department of physics - international atomic energy agency
TRANSCRIPT
NO0000041
UNIVERSITY OFDEPARTMENT OF PHYSICS
UIO/PHYS/99-04ISSN-0332-5571
SECTIONfor
NUCLEAR PHYSICS ANDENERGY PHYSICS
Annual ReportJanuary 1 - December 31 -1998
Department of Physics, University of OsloP.O.Box 1048 BlindernN-0316 Oslo, Norway
Received: 1999-08-27
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SECTIONfor
NUCLEAR PHYSICS ANDENERGY PHYSICS
Annual ReportJanuary 1 - December 31 -1998
Department of Physics, University of OsloP.O.Box 1048 BlindernN-0316 Oslo, Norway
UIO/PHYS/99-04 Received: 1999-08-27ISSN-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 2 U At 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 StrengthFunctions 44
6.1.11 iif-Hindrance in Primary 7-Decay after Thermal and ARC NeutronCapture 46
6.1.12 Spectroscopy with Entry-State Selection: Nuclides Produced in theReaction a+2 8Si 47
6.2 High Spin Properties of Nuclear States 50
6.2.1 Triaxial Superdeformed Bands in 164Lu and Enhanced El Decay-outStrength 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 m I r 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 = 28and 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
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(•.5.3 3P2-3^2 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 1078.0.10 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
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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 exclusivelya research report. The scientific staff members are also strongly engaged in the universitycourse teaching at all levels, and in various administrative duties, not reported here.
The Nuclear- and Energy Physics section 1998 staff counted 10 members in permanentpositions, two post. doc. fellows, one professor II (1/5 position for 5 years), 13 researchfellows, and 2 engineers. Despite the very professional and persistent efforts of the technicalstaff, the comprehensive experimental activities are in strongly need for more technicalsupport. The lack of technical positions is however a common university problem, of whichNorwegian universities have more than their fair share.
Experimental and theoretical nuclear physics is, and has always been, the main fields ofresearch activity in the section. However, in the early seventies a growing research activitywithin solar energy was initiated, primarily based on the experimental and instrumentationexpertise among the section members. This research, both fundamental and applied, hasproven popular among students, and also among funding sources.
The section has a long tradition in Radiation Research. In particular, fundamental pioneerwork on Radon research has been done in this section through the years. This research iscontinued 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 theavailability of skilled operation staff and the necessary time for scheduled and unscheduledmaintenance. The beamtime for external users now exceeds the beamtime allocated tonuclear physics experiments. In order to meet the urgent need for organizing and to givepriority to the different accelerator based activities, a cyclotron board, with internal andexternal members, has now been established.
The total beamtime used for experiments in 1998 was 1051 hours. 52 days were used bythe 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 onmaintenance.
In experimental nuclear physics, the section members are engaged within three main fieldsof research: Nuclei at high temperature (the local cyclotron experiments), high spin nuclearstructure (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 fromthe 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 onthe philosophy that local experimental equipment is an important asset in a universityinstitute. The SCANDITRONIX MC-35 cyclotron laboratory has been in operation since1980. The main auxiliary equipments consists of a 28 Nal-detector system CACTUS, witha 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 supportfrom 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 theprogram for sub-atomic physics). The main aim of this collaboration is the verification ofthe existence of quark-gluon plasma. The Norwegian participation in this project includesphysicists 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 inmost of the problems studied is an underlying microscopic description within the frameworkof many-body theories of the interactions between the various hadrons. Furthermore,problems related to the foundations of quantum physics, such as the non-separability ofsystems in a pure quantum state and the completeness of quantum mechanics, are alsostudied.
The solar energy research covers the study and development of solar heating and solarcooling 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 floorheating system.
Furthermore, both experimental and theoretical study of solar based hydrogen productionis 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, whichis 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 ournew web-site: www.fys.uio.no/kjerne.
Blindern, July 1999Finn IngebretsenSection leader.
Chapter 2
Personnel
2.1 Research Staff
Lisbeth BergholtFabio de BlasioØystein ElgarøyTorgeir EngelandLars E. EngvikKristoffer GjötterudMagne GuttormsenLisa. HendenMorten Hjorth-JensenAnne HoltFinn IngebretsenGunnar LøvhøidenOle Martin LøvvikMichaela G. MeirElin MelbySvein MesseltRoar A. OlsenEivind OsnesJohn RekstadAndreas SchillerSunniva SiemTerje StrandDunja SultanovitcPer Olav TjørnTrine Spedstad TveterStein W. Ødegård
Research fellowPost doc. fellow (EU)Research fellowProfessorResearch fellowAssoc. professorProfessorResearch fellowPost doc. fellowResearch fellowProfessor (elected Section Leader)ProfessorResearch fellow (NFR)( until August)Research fellow-Research fellowAssoc. professorResearch fellow (on leave of absent)ProfessorProfessorResearch fellowResearch Fellow (on leave of absent)Professor IIResearch fellow (NFR)ProfessorAssoc. professorResearch fellow
Senior and retired staff
Sven L. AndersenOtto 0grimOle H. HerbjornsenTrygve HoltebekkAnders Storruste
Senior scientist emeritusSenior scientist emeritusSenior scientistProfessor emeritusSenior scientist emeritus
2.2 Technical Staff
Eivind Atle OlsenJon VVikne
Section chief engineerSection engineer
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Chapter 3
Cyclotron operation and externaluser 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 of3He, 417 hours of 4He and 11 hours of protons. The Nuclear Chemistry Group occupied 70days, of which 25 days were used for 211At production. 52 days were used for experimentsin nuclear physics, and 12 days were used by The Norwegian Radium Hospital for 18Fproduction. 30 days were use for scheduled and 12 days for unscheduled maintenance thelatter 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 isillustrated in figure 3.1. The main non-nuclear projects are described below.
3.2.1 Production of 18F-fluorodeoxyglucose for medical PET-imaging
Arne SkrettingThe Norwegian Radium HospitalThe 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 cyclotronthat is used to produce 18F by proton activation of 18O-enriched water. The activity isthen 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,
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60
50
40
30
20
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1995 1996 1997 1998
Figure 3.1: The Cyclotron user profile for the years 1996, 97 and 98. The demand forbeamtime now exceeds the capacity.
FDG is being used in the Norwegian Radium Hospital to image the 3D distribution ofFDG in the body, thereby visualizing primary and metastatic tumours. FDG may also beused for imaging of the brain and heart, as it will be in the National Hospital. The halflifeof 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 witha 10 microampere, 16 MeV proton beam. The resulting quantity of approximately 20 GBq18F is then transported by car to the Institute of Energy Technology, where production ofFDG according to pharmaceutical good manufacturing practice (GMP) takes place. Thedistance of travel is considerable; if irradiation starts at 9 hours a.m., the first patient isinjected 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. Stablesupply of FDG requires a dedicated hospital cyclotron, but national funding has beenunavailable until now.
Imaging in the hospitals is performed with gamma cameras with two detectors operated incoincidence mode. These have lower sensitivity than dedicated PET-cameras, but the firstpatient examinations performed in The Norwegian Radium Hospital demonstrates that itis possible to obtain high quality diagnostic information.
3.2.2 Basic Nuclear Chemistry Research
J.P. OmtvedtNuclear 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 AKUFVEtechnique).
The SISAK activity in Oslo has expanded considerably over the last few years throughthe construction and use of a gas-jet transport system and target chamber at the OsloCyclotron laboratory. This has given the collaboration a unique possibility to develop andtest the chemical systems used in the main experiments. At the cyclotron the lighter nucleilike Zr and Hf are used.
The local installation has lead to a considerable improvement of the equipment and theprocedures, and given the whole collaboration a valuable running experience before theuse 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 rangecv-radiation almost exclusively onto cancer cells.
The halfiife of 211At is short (7.21 h), and the production site must therefore be locatedclose 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. Thecompany 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 dividedinto two major components:
• A front-end system responsible for data digitalization, read-out and formatting. Thissystem is based on a VMEbus with connections to CAMAC, NIM and the customSIRI 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
SIRI
NIM
VME
Pov/erPC
. BITS—r\ interface = t > Spa rcSta lion
10/512
Exabyte
cro
Figure 4.1: Schematic view of the data acquisition system
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• Software development for the PowerPC VME data-acquisition controller continued.
• The dedicated VME module ("ROCO card #3") for the SIRI readout was built, andsuccessfully 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 upgradedto revision 3.8.
• The rear-end computer systems were improved. An additional 17GB user disk waspurchased. Most of the NCD 19c X-terminals got a video memory upgrade from 8to 16MB. An additional Exabyte tape drive and a HP890c colour inkjet printer wereinstalled.
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 2.3.11 CBD 8210, CAMAC Branch Driver1 NIM Interface1 TSVME 204, EPROM socket card2 VBR 8212, VME-VME link, receiver1 VBR 8213, VME-VME link, transmitter3 TPUs, Trigger Pattern Units1 Bit3 Model 467, VME-SBus link, 25MB/s1 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 ADCs4 Silena 4418/T TDCs1 Pile-Up Rejection Module (PUR)
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b) Rear-end
Sun Sparcstation 10-512 with:Solaris 2.5.1 operating system (UNIX System V Release 4.0), OpenWindows,X-windows, MotifDual SuperSPARC TMS390Z55 50MHz CPU with 36kB cache, 128 MB memory
1 Bit3 Model 467, SBus-VME link card, 25MB/s2 SCSI mass storage expansion box2 2.0 GB disk drive2 9.0 GB disk drive1 Colour monitor, 19", 1152 x 900 pixels1 Ethernet controller, TCP/IP and NFS software1 10 GB Exabyte cartridge tape unit1 12 GB Exabyte cartridge tape unit1 Panasonic SCSI CDROM unit1 SparcPrinter QA-6 laserprinter1 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, MotifDual UltraSPARC 200MHz CPU, 448 MB memory
1 2.0 GB disk drive1 17.0 GB disk drive1 Colour monitor, 20", 1280 x 1024 pixels1 Ethernet controller, TCP/IP and NFS software1 12 GB Exabyte cartridge tape unit1 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
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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 simulatedusing experimental data.
EMMA:Calculates El, Ml, El, Ml transition probabilities between single quasiparticle statesfrom 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.
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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 HadronMagnetic 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 mainproblem at the end of the year were the multipole vacuum feedthroughs. Still anotherrevision of the mechanical design has to be made. Currently, we are implementing the useof 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 1997Department of Physics, University of Oslo Report UiO PHYS 98-06
18
SIRI Read-Out Controller * Main Block Diagram
FRONT END<H SIRIchips)
RIBBON CABLES
LL
POQT BOARD
RUNNING MS-DOS
TWISTED PfllP. COBLES KS-VZ2 LEUELS)
Figure 4.2: Block diagram of the SIRI Data-Acquisition System
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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 the90° beam line of the Oslo cyclotron. The Nal counters are fixed to the detector frameand have a distance of 24 cm to the target. The 5"x5" Nal(Tl) detectors (BICRON) areequipped with 5" PMT. The detectors are shielded laterally with 2 mm lead and collimatedwith 10 cm lead in front. The solid angle of each detector corresponds to 0.5% of 4TT. Thefront of the detectors are covered with a 2 mm Cu absorber. In addition to the Nal countersthere is space for Ge counters. At present we have four Ge-detectors with efficiencies of49, 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 tworemaining holes (32 holes in total). Beam focusing can be performed with a piece of quartzat the target place, where a TV camera through a Plexiglas window can monitor the beamspot.
Inside the ball of 7-detectors 8 Si (Li) particle detectors are mounted. Later, these detectorswill 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 measuringangular distributions have been determined with great accuracy. As an example, I presenthere measurements with 3 Ge detectors in coincidence with the 27 Nal detectors locatedat different angles. The observed angular distribution of 7-rays in 4 different 7-7-cascadesare shown in Figure 5.1.
The data points in Figure 5.1 were fitted to a series of Legendre Polynomials according toW{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).
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Angular Distributions of 4 y-y Cascades
100 150 200Polar angle (degree]
Gated on 1 1 73 keV in Co-60
100 150 200Polor angle (degree]
Gated on 1 332 keV in Co-60
5 i.O4oL)
° 1.02
tD 1ZO
S 0.98I| 0.96
0.94
0.92
0 q
-
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/ K'\
KV
1 1 1 1 1 I > 1 1 1 1 1 1 ) ,
S 1.25
- 1.15I\ 1.1
1 1.05
. 1
0.95
0.9
0.85
c\ «
IV /
L \ /1 \ | /- 1 \^j/t- j
i i > i i i i i i i i i i i
/
1 . . . .50 100 150 200
Polor angle (degree!
Gated on 778 keV in L'u-152
50 100 150 200Polar angle (degree!
Gatea on 1 408 keV in Eu - 1 52
Figure 5.1: Angular distributions of 4 different 7-7-cascades. The theoretical curve fits thedata 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 considerablylarge. 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)
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Nucleus
60Co (upper left)
60Co (upper right)
152Eu (lower left)
152Eu (lower right)
Cascade
4 -»• 2 -*• 0
4 -
3 -
2 -
• + 2 - + 0
-»2->0
• » 2 - > 0
Theory.42 = 0.102
-44 = 0.0091A2 = 0.102
Ai = 0.0091A2 = -0.071
.44 = 0A2 = 0.250
Fit0.104 ±0.005
0.0111 ±0.00810.097 ±0.005
0.0088 ± 0.0079-0.060 ±0.010
0.008 ±0.0140.233 ±0.023
0.043 ±0.035
Table 5.1: Comparison of theoretical and fitted Ai and A4 coefficients of 4 different angularcorrelations.
Read-out chips
Beam
Figure 5.2: The target chamber with one SIRI detector ring seen perpendicularly to thebeam axis. The detector ring covers a range of angles between 30° and 60° with respect tothe 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 decayproperties as a function of temperature. It consists of an array of silicon particle telescopesfor 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 coincidenceset-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. Detectorrings, target and chips are mounted on separate rings that can be moved on rods connectedwith the flange to the right. It is possible to switch between four targets inside the chamberwithout breaking the vacuum. New oil free vacuum pumps are installed. The targetchamber is designed so that cooling of the chips and detectors can be performed. Thebeam optics and focusing properties are tested in order to reduce halos and scatteringfrom 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-outchips for the system. AMS in Austria processed the ASIC chips. The mounting of thecircuitry and detectors on ceramic substrates was made by Microcomponent in Horten,
22
Guard structure
8 pads
Cables
E 130 urn \
E 2000 urn
Figure 5.3: In the upper part is shown the detector glued to the ceramic substrate withcircuitry and flat cables. In the lower part is shown the arrangement of the 8x8 telescopesinto 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 thickceramic substrate, as shown in Fig. 5.3. The front and end detectors have the sameshape (almost trapezoidal in form) and are sandwich mounted back-to-back. Each detectorelement consists of 8 pads. The detectors are glued on to the ceramic substrate, wherebonding and cabling can be performed. Surface mounted circuitry is laid on both sides ofthe left wing of the substrate, as indicated in Fig. 5.3. Flat cables are connected to thechips from the wings.
The particle telescopes are 2 mm thick and stops at least 60 MeV a-particles. It is alsoimportant 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 passthrough 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. Thesilicon 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). Eachchip is designed to handle 32 silicon strip detectors, including preamplifiers, discriminators,shapers, pattern, multiplicity and pile-up rejection circuitry. The chip is implemented inAMS 1.2/xm BiCMOS, double poly, double metal process. The power consumption is 350mW, which gives about a 6°C increase in temperature when bonded to a CLCC84 chipcarrier.
At the first stage on the chip a fast preamplifier splits the signal into a time and energybranch. 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 totake events.
The pileup inspection is performed both before and after the event of interest. If twosignals arrive within 2 /j,s, the corresponding latch will be reset (signals less than 100 nsapart cannot be separated). Pile-up on/off has a fixed level, which is set externally for thespecific experiment. The function set-latch identifies the channel fired. The latch for otherchannels 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 chipare handled using a summing technique (multiplicity) of the logical timing signals. Thismultiplicity signal is a linear sum of the logical signals from all detectors. The signal can beused 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 earlystage. The chip resets within 1 fis. In this way energies can be read out even without thepresence of set-latch.
The processing of the timing signals is a compromise in order to limit the number of cablesout of the target vacuum chamber and to reduce the pin count of the chip. The chip donot include CFD for the time signal, time walk effects will be compensated in the off-lineanalysis 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. Outsidethe chamber a read out controller (ROCO) contains ADC's and event buffers. The usercan set certain thresholds by computer control, i.e. signal widths and logical signals to thechips via the ROCO.
The data acquisition system is designed to handle the high data rate, which is more that10 times higher than earlier. The rear-end system, shown in Fig. 5.4, is built around a
24
SPARCStation512128 Mb memory11 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 boardcomputer takes care of the event builder process. The data transfer system is designed togive 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. GuttormsenSIRI, A proposal for a multi-detector AE-E particle telescopeDepartment of Physics Report, UiO/PHYS/92-21 (1992)
[2] M. GuttormsenEventbuilder for the RTPC 8067 Single Board ComputerDepartment 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 the7-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 aplastic target (mainly carbon atoms) with approximately the same target thickness as therare earth targets.
(3He,3He'y) Reaction on Different Targets
3 3.5 4Er (MeV)
5 5.5 6 6.5Paper Target
3 3.5E7 (MeV)
Figure 5.5: Part of the 3He-7 coincidence matrices of the (3He,3He') reaction on 3 differenttargets. One can clearly see the 4438 keV transition in 12C (all targets) and the 6129 keVtransition 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. Similarresults are achieved for the (3He, a) reaction on the same nucleus [1]. In the near futurethe background subtraction will be applied to all other reactions recently investigated atthe 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 detectorswill be connected to a 200 liter dewar with isolated tygothane tubes and cryogenic solenoidvalves (ASCO). To control the system we use an old PC with a commercial I/O card. TheTTL 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 voltssignals in a control module. The valves are normally closed, and the filling procedurestarts by opening the main valve at the dewar and one of the manifold valves connectedto a Ge detector. Overflow is detected by the voltage change in a light emitting diodewhen it cools down by the overflowing liquid nitrogen. The voltage change is convertedto a TTL-signal in the control module and sent to the PC, which closes the valve. If nooverflow signal is detected within a given time period, the valve to the detector is closedand an alarm is given.
This procedure is repeated for all detectors. Then the main valve at the big dewar is closedand a valve in the manifold, which is not connected to any detector, is opened for a shorttime to drain the manifold and the tube from the big dewar. The system will then waitfor 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. Usinga PC and Turbo-C makes is very easy to write and modify the control program, and alsoto 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 ofbeam time.
Private communication with Anssi Savelius in the cyclotron group in Jyvaskyla is highlyappreciated.
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 anefficient way. The need for a faster eventbuilder at the Oslo Cyclotron Laboratory (OCL) isnow mandatory when the SIRI/CACTUS system is put into operation. The previous dataacquisition computer is from 1991 and is based on a FIC8230 from CES1 with a Motorola68020@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 buffersto the Sun SPARCstation. The present development concerns the implementation of theRTPC single board computer, together with modifications and extension for the new TPU5dedicated 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 sparetime to sort events on-line for monitoring the experiment.
A double buffering technique is applied in order to achieve high throughput. Each ofthe data buffers is 32 Kwords long with 32 bit long words. The two CPUs (RTPC andSPARCstation) base the buffer handling communication on the polling of two commonsemaphores. If buffer 1 is filled up by RTPC, then semaphore 1 is set to FULL. Then RTPCloops 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 spaceof RTPC. This memory is allocated through SRAM, and has a fixed location for bothCPUs. 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 beallocated in the DRAM memory of RTPC. The total length of the buffers are 0x40000bytes = 256 Kbytes. This memory area has to be contiguous and not occupied by theLynxOS. Since the dynamic slave mapping of the present RTPC is not working, we haveused static mapping.
'Creative Electronic Systems, Switzerland, E-mail: [email protected] means Real Time PowerPC
28
The VME modules can be accessed by creating a pointer to the VME physical addressby the vme_map() function, and should then be released by the vme_rel() function. Theaddress modifier code (AM) is 0x39.
The speed performance of the PowerPC 603 microprocessor for integer and floating pointoperations are 63 SPECint92 and 58 SPECfp92, respectively. The new eventbuilder wastested out during a four-week experiment in autumn 1998. The system runs the event loop10 times faster compared to the previous system, and the limits of performance is now setby the ADC conversion times. With a typical eventlength of eight words, the eventlooptakes 60 /is including the waiting for ADC conversion, which is 30 ^s. This allows an eventrate of 5000 events/s with 23 % dead time. Thus, the new eventbuilder will match ourrequirements for many years.
Further details are given in [1].
References
[1] M. GuttormsenEventbuilder for the RTPC 8067 Single Board ComputerDepartment 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 nuclearstructure at low spin and high excitation energy. The technique is based on measuringcharged 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 energyfrom the ground state up to Ex ~ 40 MeV.
In order to increase the efficiency of the particle-7 coincidence setup further, the the SIRImulti-detector system has been build (see section 5.3). The combination of SIRI andCACTUS will be a very powerful instrument in the study of both nuclear properties andreaction mechanisms as functions of temperature.
In heated nuclei (a few MeV or higher above the yrast line), statistical concepts must beused for describing the nuclear structure due to the near exponentially increasing leveldensity and the extensive configuration mixing. The nuclear properties in this highlyexcited regime may be divided into two categories:i) average properties, which vary slowly with Ex and are related to thermodynamic conceptsii) the fluctuation properties, which provide a statistical characterization of the microscopicstructure 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 forthe simultaneous determination of the level density and the 7-ray strength function. Phasetransitions, 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. Collectiveexcitations, which contain information about correlations between nucleons, may appearas fine structure in the 7-ray strength function. Such signatures have indeed been observedexperimentally for several nuclides. Data on more nuclei has been collected during a seriesof experiments in 1997 and 1998.
30
The transition from ordered to chaotic nucleonic motion is expected to show up in thefluctuation properties of the nuclear states. Level statistics indicates that the nucleushas a rather chaotic structure in the neutron resonance region. In well-deformed nucleithe degree of A mixing may serve as a more sensitive probe for remains of order r inthe nuclear structure. Studies of the primary 7-decay after thermal neutron capture haverevealed a clear correlation between the transition intensity and the final-state A'-value,more pronounced after thermal than after average resonance capture, which might signifyremains of order. In the thermal case, the transition probability distributions for K-allowed and A"-forbidden transitions also have shapes associated with different numbersn of degrees of freedom. Several physical explanations for this puzzling observation havebeen discussed. In order to look for possible doorway state effects, a study of possiblecorrelations 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 thenuclear many body system. Unfortunately, it is extremely difficult to reach this goal - bothexperimentally and theoretically.
Recently [1, 2] the Oslo group presented a new way of extracting level densities frommeasured 7-ray spectra. One of the main advantage of this method is that the nuclearsystem is presumably thermalized prior to the 7-ray emission. In addition, the methodallows the simultaneous extraction of level density and 7-strength function over a wideenergy 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 arrayusing the (3He,cr7) reaction on 163Dy, 167Er and 173Yb self-supporting targets. The chargedejectiles were detected with eight particle telescopes placed at an angle of 45° relative tothe 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 ofinitial 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 pis 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 4Excitation energy [Me
Figure 6.1: Observed temperatures as functions of the excitation energy E (data pointswith statistical error bars). The solid lines are temperatures as functions of average exci-tation energies < E > deduced within the canonical ensemble.
32
3 4 5Average excitation energy [MeV]
Figure 6.2: The heat capacities extracted within the canonical ensemble. The dashed curvedisplays 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 thelevel density p. The level density is interpreted as the multiplicity of states at E, whichin our case is the level density of accessible states in the present nuclear reaction. Thepartition function is then given by
(6.3)J21=0
where En is the excitation energy at bin n.
The excitation energy is given by the thermal average
E(T) >oo
n=0
EnP(En)e -E"'T. (6.4)
The smoothing effect implied by the canonical ensemble can be investigated by calculatingthe 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 canonicalensemble 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 respectt o T
Cv{T) = — ^ — . (6.6)
Figure 6.2 shows the deduced heat capacities for the 162Dy, 166Er and 1(2Yb nuclei as afunction of < E >. All nuclei reach a heat capacity of about 20 at E = 6 MeV, whichis 10% of the value for an ideal gas with |iV ~ 250, due to blocking of fermions situateddeep 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 andA. 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 andOctober 1997. The analysis of the data is finished and level densities could be extractedfor the nuclei 162Dy and 161Dy according to R,ef. [1]. It is now of great interest to comparethe level densities of 162Dy obtained in this work (with 5 times better statistics) to thoseof Ref. [1] (see Fig. 6.3).
One can see that the level densities are in good agreement with each other. The errors inthe upper part are much smaller due to better statistics. A bump can be seen at around3 MeV. The origin of the bump is not clear, it might be due to a gradual breakdown ofpairing correlations [2]. The level density of 161Dy (not shown here) does not have thisbump 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 NordicMeeting 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 thesystematic study of rare earth nuclei at OCL. Of particular interest are the extraction of
34
Q.
;vel
Den
si
-jE;
Rel
21.81.6
1.4
1
0.00.60.4
0.2n
1 1 1 I 1
M I 1
- 1 >- 1 • *U •
i\*r
i\
\ • •*
i ! ,
Level
, / ••••' - ••• •• • * r - ^ X
- '
Density
\ y ^ ^ , -»
, , , , 1 1 , ,
in
^ \ / - y
> 1 , , , i , ,
• . . .
/ \
, , !t
i
/
( , i
2 3 4 5 6 7 8Excitotion Energy [MeV]
0 1
From '62Dy(3He,3He')'62Dy
« 1.4
a> 0.8
cu 0.6
• | 0.4
^ 0 . 2
\ 1 , N
, I . , I
0 1
From 163Dy(3h8,a)'62Dy2 3 4 5 6 7 8
Excitation Energy [MeV]
Figure 6.3: Level densities in 162Dy obtained from the reactions 162Dy(3He,3He') (upperpart) 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 inthe 7-decay from highly excited nuclear states.
The target of 167Er, which has a ground state A"-value of 7/2, was isotopically enrichedto 95.6% and had a thickness of 1.5 mg/cm2. The projectile energy was 45 MeV, and thereaction products were detected by the array CACTUS.
The primary 7-rays in the decay of the excited 166Er nucleus have been isolated by thesubtraction 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 thelevel 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 formp oc exp(U/T) and a cc E™, respectively, where U is the excitation energy, E^ the 7-rayenergy, 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)
3
2
10
1
— 1
y — strength function
V
Relative strength function
4 6 8 0y-energy (MeV)
2 4 6•y-energy (MeV)
Figure 6.4: Upper panel: The level density of 166Er to the left, and the same divided bya 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
1 -
c
"c -1• - 1 0
or
io"V
10
:
-
C1,
t t
'l •
: 162
He,3He
•' " I n '
D y
1
)/(JHe
, , i , ,
% • • • • ! + • . . . . • •
1 •'••! ) '••,
P *S
. i i
3 4 5 6Excitation 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 investigatethe nuclear structure at high excitation energies. In this work we study the 7-decay of rareearth 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 and1 /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 offeeding 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 thermalizationmechanisms in heated nuclei.
37
The project is in progress.
6.1.6 Gamma-Ray Angular Correlation and PolarizationMeasurements 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 thepick-tip reaction, 163Dy(3He,a7)162Dy and several nuclei around mass 160. The bump isactually 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 andstudied. The aim of this work is to measure and study angular correlation and polarizationof 7-ray, for these energy regions.
The experiment was performed using the 163Dy(3He,a7)162Dy reaction, with a beam energyof 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 wemeasured the relative anisotropies of the angular correlation of emitted 7-rays with respectto different axes and normalizing the yrast by the 1 MeV-bump, we observed that theangular correlation with respect to the recoiling nucleus direction has the most pronouncedanisotropy.
The Total Unfolded yray Spectrum
1&(A
oo
18000160001400012000100008000600040002000 J
1 Jl 2
Yrast ESSSSSS
1 MeV Bump E ^Intermediate ^ SHigh Energy • •
3 4 5 6Gamma Energy
JI31
7 8E, [MeV]
Figure 6.6: The total 7-spectrum corresponding to excitation energies up to 8 MeV, incoincidence with ce-particle. Note that the energy regions are: the yrast £^=0.17-0.29MeV. 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 MeVand 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 andtransitions at 0.3 < E., < 0.6 MeV region (due to the unfolding process), can not bestudied.
Figure 6.6 displays the total-generation 7-spectrum corresponding to excitation energy upto 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 groundstate 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 groundstate and (3) the high-energy region £^=1.53-4.0, these transitions can be described bythe Fermi gas model. The high-energy region can be studied in two parts, (i) energyregion 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 fromhigh 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-rayand 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, dipoleor unstretched quadrupole radiation. In intermediate and high energy, we find close toisotropic angular correlation which might be Ml transitions (see Table 6.1). This couldbe due to continuum radiation mixing of stretched and unstretched multipole transitionswith anisotropies canceling each other out.
In order to distinguish electric from magnetic radiations, we measured the asymmetryA = Q, where P is the polarization and Q is the polarization sensitivity with values0 < Q < +1- The 7-7 coincidence between two neighboring Nal-detectors determines thescattering direction, either parallel or perpendicular to the recoil vector. We measured apositive asymmetry for all the energy regions discussed here.
E-y [MeV]0.17-0.290.61-1.511.53-3.013.03-4.010.61-1.011.03-1.51
A2
+0.312±0.020+0.104±0.017+0.092±0.009+0.080±0.030+0.120±0.032+0.061±0.016
A4
+0.097±0.026+0.043±0.022+0.027±0.011-0.030±0.020+0.070±0.005+0.019±0.011
0.17-0.290.61-1.511.53-3.013.03-4.010.61-1.011.03-1.51
-0.094±0.015+0.105±0.018+0.055±0.018+0.080±0.020+0.069±0.032+0.135±0.008
+0.075±0.009+0.082±0.010+0.081±0.011+0.090±0.024+0.107±0.008+0.065±0.012
Table 6.1: Experimentally angular correlation coefficients A?, and A4 of 7-ray from thereaction 163Dy(3He, cry)162Dy with respect to the recoil vector (above) and respect tothe normal vector to the reaction plane (below), are listed in three tables. The angularcorrelations 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 Tables6.1).
Our initial assumption was that we could explain the anisotropy of the angular correlationwith respect to the normal vector by means of a simple geometrical transformation of theangular 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 anisotropieswith respect to both the recoil and the normal vectors are measured and geometricallytransformed. The result of these transformation reveal that the angular correlations trans-formed below ~ 1 MeV are in fairly good agreement with the experimental results withinour uncertainty but not for region E 7 > 1 MeV.
By measuring the energy of the emitted a-particle from the reaction, the excitation energyof the populated states is uniquely determined. Angular correlations of five 7-ray energyregions gating on three excitation energies up to the neutron binding energy, with respectto both the recoil and the normal vectors.are measured. One would expect that withincreasing excitation energy, the anisotropic of the angular correlation with respect to thesymmetry 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 correlationswith respect to the normal vector also have an opposite behavior compared to the recoilvector.
A close study of the reaction mechanism and the structure of residual nuclei might explainthis 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. HammarenThe decay from the two-quasiparticle regime in even-even deformed rare earth nucleiPhys. 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. WikneCACTUS a multi-detector set-up at the Oslo CyclotronDepartment 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 ) y 5 O i e 2 ^piu'I) = —muTfy—'
where 0 is the rotational parameter and a is taken as 10/A (in units of MeV""1). Thenuclear 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 experimentdone 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 StrengthFunction
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 functionfrom 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)
J
2.5
2
1.5
1
0.5
n
r
Z—i—i
172
. . i • . . . i
Yb(3He,a) 17'Yb
uflwI, , i , , uJ-.-..,...!..,
U(MeV)
Figure 6.8: Above: Level density p{U) averaged over all Ex. Below: The same functiondivided by the best fit of the trial function pjn{U) = CeulT.
generation 7-rays emitted from excited nucleus in the statistical regime can be expressedas
where U = Ex — E-y. Here, p{U) is the level density at the final state, and F(E~f) isproportional to E^x+1f(E1), where f(E-y) is the strength function. For the purpose of thiswork, 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) andF(Ey) from experimental first generation 7-ray matrices [2].
The extracted functions will of course vary with different input parameters, usually set toT = 530 keV and n — 4.2. but in this work we are mainly interested in the fine structure.The division by the best fit to the trial function will make the fine structure appear moreclearly.
The reaction used in these experiments is the (3He,«) and (3He,3He')-reactions performedon 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
104
10*
102
10
1
o"
L
r
t
rf •.•""
r . . . t
'72Yb("He
i , , ,
71Yb
• ' * * t +
t
I
2.5
2
1.5
1
0.5 -
E,(MeV)
I I , , , , I ,, , ,1
k t ll/t Jlji, . . , 1 , , I . 1 . , , I 1 , , , . 1 , , , , . _ * _ L - . - . . . ,
E,(MeV)
Figure 6.9: Above: Strengthfunction F(E-y) averaged over all Ex. Below: The samefunction 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 asa 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 developedand implemented in a FORTRAN computer code [1]. An excellent overall agreement ofthe model with our experimental data could be achieved. Especially, the so called 1 MeVpeak, which is formed by transitions from vibrational states to the ground state rotationalband, could be reproduced in the simulated spectra.
In the case of 162Dy, the agreement of the high resolution spectrum with experiment isstriking as one can see in Fig. 6.10. It is interesting to see, that the feeding of the groundstate rotational band can only be seen from high K bands [2]. This is a feature whichshould be investigated further. It might be possible to trace back a K distribution upto excitation energies around 8 MeV, applying a statistical analysis to the experimentalground 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 StrengthFunctions
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. VVikneand S.VV. Odegard
1 On leave, Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA2Oliver Lodge Laboratory, University of Liverpool, Liverpool L69 3BX, U. K."Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
44
Experimental '62Dy Spectrum882
x 10CD
<M
0)n_mcDO
U
10000
5000
0 AJLLJLL
800 900 1000 1100 1200Er(keV)
Simulated 162Dy Spectrum
800 900 1000 1100 1200Er(keV)
Figure 6.10: Comparison of experimental and simulated high-resolution spectra around 1MeV. Although no fine tuning of the model is done with respect to branching ratios in thediscrete level region, even the relative strengths of transitions around 1 MeV turn out tobe quite accurate.
Significant fine structure in both the level density and the strength function have recentlybeen 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 dipolemodes built on excited states. The measurements were made with the CACTUS detectorarray, which contains 28 Nal scintillation detectors. These results are quite unexpected andamount to an important extension of our knowledge of nuclear structure. An internationalcollaboration was formed with the goal of exploring these hitherto undiscovered featuresin 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 liketo borrow six Eurogam Phase I 70% Ge detectors with BGO shields. The detectors will beplaced perpendicular to the beam direction forming a ring, thereby the name GRIS, whichstands for Germanium Ring Setup.
We have made some rough estimates on the efficiency of 6 Ge-detectors compared to theCACTUS detector array (see table 6.2). We accumulated spectra using a 60Co source andcompared 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. Therelative efficiency curve for CACTUS is well known. To get as good statistics as previous
45
Gammaenergy
1.17 MeV1.33 MeV8.0 MeV
CACTUS28 NaI+8 telescopes
10.930.34
GRIS6 Ge+8 telescopes
0.390.360.12
GRIS + SIRI6 Ge+64 telescopes
~ 4
~ 1
Table 6.2: Comparison of the photo-efficiency (for particle-7 coincidences) of 6 Ge-detectorsand 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 planswill 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 effectin the primary 7-decay of states populated through thermal and average resonance neutroncapture in deformed nuclei. Details are explained in Ref. [1]. A striking observation is thatthe A"-hindrance seems considerably more profound in thermal neutron capture than inARC.
In order to search for possible differences in the statistical behavior of allowed and forbiddentransitions after ARC and thermal neutron capture, the observed transition probabilitydistributions were compared with theoretical model calculations [2]. The number of initialstates 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 betweenA'-allowed and A"-forbidden transitions after thermal neutron capture. The allowed andforbidden 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. Thetheoretical ARC distribution show a best fit to the experimental distribution assuminga 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 theprobabilities for populating low-lying states after the (n, 7) and (d,p) reactions, is probablyto 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 theentrance 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 inthe 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 comprehensivestudy, see [1], has located bunches of states that are interpreted to be members of anct+28Si rotational band (in 32S), an "a-cluster band", with a band head at ~ 12.6 MeVand natural-parity members up to 10+. The properties of these were thoroughly discussedin [3, 4]. This structure is totally unconnected to the low-lying "spectroscopic" structureup 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 theneighbouring 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 mightfeed into the lower-lying structures. Rather none of the nuclides reachable from an a+28Sireaction at energies Ea ~ 20 MeV, has ever been studied with in beam methods.
Only one recent comprehensive study 3 2S, especially of chosen resonances has been per-formed, cf. [5]. It uses the 29Si(cr,n7) reaction at 14.4 MeV and locates some 30 resonancesfrom n—a correlations. They also uses the reaction 31P(p,7) on a 20 ̂ g/cm2 Cd2P3 targetto 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) and27Al(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 3 1P, can be found in [2], or mostly in more detail in itspredecessor [8].
An in-beam experiment using the a+2 8Si reaction was performed with beams from theK-35 Cyclotron of the Oslo University. Beam energies of Ea = 14.8, 16.8, 19.0, 21.0 and24.0 MeV were used.
The target was natural Si (92.2% 28Si. 4.7% 29Si and 3.1% 30Si) with a thickness of about12-15 fxm. This thickness corresponds to ~ 870 keV for Ea = 14.8 MeV, and to ~ 610keV for Ea = 24.0 MeV. Thus the entry states of population are ~ 900 — 600 keV wideand 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 variouschannels 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 lowestenergy (Ea = 14.8 MeV) also a fairly thick target, ~ 55/xm corresponding to about 4.5MeV energy thickness, was used. A high-statistics run was performed at this energy toestablish the lower parts of the level schemes reachable at this energy, mainly 3 1P and 3 2S.
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 these5' X 5" Nal counters were mounted, and three large Ge counters with 50-70% efficiencywere mounted in the ±37° and 67° positions. Energy ranges were up to 4.2 MeV for theGe counters and up to 9.5 MeV for the Nal scintillators, both on 4K raw spectra, thusgiving dispersions of ~ 1.2 and 2.4 keV/channel. Charged particles were detected in 8 Sidetectors, each 3 mm thick, covering all particle energies. Due to recoil Doppler broadeningthe Ge detector effective line width varied from ~ 6 keV at 600 keV to about 25 keV at 4.0MeV.
In order to assign multipolarities to the observed levels, an angular-distribution experimentwas performed at the 104 cm isochronous cyclotron of Abo Akademi. The maximum beamenergy of 18.0 MeV was chosen. The thick target of ~ 55//m was used. Gamma-ray spectraat seven angles, viz. 80° - 165°, were recorded. The normalized distributions were fittedto the expression W{8) = Ao + A2P-2{zos8) + A4P4(cos0), and x2-tested to extract theangular-distribution coefficients A2, A4 and the mixing parameter 8. The parity cannot bedetermined directly, but a significant mixing coefficient usually implies M1/E2 admixturein favour of E1/M2.
Because of Doppler broadening in the Ge detectors and intrinsically broad lines in theNal counters lesser dispersion is sufficient. For this reason, and since the line densityin these light nuclides is fairly low, the sorting was performed to matrices the followingsize: Ge-Nal 512x2K, Ge-Ge 256x2K (maximum of 256 preselected gates), particle-Ge256x2K 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 performedusing 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
e cosy0.4
Figure 6.11: Calculated (UC) potential energy surfaces at I = 35 and 36 for the lowestconfiguration 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. vanSeveren, 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 Euroballexperiments eight new. presumably triaxial, superdeformed bands were found. For the firsttime, evidence is presented [1] for superdeformation in an odd-odd Lu isotope for whichtheory predicts large triaxiality. Calculations by the Ultimate Cranker code (UC) withextensive use of the programme NUSMA [2] have been performed. Potential energy surfacesfor the lowest expected configurations in 164Lu with positive and negative parity are shownin fig.6.11 In addition to the minima at normal deformation the calculations show localminima with large deformation and 7 ~ ±20°. Rotational bands in 164Lu were populatedusing the reaction 139La(29Si,4n) with thin self-supporting targets at a beam energy of 145MeV. The 29Si beam was provided by the Legnaro XTU tandem accelerator and the 7-rayswere detected with the Euroball array consisting, at the time of the experiment, of 13clusters, 25 clovers and 28 single element tapered detectors. Altogether, ~ 3.8 • 109 eventsrequiring 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 gatedmatrices for DCO analysis, cubes and a 4D-hypercube.
Two of the strongest populated bands, SD1 and SD3, have been connected to known NDbands in 164Lu. The band SD1, decays to several states of both positive and negativeparity. The assignments shown in fig.6.12 are consistent with the measured DCO ratiosfor 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 thelowest-energy positive and negative parity ND bands to which the new triaxial SD bandsdecay 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) = l ib) from the out-of-bandto 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 Eltransitions between some of the ND bands in the same nucleus, 164Lu. The El decay fromSDl is associated mainly with an /i9/2 SD to i13/2 ND quasineutron transition, whereasthe 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-Zrare 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 agreementwith the calculated energy difference for 7 ~ +20° at I ~ SOh. In contrast, the measuredexcitation energies of the new SD bands in 164Lu as well as the 7ri13/2 SD band in 163Luappear 0.5 - 1 MeV lower in excitation energy than calculated for 7 ~ +20°. This mightimply problems with single particle intruder levels in the cranking calculations, or couldbe 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 inthe same early Euroball experiment as described in the preceeding contribution on triaxialsuperdeformed bands in 164Lu [1]. The previously known [2] superdeformed band, SDl, hasbeen extended both at high and low spin, and its connection to the normal-deformed stateshas been firmly established. This implies that the spin of the band has been increased by2 h relative to the spin suggested in [2].
The normal-deformed structures have also been extended, including both signatures ofthe [41l]l '2+ configuration to which the previously known SDl decays. For the low-spinstates of SDl J^ shows large fluctuations which are due to mixing of the 21/2 SD statewith the state of the same spin and parity in the [411]l/2+ band. The experimental energydifference 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 bandintensity can be explained by a mixing amplitude of a — 0.04 and an interaction strengthI Vint I = 21 keV, which cause a repulsion of 5.6 keV of the two 21/2+ levels. Correction for
52
•"<-*-,. >- ^ V a a S
[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 theinteraction strength \Vint\ < 4.5 keV between SDl and the [404)7/2+ band at 1=45/2. Wetherefore conclude that the local triaxial SD minimum has a larger barrier at the higherspin value.
In addition to SDl a new band, SD2, with similar dynamic moment of inertia J^ hasbeen 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 onebranch in the spin range 33/2 - 45/2 h. The connecting transition could not be firmlyestablished from the data.
The band SD2 and its decay to SDl might be consistent with the characteristic bandstructure of the wobbling mode [3), here built on the configuration of SDl, which is uniquelyrelated to a static triaxial shape.
References
[1] Preceeding contribution on triaxial SD bands in 164Lu.
53
168Hf N= 96 Pcon= 1 Ncon.= 1 it= 1 a=0
slep=0.2000 min = 16.947
l=50 l 68HfN=96Pcon=1Ncon.= 1 71= 1 a=0
step=0.2000 min = 23.073
l=60
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 b y t h 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 andB. 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 hyperdeformedshape with the axis ratios (3:1:1) be found close to yrast at the highest spin I w 60-80h 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] largeQt values corresponding to /32 ~ 0.42 (SD) were measured earlier using both RDM andDSAM techniques, and bands of this type have also recently been identified in the heavierLu isotopes. It is believed that these large triaxial deformations are due not only to theshape-driving effect of the intruder 7ri13/i2 orbital, but also the result of a re-arrangement ofthe core structure. Therefore large deformations with triaxial shapes may be expected as ageneral phenomenon also in the Hf, and perhaps also in the Ta and VV region. Calculationsfor 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 fusionreaction 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 oftransitions which are indicated by energy labels for 3 different triaxial SD bands, all foundto feed the yrast band in 168Hf.
This experiment was carried out at the ATLAS Accelerator, in Argonne, US, collecting3 • 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 informationon 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 thehighest spins in a search for both HD and triaxial SD band structures in a H-K gatedcubes. So far 3 different new bands with the expected energy characteristics for triaxialbands has been identified, as shown in fig.6.15. The population of these bands is unusuallyweak 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 detailedspectroscopic studies as well, currently under way. So far several new band structuresin both 169Hf and 168Hf are revealed, including 2 high-K coupled bands in each of thenuclei, with connecting transitions to the low-K bands in the 169Hf case. A full directionalcorrelated triple matrix is being constructed to generally emphasize the angular correlationinformation of the many new bands, aiming for finite multipolarity and spin determinationof these weakly populated structures. Beamtime at ATLAS for determining the lifetime ofthe 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-creased significantly [1, 2, 3]. Only five nuclei in the mass region with N~134, 222>224.226Ra
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 shouldposses 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 beamdelivered by the K130 cyclotron of the University of Jyväskylä. Promt 7-rays emitted attarget position were collected with the JUROSPHERE array in delayed coincidence withthe 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 positiveand negative parity states suggest the octupole nature of this nucleus. The extractedE1/E2 7-ray branching ratios, suggest that 226U possesses one of the largest El momentnear 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
-5008 10 12 14 16 18
Spin (h)
Figure 6.16: Results of band-mixing calculations for the hn/2 bands of m 175Ir, in whicha triaxial band (t), mixes with a prolate band (p). Dots- data; dashed lines - unperturbedbands; 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 m I r , 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, andin refs[l, 2], where results for 171>172pt and 171Os, populated in the same reaction, havebeen published.
The ground-state band of 171Ir is assigned to the hn/2 configuration. Energies for theband, less a rigid rotor reference, are plotted as a function of spin in fig.6.16. An interestingfeature is the large signature splitting observed. For a prolate shape, the Fermi surfacewould be located near high-fi orbitals of the hn/2 subshell and no signature splitting wouldbe 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 anintermediate, triaxial shape. Indeed, potential energy surface calculations performed usingthe code "Ultimate Cranker" predict a large assymetry parameter of 7 = -25°. At thehighest of spins, the signature splitting is sharply reduced. One scenario is that a shapechange, towards prolate deformation, is taking place. This is supported by comparisonwith the /i11/2 bands of 173Ir[3] and 175Ir[4], as shown in fig.6.16. The band in 173Ir beginsat 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 depressedin energy. These systematics are interpreted as the crossing of a prolate hn/2 band by atriaxial hn/2 band that decreases in energy with decreasing neutron number. Also shownon the figure are the results of band-mixing calculations which model this interpretation foreach of the three nuclei. A good fit is obtained in all cases. The reduction in energy of thetriaxial 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.
In addition to the hn/2 band, candidates for bands based on the nhn/2 ® (^i3/2)2 >7r^n/2 <8> "&13/2 <8> ^9/2 a nd xh9/2 configurations have also been observed. A full reporthas 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 (CERNand Brookhaven), a new interdisciplinary field emerged from the traditional domains ofnuclear and particle physics. What makes this field particularly interesting is the predictionof QCD that at high energy densities matter will undergo a phase transition to an entirelynew state, the quark-gluon plasma (QGP).
The nuclear physics group works within the CERN collaborations WA97 and NA57. Thework has focused on the measurement and study of the strange particle production in thenuclear collisions. The enhancement of such production is seen as a possible signature ofthe creation of the quark-gluon plasma (QGP). In 1998 the NA57 collaboration did its firstPb-Pb experiment, and 230 million events were collected.
During the years 2000-2005 the accelerators in CERN will be closed while the new LargeHadron Collider (LHC) in CERN is being installed. For this period we have joined theBRAHMS project that will perform nucleus-nucleus collision experiments in the RHICcollider (Brookhaven) with a centre-of-mass energy of 200 GeV per nucleon pair. Thisexperiment will in particular address proton and antiproton production both in the centraland 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 transversemomentum will also be studied.
The building of the future LHC facility was finally decided in 1994. As an integral part ofthe experimental program for LHC, a dedicated heavy ion collider (ALICE) that will takedata 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 improvedenvironment for the study of strongly interacting matter. In 1998 the Norwegian activitywithin the ALICE detector development has been concentrated on tests of the read-outelectronics for the PHOS detector, which measures electromagnetic radiation from theplasma. Also further studies of the data acquisition system (DAQ) for ALICE have beenconducted.
The reports from these studies are given in section 6.3.
6.3.2 Strangeness Production in Ultrarelativistic Nucleus-Nucleus andProton-Nucleus Collisions - The WA97 and NA57 Experiments
F. Fayazzadeh, M. Henriquez, A.K. Holme, G. L0vh0iden, T.S. Tveter, T. Vik and theWA97 and NA57 Collaborations
A strong motivation for the increasing interest in ultra-relativistic heavy-ion collisions is thepossibility 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 theBNL AGS and CERN SPS, however, an unambiguous confirmation of the QGP formationhas not yet been achieved. One of the possible signatures for this phase transition is anenhanced production of strange particles. The measurement of strange particle production
59
pad chambers
PTCsilicontelescope
5 cm
scintillatorpetals
Pb target
beam
0.5M channels
multiplicitydetectors
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 Qare 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-strangeparticles in nucleus-nucleus reactions with respect to proton-nucleus interactions has beensuggested as one of the sensitive signatures for a phase transition to a QGP state [6, 7]. Itis expected that the enhancement should be more pronounced for multi-strange than forsingly strange particles [8].
In view of the alternative explanations (hadronic gas or quark-gluon plasma scenarios) thatexist for the features observed in the search of the QGP, it is important to look carefullyfor any indication which could suggest the onset of a new mechanism for strange particleproduction when going from proton to Pb induced collisions. A well known example of apossible change of regime is seen in the production of charmonium states where a strongdecrease 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 designedto study the yields of strange particles and antiparticles carrying one, two and three unitsof 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 magneticfield of the CERN Omega magnet.
The 158 A GeV/c lead beam from the CERN SPS was impinging on a lead target withthickness corresponding to 1% of the interaction length. Scintillator petal detectors behindthe target provided an interaction trigger selecting roughly 40% of the most central Pb-Pb collisions. Two planes of microstrip multiplicity detectors covering the pseudorapidityregion 2 < i] < 4 provided information for more detailed off-line study of the centralitydependence of particle ratios and spectra. In the proton reference runs at 158 GeV/c atrigger 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 500and 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 cmbehind the target (90 cm for the p-Pb reference run) slightly above the beam line andinclined (pointing to the target) in order to accept particles at central rapidity and mediumtransverse 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 wereimproved using the lever arm detectors (1 pixel and 5 microstrip planes) and three MWPC'swith 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 functionof collision centrality and compared with yields in p-Pb [4]. We observed a strong increasein 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 markedhierarchy, i.e. the fi enhancement is larger than that of the S, and the E enhancement islarger than that of the A. Presently these findings are supported with improved statistics (afactor 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 thePodolanski-Armenteros plot [11].
The hyperons A, S~, Q~ and their antiparticles were identified by reconstructing theirdecays 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 foreach reconstructed A, E and Q and the calculation of hyperon yields are discussed inRefs. [4, 12, 13].
The differential distributions of the yield per event for each kind of particle were fitted intheir respective acceptance windows using the expression
d2iV
where mj is the transverse mass, y is the rapidity and a = 3/2. The fit was performedusing the method of maximum likelihood.
For the present analysis with limited statistics we have assumed the rapidity distributionsto 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 ofp-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 thepublished data [14], changes the values of T by less than 2%, 5%, 5% and 10%, in thecase of the h~, K°, A and A distributions, respectively. The corresponding changes in theparticle 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-Pbsample and Pb-Pb sample. These values, given in [12], are used in the analysis whichfollows.
The WA97 multiplicity detectors allow us to study particle yields as a function of collisioncentrality as measured by the number of participants Npart. To this purpose the multiplicityspectrum is divided into four bins and the average number of participants {Npart) for eachbin is calculated as described in [4]. For the interactions p-Pb the number of participantscorresponds to the estimated average for minimum bias collisions. The particle productionyield 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 d p T
where the extrapolation to the window \y — ycm\ < 0.5 and py > 0 GeV/c is done accordingto 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 functionof the number of participants (Npart)- The vertical error bars correspond to statisticaluncertainties only, and do not include systematic errors from feed-down nor from theassumption 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~ yieldin p-Pb collisions, however, a 15% systematic error has been introduced to account for theuncertainties due to the single track background subtraction procedure. The horizontalbars show the root-mean-square values of the number of participants in the selected binsfor 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 ofparticles with at least one common valence quark with the nucleon (S~, A, h~) and of theA'°, which has contributions ds and ds. Figure 6.18b refers to particles with no commonvalence quark with the nucleon: A, E and fi~ -j- £1 . It is instructive to analyze themseparately since the particles in the two groups are empirically known to exhibit differentproduction 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 perp-Pb interaction (i.e. each yield is rescaled so that the value for p-Pb is set to one). Theparticle yields in Pb-Pb are compared to a yield curve (full line) drawn through the p-Pbpoints and proportional to the number of participants, Npart.
All yields appear to increase with centrality from p-Pb to Pb-Pb faster than linearly withthe 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 beconstant. This is illustrated in Figure 6.19c and 6.19d, where we present the particle yieldper 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<Npar t>
Figure 6.18: Yields, defined in equation (6.9), as a function of the number of participantsfor 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
E-(Y)
(Npart) Pb-Pb
(6.10)
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 valuesare obtained if we use the data before the extrapolation to the full y — pi window. Wenote that the enhancement E increases with the strangeness content:
E(A)
and
In summary, the strange particle yields per participant at central rapidity increase fromp-Pb to Pb-Pb. The enhancement is more pronounced for multistrange particles, andexceeds one order of magnitude in the case of Q. As pointed out in [16], such a behaviourcontradicts expectations from hadronic rescattering models, where secondary productionof 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 i u n i |
10 102 103 1 10 102 io3
(Noart>part'
sia.L20)
110+•»
(ISa.'ora
n i i r i0 100 200 300 400
i r i r100 200 300 400
(Npart)
Figure 6.19: Yields, expressed in units of yields observed in p-Pb collisions, as a function ofthe number of participants for a) h~, Kg, A and E~; b) A, E and Q~ + Q . The solid linerepresents a function through the p-Pb point proportional to the number of participantsimpart}- The proton points are juxtaposed on the horizontal scale.
64
til
L
Q>O
c(0c
UJ 10
-
•
t
: h"1 • ' ' i ' •
•
1 '
•
A
*
1 1 ' '
*
A
, , | . ,
tm
i -
t
Otfi
0 1 2 1 2 3Strangeness [S[
Figure 6.20: Strange particle enhancement versus strangeness content.
Within the participant range Npart > 100, corresponding to our Pb-Pb data, all yields arefound to increase proportionally to Npart, as it would be expected if strange quarks areequilibrated 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 effectwith changes in the beam energy and/or the centrality (i.e. the number of participants inthe nucleus-nucleus collision). The observation of such a threshold effect would indicate adiscontinuity in the behaviour of highly compressed matter, as expected from a first-orderphase transition, and help to locate the transition point.
To reconstruct the decays of hyperons (A, E and Q) and K mesons in the high multiplicityenvironment of a central Pb-Pb collision, a high granularity telescope of silicon pixel planesis used. The high rate capability of these detectors allows one to collect a large number ofevents.
The apparatus, shown schematically in figure 6.21, is placed inside the 1.4 T field of theGOLIATH magnet. The main features of the apparatus are:
• A silicon telescope made of 13 silicon pixel planes, with about 1.1 million channelsin total; seven planes with a pixel size of 75 X 500 fim2 read out by the 0mega2 frontend chip and six planes with a pixel size of 50 X 500 /im2 read out by the Omega3front end chip.
• An array of six scintillator petals, placed 10 cm downstream of the target, to coverthe pseudorapidity range 1 < rj < 2 and provide a fast signal for the multiplicitytrigger.
65
Y pixel plane (3£>2 + 4Q3)
Z pixel plane (4Q.2 + 2Q.3)
158AGeV/c:d = 60 cm a = 40 mrad
40 A GeV/c:d = 30 cm a = 72 mrad
Double sidep. strips
10 m
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 thepseudorapidity 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 ofthe detectors on a line pointing to the target. The inclination angle a and the distance dfrom the target to the first pixel plane depend on the beam momentum in order to coverthe central rapidity region in both cases: at 158 A GeV/c (J/LAB ~ 2.9) a = 40 mrad andd = 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 atcentral rapidity using two stations of Multiplicity Strip Detectors (MSD). The number ofparticipants is estimated from the Wounded Nucleon Model by assuming proportionalitybetween the measured multiplicity and the number of participants ((Nch) = q(Npart)), andtaking experimental smearing into account [4]. Figure 6.22 shows a comparison betweenthe 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 NA57data extends the centrality range down to iVpar( > 40 which corresponds to triggering onabout 60% of the inelastic Pb-Pb cross section.
During the 1998 data taking periods 20 million p-Pb events at 158 GeV/c, 230 millionPb-Pb events at 158 A GeV/c, and 2.3 million Pb-Pb events at 40 A GeV/c were writtento tape. The hyperons and the K mesons are identified via the decay channels with onlycharged particles in the final state (as in WA97). Figure 6.23 shows the mass distributionsfor reconstructed A, A, 5~ and E from a small fraction (about 1%) of the 158 A GeV/clead-lead events. The full statistics should give in excess of 2000 E~.
66
la
o
da/d
-210
-310
-410
'- * 00
_• 0
• *
- f:• J: i
. I
-, , i i i
o WA97 data• NA57 data
— WNMfit
V
\ii , , . , i , . . , i , , , . i . , . . i , , . . i n
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 lineshows 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 I I S 1.2 1.22 1.24M(piz') [GeV]
NA57/199S/Pb-Pb run
I"
•
I I I 1 II I
NA57/19S&Pb-Pb run
; 1.1 1.2 IJ 1.4 1.5 1.6 1.1 l.S 1.9 2M(An") [GeV)
1.1 1.2 1.1 1.4 1.5 1.6 1.1 l.S 1.9 2M(An*) [GeV|
Figure 6.23: Invariant mass distributions for A (upper left), A (upper right), E (lowerleft), 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 fromhadronic matter to quark-gluon plasma by addressing the two main questions arising fromthe WA97 results, namely: (i) how the strange particle yields behave at lower numbersof participants, and (ii) how this behaviour depends on the centre-of-mass energy of thecollision.
To further extend the present work, an analysis based on a larger statistics sample is underway. Also data on p-Be collisions will be used to add an extra point in Figure 6.18 andFigure 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 Conferenceon 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 collisionsfrom 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-Pbcollisions at the CERN SPS, in Proceedings of the 13th International Conference onUltra-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 inPb-Pb collisions at 158 A GeV/c, in Proceedings of the 4th International Conferenceon 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 inPb-Pb and p-Pb collisions at 158 A GeV/c, in Proceedings of the 4th InternationalConference 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 IonPhysics at the SPS, HIPS-98, Chamonix, France, September 1998.
[17] V. Manzari et al. (NA57 Collaboration), The International Symposium on Strangenessin 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 theWA97 collaboration.
An enhanced production of A-hyperons with one strange quark is a possible signature for aphase 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 decaymodes:
A —» p7T~
A -> p>7T +
in 63.9 % of the decays andA (A) -> n7T°
in 35.8 % of the decays.
From the telescope tracks V° candidates are constructed. The V°s are neutral particleswhich decay to one positively and one negatively charged particle. Whether the V"°s areconsistent with p7r~~ or p?r+ can be decided by cutting on various parametres. The elementsin such an analysis are briefly discussed in [1].
Also the E~- and Q~-hyperons with two and three strange quarks, respectively, produceA-hyperons by the decay modes:
E~ ->• i\n~
in 99.89 % of the decays, andfi" -> AK~
70
in 67.8 % of the decays and similar for the antihyperons. The A production from the decayof E~ and f2~, known as cascade particles, is called secondary feeding. In order to deducethe correct number of As produced in primary processes, this secondary feeding must besubtracted.
The cascade particles travel some distance before decay, and the proton and pion from thelambda decay are eventually bent out of the telescope because of the magnetic field. Forthis reason the number of lambdas from the cascades should increase with the distancebetween target and telescope.
Equal amounts of quarks and antiquarks are produced in a QGP in order to preserve thebaryon number, therefore abundant numbers of antiquarks exist, which can easily produceantibaryons. The formation of antibaryons in a hadronic phase, however, can only takeplace with the production of a baryon-antibaryon pair, which demands an energy above2 GeV and thus is unlikely to happen. Moreover, because there are several ss pairs in aQGP, one is lead to the prediction that in a deconfined phase there is a hierarchy of particleproduction ratios:
Q+/Q~ > ~:+/2:- > A/A
From WA97 data it is seen that the experimental ratios indeed are arranged according tothis 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. Inother words, the ratio A/A should increase at larger distances. Thus, it is interesting tomeasure the lambda production at different distances from the target in order to determinethe importance of this secondary feeding effect. The experiment have been conducted atdistances 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, andcompared to the E!~-baryon production at the same distances. Firstly, the A/A ratiosfor 120 cm and 90 cm data will be established. Then the E!~ particle production will beaddressed, and the number of As that originate from these cascades estimated. The presentdata 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 providingaccess to the nuclear transparency regime. The collision zone is expected to consist of acentral, 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 forcreation of a quark-gluon plasma is present both at low and high net baryon density. TheBRAHMS experiment, which has an extremely wide coverage in rapidity, will search forQGP signatures in both regions.
BRAHMS . , .J'M.',
H2,T5 RICH
Forward Spectrometer2.3 < 0 < 30
Multiplicity
• Beam Beam counters
Mid Rapidity Spectrometer30 < e < 95
DxBeam magnets
D1,D2,D3,D4,D5: dipole magnetsT1,T2,T3,T4,T5, TPC1 TPC2: tracking detectorsH1,H2,TOFW: Time-of-flight detectorsRICH, 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 largeregion in the rapidity-transverse momentum plane by varying angular settings and mag-netic fields. Particle identification is done by combining momentum determination fromtracking in TPCs and drift chambers with velocity data from time-of-fiight measurementsand Cherenkov counters. The particles p, p, K*, 7r± can be identified over the entirerange 0 < \y\ < 4 and 0.2 < px < 3 GeV/c. Beam-beam counters provide initial triggerinformation, rough vertex determination and multiplicity at rj = 3 - 4. A multiplicitydetector covering the range -2.2 < rj < 2.2, consisting of an inner layer of Si strips andan outer layer of scintillator tiles, characterizes the centrality of the collision. Zero-degreecalorimeters measure spectator neutron multiplicity and luminosity. Details are given in
72
The BRAHMS experiment will investigate the yields and pr spectra for various hadronsat different rapidity intervals, covering both the central "excited vacuum" zone and thefragmentation regions, as functions of the centrality of the collision. The dependence onthe 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 degreeof stopping (the rapidity shift of the fragmentation region), which determines the energydeposition 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 usingdifferent models as indicated by the linetype. The rapidity range to be studied by BRAHMSis 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 increasedproduction of strange hadrons. BRAHMS will investigate the enhancement of the strangemesons K+, K~. Preliminary calculations indicate that it might also be possible to identifythe singly-strange baryons A, A over the full rapidity range of the spectrometer.
A quantity surviving rescattering during thermal equilibration is the entropy, which canbe computed from the particle multiplicity dN/dy per participant. The phase transitionmight 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 partonicscattering processes during the earliest phase of the reaction, and on the energy loss dE/dxof the resulting fast coloured particles in the plasma. RHIC is the first heavy-ion colliderfacilitating experimental investigation of the QCD perturbative regime.
The first year, RHIC is expected to deliver about 1 - 10% of nominal luminosity. The goalsfor the first months are getting the spectrometer operational and understanding its re-sponse under realistic beam conditions. The first physics measurements will include globalmultiplicity distributions and charged hadron rapidity distributions at selected transversemomenta 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 betweencharged identical mesons (pions, kaons) as a function of their relative and pair-averagedmomenta. Modifications of the 4> meson (decaying to a K+K~ pair) width and masswould be evidence of possible chiral symmetry restoration. The A, A baryons (decaying top7r~ and prr+, respectively) provide both interesting strangeness signals, measures of thebaryonic 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 thedefinition 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 trackingalgorithm 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 (updated1995).
[2] F. Videbaek, The BRAHMS Experiment at RHIC, Status and Goals. Proceedings ofthe Workshop on particle distributions in hadronic and nuclear reactions, UIC, June10 - 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. inPhys. 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 trackingmethod in BRAHMS and also in NA57 and predecessors is track following. At first "trackseeds" consisting of close-lying hits are found, and a first-approximation straight line orhelical arc is fitted to those. Then a search for new hits is performed along the extrapolationof the track, along with a stepwise refinement of the track parameters. In template matchingone utilizes a lookup table of pre-generated tracks with given momentum and startingpoint, 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 amodified \ 2 minimization procedure. The Hough transform [1], which is a general tool inimage analysis, maps regular geometric patterns in hit coordinate space to local maximain another parameter space. In the BRAHMS setup there is no magnetic field inside thetracking detectors (TPCs and drift chambers), giving straight line track segments whichare 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 betweenthe a; axis and the normal to the line x(z), and ptrack = £ o s m t̂rack is its distance of closestapproach to the origin. Similarly, each point (xi,Z{) on the line can be transformed into asinusoidal 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 "onevote" 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 byiterating over all channels along the 9 axis, computing the p values, and incrementing thechannels along the curve />;(#) by 1 (or a greyvalue, for instance the ADC value). TheN curves resulting from the iV hits will intersect in one point (#track, Ptrack) given by theexpressions 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 thecurves. 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 padrow, pad number and drift time from track to pad plane.) A linear track segment in threedimensions, defined by hits (xi,yi,z\), .... (XN, J/jVi ZN), is uniquely described by fourparameters: x(z) = axz+xo, y(z) = ayz-\-yo. and can in principle be transformed to a pointin a four-dimensional parameter space (9xz,pxz,9yz,pyz). This point will emerge as theintersection between N hypersurfaces in four dimensions: pxz,i(9Xz) — %i cos 9XZ + Xi sin 9Pyz,i {9yz) = Zi cos 9yz + yt- sin 9yz.
XZ,
In the experimental situation, hits from more than one track and noise will typically bepresent, giving rise to significant background and several local maxima, some of whichmight be spurious. In order to extract the individual tracks, a so-called adaptive Houghtransform algorithm [3] is useful.
The adaptive Hough transform is a fast and memory-economic iterative procedure, wherethe "votes" are distributed among a small number of bins. For each iteration, the globalmaximum in parameter space is located. The histogram limits are redefined, centering onthe present maximum and shrinking the window of interest while keeping the number ofbins constant, thus increasing the parameter resolution. At each step, hits whose Houghtransform curves do not pass through the current central window, are discarded. In thisway, one gradually "zooms in" on one unique track. Finally, the track segment parameterscan be calculated from the remaining hits, or taken directly from the coordinates of thewindow. These hits are now marked as "assigned" and removed from the general pool ofhits. To find the next track, one returns to the original, wide histogram limits and repeatsthe 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 testedon 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 15x15channels are used. The windows around the highest maxima in the (8xz,Pxz) a n 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 trackwidth.
The first simple tests indicate that the efficiency and reliability of the Hough transformmethod is comparable with the track following method for typical events in the BRAHMSTPCs. The application of the procedure on a relatively "dirty" event is illustrated byFigure 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 bothnuclear and high-energy physics. It is a general-purpose heavy-ion experiment, sensitiveto 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 energyscale involved (temperatures « 200 MeV). The experiment is designed to cope with thehighest 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 companyof 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.
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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 MuonCollaboration (SMC). The data taking was finished in 1996 and also the data analysis isapproaching 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 givenbelow. 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 equalspin temperature. Nucl. Instr. Meth. A 419 (1998) 60
[4] SMC, Spin asymmetries A\ and structure functions g\ of the proton and the deuteronfrom 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
yz Houflh transform]
D Q D a a • •
12 1.3 1.4 1.5 1.C 1.7 1.S 1.3Uiete yi
yz Houah transform
;• a o a > • • •,D D D DD O a a '
• - »OOLj_IJa o » • •• « o C O D a o a
t.GS 1.7 1.7S Mi
yz Hough transform I
IjODDDDDDDD " •• D D D DDDDDo. . o a a Dana:
• • • O O [
1.CSl.GCJ.G7l.Gffl.G91.71.7n.721.73Uieto yi
xz Houqh transform I
10 IS 20 ZS
-5
-10 ̂-ts
-20
-25
• • n D DO D Q Q o D O -
DOODaODDCo • . • a oD D a
xz Hough transform
DD D D D D D D CDDPDDDDDnDn'
•aaDDDo• o o a •
' - 2 0
xz Hough transform |
3 D Q OO <
i ad an a a 001100° ° "o p o Q D o o • n I I i ^ n c. • D o a o a
• • - . o o o e . i Q D D
fco
8
30
ZV
10
-is -io -s a
TPC Nts xz-proi
|
\
6 ia isx-cooniiiBta
1
J -30
zo
10
One track yz-proi. j
/
I
/0 6 10 15 ?0 23
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 transformin the 8yz,pyz and 9xs.pxz plane, respectively, during successive iterations. Second andfourth column: (yz) and (xz) projections of hits compatible with the window of interestfor the respective iterations.
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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
^ e p t . of Physics, University of Oslo, Norway2Norwegian 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 dwellingswas undertaken in the period 1987 - 89. In this survey, radon measurements were madeby CR-39 etched track detectors (six months integration time) in the main bedroom ofapproximately 7500 randomly selected dwellings built before 1980. The annual averageradon concentration for the whole country was calculated to 51 Bq/m3 (recent correctedaverage 53.8 Bq/m3) and 3.7 % of the results exceeded 200 Bq/m3. In a large proportionof single-family houses (including detached, semi-detached, row and terraced houses), theliving room and the kitchen are located on the ground floor while the bedrooms are on thefirst floor. In most cases the radon concentration is higher on the ground floor than on thefirst floor, and there may also be differences between bedrooms and other rooms on thesame floor owing to different ventilation conditions and ventilation habits. An additionalfactors that could have influenced the measurements was that the winters from 87 to 89were considerably warmer than normal. Based on these considerations, the annual averageradon 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 200Bq/m3.
In a recent study, the results of the nation-wide survey have be compared with the resultsof follow-up surveys in approximately 5000 randomly selected dwellings from 31 out of thetotal 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 detectorswere 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 themeasurement 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 thesame ratio for the whole country, the annual average concentration in Norwegian dwellingswas estimated to 106 Bq/m3. It was further estimated that approximately 10% and 4% ofthe housing stock exceeds 200 and 400 Bq/m3, respectively. The differences between thenation-wide survey and the present results could be explained by changes in ventilationconditions a.nd extensive use of aerated/light weighted concrete in the foundation walls inhouses built in the last three decades.
A new nation-wide survey of radon concentrations was started i 1998. In this survey, twomeasurements by CR-39 etched track detectors will be made in houses of 2000 randomlyselected 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 ofthe total number of approximately 6300 kindergartens in Norway. The measurements weremade by CR-39 etched track detectors and the integration time in the measurements wasthree 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 45Bq/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% ofthe kindergartens have mechanical ventilation systems which in most cases are switchedoff during the night. Additional measurements were conducted in a subgroup of kinder-gartens with mechanical ventilation systems and where the primary measurements gaveresults 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 therepeated 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 wherethe ventilations systems were operated in usual regime. No significant reduction of radonconcentrations could be observed in these kindergartens.
Assessment of radon exposure in both epidemiological studies and routine surveys aremainly based on time-integrated measurements of the radon concentration using etchedtrack detectors. However, these type of measurements are only surrogates of the exposureowing to the fact that most of the dose is due to deposition of short-lived radon daughtersin the respiratory tract and that only a very small contribution is from the radon gasitself. Earlier studies show that the radon concentration is more closely related to thebronchial dose than the concentration of the short-lived radon daughters, expressed interms of equilibrium equivalent radon concentration (EEC), but this is not necessarilyvalid 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 anumber 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 ongoingstudy focuses on uncertainties in the assessment of radon exposure and health risk basedon 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-life22.3 yrs) embedded in glass and other vitreous surfaces, or in volume traps of porousmaterials, have been investigated. Recently, a method for retrospective assessment ofradon exposure based on measurements of 210Pb in the human skeleton (measurements onthe scalp) has been developed and the results of preliminary measurements been comparedwith retrospective measurements on glasses from the same homes. The results are in verygood agreement for very high exposures {CRU > 10 kBq/m3 and CPb^hody^ >100 Bq) andthis 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 measurementsof very high concentrations of radon in indoor (> 10 kBq/m3). The technique is basedon area readings (darkening) instead of individual track readings. The method is verypromising and has recently been used for measurements of radon in soil gas in a geologicalstudy [4].
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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 forRisk 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 dangerouscombination? A case study from Kinsarvik, Norway. Workshop on Radon in the LivingEnvironment, 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 Oslo2Norwegian Radiation Protection Authority, P.O.Box 55, N-1345 0steras3Dept. of Geology ans Mineral Resources, Norwegian Technical University of Science andTechnology, 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 beencarried 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 bedrockaquifers 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 violatingdrinking 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 thebedrock groundwaters exceed the recommended action level of radon, while 16.1% exceedthe 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 theseparameters.
In another study, 72 samples of groundwater derived from Norwegian Quaternary (largelyglaciofluvial 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 fromNa-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, incontrast 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 sulphateand alkalinity/pH, suggesting dominantly lithological sources for non-marine sulphate. Nogroundwaters from Quaternary deposits exceed maximum recommended concentrations forRn, F- and Na, while 10% fall outside the required pH range. This again contrasts withbedrock aquifers where 30% of waters are non-compliant with respect to one or more ofthese parameters.
An extensive nation-wide survey of radon in ground water was started in 1996. Thisstudy is part of a nation-wide survey of groundwater quality in Norway. By the end of1998 approximately 4000 samples have been analyzed. Analysis of these data show thatapproximately 15 % of all Norwegian households taking their water supply from drilledwells in bedrock have radon concentrations exceeding the recommended action level of 500Bq/1 [5]. The highest concentrations (above 10,000 Bq/1) have occurred in uranifereosgranites in the south-eastern part of Norway. Release of radon to indoor air may increasethe risk of lung cancer, but intake of radon containing drinking water may also increasethe 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 ofNorwegian Groundwaters: I The distribution of radon, Major and Minor Elements in1604 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, Kjemiskkvalitet 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 Chemistryof Norwegian Groundwaters: II. The chemistry of 72 groudwaters from Quaternarysedimentary 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, Kjemiskkvalitet av grunnvann fra l0smasser i Norge, NGU-rapport 98.089, 96 sider, Norgesgeologiske unders0kelse, 1998 (in Norwegian).
[5] T. Strand and B. Lind B, Thommesen G. Naturlig radioaktivitet i husholdningsvann fraborebr0nner i Norge, Norsk veterinasrtidsskrift 1998; 110 (19): 662-665 (in Norwegian).
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Chapter 7
Theoretical nuclear physics andnuclear astrophysics
7.1 Introduction
Nuclear physics is the science of atomic nuclei, aiming at understanding the propertiesof nuclei, their interactions and their constituents. Properties of nuclei are determinedby 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 theoreticaldevelopment 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 ofstate of nuclear matter relevant for studies of supernovae and neutron stars, to mentionjust 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, theoreticallyand experimentally. At higher energies, the substructure of nucleons and mesons interms of quarks and gluons becomes visible and one of the great challenges of modernnuclear physics is to study how elementary particles like quarks and gluons, describedby the underlying theory of quantum-chromo-dynamics (QCD), build up hadrons suchas mesons and nucleons. The study of the structure and the dynamics of hadronsform then important topics in our basic understanding of nuclear properties. The wayhadronic properties change when hadrons are inserted in a nuclear medium are keyissues in understanding, both from the point of view of QCD and nuclear physics,relativistic heavy-ion collisions where matter can be heated and compressed underextreme conditions. Huge efforts are devoted to detecting the deconfinement of quarksand 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 energiesis also important for calculations in nuclear astrophysics. It suffices to mention therelation between nuclear physics and the physics of Supernovae of type II. When theiron core of a star undergoes a core collapse to very high densities, the outcome maybe a type II supernovae and-or black hole. Nuclear physics aspects which stronglyenter the final outcome are the nuclear equation of state and how neutrinos interactwith matter, together with the treatment of the hydrodynamics of the explosion. Thenucleonsynthesis accompanying such an explosion gives rise to a large fraction of the
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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 alsoon our understanding of the equation of state for nuclear matter and neutrino processesin dense matter.
Our research covers several fields of nuclear physics and nuclear astrophysics, rangingfrom nuclear structure studies to the structure of neutron stars. Common to mostproblems studied is an underlying microscopic description, within the framework ofmany-body theories, of the interactions between the various hadrons.
We do also study problems related to the foundations of quantum physics such as thenon-separability of systems in a pure quantum state and the completeness of quantummechanics. 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 ofBohr's complementarity concept and his understanding of the nature of measurementsinvolving 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 studyof exotic nuclei far from the valley of beta stability, presents important challenges fornuclear physics. Nuclear structure studies are also important in nuclear astrophysicsstudies, e.g., for the understanding of the synthesis of the elements, and to understandweak 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 anunrestricted 2sldOg7/2Ohu/2 shell model (SM) calculation. The interaction used in thesecalculations is a realistic two-body G-matrix interaction derived from modern meson-exchange potential models for the nucleon-nucleon interaction. For the shell model allthe two-body matrix elements are renormalized by the Q-box method whereas for theMQPM 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
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We calculate the low-lying spectra of heavy tin isotopes from A = 120 to A — 130 usingthe 2.sld0<77/20/i11/2 shell to define the model space. An effective interaction has beenderived using I32Sn as closed core employing perturbative many-body techniques. Westart from a nucleon-nucleon potential derived from modern meson exchange models.This potential is in turn renormalized for the given medium, 132Sn, yielding the nuclearreaction matrix, which is then used in perturbation theory to obtain the shell modeleffective 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. Theshell 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-nucleoninteraction. The results are compared with the recently proposed experimental Yraststates. 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, Japane 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 CyclotronLaboratory, Michigan State University, E. Lansing, MI 48824h Department of Physics,University of Jyvaskyla, FIN-40351 Jyvaskyla, Finland
On-line low temperature nuclear orientation (OLNO) experiments have been performedon 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 tobe /Li(7/2+ 13oI)=2.940(2)/tiyv thereby extending the known data on these states inodd-A I isotopes up to the neutron shell closure at N=82. Shell-model calculationshave been performed for the magnetic moments of 7/2+ states in the N=82 isotonesusing free-nucleon and effective ^-factors. The effective ^-factors are obtained froma perturbation calculation that includes corrections for core polarization and meson-exchange currents. The proton number dependence of the magnetic moments in the
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sequence of N=82 isotones 133Sb - 139La is discussed in terms of blocking of the Ogg/2to 0gT/2 core polarisation with increasing 0gr/2 occupancy. Systematics of all measured7/2+ 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 theZ = 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, Poland6 GANIL, Caen, France0 University of Tennessee, Knoxville, Tennessee, USAdIPN Lyon, Villeurbane, FranceeIAP, Bucharest-Magurele, Rumania^GSI, Darmstadt, Germany5IPN, IN2P3-CNRS, Orsay , France^Physics Division, ORNL, Oak Ridge, Tennessee, USA'IKS, Leuven, BelgiumJCE Bruyres-le-Chatel, France
New isomeric states in the neutron-rich nuclei near the Z= 28 and N=40 shell closureshave been identified among the reaction products of a 60.3A MeV 86 Kr beam on a natNi target. From the measured isomeric decay properties information about the excitedstates and their nuclear structure has been obtained. The isomerism is related mostlyto the occupation of the neutron g9/2 orbital, an intruder level in the N=3 fp shell. Itis illustrated with the decay properties of 69 Ni m , 70 Ni m , and 71 Cu m interpretedwithin 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 thels-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 37831USA and Department of Physics and Astronomy, University of Tennessee, Knoxville,Tennessee, USA6Astronomy and Astrophysics Center, University of Chicago, USACW.K. Kellogg Radiation Laboratory, California Institute of Technology, USA^Institute for Physics and Astronomy, Aarhus University, Denmark
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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 saturationand 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. Theresults indicate that SMMC can reproduce binding energies, B(E2) transitions, andother 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 studiesis 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 effectiveinteraction and effective operators which enter shell-model studies of weak processeswhere 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. Muoncapture has great importance in fundamental physics theories as it can be used in thedetermination of the weak-interaction coupling constants. Compared with the moretraditional and well studied /3 decay with electrons, the energy release in the muoncapture is 200 times larger than that in the electron capture. This energy transfer fromthe muon makes it possible to excite many nuclear levels in the daughter nucleus anddue to the large momentum transfer the reaction is therefore sensitive to those partsof 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)) 16Obelow particle-emission threshold. We wish to study here medium renormalizations ofthe isoscalar axial coupling constant, as this may affect the predicted rates for theabove mentioned neutrino-scattering reactions.
Moreover, neutrino scattering processes like (.4, Z) -f- v(V) —> v(y) + (.4, Z) are alsothought to be important in the synthesis of the elements, where the so-called j/-processappears to be very promising in explaining the so-called p-process in the synthesis ofthe elements. The p-process is important in the understanding of the synthesis of theheavy 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, aprocess we wish to study is the neutrino capture 92Zr(f, e~) 92Nb and 92Nb(z/, e~) 92Mothrough 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 datawhich 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 suggesta very small value (~ 0) for Cp/C\, quite far from the PCAC prediction and recentdata on muon capture in hydrogen. We show that this rather disturbing anomaly issolved by employing effective transition operators. This finding is also very importantin 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 press2. T. Siiskonen, J. Suhonen, and M. Hjorth-Jensen, submitted to J. Phys. G
7.3 Hadron properties in the medium: Nuclear structureaspect
The last decade, through measurements done at NIKHEF in Holland, at MAMI inMainz and now TJNAF in the USA, has been marked by a remarkable interplay betweenmany-body theory and high precision electron scattering experiments. The nuclearresponse has been measured at high momentum and into the continuum. The partialoccupancy of mean-field orbits obtained from these experiments is one of the cleanestsignatures of nucleon-nucleon correlations. To understand such correlations forms a veryactive field in nuclear physics and to elucidate the short-distance structure of nucleiwill be a topic of special interest in the future. Nuclear structure studies of hyperonsprovide also a new input to the nuclear many-body problem. Hyperons are baryons witha 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 constrainthe 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 therelevant self-energies. The latter are constructed within the framework of a perturbativemany-body approach employing present realistic hyperon-nucleon interactions such asthe models of the Jiilich and Nijmegen groups. The effects of the non-locality andenergy-dependence of the self-energy on the bound states are investigated. It is alsoshown that, although the single-particle hyperon energies are well reproduced by localWoods-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 decayof 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, inpreparation for Phys. Lett. B
7.4 Nuclear astrophysics and dense matter studies
Our research in nuclear astrophysics has dealt mainly with theoretical studies of theequation of state for dense nuclear matter, determination of properties of neutron starssuch as the total mass, radius, phase transitions and the composition of matter in theinterior 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 toterrestrial 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 thousandthof nuclear matter saturation density, nuclei reach the so-called neutron drip line. Athigher densities nuclei coexist with a neutron liquid and they eventually dissolve justbelow nuclear matter saturation density.
Important issues in neutron star studies deal with theoretical determinations of theequation of state up to densities several times nuclear matter saturation density. Athigh densities matter consists of interacting baryons (neutron, protons and possiblyhyperons 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 thento 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/neutronratio and neutrino emission processes. The latter processes are also of great importancesince 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, suchmeasurement 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 regionincrease due to the decreasing centrifugal forces and phase transitions may occur in thecenter. We extract the analytic behavior near the critical angular velocity QQ, wherethe phase transitions occur in the center of a neutron star, and calculate the momentof inertia, angular velocity, rate of slow down, braking index, etc. For a first orderphase transition these quantities have a characteristic behavior, e.g., the braking indexdiverges as ~ (Qo — ^)~1 / '2 . Observational consequences for first, second and otherphase transitions are discussed.
1. H. Heiselberg and M. Hjorth-Jensen, Phys. Rev. Lett. 80 (1998) 5485-5488
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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 smoothextrapolation to high densities including causality, we constrain the equation of stateand calculate maximum masses of rotating neutron stars. First and second order phasetransitions to, e.g., quark matter at high densities are included. If neutron star massesof 2.3M® from quasi-periodic oscillation in low mass X-ray binaries are confirmed, asoft equation of state as well as strong phase transitions can be excluded in neutronstar 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 phasetransitions arising in neutron stars such as pion, kaon and hyperon condensation, su-perfluidity and quark matter. Specifically, we treat the nuclear to quark matter phasetransition, the possible mixed phase and its structure. A number of numerical cal-culations of rotating neutron stars with and without phase transitions are given andcompared 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 withnucleonic and hyperonic degrees of freedom, employing the most recent parametrizationof the baryon-baryon interaction of the Nijmegen group. The structure of /3-stablematter is presented up to total baryonic densities of 1.2 fm~3. Implications for neutronstars are discussed.
1. I. Vidana, A. Polls, A. Ramos, L. Engvik and M. Hjorth-Jensen, submitted toPhys. 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
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a KVI. Groningen, Holland
The thermal evolution of a neutron star may provide information about the interiorsof the star, and in recent years much effort has been devoted in measuring neutronstar temperatures, especially with the Einstein Observatory and ROSAT. The maincooling mechanism in the early life of a neutron star is believed to go through neutrinoemissions in the core of the neutron star. The most powerful energy losses are expectedto 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 massiveneutron stars (M < 1.3- 1.4M©), the direct URCA process is allowed at densities wherethe momentum conservation kF < kF + kp is fulfilled. This happens only at densitiesp 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 tworeactions
+ e^n + n + ve, (7.2)
occur in equal numbers. These reactions are just the usual processes of neutron /?-decayand electron capture on protons of Eq. (7.1), with the addition of an extra bystanderneutron. They produce neutrino-antineutrino pairs, but leave the composition of matterconstant on average. Eq. (7.2) is referred to as the neutron branch of the modified URCAprocess. 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 wherethe muon and the muon neutrinos (u^ and v^) replace the electron and the electronneutrinos (Fe and ue) in the above equations. In addition one also has the possibility ofneutrino-pair bremsstrahlung, processes with baryons more massive than the nucleonparticipating, such as isobars or hyperons or neutrino emission from more exotic stateslike pion and kaon condensates or quark matter.
The aim of this project is to reanalyze the various neutrino emissivities discussed aboveaccounting 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 toinfinite nuclear and neutron matter. Most efforts to describe this system have mainlyfocused on the role of nucleonic interactions at zero and finite temperature, while lessattention 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 theother hand, there are important observables of astrophysical relevance that might beinfluenced by the presence of vortex lines. A mutual check of the nuclear many bodyphysics and of the theory of neutron star interiors comes from the study of pulsar
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glitches, sudden increases in the spinning frequency of the crust of a pulsar, followedby a slower tendency to conditions close to the original ones. It is thought that glitchesand postglitch relaxation represent a direct manifestation of the presence of superfiuidvortices in the interior of the star, the triggering event being an unbalance betweenthe hydrodynamical forces acting on the vortex and the force of interaction of thevortex with the nuclei present in the crust (pinning force). There have been quite largeuncertainties regarding the value of the pinning force, leaving room for quite oppositeviews about the validity of the vortex pinning model. One source of uncertainty isrelated to the value of the pairing energy gap in uniform neutron matter, a quantitystrongly dependent on the value of the neutron particle-particle matrix element nearthe Fermi surface. A second problem is due to the very approximate way of treatingvortex 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 wherekp 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 tothe loss of superfluidity that occurs when the two objects superimpose.
In our project we study the structure of a vortex in superfiuid neutron matter usinga microscopic, fully quantum-mechanical approach, using the Bogoliubov-de Gennesequations which have been successfully employed to study vortices in type II super-conductors and more in general non-homogeneous superconductivity. One of our maingoals 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 havea number of consequences directly related to observation. Among processes that willbe affected is the emission of neutrinos. Neutrino emission from e.g. various URCAprocesses is expected to be the dominant cooling mechanism in neutron stars less than105 —106 years old. Typically, proton superconductivity reduces considerably the energylosses in so-called modified URCA processes and may have important consequencesfor the cooling of young neutron stars. Another possible manifestation of superfiuidphenomena in neutron stars is glitches in rotational frequencies observed in a numberof pulsars. Moreover, the estimation of superfluid gaps and studies of pairing are notonly important issues in neutron star matter, but also in the rapidly developing fieldof neutron-rich systems such as heavy nuclei close to the neutron drip line or the studyof light halo nuclei. Therefore, theoretical studies of pairing in neutron-rich assembliesform currently a central issue in nuclear physics and nuclear astrophysics.
7.5.1 Nucleon-nucleon phase shifts and pairing in neutron matter andnuclear matter
0. Elgaroy, M. Hjorth-Jensen
We consider 1SQ pairing in infinite neutron matter and nuclear matter and show thatin the lowest order approximation, where the pairing interaction is taken to be the bare
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nucleon-nucleon (NN) interaction in the 1SQ channel, the pairing interaction and theenergy gap can be determined directly from the 1So phase shifts. This is due to thealmost separable character of the nucleon-nucleon interaction in this partial wave. Sincethe most recent NN interactions are charge-dependent, we have to solve coupled gapequations for proton-proton, neutron-neutron, and neutron-proton pairing in nuclearmatter. 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 nuclearmatter
0 . Elgar0y, L. Engvik, M. Hjorth-Jensen, E. Osnes
After presenting solutions of the coupled, non-relativistic 3Si-3Di gap equations forneutron-proton pairing in symmetric nuclear matter, we proceed to estimate relativisticeffects by solving the same gap equations modified according to minimal relativityand using single-particle energies from a Dirac-Brueckner-Hartree-Fock calculation. Wefind that the relativistic effects decrease the value of the gap at the saturation densitykp — 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
7.5.3 3P2-3F2 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
We present results for the 3P2-3F2 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 1.7poiwhere po is the saturation density for symmetric nuclear matter. In order to makepredictions above that density, potential models which fit the nucleon-nucleon phaseshifts 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
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7.6 Nucleon-nucleon interactions and nuclear many-bodytheory
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, USA6 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. Significantdifferences are found, which are traced back to the matrix elements of the potentials atmedium and large momenta. The influence of the localization of the one-pion-exchangecontribution 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 thiswork. Especially, I focus on the summation of so-called Parquet diagrams with emphasison applications to finite nuclei. Here, the subset of two-body Parquet diagrams will bediscussed. 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 JoakimBergli's Cand.scient. thesis "The vacuum in quantum field theory. A challenge to presentday physics"'. Special attention was given to the problems arising form the zero pointenergy 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 invarianceof the vacuum energy density was discussed and it it was shown that the only finitespectral energy density preserving Lorentz invariance is the spectral density identicallyequal 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 thesame time is Lorentz invariant.
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We have also studied the possibility that quantum theory results as a consequenceof symmetry is continued. The study is based on the work by Aage Bohr and OleUlfbeck: "Primary manifestation of symmetry. Origin of quantal indeterminacy" Rev.Mod. Phys. Vol. 67 1995 pp 1-35.
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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. RekstadThe solar energy laboratory, abbreviated the Sun-Lab, is located in front of the PhysicsDepartment building. This is a small test facility for solar heating and radiative coolingsystems.
. :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 Norwegianbuilding traditions. The orientation of the house is south-west, with a surface asimuthangle of 7=+18°. The tilt angle of the roof is 32°. The house is equipped with a thermalsolar 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 thesouth, with an aperture area of 5.3 m2. The cooling system, placed on the north facingpart of the roof, consist of an array of 8 modified solar flat plate collectors, with anaperture area of 10.8 m2.
96
The structure of the solar collector is shown in Fig. 8.2. It consists of a black absorberplate in Noryl PX507 plastics, and a transparent cover sheet in PC-plastics. The heatcarrier fluid is water, which is being pumped to the top of the collector and drivenby gravity trickles down through the absorber to remove heat. By filling the absorberwith ceramic granulates, a capillary effect is achieved which ensures optimum thermalcontact between the water and the hot absorber surface [1].
The cooling panels have a similar construction to the solar panels, but slightly modifiedin that the cover sheet has been removed to enhance the emissive cooling capacity. Bycirculating water through the cooling panels during night time, temperature loss isbrought forward by radiation and convection. The hot panel surface will be a strongemitter of infrared radiation and exchange heat with the cold air layers higher up inthe 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 allowsswitching 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 toincrease when heat exchangers are avoided [2], [3]. The water from the solar loop isthus directly coupled to the heat store.
Both the cooling and heating systems can be connected to the two storages. Testingdifferent 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 heatexchange processes, as well as a determination of the optimum operation conditions forthe 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 floorconstruction. The concept is based on a combined system for domestic hot water andlow temperature space heating. The floor heating system is directly connected to the1000 liter store. Auxiliary heating is supplied when the irradiation is not sufficient tocover the load.
97
An electronic control unit starts and stops the system when heat gain or loss is achievedrespectively. The controller ensures a safely operating system by draining the systemwhen approaching temperatures close to boiling or freezing limits. The system is opento atmospheric pressure [4].
Several experiments are presently being carried out at the Sun-Lab. The main fieldsinclude measurements of collector performance, studies of radiative cooling panels, acombined system for domestic hot water and low temperature space heating, a combinedthermal and photovoltaic solar collector, and development of an energy measuringsystem.
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 ogsolvarmeanlegg, 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 / ,temperature rise in the heat store Ts iore, ambient temperature Tambient, and indoortemperature TindOOr- The storage volume was in this case 300 liter and the flow rate720 1/h.
in
3D
Temperatire(pegr.C) ^
10
D
1 1 1 r-
-
_
6999:1DSD1I}
i | i t
. . —
¥i
6999:12mm
— i j 1 1 1 1 1
> ^ ;
Tflidoor) — •—-—.=~—~^
i — , — ;6993:UmO) 6999:16fflm
3000
2500
2000
1500
1000
500
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 thereceived energy from the sun;
Wstored
Qsun(8.1)
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 timeinterval At,-, during which steady temperature conditions and constant irradiation canbe approximated. The calculated efficiency curve corresponding to the dataset of the1st of March 1999 is shown in Fig.8.4.
The efficiency is plotted as a function of the parameter [TstOre - Tambient\l'I', therebyassuring a result unaffected by the varying irradiation levels. The efficiency is propor-tional to the temperature difference between the heat store (and hence the temperatureof 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 constantrate.
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 recordedvalues, giving considerable uncertainties connected to the received solar energy.
The Hottel-Whillier equation states that thermal efficiency is a linearly decreasingfunction of [TstOre - Tambient\/I,
V =[̂ store J- ambientJ (8.2)
where FR is the collector heat removal factor, r)0 the maximal efficiency, reduced byoptical losses (?7o=roQ'o)i ar>d UL the collector heat loss coefficient [1]. When rj is plottedagainst [Tiager — Tambient]/1 > the intersection with the Y-axis is given by FRTJO, andFRUL is the slope of the curve. By applying a linear curve fit to the efficiency data, asshown 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 fluidcirculating through the collector. The efficiency is then determined by
mC[To -
I A*(8.3)
99
where C is the heat capacity of the fluid and Ac is the collector aperture area [2]. Exactmeasurements of the inlet- and outlet temperatures are demanding, and thus oftenperformed in test facilities where sun- and wind simulators assure steady conditionsduring the measuring period. The collectors are irradiated at a normal incidence angle,while inlet and outlet are held at fixed temperatures. The calorimetric method introducea convenient tool to avoid these procedures. However, in order to compare the efficiencymeasurements performed at the Sun-Lab with international standards, a few correctionshave to be done.
Firstly, the incidence angle will vary throughout the day as the sun moves across thesky. 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 thereforebe reduced by a factor equal to the decrease in transmission of the cover sheet at thegiven incidence angle,
/ -r(0)
where / is the recorded irradiation, Icorr the corrected value, r{9) the transmission ofthe coversheet at an incidence angle 6, and r(0) the transmission at normal incidenceangle. 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 thermalequilibrium 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 additional33,5 kj per square meter collector area has been stored in the system. This energymust be added to the stored energy in the water tank as a compensation for unsteadytemperature conditions,
Q stored = Qw + Qp (8.6)
where Qw refers to the stored energy in the water storage, and Qp refers to storedenergy 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 benoted that this efficiency is a system efficiency, rather than a collector efficiency. Fig.8.5displays the efficiency points before and after corrections are applied. The effect of thecorrections is to increase the system efficiency.
The heat carrier's ability to remove heat will depend on the flow rate. Fig.8.6 displaysthe system efficiency at four different flow rates for the 300 liter store volume. Theresults show an increased maximal efficiency at the higher flow rates. In addition, thecurves indicate that the flow rate should be reduced when approaching temperatures inthe 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 presentlybeing 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 theheat storage. In order to approximate steady conditions, time intervals of about 10-20minutes are chosen for the determination of one point on the efficiency curve. Thisimplies measuring quite small temperature differences, requiring reliable temperature
101
readings. However, the temperature sensors. 10K thermistors, seem to be influenced bythe humid environment in the water store. Their resistance have changed over time,giving differing temperature readings. This has called for a thorough calibration of allsensors involved. One of the encountered problems has been drift of sensor values, evenafter calibration. In an attempt to find a permanent solution of the problem, the sensorshave been placed inside a closed glass tube, filled with a highly conductive powder andsealed with silicon. Regular control procedures will reveal any new incidences of defectsensors 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 thelocal wind conditions during heating and cooling experiments. Based upon 3 series ofmeasurements performed in a wind tunnel at the Agricultural University of Norway,the anemometer has been given a calibration function converting the recorded signalsto units of meter per second. Fig.8.7 shows a) the anemometer mounted at the centerof 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 windtunnel. b)A graphical presentation of the calibration results.
8.0.5 Data acquisition system for a building integrated solar heatingsystem
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 ayear. 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 aflat plate collector [2], a heat store, circulation pumps for solar and floor loop and atemperature controller. The electronic controller is reading out different temperaturesand the intensity of the solar radiation. The operation of the solar heating system iscontrolled by these parameters in a way that the system's efficiency is optimized.
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TEMPERATUR-F0LER
OVERL0PSR0R"PAFYLL1NGSROR
IED KRAN
TUR
OVERTEMP. SHUNT
VARMELAGER
Figure 8.8: Combined solar system for domestic hot water and space heating [SolarNoras].
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 minuteduring 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 theuser of a solar heating system gets information about the functionality of the systemshort time after startup.
The first approach was to study solar thermal heating systems, methods for calculatingthe energy demand to domestic hot water and floor heating, and methods for calculatingthe solar contribution.
An usual way to calculate the energy output is to measure the flow of energy in aheating system [3]. This method is often used to calculate the solar gain by measuringthe flow of energy transfered from the heat store into the house.
When the amount of energy consumed during a certain period and the amount ofenergy transfered from other sources are known, the solar contribution to heating canbe calculated. There is an usual way to calculate the need of energy for domesticheating. In the present study we estimate the heating demand in a building by meansof the so-called "response function". To the first order this function is proportional tothe difference between the ambient and the indoor temperature (eq. 8.8).
Q6r(AT) = kA{AT - &TC) = kAAT - konst.
~ 1 inndoor 1 ambient
(8.8)
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 theresponse function. The program is written in the computer language C. And finally, topresent 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. UniversityofOslo(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, Energimalingeri 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. IngebretsenIn order to design an optimal solar collector system, it is necessary to simulate theoutcome on a computer, by varying and optimizing the system parameters. During thelast year, a simulation program has been developed for this purpose. This is a new andimproved 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 programwill calculate the solar gain of the system. It can also simulate the effect which a changein one or several system parameters has on the solar fraction. A one year's calculationwith one hour steps takes 3-4 seconds on a 200 MHz Pentium PC, which is faster thanother simulation tools (for instance TRNSYS and Tsol). The figure below shows anexample of a screenshot, the graphical user interface after a calculation of the solarfraction 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 surfacesto horizontal surface values
G.M. Haugen and F. IngebretsenIn 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 varyingcollector slope.
tilted 45° has been measured and accumulated at over 70 schools in Norway and othercountries in Northern Europe. Most data and insolation maps are based on measure-ments against horizontal surfaces.Therefore it is useful to transform the SOLIS datato horizontal insolation values. During the last 1/2 years a transformation model andcomputer program has been developed. The model is based on the assumption that theinsolation consists of three different components which can be treated independentlyof 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 diffusecomponent is directly determined by the zenith angle of the sun and the amount ofextraterrestrial solar insolation that reaches the surface. Different models have beentested [1] [2]. The results are compared to solar irradiation recordings simultaneouslymeasured 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 (SolarEnergy, 36, 1983) 333-344
8.0.8 A Combined Thermal and Photovoltaic Solar Energy Collector
B. Sandnes and J. RekstadA solar energy heat collector was combined with photovoltaic cells to form one singlehybrid 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 componentsdisappear for low atmospheric transmission.
and electricity. The thermal system removes absorbed heat from the collector, therebycooling the photovoltaic cells. Increased solar cell power output is thus achieved, sincephotovoltaic conversion efficiency is a linearly decreasing function of temperature [1].
A combined thermal and photovoltaic test collector was successfully constructed bypasting single-crystal silicon cells on a black flat-plate solar heat absorber. This unitwas 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 withan additional cover glass (g). Current-voltage characteristics were recorded for seriesand parallel connection of the photovoltaic cells, over a range of temperatures.
The experimental results revealed a and c as efficient absorbers of sunlight, but withhigh 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 reflectionfrom the glass surface. Efficiency curves are plotted in Figure 8.11. A reduced solarenergy absorption in c compared to a was attributed to a lower optical absorptionin the photovoltaic cells compared to the black absorber plate, and also to the heattransfer resistance introduced in the cell/absorber interface. When electrical power isextracted from the photovoltaic unit, the incident solar energy available for the thermalsystem 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 celltemperature was shown to be strongly correlated to the inlet fluid temperature, andalso a function of thermal efficiency, irradiation and collector properties (different forthe 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 photovoltaiccells [3]. The model simulated the temperature development of the system, and the
106
>oc<D
0.90-
0.70
0.50--
0.30--
I I I 1 I I
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: blackabsorber 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 resultswere 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 powersource. In the present system a solar cell is used to power the pump which circulateswater in the solar loop. We investigate a system which consist of a solar collectorarray, 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 governsthe power generated by the photovoltaic cells. The performance of the thermal systemwill be investigated by measuring the heat delivered to the store as a function of theambient 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 theperformance tests was carried out in a one-family house [1] during the winter season98/99.
In conventional heating systems the temperature regulation is based on indoor thermo-stat control. In low temperature heating systems as hydronic floor heating, the largeheat capacity of the floor mass would cause an unacceptable long response time forindoor temperature regulation.
The temperature control principle investigated is based on the dependency betweenspace heating demand and ambient temperature. The controller calculates the energydemand 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 isdelivered in terms of an "energy pulse" within the time top,j. In practice the controllerdetermines the operation time t0P); of the circulation pump for the time interval Att-.
TEMPERATURE CONTROLLER
ownp £tstns
1 nAt,
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 ambienttemperature and the supply temperature to the floor heating system.
The controller unit is directly regulating the floor circulation pump or a motor drivenshunt valve. The heat delivered to each single floor circuit is controlled by manualmixing valves at the manifold. One aim of the experiments was to investigate theindoor temperature stabilisation by a control principle which is based on sequentialpump operation.
A motivation for developing this control strategy was the possibility to easily performenergy 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 consciousconsumption behavior. In low temperature heating systems, energy monitoring to af-fordable cost and limited technical installations represents a technical challenge. Thesequential pump operation by the controller introduces a straight forward possibilityfor energy monitoring. As the energy is delivered in pulses, the total operation time ofthe 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 ortemperature - 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 controllerstabilizes the indoor temperature while outdoor and inlet water temperature to the floorcircuit show fluctuations.
References
[1] J. Rekstad, S. Bjerke, F. Ingebretsen, Rapport om solenergifors0k ved fors0kshusi 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 floorshave been evaluated [1]. One distributor (A) is a new product with a specially extrudedaluminium 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 thedistributors was compared by testing them in parallel integrated in the floor heatingsystem at the Sol-Lab.
The heat transfer coefficient represents the heat conductivity from the liquid inside thePEX-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 heatdistribution plates in wooden floor heating systems, internal test report, Universityof Oslo, Dept. of Physics, 1998
109
40 . ,L.
I
35 i-
At
\
t r| 3 0 S-s tS.* 25
,7(supply) ^
,T(relurn)
V/. \
20
15
- T (alum, distributor) (A)
r T (floor surface)
T (indoor)
6959:21-.00:00 6959:22:00:00 6959:23:00:00
time (day#: hh: rnm: ss)
6980.00.00:00
Figure 8.14: Heat transfer in a suspended wooden floor construction. Illustrated are thesupply and return temperature to the floor circuit, the temperature of the aluminiumdistributor (here only type A). To the top the operation time t0Pin of the pump within theconstant time interval Atn is shown (see also fig. 8.12).
110
Chapter 9
Seminars
Date:19.02 J. M. Hansteen:
Universitetet i BergenRefleksjoner om kvantemekanisk "entanglement"og muligheten for kvantisk teleportasjon
26.02 S. Furbo: Aktiviteter vedr0rende solvarmeanlegg vedDanmark Tekniske Universitet Danmark Tekniske Universitet
24.04 P. J. Ellis:University of Minnesota
29.04 F. D. Blasio:Universitetet i Oslo
Effective Lagrangian with Broken Scale andChiral Symmetry
Topics on the Physics of Neutron Star Crusts
12.08 S. Siem: Eksperimenter ved ArgonneArgonne National Laboratory
28.08 A. Rej:SN Bose School forMathematics andMathematical ScienceCalcutta
Planck Scale Cutoffs, Causality andPath Integral Duality
04.12 T. Lonnroth:Abo Akademi
Alfa-spedning mot silisium- modellinterpretasjoner?
I l l
Chapter 10
Committees, Conferences andVisits
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, NuclearPhysics 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:
G. Lovhoiden:
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
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 ofOslo.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 Scienceand Letters/Chairman of the Class of Mathematics and Science.Co-editor (with T. T. S. Kuo) of International Review of NuclearPhysics, 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 theRoyal Norwegian Society of Sciences and Letters.
J. Rekstad Referee for Nuclear Physics, Physical Review, Physical Review Lettersand 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 FundamentalEnergy Research.Member of the program planning committee for energy research, TheNorwegain 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 theNorwegian Physical Society, Oslo, June 1998
10.2 Conferences
The Section of Nuclear Physics and Energy Physics participated in the Annual Meetingof 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 samemeeting.
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-fieldmethods 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,
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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 Methodsand Effective Interactions", 17-20 december 1998, Nordita, Copenhagen, (Denmark).Talks were given at the conferences/workshops "Mean-field methods in nuclearstructure", 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 QuarkMatter", Padua, Italy, 20-24 July 1998.
E. Melby participated in the "NorFA post-graduate course on Weak Processes inNuclei", 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 UrbanPlanning", 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 energypolicy planning,and gave an invited talk at the "Conference for Teachers in the University and TechnicalHigh School Sector", NTNU, Trondheim, Januay 20, 1998.
A. Schiller participated in the "NorFA post-graduate course on Weak Processes inNuclei", Jyvaskyla, Finland, Jan. 12-23, 1998, and in "The 9th Nordic Meeting onNuclear 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 ofnuclear 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 TheLast 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,
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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 PHYSICSDIVISIONAL CONFERENCE, Structure of Nuclei under Extreme Conditions",Padova, Italy, March 31 - April 4, 1998, the "NBI-LUND Experimental Group meetingand The Last Supper at TAL", Ris0, Danmark, Dec. 14-15, 1998, and the "NorFApost-graduate course on Weak Processes in Nuclei", Jyvaskyla, Finland, Jan. 12-23,1998.
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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 andQuantum Dynamical Calculations
Are Haugan: Development of Methods for Obtaining Position Image and ChemicalBinding 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. OsnesMinimal relativity and 3Si3.Di pairing in symmetric nuclear matterPhys. Rev. C57 (1998) 1069 1072
A. Holt, T. Engeland, M. Hjorth-Jensen and E. OsnesEffective Interactions and Shell-Model Studies in Heavy Tin IsotopesNuclear Physics A634 (1998) 41-56
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0 . Elgaroy and M. Hjorth-JensenNucleon-nucleon phase shifts and pairing in neutron matter and nuclear matterPhys. Rev. C57 (1998) 1174 1177
M. Baldo, 0 . Elgar0y, L. Engvik, M. Hjorth-Jensen and H.J. Schulze3P23jp2 pairing in neutron matter with modern nucleon-nucleon potentialsPhys. Rev. C58 (1998) 1921 1928
J. Suhonen and J. Toivanen, T. Engeland, M. Hjorth-Jensen, A. Holt and E. OsnesStudy of odd-mass N=82 isotones: comparison of the microscopic quasiparticle-phononmodel and the nuclear shell modelNuclear Physics A628 (1998) 41-61
F.V. De Blasio and G. LazzariNuclear Effects on Superfluid Neutron Star MatterModern Phys. Lett., A13 (1998) 1383
F.V. De BlasioCrustal Impurities and the Internal Temperature of a Neutron Star CrustMonthly Not. Roy. Astr. Soc. 299 (1998) 118
F.V. De Blasio and G. LazzariLattice Defects in the Crust of a Neutron StarNucl.Phys. A633 (1998) 391 - 395
H. Heiselberg and M. Hjorth-JensenPhase transitions in rotating neutron starsPhysical Review Letters 80 (1998) 5485-5488
A. Polls, H. Miither, R. Machleidt and M. Hjorth-JensenPhaseshift equivalent NN potentials and the deuteronPhysics 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. WinfieldNew island of ^zs-isomers in neutron-rich nuclei around the Z=28 and N=40 shellclosuresPhysical Review Letters 81 (1998) 766-769
1. Vidanya. A. Polls. A. Ramos and M. Hjorth-JensenHyperon properties in finite nuclei using realistic YN interactionsNuclear Physics A644 (1998) 201-220
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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-JensenGround State Magnetic Dipole Moment of 13oINucl.Phys. Axxx (1998) 277 - 288.
0 . Elgar0y and M. Hjorth-JensenPairing in Infinite Matter and Finite NucleiIn proceedings of Condensed Matter theories 21, Luso, Portugal, September 21-271997, Condensed Matter Theories 13 (1998) 221
H. Heiselberg and M. Hjorth-JensenPhase transitions in neutron starsIn proceedings of the Nuclear Astrophysics workshop, Hirschegg, Germany, January12-16 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/cNucl. 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 228RaNucl. 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. TveterEnhancement of central A, E and Q yields in Pb-Pb collisions at 158 AGeV/cPhys. 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. TveterA,H and f2 production in Pb-Pb and p-Pb interactions at 158 AGeV/cProc. 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. TveterA, E and Q Production at Central Rapidity in Pb-Pb and p-Pb Collisions at 158AGeV/cProc. 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 Collisionsat 158 AGeV/cProc. Strangeness in Quark Matter, Padova, Italy, July 20-24, 1998
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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 withthe VENUS ModelProc. 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. KingHigh Spin Studies of 164Lu Using EUROBALLII 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. TjørnBand structures and proton-neutron interactions in 174TaNuclear 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. WyssCollective rotational - vibrational transition in the very neutron-deficient nucleim,i72pt
Phys. Lett. B443 (1998) 69-76
Spin Myon Collaboration (SMC) and A. SchillerMeasurement of Proton and Nitrogen Polarization in Ammonia and a Test of EqualSpin TemperatureNucl. Instr. Meth. A 419(1998)60-82
A. Schiller and the SMC collaborationPolarised Quark Distributions in the Nucléon from Semi-Inclusive Spin AsymmetriesPhys. Lett. B420(1998) 180190
A. Schiller and the SMC collaborationSpin asymmetries ,4i and structure functions g\ of the proton and the deuteron frompolarized high energy muon scatteringPhys. Rev. D58(1998) Article Number 112001
A. Schiller and the SMC collaborationNext-to-leading order QCD analysis of the spin structure function g\Phys. Rev. D58(1998) Article Number 112002
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A. Schiller, L. Bergholt, M. Guttormsen, E. Melby, S. Messelt, E.A. Olsen, J. Rekstad,S. Siem, T.S. Tveter J.C. WikneFirst test measurements of the SIRI AE-E particle telescope arrayProc. 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. UusitaloFirst observation of excited states in 226UJ. Phys. G24(1998)L63-L70
E. Melby, L. Bergholt, M. Guttormsen, S. Messelt, J. Rekstad, A. Schiller, S. SiemThe influence of the A'-quantum number in the 7-decay of 166ErProc. 9th Nordic Meeting on Nucl. Phys. Jyväskylä, Finland, August 4 - 8, (1998)
11.2.2 Energy
J. EriksenDevelopment of a Data Acquisition and Control System for a Small-Scale PV-H?System - First Design PhaseHydrogen Energy Progress XII (1998)195-204
L. Henden, M. Meir, J. RekstadThermal Performance of a solar collector made of plastic materialsProceedings ISES-Europe Solar Congress-EuroSun '98, Portoroz, Slovenia, Sept. 14-17,(1998)
M. Meir, J. Rekstad, L. Henden, B. BjerkeBuilding integrated solar systemsGleisdorf 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. StrandThe Chemistry of Norwegian Groundwaters: I The distribution of radon, Major andMinor Elements in 1604 Crystaline Bedrock GroundwatersThe Science of the Total Environment, 222 (1-2), p. 71-91, 1998.
D. Banks, B. Frengstad, Aa.K. Midtgård, J.R. Krog and T. StrandThe Chemistry of Norwegian Groundwaters: II. The chemistry of 72 groudwaters fromQuaternary sedimentary aquifers.
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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.LindDrinking 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. BanksRadon concentrations in groundwater from Quaternary sedimentary aquifers inrelation 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 NorgeNorsk veterinaertidsskrift 110 (19), p. 662-665, 1998.
11.2.4 Other Fields of Research
F.V. De BlasioMirroring of Environmental Colored Noise in Species Extinction StatisticsPhys. Rev. E58 (1988) 6877
F.V. De BlasioDiversity Variation in Isolated Environments: Species-area Effects from a StochasticModelEcological Modelling, 111 (1998) 93.
11.3 Reports and Abstracts
11.3.1 General
F. IngebretsenSection for Nuclear and Energy Physics: Annual ReportDepartment of Physics Report, UiO/PHYS/98-08 (1998)
11.3.2 Nuclear Physics and Instrumentation
M. GuttormsenEventbuilder for the RTPC 8067 Single Board ComputerDepartment 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 ArrayDepartment 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. TveterEnhancement of central A,E and Q, yields in Pb-Pb collisions at 158 AGeV/cCERN-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. Amza1, 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. UusitaloCoexistence in proton rich A-90 and A-170 nucleiAbstracts of papers of the American Chemical Society Vol. 215, 2. Apr. 1998, p93-NUCL
11.3.3 Energy
O.M. LøvikHydrogen on a palladium surface - Potential energy surfaces and quantum dynamicalcalculationsPhD -tesis, Dept. of Physics, University of Oslo, May (1998)
M. Meir, J. Rekstad, L. Henden, A.G. ImenesA study of two different heat distribution plates in wooden floor heating systemsInternal test report, University of Oslo, Dept. of Physics, Aug. (1998)
R. Aspesæther OlsenDirect subsurface absorption of hydrogen on Pd (111) - Potential energy surfaces andquantum dynamical calculationsPhD thesis, University of Amsterdam, Nov. (1998)
11.3.4 Radiation Research
D. Banks, B. Frengstad, J. R. Krog, Aa. K. Midtgård, T. Strand, B. LindKjemisk 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. LindKjemisk kvalitet av grunnvann fra løsmasser i NorgeNGU-rapport 98.089, 96 p. , Norges geologiske undersøkelse, 1998.
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D. Banks, Aa. K. Midtgård, B. Frengstad, J. R. Krog, T. Strand and B. LindUtjevningsbassengs 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. VoldenEnvironmental Ceochemical Atlas of the Central Barents Region, Geological Survey ofNorway, 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. SiemA'-dependence in the 7-decay after Neutron CaptureThe 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/cProc.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. Jensen, H. Ryde, A. Bracco, S. Frattini, R. Chapman, D.M. Cullen, and S.L. KingMultiple Triaxial SD Bands in 163-164Lu Studied with EUROBALL9th 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, andS.L. KingMultiple Triaxial SD Bands in 163'164Lu Studied with EUROBALLGatlinburg, 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. KingHigh" Spin Studies of 164Lu Using EUROBALLXVI Nuclear physics divisional conference, Structure of Nuclei under Extreme Condi-tions, March 31 - April 4, 1998 - Padova, Italy
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T. Døssing, M. Matsuo, B. Herskind, G.B. Hagemann, A. Harsmann, S. Törmänen,S.W. Ødegård, E. Vigezzi and R.A. BrogliaInteracting Excited Rotational BandsTopical 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 lineTalk at APS conf. New Mexico Oct. 28-31 (1998) and Bull. Am. Phys. Soc. vol.43no.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 254NoTalk at APS conf. New Mexico Oct. 28-31 (1998) and Bull. Am. Phys. Soc. vol.43no.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. Seabury, D. Cline, C.Y. Wu.Unsafe coulomb excitation of 240Pu and 244PuTalk at APS conf. New Mexico Oct. 28-31 (1998) and Bull. Am. Phys. Soc. vol.43no.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. MooreThe decay out of a superdeformed band in 191HgTalk at APS conf. New Mexico Oct. 28-31 (1998) and Bull. Am. Phys. Soc. vol.43no.6 Oct. (1998)
L. Bergholt, M. Guttormsen, E. Melby, J. Rekstad, A. Schiller and S. SiemEr atomkjernen kaotisk?Fysikermøtet, Oslo, 10.-12. juni (1998)
T. Engeland, M. Hjorth-Jensen, A. Holt and E. OsnesRealistic Effective Interactions and Large-Scale Nuclear Structure Calculation6th International Spring Seminar on Nuclear Physics, S. Agata sui Due Golfi, Italy,18-22 Mav 1998
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E. OsnesEffective Interactions for the Shell ModelInvited Talk at the NORDITA Mini-Meeting on "Shell Model Related Problems",Copenhagen, December 17-19 (1998)
E. OsnesRealistic Effective Interactions and Large-Scale Nuclear Structure CalculationsInvited Talk at the Institute for Nuclear Theory, University of Washington, Seattle,USA, July 31 (1998)
T. EngelandLarge Shell Model Calculations with Effective Interactions from Meson TheoryInvitet talk at the NORDITA Minimeeting on Shell Model Related Problems, Copen-hagen Dec. 17 - 19 (1998)
T. EngelandLarge Scale Shell Model CalculationsInvitet talk at the international workshop on Mean-field methods in low-energy nuclearstructure, ECT*, Trento, March 23 - April 4 (1998)
F.V. De BlasioStructure Vortices in Infinite MatterTalk at the international workshop on mean-field methods in low-energy nuclearstructure, ECT*, Trento, March 24 - April 4 (1998)
0 . Elgar0yPairing in infinite matterInternational Workshop on MeanField Methods in Low Energy Nuclear Structure,ECT*, Trento, Italia, March 23-April 4 (1998)
0 . Elgar0ySuperfluiditet i n0ytronstjernerArsmotet i Norsk Fysisk Selskap, Universitetet i Oslo, Norge, 10.12. juni (1998)
L. EngvikEquation of state for dense matterArsmotet i Norsk Fysisk Selskap, Universitetet i Oslo, Norge, 10.12. juni (1998)
M. Hjorth-JensenFrom the Nucleon-Nucleon interaction to finite nucleiInvited talk at the workshop on Mean-field methods in nuclear structure, ECT*,Trento, March 23- April 4 1998 (Italy)
M. Hjorth-JensenPerturbative many-body approachesInvited talk at the workshop on Microscopic approaches to the structure of light nuclei,University of Manchester. Manchester, June 8 - 1 3 (1998) (England)
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E. Melby. L. Bergholt, M. Guttormsen, S. Messelt, J. Rekstad, A. Schiller, S. SiemHva 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. Jensen, H. Ryde, A. Bracco, S. Frattini, R. Chapman, D.M. Cullen, and S.L. KingTriaxial Superdeformasjon i 164LuFysikermøtet, Oslo, Juni 98
S. SiemDecay out of a superdeformed band in 191HgNordic meeting, Jyväskylä, Finland, 3-8 august (1998)
A. Schiller, L. Bergholt, M. Guttormsen, E. Melby, S. Messelt, J. Rekstad, S. SiemAlternative Measurements of Level Density in 162DyBook of Abstracts, Fysikermøtet, Oslo (Norway), June 10-12, (1998)
A. Schiller, L. Bergholt, M. Guttormsen, E. Melby, S. Messelt, J. Rekstad, S. SiemNew Measurements of Level Density in 162DyBook of Abstracts of the 9th Nordic Meeting on Nucl. Phys, Jyväskylä (Finland),August 4-8, (1998)
K. GjötterudPerspektivendringer i fysikken de siste hundre år og i dagForelesning i serien Grunnlagsproblemer i fysikk UiB Fysisk institutt/Senter forvitskapsteori 18.03 1998
K. GjötterudUtvikler fysikken seg til en ironisk vitenskap?Forelesning i Vitenskapsteoretisk Forum NTNU 06.10.1998
M. Hjorth-JensenMany-body problems in nuclear astrophysicsTalk at KVI, Groningen, January 6 (1998)
M. Hjorth-JensenEffective interactions and the nuclear shell modelTalk at the Dept. of Physics, University of Jyväskylä, October 1 (1998)
A.K.HolmeA, E and Q production in Pb-Pb collisions at 158 AGeV/cEP-seminar, CERN, Geneva, January 26,1998
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S. SiemLevel densities in rare earth nucleiTalk at Argonne National Lab. Febr. 20 (1998)
11.4.2 Energy
J. Rekstad, L. Henden, M. Meir, B. BjerkeBuilding integrated solar systemsTalk and paper at the 5th European Conference in Solar Architecture and UrbanPlanning, May 25-30, (1998)
J. RekstadBruk av solenergi i Norge - Potensiale og praktiske l0sningerFaglsererkonferanse om EN0K-undervisning, NTNU, Trondheim, 20 Januar (1998)
11.4.3 Radiation
A. Birovljev, T. Strand, A. HeibergRadon concentrations in Norwegian kindergartens.YUNSC '98, Sept. 28 - October 1, 1998, Belgrade, Yugoslavia
T. StrandUncertainties in assessment of indoor radon exposure. 1998 Society for Risk AnalysisAnnual 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. StrandMethods for monitoring of NORM on equipment offshore and onshore.Proceedings of the Second Int. Symp. on the Treatment of Naturally OccurringRadioactive Materials. Krefeld, Germany, November, 10-13, 1998, p. 35-37.
I. Lysebo and T. StrandNORM in Oil Production - Activity Levels and Occupational Doses.Proceedings of the Second Int. Symp. on the Treatment of Naturally OccurringRadioactive Materials. Krefeld, Germany, November, 10-13, 1998, p. 114-119.
T. Strand and I. LyseboNORM in Oil and Gas Production . Waste Management and Disposal AlternativesProceedings of the Second Int. Symp. on the Treatment of Naturally OccurringRadioactive Materials, Krefeld, Germany, November, 10-13, 1998, p. 137-141.
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11.5 Popular Science
K. GjötterudGrunnleggende problemer i kvantefysikk. Referat fra Nordisk symposium i Rosendal,juni 1997Artikkel i Fra Fysikkens Verden Nr. 1 - 1998
K. GjötterudRyktene 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. GjötterudPerspekti vend ringer i fysikken de siste hundre år og i dag - fra skråplantil superstrengerForelesning Fysisk institutt UiO Bjørngilde 06.02.1998
K. GjötterudJohn Horgans bok "The End of Science" i lys av dagens perspektiver i fysikkForelesning Mandagsseminar Biologisk institutt - avdeling for generell fysiologi16.02.1998
K. GjötterudFysikk og naturforståelseForelesning for elever ved Asker kunstskole 18.02.1998
K. GjötterudVitenskapelige perspektiver på fysikkens forskningsfrontSamtale med Olav Høgetveit i programmet "Møtested" NRK TO 23.09.1998
K. Gjötterud, J. SivertsenVitenskapen ved veis ende? John Horgans bokIntervju ved Erik Tunstad NRKP2 WOK 27.01.1997
G. LøvhøidenALICE-ultrarelativistiske kjernekollisjoner-et studium av det fysiske vakuumFysikkforeningen,UiO,Oslo, October 12, 1998
J. Rekstad, B. Bjerke, M. MeirCombined solar heating systemsCADDET-Renewable Energy newsletter, issue 3/98, (1998) 21-23
J. RekstadCost-efficient solar energy technology from NorwayPresentation at EXPO '98 Lisbon, July 22, (1998) (manuscript 8 pages)
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J. RekstadEnergifleksibilitet på sluttbrukertrinnet i energikjeclen -Teknologiske muligheter ogvirkninger på energibrukForedrag for regjeringens energiutvalg. Oslo, 17 mars (1998)
J. RekstadSolvarme eller varmepumpe - eller kombinasjon?InternaL report, SolarNor AS, Sept. (1998)
T. StrandRisiko for lungekreft ved innendørs radoneksponering.Miljø og helse nr. 1/98, p. 6-8, 1998.
V. Valen, O. Soldal and T. StrandRadon i løsmasser.Kommunalteknikk, 7-1998
A. Birovljev, T. Strand and G. ThommesenKartlegging 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. ParrFysikk og EnergiressurserISBN 82-00-22927-0, Universitetsforlaget (1998)
11.6 Pedagogical reports and talks
S.L. Andersen og O. ØgrimDel E: KrefterHefte (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. ØgrimDel F: GodbiterHefte (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. ØgrimDel G: Spill og lekerHefte (ISBN 82-90904-49-5) og Video (ISBN 82-90904-50) med fysikkdemonstrasjoner.
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Fysisk Institutt / Senter for lærerutd. (1998) 1-25
J.R. Lien, G. LøvhøidenKompendium i mekanikkFysisk institutt, Universitetet i Bergen
S.L. Andersen og O. ØgrimFysikkdemonstrasjonerForelesning på faglig pedagogisk dag, Universitetet i Oslo, januar 1998
S.L. Andersen og O. ØgrimDemonstrasjonsforelesningForelesning på Biørnegildet, Fysisk Institutt, Universitetet i Oslo, våren 1998
S.L. Andersen og O. ØgrimTre demonstrasjonsforelesningerForedrag på Østlandske lærersevne, oktober 1998
S.L. Andersen og O. ØgrimDemonstrasjonsforelesningForedrag i fysikkforeningen, Fysisk Inst., Universitetet i Oslo, høst 1998
K. GjötterudFysikkens utvikling i vart århundre - perspektivendringerTre forelesninger Etterutdanningskurs i fysikk i Videregående skoler i Vest-AgderRessurssenteret på Gimle Kristiansand 04.09.1998
G. LøvhøidenVart fysiske verdensbildeKurs, Fysisk institutts skolelaboratorium, Horten, 1.12.1998
O. Øgrim og P.T. ZagierskiDemonstrasjonsforelesninForedrag på Norks Fysisk Selskaps årsmøte, juni 1998
J. Rekstad, M. MeirNew technology for cost effective and energy saving heating systemsInformation brochure from SolarNor AS, June (1998)
11.7 Science Policy and Science Philosophy
E. OsnesFornebusaken, ad evnt. flytting av Institutt for informatikk, UiO til Fornebu:a) Intervju i Østlandssendingen 20 aug. 1998
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b Debatt i PI med Gudmund Hernes 20. august 1998c) Debatt i Østlandssendingen med Jon Lilletun og Lucy Smith 20. august 1998II. AviserIntervju i Universitas, nr. 22, 23. september 1998
E. OsnesFem år med Forskningsrådet - Grunnforskningen blir forsømtIntervju i Uniforum nr. 12, 26 mars (1998)
E. OsnesRektorvalget 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. OsnesRektorvalget ved Universitetet i Oslo 1998, paneldebattera) Studentfestivalen 2. september 1998b) Studenutvalgslederforum 23. september 1998c) Realistforeningen 30. september 1998d) Det sentrale valgstyret, UiO 5. oktober 1998
E. OsnesRektorvalget ved Universitetet i Oslo, intervjuer:a) "Rektorkandidat Eivind Osnes - Ikke fra Kollegiet", Uniforum nr. 10, 20. august1998b) "Fem vil bli rektor", Aftenposten aften 17. september 1998c) "Store endringer", Universitas nr. 23, 30. september 1998d) "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. ThonstadObservatoriets fremtid må bli egen kollegiesakUniforum nr. 17 12. november (1998)
0 . Holter og F, IngebretsenFra RedaktøreneFra Fysikkens Verden (1, 2, 3, 4), Vol. 60 (1998)
K. GjötterudYtringsfrihet og unnfallenhetKronikk Monitor - antifascistisk tidsskrift nr: 1 1998
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K. GjötterudOppgjør med Luthers jødehetsReferat fra foredraget i Nysæter kirke 22.03.1998 ved Håkon C. HartvedtDagen 24.03.1998
K. GjötterudFra arbeidet for jøder i det tidligere SovjetArtikkel i Informasjonsavis for Hjelp Jødene Hjem, våren 1998
K. GjötterudAntisemittiske strømninger i ex-SovjetArtikkel i boken Israel 50 år, red. Nils Jacob Tønnessen, Luther Forlag Oslo 1998
K. GjötterudSå skjer det igjen: Krav om at jøder skal drepesJødene i ex-Sovjet Nr.2/98 desember - 15. årgang
K. Gjötterud, M. SpandowRapport fra Moskvareisen 26.11 - 01.12.98Jødene i ex-Sovjet Nr.2/98-desember-15.årgang
K. Gjötterud, M. SpandowFra et besøk i Moskva: Igjen godtas det å være åpen antisemittNyhetsbrev desember 1998 Aksjonskomiteen HJH
K. GjötterudAntisemittisme og rasisme i Norge og Europa i dagForedrag Sentrumsgruppa Oslo KFUM 24.01.1998
K. GjötterudFra antisemittismens historie, blodanklager fra Apion til Jan Bergman vedUppsalaUniversitetForedrag i Seminar om antisemittisme og historisk revisjonisme arrangert av NorskForening Mot Antisemittisme og tidsskriftene Monitor og Humanistdagene 21. og 22.februar Humanismens Hus Oslo 21.02.1998
K. GjötterudJødenes situasjon i tidligere SovjetunionenForedrag for Hovedstyret i Den norske israelsmisjonen Hotell Norrøna 13.03.1998
K. GjötterudKristen antisemittisme - finnes den?Foredrag i Nysæter kirke Stord arrangert av MIFF og Norge - Israel Foreiningen påStord 22.03.1998
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K. Gjötterud, A. DemaciKosovaForelesning Rønningen Folkehøgskole Oslo 20.05.98
K. GjötterudAntisemittisme - professor August Rohling Universitetet i Praha i 1880-årene ogprofessor Jan Bergman Uppsala Universitet i 1990-åreneForedrag i Shofar-gruppen (Ordet og Israel) i Vestby 18.10.1998
K. GjötterudForfølgelse av jøder før og nåForedrag Ringstabekk skole 10. skoletrinn 19.10.1998
K. GjötterudAntisemittisme i Russiand og xenofobi og asylpolitikk i NorgeInnlegg på OSSE's implementeringsmøte i Warszawa om den menneskelige dimensjon30.10.1998
K. GjötterudAppel! for KosovaAppell ved Utenriksdepartementet i Oslo under demonstrasjonen 06.03.1998
K. GjötterudAppell for KosovaAppell under Solidaritetskonserten for Kosova på Rockefeller 19.03.1998
K. GjötterudJødehetsen 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. GjötterudZions Vises ProtokollerIntervju ved Erik Tunstad NRK-radio P2 VOK 02.06.98
K. GjötterudEtiske utfordringer ved presseoppslagInnlegg på seminar om forholdet mellom tatere, forskere og medier arrangert avRomanifolkets Landsforening 08.10.1998
K. GjötterudAntisemittisme, er det bare "rasisme"?Foredrag Temadag Manglerud videregående skole 09.01.1998
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