. Stable supply of FDG requires a dedicated hospital cyclotron, but national funding has been unavailable until now. Imaging in the hospitals is performed with gamma cameras with two detectors operated in coincidence mode. These have lower sensitivity than dedicated PET-cameras, but the first patient examinations performed in The Norwegian Radium Hospital demonstrates that it is possible to obtain high quality diagnostic information.
3.2.2 Basic Nuclear Chemistry Research
J.P. Omtvedt Nuclear Chemistry Branch, University of Oslo
12 The main aim of this project is to study trans-actinides. The project is part of an inter- national collaboration (SISAK - Studies of Short-lived isotopes Studied by the AKUFVE technique). The SISAK activity in Oslo has expanded considerably over the last few years through the construction and use of a gas-jet transport system and target chamber at the Oslo Cyclotron laboratory. This has given the collaboration a unique possibility to develop and test the chemical systems used in the main experiments. At the cyclotron the lighter nuclei like Zr and Hf are used. The local installation has lead to a considerable improvement of the equipment and the procedures, and given the whole collaboration a valuable running experience before the use of large a scale (and expensive) accelerator facility.
3.2.3 The application and study of 211At
Nuclear Chemistry Group, University of Oslo
The use of target-searching a-active molecules might be very effective in cancer treat- ment. The use of 211At coupled to tumor-searching molecules can focus the short range cv-radiation almost exclusively onto cancer cells. The halfiife of 211At is short (7.21 h), and the production site must therefore be located close to the user. Access to the Oslo Cyclotron is therefore a necessity for this project. A company (ATI AS), with basis in this project, has recently been established. The company will commercialize a-emission technology for cancer therapy.
13 Chapter 4
Data Acquisition and Analysis
4.1 Introduction
Currently, the data acquisition system at the Oslo Cyclotron Laboratory may be divided into two major components:
• A front-end system responsible for data digitalization, read-out and formatting. This system is based on a VMEbus with connections to CAMAC, NIM and the custom SIRI detector readout devices.
A rear-end system consisting of a Sun Sparcstation with a separate hardware inter- face to the front-end VMEbus.
The acquisition system is shown in fig. 4.1.
4.2 Configuration
Developments in 1998 on the computer / data-acquisition system were:
CAMAC Exabyte VME . BITS Spa rcSta lion SIRI —r\ interface =t> 10/512 Pov/erPC cro NIM
Figure 4.1: Schematic view of the data acquisition system
14 • Software development for the PowerPC VME data-acquisition controller continued.
• The dedicated VME module ("ROCO card #3") for the SIRI readout was built, and successfully debugged / tested. A special test program for the module was written.
• Software for ROCO card #3 was also integrated into the SIRIUS package.
• Software for the Bit3 interface system on the rear-end (Sun, Sbus) side was upgraded to revision 3.8.
• The rear-end computer systems were improved. An additional 17GB user disk was purchased. Most of the NCD 19c X-terminals got a video memory upgrade from 8 to 16MB. An additional Exabyte tape drive and a HP890c colour inkjet printer were installed.
The current configuration is given below: a) Front-end
VMEbus system with: 1 CES RTPC 8067EA, PowerPC 603 64MHz CPU, 128kB SRAM, 64 MB DRAM, 1 GB disk, LynxOS 2.3.1 1 CBD 8210, CAMAC Branch Driver 1 NIM Interface 1 TSVME 204, EPROM socket card 2 VBR 8212, VME-VME link, receiver 1 VBR 8213, VME-VME link, transmitter 3 TPUs, Trigger Pattern Units 1 Bit3 Model 467, VME-SBus link, 25MB/s 1 ROCO card #3 (interface for SIRI, dual port RAM) NIM ADC Interface System with: 16 Silena7411/7420G ADCs CAMAC system with: 4 Silena 4418/V ADCs 4 Silena 4418/T TDCs 1 Pile-Up Rejection Module (PUR)
15 b) Rear-end
Sun Sparcstation 10-512 with: Solaris 2.5.1 operating system (UNIX System V Release 4.0), OpenWindows, X-windows, Motif Dual SuperSPARC TMS390Z55 50MHz CPU with 36kB cache, 128 MB memory 1 Bit3 Model 467, SBus-VME link card, 25MB/s 2 SCSI mass storage expansion box 2 2.0 GB disk drive 2 9.0 GB disk drive 1 Colour monitor, 19", 1152 x 900 pixels 1 Ethernet controller, TCP/IP and NFS software 1 10 GB Exabyte cartridge tape unit 1 12 GB Exabyte cartridge tape unit 1 Panasonic SCSI CDROM unit 1 SparcPrinter QA-6 laserprinter 1 Hewlett-Packard HP890c colour inkjet printer Sun UltraSparc 2 Creator with: Solaris 2.5.1 operating system (UNIX System V Release 4.0), OpenWindows, X-windows, Motif Dual UltraSPARC 200MHz CPU, 448 MB memory 1 2.0 GB disk drive 1 17.0 GB disk drive 1 Colour monitor, 20", 1280 x 1024 pixels 1 Ethernet controller, TCP/IP and NFS software 1 12 GB Exabyte cartridge tape unit 1 10 GB Exabyte cartridge tape unit Our Suns share the following X-terminal resources: 10 NCD X-terminals, colour monitor, 19-20", 1280 X 1024 pixels 1 TDV X-terminal, colour monitor, 17", 1024 x 768 pixels
16 4.3 Acquisition and Data Analysis Software
MAMA: Program to manipulate large 2-dimensional matrices. It contains more than 80 commands. Some examples are: read, write, add, subtract, multiply, smooth, compress, project, cut, etc. In addition, the package contains more complex functions like - unfolding of Nal 7-spectrum. - folding spectra with Nal response function. - extraction of first generation 7-spectra. - extraction of nuclear temperature from 7-spectra.
MIMA: MAMA without graphics, for use on "dumb" terminals.
CSMA: Cranked shell model with asymmetric nuclear shape.
DECAY: Calculates the 7-decay for a Fermi gas system. The lowest excitation region is simulated using experimental data.
EMMA: Calculates El, Ml, El, Ml transition probabilities between single quasiparticle states from the RPC program (see below).
GAP: Solves the BCS gap-equation.
HFBC: Hartree-Fock-Bogoliobov Cranking model based on Nilsson orbitals from the RPC pro- gram (see below).
KINEMATIC: Calculates relativistic energy loss at a given scattering angle. Bethes formula. Straggeling. Also available on IBM-PC
PAW: CERN-developed Physics Analysis Workstation running on the Apollo and the Sun Sparc- station.
SIRIUS: This is the new main data-acquisition and on-line analysis program at the lab.
17 ZIGZAG: Calculates the 7-decay as a function of evaporated neutrons. RHOSIG: Extracts the 7-strength function and level density from first generation 7-spectra. OFFLINE: The off-line counterpart of SIRIUS. GBRAHMS: Version of Geant for simulations of particle tracks in the BRAHMS (Broad RAnge Hadron Magnetic Spectrometer) detector. BRAT: BRahms Analysis Toolkit for analysis of track data in the BRAHMS detector.
4.4 Progress of the SIRI Data-Acquisition System Develop- ment
J. Wikne
The last readout module, "ROCO card #3" (VME), was built and tested. The complete detector and readout system still remain to be tested together. The main problem at the end of the year were the multipole vacuum feedthroughs. Still another revision of the mechanical design has to be made. Currently, we are implementing the use of 25 pin D-type feedthroughs from Ceramaseal, type 14442-01-W.
A block diagram of the SIRI Data-Acquisition System is shown in fig. 4.2.
References:
1. Section for Nuclear and Energy Physics Annual Report 1997 Department of Physics, University of Oslo Report UiO PHYS 98-06
18 SIRI Read-Out Controller * Main Block Diagram
RIBBON CABLES TWISTED PfllP. COBLES KS-VZ2 LEUELS) FRONT END POQT BOARD Figure 4.2: Block diagram of the SIRI Data-Acquisition System 19 Chapter 5 Nuclear Instrumentation 5.1 The CACTUS Detector M. Guttormsen and S. Messelt The CACTUS detector accommodates 28 Nal and 2 Ge detectors and is mounted on the 90° beam line of the Oslo cyclotron. The Nal counters are fixed to the detector frame and have a distance of 24 cm to the target. The 5"x5" Nal(Tl) detectors (BICRON) are equipped with 5" PMT. The detectors are shielded laterally with 2 mm lead and collimated with 10 cm lead in front. The solid angle of each detector corresponds to 0.5% of 4TT. The front of the detectors are covered with a 2 mm Cu absorber. In addition to the Nal counters there is space for Ge counters. At present we have four Ge-detectors with efficiencies of 49, 60, 67 and 72%. The main investment for 1998 was a new Ge detector. The target chamber can be removed from the center of the Nal ball through the two remaining holes (32 holes in total). Beam focusing can be performed with a piece of quartz at the target place, where a TV camera through a Plexiglas window can monitor the beam spot. Inside the ball of 7-detectors 8 Si (Li) particle detectors are mounted. Later, these detectors will be replaced by the SIRI particle telescope system. 5.2 Properties of the CACTUS Detector Array A. Schiller During the last years, many properties of the CACTUS detector array, like time resolution, detection efficiency of various detectors, polarization efficiency and the ability of measuring angular distributions have been determined with great accuracy. As an example, I present here measurements with 3 Ge detectors in coincidence with the 27 Nal detectors located at different angles. The observed angular distribution of 7-rays in 4 different 7-7-cascades are shown in Figure 5.1. The data points in Figure 5.1 were fitted to a series of Legendre Polynomials according to W{d) = 1 + A2 F2(costi) + AA P4(cos0), using the program LEGENDRE. Also the theo- retical A2 and Ai coefficients were calculated using the program ANGLE (see Table 5.1). 20 Angular Distributions of 4 y-y Cascades 100 150 200 100 150 200 Polar angle (degree] Polor angle (degree] Gated on 1 1 73 keV in Co-60 Gated on 1 332 keV in Co-60 5 i.O4 o S 1.25 L) ° 1.02 - 1.15 / t / I ZD 1 K O \ 1.1 S 0.98 - IV / I '\ 1 1.05 | 0.96 . 1 L \ / K 0.95 1 0.94 \| / V 0.9 0.92 - 1 \^j/t 0.85 - j 0 q • i t i 1 1 1 1 1 I > 1 1 1 1 1 1 ) , c\ « i i > i i i i i i i i i i i 1 .... 50 100 150 200 50 100 150 200 Polor angle (degree! Polar angle (degree! Gated on 778 keV in L'u-152 Gatea on 1 408 keV in Eu - 1 52 Figure 5.1: Angular distributions of 4 different 7-7-cascades. The theoretical curve fits the data very well. The fitted A2 coefficients agree very well with the theoretical values. Also the fitted A4 co- efficients are in very good agreement with theory, even though their errors are considerably large. A detailed description of all measurements can be found in [1]. References [1] A. Schiller et al. Department of Physics Report, UiO/PHYS/98-02 (1998) 21 Nucleus Cascade Theory Fit .42 = 0.102 0.104 ±0.005 60Co (upper left) 4 -»• 2 -*• 0 -44 = 0.0091 0.0111 ±0.0081 60 A2 = 0.102 0.097 ±0.005 Co (upper right) 4- •+2-+0 Ai = 0.0091 0.0088 ± 0.0079 A2 = -0.071 -0.060 ±0.010 152Eu (lower left) 3- -»2->0 .44 = 0 0.008 ±0.014 152 A2 = 0.250 0.233 ±0.023 Eu (lower right) 2- •»2->0 0.043 ±0.035 Table 5.1: Comparison of theoretical and fitted Ai and A4 coefficients of 4 different angular correlations. Read-out chips Beam Figure 5.2: The target chamber with one SIRI detector ring seen perpendicularly to the beam axis. The detector ring covers a range of angles between 30° and 60° with respect to the beam direction. The distance from the target to the active detector surface is 40 mm. 5.3 The SIRI Strip Detector Project M. Guttormsen, S. Messelt, E. Olsen and J. Wikne The SIRI (Silicon Ring) system will be used in the study of nuclear structure and decay properties as a function of temperature. It consists of an array of silicon particle telescopes for the detection of light particles. The telescopes will be placed inside the CACTUS detec- tor, and the CACTUS/SIRI combination represent a very powerful particle-7 coincidence set-up. The project has been supported by the Norwegian Research Council (NFR). Fig. 5.2 shows the target chamber, which is placed inside the CACTUS Nal array. Detector rings, target and chips are mounted on separate rings that can be moved on rods connected with the flange to the right. It is possible to switch between four targets inside the chamber without breaking the vacuum. New oil free vacuum pumps are installed. The target chamber is designed so that cooling of the chips and detectors can be performed. The beam optics and focusing properties are tested in order to reduce halos and scattering from slits along the beam line. The detector and read-out chips are user specified, and represent high technology develop- ments. The SINTEF group in Oslo has designed and delivered the detectors and read-out chips for the system. AMS in Austria processed the ASIC chips. The mounting of the circuitry and detectors on ceramic substrates was made by Microcomponent in Horten, 22 Guard structure Cables 8 pads E 130 urn \ E 2000 urn Figure 5.3: In the upper part is shown the detector glued to the ceramic substrate with circuitry and flat cables. In the lower part is shown the arrangement of the 8x8 telescopes into a ring-structure. Norway. 5.3.1 The Detectors One SIRI element consists of one AE and one E detector mounted on a 1 mm thick ceramic substrate, as shown in Fig. 5.3. The front and end detectors have the same shape (almost trapezoidal in form) and are sandwich mounted back-to-back. Each detector element consists of 8 pads. The detectors are glued on to the ceramic substrate, where bonding and cabling can be performed. Surface mounted circuitry is laid on both sides of the left wing of the substrate, as indicated in Fig. 5.3. Flat cables are connected to the chips from the wings. The particle telescopes are 2 mm thick and stops at least 60 MeV a-particles. It is also important to stop protons in the telescope for the purpose of appropriate particle identifi- cation. The front detector is 135 jj.m thick, so that o-particles of around 15 MeV can pass through the detector. Thus, the thickness of one element is 3.2 mm. The arrangement of 23 the elements into one ring is shown in the lower part of Fig. 5.3. For the front detectors a leakage current less than 0.5 nA per pad were obtained. The silicon wafer for the 2 mm detectors is made of very high resistivity substrate. A multi- guard ring of 2.5 mm is designed around the detector to reduce the leakage current. Also, new 1.5 mm thick end detectors have been purchased. 5.3.2 The Chip Read-Out System In the read-out part of the system, we use a custom designed, monolithic chip (ASIC). Each chip is designed to handle 32 silicon strip detectors, including preamplifiers, discriminators, shapers, pattern, multiplicity and pile-up rejection circuitry. The chip is implemented in AMS 1.2/xm BiCMOS, double poly, double metal process. The power consumption is 350 mW, which gives about a 6°C increase in temperature when bonded to a CLCC84 chip carrier. At the first stage on the chip a fast preamplifier splits the signal into a time and energy branch. The ready signal from the acquisition system resets the latches and energy buffers, but not the multiplicity and pile-up detection. This part of the circuit is always ready to take events. The pileup inspection is performed both before and after the event of interest. If two signals arrive within 2 /j,s, the corresponding latch will be reset (signals less than 100 ns apart cannot be separated). Pile-up on/off has a fixed level, which is set externally for the specific experiment. The function set-latch identifies the channel fired. The latch for other channels cannot be set (only reset) after the multiplicity signal for the event is back to 0. The chip gives both good energy and timing signals. Generally, only one or possibly two (or three) detectors per chip will fire. Therefore, the coincidences detected within the chip are handled using a summing technique (multiplicity) of the logical timing signals. This multiplicity signal is a linear sum of the logical signals from all detectors. The signal can be used to make multiplicity requirements or fast coincidences with other types of detectors. In this way, reset for bad events can be performed (the computer ready signal) at an early stage. The chip resets within 1 fis. In this way energies can be read out even without the presence of set-latch. The processing of the timing signals is a compromise in order to limit the number of cables out of the target vacuum chamber and to reduce the pin count of the chip. The chip do not include CFD for the time signal, time walk effects will be compensated in the off-line analysis using the associated energy pulse. 5.3.3 The Data Acquisition System The chips are connected to each other on a common bus within the target chamber. Outside the chamber a read out controller (ROCO) contains ADC's and event buffers. The user can set certain thresholds by computer control, i.e. signal widths and logical signals to the chips via the ROCO. The data acquisition system is designed to handle the high data rate, which is more that 10 times higher than earlier. The rear-end system, shown in Fig. 5.4, is built around a 24 SPARCStation512 128 Mb memory 11 Gbdisk, Exabyte NCD X-terminals SIRI Figure 5.4: Rear-end acquisition system. SparcStation 10/512, with an interface (Bit3) to the VME crate, where a single board computer takes care of the event builder process. The data transfer system is designed to give a fast data stream out to an Exabyte tape. Further details on this project are given in Refs. [1, 2] and in section 4.4 of this report. References [1] M. Guttormsen SIRI, A proposal for a multi-detector AE-E particle telescope Department of Physics Report, UiO/PHYS/92-21 (1992) [2] M. Guttormsen Eventbuilder for the RTPC 8067 Single Board Computer Department of Physics Report, UiO/PHYS/98-08 (1998) 5.4 Background Radiation from Target Impurities A. Schiller Due to target impurities (mainly carbon and oxygen isotopes) the coincident 7-spectra of (3He.3He') and (3He, a) reactions on rare earth nuclei are distorted. In order to restore the 7-spectra, one has to subtract this kind of background radiation. For that reason these 25 two reactions were studied on a paper target (mainly carbon and oxygen atoms) and on a plastic target (mainly carbon atoms) with approximately the same target thickness as the rare earth targets. (3He,3He'y) Reaction on Different Targets 3 3.5 4 5 5.5 6 6.5 Er (MeV) Paper Target 3 3.5 E7 (MeV) Figure 5.5: Part of the 3He-7 coincidence matrices of the (3He,3He') reaction on 3 different targets. One can clearly see the 4438 keV transition in 12C (all targets) and the 6129 keV transition in 16O (only paper and 162Dy targets). The subtracted spectrum is not shown. In Figure 5.5 the results are shown in the case of the (3He,3He') reaction on 162Dy. Similar results are achieved for the (3He, a) reaction on the same nucleus [1]. In the near future the background subtraction will be applied to all other reactions recently investigated at the Oslo Cyclotron Laboratory. References [1] A. Schiller et al. Department of Physics Report, UiO/PHYS/99-xx (1999), in preparation 5.5 Liquid Nitrogen Filling System for Ge Detectors S. Messelt and M. Guttormsen 26 An automatic liquid nitrogen filling system for Ge detectors has been build. The detectors will be connected to a 200 liter dewar with isolated tygothane tubes and cryogenic solenoid valves (ASCO). To control the system we use an old PC with a commercial I/O card. The TTL input/output card provides eight ports selectable as input or output, each 8 bits wide. The program is written in Turbo-C. Ge-detect. Figure 5.6: The liquid nitrogen filling system (with only one detector connected). To operate the solenoid valves, the TTL-signals from the PC are converted to 24 volts signals in a control module. The valves are normally closed, and the filling procedure starts by opening the main valve at the dewar and one of the manifold valves connected to a Ge detector. Overflow is detected by the voltage change in a light emitting diode when it cools down by the overflowing liquid nitrogen. The voltage change is converted to a TTL-signal in the control module and sent to the PC, which closes the valve. If no overflow signal is detected within a given time period, the valve to the detector is closed and an alarm is given. This procedure is repeated for all detectors. Then the main valve at the big dewar is closed and a valve in the manifold, which is not connected to any detector, is opened for a short time to drain the manifold and the tube from the big dewar. The system will then wait for a given number of hours before starting filling the detector dewars again. The status of the system is displayed on the PC monitor and also written to a file. Using a PC and Turbo-C makes is very easy to write and modify the control program, and also to provide a remote connection to the system via the RS-232 serial port. The system was successfully put into operation in 1998. and tested for several weeks of beam time. Private communication with Anssi Savelius in the cyclotron group in Jyvaskyla is highly appreciated. 27 5.6 The New Eventbuilder Single Board Computer M. Guttormsen New compact multidetector systems make it important to handle the event read-out in an efficient way. The need for a faster eventbuilder at the Oslo Cyclotron Laboratory (OCL) is now mandatory when the SIRI/CACTUS system is put into operation. The previous data acquisition computer is from 1991 and is based on a FIC8230 from CES1 with a Motorola 68020@16MHz. The new RTPC 8067 LK single board computer2 from CES runs LynxOS at a Pow- erPC603@66MHz CPU. It is equipped with all features usually found on UNIX systems. In addition, the RTPC is a full VME real-time processor with the features: • Full VME D64 master/slave interface • Single slot VME module • PCI extension slot • Independent VME/PCI list processor (I/O server). The main task of the system is to read event by event and transmit these as long buffers to the Sun SPARCstation. The present development concerns the implementation of the RTPC single board computer, together with modifications and extension for the new TPU5 dedicated for the SIRI events. Several new test programs have been written: eventbuilder+ and campari+ are totally rewritten, and minor modifications are done for sirius+, offline-h, reduc+ and mama. The sirius+ program transfers the eventbuffers to tape and uses spare time to sort events on-line for monitoring the experiment. A double buffering technique is applied in order to achieve high throughput. Each of the data buffers is 32 Kwords long with 32 bit long words. The two CPUs (RTPC and SPARCstation) base the buffer handling communication on the polling of two common semaphores. If buffer 1 is filled up by RTPC, then semaphore 1 is set to FULL. Then RTPC loops on semaphore 2 that by now should have been set to EMPTY by SPARCstation (EMPTY means that SPARCstation have fetched this buffer). If semaphore 2 is EMPTY, RTPC starts filling up buffer 2. When it is full, the semaphore 2 is set to FULL by RTPC, and SPARCstation starts to read this buffer, and so on. The semaphores and status of RTPC and SPARCstation is located in the A24 slave space of RTPC. This memory is allocated through SRAM, and has a fixed location for both CPUs. In this message box RTPC writes the dynamic memory address of the buffer area, so that SPARCstation knows where to look for the buffers. The SRAM has not enough memory to house the two event buffers, so these have to be allocated in the DRAM memory of RTPC. The total length of the buffers are 0x40000 bytes = 256 Kbytes. This memory area has to be contiguous and not occupied by the LynxOS. Since the dynamic slave mapping of the present RTPC is not working, we have used static mapping. 'Creative Electronic Systems, Switzerland, E-mail: [email protected] 2RTPC means Real Time PowerPC 28 The VME modules can be accessed by creating a pointer to the VME physical address by the vme_map() function, and should then be released by the vme_rel() function. The address modifier code (AM) is 0x39. The speed performance of the PowerPC 603 microprocessor for integer and floating point operations are 63 SPECint92 and 58 SPECfp92, respectively. The new eventbuilder was tested out during a four-week experiment in autumn 1998. The system runs the event loop 10 times faster compared to the previous system, and the limits of performance is now set by the ADC conversion times. With a typical eventlength of eight words, the eventloop takes 60 /is including the waiting for ADC conversion, which is 30 ^s. This allows an event rate of 5000 events/s with 23 % dead time. Thus, the new eventbuilder will match our requirements for many years. Further details are given in [1]. References [1] M. Guttormsen Eventbuilder for the RTPC 8067 Single Board Computer Department of Physics Report, UiO/PHYS/98-08 (1998) 29 Chapter 6 Experimental Nuclear Physics 6.1 Experiments at the Oslo Cyclotron 6.1.1 Introduction The experimental work at the Cyclotron Laboratory is dedicated to the study of nuclear structure at low spin and high excitation energy. The technique is based on measuring charged particles from light-ion transfer reactions, mainly (3He,a) in coincidence with 7- rays, using the 28 Nal 7-ray detector array CACTUS combined with Si particle telescopes. In this way the 7-decay pattern can be studied as a function of the initial excitation energy from the ground state up to Ex ~ 40 MeV. In order to increase the efficiency of the particle-7 coincidence setup further, the the SIRI multi-detector system has been build (see section 5.3). The combination of SIRI and CACTUS will be a very powerful instrument in the study of both nuclear properties and reaction mechanisms as functions of temperature. In heated nuclei (a few MeV or higher above the yrast line), statistical concepts must be used for describing the nuclear structure due to the near exponentially increasing level density and the extensive configuration mixing. The nuclear properties in this highly excited regime may be divided into two categories: i) average properties, which vary slowly with Ex and are related to thermodynamic concepts ii) the fluctuation properties, which provide a statistical characterization of the microscopic structure of the various eigenstates. The study of the average properties of nuclear structure involves the determination of ther- modynamic quantities as level density and temperature as functions of excitation energy, and the search for thermodynamic phase transitions. A method has been developed for the simultaneous determination of the level density and the 7-ray strength function. Phase transitions, like the quenching of pair correlations, are expected to be revealed as irregu- larities in the level density, as step structures or constant temperature regions. Collective excitations, which contain information about correlations between nucleons, may appear as fine structure in the 7-ray strength function. Such signatures have indeed been observed experimentally for several nuclides. Data on more nuclei has been collected during a series of experiments in 1997 and 1998. 30 The transition from ordered to chaotic nucleonic motion is expected to show up in the fluctuation properties of the nuclear states. Level statistics indicates that the nucleus has a rather chaotic structure in the neutron resonance region. In well-deformed nuclei the degree of A mixing may serve as a more sensitive probe for remains of order r in the nuclear structure. Studies of the primary 7-decay after thermal neutron capture have revealed a clear correlation between the transition intensity and the final-state A'-value, more pronounced after thermal than after average resonance capture, which might signify remains of order. In the thermal case, the transition probability distributions for K- allowed and A"-forbidden transitions also have shapes associated with different numbers n of degrees of freedom. Several physical explanations for this puzzling observation have been discussed. In order to look for possible doorway state effects, a study of possible correlations between probabilities for populating known low-lying states through (n,7) and (d,p) reactions is planned. 6.1.2 Temperature and Heat Capacity of Rare-Earth Nuclei E. Melby, L. Bergholt, M. Guttormsen, M. Hjorth-Jensen, F. Ingebretsen, S. Messelt, J. Rekstad, A. Schiller, S. Siem and S. 0degard One of the most challenging goals of nuclear physics is to trace thermodynamical quanti- ties as function of excitation energy. These quantities reveal statistical properties of the nuclear many body system. Unfortunately, it is extremely difficult to reach this goal - both experimentally and theoretically. Recently [1, 2] the Oslo group presented a new way of extracting level densities from measured 7-ray spectra. One of the main advantage of this method is that the nuclear system is presumably thermalized prior to the 7-ray emission. In addition, the method allows the simultaneous extraction of level density and 7-strength function over a wide energy region. The experiment was carried out with 45 MeV 3He-particles at the Oslo Cyclotron Labora- tory (OCL). The experimental data are obtained with the CACTUS multidetector array using the (3He,cr7) reaction on 163Dy, 167Er and 173Yb self-supporting targets. The charged ejectiles were detected with eight particle telescopes placed at an angle of 45° relative to the beam direction. An array of 28 Nal 7-ray detectors with a total efficiency of ~ 15 % were surrounding the target and particle detectors. The experimental level density is deduced from 7-ray spectra recorded at a number of initial excitation energies E. These data are then the basis for making the first-generation (or primary) 7-ray matrix, which is factorized according to From this expression the 7-ray energy dependent function a as well as the level density p is deduced by an iteration procedure. The temperatures are found by where 5 = So + \np(E). The deduced temperatures are shown in Figure 6.1. 31 2 S 4 Excitation energy [Me Figure 6.1: Observed temperatures as functions of the excitation energy E (data points with statistical error bars). The solid lines are temperatures as functions of average exci- tation energies < E > deduced within the canonical ensemble. 32 3 4 5 Average excitation energy [MeV] Figure 6.2: The heat capacities extracted within the canonical ensemble. The dashed curve displays the simplified Fermi gas expression Cv — 2y/aE for a = 18.5 MeV"1. The partition function in the canonical ensemble Z is given by the Laplace transform of the level density p. The level density is interpreted as the multiplicity of states at E, which in our case is the level density of accessible states in the present nuclear reaction. The partition function is then given by J2 (6.3) 1=0 where En is the excitation energy at bin n. The excitation energy is given by the thermal average oo E T E(T) > EnP(En)e - "' . (6.4) n=0 The smoothing effect implied by the canonical ensemble can be investigated by calculating the standard deviation for the thermal average of the energy with < E (6.5) givin = 3 MeV at E = 7 MeV. Thus, one cannot expect to discover sudden thermo- dynamical changes within the canonical ensemble of nuclei in this temperature region. This gratifying behaviour of the canonical temperature encourages us to use the canonical ensemble to estimate the heat capacity Cv as well. The heat capacity can be deduced by 33 simply calculating the. increase in the thermal average of the energy < E > with respect toT Cv{T) = —^—. (6.6) Figure 6.2 shows the deduced heat capacities for the 162Dy, 166Er and 1(2Yb nuclei as a function of < E >. All nuclei reach a heat capacity of about 20 at E = 6 MeV, which is 10% of the value for an ideal gas with |iV ~ 250, due to blocking of fermions situated deep in the potential well. Further details are given in Ref. [3]. References [1] L. Henden et al, Nucl. Phys. A589 249 (1995) [2] T.S. Tveter et al., Phys. Rev. Lett. 77(1996) 2404 and A. Schiller et al., to be published [3] E. Melby et al., submitted to Phys. Rev. Lett. (1999) 6.1.3 The 162Dy(3He,a) and 162Dy(3He,3He') Reactions A. Schiller, L. Bergholt, M. Guttormsen, E. Melby, S. Messelt, J. Rekstad and S. Siem Two 162Dy(3He,ct) and 162Dy(3He,3He') experiments have been carried out in April and October 1997. The analysis of the data is finished and level densities could be extracted for the nuclei 162Dy and 161Dy according to R,ef. [1]. It is now of great interest to compare the level densities of 162Dy obtained in this work (with 5 times better statistics) to those of Ref. [1] (see Fig. 6.3). One can see that the level densities are in good agreement with each other. The errors in the upper part are much smaller due to better statistics. A bump can be seen at around 3 MeV. The origin of the bump is not clear, it might be due to a gradual breakdown of pairing correlations [2]. The level density of 161Dy (not shown here) does not have this bump structure. This might be explained by the presence of an unpaired nucleon. References [1] T. S. Tveter et al., Phys. Rev. Lett. 77(1996) 2404 [2] A. Schiller et al., 'Fysikerm0tet\ Oslo (Norway), June 10-12, 1998 and The 9th Nordic Meeting on Nuclear Physics, Jyvaskyla (Finland), August 4-8, 1998 6.1.4 Structure and Decay Properties of Heated 166Er E. Melby, L. Bergholt, M. Guttormsen, S. Messelt, J. Rekstad, A. Schiller and S. Siem An experimental run with the reaction 16'Er(3He,a)166Er was performed as a part of the systematic study of rare earth nuclei at OCL. Of particular interest are the extraction of 34 Level Density in 2 1 I M 1.8 Q. 1.6 1.4 - 1 > - 1 • * U • i / 1 \ , •••• ;ve l Dens i '- ••• • i\* X 0.0 • •* r - ^ 0.6 \ y ^ ^, -» •... \ • •* ^ \ /- y / \ -jE; 0.4 -' i 0.2 r / Re l t n i! , ,,,,11,, > 1 , , , i , , , , ! ( , i 0 1 2 3 4 5 6 7 8 From '62Dy(3He,3He')'62Dy Excitotion Energy [MeV] « 1.4 a> 0.8 cu 0.6 •| 0.4 \ 1 ,N ^0.2 , I . , I 0 1 2 3 4 5 6 7 8 From 163Dy(3h8,a)'62Dy Excitation Energy [MeV] Figure 6.3: Level densities in 162Dy obtained from the reactions 162Dy(3He,3He') (upper part) and 163Dy(3He,a) (lower part). Both level densities are divided by an exponential. thermodynamical quantities and the search for dependency of the ii-quantum number in the 7-decay from highly excited nuclear states. The target of 167Er, which has a ground state A"-value of 7/2, was isotopically enriched to 95.6% and had a thickness of 1.5 mg/cm2. The projectile energy was 45 MeV, and the reaction products were detected by the array CACTUS. The primary 7-rays in the decay of the excited 166Er nucleus have been isolated by the subtraction technique of Ref. [1]. From the primary 7-ray spectra the level density and 7- ray strength function of 166Er are determined by an iterative procedure [2]. In Fig. 6.4 the level density and the 7-ray strength function are shown. To emphasize the fine structure, the level density and 7-ray strength function are divided by best fit functions of the form p oc exp(U/T) and a cc E™, respectively, where U is the excitation energy, E^ the 7-ray energy, and T and n are constants. References [1] M. Guttormsen et al, Nucl. Inst. Meth. A255 (1987) 518 [2] T.S. Tveter et al. Phys. Rev. Lett. 77 (1996) 2404 and //A. Schiller et ai, to be 35 Level density Relative level density Exitation energy (MeV) Exitation energy (MeV) y — strength function Relative strength function 3 V 2 10 1 — 1 4 6 8 0 2 4 6 y-energy (MeV) •y-energy (MeV) Figure 6.4: Upper panel: The level density of 166Er to the left, and the same divided by a fit function to the right. Lower panel: The 7-ray strength function of 166Er to the left, and the same divided by a fit function to the right. 36 10 : CHe,3He )/(JHe 1, 1 - •' "In' t t - c 'l • "c -1 •-10 %•••• !+•....•• or 1 •'••! ) '••, io"V S : 162Dy P * 10 1 , , i , , .i i 3 4 5 6 Excitation energy Figure 6.5: Ratios for feeding the ground state band in 162Dy. published 6.1.5 Direct 7-Feeding of the Ground State Band in Rare Earth Nuclei L. Bergholt, M. Guttormsen, F. Ingebretsen, E. Melby, S. Messelt. J. Rekstad, A. Schiller. S. Siem and S. 0degard The transition rate for direct 7-feeding of the ground band can be utilised to investigate the nuclear structure at high excitation energies. In this work we study the 7-decay of rare earth nuclei and search for non-equilibrium phenomena in the 0-8 MeV excitation region. The experiment was carried out with 45 MeV 3He-particles. The final nuclei 162Dy and 1/2Yb is populated through inelastic scattering (3He,3He" 7) and pickup (3He,cry) reactions. From these data sets first generation (Er,E-y) matrices have been extracted. The ratio of feeding the ground state band for 162Dy is compared for the two reactions in Figure 6.5. There is stronger direct feeding of the ground band in the inelastic scattering. This feature is probably connected to the time of thermalization of the compound sys- tem. A simple model has been developed that may serve as a clock for thermalization mechanisms in heated nuclei. 37 The project is in progress. 6.1.6 Gamma-Ray Angular Correlation and Polarization Measurements of the 163Dy(3He,ct7)162Dy Reaction S. Rezazadeh, M. Guttormsen, E. Melby, J. Rekstad, A. Schiller and S. Siem A prominent 1 MeV 7-ray bump has been observed [1] in the 7-spectra obtained from the pick-tip reaction, 163Dy(3He,a7)162Dy and several nuclei around mass 160. The bump is actually composed of two separate bumps. These bumps are believed to be built up by 7- ray transitions from vibrational bands to the ground state. In addition to the 1 MeV-bump, collective E2 radiation, the yrast and high-energy 7-ray transitions can be observed and studied. The aim of this work is to measure and study angular correlation and polarization of 7-ray, for these energy regions. The experiment was performed using the 163Dy(3He,a7)162Dy reaction, with a beam energy of E3He=45 MeV at the Cyclotron Laboratory at the University of Oslo using the MC- 35 cyclotron to produce the beam, and the CACTUS multi-detector system to measure ^-coincidences [2]. Our initial assumption was that we could have angular correlation on every axis (i.e. the beam, the recoil and the normal vector to the reaction plane). However, when we measured the relative anisotropies of the angular correlation of emitted 7-rays with respect to different axes and normalizing the yrast by the 1 MeV-bump, we observed that the angular correlation with respect to the recoiling nucleus direction has the most pronounced anisotropy. The Total Unfolded yray Spectrum 18000 1 16000 14000 Yrast ESSSSSSJ 12000 1 MeV Bump E^I & 10000 Intermediate ^S (A 3 8000 High Energy ••1 o 6000 o 4000 2000 1 J l 2 3 4 5 6 7 8 Gamma Energy E, [MeV] Figure 6.6: The total 7-spectrum corresponding to excitation energies up to 8 MeV, in coincidence with ce-particle. Note that the energy regions are: the yrast £^=0.17-0.29 MeV. the 1 MeV-bump £-,=0.61-1.51 MeV, intermediate £7=1.53-3.01 MeV and high- energy E7=3.03-4.01 MeV. The low-energy part of the 1 MeV-bump £7=0.61-1.01 MeV and the high-energy part is £-,=1.03-1.51 MeV. Due to poor statistics in the Nal spectrum, + + the decay from low-lying. 2 —> 0 , the yrast transition, higher-lying Z?7 > 4 MeV and transitions at 0.3 < E., < 0.6 MeV region (due to the unfolding process), can not be studied. Figure 6.6 displays the total-generation 7-spectrum corresponding to excitation energy up to the neutron binding energy, in coincidence with a-particle. In general, the spectrum 38 reveals three types of 7-transitions: (1) the yrast 4+ -» 2+ and 6+ —» 4+, which are ground state rotation band transitions, at the energy region £7=0.18-0.29 MeV, (2) at £,.,=0.6- 1.5 MeV, the 1 MeV-bump, which are transitions from vibrational bands to the ground state and (3) the high-energy region £^=1.53-4.0, these transitions can be described by the Fermi gas model. The high-energy region can be studied in two parts, (i) energy region E-y=1.53-3.0 MeV, intermediate, which are transitions from medium statistical 7- ray decays and (ii) energy region £7=3.1-4.0 MeV, high energy, which are transitions from high statistical 7-ray decays (see Figure 6.6). The analysis was performed by least-squares fit to the theoretical expression W{Q) = Ao + A2 P2(cos0) + A4 P4(cosG). The PL(COSQ) are Legendre polynomials with 0 being the angle between emitted 7-ray and recoiling nucleus direction. The angular correlation for the yrast, suggests stretched E2 radiation (see Table 6.1). Furthermore the angular correlation for the 1 MeV-bump, suggests multipole mixing, dipole or unstretched quadrupole radiation. In intermediate and high energy, we find close to isotropic angular correlation which might be Ml transitions (see Table 6.1). This could be due to continuum radiation mixing of stretched and unstretched multipole transitions with anisotropies canceling each other out. In order to distinguish electric from magnetic radiations, we measured the asymmetry A = Q, where P is the polarization and Q is the polarization sensitivity with values 0 < Q < +1- The 7-7 coincidence between two neighboring Nal-detectors determines the scattering direction, either parallel or perpendicular to the recoil vector. We measured a positive asymmetry for all the energy regions discussed here. E-y [MeV] A2 A4 0.17-0.29 +0.312±0.020 +0.097±0.026 0.61-1.51 +0.104±0.017 +0.043±0.022 1.53-3.01 +0.092±0.009 +0.027±0.011 3.03-4.01 +0.080±0.030 -0.030±0.020 0.61-1.01 +0.120±0.032 +0.070±0.005 1.03-1.51 +0.061±0.016 +0.019±0.011 0.17-0.29 -0.094±0.015 +0.075±0.009 0.61-1.51 +0.105±0.018 +0.082±0.010 1.53-3.01 +0.055±0.018 +0.081±0.011 3.03-4.01 +0.080±0.020 +0.090±0.024 0.61-1.01 +0.069±0.032 +0.107±0.008 1.03-1.51 +0.135±0.008 +0.065±0.012 Table 6.1: Experimentally angular correlation coefficients A?, and A4 of 7-ray from the reaction 163Dy(3He, cry)162Dy with respect to the recoil vector (above) and respect to the normal vector to the reaction plane (below), are listed in three tables. The angular correlations of the four 7-energy regions (see caption to Figur 6.6) and the low and high- energy part of the 1 MeV-bump. By a close study of the angular correlation with respect to the normal vector to the reaction 39 plane, we found several anisotropic angular correlations with respect to this vector above ~ 1 MeV. In fact, wherever the angular correlation is isotropic with respect to the recoil, there will be anisotropic angular correlation with respect to the normal vector (See Tables 6.1). Our initial assumption was that we could explain the anisotropy of the angular correlation with respect to the normal vector by means of a simple geometrical transformation of the angular correlation from one axis to a perpendicular axis in the isotropic spherical coordi- nates. The angular correlations of two 7-ray regions, with highest and lowest anisotropies with respect to both the recoil and the normal vectors are measured and geometrically transformed. The result of these transformation reveal that the angular correlations trans- formed below ~ 1 MeV are in fairly good agreement with the experimental results within our uncertainty but not for region E7 > 1 MeV. By measuring the energy of the emitted a-particle from the reaction, the excitation energy of the populated states is uniquely determined. Angular correlations of five 7-ray energy regions gating on three excitation energies up to the neutron binding energy, with respect to both the recoil and the normal vectors.are measured. One would expect that with increasing excitation energy, the anisotropic of the angular correlation with respect to the symmetry axis would decrease. This assumption seems to be correct up to ~ 1 MeV 7- energy, but we observed an opposite behavior above this region. The angular correlations with respect to the normal vector also have an opposite behavior compared to the recoil vector. A close study of the reaction mechanism and the structure of residual nuclei might explain this anisotropic behavior of the angular correlations with respect to the normal vector. Studies of angular distributions for different excitation energy regions are in progress. References [1] A. Henriquez, J. Rekstad, F. Ingebretsen, M. Guttormsen, K. Eldhuset, B. Nordmoen, T. Rams0y, R. Renstr0m-Pedersen, R. M. Aasen, T. F. Thorsteinsen and E. Hammaren The decay from the two-quasiparticle regime in even-even deformed rare earth nuclei Phys. Lett. 130B (1983) 171 [2] M. Guttormsen, B. Bjerke, J. Kownacki, S. Messelt, E. A. Olsen, T. Rams0y, J. Rek- stad, T. S. Tveter and J. C. Wikne CACTUS a multi-detector set-up at the Oslo Cyclotron Department of Physics Report, UiO/PHYS/89-14 (1989) 6.1.7 Back-Shifted Fermi Gas Model K. Ingeberg, M. Guttormsen, E. Melby , J. Rekstad, A. Schiller and S. Siem There has been some discussion on whether the back-shifted Fermi gas model is justified. 40 The level density of the model can be described by the formula (2/+l)y5Oie2^ piu'I) = —muTfy—' where 0 is the rotational parameter and a is taken as 10/A (in units of MeV""1). The nuclear temperature T is related to the intrisic energy U by U = ciT2 - T, where the intrisic energy is given by U(I) = Ex-Eyrast(I)-5. Here, 5 is called the back-shift parameter. A preliminary test on the extracted experimental level density [1] of the 162Dy nucleus, indicates that the back shifted Fermi gas formula gives a poor description. Leve Densl'.y fo- "*Sm Figure 6.7: Level density from 148Sm taken from table of isotopes and from an experiment done at the Oslo Cyclotron in May 1997. References [1] T.S. Tveter, L. Bergholt, M. Guttormsen, E. Melby and J. Rekstad, Phys. Rev. Lett. 77 (1996) 2404 6.1.8 Simultaneous Extraction of Level Density and 7-R.ay Strength Function A. Bjerve. M. Guttormsen, E. Melby, J. Rekstad. A. Schiller and S. Siem In this work, we use a method developed to extract level density and 7-ray strength function from experimental data [1, 2]. It is assumed that the energy distribution T(EX, 2?7) of first 41 '72Yb(3He,a)'7'Yb U(MeV) 172 Yb(3He,a) 17'Yb J 2.5 r 2 1.5 1 ufl 0.5 I Z—i—i .. i •... i w,, i,, uJ-.-..,...!.., n U(MeV) Figure 6.8: Above: Level density p{U) averaged over all Ex. Below: The same function divided by the best fit of the trial function pjn{U) = CeulT. generation 7-rays emitted from excited nucleus in the statistical regime can be expressed as where U = Ex — E-y. Here, p{U) is the level density at the final state, and F(E~f) is x+1 proportional to E^ f(E1), where f(E-y) is the strength function. For the purpose of this work, the 7-energy dependent factor that will be extracted, is approximated by F(E^) = £" where n w 4.2. A computer program rhosig has been developed to simultaneously calculate p{U) and F(Ey) from experimental first generation 7-ray matrices [2]. The extracted functions will of course vary with different input parameters, usually set to T = 530 keV and n — 4.2. but in this work we are mainly interested in the fine structure. The division by the best fitt o the trial function will make the fine structure appear more clearly. The reaction used in these experiments is the (3He,«) and (3He,3He')-reactions performed on nuclei in the rare earth region (see Figs. 6.8 and 6.9). It is of interest to compare p{U) and F(E-y) from the different reactions on neighboring nuclei to see if the way of formation 42 '72Yb("He 71Yb L 104 t 10* r + 102 t •'** t I 10 r 1 f •.•"" o" r...t i , , , E,(MeV) 2.5 2 I , 1 1.5 k t ll/t Jlji 1 0.5 - , . . , 1 , , I . 1 . , , I 1 , , , . 1 , , , , ._*_L-.- ... , E,(MeV) Figure 6.9: Above: Strengthfunction F(E-y) averaged over all Ex. Below: The same function divided by the best fit of the trial function F{E1)jit — CnE™. 43 influences p{U) and F{E~t). The logarithm of the level density is essentially the entropy, and by taking the derivative of the entropy one obtains the temperature of the nucleus as a function of internal energy. References [1] L. Henden, L. Bergholt, M. Guttormsen, J. Rekstad and T.S. Tveter, Nucl. Phys. A589 (1995) 249 [2] T.S. Tveter, L. Bergholt, M. Guttormsen, E. Melby and J. Rekstad, Phys. Rev. Lett. 77 (1996) 2404 6.1.9 Simulation of Statistical 7-Ray Spectra A. Schiller, G. Murioz, L. Bergholt, M. Guttormsen, E. Melby, J. Rekstad and S. Siem A model for the statistical decay of even-even excited rare earth nuclei has been developed and implemented in a FORTRAN computer code [1]. An excellent overall agreement of the model with our experimental data could be achieved. Especially, the so called 1 MeV peak, which is formed by transitions from vibrational states to the ground state rotational band, could be reproduced in the simulated spectra. In the case of 162Dy, the agreement of the high resolution spectrum with experiment is striking as one can see in Fig. 6.10. It is interesting to see, that the feeding of the ground state rotational band can only be seen from high K bands [2]. This is a feature which should be investigated further. It might be possible to trace back a K distribution up to excitation energies around 8 MeV, applying a statistical analysis to the experimental ground state band side feeding. References [1] G. Mufioz cand. scient. thesis, Department of Physics, University of Oslo, 1996, anu the computer code Decay, G. Murioz et al. Department of Physics, University of Oslo, 1996, unpublished. [2] A. Schiller et al., Department of Physics Report UiO/PHYS/97-07 (1997) 6.1.10 High-Resolution Measurements of Level Densities and 7-Ray Strength Functions S. Siem1. P.A. Butler2, T.L. Khoo3. L. Bergholt, M. Guttormsen, F. Ingebretsen, G. Ldvh0i- den. E, Melby. S. Messelt, E, A. Olsen, J. Rekstad, A. Schiller, P.O. Tjtfm, J.C. VVikne and S.VV. Odegard 1 On leave, Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA 2Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 3BX, U. K. "Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA 44 Experimental '62Dy Spectrum 882 800 900 1000 1100 1200 Er(keV) Simulated 162Dy Spectrum x 10 CD Er(keV) Figure 6.10: Comparison of experimental and simulated high-resolution spectra around 1 MeV. Although no fine tuning of the model is done with respect to branching ratios in the discrete level region, even the relative strengths of transitions around 1 MeV turn out to be quite accurate. Significant fine structure in both the level density and the strength function have recently been revealed in the rare earth nuclei 162Dy and 172Yb, produced by the (3He,a) reaction. This might be signatures of the breakdown in pairing correlations and of collective dipole modes built on excited states. The measurements were made with the CACTUS detector array, which contains 28 Nal scintillation detectors. These results are quite unexpected and amount to an important extension of our knowledge of nuclear structure. An international collaboration was formed with the goal of exploring these hitherto undiscovered features in more detail. Our plans are to perform high-resolution measurements at the Oslo Cyclotron Laboratory, employing high-efficiency Ge detectors with Compton suppression. We would therefore like to borrow six Eurogam Phase I 70% Ge detectors with BGO shields. The detectors will be placed perpendicular to the beam direction forming a ring, thereby the name GRIS, which stands for Germanium Ring Setup. We have made some rough estimates on the efficiency of 6 Ge-detectors compared to the CACTUS detector array (see table 6.2). We accumulated spectra using a 60Co source and compared the photo efficiency of a 65% Ge-detector and CACTUS. The efficiency at E-r = 8 MeV was found using the relative efficiency curve for Gammasphere detectors. The relative efficiency curve for CACTUS is well known. To get as good statistics as previous 45 Gamma CACTUS GRIS GRIS + SIRI energy 28 NaI+8 telescopes 6 Ge+8 telescopes 6 Ge+64 telescopes 1.17 MeV 1 0.39 ~ 4 1.33 MeV 0.93 0.36 8.0 MeV 0.34 0.12 ~ 1 Table 6.2: Comparison of the photo-efficiency (for particle-7 coincidences) of 6 Ge-detectors and the CACTUS detector array. experiments with CACTUS (see table 6.2) we will use the new particle detector SIRI, which will increase the efficiency by a factor of 10. At present the Eurogam Phase I detectors are not available, but we hope that the plans will be realized in near future. 6.1.11 A'-Hindrance in Primary 7-Decay after Thermal and ARC Neu- tron Capture E. Melby, L. Bergholt, M. Guttormsen, J. Rekstad, A. Schiller, S. Siem and R. K. Sheline4 In a series of recent papers, evidence has been presented for an apparent /^'-hindrance effect in the primary 7-decay of states populated through thermal and average resonance neutron capture in deformed nuclei. Details are explained in Ref. [1]. A striking observation is that the A"-hindrance seems considerably more profound in thermal neutron capture than in ARC. In order to search for possible differences in the statistical behavior of allowed and forbidden transitions after ARC and thermal neutron capture, the observed transition probability distributions were compared with theoretical model calculations [2]. The number of initial states decaying, n, is the degrees of freedom of the theoretical distribution. Comparison of the theoretical and the experimental distributions of reduced relative tran- sition probabilities after thermal neutron capture shows an astonishing difference between A'-allowed and A"-forbidden transitions after thermal neutron capture. The allowed and forbidden distributions have shapes associated with different numbers n of degrees of free- dom. The allowed transitions roughly follow a distribution with five degrees of freedom, n = 5, and the distribution of forbidden transitions is well reproduced assuming n = 2. The theoretical ARC distribution show a best fit to the experimental distribution assuming a number of n ~ 110 degrees of freedom for both the forbidden and allowed transitions. More details on this investigation and possible interpretations are found in Ref. [2]. The fact that there is sometimes correlation and sometimes anti-correlation between the probabilities for populating low-lying states after the (n, 7) and (d,p) reactions, is probably to be understood in terms of the specific character of the capturing states [3]. A compar- ison between these two reaction types might therefore be a valuable tool for studying the entrance configuration. 4 Departments of Chemistry and Physics, Florida State University, Tallahassee, Florida 32306, USA 46 References [1] R.K. Sheline et al., Phys. Rev. C51 (1995) 3078, and references therein. [2] I. Huseby et al., Phys. Rev. C55 (1997) 1805 [3] R.K. Sheline et al., Phys. Rev. 143 (1966) 857, H.T. Motz et al., Phys. Rev. 155 (1967) 1265. 6.1.12 Spectroscopy with Entry-State Selection: Nuclides Produced in the Reaction a+28Si T. Lonnroth5, M. Guttormsen, L. Bergholt, A. Bjerve, K. Ingeberg, K.-M. Kallman5, E. Melby, S. Rezazadeh and A. Schiller There has been an increasing interest in studying high-resolution elastic a—particle scat- tering on medium-mass nuclei, i.e. in the mass range A ~ 20 — 40. A recent comprehensive study, see [1], has located bunches of states that are interpreted to be members of an ct+28Si rotational band (in 32S), an "a-cluster band", with a band head at ~ 12.6 MeV and natural-parity members up to 10+. The properties of these were thoroughly discussed in [3, 4]. This structure is totally unconnected to the low-lying "spectroscopic" structure up to Jn5~ (plus some higher-lying low-spin states) at ~ 6.8 MeV [2]. It would therefore be of interest to extend the yrast structure of this nuclide, and the neighbouring ones for comparison, up to energies in excess of 10 MeV, and larger spins. Thus one gets detailed information which may be interpreted via shell-model calculations, and clues to where presumptive gamma-ray decay from the mentioned cluster states might feed into the lower-lying structures. Rather none of the nuclides reachable from an a+28Si reaction at energies Ea ~ 20 MeV, has ever been studied with in beam methods. Only one recent comprehensive study 32S, especially of chosen resonances has been per- formed, cf. [5]. It uses the29 Si(cr,n7) reaction at 14.4 MeV and locates some 30 resonances 31 2 from n—a correlations. They also uses the reaction P(p,7) on a 20 ^g/cm Cd2P3 target to locate g-wave resonances (Jv — 4+, 5+). For the case of 29Si there is a work using the reactions 29Si(d,p7), 26Mg(a,n7) and 27Al(3He,p7), also to populate specific resonances and to study their gamma-decay, see [6]. Finally, the nuclide 30Si has been studied only via the reaction 27Al(a,p7) in [7]. All other information, e.g. on 31P, can be found in [2], or mostly in more detail in its predecessor [8]. An in-beam experiment using the a+28Si reaction was performed with beams from the K-35 Cyclotron of the Oslo University. Beam energies of Ea = 14.8, 16.8, 19.0, 21.0 and 24.0 MeV were used. The target was natural Si (92.2% 28Si. 4.7% 29Si and 3.1% 30Si) with a thickness of about 12-15 fxm. This thickness corresponds to ~ 870 keV for Ea = 14.8 MeV, and to ~ 610 keV for Ea = 24.0 MeV. Thus the entry states of population are ~ 900 — 600 keV wide and located at E' = 19.9 - 28.0 MeV, see Table 1. The maximum spin values range from ./ ~ 8 at 14.8 MeV to J ~ 11 at 24.0 MeV, cf. [3, 4]. The relative production of various channels for the five beam energies is extracted from the intensities of coincidences with department of Physics, Abo Akademi, FIN-20500 Turku, Finland 47 the ground-state transition(s), and does not give absolute cross sections. For the lowest energy (Ea = 14.8 MeV) also a fairly thick target, ~ 55/xm corresponding to about 4.5 MeV energy thickness, was used. A high-statistics run was performed at this energy to establish the lower parts of the level schemes reachable at this energy, mainly 31P and 32S. The detector set-up consists of the multi-module array CACTUS, equipped with a pile- up rejection system. CACTUS consists of 30 detector positions in six rings, viz. at 37°, 63° and 79°, and three symmetrically with respect to the beam direction. In 27 of these 5' X 5" Nal counters were mounted, and three large Ge counters with 50-70% efficiency were mounted in the ±37° and 67° positions. Energy ranges were up to 4.2 MeV for the Ge counters and up to 9.5 MeV for the Nal scintillators, both on 4K raw spectra, thus giving dispersions of ~ 1.2 and 2.4 keV/channel. Charged particles were detected in 8 Si detectors, each 3 mm thick, covering all particle energies. Due to recoil Doppler broadening the Ge detector effective line width varied from ~ 6 keV at 600 keV to about 25 keV at 4.0 MeV. In order to assign multipolarities to the observed levels, an angular-distribution experiment was performed at the 104 cm isochronous cyclotron of Abo Akademi. The maximum beam energy of 18.0 MeV was chosen. The thick target of ~ 55//m was used. Gamma-ray spectra at seven angles, viz. 80° - 165°, were recorded. The normalized distributions were fitted 2 to the expression W{8) = Ao + A2P-2{zos8) + A4P4(cos0), and x -tested to extract the angular-distribution coefficients A2, A4 and the mixing parameter 8. The parity cannot be determined directly, but a significant mixing coefficient usually implies M1/E2 admixture in favour of E1/M2. Because of Doppler broadening in the Ge detectors and intrinsically broad lines in the Nal counters lesser dispersion is sufficient. For this reason, and since the line density in these light nuclides is fairly low, the sorting was performed to matrices the following size: Ge-Nal 512x2K, Ge-Ge 256x2K (maximum of 256 preselected gates), particle-Ge 256x2K and particle-particle 256x256, see Table 1 for the statistics of each partial run. A "background-subtraction" of uncorrelated events in the gamma matrices was performed using the method of Andersen et al. [9], and so was the particle-particle matrix. References [1] K.-M. Kailman, M. Brenner, V.Z. Goldberg, E. Indola, T. Lonnroth, P. Manngard, A.E. Pakhomov and V.V. Pankratov, Eur. Phys. J. A (1999), in preparation [2] P.M. Enclt, Nucl. Phys. A521 (1990) 1 [3] P. Manngard, thesis, Department of Physics, Abo Akademi, Turku, Finland, 1996 [4] K.-M. Kallman, thesis, Department of Physics, Abo Akademi, Turku, Finland, 1998 [5] J. Brenneisen. B. Eberhardt, F. Glatz, Th. Kern, Ft. Ott, H. Ropka, J. Schmalzlin, P. Siedle and B.H. Wildenthal, Z.Physik A357 (1997) 157, 377 [6] P. Betz et al., Z. Phys. A309 (1982) 163 [7] Bittenvolf et al., Z. Phys. A298 (1980) 279 [8] P.M. Endt et al., Nucl. Phys. A310 (1978) 48 [9] O. Andersen. J.D. Garrett, G.B. Hageman. B. Herskind, D.L. Hillis and L.L. Riedinger. Phys. Rev. Lett. 43 (1979) 687 49 0.3 0.4 e cosy Figure 6.11: Calculated (UC) potential energy surfaces at I = 35 and 36 for the lowest configuration with positive (left) and negative (right) parity in 164Lu. 6.2 High Spin Properties of Nuclear States 6.2.1 Triaxial Superdeformed Bands in 164Lu and Enhanced El Decay- out Strength S. Tormanen, S.W. 0degard, G.B. Hagemann, A. Harsmann, M. Bergstrom, R.A. Bark, B. Herskind, G. Sletten, P.O. Tj0m, A. Gorgen, H. Hiibel, B. Aengenvoort, U.J. van Severen, C. Fahlander, D. Napoli, S. Lenzi, C. Petrache, C. Ur, H.J. Jensen, H. Ryde, R. Bengtsson, A. Bracco, S. Frattini, R. Chapman, D.M. Cullen, and S.L. King In a search for exotic structures in odd-odd 164Lu, performed as one of the first Euroball experiments eight new. presumably triaxial, superdeformed bands were found. For the first time, evidence is presented [1] for superdeformation in an odd-odd Lu isotope for which theory predicts large triaxiality. Calculations by the Ultimate Cranker code (UC) with extensive use of the programme NUSMA [2] have been performed. Potential energy surfaces for the lowest expected configurations in 164Lu with positive and negative parity are shown in fig.6.11 In addition to the minima at normal deformation the calculations show local minima with large deformation and 7 ~ ±20°. Rotational bands in 164Lu were populated using the reaction 139La(29Si,4n) with thin self-supporting targets at a beam energy of 145 MeV. The29 Si beam was provided by the Legnaro XTU tandem accelerator and the 7-rays were detected with the Euroball array consisting, at the time of the experiment, of 13 clusters, 25 clovers and 28 single element tapered detectors. Altogether, ~ 3.8 • 109 events requiring six or more coincident Ge signals before Compton suppression were collected. After presorting, ~ 2.3 • 109 clean, three- or higher-fold events were sorted into gated matrices for DCO analysis, cubes and a 4D-hypercube. Two of the strongest populated bands, SD1 and SD3, have been connected to known ND bands in 164Lu. The band SD1, decays to several states of both positive and negative parity. The assignments shown in fig.6.12 are consistent with the measured DCO ratios for the strongest El transitions. 16" ->• 15+ and 15+ -» 14~ from SD1 and SD3 to the ND 50 Figure 6.12: Partial level scheme showing the new triaxial SD bands in 164Lu. Only the lowest-energy positive and negative parity ND bands to which the new triaxial SD bands decay are included. For the 'hanging' bands the excitation energy is estimated (roughly) from their intensities. 51 sta.tes. respectively. The strength of the El decay is estimated (assuming Q4(SD) = lib) from the out-of-band to in-band branching to be B(E1) ~ 0.8 • 10~4e2 fm2 (= 0.4 • 10-4WU) for both bands, which is around 400 times faster than the El-decay found for the (axially symmetric) SD to ND states in 194Hg [3], and only ~ 6 times slower than octupole-enhanced El transitions between some of the ND bands in the same nucleus, 164Lu. The El decay from SDl is associated mainly with an /i9/2 SD to i13/2 ND quasineutron transition, whereas the El-decay from SD3 is associated with an i13/2 SD to /in/2 ND quasiproton transition. Octupole enhancement is found between ND bands of similar structure in odd-N and odd-Z rare earth nuclei and may therefore be present in both of these different El transitions. The measured difference in energy between the bands SD3 and SDl in 164Lu is in agreement with the calculated energy difference for 7 ~ +20° at I ~ SOh. In contrast, the measured 164 163 excitation energies of the new SD bands in Lu as well as the 7ri13/2 SD band in Lu appear 0.5 - 1 MeV lower in excitation energy than calculated for 7 ~ +20°. This might imply problems with single particle intruder levels in the cranking calculations, or could be an indication for tilted rotation. References [1] S. Tormanen et al., II Nuovo Cimento 111A (1998) 685 and to be published in Phys. Lett. B. [2] see http://www.matfys.lth.Se/~ ragnar/ultimate.html [3] G. Hackman et al., Phys. Rev. Lett. 79 (1997) 4100 6.2.2 Triaxial Superdeformed Bands in 163Lu J. Domscheit, S. Tormanen, S.W. 0degard, G.B. Hagemann, A. Harsmann, M. Bergstrom, R.A. Bark, B. Herskind, G. Sletten, P.O. Tj0m, A. Gorgen, H. Hiibel, B. Aengenvoort, U.J. van Severen, C. Fahlander, D. Napoli, S. Lenzi, C. Petrache, C. Ur, H.J. Jensen, H. Ryde, A. Bracco, S. Frattini, R. Chapman, D.M. Cullen, and S.L. King High-spin states in 163Lu have been investigated using the Euroball spectrometer array in the same early Euroball experiment as described in the preceeding contribution on triaxial superdeformed bands in 164Lu [1]. The previously known [2] superdeformed band, SDl, has been extended both at high and low spin, and its connection to the normal-deformed states has been firmly established. This implies that the spin of the band has been increased by 2 h relative to the spin suggested in [2]. The normal-deformed structures have also been extended, including both signatures of the [41l]l'2+ configuration to which the previously known SDl decays. For the low-spin states of SDl J^ shows large fluctuations which are due to mixing of the 21/2 SD state with the state of the same spin and parity in the [411]l/2+ band. The experimental energy difference of the two levels is 111 keV. The strong decay branches from SDl to the [411]l/2+ band via the 427 and 697 keV transitions which comprise about 40 % of the SDl band intensity can be explained by a mixing amplitude of a — 0.04 and an interaction strength I Vint I = 21 keV, which cause a repulsion of 5.6 keV of the two 21/2+ levels. Correction for 52 •"<-*-,. >- ^ VaaS [404]7/2* [523J7/2- Figure 6.13: Partial level scheme of 163Lu based on previous and present work this energy shift makes the jW vs w smooth. At I = 45/2 SDl is close to the [404)7/2+ band without showing any cross band transitions, which provides an upper limit of the interaction strength \Vint\ < 4.5 keV between SDl and the [404)7/2+ band at 1=45/2. We therefore conclude that the local triaxial SD minimum has a larger barrier at the higher spin value. In addition to SDl a new band, SD2, with similar dynamic moment of inertia J^ has been established. The population of SDl and SD2 are about 10% and 2% , respectively, relative to the yrast band. The new band, SD2, feeds into SDl most strongly at I = 37/2, as indicated on the partial level scheme shown in fig.6.13, probably with more than one branch in the spin range 33/2 - 45/2 h. The connecting transition could not be firmly established from the data. The band SD2 and its decay to SDl might be consistent with the characteristic band structure of the wobbling mode [3), here built on the configuration of SDl, which is uniquely related to a static triaxial shape. References [1] Preceeding contribution on triaxial SD bands in 164Lu. 53 168 l68 Hf N= 96 Pcon= 1 Ncon.= 1 it= 1 a=0 l=50 HfN=96Pcon=1Ncon.= 1 71= 1 a=0 l=60 slep=0.2000 min = 16.947 step=0.2000 min = 23.073 Figure 6.14: Calculated potential energy surfaces by the "Ultimate Cranker" at I = 50ft (right) and 60/i (left) for the lowest configuration with positive parity in 168Hf. [2] W. Schmitz et al.,Nuc. Phys. A539 (1992) 112 and Phys. Lett. B303 (1993) 230 [3] A. Bohr and B.R. Mottelson, Nuclear Structure, Vol. II (Benjamin, New York, 1975), Chap. 4, pl90 6.2.3 A Search for Exotic Rotational Structures in i67-i69Hf byth e Symmetric Cold Fusion Reaction 76Ge+96Zr. M. Bergstrom, G.B. Hagemann, B. Herskind, A. Maj, G. Sletten, S.W. 0degard, W.C. Ma, K.A. Schmidt, P.G. Varmette, M. Carpenter, T. Lauritzen, T.L. Khoo, K. Lister, R. Jansenss, S. Siem, D. Hartley, L.L. Riedinger, J. Domsheit, H. Hubel, A. Bracco, S. Frattini and B. Million. Potential energy surface calculations for the isotopes 164~170Hf show consistently the exis- tence of two different types of exotic shapes in these nuclei. Not only may a hyperdeformed shape with the axis ratios (3:1:1) be found close to yrast at the highest spin I w 60-80 h these nuclei can sustain, but also two superdeformed minima with j ~ ±20°, symmet- rically about 7 = 0° may be found in the spin range (I & 30-60 h). In 163Lu[3] large Qt values corresponding to /32 ~ 0.42 (SD) were measured earlier using both RDM and DSAM techniques, and bands of this type have also recently been identified in the heavier Lu isotopes. It is believed that these large triaxial deformations are due not only to the shape-driving effect of the intruder 7ri13/i2 orbital, but also the result of a re-arrangement of the core structure. Therefore large deformations with triaxial shapes may be expected as a general phenomenon also in the Hf, and perhaps also in the Ta and VV region. Calculations for the lowest configuration in 168Hf are shown in Fig.6.14. A search program for exotic shapes was initiated, by means of the semi-symmetric fusion reaction 76Ge + 96Zr, to obtain the coldest population of the high spin states in 167-169Hf. 54 200 400 600 800 1000 1200 1400 Ey(keV) Figure 6.15: Spectra produced by the "sum of double gates" taken for all combinations of transitions which are indicated by energy labels for 3 different triaxial SD bands, all found to feed the yrast band in 168Hf. This experiment was carried out at the ATLAS Accelerator, in Argonne, US, collecting 3 • 109 events of fold-5 and higher with the Gammasphere multidetector array, with colli- mators in place to obtain the most clean conditions. Nevertheless, important information on the distributions of fold K (clean Ge + dirty Ge + clean BGO) with < K >« 13, and the summed energy < H > was obtained and proved to be useful in emphasizing the highest spins in a search for both HD and triaxial SD band structures in a H-K gated cubes. So far 3 different new bands with the expected energy characteristics for triaxial bands has been identified, as shown in fig.6.15. The population of these bands is unusually weak and all in the range of 1 — 4 • 10~4 of the yrast population. The data was sorted into both triple-(3D) and hyper-(4D) cubes, allowing for very detailed spectroscopic studies as well, currently under way. So far several new band structures in both 169Hf and 168Hf are revealed, including 2 high-K coupled bands in each of the nuclei, with connecting transitions to the low-K bands in the 169Hf case. A full directional correlated triple matrix is being constructed to generally emphasize the angular correlation information of the many new bands, aiming for finite multipolarity and spin determination of these weakly populated structures. Beamtime at ATLAS for determining the lifetime of the new "triaxial superdeformed bands", is planned for April 99. 55 6.2.4 Octupole Structures in 226U P.T. Greenless, N. Amzal, P.A. Butler, K.J. Cann, J.F.C. Cocks, D. Hawcroft, G.D. Jones, A. Andreyev, T. Enqvist, P. Fallon, M. Guttormsen, K. Helariutta, P.M. Jones, R. Julin, S. Juutinen, H. Kankaanpää, P. Kuusiniemi, M. Leino, S. Messelt, M. Muikku, A. Salvelius, A. Schiller, S. Siem, W.H. Trzaska, T. Tveter and F. Uusitalo Our knowledge and understanding of octupole structures in the actinide region has been in- 222 224 226 creased significantly [1, 2, 3]. Only five nuclei in the mass region with N~134, > . Ra and 224.226Th, exhibit alignment properties expected for octupole deformation at suffi- ciently high rotational frequencies (h > 0.2 MeV). It is expected [4] that 226U should posses a deep minimum in the potation surface for non-zero ßs. The experiment was performed using the 208Pb(22Ne, 4n) 226U reaction with 112 MeV beam delivered by the K130 cyclotron of the University of Jyväskylä. Promt 7-rays emitted at target position were collected with the JUROSPHERE array in delayed coincidence with the implants into the RITU detector. The technique of recoil-decay tagging was employed. For the first time excited states of 226U could be identified. Interleaved bands of positive and negative parity states suggest the octupole nature of this nucleus. The extracted E1/E2 7-ray branching ratios, suggest that 226U possesses one of the largest El moment near to the ground state of the nuclei in this mass region. More details on this project are given in Ref. [5]. References [1] J.F.C. Cocks et al., Phys. Rev. Lett. 78 (1997) 2920. [2] P.A. Butler and W. Nazarewicz, Rev. Mod. Phys.68 (1996) 349 [3] J.F. Smith et al, Phys. Rev. Lett. 75 (1995) 1050 [4] W. Nazarewicz et al., Nucl. Phys. A429 (1984) 269 [5] P.T. Greenlees et al., J. Phys. G 24 (1998) L63 56 -500 8 10 12 14 16 18 Spin (h) m 175 Figure 6.16: Results of band-mixing calculations for the hn/2 bands of Ir, in which a triaxial band (t), mixes with a prolate band (p). Dots- data; dashed lines - unperturbed bands; solid lines - mixed bands. 6.2.5 Shape coexistence in mIr R.A. Bark, S. Tormanen, T. Back, B. Cederwall, S.W. 0degard, J.F.C. Cocks, K. Helari- utta, P. Jones, R. Julin, S. Juutinen, H.Kankaanpaa, H. Kettunen, P. Kuusiniemi, M. Leino, M. Muikku, P. Rahkila and A. Savelius. Analysis of the data on mIr, formed in the reaction n6Sn(58Ni,p2n) at 267 MeV, is com- plete. Details of the experimental conditions can be found in last years annual report, and in refs[l, 2], where results for 171>172pt and 171Os, populated in the same reaction, have been published. 171 The ground-state band of Ir is assigned to the hn/2 configuration. Energies for the band, less a rigid rotor reference, are plotted as a function of spin in fig.6.16. An interesting feature is the large signature splitting observed. For a prolate shape, the Fermi surface would be located near high-fi orbitals of the hn/2 subshell and no signature splitting would be expected, while for an oblate shape, the Fermi surface would lie near low-Q components, and the splitting would be expected to be much larger. Hence the splitting indicates an intermediate, triaxial shape. Indeed, potential energy surface calculations performed using the code "Ultimate Cranker" predict a large assymetry parameter of 7 = -25°. At the highest of spins, the signature splitting is sharply reduced. One scenario is that a shape change, towards prolate deformation, is taking place. This is supported by comparison 173 175 173 with the /i11/2 bands of Ir[3] and Ir[4], as shown in fig.6.16. The band in Ir begins at low spin with a large signature splitting, which disappears after spin 17/2, while in 175Ir, 57 there is almost no signature splitting except that the 11/2 level appears to be depressed in energy. These systematics are interpreted as the crossing of a prolate hn/2 band by a triaxial hn/2 band that decreases in energy with decreasing neutron number. Also shown on the figure are the results of band-mixing calculations which model this interpretation for each of the three nuclei. A good fit is obtained in all cases. The reduction in energy of the triaxial band with decreasing neutron number follows the systematics of the Pt isotopes (see e.g. [1]) where coexistence between triaxial and prolate shapes is also known. 2 In addition to the hn/2 band, candidates for bands based on the nhn/2 ® (^i3/2) > 7r an ^n/2 <8> "&13/2 <8> ^9/2 d xh9/2 configurations have also been observed. A full report has been submitted for publication. References [1] B. Cederwall et al, Phys.Lett. B443( 1998)69 [2] R.A. Bark et al, Nucl.Phys. A, in press. [3] S. Juutinen et al, Nucl.Phys.A526(1991)346 [4] G.D. Dracoulis et al, Nucl.Phys.A534(1991)173 58 6.3 High and Intermediate Energy Nuclear Physics 6.3.1 Introduction With the advent of ultra-relativistic heavy-ion collisions in the laboratory in 1986 (CERN and Brookhaven), a new interdisciplinary field emerged from the traditional domains of nuclear and particle physics. What makes this field particularly interesting is the prediction of QCD that at high energy densities matter will undergo a phase transition to an entirely new state, the quark-gluon plasma (QGP). The nuclear physics group works within the CERN collaborations WA97 and NA57. The work has focused on the measurement and study of the strange particle production in the nuclear collisions. The enhancement of such production is seen as a possible signature of the creation of the quark-gluon plasma (QGP). In 1998 the NA57 collaboration did its first Pb-Pb experiment, and 230 million events were collected. During the years 2000-2005 the accelerators in CERN will be closed while the new Large Hadron Collider (LHC) in CERN is being installed. For this period we have joined the BRAHMS project that will perform nucleus-nucleus collision experiments in the RHIC collider (Brookhaven) with a centre-of-mass energy of 200 GeV per nucleon pair. This experiment will in particular address proton and antiproton production both in the central and in the fragmentation region, and A-production in the mid-rapidity region. The semi- inclusive spectra of charged pions and kaons over a wide range of rapidity and transverse momentum will also be studied. The building of the future LHC facility was finally decided in 1994. As an integral part of the experimental program for LHC, a dedicated heavy ion collider (ALICE) that will take data in year 2005 has been accepted. With a center-of-mass energy of 6.1 TeV per nucleon, this will bring us into the true high-energy heavy-ion regime with a qualitatively improved environment for the study of strongly interacting matter. In 1998 the Norwegian activity within the ALICE detector development has been concentrated on tests of the read-out electronics for the PHOS detector, which measures electromagnetic radiation from the plasma. Also further studies of the data acquisition system (DAQ) for ALICE have been conducted. The reports from these studies are given in section 6.3. 6.3.2 Strangeness Production in Ultrarelativistic Nucleus-Nucleus and Proton-Nucleus Collisions - The WA97 and NA57 Experiments F. Fayazzadeh, M. Henriquez, A.K. Holme, G. L0vh0iden, T.S. Tveter, T. Vik and the WA97 and NA57 Collaborations A strong motivation for the increasing interest in ultra-relativistic heavy-ion collisions is the possibility to observe a phase transition from hadronic matter to the quark-gluon plasma. A number of experimental signatures which could signal the QGP have been proposed (for a review see e.g. [l]). They are being studied in a number of experiments at the BNL AGS and CERN SPS, however, an unambiguous confirmation of the QGP formation has not yet been achieved. One of the possible signatures for this phase transition is an enhanced production of strange particles. The measurement of strange particle production 59 pad chambers PTC beam silicon telescope 5 cm 0.5M channels scintillator petals multiplicity Pb target detectors Figure 6.17: The WA97 set-up. in heavy-ion collisions is the main objective of the WA97 and NA57 CERN collaborations. In these experiments the strange particles K°, A, A, 3 and H and recently also Q and Q are detected with a combination of tracking devices mounted in strong magnetic fields. Strange particles produced in heavy-ion collisions give important information on the col- lision mechanism. In particular, the enhanced relative yield of strange and multi-strange particles in nucleus-nucleus reactions with respect to proton-nucleus interactions has been suggested as one of the sensitive signatures for a phase transition to a QGP state [6, 7]. It is expected that the enhancement should be more pronounced for multi-strange than for singly strange particles [8]. In view of the alternative explanations (hadronic gas or quark-gluon plasma scenarios) that exist for the features observed in the search of the QGP, it is important to look carefully for any indication which could suggest the onset of a new mechanism for strange particle production when going from proton to Pb induced collisions. A well known example of a possible change of regime is seen in the production of charmonium states where a strong decrease in the J/tp production has been observed by the CERN experiment NA50 [2]. The WA97 experiment addresses strangeness production in Pb-Pb collisions and is designed to study the yields of strange particles and antiparticles carrying one, two and three units of strangeness as a function of the number of nucleons taking part in the collision. The WA97 set-up, shown schematically in Figure 6.17, is described in detail in ref. [4]. The target and the silicon telescope were placed inside the homogeneous 1.8 T magnetic field of the CERN Omega magnet. The 158 A GeV/c lead beam from the CERN SPS was impinging on a lead target with thickness corresponding to 1% of the interaction length. Scintillator petal detectors behind the target provided an interaction trigger selecting roughly 40% of the most central Pb- Pb collisions. Two planes of microstrip multiplicity detectors covering the pseudorapidity region 2 < i] < 4 provided information for more detailed off-line study of the centrality dependence of particle ratios and spectra. In the proton reference runs at 158 GeV/c a trigger was applied to select events with at least two tracks in the telescope. The heart of the WA97 spectrometer was the silicon telescope (Pixel-Tracking-Chamber 60 - PTC) consisting of 7 planes of silicon pixel detectors with a pixel size 75 x 500 and of 10 planes of silicon microstrips with a 50 /zm pitch. The telescope has 5x5 cm2 cross section and contained ^0.5xl06 channels. This tracking device was placed 60 cm behind the target (90 cm for the p-Pb reference run) slightly above the beam line and inclined (pointing to the target) in order to accept particles at central rapidity and medium transverse momentum. The track recognition was done in the compact part of the silicon telescope (30 cm long, with 6 pixel and 5 microstrip planes). The momentum resolution of fast tracks were improved using the lever arm detectors (1 pixel and 5 microstrip planes) and three MWPC's with a cathode pad readout placed outside the magnet. Recently we published data on the A, S and J7 yields in Pb-Pb interactions as a function of collision centrality and compared with yields in p-Pb [4]. We observed a strong increase in the production at mid-rapidity for A, E and Q hyperons and anti-hyperons in Pb- Pb collisions with respect to p-Pb collisions and this enhancement exhibited a marked hierarchy, i.e. the fi enhancement is larger than that of the S, and the E enhancement is larger than that of the A. Presently these findings are supported with improved statistics (a factor of two higher than in the previous work). The analysis of A'° and negative particles (h~) is now also included. We selected as h~ those negative tracks which pointed to the interaction vertex. The K° were identified by their decay To ensure that ii'° is not ambiguous with A, a cut for |a^| < 0.45 was made in the Podolanski-Armenteros plot [11]. The hyperons A, S~, Q~ and their antiparticles were identified by reconstructing their decays into final states containing charged particles only: A ->• p + 7T~ The details of the analysis, i.e. the extraction of the hyperon signals, the weighting for each reconstructed A, E and Q and the calculation of hyperon yields are discussed in Refs. [4, 12, 13]. The differential distributions of the yield per event for each kind of particle were fitted in their respective acceptance windows using the expression d2iV where mj is the transverse mass, y is the rapidity and a = 3/2. The fit was performed using the method of maximum likelihood. For the present analysis with limited statistics we have assumed the rapidity distributions to be flat for \y — ycm\ < 0.5, i.e. in expression (6.8) f(y) is taken to be a constant. We 61 have investigated the systematic error which this assumption could introduce in the case of p-Pb for h~, Kg, A and A, where published data exist for p-Au [14] and p-S [15] collisions. We find that using a flat rapidity distribution, instead of one obtained from a fit to the published data [14], changes the values of T by less than 2%, 5%, 5% and 10%, in the case of the h~, K°, A and A distributions, respectively. The corresponding changes in the particle yields, defined by equation (6.9) below, are less than 10%, 5%, 5% and 6%. For each particle species, the values for the slope T were calculated both for the p-Pb sample and Pb-Pb sample. These values, given in [12], are used in the analysis which follows. The WA97 multiplicity detectors allow us to study particle yields as a function of collision centrality as measured by the number of participants Npart. To this purpose the multiplicity spectrum is divided into four bins and the average number of participants {Npart) for each bin is calculated as described in [4]. For the interactions p-Pb the number of participants corresponds to the estimated average for minimum bias collisions. The particle production yield per event, Y, in each centrality bin is defined by the integral /•oo rycm+0.5 A2J\T Y = / dpT / dy -H-L_ (6.9) Jo Jycm-o.5 ay dpT where the extrapolation to the window \y — ycm\ < 0.5 and py > 0 GeV/c is done according to expression (6.8) using the values of T given in [12]. Figure 6.18 shows particle yields per event for p-Pb and Pb-Pb interactions as a function of the number of participants (Npart)- The vertical error bars correspond to statistical uncertainties only, and do not include systematic errors from feed-down nor from the assumption of a flat rapidity distribution in our acceptance window. As discussed above, these are estimated to be small relative to the current statistical errors. For the h~ yield in p-Pb collisions, however, a 15% systematic error has been introduced to account for the uncertainties due to the single track background subtraction procedure. The horizontal bars show the root-mean-square values of the number of participants in the selected bins for Pb-Pb collisions, and the range corresponding to 80% of the cross section in p-Pb. In Figure 6.18 the particles are divided into two groups. Figure 6.18a shows the yields of particles with at least one common valence quark with the nucleon (S~, A, h~) and of the A'°, which has contributions ds and ds. Figure 6.18b refers to particles with no common valence quark with the nucleon: A, E and fi~ -j- £1 . It is instructive to analyze them separately since the particles in the two groups are empirically known to exhibit different production features, e.g. A and A have different rapidity spectra both in p-S and S-S [14]. Figure 6.19a,b shows the particle yields expressed in units of the corresponding yield per p-Pb interaction (i.e. each yield is rescaled so that the value for p-Pb is set to one). The particle yields in Pb-Pb are compared to a yield curve (full line) drawn through the p-Pb points and proportional to the number of participants, Npart. All yields appear to increase with centrality from p-Pb to Pb-Pb faster than linearly with the number of participants. However, within our experimental centrality range for Pb- Pb, i.e. for Npn-t > 100. we observe that all particle yields per participant appear to be constant. This is illustrated in Figure 6.19c and 6.19d, where we present the particle yield per participant, (Y)/(Npart), as a function of (Npart). For each particle species we then compute a global enhancement, E, going from p-Pb to 62 10 10 10 10 Figure 6.18: Yields, defined in equation (6.9), as a function of the number of participants for a) ft", Kg. A and E~; b) A, S and Q~ +0, . Note that the yields for H and Q,~ +11, are very similar. Pb-Pb collisions, defined as (Y) E- (6.10) (Npart) Pb-Pb where (Y) and (Npart) are averaged over the full centrality range covered by the experiment. E measures the enhancement at midrapidity for the various hadron species. The values E for each particle are displayed in Figure 6.20. Similar enhancement values are obtained if we use the data before the extrapolation to the full y — pi window. We note that the enhancement E increases with the strangeness content: E(A) and In summary, the strange particle yields per participant at central rapidity increase from p-Pb to Pb-Pb. The enhancement is more pronounced for multistrange particles, and exceeds one order of magnitude in the case of Q. As pointed out in [16], such a behaviour contradicts expectations from hadronic rescattering models, where secondary production of multi-strange (anti)baryons is hindered by high mass thresholds and low cross sections. 63 o10 0) JO a> 75 10 10 - 1 - -r i iuni| 10 102 103 1 10 102 io3 (Noartpart>' a.si L 2 0) 110 +•» (IS a. 'o r a niiri i r i r 0 100 200 300 400 100 200 300 400 (Npart) Figure 6.19: Yields, expressed in units of yields observed in p-Pb collisions, as a function of the number of participants for a) h~, Kg, A and E~; b) A, E and Q~ + Q . The solid line represents a function through the p-Pb point proportional to the number of participants impart}- The proton points are juxtaposed on the horizontal scale. 64 til L Q> - O c (0 c t UJ 10 * • t • • t * m i - : h" A A Otfi 1 • ' ' i ' • 1 ' 1 1 ' ' , , | . , 0 12 12 3 Strangeness [S[ Figure 6.20: Strange particle enhancement versus strangeness content. Within the participant range Npart > 100, corresponding to our Pb-Pb data, all yields are found to increase proportionally to Npart, as it would be expected if strange quarks are equilibrated in a deconfined and chirally symmetric quark gluon plasma. The obvious question arises whether the increase in the hyperon production is smooth with {Npart), or if any discontinuity is present; and the principal aim of the present NA57 exper- iment [17] is to investigate the existence of an onset for the strangeness enhancement effect with changes in the beam energy and/or the centrality (i.e. the number of participants in the nucleus-nucleus collision). The observation of such a threshold effect would indicate a discontinuity in the behaviour of highly compressed matter, as expected from a first-order phase transition, and help to locate the transition point. To reconstruct the decays of hyperons (A, E and Q) and K mesons in the high multiplicity environment of a central Pb-Pb collision, a high granularity telescope of silicon pixel planes is used. The high rate capability of these detectors allows one to collect a large number of events. The apparatus, shown schematically in figure 6.21, is placed inside the 1.4 T field of the GOLIATH magnet. The main features of the apparatus are: • A silicon telescope made of 13 silicon pixel planes, with about 1.1 million channels in total; seven planes with a pixel size of 75 X 500 fim2 read out by the 0mega2 front end chip and six planes with a pixel size of 50 X 500 /im2 read out by the Omega3 front end chip. • An array of six scintillator petals, placed 10 cm downstream of the target, to cover the pseudorapidity range 1 < rj < 2 and provide a fast signal for the multiplicity trigger. 65 Double side p. strips Y pixel plane (3£>2 + 4Q3) Z pixel plane (4Q.2 + 2Q.3) 10 m 158AGeV/c: d = 60 cm a = 40 mrad 40 A GeV/c: d = 30 cm a = 72 mrad S2 _' 70 m Figure 6.21: A schematic view of the NA57 set-up • A set of silicon multiplicity detectors sampling the charged particle multiplicity in the pseudorapidity region 2 < r) < 4 in order to measure the centrality of the nucleus- nucleus collision. The telescope is placed above the beam line, inclined and aligned with the lower edge of the detectors on a line pointing to the target. The inclination angle a and the distance d from the target to the first pixel plane depend on the beam momentum in order to cover the central rapidity region in both cases: at 158 A GeV/c (J/LAB ~ 2.9) a = 40 mrad and d = 60 cm, at 40 A GeV/c (yLAB ~ 2.2) a = 72 mrad and d = 30 cm. The centrality of the collisions is measured by sampling the charged particle multiplicity at central rapidity using two stations of Multiplicity Strip Detectors (MSD). The number of participants is estimated from the Wounded Nucleon Model by assuming proportionality between the measured multiplicity and the number of participants ((Nch) = q(Npart)), and taking experimental smearing into account [4]. Figure 6.22 shows a comparison between the distribution of number of participants extracted from the measured multiplicity dis- tributions in WA97 and NA57 and the fit from the Wounded Nucleon Model. The NA57 data extends the centrality range down to iVpar( > 40 which corresponds to triggering on about 60% of the inelastic Pb-Pb cross section. During the 1998 data taking periods 20 million p-Pb events at 158 GeV/c, 230 million Pb-Pb events at 158 A GeV/c, and 2.3 million Pb-Pb events at 40 A GeV/c were written to tape. The hyperons and the K mesons are identified via the decay channels with only charged particles in the final state (as in WA97). Figure 6.23 shows the mass distributions for reconstructed A, A, 5~ and E from a small fraction (about 1%) of the 158 A GeV/c lead-lead events. The full statistics should give in excess of 2000 E~. 66 la o WA97 data • NA57 data -2 — WNMfit 10 o '- * 0 0 _• 0 • * - f da/ d -3 10 :• J : i . I V -4- 10 \i ,, i i i i,,., i,.., i,,,. i.,.. i,,.. in 0 50 100 150 200 250 300 350 400 450 N ./q (= N ) ch " v parF Figure 6.22: Distribution of the number of participants extracted from the measured mul- tiplicity distributions in WA97 (open circles) and NA57 (closed circles). The solid line shows the fit using the Wounded Nucleon Model. 67 NA57/199B/Pb-Pb run NAS7/1998/Pb-Pb run I.I 1.12 1.14 1.16 IIS 1.2 1.22 1.24 M(piz') [GeV] NA57/199S/Pb-Pb run NA57/19S&Pb-Pb run I" • III 1 II I ; 1.1 1.2 IJ 1.4 1.5 1.6 1.1 l.S 1.9 2 1.1 1.2 1.1 1.4 1.5 1.6 1.1 l.S 1.9 2 M(An") [GeV) M(An*) [GeV| Figure 6.23: Invariant mass distributions for A (upper left), A (upper right), E (lower left), and E (lower right) from the test production of 2M events of the 1998 Pb+Pb data. 68 The NA57 experiment can play a unique role to explore the onset of a phase transition from hadronic matter to quark-gluon plasma by addressing the two main questions arising from the WA97 results, namely: (i) how the strange particle yields behave at lower numbers of participants, and (ii) how this behaviour depends on the centre-of-mass energy of the collision. To further extend the present work, an analysis based on a larger statistics sample is under way. Also data on p-Be collisions will be used to add an extra point in Figure 6.18 and Figure 6.19. More details may be found in: http://www.cern.ch/WA97/ and in: http://www.cern.ch/NA57/ References [1] J.VV. Harris and B. Muller, Annu. Rev. Nucl. Part. Sci. 46 (1996) 71. [2] M.C. Abreu et al, Phys. Lett. B410 (1997) 327 and Phys. Lett. B410 (1997) 337. L. Ramello et al., (NA50 Collaboration), Charmonium production in Pb-Pb interac- tions at 158 GeV/c per nucleon, in Proceedings of the 13th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, Tsukuba, Japan, December 1997, Nucl. Phys. A638 (1998) 261c. [3] G. Roland et al. (NA49 Collaboration), Recent results on central Pb-Pb collisions from experiment NA49, in Proceedings of the 13th International Conference on Ultra- Relativistic Nucleus-Nucleus Collisions, Tsukuba, Japan, December 1997, Nucl. Phys. A638 (1998) 91c. [4] E. Andersen et al. (WA97 Collaboration), Phys. Lett. B433 (1998) 209. [5] M. Kaneta et al. (NA44 Collaboration), Kaon and proton ratios from central Pb-Pb collisions at the CERN SPS, in Proceedings of the 13th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, Tsukuba, Japan, December 1997, Nucl. Phys. A638 (1998) 419c. [6] J. Rafelski and B. Muller, Phys. Rev. Lett. 48 (1982) 1066, J. Rafelski and B. Muller, Phys. Rev. Lett. 56 (1986) 2334. [7] P. Koch, B. Muller and J. Rafelski, Phys. Rep. 142 (1986) 167. [8] J. Rafelski, Phys. Lett. B262 (1991) 333. [9] U. Heinz, Strange messages: chemical and thermal freezeout in nuclear collisions, in Proceedings of the 4th International Conference on Strangeness in Quark Matter, Padova, Italy, July 1998. J. Phys. G: Nucl. Part. Phys. 25 (1999) 263. [10] J. Rafelski. Quo vadis strangeness ?. in Proceedings of the 4th International Confer- ence on Strangeness in Quark Matter, Padova, Italy, July 1998, J. Phys. G, Nucl. Part, Phys. 25 (1999) 451. [11] J. Podolanski and R. Armenteros, Phil. Mag. 45 (1954) 13. 69 [12] R. Lietava et al. (VVA97 Collaboration), Strangeness enhancement at mid-rapidity in Pb-Pb collisions at 158 A GeV/c, in Proceedings of the 4th International Conference on Strangeness in Quark Matter, Padova, Italy, July 1998, J. Phys. G: Nucl. Part. Phys. 25 (1999) 181. [13] R. Caliandro et al. (WA97 Collaboration), A,H and Q production at mid-rapidity in Pb-Pb and p-Pb collisions at 158 A GeV/c, in Proceedings of the 4th International Conference on Strangeness in Quark Matter, Padova, Italy, July 1998, J. Phys. G: Nucl. Part. Phys. 25 (1999) 171. [14] T. Alber et al., Z. Phys. C64 (1994) 195. [15] A. Bamberger et al, Z. Phys. C43 (1989) 25. [16] P. Braun-Munzinger and B. Miiller, Summary report from the meeting Heavy Ion Physics at the SPS, HIPS-98, Chamonix, France, September 1998. [17] V. Manzari et al. (NA57 Collaboration), The International Symposium on Strangeness in Quark Matter, Padua, Italy, July 20-24,1998, J. Phys. G: Nucl.Part.Phys. 25 (1999) 473. 6.3.3 Hyperon production in Pb-Pb collisions at 158 A Gev/c T. Vik, F. Fayazzadeh, M. Henriquez, A.K. Holme, G. L0vh0iden, T.S. Tveter, and the WA97 collaboration. An enhanced production of A-hyperons with one strange quark is a possible signature for a phase transition to the quark-gluon-plasma. The A-particles are identified by reconstruct- ing their decays into final states containing only charged particles. The A has the decay modes: A —» p7T~ A -> p>7T + in 63.9 % of the decays and A (A) -> n7T° in 35.8 % of the decays. From the telescope tracks V° candidates are constructed. The V°s are neutral particles which decay to one positively and one negatively charged particle. Whether the V"°s are consistent with p7r~~ or p?r+ can be decided by cutting on various parametres. The elements in such an analysis are briefly discussed in [1]. Also the E~- and Q~-hyperons with two and three strange quarks, respectively, produce A-hyperons by the decay modes: E~ ->• i\n~ in 99.89 % of the decays, and fi" -> AK~ 70 in 67.8 % of the decays and similar for the antihyperons. The A production from the decay of E~ and f2~, known as cascade particles, is called secondary feeding. In order to deduce the correct number of As produced in primary processes, this secondary feeding must be subtracted. The cascade particles travel some distance before decay, and the proton and pion from the lambda decay are eventually bent out of the telescope because of the magnetic field. For this reason the number of lambdas from the cascades should increase with the distance between target and telescope. Equal amounts of quarks and antiquarks are produced in a QGP in order to preserve the baryon number, therefore abundant numbers of antiquarks exist, which can easily produce antibaryons. The formation of antibaryons in a hadronic phase, however, can only take place with the production of a baryon-antibaryon pair, which demands an energy above 2 GeV and thus is unlikely to happen. Moreover, because there are several ss pairs in a QGP, one is lead to the prediction that in a deconfined phase there is a hierarchy of particle production ratios: Q+/Q~ > ~:+/2:- > A/A From WA97 data it is seen that the experimental ratios indeed are arranged according to this prediction [1]. This shows that in a QGP phase, multistrange antihyperons contribute more to the anti- lambda production, than multistrange hyperons contribute to the lambda production. In other words, the ratio A/A should increase at larger distances. Thus, it is interesting to measure the lambda production at different distances from the target in order to determine the importance of this secondary feeding effect. The experiment have been conducted at distances of 60, 90 and 120 cm between target and the telescope. In this project the A-baryon production at distances of 120 and 90 cm is studied, and compared to the E!~-baryon production at the same distances. Firstly, the A/A ratios for 120 cm and 90 cm data will be established. Then the E!~ particle production will be addressed, and the number of As that originate from these cascades estimated. The present data have been obtained from Pb-Pb runs in the autumns of 1994 and 1995. References [1] WA97 Collaboration: E. Andersen et al, Nucl. Phys. A638 (1998) 115c 6.3.4 The BRAHMS - Broad RAnge Hadron Magnetic Spectrometer - Experiment at the RHIC Accelerator A. K. Holme, G. Lovheiden, B. Samset, T. S. Tveter and the BRAHMS Collaboration The RHIC accelerator at Brookhaven is scheduled to commence operation at November 1, 1999. 71 The machine will deliver colliding beams at \/s — 200 GeV per nucleon pair, thus providing access to the nuclear transparency regime. The collision zone is expected to consist of a central, baryon-poor region with high energy density (y ~ 0), and a baryon-rich fragmen- tation region closer to the rapidity of the original collision partners. The possibility for creation of a quark-gluon plasma is present both at low and high net baryon density. The BRAHMS experiment, which has an extremely wide coverage in rapidity, will search for QGP signatures in both regions. BRAHMS . , .J'M.', H2,T5 RICH Forward Spectrometer 2.3 < 0 < 30 Multiplicity • Beam Beam counters Dx Mid Rapidity Spectrometer Beam magnets 30 < e < 95 D1,D2,D3,D4,D5: dipole magnets T1,T2,T3,T4,T5, TPC1 TPC2: tracking detectors H1,H2,TOFW: Time-of-flight detectors RICH, GASC: Cherenkov detectors Figure 6.24: The BRAHMS detector. 0 The BRAHMS detector, shown in Figure 6.24, consists of two moveable magnetic spectrom- eter arms, the forward spectrometer (1.3 < r\ < 4.0) and the mid-rapidity spectrometer (-0.1 < T] < 1.3). Despite its small geometric acceptance, the detector covers a large region in the rapidity-transverse momentum plane by varying angular settings and mag- netic fields. Particle identification is done by combining momentum determination from tracking in TPCs and drift chambers with velocity data from time-of-fiight measurements and Cherenkov counters. The particles p, p, K*, 7r± can be identified over the entire range 0 < \y\ < 4 and 0.2 < px < 3 GeV/c. Beam-beam counters provide initial trigger information, rough vertex determination and multiplicity at rj = 3 - 4. A multiplicity detector covering the range -2.2 < rj < 2.2, consisting of an inner layer of Si strips and an outer layer of scintillator tiles, characterizes the centrality of the collision. Zero-degree calorimeters measure spectator neutron multiplicity and luminosity. Details are given in 72 The BRAHMS experiment will investigate the yields and pr spectra for various hadrons at different rapidity intervals, covering both the central "excited vacuum" zone and the fragmentation regions, as functions of the centrality of the collision. The dependence on the colliding system (Au-Au, Si-Si, p-A or p-p) will also be studied. Some of the most basic questions connected with RHIC experiments address the degree of stopping (the rapidity shift of the fragmentation region), which determines the energy deposition in the reaction zone, and the baryochemical potential in the central region. Both can be extracted from the net proton (p—p) distribution as a function of rapidity. • Fritlof 1.7 — — Vimui 4.02 RQUD 1.07 — - - Fritiof 7.2 Figure 6.25: Predicted net baryon rapidity distributions for central Au+Au collisions using different models as indicated by the linetype. The rapidity range to be studied by BRAHMS is shown by the arrows. The figure is taken from [2]. The yields of various hadrons give information on the conditions (chemical potentials, temperature, phase space saturation) at chemical freezeout. One QGP signal is increased production of strange hadrons. BRAHMS will investigate the enhancement of the strange mesons K+, K~. Preliminary calculations indicate that it might also be possible to identify the singly-strange baryons A, A over the full rapidity range of the spectrometer. A quantity surviving rescattering during thermal equilibration is the entropy, which can be computed from the particle multiplicity dN/dy per participant. The phase transition might also be revealed by the dependence of the temperature extracted from spectral slopes (oc (PT)) on the energy density (oc dN/dy). The yield of hadrons with high PT (> 2 GeV) is strongly dependent on hard partonic scattering processes during the earliest phase of the reaction, and on the energy loss dE/dx of the resulting fast coloured particles in the plasma. RHIC is the first heavy-ion collider facilitating experimental investigation of the QCD perturbative regime. The first year, RHIC is expected to deliver about 1 - 10% of nominal luminosity. The goals for the first months are getting the spectrometer operational and understanding its re- sponse under realistic beam conditions. The first physics measurements will include global multiplicity distributions and charged hadron rapidity distributions at selected transverse momenta and rapidities. Hopefully it will be possible to accumulate higher-statistics spec- tra of protons, pions and kaons at a few y values, with transverse momenta up to 1 - 1.2 GeV-c, for central, peripheral and minimum bias collisions. Measurements requiring higher statistics will be undertaken when full luminosity is avail- able. This includes the hard tail of hadron pr spectra, and two-particle correlation studies. The space-time evolution of the emitting source can be deduced from correlations between charged identical mesons (pions, kaons) as a function of their relative and pair-averaged momenta. Modifications of the 4> meson (decaying to a K+K~ pair) width and mass would be evidence of possible chiral symmetry restoration. The A, A baryons (decaying to p7r~ and prr+, respectively) provide both interesting strangeness signals, measures of the baryonic chemical potential and important corrections to the observed net proton yield. A more comprehensive overview of the physics is found in [2]. The Oslo group participates in simulations and software development, among others the definition of a convenient /zDST (event summary) format for storage as entries in ROOT [3] trees and thus allowing fast and simple I/O and analysis. An alternative tracking algorithm is also under investigation. Further details can be obtained at the URL: http://www.rhic.bnl.gov/exportl/brahms/WWW/brahms.html References [1] BRAHMS Conceptual Design Report, The BRAHMS collaboration, 1994 (updated 1995). [2] F. Videbaek, The BRAHMS Experiment at RHIC, Status and Goals. Proceedings of the Workshop on particle distributions in hadronic and nuclear reactions, UIC, June 10 - 12, 1998. [3] Rene Brun and Fons Rademakers, ROOT - An Object Oriented Data Analysis Frame- work, Proceedings AIHENP'96 Workshop, Lausanne, Sep. 1996, Nucl. Inst. & Meth. in Phys. Res. A 389 (1997) 81-86. See also http://root.cern.ch/. 6.3.5 Track recognition in BRAHMS using the Hough transform method T. S. Tveter, A. K. Holme, G. Levhoiden, B. Samset and the BRAHMS Collaboration Several tracking methods are in common use in high energy physics. The standard tracking method in BRAHMS and also in NA57 and predecessors is track following. At first "track seeds" consisting of close-lying hits are found, and a first-approximation straight line or helical arc is fitted to those. Then a search for new hits is performed along the extrapolation of the track, along with a stepwise refinement of the track parameters. In template matching one utilizes a lookup table of pre-generated tracks with given momentum and starting point, and finds the closest match to the experimental hits. In elastic tracking one starts 74 with a template which is gradually attracted to the closest experimental points through a modified \2 minimization procedure. The Hough transform [1], which is a general tool in image analysis, maps regular geometric patterns in hit coordinate space to local maxima in another parameter space. In the BRAHMS setup there is no magnetic field inside the tracking detectors (TPCs and drift chambers), giving straight line track segments which are well suited for Hough transform pattern recognition. A straight line in two dimensions, x{z) = axz+xo, is transformed into the point (#track> Ptrack) in the Hough parameter plane (0,p), where #track = arctan( — I/ax) is the angle between the a; axis and the normal to the line x(z), and ptrack = £osm ^track is its distance of closest approach to the origin. Similarly, each point (xi,Z{) on the line can be transformed into a sinusoidal curve in the (0,p) plane: pi{9) = zi cosO + X{sin 9. When a straight line is extracted from a series of N separate space points (xi,zy), .... (XN, ZJV), the Hough plane can be visualized as a two-dimensional histogram, where "one vote" is given to each possible (9,p) value consistent with the observed hit (x{,Zi), cor- responding to all straight lines that can be drawn through this point. This is done by iterating over all channels along the 9 axis, computing the p values, and incrementing the channels along the curve />;(#) by 1 (or a greyvalue, for instance the ADC value). The N curves resulting from the iV hits will intersect in one point (#track, Ptrack) given by the expressions above. The intersection point shows up as a local maximum in the histogram, enhanced with a factor ss N above the "background", the general count level along the curves. This method has been used for instance in streamer chamber image analysis [2]. Hits in a TPC (time projection chamber) are defined in three dimensions (given by pad row, pad number and drift time from track to pad plane.) A linear track segment in three dimensions, defined by hits (xi,yi,z\), .... (XN, J/jVi ZN), is uniquely described by four parameters: x(z) = axz+xo, y(z) = ayz-\-yo. and can in principle be transformed to a point in a four-dimensional parameter space (9xz,pxz,9yz,pyz). This point will emerge as the intersection between N hypersurfaces in four dimensions: pxz,i(9Xz) — %i cos 9XZ + Xi sin 9 XZ, Pyz,i {9yz) = Zi cos 9yz + yt- sin 9yz. In the experimental situation, hits from more than one track and noise will typically be present, giving rise to significant background and several local maxima, some of which might be spurious. In order to extract the individual tracks, a so-called adaptive Hough transform algorithm [3] is useful. The adaptive Hough transform is a fast and memory-economic iterative procedure, where the "votes" are distributed among a small number of bins. For each iteration, the global maximum in parameter space is located. The histogram limits are redefined, centering on the present maximum and shrinking the window of interest while keeping the number of bins constant, thus increasing the parameter resolution. At each step, hits whose Hough transform curves do not pass through the current central window, are discarded. In this way, one gradually "zooms in" on one unique track. Finally, the track segment parameters can be calculated from the remaining hits, or taken directly from the coordinates of the window. These hits are now marked as "assigned" and removed from the general pool of hits. To find the next track, one returns to the original, wide histogram limits and repeats the procedure for the "unassigned" hits, now obtaining a transformed image with (at least) one local maximum less and with less background. A sketchy, preliminary version of an adaptive Hough transform algorithm has been tested on simulated BRAHMS TPC hits. Here, the (xz) and (yz) projections are transformed 75 separately in order to utilize the predefined two-dimensional ROOT histogram classes. The transform of each hit has been weighted with its ADC value. Histograms with 15x15 an channels are used. The windows around the highest maxima in the (8xz,Pxz) d (dyz,Pyz) planes are shrunk alternately to one-third of the previous width in each direction. The "zooming in" is terminated when the window aperture is of the same size as the track width. The first simple tests indicate that the efficiency and reliability of the Hough transform method is comparable with the track following method for typical events in the BRAHMS TPCs. The application of the procedure on a relatively "dirty" event is illustrated by Figure 6.26. References [1] P. C. V. Hough, Machine Analysis of Bubble Chamber Pictures, International Con- ference on High Energy Accelerators and Instrumentation, CERN, 1959. [2] D. Brinkmann et al., Nucl. Instr. Meth. A354 (1995) 419. [3] D. Rohrich, private communication 6.3.6 A Large Ion Collider Experiment (ALICE) at the CERN LHC A.K. Holme, B. Kvamme, G. L0vh0iden, B. Skaali, T.S. Tveter, D. Wormald, B. Wu, J.Yuan and the ALICE Collaboration The heavy-ion detector ALICE has emerged as a common design from the heavy-ion com- munity currently working at CERN and a number of groups new to this field from both nuclear and high-energy physics. It is a general-purpose heavy-ion experiment, sensitive to the majority of known observables (including hadrons, electrons, muons and photons), and it will be operational at the start-up of the LHC. With ALICE the flavour content and phase-space distribution will be measured event-by- event for a large number of particles whose momenta are of the order of the typical energy scale involved (temperatures « 200 MeV). The experiment is designed to cope with the highest particle multiplicities anticipated for Pb-Pb reactions {dNch/dy « 8000). For ALICE, the Norwegian groups have taken responsibilities for the DAQ system (Oslo) and the design of the read-out system of the PHOS detector (Bergen). The AME company of Horten, Norway, is also participating in this study. More detailed information on the ALICE detector system may be found in ref. [1]. References [1] N. Ahmad et al.(ALICE collaboration) (...B.Kvamme, G.Ltfvhoiden, B.Skaali, D.Wormald, B.Wu, J.Yuan...): Technical proposal for A Large Ion Collider Experi- ment at the CERN LHC, Technical Report CERN/LHCC/95-71,Dec.l995. 76 6.3.7 The Spin of the Nucleons A. Schiller and the SMC collaboration The spin of the nucleons is investigated in a large collaboration at CERN, the Spin Muon Collaboration (SMC). The data taking was finished in 1996 and also the data analysis is approaching its end. Many publications were written during the last years [1, 2, 3, 4, 5]. A list of publications where one of the Oslo staff (Andreas Schiller) was involved is given below. Some more articles are in preparation. References [1] SMC, The spin-dependent structure function gi(x) of the proton from polarized deep- inelastic muon scattering. Phys. Lett. B 412 (1997) 414 [2] SMC, Polarised quark distributions in the nucleon from semi-inclusive spin asymme- tries. Phys. Lett. B 420 (1998) 180 [3] SMC, Measurement of proton and nitrogen polarization in ammonia and a test of equal spin temperature. Nucl. Instr. Meth. A 419 (1998) 60 [4] SMC, Spin asymmetries A\ and structure functions g\ of the proton and the deuteron from polarized high energy muon scattering. Phys. Rev. D 58 (1998) 112001 [5] SMC, Next-to-leading order QCD analysis of the spin structure function g\. Phys. Rev. D 58 (1998) 112002 77 xz Houqh transform I • • n D DO DQQoDO- -5 DOODaODDC -10 ^ o • . • a oDDa -ts -20 -25 10 IS 20 ZS yz Houflh transform] xz Hough transform DD DDDDDDC D Q D a a • • DDPDDDDDnDn' •aaDDDo • o o a • 12 1.3 1.4 1.5 1.C 1.7 1.S 1.3 -is -io -s a 6 ia is Uiete yi x-cooniiiBta yz Houah transform xz Hough transform | TPC Nts xz-proi '-2 0 fco 1 8 ;• a o a > • • • ,D D D DD O a a ' 3 D Q OO < • - »OOLj_IJa o » • • 30 | • « o COD a o a i ad an a a 001100° ° " o p o Q D o o • n I I i ^ n c . • D o a o a ZV ••-.oooe.iQDD 10 \ t.GS 1.7 1.7S Mi yz Hough transform I One track yz-proi. j J- / IjODDDDDDDD " • • D D D DDDDDo 30 . . o a a Dana: I • • • OO[ zo 10 / 1.CSl.GCJ.G7l.Gffl.G91.71.7n.721.73 0 6 10 15 ?0 23 Uieto yi y - coonNiiate Figure 6.26: Adaptive Hough transform applied to a selected event. Upper left subframes: {xz) and {yz) projection of all hits in TPC1. Lower right subframes: (xz) and (yz) projec- tion of hits belonging to the first track found. First and third column: Hough transform in the 8yz,pyz and 9xs.pxz plane, respectively, during successive iterations. Second and fourth column: (yz) and (xz) projections of hits compatible with the window of interest for the respective iterations. 78 6.4 Radiation physics and radiation protection 6.4.1 Radon and radon progeny in indoor air T. Strand1'2, A. Birovljev2, A. Heiberg2, B. Lind2, G. Thommesen2 ^ept. of Physics, University of Oslo, Norway 2Norwegian Radiation Protection Authority, 0steras, Norway. Radon in indoor air is the main source of exposure to ionising radiation of the Norwe- gian population. A nation-wide survey of radon concentrations in Norwegian dwellings was undertaken in the period 1987 - 89. In this survey, radon measurements were made by CR-39 etched track detectors (six months integration time) in the main bedroom of approximately 7500 randomly selected dwellings built before 1980. The annual average radon concentration for the whole country was calculated to 51 Bq/m3 (recent corrected average 53.8 Bq/m3) and 3.7 % of the results exceeded 200 Bq/m3. In a large proportion of single-family houses (including detached, semi-detached, row and terraced houses), the living room and the kitchen are located on the ground floor while the bedrooms are on the first floor. In most cases the radon concentration is higher on the ground floor than on the first floor, and there may also be differences between bedrooms and other rooms on the same floor owing to different ventilation conditions and ventilation habits. An additional factors that could have influenced the measurements was that the winters from 87 to 89 were considerably warmer than normal. Based on these considerations, the annual average radon concentration in Norwegian dwellings was assumed to be between 55 and 65 Bq/m3 and it was further estimated that approximately 5 % of the housing stock exceeded 200 Bq/m3. In a recent study, the results of the nation-wide survey have be compared with the results of follow-up surveys in approximately 5000 randomly selected dwellings from 31 out of the total 430 municipalities [1]. These 31 municipalities covers 7% of the Norwegian population. The measurements were made by CR-39 etched track detectors and one to two detectors were placed in each dwelling for a period of two to three months in the heating season (October to April). The population weighted average radon concentration during the measurement period was calculated to 149 Bq/m3, and the annual average concentration (each result was corrected to an annual average concentration) was estimated to 112 Bq/m3, compared to 56 Bq/m3 for the same municipalities in the nation-wide survey. By using the same ratio for the whole country, the annual average concentration in Norwegian dwellings was estimated to 106 Bq/m3. It was further estimated that approximately 10% and 4% of the housing stock exceeds 200 and 400 Bq/m3, respectively. The differences between the nation-wide survey and the present results could be explained by changes in ventilation conditions a.nd extensive use of aerated/light weighted concrete in the foundation walls in houses built in the last three decades. A new nation-wide survey of radon concentrations was started i 1998. In this survey, two measurements by CR-39 etched track detectors will be made in houses of 2000 randomly selected persons throughout the whole country. The integration time in each of the mea- surement is one year, and the results of this survey will be available by the end of 1999. Measurements for doses from external background radiation will be conducted An extensive survey of radon concentrations in kindergartens was undertaken during the 79 heating seasons from 1996 to 1998. Radon measurements were conducted in 3660 out of the total number of approximately 6300 kindergartens in Norway. The measurements were made by CR-39 etched track detectors and the integration time in the measurements was three months. The results of the survey show that the distribution of radon concentra- tions is close to log-normal with arithmetic and geometric means of 88 Bq/m3 and 45 Bq/m3, respectively [2]. The highest concentration was 2800 Bq/m3 and 9.2% and 2.7% of the kindergartens exceeded 200 and 400 Bq/m3, respectively. However, the measure- ments may have been influenced by the ventilation regime and the fact that nearly 50% of the kindergartens have mechanical ventilation systems which in most cases are switched off during the night. Additional measurements were conducted in a subgroup of kinder- gartens with mechanical ventilation systems and where the primary measurements gave results above the action level of 200 Bq/m3. During repeated measurements the ventila- tion systems very operated continuously 24 hours in the 22 kindergartens. Only one of the repeated measurements exceeded 200 Bq/m3 and the reduction was on the average 77%. In the same period, measurements were also made in a subgroup of kindergartens where the ventilations systems were operated in usual regime. No significant reduction of radon concentrations could be observed in these kindergartens. Assessment of radon exposure in both epidemiological studies and routine surveys are mainly based on time-integrated measurements of the radon concentration using etched track detectors. However, these type of measurements are only surrogates of the exposure owing to the fact that most of the dose is due to deposition of short-lived radon daughters in the respiratory tract and that only a very small contribution is from the radon gas itself. Earlier studies show that the radon concentration is more closely related to the bronchial dose than the concentration of the short-lived radon daughters, expressed in terms of equilibrium equivalent radon concentration (EEC), but this is not necessarily valid in indoor environments where the aerosol concentration is very high or very low, and/or the particle size distribution is very different from normal. In addition there are a number of uncertainties in the assessment of average radon concentration owing to short- term (days/weeks) and long-term (months/years) variations in the radon concentration, placing of the detectors, ventilation habits during indoor occupancy, etc. An ongoing study focuses on uncertainties in the assessment of radon exposure and health risk based on time-integrated measurements of the radon concentration [3]. Methods for retrospective assessment of radon exposure based on measurements on long- lived radon daughters (210Po; half-life of 138 days - as decay product of 210Pb; half-life 22.3 yrs) embedded in glass and other vitreous surfaces, or in volume traps of porous materials, have been investigated. Recently, a method for retrospective assessment of radon exposure based on measurements of 210Pb in the human skeleton (measurements on the scalp) has been developed and the results of preliminary measurements been compared with retrospective measurements on glasses from the same homes. The results are in very 3 good agreement for very high exposures {CRU > 10 kBq/m and CPb^hody^ >100 Bq) and this could be a method to be used in the future in epidemiological studies. A passive method based on etched track detectors has been developed for measurements of very high concentrations of radon in indoor (> 10 kBq/m3). The technique is based on area readings (darkening) instead of individual track readings. The method is very promising and has recently been used for measurements of radon in soil gas in a geological study [4]. 80 References [1] T. Strand, A. Heiberg and G. Thommesen, Radon concentrations in the 1998 Norwe- gian housing stock, Workshop on Radon in the Living Environment, 19-23 April 1999, Athens, Greece. [2] A. Birovljev, T. Strand, A. Heiberg, Radon concentrations in Norwegian kindergartens. YUNSC '98, Sept. 28 - October 1, 1998, Belgrade, Yugoslavia [3] T. Strand, Uncertainties in assessment of indoor radon exposure. 1998 Society for Risk Analysis, Annual Conference, Risk Analysis: Opening the Process, Paris, France, October 11-14, 1998. [4] V. Valen, O. Soldal, A. V. Sundal and T. Strand, Sediments and radon - a dangerous combination? A case study from Kinsarvik, Norway. Workshop on Radon in the Living Environment, 19-23 April 1999, Athens, Greece. 6.4.2 Radon concentrations in groundwaters T. Strand1-2, D. Banks2, B. Frengstad4, Aa.K. Midtgard3, J.R.Krog , B. Lind2 xDept. of Physics, University of Oslo 2Norwegian Radiation Protection Authority, P.O.Box 55, N-1345 0steras 3Dept. of Geology ans Mineral Resources, Norwegian Technical University of Science and Technology, N-7034 Trondheim. 4Geological Survey of Norway, P.O.Box 3006 Lade, N-7002 Trondheim Several studies of naturally occurring radioactivity in Norwegian groundwater have been carried out in the last ten years. In one of these studies [1], [2], a quality-controlled hy- drogeochemical dataset of 1604 groundwater samples from Norwegian crystalline bedrock aquifers has been obtained and subject to analysis of radon (by scintillation counting), major and minor elements (by chromatography and ICP-AES), pH and alkalinity. Cumu- lative probability curves may be constructed to assess the risk of given parameters violating drinking water norms. Parameters such as radon and fluoride show clear lithological corre- lation, occurring at high concentrations in granite and low concentrations in anorthosites. Other parameters exhibits a lower degree of correlation with aquifer geochemistry (e.g. pH, major ions) and are likely to be governed by more universal thermodynamic equilib- ria (the calcium carbonate system) and kinetic factors. On a national basis 13.9% of the bedrock groundwaters exceed the recommended action level of radon, while 16.1% exceed the drinking water norm for fluoride. Considering pH, sodium, radon and fluoride together, 29.9% of all wells violate drinking water maximum concentrations for one or more of these parameters. In another study, 72 samples of groundwater derived from Norwegian Quaternary (largely glaciofluvial or glacial) aquifers were analyzed for a wide range of major and minor hodro- chemical parameters [3], [4]. The waters exhibits a relatively uncomplex evolution from Na-Cl dominated, immature waters (which reflect marine salts in precipitation) to Ca- HCO3 dominated waters via calcite dissolution. The median pH of these waters is 7.37, in contrast to similar waters from crystaline bedrock aquifers with a median pH of 8.07. The 81 water samples provide little evidence of significant acidification or sulphatisation of ground- waters by "acid rain". In fact, a positive correlation emerges between non-marine sulphate and alkalinity/pH, suggesting dominantly lithological sources for non-marine sulphate. No groundwaters from Quaternary deposits exceed maximum recommended concentrations for Rn, F- and Na, while 10% fall outside the required pH range. This again contrasts with bedrock aquifers where 30% of waters are non-compliant with respect to one or more of these parameters. An extensive nation-wide survey of radon in ground water was started in 1996. This study is part of a nation-wide survey of groundwater quality in Norway. By the end of 1998 approximately 4000 samples have been analyzed. Analysis of these data show that approximately 15 % of all Norwegian households taking their water supply from drilled wells in bedrock have radon concentrations exceeding the recommended action level of 500 Bq/1 [5]. The highest concentrations (above 10,000 Bq/1) have occurred in uranifereos granites in the south-eastern part of Norway. Release of radon to indoor air may increase the risk of lung cancer, but intake of radon containing drinking water may also increase the radiation dose significantly giving higher doses to small children. References [1] D. Banks, B. Frengstad, Aa. K. Midtgard, J. R. Krog, T. Strand, The Chemistry of Norwegian Groundwaters: I The distribution of radon, Major and Minor Elements in 1604 Crystaline Bedrock Groundwaters, The Science of the Total Environment, 1998; 222 (1-2), pp. 71-91. [2] D. Banks, B. Frengstad, J. R. Krog, Aa. K. Midtgard, T. Strand, B Lind, Kjemisk kvalitet av grunnvann i fast fjell i Norge. NGU-rapport 98.058, 177 sider, Norges geol- ogiske unders0kelse, 1998 (in Norwegian). [3] D. Banks, B. Frengstad, Aa. K. Midtgard, J. R. Krog, T. Strand, The Chemistry of Norwegian Groundwaters: II. The chemistry of 72 groudwaters from Quaternary sedimentary aquifers. The Science of the Total Environment, 1998; 222 (1-2): pp. 93- 105. [4] D. Banks, B. Frengstad, J. R. Krog, Aa. K. Midtgard, T. Strand, B. Lind, Kjemisk kvalitet av grunnvann fra l0smasser i Norge, NGU-rapport 98.089, 96 sider, Norges geologiske unders0kelse, 1998 (in Norwegian). [5] T. Strand and B. Lind B, Thommesen G. Naturlig radioaktivitet i husholdningsvann fra borebr0nner i Norge, Norsk veterinasrtidsskrift 1998; 110 (19): 662-665 (in Norwegian). 82 Chapter 7 Theoretical nuclear physics and nuclear astrophysics 7.1 Introduction Nuclear physics is the science of atomic nuclei, aiming at understanding the properties of nuclei, their interactions and their constituents. Properties of nuclei are determined by the interplay between strong, electromagnetic and weak interactions. In addition, nuclear physics has many links to both particle physics and astrophysics. Modern re- search in the latter fields is closely related to current experimental and theoretical development in nuclear physics, such as experiments to detect the quark-gluon plasma, the study of the abundance of the lightest elements in the universe, the equation of state of nuclear matter relevant for studies of supernovae and neutron stars, to mention just a few open problems shared by nuclear physics, particle physics and astrophysics. At low energies, nuclear properties are determined in terms of nucleons and mesons. Information on these properties is derived from nuclear structure studies, theoretically and experimentally. At higher energies, the substructure of nucleons and mesons in terms of quarks and gluons becomes visible and one of the great challenges of modern nuclear physics is to study how elementary particles like quarks and gluons, described by the underlying theory of quantum-chromo-dynamics (QCD), build up hadrons such as mesons and nucleons. The study of the structure and the dynamics of hadrons form then important topics in our basic understanding of nuclear properties. The way hadronic properties change when hadrons are inserted in a nuclear medium are key issues in understanding, both from the point of view of QCD and nuclear physics, relativistic heavy-ion collisions where matter can be heated and compressed under extreme conditions. Huge efforts are devoted to detecting the deconfinement of quarks and gluons into a plasma phase within such a hot and compressed nuclear medium. Knowledge of the above properties of nuclear systems, ranging from low to high energies is also important for calculations in nuclear astrophysics. It suffices to mention the relation between nuclear physics and the physics of Supernovae of type II. When the iron core of a star undergoes a core collapse to very high densities, the outcome may be a type II supernovae and-or black hole. Nuclear physics aspects which strongly enter the final outcome are the nuclear equation of state and how neutrinos interact with matter, together with the treatment of the hydrodynamics of the explosion. The nucleonsynthesis accompanying such an explosion gives rise to a large fraction of the 83 present day abundance of elements. Final stages of a supernova explosion may be so- called neutron stars, and the understanding of their structure and properties relies also on our understanding of the equation of state for nuclear matter and neutrino processes in dense matter. Our research covers several fields of nuclear physics and nuclear astrophysics, ranging from nuclear structure studies to the structure of neutron stars. Common to most problems studied is an underlying microscopic description, within the framework of many-body theories, of the interactions between the various hadrons. We do also study problems related to the foundations of quantum physics such as the non-separability of systems in a pure quantum state and the completeness of quantum mechanics. Further studies will be made of some of the main interpretations of the quan- tum theory and of alternative theories. An analysis will be attempted on the basis of Bohr's complementarity concept and his understanding of the nature of measurements involving actions of the order of the Planck constant. The different research projects are listed below. 7.2 Nuclear structure research Research in nuclear structure, especially under extreme conditions such as the study of exotic nuclei far from the valley of beta stability, presents important challenges for nuclear physics. Nuclear structure studies are also important in nuclear astrophysics studies, e.g., for the understanding of the synthesis of the elements, and to understand weak interactions through e.g., neutrino induced reactions on nuclei. 7.2.1 Study of odd-mass N = 82 isotones with realistic effective in- teractions T. Engeland, M. Hjorth-Jensen, A. Holt, E. Osnes, J. Suhonena, J. Toivanen" a Department of Physics, University of Jyvaskyla The microscopic quasiparticle-phonon model, MQPM, is used to study the energy spec- tra of the odd Z = 53 — 63, N = 82 isotones. The results are compared with exper- imental data, with the extreme quasiparticle-phonon limit and with the results of an unrestricted 2sldOg7/2Ohu/2 shell model (SM) calculation. The interaction used in these calculations is a realistic two-body G-matrix interaction derived from modern meson- exchange potential models for the nucleon-nucleon interaction. For the shell model all the two-body matrix elements are renormalized by the Q-box method whereas for the MQPM the effective interaction is defined by the G-matrix. 1. J. Suhonen and J. Toivanen, T. Engeland, M. Hjorth-Jensen, A. Holt and E. Osnes, Nucl. Phys. A628 (1998) 41-61 7.2.2 Effective interactions and shell model studies of heavy tin iso- topes T. Engeland, M. Hjorth-Jensen, A. Holt, E. Osnes 84 We calculate the low-lying spectra of heavy tin isotopes from A = 120 to A — 130 using the 2.sld0<77/20/i11/2 shell to define the model space. An effective interaction has been derived using I32Sn as closed core employing perturbative many-body techniques. We start from a nucleon-nucleon potential derived from modern meson exchange models. This potential is in turn renormalized for the given medium, 132Sn, yielding the nuclear reaction matrix, which is then used in perturbation theory to obtain the shell model effective interaction. 1. T. Engeland, M. Hjorth-Jensen, A. Holt and E. Osnes, Nucl. Phys. A634 (1998) 41-56 7.2.3 Shell model studies of the proton drip line nucleus 106Sb T. Engeland, M. Hjorth-Jensen, E. Osnes We present results of shell model calculations for the proton drip line nucleus 106Sb. The shell model calculations were performed based on an effective proton-neutron interac- tion for the 2slrf0^7/20/illii/2 shells employing modern models for the nucleon-nucleon interaction. The results are compared with the recently proposed experimental Yrast states. An excellent agreement with experiment is found lending support to the exper- imental spin assignments. 1. T. Engeland, M. Hjorth-Jensen, and E. Osnes, Phys. Rev. C, submitted 7.2.4 Ground state magnetic dipole moment of 135I M. Hjorth-Jensen, G.N. White", N.J. Stonea, J. Rikovskaa'c, S. Ohyad, J. CopnelP, T.J. Giles3, Y. Koha, I.S. Towner6^, B.A.Browna'S, B. Fogelberg6, L. Jacobsson6, P. Rahkilaa-A a Department of Physics, Oxford University, Parks Road, Oxford 0X1 3PU, UK. 6 Department of Neutron Research, Uppsala University, S-611 82 Nykoping, Sweden. c Department of Chemistry, University of Maryland, College Park, MD 20742 USA. d Department of Physics, Niigata University, Ikarishi-2, Niigata 950-2181, Japan e Physics Department, Queen's University, Kingston, Ontario, K7L 3N6, Canada. 1 TRIUMF, 4004 Wesbrook Mall, Vancouver, B.C., V6T 2A3, Canada. 9 Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University, E. Lansing, MI 48824 h Department of Physics,University of Jyvaskyla, FIN-40351 Jyvaskyla, Finland On-line low temperature nuclear orientation (OLNO) experiments have been performed on the isotope 135I using the technique of nuclear magnetic resonance on oriented nuclei (NMR/ON). The magnetic moment of the 7/2+ ground state has been measured to + 13o be /Li(7/2 I)=2.940(2)/tiyv thereby extending the known data on these states in odd-A I isotopes up to the neutron shell closure at N=82. Shell-model calculations have been performed for the magnetic moments of 7/2+ states in the N=82 isotones using free-nucleon and effective ^-factors. The effective ^-factors are obtained from a perturbation calculation that includes corrections for core polarization and meson- exchange currents. The proton number dependence of the magnetic moments in the 85 sequence of N=82 isotones 133Sb - 139La is discussed in terms of blocking of the Ogg/2 to 0gT/2 core polarisation with increasing 0gr/2 occupancy. Systematics of all measured 7/2+ odd-proton moments for 74 < N < 82 are reviewed. 1. G.N. White, N.J. Stone, J. Rikovska, S. Ohya, J. Copnell, T.J. Giles, Y. Koh, I.S. Towner, B.A.Brown, B. Fogelberg, L. Jacobsson, P. Rahkila and M. Hjorth- Jensen, Nucl. Phys. A644 (1998) 277-288 7.2.5 New island of ms isomers in neutron-rich nuclei around the Z = 28 and N = 40 shell closures M. Hjorth-Jensen, R. Grzywacza'6>c, R. Beraudd, C. Borcea6, A. Emsallem^, M. Glogowskia, H. Grawe-^, D. Guillemaud-Mueller3, M. Houryd, M. Lewitowiczc, A. C. Mueller3, A. Nowaka, A. Plochockia, M. Pfuetznera>/, K. Rykaczewskia'/l'i, M. G. Saint-Laurent6, J. E. Sauvestre', M. Schaefer-7', O. Sorlin5, J. Szerypoa, W. Trinder6, S. Viterittid and J. Winfieldd aIFD, Warsaw University, Pl-00681 Warsaw, Poland 6 GANIL, Caen, France 0 University of Tennessee, Knoxville, Tennessee, USA dIPN Lyon, Villeurbane, France eIAP, Bucharest-Magurele, Rumania ^GSI, Darmstadt, Germany 5IPN, IN2P3-CNRS, Orsay , France ^Physics Division, ORNL, Oak Ridge, Tennessee, USA 'IKS, Leuven, Belgium JCE Bruyres-le-Chatel, France New isomeric states in the neutron-rich nuclei near the Z= 28 and N=40 shell closures have been identified among the reaction products of a 60.3A MeV 86 Kr beam on a nat Ni target. From the measured isomeric decay properties information about the excited states and their nuclear structure has been obtained. The isomerism is related mostly to the occupation of the neutron g9/2 orbital, an intruder level in the N=3 fp shell. It is illustrated with the decay properties of 69 Ni m , 70 Ni m , and 71 Cu m interpreted within the nuclear shell model. 1. R. Grzywacz et al, Phys. Rev. Letters 81 (1998) 766-769 7.2.6 Shell model Monte Carlo studies of neutron-rich nuclei in the ls-Qd-lp-df shells M. Hjorth-Jensen, D.J. Deana, M.T. Ressell6'0, S.E. Koonin0, K. Langanke^ A.P. Zukere aPhysics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 USA and Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee, USA 6Astronomy and Astrophysics Center, University of Chicago, USA CW.K. Kellogg Radiation Laboratory, California Institute of Technology, USA ^Institute for Physics and Astronomy, Aarhus University, Denmark 86 eIRES, Bat27, IN2P3-CNRS/Universite Louis Pasteur, Strasbourg, France We demonstrate the feasibility of realistic Shell-Model Monte Carlo (SMMC) calcula- tions spanning multiple major shells, using a realistic interaction whose bad saturation and shell properties have been corrected by a newly developed genera] prescription. Particular attention is paid to the approximate restoration of translational invariance. The model space consists of the full sd-pf shells. We include in the study some well- known T=0 nuclei and several unstable neutron-rich ones around N = 20,28. The results indicate that SMMC can reproduce binding energies, B(E2) transitions, and other observables with an interaction that is practically parameter free. Some interest- ing insight is gained on the nature of deep correlations. The validity of previous studies is confirmed. 1. D.J. Dean, M.T. Ressell, M. Hjorth-Jensen, S.E. Koonin, K. Langanke and A.P. Zuker, Phys. Rev. C, in press 7.2.7 Towards the solution of the CP/CA anomaly in shell-model cal- culations of muon capture M. Hjorth-Jensen, T. Siiskonena and J. Suhonena a Department of Physics, University of Jyvaskyla The aim of this project is to study the role of various renormalizations of the effective interaction and effective operators which enter shell-model studies of weak processes where a muon is captured and of weak processes with neutrino scattering. A typical example for muon capture that we study is the reaction 16O(/x, v) 16N. Muon capture has great importance in fundamental physics theories as it can be used in the determination of the weak-interaction coupling constants. Compared with the more traditional and well studied /3 decay with electrons, the energy release in the muon capture is 200 times larger than that in the electron capture. This energy transfer from the muon makes it possible to excite many nuclear levels in the daughter nucleus and due to the large momentum transfer the reaction is therefore sensitive to those parts of the weak interaction hamiltonian that are not observed in ordinary /? decay. For neutrino scattering on nuclei we plan to look at the reaction 16O(^(7/), v{v)) 16O below particle-emission threshold. We wish to study here medium renormalizations of the isoscalar axial coupling constant, as this may affect the predicted rates for the above mentioned neutrino-scattering reactions. Moreover, neutrino scattering processes like (.4, Z) -f- v(V) —> v(y) + (.4, Z) are also thought to be important in the synthesis of the elements, where the so-called j/-process appears to be very promising in explaining the so-called p-process in the synthesis of the elements. The p-process is important in the understanding of the synthesis of the heavy elements in nucleosynthesis theories. The p-process nuclides are also expected to be synthesized from nearby r-process prod- ucts through charged current interactions with the electron neutrinos. For example, a process we wish to study is the neutrino capture 92Zr(f, e~) 92Nb and 92Nb(z/, e~) 92Mo through which a great deal of 92Mo could be produced. Recently many authors have performed shell-model calculations of nuclear matrix ele- ments determining the rates of the ordinary muon capture in light nuclei. These calcula- tions have employed well-tested effective interactions in large scale shell-model studies. For one of the nuclei of interest, namely 28Si, there exists recent experimental data which can be used to deduce the value of the ratio Cp/C\ by using the calculated ma- trix elements. Surprisingly enough, all the abovementioned shell-model results suggest a very small value (~ 0) for Cp/C\, quite far from the PCAC prediction and recent data on muon capture in hydrogen. We show that this rather disturbing anomaly is solved by employing effective transition operators. This finding is also very important in studies of the scalar coupling of the weak charged current of leptons and hadrons. 1. T. Siiskonen, J. Suhonen, and M. Hjorth-Jensen, Phys. Rev. C, in press 2. T. Siiskonen, J. Suhonen, and M. Hjorth-Jensen, submitted to J. Phys. G 7.3 Hadron properties in the medium: Nuclear structure aspect The last decade, through measurements done at NIKHEF in Holland, at MAMI in Mainz and now TJNAF in the USA, has been marked by a remarkable interplay between many-body theory and high precision electron scattering experiments. The nuclear response has been measured at high momentum and into the continuum. The partial occupancy of mean-field orbits obtained from these experiments is one of the cleanest signatures of nucleon-nucleon correlations. To understand such correlations forms a very active field in nuclear physics and to elucidate the short-distance structure of nuclei will be a topic of special interest in the future. Nuclear structure studies of hyperons provide also a new input to the nuclear many-body problem. Hyperons are baryons with a strangeness content. Studies of nuclei with a hyperon content, so-called hypernuclei, allow for both a study of weak interaction and to gain information in order to constrain the strong interaction between hyperons and nucleons. 7.3.1 Hyperon properties in finite nuclei using realistic YN interac- tions M. Hjorth-Jensen, A. Pollsa, A. Ramosa and I. Vidanaa a Departament d'Estructura y Constituentes de la Materia, Universitat de Barcelona Single-particle energies of A and S hyperons in several nuclei are obtained from the relevant self-energies. The latter are constructed within the framework of a perturbative many-body approach employing present realistic hyperon-nucleon interactions such as the models of the Jiilich and Nijmegen groups. The effects of the non-locality and energy-dependence of the self-energy on the bound states are investigated. It is also shown that, although the single-particle hyperon energies are well reproduced by local Woods-Saxon hyperon-nucleus potentials, the wave functions from the non-local self- energy are far more extended. Implications of this behavior on the mesonic weak decay of A hypernuclei are discussed. 1. I. Vidana, A. Polls, A. Ramos and M. Hjorth-Jensen, Nucl. Phys. A644 (1998) 201-220 2. I. Vidana, A. Polls, A. Ramos and M. Hjorth-Jensen, Weak decays in ^He, in preparation for Phys. Lett. B 7.4 Nuclear astrophysics and dense matter studies Our research in nuclear astrophysics has dealt mainly with theoretical studies of the equation of state for dense nuclear matter, determination of properties of neutron stars such as the total mass, radius, phase transitions and the composition of matter in the interior of a neutron star and the interesting topic of superfluidity in neutron stars. Neutron stars have a rich structure, where the outermost layers are rather similar to terrestrial matter. With increasing depth in the star, and thereby increasing density, nuclei become more and more neutron rich until at a density of about one thousandth of nuclear matter saturation density, nuclei reach the so-called neutron drip line. At higher densities nuclei coexist with a neutron liquid and they eventually dissolve just below nuclear matter saturation density. Important issues in neutron star studies deal with theoretical determinations of the equation of state up to densities several times nuclear matter saturation density. At high densities matter consists of interacting baryons (neutron, protons and possibly hyperons and other particles) and/or quarks in beta-equilibrium with leptons. In addi- tion, bose condensates of pions or kaons may be present. The central problem is then to develop reliable techniques for calculating properties of strongly correlated matter. This is crucial since 95% of the matter in a neutron star is located in regions with densi- ties above nuclear matter saturation density. Other topics are the tota! proton/neutron ratio and neutrino emission processes. The latter processes are also of great importance since the loss of heat through neutrino emissions and the measurement of surface tem- peratures of a neutron star provides a way of probing neutrino processes in the star. Since neutrino emissions are very sensitive to the composition of dense matter, such measurement may therefore provide information on the interior of neutron stars. 7.4.1 Phase transitions in rotating neutron stars M. Hjorth-Jensen and H. Heiselberga a Nordita, Copenhagen As rotating neutron stars slow down, the pressure and the density in the core region increase due to the decreasing centrifugal forces and phase transitions may occur in the center. We extract the analytic behavior near the critical angular velocity QQ, where the phase transitions occur in the center of a neutron star, and calculate the moment of inertia, angular velocity, rate of slow down, braking index, etc. For a first order phase transition these quantities have a characteristic behavior, e.g., the braking index 1/ 2 diverges as ~ (Qo — ^)~ ' . Observational consequences for first, second and other phase transitions are discussed. 1. H. Heiselberg and M. Hjorth-Jensen, Phys. Rev. Lett. 80 (1998) 5485-5488 89 7.4.2 Phase transitions in neutron stars and maximum masses M. Hjorth-Jensen and H. Heiselberga a Nordita, Copenhagen Using the most recent realistic effective interactions for nuclear matter with a smooth extrapolation to high densities including causality, we constrain the equation of state and calculate maximum masses of rotating neutron stars. First and second order phase transitions to, e.g., quark matter at high densities are included. If neutron star masses of 2.3M® from quasi-periodic oscillation in low mass X-ray binaries are confirmed, a soft equation of state as well as strong phase transitions can be excluded in neutron star cores. 1. H. Heiselberg and M. Hjorth-Jensen, Astrophys. Journal Letters in press 7.4.3 Phases of dense matter in neutron stars M. Hjorth-Jensen and H. Heiselberga a Nordita, Copenhagen Recent equations of state for dense nuclear matter are discussed with possible phase transitions arising in neutron stars such as pion, kaon and hyperon condensation, su- perfluidity and quark matter. Specifically, we treat the nuclear to quark matter phase transition, the possible mixed phase and its structure. A number of numerical cal- culations of rotating neutron stars with and without phase transitions are given and compared to observed masses, radii, temperatures and glitches. 1. H. Heiselberg and M. Hjorth-Jensen, Physics Reports, in press 7.4.4 Structure of /3-stable neutron star matter with hyperons L. Engvik, M. Hjorth-Jensen, A. Polls", A. Ramos" and I. Vidaiiaa a Departament d'Estructura y Constituentes de la Materia, Universitat de Barcelona We present results from many-body calculations for /3-stable neutron star matter with nucleonic and hyperonic degrees of freedom, employing the most recent parametrization of the baryon-baryon interaction of the Nijmegen group. The structure of /3-stable matter is presented up to total baryonic densities of 1.2 fm~3. Implications for neutron stars are discussed. 1. I. Vidana, A. Polls, A. Ramos, L. Engvik and M. Hjorth-Jensen, submitted to Phys. Rev. Letters 7.4.5 Neutrino emissivities in neutron stars F.V. De Blasio, 0. Elgar0y, L. Engvik, M. Hjorth-Jensen, A.E.L. Dieperink0 and A. Sedrakiana 90 a KVI. Groningen, Holland The thermal evolution of a neutron star may provide information about the interiors of the star, and in recent years much effort has been devoted in measuring neutron star temperatures, especially with the Einstein Observatory and ROSAT. The main cooling mechanism in the early life of a neutron star is believed to go through neutrino emissions in the core of the neutron star. The most powerful energy losses are expected to be given by the so-called direct URCA mechanism n->p+e + T7e, p + e ->• n + ue. (7.1) However, in the outer cores of massive neutron stars and in the cores of not too massive neutron stars (M < 1.3- 1.4M©), the direct URCA process is allowed at densities where the momentum conservation kF < kF + kp is fulfilled. This happens only at densities p several times the nuclear matter saturation density po = 0.16 fm~3. Thus, for long time the dominant processes for neutrino emission have been the so- called modified URCA processes first discussed by Chiu and Salpeter, in which the two reactions + e^n + n + ve, (7.2) occur in equal numbers. These reactions are just the usual processes of neutron /?-decay and electron capture on protons of Eq. (7.1), with the addition of an extra bystander neutron. They produce neutrino-antineutrino pairs, but leave the composition of matter constant on average. Eq. (7.2) is referred to as the neutron branch of the modified URCA process. Another'branch is the proton branch n + p-+ p + p + e + 17e, p + p + e -+n + p + ve. (7.3) Similarly, at higher densities, if muons are present we may also have processes where the muon and the muon neutrinos (u^ and v^) replace the electron and the electron neutrinos (Fe and ue) in the above equations. In addition one also has the possibility of neutrino-pair bremsstrahlung, processes with baryons more massive than the nucleon participating, such as isobars or hyperons or neutrino emission from more exotic states like pion and kaon condensates or quark matter. The aim of this project is to reanalyze the various neutrino emissivities discussed above accounting for the short-range part in a self-consistent way. 7.4.6 Vortex lines in the crust superfluid of a neutron star F. V. De Blasio and 0. Elgar0y The interior of a neutron star constitutes the only known physical system close to infinite nuclear and neutron matter. Most efforts to describe this system have mainly focused on the role of nucleonic interactions at zero and finite temperature, while less attention has been paid to a microscopic description of excited states of the system, including superfluid vortex lines induced by the rotational state of the star. On the other hand, there are important observables of astrophysical relevance that might be influenced by the presence of vortex lines. A mutual check of the nuclear many body physics and of the theory of neutron star interiors comes from the study of pulsar 91 glitches, sudden increases in the spinning frequency of the crust of a pulsar, followed by a slower tendency to conditions close to the original ones. It is thought that glitches and postglitch relaxation represent a direct manifestation of the presence of superfiuid vortices in the interior of the star, the triggering event being an unbalance between the hydrodynamical forces acting on the vortex and the force of interaction of the vortex with the nuclei present in the crust (pinning force). There have been quite large uncertainties regarding the value of the pinning force, leaving room for quite opposite views about the validity of the vortex pinning model. One source of uncertainty is related to the value of the pairing energy gap in uniform neutron matter, a quantity strongly dependent on the value of the neutron particle-particle matrix element near the Fermi surface. A second problem is due to the very approximate way of treating vortex states in neutron matter. Usually a vortex is seen as a cylinder of normal matter (the vortex core) of radius equal to the BCS coherence length fo « 0.8h2kp/2mA where kp is the Fermi wavenumber, m is the neutron mass and A is the neutron pairing gap. The pinning of the vortex to the nucleus, also treated as a classical object, is due to the loss of superfluidity that occurs when the two objects superimpose. In our project we study the structure of a vortex in superfiuid neutron matter using a microscopic, fully quantum-mechanical approach, using the Bogoliubov-de Gennes equations which have been successfully employed to study vortices in type II super- conductors and more in general non-homogeneous superconductivity. One of our main goals is to calculate the pinning forces on vortex lines in a neutron star crust. 1. F. V. De Blasio and 0. Elgar0y, Phys. Rev. Lett. 82 (1999) 1815-1818 7.5 Superfluidity in infinite matter Superfluidity and superconductivity of matter in neutron stars is expected to have a number of consequences directly related to observation. Among processes that will be affected is the emission of neutrinos. Neutrino emission from e.g. various URCA processes is expected to be the dominant cooling mechanism in neutron stars less than 105 —106 years old. Typically, proton superconductivity reduces considerably the energy losses in so-called modified URCA processes and may have important consequences for the cooling of young neutron stars. Another possible manifestation of superfiuid phenomena in neutron stars is glitches in rotational frequencies observed in a number of pulsars. Moreover, the estimation of superfluid gaps and studies of pairing are not only important issues in neutron star matter, but also in the rapidly developing field of neutron-rich systems such as heavy nuclei close to the neutron drip line or the study of light halo nuclei. Therefore, theoretical studies of pairing in neutron-rich assemblies form currently a central issue in nuclear physics and nuclear astrophysics. 7.5.1 Nucleon-nucleon phase shifts and pairing in neutron matter and nuclear matter 0. Elgaroy, M. Hjorth-Jensen We consider 1SQ pairing in infinite neutron matter and nuclear matter and show that in the lowest order approximation, where the pairing interaction is taken to be the bare 92 nucleon-nucleon (NN) interaction in the 1SQ channel, the pairing interaction and the energy gap can be determined directly from the 1So phase shifts. This is due to the almost separable character of the nucleon-nucleon interaction in this partial wave. Since the most recent NN interactions are charge-dependent, we have to solve coupled gap equations for proton-proton, neutron-neutron, and neutron-proton pairing in nuclear matter. The results are, however, found to be close to those obtained with charge- independent potentials. 1. 0. Elgar0y and M. Hjorth-Jensen, Phys. Rev. C57 (1998) 1174-1177 7.5.2 Minimal relativity and 3S'i-3J9i pairing in symmetric nuclear matter 0. Elgar0y, L. Engvik, M. Hjorth-Jensen, E. Osnes After presenting solutions of the coupled, non-relativistic 3Si-3Di gap equations for neutron-proton pairing in symmetric nuclear matter, we proceed to estimate relativistic effects by solving the same gap equations modified according to minimal relativity and using single-particle energies from a Dirac-Brueckner-Hartree-Fock calculation. We find that the relativistic effects decrease the value of the gap at the saturation density kp — 1.36 fm"1 considerably, in conformity with the lack of evidence for strong neutron- proton pairing in finite nuclei. 1. 0. Elgaroy, L. Engvik, M. Hjorth-Jensen and E. Osnes, Phys. Rev. C57 (1998) R1069-R1072 3 3 7.5.3 P2- F2 pairing in neutron matter with modern nucleon-nucleon potentials 0. Elgar0ya, L. Engvik, M. Hjorth-Jensen, M. Baldoa and H.-J. Schulzea a INFN and Department of Physics, University of Catania 3 3 We present results for the P2- F2 pairing gap in neutron matter with several realistic nucleon-nucleon potentials, in particular with recent, phase-shift equivalent potentials. We find that their predictions for the gap cannot be trusted at densities above p ss 1.7poi where po is the saturation density for symmetric nuclear matter. In order to make predictions above that density, potential models which fit the nucleon-nucleon phase shifts up to about 1 GeV are required. 1. M. Baldo, 0. Elgar0y, L. Engvik, M. Hjorth-Jensen and H.-J. Schulze, Phys. Rev. C58 (1998) 1921-1928 93 7.6 Nucleon-nucleon interactions and nuclear many-body theory 7.6.1 Phaseshift equivalent NN potentials and the deuteron M. Hjorth-Jensen, R. Machleidt0, H. Muther6, A. Pollsc a Department of Physics, University of Idaho, USA 6 Institut fur Theoretische Physik, Universitat Tubingen, c Departament d'Estructuray Constituentes de la Materia, Universitat de Barcelona Different modern phase shift equivalent NN potentials are tested by evaluating the par- tial wave decomposition of the kinetic and potential energy of the deuteron. Significant differences are found, which are traced back to the matrix elements of the potentials at medium and large momenta. The influence of the localization of the one-pion-exchange contribution to these potentials is analyzed in detail. 1. A. Polls, R. Machleidt, H. Muther and M. Hjorth-Jensen, Phys. Lett. B432 (1998) 1-7 7.6.2 Perturbative many-body approaches M. Hjorth-Jensen Various perturbative and non-perturbative many-body techniques are discussed in this work. Especially, I focus on the summation of so-called Parquet diagrams with emphasis on applications to finite nuclei. Here, the subset of two-body Parquet diagrams will be discussed. Comparisons are made with exact results from shell-model calculations. 1. M. Hjorth-Jensen, Advances in Many-Body theories, Vol. 2, in press 7.7 Project: The Foundation of Quantum Physics 7.7.1 Description of vacuum in quantum field theory K. Gjotterud, Harald Andas, J. Bergli and A. Haug The description of vacuum in quantum field theory has been studied resulting in Joakim Bergli's Cand.scient. thesis "The vacuum in quantum field theory. A challenge to present day physics"'. Special attention was given to the problems arising form the zero point energy associated with each mode of the field and to the inconsistencies arising in con- nection with the resulting infinite energy density of the vacuum. The Lorentz invariance of the vacuum energy density was discussed and it it was shown that the only finite spectral energy density preserving Lorentz invariance is the spectral density identically equal to zero , which corresponds to a normal ordering of the operators. It is not pos- sible to have an electromagnetic vacuum that has a finite energy density and at the same time is Lorentz invariant. 94 We have also studied the possibility that quantum theory results as a consequence of symmetry is continued. The study is based on the work by Aage Bohr and Ole Ulfbeck: "Primary manifestation of symmetry. Origin of quantal indeterminacy" Rev. Mod. Phys. Vol. 67 1995 pp 1-35. 95 Chapter 8 Energy Physics 8.0.2 Solar heating and cooling systems at the Sun-Lab A.G. Imenes, L. Henden, M. Meir and J. Rekstad The solar energy laboratory, abbreviated the Sun-Lab, is located in front of the Physics Department building. This is a small test facility for solar heating and radiative cooling systems. . :4^;:. ***$£ ; ; 1 •* #: Figure 8.1: The Sun-Lab is a test facility for solar heating and cooling systems. The Sun-Lab is a standard wooden house of 20 m2, built in accordance with Norwegian building traditions. The orientation of the house is south-west, with a surface asimuth angle of 7=+18°. The tilt angle of the roof is 32°. The house is equipped with a thermal solar collector system, a cooling system, two heat stores and a floor heating system. The Sun-Lab is shown in Fig. 8.1. The heating system consist of an array of 4 solar fiat plate collectors faced towards the south, with an aperture area of 5.3 m2. The cooling system, placed on the north facing part of the roof, consist of an array of 8 modified solar flat plate collectors, with an aperture area of 10.8 m2. 96 The structure of the solar collector is shown in Fig. 8.2. It consists of a black absorber plate in Noryl PX507 plastics, and a transparent cover sheet in PC-plastics. The heat carrier fluid is water, which is being pumped to the top of the collector and driven by gravity trickles down through the absorber to remove heat. By filling the absorber with ceramic granulates, a capillary effect is achieved which ensures optimum thermal contact between the water and the hot absorber surface [1]. The cooling panels have a similar construction to the solar panels, but slightly modified in that the cover sheet has been removed to enhance the emissive cooling capacity. By circulating water through the cooling panels during night time, temperature loss is brought forward by radiation and convection. The hot panel surface will be a strong emitter of infrared radiation and exchange heat with the cold air layers higher up in the atmosphere. Figure 8.2: The structure of the solar fiat plate collector. The heated, or cooled, water is collected in stores inside the house. The setup allows switching between a 1000 liter aluminium store and a smaller 300 liter hot water tank. Comparative experiments have shown the performance of the solar heating system to increase when heat exchangers are avoided [2], [3]. The water from the solar loop is thus directly coupled to the heat store. Both the cooling and heating systems can be connected to the two storages. Testing different storage volumes and flow rates of the circulating water, enables a charac- terization of the system parameters and their influence on the overall performance. The purpose is to accomplish a physical description and understanding of the heat exchange processes, as well as a determination of the optimum operation conditions for the system. A low temperature floor heating system with water as a heat carrier has been installed. Water is circulating through cross-linked polyethylene tubes integrated in the floor construction. The concept is based on a combined system for domestic hot water and low temperature space heating. The floor heating system is directly connected to the 1000 liter store. Auxiliary heating is supplied when the irradiation is not sufficient to cover the load. 97 An electronic control unit starts and stops the system when heat gain or loss is achieved respectively. The controller ensures a safely operating system by draining the system when approaching temperatures close to boiling or freezing limits. The system is open to atmospheric pressure [4]. Several experiments are presently being carried out at the Sun-Lab. The main fields include measurements of collector performance, studies of radiative cooling panels, a combined system for domestic hot water and low temperature space heating, a combined thermal and photovoltaic solar collector, and development of an energy measuring system. References [1] Technical data sheet - Solar collector, SolarNor AS, 2/1998 [2] S. Furbo, Ydelser af solvarmeanlegg under laboratoriemaessige forhold, SR-98-01, IBE, Danmarks Tekniske Universitet (1998) [3] J. Rekstad et al., Kombinerte soloppvarmingsanlegg for varmtvann og romoppvarm- ing - malinger av energiutbytte, Rapport, SolarNor AS (1999) [4] Effektiv og energisparende temperaturstyring for vannbarne gulvvarmesystemer og solvarmeanlegg, SolarNor AS, July 1998 8.0.3 Efficiency measurements of a solar thermal heating system A.G. Imenes, L. Henden, M. Meir and J. Rekstad A typical set of data during operation of the solar heating system is shown in Fig.8.3. A datalogger keeps record of the system parameters, including solar irradiation /, a temperature rise in the heat store Tsiore, ambient temperature Tambient, nd indoor temperature TindOOr- The storage volume was in this case 300 liter and the flow rate 720 1/h. 1 1 1 r- i | i t —i j 1 1 1 1 1 3000 in - 2500 >^ ; 3D _ Tflidoor) — •—-—.= 2000 Temperatire ~—~^ (pegr.C) ^ 1500 10 1000 . . — D 500 ¥ i i —,—; 6999:1DSD1I} 6999:12mm 6993:UmO) 6999:16fflm Figure 8.3: 1.03.1999: Solar heating of the 300 liter store, flow rate 720 1/h. The system efficiency rjs is calculated as the rate of stored heat in the system to the received energy from the sun; Wstored (8.1) Qsun 98 Calculations are done in accordance with the calorimetric method. This implies deter- mining Qstored by means of the temperature rise in the heat store during a short time interval At,-, during which steady temperature conditions and constant irradiation can be approximated. The calculated efficiency curve corresponding to the dataset of the 1st of March 1999 is shown in Fig.8.4. The efficiency is plotted as a function of the parameter [TstOre - Tambient\l'I', thereby assuring a result unaffected by the varying irradiation levels. The efficiency is propor- tional to the temperature difference between the heat store (and hence the temperature of the solar panel), and the ambient temperature. The heat loss from the collector sur- face is moderate at low temperature differences, this give a high efficiency left in figure. As the temperature difference increases, the efficiency decreases at an almost constant rate. Efficiency 0.04 0.05 0.03 T(storei-T(ambient)/I Figure 8.4: Efficiency curve for the heating experiment. 1.03.1999. Scattering of the data points are expected due to wind effects, angle of incidence vari- ation and higher order temperature dependence of collector parameters. In addition, the datalogger has a sampling interval of about 2 minutes. In partly cloudy weather, rapidly changing solar radiation will not be adequately represented by the recorded values, giving considerable uncertainties connected to the received solar energy. The Hottel-Whillier equation states that thermal efficiency is a linearly decreasing function of [TstOre - Tambient\/I, [^ store J- ambientJ V = (8.2) where FR is the collector heat removal factor, r)0 the maximal efficiency, reduced by optical losses (?7o=roQ'o)i ar>d UL the collector heat loss coefficient [1]. When rj is plotted against [Tiager — Tambient]/1 > the intersection with the Y-axis is given by FRTJO, and FRUL is the slope of the curve. By applying a linear curve fit to the efficiency data, as shown in Fig.8.4, these values can be determined. According to international standards, collector performance tests are clone by measur- ing instant flow rate m. inlet temperature T(, and outlet temperature To of the fluid circulating through the collector. The efficiency is then determined by mC[T - o (8.3) I A* 99 where C is the heat capacity of the fluid and Ac is the collector aperture area [2]. Exact measurements of the inlet- and outlet temperatures are demanding, and thus often performed in test facilities where sun- and wind simulators assure steady conditions during the measuring period. The collectors are irradiated at a normal incidence angle, while inlet and outlet are held at fixed temperatures. The calorimetric method introduce a convenient tool to avoid these procedures. However, in order to compare the efficiency measurements performed at the Sun-Lab with international standards, a few corrections have to be done. Firstly, the incidence angle will vary throughout the day as the sun moves across the sky. Due to the channel structure of the cover sheet and increasing optical thickness, the transmission of sunlight is reduced as the incidence angle increases from 0 to 90°. The solar irradiation recorded by the angle-independent pyranometer should therefore be reduced by a factor equal to the decrease in transmission of the cover sheet at the given incidence angle, / - r(0) where / is the recorded irradiation, Icorr the corrected value, r{9) the transmission of the coversheet at an incidence angle 6, and r(0) the transmission at normal incidence angle. The energy received from the sun during a time interval At{ is then Qsun,i = ICOrr,iAcAti (8.5) Secondly, as the circulating water heats up during day, the solar collector will experi- ence the same temperature increase as the water storage in order to stay in thermal equilibrium with its interior. The heat capacity of the solar collector is 33,5 kJ/m2K, implying that during every degree of temperature rise in the heat store, an additional 33,5 kj per square meter collector area has been stored in the system. This energy must be added to the stored energy in the water tank as a compensation for unsteady temperature conditions, Q stored = Qw + Qp (8.6) where Qw refers to the stored energy in the water storage, and Qp refers to stored energy in the panel. The system efficiency is then determined by eqn.(8.7); + cpATWii TKt- ( > where the subscripts w and p refer to water and panel, respectively. It should be noted that this efficiency is a system efficiency, rather than a collector efficiency. Fig.8.5 displays the efficiency points before and after corrections are applied. The effect of the corrections is to increase the system efficiency. The heat carrier's ability to remove heat will depend on the flow rate. Fig.8.6 displays the system efficiency at four different flow rates for the 300 liter store volume. The results show an increased maximal efficiency at the higher flow rates. In addition, the curves indicate that the flow rate should be reduced when approaching temperatures in the range of high thermal losses, in order to stay at optimum performance. The latter 100 Efficiency 002 004 006 038 0.1 0.1: T(stCT6] - T(ambioni) / i Figure 8.5: Efficiency plot displaying both corrected and uncorrected values, 1.March 1999. Efficiency . . , I i . , I i i , I • . . I , i , I 0 0.02 0.04 0.06 008 0.1 0.12 0 14 TJ'stae! - Tjambient) /1 Figure 8.6: System efficiency for the 300 liter store at four different flow rates. result is not as expected, and a new theory explaining the phenomenon is presently being investigated. References [1] J.A. Duffie and W.A. Beckman, Solar Engineering of Thermal Processes, 2nd ed., USA, 1991 [2] J. Twidell and T. Weir, Renewable Energy Resources, United Kingdom, 1996 8.0.4 Calibration of the measuring equipment A.G. Imenes and J. Rekstad The work at the Sun-Lab has included calibration and control of the parameters mea- sured during experiments. The calorimetric method involves determination of the temperature increase in the heat storage. In order to approximate steady conditions, time intervals of about 10-20 minutes are chosen for the determination of one point on the efficiency curve. This implies measuring quite small temperature differences, requiring reliable temperature 101 readings. However, the temperature sensors. 10K thermistors, seem to be influenced by the humid environment in the water store. Their resistance have changed over time, giving differing temperature readings. This has called for a thorough calibration of all sensors involved. One of the encountered problems has been drift of sensor values, even after calibration. In an attempt to find a permanent solution of the problem, the sensors have been placed inside a closed glass tube, filled with a highly conductive powder and sealed with silicon. Regular control procedures will reveal any new incidences of defect sensors and guarantee the validity of the calibration. Wind strength is a most important parameter when describing the system performance. A 6-cup anemometer has been mounted on the roof of the Sun-Lab, recording the local wind conditions during heating and cooling experiments. Based upon 3 series of measurements performed in a wind tunnel at the Agricultural University of Norway, the anemometer has been given a calibration function converting the recorded signals to units of meter per second. Fig.8.7 shows a) the anemometer mounted at the center of the wind tunnel and b)the wind calibration results. Wind (m/s) 500 1000 1500 2000 2500 3000 3500 400C Display value Figure 8.7: Calibration of the anemometer, a) The anemometer placed in front of the wind tunnel. b)A graphical presentation of the calibration results. 8.0.5 Data acquisition system for a building integrated solar heating system Martin Hansen and J. Rekstad Our earth is continuously hit by solar radiation and a large amount of solar energy. The solar energy incident on a. horizontal surfa.ce in South-Norway is 1000 kWh/m2 a year. This energy can be utilized by solar thermal heating systems. The solar heating system [1] actively transfers solar energy to the interior of the build- ing for domestic hot water a.nd space heating. The solar heating system consists of a flat plate collector [2], a heat store, circulation pumps for solar and floor loop and a temperature controller. The electronic controller is reading out different temperatures and the intensity of the solar radiation. The operation of the solar heating system is controlled by these parameters in a way that the system's efficiency is optimized. 102 TEMPERATUR- F0LER OVERL0PSR0R "PAFYLL1NGSROR IED KRAN TUR OVERTEMP. SHUNT VARMELAGER Figure 8.8: Combined solar system for domestic hot water and space heating [SolarNor as]. The present work is to design a data acquisition system based upon a microprocessor. The acquisition system will be able to store the data that are sampled every minute during a whole year. The system will also be able to calculate the hourly consumed (exploited) solar energy on the basis of the measured parameters. This means that the user of a solar heating system gets information about the functionality of the system short time after startup. The first approach was to study solar thermal heating systems, methods for calculating the energy demand to domestic hot water and floor heating, and methods for calculating the solar contribution. An usual way to calculate the energy output is to measure the flow of energy in a heating system [3]. This method is often used to calculate the solar gain by measuring the flow of energy transfered from the heat store into the house. When the amount of energy consumed during a certain period and the amount of energy transfered from other sources are known, the solar contribution to heating can be calculated. There is an usual way to calculate the need of energy for domestic heating. In the present study we estimate the heating demand in a building by means of the so-called "response function". To the first order this function is proportional to the difference between the ambient and the indoor temperature (eq. 8.8). Q6r(AT) = kA{AT - &TC) = kAAT - konst. (8.8) ~ 1 inndoor 1 ambient 103 kA: &-4-value to a. specific building. ATC: Constant value for a specific building. The response function method requires few input parameters, which are basically avail- able from the controller of a solar heating system. The installation of measuring equip- ment is minimized. The next step in the project was to make a program for data analysis based upon the response function. The program is written in the computer language C. And finally, to present a data acquisition system design and to test the program. References [1] B. Bjerke. S.L. Andersen, H. Arnesen, I. Espe, 0. Herbj'rnsen, M. Mehlen, J. Rek- stad, J. Wikne, A. Amundsen, Soltun, Dept. of Physics Report 90-07. University ofOslo(1990) [2] J. Rekstad, L. Henden, M. Meir, E. Cipera, G.J Kooij, New Plastic Solar Collector, Dept. of Physics Report 95-12. University of Oslo(1995) [3] 0. Aschehoug, B.T. Larsen, T. Ormhaug, E. R0dahl, F. Salvesen, Energimalinger i bygninger, anvisninger for mating og rapportering; Aktive solvarmesystemer, NTNF, 1981 8.0.6 Simulation of active thermal solar collector systems G.M. Haugen and F. Ingebretsen In order to design an optimal solar collector system, it is necessary to simulate the outcome on a computer, by varying and optimizing the system parameters. During the last year, a simulation program has been developed for this purpose. This is a new and improved version of an earlier simulation code [1] and programmed in Java language. Therefore this program can be used on any computer platform which supports Java 1.2. From the user's energy demands, system design and weather parameters the program will calculate the solar gain of the system. It can also simulate the effect which a change in one or several system parameters has on the solar fraction. A one year's calculation with one hour steps takes 3-4 seconds on a 200 MHz Pentium PC, which is faster than other simulation tools (for instance TRNSYS and Tsol). The figure below shows an example of a screenshot, the graphical user interface after a calculation of the solar fraction with varying collector tilting angle. References [1] F. Ingebretsen, Computer simulation of the SOLNOR solar heating system (Pro- ceedings, North Sun, 1992) 351-355 8.0.7 Transformation of the solar insolation values on sloped surfaces to horizontal surface values G.M. Haugen and F. Ingebretsen In connection to the SOLIS project, measurements of the solar insolation on surfaces 104 tagre tt J Figure 8.9: The graphical user interface after a calculation of the solar fraction with varying collector slope. tilted 45° has been measured and accumulated at over 70 schools in Norway and other countries in Northern Europe. Most data and insolation maps are based on measure- ments against horizontal surfaces.Therefore it is useful to transform the SOLIS data to horizontal insolation values. During the last 1/2 years a transformation model and computer program has been developed. The model is based on the assumption that the insolation consists of three different components which can be treated independently of each other, namely beam, diffuse and reflected [1]. The diffuse component is sep- arated into four different components according to their direction on the sky dome - the isotropic, the zenith, the circumsolar and the horizon component [2]. The diffuse component is directly determined by the zenith angle of the sun and the amount of extraterrestrial solar insolation that reaches the surface. Different models have been tested [1] [2]. The results are compared to solar irradiation recordings simultaneously measured on surfaces tilted 45° and horizontal. References [1] J. A. Duffle and W. A. Beckman, Solar Engineering of Thermal Processes (Wiley, New York, 1991) 919 [2] A. Skartveit and J. A. Olseth, Modelling slope irradiance at high latitudes (Solar Energy, 36, 1983) 333-344 8.0.8 A Combined Thermal and Photovoltaic Solar Energy Collector B. Sandnes and J. Rekstad A solar energy heat collector was combined with photovoltaic cells to form one single hybrid energy generating unit. The combined thermal and photovoltaic system pro- duces the two types of energy required by most consumers: low temperature heat 105 Figure 8.10: The angular insolation distribution. The diffuse zenith component only ap- pears when the atmospheric transmission is low; the horizon and circumsolar components disappear for low atmospheric transmission. and electricity. The thermal system removes absorbed heat from the collector, thereby cooling the photovoltaic cells. Increased solar cell power output is thus achieved, since photovoltaic conversion efficiency is a linearly decreasing function of temperature [1]. A combined thermal and photovoltaic test collector was successfully constructed by pasting single-crystal silicon cells on a black flat-plate solar heat absorber. This unit was tested experimentally in a series of field trials to assess it's thermal and pho- tovoltaic performance, in addition to the coupling between the two energy systems. Thermal efficiency measurements for three different collector configurations were com- pared; black absorber plate (a), photovoltaic cells pasted on absorber to form a com- bined thermal/photovoltaic absorber (c), and the thermal/photovoltaic absorber with an additional cover glass (g). Current-voltage characteristics were recorded for series and parallel connection of the photovoltaic cells, over a range of temperatures. The experimental results revealed a and c as efficient absorbers of sunlight, but with high heat loss at elevated operating temperatures. (Typical for unglazed collectors [2]). The addition of the cover glass (g) reduced the heat loss, but also introduced reflection from the glass surface. Efficiency curves are plotted in Figure 8.11. A reduced solar energy absorption in c compared to a was attributed to a lower optical absorption in the photovoltaic cells compared to the black absorber plate, and also to the heat transfer resistance introduced in the cell/absorber interface. When electrical power is extracted from the photovoltaic unit, the incident solar energy available for the thermal system is reduced correspondingly. The photovoltaic conversion efficiency is, because of it's temperature dependence, gov- erned to some extent by the operating temperature of the thermal system. The cell temperature was shown to be strongly correlated to the inlet fluid temperature, and also a function of thermal efficiency, irradiation and collector properties (different for the a, c and g configurations). A mathematical model for the combined system was developed by modifying stan- dard thermal collector equations to include the effects of the additional photovoltaic cells [3]. The model simulated the temperature development of the system, and the 106 0.90- I I I 1 I I 0.70 o> c 0.30-- 0.10- 0.00 0.01 0.02 0.03 0.04 (T. - (0Cm2/W) Figure 8.11: Thermal efficiency curves for the different collector configurations: black absorber plate (a), solar cells covering absorber (c) and c with additional cover glass (g). Averaged values for intersection and slope. performance of both the thermal and photovoltaic units. The model simulation results were in agreement with the experimental data. References [1] A. L. Fahrenbruch and R. H. Bube, Fundamentals of Solar Cells (Academic Press, Inc., New York, 1983) [2] J. A. Duffie and W. A. Beckman, Solar Engineering of Thermal Processes (Wiley, New York, 1991) [3] T. Bergene and O. M. L0vvik, Solar Energy 55 (1995) 453 8.0.9 Stand alone solar system for domestic hot water iieating K. Vasanthakumar and J. Rekstad A stand alone solar system operates without connections to a external power source. In the present system a solar cell is used to power the pump which circulates water in the solar loop. We investigate a system which consist of a solar collector array, photovoltaic solar cells, d.c. circulation pump, voltage controller and heat store. The electric power produced by the photovoltaic array operates the dc pump. In the present study the main task is to design a control unit which governs the power generated by the photovoltaic cells. The performance of the thermal system will be investigated by measuring the heat delivered to the store as a function of the ambient temperature and the solar radiation. 107 8.0.10 Regulation and Energy Monitoring in Low Temperature Heat- ing Systems M. Meir, J. Rekstad, B. Bjerke A new principle for temperature regulation and energy monitoring in low tem- perature heating systems has been developed at the University of Oslo. One of the performance tests was carried out in a one-family house [1] during the winter season 98/99. In conventional heating systems the temperature regulation is based on indoor thermo- stat control. In low temperature heating systems as hydronic floor heating, the large heat capacity of the floor mass would cause an unacceptable long response time for indoor temperature regulation. The temperature control principle investigated is based on the dependency between space heating demand and ambient temperature. The controller calculates the energy demand for the coming, constant time interval At, dependent on the ambient tempera- ture and the inlet temperature to the floor circuit (see fig. 8.12). The required energy is delivered in terms of an "energy pulse" within the time top,j. In practice the controller determines the operation time t0P); of the circulation pump for the time interval Att-. TEMPERATURE CONTROLLER ownp £tstns 1 n At, Figure 8.12: Principle for temperature regulation by sequential pump operation. The con- troller calculates the operation the time of the floor circulation pump from the ambient temperature and the supply temperature to the floor heating system. The controller unit is directly regulating the floor circulation pump or a motor driven shunt valve. The heat delivered to each single floor circuit is controlled by manual mixing valves at the manifold. One aim of the experiments was to investigate the indoor temperature stabilisation by a control principle which is based on sequential pump operation. A motivation for developing this control strategy was the possibility to easily perform energy monitoring. In buildings in which several users are connected to a common heat- ing central the monitoring of individual energy use is necessary for energy conscious consumption behavior. In low temperature heating systems, energy monitoring to af- fordable cost and limited technical installations represents a technical challenge. The sequential pump operation by the controller introduces a straight forward possibility for energy monitoring. As the energy is delivered in pulses, the total operation time of the circulation pump is a measure for the energy delivered to the floor heating system (see fig. 8.13). The precision for energy monitoring was in these first experiments 10- 108 15% which is already better than conventional instruments in use, e.g. evaporators or temperature - flow rate monitoring. 12.01.-2.02.93 v' •20 ' : • ..:-...... ,-, i 10-1-1W90XWKI 18-1-1999000:00 21-1-19S9ttOO:«J 24-1-19SS0.00:CO 2T-1-1939 DCO00 30-MS9SCV.CC:CO 2-2-iSS9CflOC (dd-mm-yy hh:mm:ss) Figure 8.13: Measurements from 12.01.-2.02.99 at a test house in L0renskog. The controller stabilizes the indoor temperature while outdoor and inlet water temperature to the floor circuit show fluctuations. References [1] J. Rekstad, S. Bjerke, F. Ingebretsen, Rapport om solenergifors0k ved fors0kshus i L0renskog, Report Series University of Oslo, Report 81-05, 1981 8.0.11 A study of heat distributors in wooden floor heating systems M. Meir, J. Rekstad, L. Henden, A. G. Imenes Two different heat distributors for floor heating systems in suspended wooden floors have been evaluated [1]. One distributor (A) is a new product with a specially extruded aluminium profile for 20 mm cross-linked polyethylene pipes. The other distributor (B) is a standard product based on a roll-formed aluminium plate. The performance of the distributors was compared by testing them in parallel integrated in the floor heating system at the Sol-Lab. The heat transfer coefficient represents the heat conductivity from the liquid inside the PEX-pipe to the plate of the distributor in a certain distance from the plate center. The heat transfer coefficient for distributor (A) is 3.7±0.7 W/(mK) and for distributor (B) 2.0±0.4 W/(mK) in a distance of 7 cm to the center. Distributor (A) has a ca. 80 % higher heat transfer coefficient. References [1] M. Meir, J. Rekstad, L. Henden. A.G. Imenes, A study of two different heat distribution plates in wooden floor heating systems, internal test report, University of Oslo, Dept. of Physics, 1998 109 At 40 . , L. ,7(supply) ^ I \ ,T(relurn) 35 i- V/. \ t r - T (alum, distributor) (A) |s 30t S- S. r T (floor surface) * 25 20 T (indoor) 15 6959:21-.00:00 6959:22:00:00 6959:23:00:00 6980.00.00:00 time (day#: hh: rnm: ss) Figure 8.14: Heat transfer in a suspended wooden floor construction. Illustrated are the supply and return temperature to the floor circuit, the temperature of the aluminium distributor (here only type A). To the top the operation time t0Pin of the pump within the constant time interval Atn is shown (see also fig. 8.12). 110 Chapter 9 Seminars Date: 19.02 J. M. Hansteen: Refleksjoner om kvantemekanisk "entanglement" Universitetet i Bergen og muligheten for kvantisk teleportasjon 26.02 S. Furbo: Aktiviteter vedr0rende solvarmeanlegg ved Danmark Tekniske Universitet Danmark Tekniske Universitet 24.04 P. J. Ellis: Effective Lagrangian with Broken Scale and University of Minnesota Chiral Symmetry 29.04 F. D. Blasio: Topics on the Physics of Neutron Star Crusts Universitetet i Oslo 12.08 S. Siem: Eksperimenter ved Argonne Argonne National Laboratory 28.08 A. Rej: Planck Scale Cutoffs, Causality and SN Bose School for Path Integral Duality Mathematics and Mathematical Science Calcutta 04.12 T. Lonnroth: Alfa-spedning mot silisium Abo Akademi - modellinterpretasjoner? Ill Chapter 10 Committees, Conferences and Visits 10.1 Committees and Various Activities External committees and activities only are listed. 0. Elgar0y: Referee for Phys. Rev. C M. Guttormsen: Member of the Board of the Nuclear Physics Committee of the Norwe- gian Physical Society. Referee for Nuclear Physics and Zeitschrift fur Physik. M. Hjorth-Jensen: Referee for Physical Review C, D, Physical Review Letters, Nuclear Physics A, Physics Letters B and Journal of Physics G. Norwegian Link-member for the European Centre for Theoretical Stud- ies in Nuclear Physics and Related Areas (ECT*). F. Ingebretsen: Deputy Member of the University Board (Det Akademiske kollegium). Editor of the periodical "Fra Fysikkens Verden". Member of the advisory committee for the "SOLIS" project: Solar en- ergy in the school. Member of the European PANS (Public Awareness of Nuclear Science) Committee G. Lovhoiden: Member of the LHC ALICE Collaboration Board. Referee for Nuclear Physics and Physica Scripta. Member of the Norwegian Academy of Science and Letters. Member of the Nuclear Physics European Collaboration Committee (NuPECC) under the European Science Foundation. 112 E. Osnes: Member of the Senate (Det Akademiske Kollegium) of the University of Oslo. Chairman of the Norwegian Board of Technology (Teknologiradet). Norwegian Scientific Delegate to the CERN Council. Member of the Executive Board of the Norwegian Academy of Science and Letters/Chairman of the Class of Mathematics and Science. Co-editor (with T. T. S. Kuo) of International Review of Nuclear Physics, published by World Scientific Publishing Company. Referee for Nuclear Physics, Physics Letters B, Physica Scripta, Phys- ical Review Cand Physical Review Letters. Member of the Norwegian Academy of Science and Letters, and of the Royal Norwegian Society of Sciences and Letters. J. Rekstad Referee for Nuclear Physics, Physical Review, Physical Review Letters and Physics Letters. Managing director of SOLARNOR A/S. Chairman of the Board of Directors of SOLNOR AB (Sweden). Member of the Board of Directors of IFE. Member of Research Council Program Committee for Fundamental Energy Research. Member of the program planning committee for energy research, The Norwegain Research Council. Member of the Board of the Norwegian Solar Energy Society. Member of The Norwegian Academy of Science. P. O. Tj0m: Member of the NORDBALL Committee. Referee for Nuclear Physics. S.W. 0degaxd Member of the organizing committee for the Annual Meeting of the Norwegian Physical Society, Oslo, June 1998 10.2 Conferences The Section of Nuclear Physics and Energy Physics participated in the Annual Meeting of the Norwegian Physical Society, Oslo, June 1998, where E. Melby, L. Bergholt, A. Schiller, A. Bjerve, L. Engvik, 0. Elgar0y and S.W. 0degard gave talks at the same meeting. L. Bergholt gave a talk at "The 9th Nordic Meeting on Nuclear Physics", Jyvaskyla, Finland, August 4-8, 1998. 0. Elgaroy gave a talk and participated in the "International Workshop on Mean-field methods in low-energy nuclear structure", ECT*, Trento, Italy, June 26 to June 6, 1997, and participated in the "NorFA post-graduate course on Weak Processes in Nuclei", Jyvaskyla, Finland, Jan. 12-23, 1998, 113 M. Guttormsen participated in "The 9th Nordic Meeting on Nuclear Physics, Jyvaskyla', Finland, Aug. 4-8, 1998. M. Hjorth-Jensen organized a workshop (with B. Mottelson) on "Shell-Model Methods and Effective Interactions", 17-20 december 1998, Nordita, Copenhagen, (Denmark). Talks were given at the conferences/workshops "Mean-field methods in nuclear structure", ECT*, Trento, 23 march-4 april 1998 (Italy), and "Microscopic approaches to the structure" of light nuclei, University of Manch- ester, Manchester, 8-13 June 1998 (England), in addition, Institute Colloquia were given at KVI, Groningen, January 6 1998, (Holland) and Dept. of Physics, University of Jyvaskyla, October 1 1998, (Finland). G. L0vh0iden participated in "The international symposium on Strangeness in Quark Matter", Padua, Italy, 20-24 July 1998. E. Melby participated in the "NorFA post-graduate course on Weak Processes in Nuclei", Jyvaskyla, Finland, Jan. 12-23, 1998, and "The 9th Nordic Meeting on Nuclear Physics, Jyvaskyla", Finland, Aug. 4-8, 1998. Eivind-Atle Olsen held a talk at "The Scanditronix Cyclotron User's Meeting" JRC- Ispra, May 13-15 1998, J. Rekstad gave a talk at "The 9th Nordic Meeting on Nuclear Physics Jyvaskyla", Finland, August 4-8, 1998, and gave a talk at the "5th European Conference in Solar Architecture and Urban Planning", May 25-30, 1998, Bonn, Germany, and gave an invited talk at the Norwegian Government conference at "EXPO '98", Lisbon, July 22, 1998, and gave an invited presentation for the Government-appointed committee for energy policy planning, and gave an invited talk at the "Conference for Teachers in the University and Technical High School Sector", NTNU, Trondheim, Januay 20, 1998. A. Schiller participated in the "NorFA post-graduate course on Weak Processes in Nuclei", Jyvaskyla, Finland, Jan. 12-23, 1998, and in "The 9th Nordic Meeting on Nuclear Physics, Jyvaskyla", Finland, Aug. 4-8, 1998. S. Siem gave a talk at the "The 9th Nordic Meeting on Nuclear Physics", Jyvaskyla, Finland. Aug. 4-8, 1998, and gave a talk at "The Fall meeting of the APS division of nuclear physics", Santa Fe, New Mexico, USA 28-31 October 1998, and participated in "ENAM 98, 2nd International conference on exotic nuclei and atomic masses", Bellaire, Michigan, USA 23-27 June 1998 P. O. Tjom participated in the "NBI-LUND Experimental Group meeting and The Last Supper at TAL", Ris0, Danmark. Dec. 14-15, 1998. Jon Wikne held a talk at "The Scanditronix Cyclotron User's Meeting" JRC-Ispra, May 13-15 1998, 114 S.W. 0degard gave a talk at "The 9th Nordic Meeting on Nuclear Physics", Jyvaskyla, Finland, August 4-8, 1998, and participated in: the "XVI NUCLEAR PHYSICS DIVISIONAL CONFERENCE, Structure of Nuclei under Extreme Conditions", Padova, Italy, March 31 - April 4, 1998, the "NBI-LUND Experimental Group meeting and The Last Supper at TAL", Ris0, Danmark, Dec. 14-15, 1998, and the "NorFA post-graduate course on Weak Processes in Nuclei", Jyvaskyla, Finland, Jan. 12-23, 1998. 115 Chapter 11 Theses, Publications and Talks 11.1 Theses 11.1.1 Cand. Scient. Theses Jarl Inge Holmen: En studie av 163Dy(3He,o;) - reaksjonen basert pa statistisk 7- multiplisitet. A Study of the l63Dy(3He,a) - reaction based on statistical 7-multiplicity. 11.1.2 Dr. Scient. Theses Ole Martin L0vvik: Hydrogen on a Palladium Surface: Potential Energy Surfaces and Quantum Dynamical Calculations Are Haugan: Development of Methods for Obtaining Position Image and Chemical Binding Information from Flow Experiments of Porous Media Lisbeth Bergholt: Studies of Nonstatistical Features of Nuclei in the Rare Earth Region 11.2 Scientific Publications and Proceedings 11.2.1 Nuclear Physics and Instrumentation 0. Elgaresy, L. Engvik, M. Hjorth-Jensen and E. Osnes Minimal relativity and 3Si3.Di pairing in symmetric nuclear matter Phys. Rev. C57 (1998) 1069 1072 A. Holt, T. Engeland, M. Hjorth-Jensen and E. Osnes Effective Interactions and Shell-Model Studies in Heavy Tin Isotopes Nuclear Physics A634 (1998) 41-56 116 0. Elgaroy and M. Hjorth-Jensen Nucleon-nucleon phase shifts and pairing in neutron matter and nuclear matter Phys. Rev. C57 (1998) 1174 1177 M. Baldo, 0. Elgar0y, L. Engvik, M. Hjorth-Jensen and H.J. Schulze 3P23jp2 pairing in neutron matter with modern nucleon-nucleon potentials Phys. Rev. C58 (1998) 1921 1928 J. Suhonen and J. Toivanen, T. Engeland, M. Hjorth-Jensen, A. Holt and E. Osnes Study of odd-mass N=82 isotones: comparison of the microscopic quasiparticle-phonon model and the nuclear shell model Nuclear Physics A628 (1998) 41-61 F.V. De Blasio and G. Lazzari Nuclear Effects on Superfluid Neutron Star Matter Modern Phys. Lett., A13 (1998) 1383 F.V. De Blasio Crustal Impurities and the Internal Temperature of a Neutron Star Crust Monthly Not. Roy. Astr. Soc. 299 (1998) 118 F.V. De Blasio and G. Lazzari Lattice Defects in the Crust of a Neutron Star Nucl.Phys. A633 (1998) 391 - 395 H. Heiselberg and M. Hjorth-Jensen Phase transitions in rotating neutron stars Physical Review Letters 80 (1998) 5485-5488 A. Polls, H. Miither, R. Machleidt and M. Hjorth-Jensen Phaseshift equivalent NN potentials and the deuteron Physics Letters B432 (1998) 1-7 R. Grzywacz, R. Beraud, C. Borcea, A. Ensallem, M. Glogowski, H. Grawe, D. Guillemaud-Mueller, M. Hjorth-Jensen, M. Houry, M. Lewitowicz, A.C. Mueller, A. Nowak, A. Plochocki, M. Pfiitzner, K. Rykaczewski, M.G. Saint-Laurent, J.E. Sauvestre, M. Schaefer, O. Sorlin, J. Szerypo, W. Trinder, S. Viteritti, J. Winfield New island of ^zs-isomers in neutron-rich nuclei around the Z=28 and N=40 shell closures Physical Review Letters 81 (1998) 766-769 1. Vidanya. A. Polls. A. Ramos and M. Hjorth-Jensen Hyperon properties in finite nuclei using realistic YN interactions Nuclear Physics A644 (1998) 201-220 117 G. White, N.J. Stone, J. Rikovska, Y. Koh, J. Copell, T. Giles, I.S. Towner, B.A. Brown, S. Ohya, B. Fogelberg, L. Jacobsson, P. Rahkila and M. Hjorth-Jensen Ground State Magnetic Dipole Moment of 13oI Nucl.Phys. Axxx (1998) 277 - 288. 0. Elgar0y and M. Hjorth-Jensen Pairing in Infinite Matter and Finite Nuclei In proceedings of Condensed Matter theories 21, Luso, Portugal, September 21-27 1997, Condensed Matter Theories 13 (1998) 221 H. Heiselberg and M. Hjorth-Jensen Phase transitions in neutron stars In proceedings of the Nuclear Astrophysics workshop, Hirschegg, Germany, January 12-16 1998, p. 38-43 E. Andersen et al.(WA97 Collaboration) (K. Fanebust, H. Helstrup, A.K. Holme, G. L0vh0iden, T.F. Thorsteinsen, T.S. Tveter) A, E! and Q production in Pb-Pb collisions at 158 A GeV/c Nucl. Phys. A638 (1998)115c K. Gulda et al.(J. Aas, E. Hageb0 P. Hoff, G. L0vh0iden, K. Nyb0 T.F. Thorsteinsen) Quadrupole Deformed and Octupole Collective Bands in 228Ra Nucl. Phys. A636 (1998)28 E. Andersen et al. (WA97 Collaboration) (H. Bakke, K. Fanebust, H. Helstrup, A.K. Holme, B.T.H. Knudsen, G. L0vh0iden, T.F. Thorsteinsen, T.S. Tveter Enhancement of central A, E and Q yields in Pb-Pb collisions at 158 AGeV/c Phys. Lett. B433 (1998) 209 R. Caliandro et al. (WA97 Collaboration) (E. Andersen, H. Bakke, K. Fanebust, H. Helstrup, A.K. Holme, B.T.H. Knudsen, G. L0vh0iden, T.F. Thorsteinsen, T.S. Tveter A,H and f2 production in Pb-Pb and p-Pb interactions at 158 AGeV/c Proc. XXXIIIth Rencontres de Moriond-QCD and high energy hadronic interactions, Les Arcs 1800, France, March 21-28, 1998 R. Caliandro et al. (WA97 Collaboration) (E. Andersen, H. Bakke, K. Fanebust, H. Helstrup, A.K. Holme, B.T.H. Knudsen, G. L0vh0iden, T.F. Thorsteinsen, T.S. Tveter A, E and Q Production at Central Rapidity in Pb-Pb and p-Pb Collisions at 158 AGeV/c Proc. Strangeness in Quark Matter, Padova, Italy, July 20-24, 1998 R. Lietava et al. (VVA97 Collaboration) (E. Andersen, H. Bakke, K. Fanebust. H. Helstrup, A.K. Holme, B.T.H. Knudsen, G. L0vh0iden, T.F.Thorsteinsen, T.S. Tveter) K° and Negative Particle Production at Central Rapidity in Pb-Pb and p-Pb Collisions at 158 AGeV/c Proc. Strangeness in Quark Matter, Padova, Italy, July 20-24, 1998 118 T. Virgili et al.(WA97 Collaboration) (E. Andersen, H. Bakke, K. Fanebust, H. Helstrup, A.K. Holme, B.T.H. Knudsen, G. Løvhøiden, T.F. Thorsteinsen, T.S. Tveter) Strange Baryon Production in p-Pb Collisions at 158 AGeV/c: A Comparison with the VENUS Model Proc. Strangeness in Quark Matter, Padova, Italy, July 20-24, 1998 S. Törmänen, G.B. Hagemann, A. Harsmann, M. Bergström, R.A. Bark, B. Herskind, G. Sletten, S.W. Ødegård, P.O. Tjørn, A. Görgen, H. Hübel, B. Aengenvoort, U. van Severen, C. Fahlander, D. Napoli, S. Lenzi, C. Petrache, C. Ur, H.J. J ensen, H. Ryde, A. Bracco, S. Frattini, R. Chapman, D.M. Cullen, and S.L. King High Spin Studies of 164Lu Using EUROBALL II NuovoCimento 111A (1998) 685-690 R.A. Bark, H. Carlsson, S.J. Freeman, G.B. Hagemann, F. Ingebretsen, H.J. Jensen, T. Lönnroth, M.J. Piiparinen, I. Ragnarsson, H. Ryde, H. Schnack-Pedersen, P.B. Semmes, P.O. Tjørn Band structures and proton-neutron interactions in 174Ta Nuclear Physics A 630 (1998) 603-630 B. Cederwall, T. Back, R. Bark, S. Törmänen, S.W. Ødegård, S.L. King, J. Simp- son, R.D. Page, N. Amzal, D.M. Cullen, P.T. Greenlees, A Keenan, R. Lemmon, J.F.C. Cocks, K. Helariutta, P.M. Jones, R Julin, S. Juutinen, H. Hettunen, H. Kankaanpää, P. Kuusiniemi, M. Leino, M. Muikku, P. Rahkila, A. Savelius. J. Uusitalo, P. Magierski, R. Wyss Collective rotational - vibrational transition in the very neutron-deficient nuclei m,i72pt Phys. Lett. B443 (1998) 69-76 Spin Myon Collaboration (SMC) and A. Schiller Measurement of Proton and Nitrogen Polarization in Ammonia and a Test of Equal Spin Temperature Nucl. Instr. Meth. A 419(1998)60-82 A. Schiller and the SMC collaboration Polarised Quark Distributions in the Nucléon from Semi-Inclusive Spin Asymmetries Phys. Lett. B420(1998) 180190 A. Schiller and the SMC collaboration Spin asymmetries ,4i and structure functions g\ of the proton and the deuteron from polarized high energy muon scattering Phys. Rev. D58(1998) Article Number 112001 A. Schiller and the SMC collaboration Next-to-leading order QCD analysis of the spin structure function g\ Phys. Rev. D58(1998) Article Number 112002 119 A. Schiller, L. Bergholt, M. Guttormsen, E. Melby, S. Messelt, E.A. Olsen, J. Rekstad, S. Siem, T.S. Tveter J.C. Wikne First test measurements of the SIRI AE-E particle telescope array Proc. VI Int. School Seminar on Heavy Ion Physics, Dubna (Russia), September 2227, (1997), 728-730 P. T. Greenlees, N. Amzal, P. A. Butler, K. J. Cann, J. F. C. Cocks, D. Hawcroft, G. D. Jones, R. D. Page, A. Andreev, T. Enqvist, P. Fallon, B. Gall, M. Guttormsen, K. Helariutta, F. Hoellinger, P. M. Jones, R. Julin, S. Juutinen, H. Kankaanpää, H. Kettunen, P. Kuusiniemi, M. Leino, S. Messelt, M. Muikku, A. Savelius, A. Schiller, S. Siem, W. H. Trzaska, T. Tveter, J. Uusitalo First observation of excited states in 226U J. Phys. G24(1998)L63-L70 E. Melby, L. Bergholt, M. Guttormsen, S. Messelt, J. Rekstad, A. Schiller, S. Siem The influence of the A'-quantum number in the 7-decay of 166Er Proc. 9th Nordic Meeting on Nucl. Phys. Jyväskylä, Finland, August 4 - 8, (1998) 11.2.2 Energy J. Eriksen Development of a Data Acquisition and Control System for a Small-Scale PV-H? System - First Design Phase Hydrogen Energy Progress XII (1998)195-204 L. Henden, M. Meir, J. Rekstad Thermal Performance of a solar collector made of plastic materials Proceedings ISES-Europe Solar Congress-EuroSun '98, Portoroz, Slovenia, Sept. 14-17, (1998) M. Meir, J. Rekstad, L. Henden, B. Bjerke Building integrated solar systems Gleisdorf Solar '98, Austria, Sept. 9-12, (1998) 90-96 11.2.3 Radiation Research D. Banks, B. Frengstad, Aa. K. Midtgård, J. R. Krog, T. Strand The Chemistry of Norwegian Groundwaters: I The distribution of radon, Major and Minor Elements in 1604 Crystaline Bedrock Groundwaters The Science of the Total Environment, 222 (1-2), p. 71-91, 1998. D. Banks, B. Frengstad, Aa.K. Midtgård, J.R. Krog and T. Strand The Chemistry of Norwegian Groundwaters: II. The chemistry of 72 groudwaters from Quaternary sedimentary aquifers. 120 The Science of the Total Environment, 222 (1-2): p. 93-105, 1998. Aa.K. Midtgard, B. Frengstad, D. Banks, J.R. Krogh, T. Strand, U. Siewers and B. Lind Drinking Water from Crystaline Bedrock Aquifers - not just H2O. Mineralogical Society Bulletin 121, p. 9-16, 1998. G. Morland, T. Strand, L. Furuhaug, H. Skarphagen and D. Banks Radon concentrations in groundwater from Quaternary sedimentary aquifers in relation to underlying bedrock geology. Ground Water 36 (1), p. 143-146, 1998. T. Strand and B. Lind B, Thommesen G. Naturlig radioaktivitet i husholdningsvann fra borebr0nner i Norge Norsk veterinaertidsskrift 110 (19), p. 662-665, 1998. 11.2.4 Other Fields of Research F.V. De Blasio Mirroring of Environmental Colored Noise in Species Extinction Statistics Phys. Rev. E58 (1988) 6877 F.V. De Blasio Diversity Variation in Isolated Environments: Species-area Effects from a Stochastic Model Ecological Modelling, 111 (1998) 93. 11.3 Reports and Abstracts 11.3.1 General F. Ingebretsen Section for Nuclear and Energy Physics: Annual Report Department of Physics Report, UiO/PHYS/98-08 (1998) 11.3.2 Nuclear Physics and Instrumentation M. Guttormsen Eventbuilder for the RTPC 8067 Single Board Computer Department of Physics Report, UiO/PHYS/98-08 (1998) Schiller, L. Bergholt, M. Guttormsen, E. Melby, S. Messelt, E. A. Olsen, J. Rekstad, S. Rezazadeh, S. Siem, T. S. Tveter, P. H. Vreim, J. Wikne 121 Recent Upgrades and Performance of the CACTUS Detector Array Department of Physics Report, UiO/PHYS/98-02 (1998) E.Andersen et al.(WA97 Collaboration) (H. Bakke, K. Fanebust, H. Helstrup, A.K. Holme, B.T.H. Knudsen.G. Løvhøiden, T.F. Thorsteinsen, T.S. Tveter Enhancement of central A,E and Q, yields in Pb-Pb collisions at 158 AGeV/c CERN-PPE/98-64 B. Cederwall, T. Back, J. Cederkall, A. Johnson, D.R. LaFosse, M. Devlin, J. Elson, F. Lerma, D.G. Sarantites, R.M. Clark, I.Y. Lee, A.O. Macchiavelli, R.W. Macleod, R. Bark, S. Tormanen, S.W. Ødegård, S.L. King, J. Simpson, R.D. Page, N. Amza 1, D.M. Cullen, P.T. Greenlees, A. Keenan, R. Lemmon, J.F.C. Cocks, K. Helariutta, P.M. Jones, R. Julin, S. Juutinen, H. Hettunen, H. Kankaanp, P. Kuusiniemi, M. Leino, M. Muikko, A. Savelius, J. Uusitalo Coexistence in proton rich A-90 and A-170 nuclei Abstracts of papers of the American Chemical Society Vol. 215, 2. Apr. 1998, p 93-NUCL 11.3.3 Energy O.M. Løvik Hydrogen on a palladium surface - Potential energy surfaces and quantum dynamical calculations PhD -tesis, Dept. of Physics, University of Oslo, May (1998) M. Meir, J. Rekstad, L. Henden, A.G. Imenes A study of two different heat distribution plates in wooden floor heating systems Internal test report, University of Oslo, Dept. of Physics, Aug. (1998) R. Aspesæther Olsen Direct subsurface absorption of hydrogen on Pd (111) - Potential energy surfaces and quantum dynamical calculations PhD thesis, University of Amsterdam, Nov. (1998) 11.3.4 Radiation Research D. Banks, B. Frengstad, J. R. Krog, Aa. K. Midtgård, T. Strand, B. Lind Kjemisk kvalitet av grunnvann i fast fjell i Norge. NGU-rapport 98.058, 177 p. , Norges geologiske undersøkelse, 1998. D. Banks, B. Frengstad, J. R. Krog, Aa. K. Midtgård, T. Strand, B. Lind Kjemisk kvalitet av grunnvann fra løsmasser i Norge NGU-rapport 98.089, 96 p. , Norges geologiske undersøkelse, 1998. 122 D. Banks, Aa. K. Midtgård, B. Frengstad, J. R. Krog, T. Strand and B. Lind Utjevningsbassengs innvirkning på radoninnholdet i grunnvann fra fast fjell. NGU-rapport 98.097, 16 sider, Norges geologiske undersøkelse, 1998. C. Reimann, M. Äyräs, V. Chekushin, I. Bogartyrev, R. Boyd, P. de. Caritat, R. Dutter, T. E. Finne, J. H. Halleraker jr, 0. Jæger, G. Kashulina, O. Lehto, H. Niskavaara, V. Pavlov, M. L. Räisänen, T. Strand, T. Volden Environmental Ceochemical Atlas of the Central Barents Region, Geological Survey of Norway, 1998, ISBN 82-7385-176-1, 745 p. 11.4 Scientific Talks and Conference Reports 11.4.1 Nuclear Physics and Instrumentation L. Bergholt, M. Guttormsen, E. Melby, J. Rekstad, A. Schiller and S. Siem A'-dependence in the 7-decay after Neutron Capture The 9'th Nordic Meeting on Nucl. Phys. Jyväskylä, Finland, August 4-8, (1998) H. Bakke et al. (WA97 Collaboration) (E. Andersen, K. Fanebust, H. Helstrup, A.K. Holme, B.T.H. Knudsen, G. Løvhøiden, T.F. Thorsteinsen, T.S. Tveter) Analysis of A and A Production in Pb-Pb Collisions at 160 AGeV/c Proc.Strangeness in Quark matter, July 20-24, 1998, Padova, Italy S.W. Ødegård, P.O. Tjørn, S. Törmänen, G.B. Hagemann, A. Harsmann, M. Bergström, R.A. Bark, B. Herskind, G. Sletten, A. Görgen, H. Hübel, B. Aengen- voort, U. van Severen, C. Fahlander, D. Napoli, S. Lenzi, C. Petrache, C. Ur, H.J. J ensen, H. Ryde, A. Bracco, S. Frattini, R. Chapman, D.M. Cullen, and S.L. King Multiple Triaxial SD Bands in 163-164Lu Studied with EUROBALL 9th Nordic Meeting on Nuclear Physics, Jyväskylä , Finland, August 4.-8. 1998 S. Törmänen, G.B. Hagemann, A. Harsmann, M. Bergström, R.A. Bark, B. Herskind, G. Sletten, S.W. Ødegård, P.O. Tjørn, A. Görgen, H. Hübel, J. Domscheit, B. Aengenvoort, U. van Severen, C. Fahlander, D. Napoli, S. Luizi, C. Petrache, C. Ur, H.J. Jensen, H. Ryde, A. Bracco, S. Frattini, R. Chapman, D.M. Cullen, and S.L. King Multiple Triaxial SD Bands in 163'164Lu Studied with EUROBALL Gatlinburg, Tennessee, USA, August 10-15, 1998 S. Törmänen, G.B. Hagemann, A. Harsmann, M. Bergström, R.A. Bark, B. Herskind, G. Sletten, S.W. Ødegård, P.O. Tjørn, A. Görgen, H. Hübel, B. Aengenvoort, U. van Severen, C. Fahlander, D. Napoli, S. Lenzi, C. Petrache, C. Ur, H.J. J ensen, H. Ryde, A. Bracco, S. Frattini, R. Chapman, D.M. Cullen, and S.L. King High" Spin Studies of 164Lu Using EUROBALL XVI Nuclear physics divisional conference, Structure of Nuclei under Extreme Condi- tions, March 31 - April 4, 1998 - Padova, Italy 123 T. Døssing, M. Matsuo, B. Herskind, G.B. Hagemann, A. Harsmann, S. Törmänen, S.W. Ødegård, E. Vigezzi and R.A. Broglia Interacting Excited Rotational Bands Topical Conference on Giant Resonances, Varenna, Italy, May 11.-16. 1998 M.P. Carpenter, R.V.F. Janssens, T.L. Khoo, D. Seweryniak, A.A. Sonzogni, I. Ahmad, L.T. Brown, C.N. Davids, G. Hackman, T. Lauritsen, C.J. Lister, P. Reiter, S. Siem, J. Uusitalo, I. Wiedenhover, P.J. Woods, J.A. Cizewski, W. Reviol, L.L. Riedinger , S.M. Fischer, J.J. Ressler, W.B. Walters, D.G. Sarantites, S. Heany. Study of excited states in 167Ir: Probing states beyond the proton drip line Talk at APS conf. New Mexico Oct. 28-31 (1998) and Bull. Am. Phys. Soc. vol.43 no.6 Oct. (1998) P. Reiter, T.L. Khoo, C.J. Lister, I. Ahmad, M.P. Carpenter, C.N. Davids, W.H. Henning, R.V.F. Janssens, T. Lauritsen, D. Seweryniak, S. Siem, J. Uusitalo, I. Wiedenhover, J.A. Cizewski, K.Y. Ding, N. Fotiades, P.A. Butler, N. Amzal, A.J. Chewter, P .T. Greenless, R.D. Herzberg, G. Jones, K. Vetter, W. Korten, M. Leino. Structure and formation mechanism of the transfermium isotope 254No Talk at APS conf. New Mexico Oct. 28-31 (1998) and Bull. Am. Phys. Soc. vol.43 no.6 Oct. (1998) I. Wiedenhover, G. Hackman, R.V. F. Janssens, I. Ahmad, J.P. Greene, H. Amro, M.P. Carpenter, D.T. Nisius, P. Reiter, T. Lauritsen, C.J. Lister, T.L. Khoo, S. Siem, J. Cizewski, D. Seweryniak, J. Uusitalo, A.O. Macchiavelli, P. Chowdhury, E.H. Seabur y, D. Cline, C.Y. Wu. Unsafe coulomb excitation of 240Pu and 244Pu Talk at APS conf. New Mexico Oct. 28-31 (1998) and Bull. Am. Phys. Soc. vol.43 no.6 Oct. (1998) S. Siem, P. Reiter, T.L. Khoo, M.P. Carpenter, T. Lauritsen, I. Ahmad, H. Amro, I. Calderin, S. Fischer, D. Gassmann, G. Hackman, R.V. F. Janssens, D.T. Nisius, T. Dossing, U. Garg, B. Kharraja, F. Hannachi, A. Korichi, A. Lopez-Martens, C. Schuck, I .Y. Lee, A.O. Macchiavelli, E.F. Moore The decay out of a superdeformed band in 191Hg Talk at APS conf. New Mexico Oct. 28-31 (1998) and Bull. Am. Phys. Soc. vol.43 no.6 Oct. (1998) L. Bergholt, M. Guttormsen, E. Melby, J. Rekstad, A. Schiller and S. Siem Er atomkjernen kaotisk? Fysikermøtet, Oslo, 10.-12. juni (1998) T. Engeland, M. Hjorth-Jensen, A. Holt and E. Osnes Realistic Effective Interactions and Large-Scale Nuclear Structure Calculation 6th International Spring Seminar on Nuclear Physics, S. Agata sui Due Golfi, Italy, 18-22 Mav 1998 124 E. Osnes Effective Interactions for the Shell Model Invited Talk at the NORDITA Mini-Meeting on "Shell Model Related Problems", Copenhagen, December 17-19 (1998) E. Osnes Realistic Effective Interactions and Large-Scale Nuclear Structure Calculations Invited Talk at the Institute for Nuclear Theory, University of Washington, Seattle, USA, July 31 (1998) T. Engeland Large Shell Model Calculations with Effective Interactions from Meson Theory Invitet talk at the NORDITA Minimeeting on Shell Model Related Problems, Copen- hagen Dec. 17 - 19 (1998) T. Engeland Large Scale Shell Model Calculations Invitet talk at the international workshop on Mean-field methods in low-energy nuclear structure, ECT*, Trento, March 23 - April 4 (1998) F.V. De Blasio Structure Vortices in Infinite Matter Talk at the international workshop on mean-field methods in low-energy nuclear structure, ECT*, Trento, March 24 - April 4 (1998) 0. Elgar0y Pairing in infinite matter International Workshop on MeanField Methods in Low Energy Nuclear Structure, ECT*, Trento, Italia, March 23-April 4 (1998) 0. Elgar0y Superfluiditet i n0ytronstjerner Arsmotet i Norsk Fysisk Selskap, Universitetet i Oslo, Norge, 10.12. juni (1998) L. Engvik Equation of state for dense matter Arsmotet i Norsk Fysisk Selskap, Universitetet i Oslo, Norge, 10.12. juni (1998) M. Hjorth-Jensen From the Nucleon-Nucleon interaction to finite nuclei Invited talk at the workshop on Mean-field methods in nuclear structure, ECT*, Trento, March 23- April 4 1998 (Italy) M. Hjorth-Jensen Perturbative many-body approaches Invited talk at the workshop on Microscopic approaches to the structure of light nuclei, University of Manchester. Manchester, June 8-13 (1998) (England) 125 E. Melby. L. Bergholt, M. Guttormsen, S. Messelt, J. Rekstad, A. Schiller, S. Siem Hva foregår på Syklotronlaboratoriet? Fysikermøtet, Oslo 10.- 12. juni, (1998) S.W. Ødegård, P.O. Tjørn, S. Törmänen, G.B. Hagemann, A. Harsmann, M. Bergström, R.A. Bark, B. Herskind, G. Sletten, A. Görgen, H. Hübel, B. Aengen- voort, U. van Severen, C. Fahlander, D. Napoli, S. Lenzi, C. Petrache, C. Ur, H.J. J ensen, H. Ryde, A. Bracco, S. Frattini, R. Chapman, D.M. Cullen, and S.L. King Triaxial Superdeformasjon i 164Lu Fysikermøtet, Oslo, Juni 98 S. Siem Decay out of a superdeformed band in 191Hg Nordic meeting, Jyväskylä, Finland, 3-8 august (1998) A. Schiller, L. Bergholt, M. Guttormsen, E. Melby, S. Messelt, J. Rekstad, S. Siem Alternative Measurements of Level Density in 162Dy Book of Abstracts, Fysikermøtet, Oslo (Norway), June 10-12, (1998) A. Schiller, L. Bergholt, M. Guttormsen, E. Melby, S. Messelt, J. Rekstad, S. Siem New Measurements of Level Density in 162Dy Book of Abstracts of the 9th Nordic Meeting on Nucl. Phys, Jyväskylä (Finland), August 4-8, (1998) K. Gjötterud Perspektivendringer i fysikken de siste hundre år og i dag Forelesning i serien Grunnlagsproblemer i fysikk UiB Fysisk institutt/Senter for vitskapsteori 18.03 1998 K. Gjötterud Utvikler fysikken seg til en ironisk vitenskap? Forelesning i Vitenskapsteoretisk Forum NTNU 06.10.1998 M. Hjorth-Jensen Many-body problems in nuclear astrophysics Talk at KVI, Groningen, January 6 (1998) M. Hjorth-Jensen Effective interactions and the nuclear shell model Talk at the Dept. of Physics, University of Jyväskylä, October 1 (1998) A.K.Holme A, E and Q production in Pb-Pb collisions at 158 AGeV/c EP-seminar, CERN, Geneva, January 26,1998 126 S. Siem Level densities in rare earth nuclei Talk at Argonne National Lab. Febr. 20 (1998) 11.4.2 Energy J. Rekstad, L. Henden, M. Meir, B. Bjerke Building integrated solar systems Talk and paper at the 5th European Conference in Solar Architecture and Urban Planning, May 25-30, (1998) J. Rekstad Bruk av solenergi i Norge - Potensiale og praktiske l0sninger Faglsererkonferanse om EN0K-undervisning, NTNU, Trondheim, 20 Januar (1998) 11.4.3 Radiation A. Birovljev, T. Strand, A. Heiberg Radon concentrations in Norwegian kindergartens. YUNSC '98, Sept. 28 - October 1, 1998, Belgrade, Yugoslavia T. Strand Uncertainties in assessment of indoor radon exposure. 1998 Society for Risk Analysis Annual Conference, Risk Analysis: Opening the Process, Paris, France, October 11-14, 1998. T. Rams0y, T. Bj0nstad, G. C. Christensen, D. 0. Eriksen, I. Lysebo and T. Strand Methods for monitoring of NORM on equipment offshore and onshore. Proceedings of the Second Int. Symp. on the Treatment of Naturally Occurring Radioactive Materials. Krefeld, Germany, November, 10-13, 1998, p. 35-37. I. Lysebo and T. Strand NORM in Oil Production - Activity Levels and Occupational Doses. Proceedings of the Second Int. Symp. on the Treatment of Naturally Occurring Radioactive Materials. Krefeld, Germany, November, 10-13, 1998, p. 114-119. T. Strand and I. Lysebo NORM in Oil and Gas Production . Waste Management and Disposal Alternatives Proceedings of the Second Int. Symp. on the Treatment of Naturally Occurring Radioactive Materials, Krefeld, Germany, November, 10-13, 1998, p. 137-141. 127 11.5 Popular Science K. Gjötterud Grunnleggende problemer i kvantefysikk. Referat fra Nordisk symposium i Rosendal, juni 1997 Artikkel i Fra Fysikkens Verden Nr. 1 - 1998 K. Gjötterud Ryktene om at naturvitenskapen har nådd veis ende. Diskusjon av John Horgans bok "The End of Science" Forelesning Faglig-pedagogisk dag UiO 05.01.1998 K. Gjötterud Perspekti vend ringer i fysikken de siste hundre år og i dag - fra skråplantil superstrenger Forelesning Fysisk institutt UiO Bjørngilde 06.02.1998 K. Gjötterud John Horgans bok "The End of Science" i lys av dagens perspektiver i fysikk Forelesning Mandagsseminar Biologisk institutt - avdeling for generell fysiologi 16.02.1998 K. Gjötterud Fysikk og naturforståelse Forelesning for elever ved Asker kunstskole 18.02.1998 K. Gjötterud Vitenskapelige perspektiver på fysikkens forskningsfront Samtale med Olav Høgetveit i programmet "Møtested" NRK TO 23.09.1998 K. Gjötterud, J. Sivertsen Vitenskapen ved veis ende? John Horgans bok Intervju ved Erik Tunstad NRKP2 WOK 27.01.1997 G. Løvhøiden ALICE-ultrarelativistiske kjernekollisjoner-et studium av det fysiske vakuum Fysikkforeningen,UiO,Oslo, October 12, 1998 J. Rekstad, B. Bjerke, M. Meir Combined solar heating systems CADDET-Renewable Energy newsletter, issue 3/98, (1998) 21-23 J. Rekstad Cost-efficient solar energy technology from Norway Presentation at EXPO '98 Lisbon, July 22, (1998) (manuscript 8 pages) 128 J. Rekstad Energifleksibilitet på sluttbrukertrinnet i energikjeclen -Teknologiske muligheter og virkninger på energibruk Foredrag for regjeringens energiutvalg. Oslo, 17 mars (1998) J. Rekstad Solvarme eller varmepumpe - eller kombinasjon? InternaL report, SolarNor AS, Sept. (1998) T. Strand Risiko for lungekreft ved innendørs radoneksponering. Miljø og helse nr. 1/98, p. 6-8, 1998. V. Valen, O. Soldal and T. Strand Radon i løsmasser. Kommunalteknikk, 7-1998 A. Birovljev, T. Strand and G. Thommesen Kartlegging av radon i boliger. Strålevernhefte nr. 17, Norwegian Radiation Protection Authority, October 1998, 18 P- 11.5.1 Books 0. Holter, F. Ingebretsen og H. Parr Fysikk og Energiressurser ISBN 82-00-22927-0, Universitetsforlaget (1998) 11.6 Pedagogical reports and talks S.L. Andersen og O. Øgrim Del E: Krefter Hefte (ISBN 82-90904-39-8) og Video (ISBN 82-90904-40) med fysikkdemonstrasjoner. Fysisk Institutt / Senter for lærerutd. (1998) 1-25 S.L. Andersen og O. Øgrim Del F: Godbiter Hefte (ISBN 82-90904-45-2) og Video (ISBN 82-90904-46) med fysikkdemonstrasjoner. Fysisk Institutt • Senter for lærerutd. (1998) 1-25 S.L. Andersen og O. Øgrim Del G: Spill og leker Hefte (ISBN 82-90904-49-5) og Video (ISBN 82-90904-50) med fysikkdemonstrasjoner. 129 Fysisk Institutt / Senter for lærerutd. (1998) 1-25 J.R. Lien, G. Løvhøiden Kompendium i mekanikk Fysisk institutt, Universitetet i Bergen S.L. Andersen og O. Øgrim Fysikkdemonstrasjoner Forelesning på faglig pedagogisk dag, Universitetet i Oslo, januar 1998 S.L. Andersen og O. Øgrim Demonstrasjonsforelesning Forelesning på Biørnegildet, Fysisk Institutt, Universitetet i Oslo, våren 1998 S.L. Andersen og O. Øgrim Tre demonstrasjonsforelesninger Foredrag på Østlandske lærersevne, oktober 1998 S.L. Andersen og O. Øgrim Demonstrasjonsforelesning Foredrag i fysikkforeningen, Fysisk Inst., Universitetet i Oslo, høst 1998 K. Gjötterud Fysikkens utvikling i vart århundre - perspektivendringer Tre forelesninger Etterutdanningskurs i fysikk i Videregående skoler i Vest-Agder Ressurssenteret på Gimle Kristiansand 04.09.1998 G. Løvhøiden Vart fysiske verdensbilde Kurs, Fysisk institutts skolelaboratorium, Horten, 1.12.1998 O. Øgrim og P.T. Zagierski Demonstrasjonsforelesnin Foredrag på Norks Fysisk Selskaps årsmøte, juni 1998 J. Rekstad, M. Meir New technology for cost effective and energy saving heating systems Information brochure from SolarNor AS, June (1998) 11.7 Science Policy and Science Philosophy E. Osnes Fornebusaken, ad evnt. flytting av Institutt for informatikk, UiO til Fornebu: a) Intervju i Østlandssendingen 20 aug. 1998 130 b Debatt i PI med Gudmund Hernes 20. august 1998 c) Debatt i Østlandssendingen med Jon Lilletun og Lucy Smith 20. august 1998 II. Aviser Intervju i Universitas, nr. 22, 23. september 1998 E. Osnes Fem år med Forskningsrådet - Grunnforskningen blir forsømt Intervju i Uniforum nr. 12, 26 mars (1998) E. Osnes Rektorvalget ved Universitetet i Oslo, artikler: a) Rektorkandidat Eivind Osnes' plattform. Uniforum nr. 12 17. sept. (1998) b) Universitetet - tid for prøveordninger. Kronikk i Aftenposten 22 sept. (1998) c) Næringslivet på villspor. Dagens Næringsliv 2 okt. (1998) d) Universitetet og studentene. Kronikk i Universitas nr. 24, 7. okt. (1998) e) Forskning, utdanning og rektorvalget - en sluttreplikk. Uniforum nr. 14, 8. okt. (1998) f) Gult kort til redaktørene. Universitas nr. 27, 28. okt. (1998) E. Osnes Rektorvalget ved Universitetet i Oslo 1998, paneldebatter a) Studentfestivalen 2. september 1998 b) Studenutvalgslederforum 23. september 1998 c) Realistforeningen 30. september 1998 d) Det sentrale valgstyret, UiO 5. oktober 1998 E. Osnes Rektorvalget ved Universitetet i Oslo, intervjuer: a) "Rektorkandidat Eivind Osnes - Ikke fra Kollegiet", Uniforum nr. 10, 20. august 1998 b) "Fem vil bli rektor", Aftenposten aften 17. september 1998 c) "Store endringer", Universitas nr. 23, 30. september 1998 d) "Rektorkandidatene", Uniforum nr. 13, 1. oktober 1998 M. Carlsson, A. Løvlie, O. Engvold, A.-L. Seip, H. Høgåsen, A.B. Slettsjøe, I. Nordal, E. Osnes, J. Taftø og T. Thonstad Observatoriets fremtid må bli egen kollegiesak Uniforum nr. 17 12. november (1998) 0. Holter og F, Ingebretsen Fra Redaktørene Fra Fysikkens Verden (1, 2, 3, 4), Vol. 60 (1998) K. Gjötterud Ytringsfrihet og unnfallenhet Kronikk Monitor - antifascistisk tidsskrift nr: 1 1998 131 K. Gjötterud Oppgjør med Luthers jødehets Referat fra foredraget i Nysæter kirke 22.03.1998 ved Håkon C. Hartvedt Dagen 24.03.1998 K. Gjötterud Fra arbeidet for jøder i det tidligere Sovjet Artikkel i Informasjonsavis for Hjelp Jødene Hjem, våren 1998 K. Gjötterud Antisemittiske strømninger i ex-Sovjet Artikkel i boken Israel 50 år, red. Nils Jacob Tønnessen, Luther Forlag Oslo 1998 K. Gjötterud Så skjer det igjen: Krav om at jøder skal drepes Jødene i ex-Sovjet Nr.2/98 desember - 15. årgang K. Gjötterud, M. Spandow Rapport fra Moskvareisen 26.11 - 01.12.98 Jødene i ex-Sovjet Nr.2/98-desember-15.årgang K. Gjötterud, M. Spandow Fra et besøk i Moskva: Igjen godtas det å være åpen antisemitt Nyhetsbrev desember 1998 Aksjonskomiteen HJH K. Gjötterud Antisemittisme og rasisme i Norge og Europa i dag Foredrag Sentrumsgruppa Oslo KFUM 24.01.1998 K. Gjötterud Fra antisemittismens historie, blodanklager fra Apion til Jan Bergman vedUppsala Universitet Foredrag i Seminar om antisemittisme og historisk revisjonisme arrangert av Norsk Forening Mot Antisemittisme og tidsskriftene Monitor og Humanistdagene 21. og 22. februar Humanismens Hus Oslo 21.02.1998 K. Gjötterud Jødenes situasjon i tidligere Sovjetunionen Foredrag for Hovedstyret i Den norske israelsmisjonen Hotell Norrøna 13.03.1998 K. Gjötterud Kristen antisemittisme - finnes den? Foredrag i Nysæter kirke Stord arrangert av MIFF og Norge - Israel Foreiningen på Stord 22.03.1998 132 K. Gjötterud, A. Demaci Kosova Forelesning Rønningen Folkehøgskole Oslo 20.05.98 K. Gjötterud Antisemittisme - professor August Rohling Universitetet i Praha i 1880-årene og professor Jan Bergman Uppsala Universitet i 1990-årene Foredrag i Shofar-gruppen (Ordet og Israel) i Vestby 18.10.1998 K. Gjötterud Forfølgelse av jøder før og nå Foredrag Ringstabekk skole 10. skoletrinn 19.10.1998 K. Gjötterud Antisemittisme i Russiand og xenofobi og asylpolitikk i Norge Innlegg på OSSE's implementeringsmøte i Warszawa om den menneskelige dimensjon 30.10.1998 K. Gjötterud Appel! for Kosova Appell ved Utenriksdepartementet i Oslo under demonstrasjonen 06.03.1998 K. Gjötterud Appell for Kosova Appell under Solidaritetskonserten for Kosova på Rockefeller 19.03.1998 K. Gjötterud Jødehetsen er på nivå med mellomkrigstiden ( i høyreekstreme miljøer i Norge) Intervju i Vart Land 23.04.98 og i P7 Kristen Riksradio 24.04.98 K. Gjötterud Zions Vises Protokoller Intervju ved Erik Tunstad NRK-radio P2 VOK 02.06.98 K. Gjötterud Etiske utfordringer ved presseoppslag Innlegg på seminar om forholdet mellom tatere, forskere og medier arrangert av Romanifolkets Landsforening 08.10.1998 K. Gjötterud Antisemittisme, er det bare "rasisme"? Foredrag Temadag Manglerud videregående skole 09.01.1998 133 INSTITUTT DEPARTMENT OF PHYSICS RESEARCH SECTIONS Biophysics lektronikkj Electronics Elementaerpartikkelfysikk Experimental Elementary Particle Physics Faste staffers fysikk Condensed Matter Physics Nuclear and Energy Physics 'lasma-og romfysikk Plasma and Space Physics 5trukturfysikk Structural Physics feoretisk fysikk Theoretical Physics ISSN - 0332 - 5571 -••==*«•'•'