Physics Group Research Plan. May 2007

Transcription

1 P O Box 722 Somerset West 7129 South Africa Tel : Fax : director@tlabs.ac.za Internet : Laboratory for Accelerator Based Sciences Physics Group Research Plan May 2007 Abstract The Separated Sector Cyclotron (SSC) at ithemba LABS is currently the largest investment in a single research entity on the African continent. South Africa is very fortunate that this investment is in a very versatile and flexible installation that can be used for the next 30 years to meet the research and human skills building needs that are required to address current national and international priorities. These priorities include; skills building in sub-atomic science and technologies, fundamentals of nuclear power generation, materials science, radiation biology, isotope applications to health and industry, radiation therapy and basic research in many fields. The Forward Look for ithemba LABS for the next decade involves the transfer of radiation therapy to the MRMC and the production of radioisotopes to a stand-alone accelerator. Thus the SSC will be released full time for what it is most efficient at, applied and pure research unencumbered by the current necessities of the weekly schedule to meet treatment and production needs. This Research Plan spells out a 5 and 10 year path to achieve an internationally leading position in sub-atomic research while training a transformed cohort of young scientists to meet South Africa s economic, social and intellectual needs. Introduction A part of the mandate of the NRF is to promote research by providing necessary research facilities to facilitate the creation of knowledge, innovation and development in all fields of science and technology. As a National Facility operating within the NRF, ithemba LABS provides facilities and skills in pure and applied sub-atomic sciences and associated technologies and has as objective to Grow the research facilities to increase training, human resource development, international collaborations and the Science and Technology profile of South Africa. The Physics Group has the following objectives: To promote and pursue internationally competitive in-house nuclear-related research, development and training/education programs. To develop and maintain a critical mass of the laboratory facility user base, the national component being fully representative of the demographic profile of South Africa.

2 These objectives define three activities relevant to the Physics Group: a) Internationally Competitive Research In the While Paper on Science and Technology Knowledge Generation is recognized as an important dimension of South African science. Research of internationally recognized quality in nuclear physics is mentioned in the DACST review of the National Facilities as a core competency of ithemba LABS and it recognizes the need in South Africa for such a competency as an example of flagship science. b) Education and Training In view of the importance of human resources for the country the NRF in its 2005/ /08 business plan announced as key driver of the NRF To produce large numbers of high-quality PhDs required to provide the bedrock for an innovative and entrepreneurial society. c) Developing, maintaining and supporting the user base This is achieved i) by developing and maintaining world-class facilities aligned with the needs of our users, ii) by attracting international participation with the aim of exposing local students to world class research, and iii) by participating in science awareness programs. Nuclear Physics and Human Resource Development in South Africa It is the policy of the Government of South Africa to develop the pebble bed modular reactor and to build a substantial nuclear power industry. In 2005, the Minister of Public Enterprises Alec Erwin, said that the government was seeking to produce between 4 5 GW of power from pebble bed reactors, while more recently, the chief executive of the Nuclear Energy Corporation of SA (NECSA), Dr Rob Adam, indicated that NECSA expects electricity generated from nuclear energy to increase by 25 GigaWatts by 2030, needing an investment of as much as R100 billion. Sub-Atomic skills are widely needed in many industries besides electrical power generation: in radiation monitoring in the mining, construction, food and health industries; in environmental studies and palaeontology and geological dating; in water resource studies using isotope ratios; in analytical methods in geology and materials sciences etc. Clearly, the demands on human resources required to support a nuclear industry of the proposed dimensions are considerable. At the same time, transformation in order to attain an equitable race and gender distribution in both industry and academia remains an urgent need. Presently, the flow of appropriate graduate and postgraduate degrees, needed to address the above imbalances, is totally inadequate. To support a nuclear industry and to further the progress of transformation, a substantial investment in human resources is required at the highest levels.

3 ithemba LABS has been vigorously attempting to address the skills shortage with training programs that include its jointly run graduate schools, MARST (Masters in Applied Radiation Science and Technology) at the North West University, and MANuS (Masters in Accelerator and Nuclear Science) and MATSCI (Masters in Materials Science), a joint graduate school run by the University of the Western Cape, University of Zululand and ithemba LABS. We contribute towards transformation with more that 80% of our post-graduates being black South Africans, who upon completion find employment at for example NECSA, PBMR, and in government departments. It is however of concern that not enough students continue with PhDs. The Physics Group in particular plays an important role in post-graduate nuclear physics training in South Africa, with its staff being directly involved in the supervision of post graduate students and in lecturing in specialized topics at universities in the MANUS and MATSCI courses. Strong links exist between research and training through the involvement of post-graduate students in research projects by making research facilities and expertise available to students from all Universities. In order to expand the present training programs and to maintain quality as a non-negotiable principle, strong teaching and research groups in both the Universities and in National Laboratories are needed. The latter are essential for the location of major and expensive items of equipment to ensure their maintenance, development and full utilization by all the scientific community. Furthermore research infrastructure has to be continuously upgraded in order to allow scientists to contribute to research at the forefront of developments in these fields. Presently, students and research groups from the Universities of Cape Town, Stellenbosch, Western Cape, Witwatersrand, and Zululand are regular users of the facility. The next five years The direction of nuclear physics research at ithemba LABS for the next five years is summarized in Table 1. The research topics are broadly classified into research into Nuclear Reaction Studies, Nuclear Structure Studies and Applications of Nuclear Physics. The projects reflect the interests of our users as well as in-house researchers and are discussed in detail in Appendix A. A major focus during the next 5 years would be the optimal use of the zero degree mode of operation of the k=600 magnetic spectrometer and the upgrades to the focal plane detectors and electronics that is expected to be completed in the second half of Research topics that will benefit from this development are the studies of giant resonances, exotic excitation modes and studies of the level structure of exotic nuclei (2.1 to 2.3 in table 1 below). The research programs with the AFRODITE array would involve a variety of studies of exotic shapes and symmetries in nuclei (2.4 in table 1) as well as the measurements of lifetimes (2.5) of nuclear states. While many of the topics are currently of great interest, our ability to compete internationally is severely constrained by the size of our array and the limitation of stable beams. The new ECR ion source will in the short term contribute to new research directions e.g. through the availability of new beams ( 6,7 Li and 40,48 Ca) (topics 1.1, 1.5 and 2.7), and higher intensities and energies needed for studies of neutron rich nuclei in deep inelastic scattering reactions (2.6).

4 The major equipment needs for the next five years, classified according to research topic, are summarized in Table 2, with further details in Appendix A. These can again be broadly divided into developments on the k=600 spectrometer and on the AFRODITE array. It is clear that the total efficiency of AFRODITE is insufficient and that it would be advisable to increase the array to have 15 clover detectors. Highly segmented detectors that will allow for γ- tracking would be highly advantageous for use with higher energy beams used for studies of neutron rich nuclei and for inverse kinematics reactions. A γ-tracking array would also be essential should we proceed with the development of any form of radio-active beam facility. A permanent particle ball for use with AFRODITE is also proposed. In the latter half of the next five year period an investigation into the construction of a focal plane polarimeter should be started. This plan should contain a clear indication of the physics that will be addressed. Measurements of high resolution polarization phenomena in order to study the effective N-N interaction (topic 1.2) have already been proposed. The above projects will only be feasible with a substantial increase in capital funding and technical support for the physics group. An exciting development may be the use of AFRODITE Ge detectors in conjunction with the k=600 spectrometer which would form a unique facility to measure simultaneously particle and γ- rays with high resolution. A physics case for the study of the Pygmy Dipole Resonance in (α,α γ) at 0 has been put forward and other possibilities should be investigated. While investigations into the use of high-intensity femto-second lasers for the acceleration of charged particles have been proposed, it is not included in this plan. Developments in this field, as well as potential physics programs where such beams would have a competitive advantage would however be monitored.

5 TABLE 1: RESEARCH PROGRAMMES 1. Nuclear reactions Previous work Next Five years 1.1 Fusion barriers 86 Kr Pb 40 Ca U and 48 Ca U when beams are available. Investigate feasibility of using artificially produced neutron rich beams 1.2 Properties of the effective NN interaction Measurements of analyzing power in (p,2p) reactions 1.3 Intermediate mass fragment production Extensive measurements of He, Li, Be and B fragments from 12 C and 16 O induced reactions on heavy nuclei at E ~ 30 MeV/amu 1.4 Pre-equilibrium reactions Analyzing power for proton-induced 3 He and α-particle emission 1.5 Charged particle reactions to populate high-spin states Studies of incomplete fusion with AFRODITE using the DIAMANT array Measurements on lighter targets, use of inverse kinematics, and extensions to higher incident energies. Investigate possible use of neutron rich projectiles Improved statistical accuracy of analyzing power data; investigation of proton-induced light-heavy ion emission Studies the population region in angular momentum of incomplete fusion using 6,7 Li beams (and 9 Be if available) 1.6 Neutron cross-sections Studies of neutron-induced activation cross sections on Fe, Pb and U as well as light ion production on targets from C to U 2. Nuclear structure 2.1 Giant resonances Fine structure in the ISGQR region over a wide mass region 2.2 Level structure of exotic nuclei Fine structure in the Spin-Dipole region Studies of electric and magnetic dipole resonances in (p,p ) at 0 degrees Isospin structure of the Pygmy Dipole Resonance Investigations into high resolution particlegamma coincidences using the K600 and HPGe detectors (from AFRODITE) High resolution (p,t) measurements on S, Ar and Ca at small angles and at zero degrees

6 2.3 Exotic excitation modes: Mixed Symmetry states Giant Pairing vibrations Stretched states 2.4 Exotic nuclear shapes and nuclear symmetries hyperdeformed, superdeformed, tetrahedral shapes; chiral, shears bands etc. 2.5 Lifetime measurements - high-k isomers, short lifetimes 2.6 Spectroscopy of neutron rich nuclei 1. Identification of Stretched High Spin States in 48,50 Ti via High Resolution Proton Inelastic Scattering 2. Searching for Giant Pairing Vibrations with the 120 Sn(p,t) reaction 3. High resolution proton scattering and the nature of Mixed-Symmetry 2+ states in 94 Mo 1. Hyperdeformation and spectroscopy in actinide region: Tests of recoil detector 2. Tetrahedral Shapes: Study of 160 Y 3. Chiral Bands: Possible case in 198 Tl 4. Sheers Mechanism: Studies in 195,197 Bi First measurement on lifetimes with AFRODITE using DSAM Lifetimes of isomers in A=150 and 190 regions Incomplete fusion reaction to populate 70 Zn and 71 Ga. Searching for Giant Pairing Vibrations 1. Search for Hyperdef. in U and γ and e spectroscopy of U, Th, Pu 2. Further searches for tetrahedral shapes 3. Searches for chirality in mass 180 region 4. Further studies of rotational and shears mechanism in A=190 region (Bi and Tl) including lifetime measurements Lifetimes of states in shears bands Lifetimes of isomers using improved time structure (longer lifetimes) Exploiting deep inelastic reactions to populate neutron-rich nuclei. Investigate the use of radioactive beams. 2.7 Clustering in nuclei Measurements of cross sections and analyzing powers in (p,pα) 3. Applications 3.1 Neutron dosimetry Testing instruments for dosimetry, and biological effectiveness of highenergy neutrons 3.2 Environmental radioactivity in soil, sediments, water and biological samples Radon measurements based on γ spectroscopy Clustering in heavy nuclei using Li beams Clustering and resonant states in light nuclei Tests of new detectors e.g. those developed for space missions Measurements of radon in ground water and rivers with α, β and γ spectroscopy 3.3 The Earth project Set up and test a proof-of-principle direction sensitive neutrino detector. Assess feasibility of a geo-neutrino detector

7 TABLE 2: RESEARCH EQUIPMENT PROGRAMMES existing new - next 5 years new - next 10 years 1. Nuclear reactions 1.1 Fusion barriers Scattering chamber PF radioactive beams PF, ISOL radioactive beams large acceptance spectrometer (LAS) 1.2 Properties of the effective K600 Magnetic spectrometer Focal plane polarimeter NN interaction Polarized proton beam 1.3 Intermediate mass Scattering chamber New ECR source PF radioactive beams, LAS fragment production 1.4 Pre-equilibrium reactions A-line scattering chamber Polarized proton beam 1.5 Charged particle reactions to populate high-spin states AFRODITE, DIAMANT Charge sensitive detectors, new data acquisition system and appropriate electronics 5 extra clover detectors 1 test tracking clover New polarized ion source, require higher beam intensities 8 tracking clovers 1.6 Neutron cross-sections Quasi-monoenergetic neutron beam line Dedicated electronics and detectors for neutron fluence monitoring 1.7 Scattering of Radioactive ion beams off hydrogen 3. Nuclear structure 2.1 Giant resonances K600 Magnetic spectrometer K600 Zero-degree mode Focal plane polarimeter 2.2 Level structure of exotic Nuclei K600 Magnetic spectrometer in (p,t) mode at finite angles K600 Zero-degree mode for (p,t) PF radioactive beams Inverse kinematics, radioactive beams, LAS Extreme high resolution at 200 MeV (<15 kev) AFRODITE spectrometer Heavy ion detector in focal plane Extreme high resolution at 200 MeV (<15keV)

8 2.3 Exotic excitation modes: Mixed Symmetry states Giant Pairing vibrations Stretched states 2.4 Exotic nuclear shapes and nuclear symmetries hyperdeformed, superdeformed, tetrahedral shapes; chiral, shears bands etc. 2.5 Lifetime measurements - high-k isomers, short lifetimes K600 Magnetic spectrometer AFRODITE, Recoil detector, DIAMANT AFRODITE, Beam pulsing (up to ~300ns), DIAMANT 5 extra clover systems 1 test tracking clover electron spectrometer, Fragmentation beams (ECR source) Microsecond beam pulsing, plunger, Electron spectrometer LAS 8 tracking clovers 8 tracking clovers 2.6 Spectroscopy of neutron rich nuclei Transfer, deep inelastic and incomplete fusion reactions, AFRODITE spectrometer 5 extra clover systems PF radioactive beams (ECR source) ISOL radioactive beams LAS 8 tracking clovers 2.7 Clustering in nuclei AFRODITE, K600 Magnetic spectrometer polarized proton beam 3. Applications 3.1 Neutron dosimetry Quasi-monoenergetic neutron beam line 3.2 Environmental radioactivity in soil, sediments, water and biological samples 1 low-level counting facility (HPGe), MEDUSA in-situ gamma spectrometer (CsI) linked to GPS. 5 extra clover systems ECR source Dedicated electronics and detectors for neutron fluence monitoring 2 nd low-level γ-counting facility, alpha/beta spectrometry, biological sample preparation facilities. Exotic projectiles Liquid scintillation spectrometer 3.3 The Earth project A direction sensitive neutrino detector and DSP electronics for a proof of principle experiment

9 Beyond the next five years The accelerators at ithemba LABS have been in operation for the last twenty years without any major upgrade. Likewise experimental facilities for Nuclear Physics like the AFRODITE γ- array (10 years old) and the magnetic spectrometer (15 years old) are aging. As a result South Africa's premier nuclear research facility, ithemba LABS, is presently losing competitiveness in its field. Very essential limited modernisation of the magnetic spectrometer will be completed early in 2007 and a new ECR ion source is expected to be installed late in This essential change will not be sufficient to allow the present research and training programs to maintain their International competitiveness over the next 5 year period. Currently the Nuclear Physics Group shares the SSC with Radiation Therapy and Isotope Production. Nuclear physics experiments only take place at weekends and more than two days continuous running can only be allocated once a year at most. This currently enforced scheduling makes reliable and efficient use of the facilities extremely difficult and is seen as a great disadvantage by would-be international collaborators. With this in mind the present research plan aims at highlighting topical research that will be done in the next 5 years with existing facilities, as well as projects that will require major new investment in equipment. These proposed new facilities, we believe are essential for nuclear physics research in South Africa to grow to meet the training and research demands of current Government policy. This growth will require; [a] Full use of the SSC by pure and applied physics research by 2012 [b] Increased dedicated technical support for the nuclear physics group [c] Increased funding for equipment and facility development [d] Increased teaching capacity at User Universities to be able to produce the graduates and postgraduates required by the economy. Major equipment for ithemba LABS The facilities required to sustain the research programme at an internationally competitive level for the next 10 years are also listed in the table 2. They can be broadly divided into two categories - beams and detector systems. A detailed proposal for RIB s and detector systems at ithemba LABS is beyond the scope of the five year plan. However, the five year plan must take cognizance of the long term view. For this reason, some options are discussed in general terms below. Radioactive Beams The usefulness and competitiveness of an accelerator facility for nuclear physics research depends to a large part on its ability to deliver useful beams to experimenters. Important are the energy, intensity and the variety of species of beams available. The energy and intensity of the stable beams provided by the Separated Sector Cyclotron (SSC) will be given a huge boost when the installation of the new ECR ion source, funded under the National Equipment Programme for 2006, is completed in early However, the competitiveness of ithemba LABS in providing the required variety of beam species is under threat. Internationally, the forefront of nuclear physics research is steadily 9

10 focusing on the great unknown of nuclear physics: the properties of the so-called neutron rich nuclei - artificially produced nuclei with many more neutrons than protons compared to those encountered in nature. To produce neutron rich nuclei, a radioactive ion beam (RIB) facility is required. Approximately twenty such facilities exist or are under construction worldwide. Within 10 years, nearly all of the proposed research topics at ithemba LABS will require the use of radioactive beams. We recommend the upgrade of the ithemba LABS facility to allow the production and exploitation of radioactive beams. Production of Radioactive Beams at ithemba LABS There are two methods of producing radioactive beams, both have different strengths and weaknesses and both are in continuous state of development and improvement. They are Projectile Fragmentation (PF) and Isotope Separation On Line (ISOL). Projectile Fragmentation A primary, stable beam is accelerated to relativistic energies and is broken up into fragments by colliding it with a thin production target. Because of the relativistic energies, the fragments pass through the target and continue in the original direction and thus a radioactive secondary ion beam is created. The different fragment species must then be separated and directed onto a yet another target to study the neutron rich nuclei. Projectile Fragmentation will become feasible at ithemba with the installation of the new ECR ion source, as it will be capable of delivering 40 MeV/u beams of several microamperes of intensity for masses below 40u. It requires a separator and an upgrade of the existing beamlines. It may be possible that an existing section of beamline can be modified to operate as a separator, which would allow considerable cost savings. A preliminary study into this option will commence in Due to energy and intensity limitations of the SSC, such a facility will only be competitive for light ions; and the relativistic nature of the beam restricts the kind of experiments that are possible. ISOL A primary, non-relativistic beam is directed on a thick production target such as uranium, which is fissioned to produce neutron-rich nuclei. In contrast to PF, the fission products are stationary, and must be re-accelerated by a second, post-accelerator to be directed on to a target for further study. A possibility at ithemba LABS is a fixed energy, high-current intensity (2mA of protons) K70 cyclotron, which could also be used for isotope production, as a primary accelerator. An RFQ could then be used to inject the radioactive ions into the SSC for post-acceleration. Alternatively, the SSC could be used to deliver the primary beam of up to 300 µa of 66 MeV protons, and a new post-accelerator be constructed. 10

11 Budget A possible budget for developing RIB in stages over a ten year period, based on similar facilities such as TRIUMF or the INFN Legnaro SPES proposal, is outlined below. STAGE FACILITY Approximate Budget Rand Millions Approximate Timescale I Installation of new ECR source R5 (funded) II Projectile Fragmentation R III Civil Engineering and construction of ISOL source R IV Post-acceleration of ISOL beams with LINAC R TOTAL R315 The final enlarged facility will require additional recurrent funding of R50 million. Detector Systems To exploit the enhanced beams and develop international competitiveness at the forefront of nuclear science, improved detector systems and associated electronics will be required. Major capital items, with estimated costs, include: Five current HPGe clovers, shields, electronics, R8.5m A γ-ray tracking spectrometer, R25m A focal plane polarimeter, R5m A large acceptance spectrometer, R25m A Gamma-Ray Tracking Spectrometer To carry out high-precision γ-ray spectroscopy with radioactive ion beams (RIB) a detector array is required with the specific aim to study the electromagnetic radiation from fast moving short lived exotic nuclei, with beam intensities several orders of magnitude lower than that which is typically used at stable beam facilities, and with recoil velocities up to v/c = 50%. Therefore, a γ-ray spectrometer with high position sensitivity and large detection efficiency at high γ-ray multiplicities is required. These goals can only be reached with highly segmented γ-ray tracking detectors representing the newest generation of γ-ray detectors. Powerful computer algorithms that are under development in several international laboratories are used to reconstruct the track of the γ-ray in the detector. We propose to build a γ-ray tracking spectrometer consisting of eight segmented detectors. In a geometry for RIB experiments the γ-ray tracking spectrometer will have an efficiency of 3.3% and an energy resolution of 4.5 kev for v/c=50% at a distance of 23 cm from the target. In a geometry for stable beam experiments (8cm from the target) an efficiency of up to 12% exceeding that of the present-day largest γ-ray arrays, can be obtained. A Large Acceptance Spectrometer The uses of high-energy heavy-ion beams, which will be provided by the new ECR ion source, allow nuclear reactions to be performed in inverse kinematics. For radioactive beams, particularly ISOL beams, inverse kinematics will often be a necessity. In order to separate out the products from such reactions, a Large Acceptance Spectrometer (LAS) will be required. 11

12 The research programmes requiring a LAS are: Nuclear Reaction Studies of Fusion barriers, Intermediate mass fragment production and Properties of the effective NN interaction Nuclear Structure Studies of Giant resonances and Spectroscopy of neutron rich nuclei Similar spectrometers have been constructed at other laboratories around the world, such as VAMOS at GANIL and PRISMA at Legnaro. These could serve as models for a LAS at ithemba LABS. 12

13 APPENDIX A Research Topic 1.1: Reaction Mechanisms for Super Heavy Element Production Fusion reactions that lead to the formation of superheavy elements are poorly understood because of the low reaction probabilities involved. It is believed that fusion is most probable at energies near the Coulomb barrier, where quantum mechanical tunnelling processes are important. It is now known that a distribution of barriers, due to collective excitations, rather than a single barrier, is generally necessary to explain the data. For the creation of superheavy elements near the predicted doubly magic island of stability at Z=114 and N=184, extremely neutron rich beams will be required, but the influence of neutron transfer reactions on the fusion probability needs to be investigated. This can be done by inferring the fusion barrier distribution by measuring quasi-elastic scattering, rather than measuring fusion probabilities directly. Rationale and Motivation A long standing prediction of nuclear shell models is the existence of an island of stability in the superheavy elements near Z=114 and N=184. The existence of such an island is a critical test of these models but the production of such nuclei has so far been elusive. Not only are the reaction cross-sections extremely small, but they will require the use of artificially produced, high intensity radioactive beams. These beams are also difficult to produce and therefore the understanding of the reaction mechanisms leading to the superheavies is also poorly understood. Work plan In collaboration with the University of the Western Cape and University of Zululand, the programme to measure of fusion barrier distributions at ithemba LABS commenced with the study of the 86 Kr Pb system which formed the MSc thesis of Mr S. Ntshangase. The next stage is to study the influence of neutron transfer on fusion probabilities by comparing the reaction of 40 Ca on 238 U with 48 Ca on 238 U. These beams are stable - ultimately it will be necessary to study the fusion probability using the artificially produced, neutron rich radioactive beams. This can only commence when such beams become available at ithemba LABS, initially through projectile fragmentation. Time Frame: First 18 months Study of the 40 Ca U system. Time Frame: Second 18 months Study of the 48 Ca U system. Time Frame: Third 18 months Development of measurements using neutron rich radioactive beams. Time Frame: 5 to 10 years Measurements using radioactive beams. 13

14 Resources: existing and required Existing The A-line scattering chamber is equipped with arrays of photovoltaic detectors required for the measurements. Required Radioactive beams supplied by the facility. Detectors with coverage of up to 2π of solid angle to compensate for low intensity of the radioactive beams together with associated electronics. Detectors for the energy measurement of degraded radioactive beams. Outcomes Publications, Conference presentations, M.Sc. and Ph.D. graduate training. 14

15 Research Topic 1.2: Measurement of high resolution polarization phenomena for nuclear reactions with polarized proton beams (Properties of the effective interaction) Rationale and Motivation This project presents a worldwide niche by exploiting and further developing the K600 spectrometer at ithemba LABS. The only potential competitor is the Research Center for Nuclear Physics in Osaka, Japan, the latter facility being optimized for incident proton energies at about 400 MeV, whereas ithemba LABS, on the other hand, focuses on lower energies ranging from 100 to 200 MeV. The interaction of polarized proton beams with nuclei, and resulting polarization observables, yields a wealth of information about the nuclear phenomena which would otherwise be inaccessible employing unpolarized probes. In particular, for the scattering of polarized protons from nucleons in specific single-particle states in nuclei, one can measure 7 independent polarization transfer observables compared to commonly measured unpolarized nuclear cross sections. These polarization observables, in turn, allow one to disentangle subtle dynamical aspects of the scattering process, thus subjecting existing reaction models to extremely stringent tests and also providing guidance for the development of the next generation of nuclear models. One of the most important, and as yet unsolved, questions in nuclear physics is to understand how the free nucleon-nucleon (NN) interaction - which is relatively well understood at energies between 100 and 200 MeV is modified by the presence of surrounding nucleons in nuclei. This problem can be addressed at ithemba LABS by performing high resolution measurements of complete sets of polarization observables for exclusive proton-induced proton-knockout reactions as well as inelastic proton scattering to discrete states. In particular, we plan to measure the polarization observables associated with exclusive (p,2p) reactions - whereby an incident proton knocks out a proton from a specific single-particle state in the nucleus and the two outgoing protons are detected in coincidence since these reactions offer the possibility to systematically map the density dependence of the NN interaction by selectively knocking out protons from deeply bound to the lower lying single-particle states. However, before tackling the latter question, it is important to develop reliable theoretical models capable of providing a quantitative description of all polarization phenomena for cases where density-dependent corrections to the NN interaction are NOT expected to play a significant role. For this reason our pilot project will be devoted to the measurement of complete sets of polarization transfer observables (A y, P, D NN, D S S, D L L, D S L, D L S ) for exclusive proton knockout from the single-particle states in 208 Pb close to the Fermi surface, namely the 3s 1/2, 2d 3/2 and 2d 5/2 orbitals, at an incident energy of 200 MeV, and for a variety of kinematic conditions. In addition, we will address the problem of whether the non-relativistic Schrödinger equation or relativistic Dirac equation is the most appropriate dynamical equation for the description of nuclear phenomena. Recently the nuclear theory group at Stellenbosch University demonstrated that sophisticated non-relativistic distorted wave models fail to describe (p,2p) analysing power data measured at ithemba LABS and RCNP. On the other hand, relativistic models provide an excellent description. The consistency of this result needs to be confirmed or refuted by comparing model predictions to other polarization data. Once the correct theoretical framework has been established for describing (p,2p) reactions where nuclear medium effects are not important, we will embark 15

16 on an extensive program to include knockout from the deeper lying single particle states in an effort to study density-dependent corrections to the NN interaction. It is important to note that the capability to measure polarization transfer observables is seen as desirable not only by this collaboration, but was also identified as important by the international committee of the 1996 Review of the laboratory as well as the international committee of the 2004 Review of the laboratory. Work plan The above scientific program can only be realized with the following equipment: - A polarized ion source capable of providing polarized proton beams with an average degree of polarization of 75% or better - A magnetic spectrometer with position sensitive focal plane detectors (consisting of 2 Vertical Drift Chamber (VDC) detectors) and fast readout electronics - A focal plane polarimeter (FPP), consisting of 4 multi wire proportional chambers (MWPCs), a graphite analyzer, a spin rotation (DSR) magnet in the focal plane and fast readout electronics ithemba LABS already possess a world class magnetic spectrometer and associated focal plane detector system with associated electronics in the K600 magnetic spectrometer. The polarized ion source at ithemba LABS has shown itself capable to routinely provide proton beams with a polarization degree of 75%. All that is then required to be able to measure polarization transfer observables is to instrument the K600 magnetic spectrometer with a focal plane polarimeter. The cost of building up a FPP, according to recent estimations, can be put to around five million Rand (R ). This excludes the cost of the DSR magnet. A fair amount of manpower is required to design, build and commission such a facility. Time Frame: First 18 months During this period technical aspects of FPP system will be investigated. This will help in determining the properties for a FPP that will suit the K600 magnetic spectrometer. Time Frame: Second 18 months The design of a FPP can commence once it becomes clear that the lab is committed to build a FPP. Time Frame: Third eighteen months Final designs. Commence with manufacturing of the various subsystems. Resources: existing and required Existing The polarized ion source and the K600 magnetic spectrometer. Required A focal plane polarimeter for the K600 magnetic spectrometer. Additional manpower at ithemba LABS, physicist as well as support staff, will be essential for the design and installation of the FPP. 16

17 Outcomes This project represents a unique collaboration between theorists and experimentalists in South Africa and as such present the opportunity to train postgraduate students in both theoretical and experimental aspects of cutting-edge nuclear physics. This program represents the development of a niche research areas based on the use of extended facilities at ithemba LABS and with the aim of addressing a topical question in nuclear physics. We expect to present the results of our work at national and international conferences as well as publish in international refereed journals. 17

18 Research Topic 1.3: Intermediate Mass Fragment production Most of the studies involving the interaction of light nuclei were performed at incident energies well below 10 MeV/amu where mean field processes together with deep inelastic collisions and particle evaporation are able to describe the data. Above 10 MeV/amu, however, nucleonic degrees of freedom become increasingly important. The need for a better understanding of the predominant reaction mechanisms regarding the interactions of light nuclei at these energies is further stimulated by the increasing number of applications e.g. in hadron therapy with carbon beams. Rationale and Motivation Previous studies of Intermediate Mass Fragments (IMFs) emitted in the interaction of light nuclei such as 12 C and 16 O with medium to heavy mass nuclei at incident energies of some tens of MeV/amu have convincingly demonstrated that the IMFs can originate from two unrelated mechanisms: binary fragmentation of the projectile and nucleon coalescence. The latter occurs during thermalization induced by the cascade of nucleon nucleon interactions by which the excited composite nuclei created in the primary two-ion interaction reach a statistical equilibrium state. The main mechanisms to be considered in this respect are found to be the complete fusion and the break-up-fusion (or incomplete fusion), i.e., projectile break-up followed by the absorption of one of the produced fragments by the target nucleus. Other important conclusions of these studies were the recognition that, before breaking up, the projectile may suffer a quite significant energy loss and that it may break-up in many different ways. These binary fragmentations occur with non-negligible probabilities so that, for instance, the break-up of 12 C into α-type fragments, although giving an important contribution, is by no means the only break-up mode to be taken into account in the theoretical calculations. In previous studies performed at ithemba LABS spectra of 3,4,6 He, Li, 7,8,9 Be and B fragments produced in the interaction of 12 C with nuclei in the mass range of about 60 to 200, at energies up to about 35 MeV/nucleon were measured and analyzed. Two aspects of the reaction mechanism are since being investigated closer, i.e. binary projectile fragmentation where fragments are detected either without further interactions with the target (quasi-elastic fragmentation), or in terms of a final state interaction in which the stable fragments further interact with the target nucleus (inelastic fragmentation). The relative importance of these two mechanisms was investigated in a coincidence experiment at ithemba LABS by measuring the correlations between 8 Be fragments and α-particles emitted in the interaction of 12 C with 93 Nb at an incident energy of 400 MeV. Since it is very improbable that the unstable/unbound 8 Be fragments will survive any further interactions after projectile break-up, only final state interactions of the partnering α-particles need to be considered. The other study focuses on the interaction of two light nuclei. If it is assumed that fragments emitted from this interaction are due in part to projectile and in part to target fragmentation, a significant dependence on the entrance channel of the fragment yield is to be expected. It is possible however to place stringent constraints on the data by measuring and analyzing the IMF spectra in both the direct as well as the inverse reaction of two light non-identical nuclei. 18

19 A further aim is to establish the amount of fragments with masses greater than those of the interacting ions and whether these are produced from deep inelastic collisions or as evaporation residues with relatively low energies. Since both these programs are not completed yet, more experiments will be performed as part of the five-year plan. These programs are especially set out to make use of the new ECR ion source and the higher incident energies of the species the ion source will provide. The relative contributions of the different mechanisms to the measured yields are believed to change as function of increasing incident energy. More experimental data at these energies will therefore be needed to further test and extend the current theoretical model with regard to the assumed reaction mechanisms. Furthermore these studies will also benefit from the envisaged program to produce neutron rich nuclei through projectile fragmentation in order to refine our understanding of the inferred reaction mechanisms. Work plan The high-precision scattering chamber positioned in the A-line, together with different detectors like a resonant particle spectrometer, silicon surface barrier detectors, NaI detectors, plastic scintillators, Bragg Curve Detectors provide the experimental apparatus for these experiments. In order to perform more of these types of experiments, more silicon surface barrier detectors, Bragg curve detectors and appropriate electronics will be required. Time Frame: First 18 months More experiments with C and O beams on light targets are envisaged during this period with similar setups as used in the past. Time Frame: Second 18 months As part of the envisaged programs to deliver higher incident energies with the new ECR ion source as well as to produce neutron rich nuclei through projectile fragmentation, developments of more Bragg Curve Detectors will be required. Time Frame: Third eighteen months Continue experimental program with beams at higher incident energies as well as with exotic projectiles as produced in the projectile fragmentation process. Resources: existing and required Existing The A-line scattering chamber is equipped with detectors as described above. Required Additional Bragg Curve and silicon surface barrier detectors, charge sensitive preamplifiers with low energy gains together with corresponding electronic readout modules. Outcomes Publications, Conference presentations, M.Sc. and Ph.D. graduate training. 19

20 Research Topic 1.4: Pre-equilibrium reactions The interaction of energetic nucleons with nuclear matter is of interest for fundamental reasons as well as for applications in fields as diverse as transmutation of nuclear waste, medical treatment of cancer patients in radiotherapy, production of radioisotopes for medical diagnostic purposes and production of nuclear fusion fuel. Rationale and Motivation Past ithemba research on this topic concentrated on the reaction mechanism of importance to (p,p ) reactions in the energy region up to 200 MeV and this served as a critical test of the statistical multistep direct reaction theory of Feshbach, Kerman and Koonin for preequilibrium proton emission induced by protons in that energy region. This was followed by studies of analyzing power, as well as reactions that involve composite ejectiles such as 3 He and α-particles. Although initial investigations reveal that a statistical multistep mechanism shows promise, a more refined understanding of the reaction mechanism needs to be developed. Further experimental studies with improved statistical accuracy of analysing power data are required. In addition, the reaction mechanism involved in proton-induced light-heavy ion emission needs to be investigated. Work plan The high-precision scattering chamber positioned in the A-line, together with different detectors like a resonant particle spectrometer, silicon surface barrier detectors, NaI detectors, plastic scintillators, provide the experimental apparatus for these experiments. In order to perform more of these types of experiments, more silicon surface barrier detectors as well as appropriate electronics will be required. Time Frame: First 18 months More experiments with beams of polarized protons on light targets are envisaged during this period using similar setups as in the past. Time Frame: Second 18 months As part of the envisaged programs to change over to a new data acquisition system certain electronic modules will have to be replaced with appropriate VME modules. Implementation of new data acquisition system will require some test beam time. Continue with experimental program. Time Frame: Third eighteen months In order to reach the eventual goal by extending experimental program of studying the emission of also light nuclei in reactions induced by polarized protons a new polarized ion source which will deliver high enough beam intensities will be required. Resources: existing and required Existing The A-line scattering chamber is equipped with detectors as described above. 20

21 Required Additional silicon surface barrier detectors, charge sensitive preamplifiers with low energy gains together with corresponding VME electronic readout modules will be required. Outcomes Publications, Conference presentations, M.Sc. and Ph.D. graduate training Collaboration with University of Stellenbosch 21

22 Research Topic 1.5: Charged particle reactions to populate high-spin states Rational and Motivation: Incomplete fusion reactions Incomplete fusion reactions depend strongly on the cluster-type structure of the beam. For example relatively light heavy ions such as 7 Li, 9 Be, 11 B and 12 C have t-α, α-α-n, α- 7 Li (or α- α-t) and α-α-α cluster structures, respectively. A consequence of this is that these species have a tendency to break-up when they impinge on targets, so that part of the beam can fuse with the target, while the complementary fragment continues with essentially the same energy-per-nucleon as the incident beam. There are indications that the break-up process occurs in a narrow entry region corresponding to the grazing angle for the collision, which has a strong dependence on the incident energy of the beam. This is expected to lead to a highly localized (in angular momentum) feeding region from which states in the residual nuclei will be populated. The narrowness (in spin) of the entry region offers the possibility to probe the population of superdeformed (SD) bands around the point where these structures cross the normal-deformed states in the energy-spin place, and thus attain yrast status. Furthermore, if a particular beam-target system employed to populate SD states via incomplete fusion (IF) possesses a series of barriers corresponding to different relative orientations and/or entrance-channel excitations, it might be possible to observe features in the IF-charged particle spectra. This would also offer the possibility of selecting particular entry regions by gating on the corresponding IF-charged particles. The incomplete fusion reactions are also a major tool to produce nuclei close to the line of stability using stable projectiles. Thus, high-spin states in nuclei not accessible by standard fusion-(neutron) evaporation reactions can be populated and studied. Charged-particle emission from strongly distorted nuclei The Coulomb barrier at the tips of highly elongated nucleus is expected to be considerably lower than on average, and this feature may lead to preferential emission of light charged particles from these locations. Hence, a study of charged particles in coincidence with a sequence of superdeformed or hyperdeformed gamma-ray transitions may show evidence for a low energy component corresponding to emission from the tips. This would also offer the possibility of preferentially selecting the feeding of superdeformed or hyperdeformed bands in neutron deficient nuclei that can only be studied via pure charged-particle exit channels. Work Plan Incomplete Fusion Reactions, charged-particle spectroscopy, neutron-deficient nuclei During the period , the DIAMANT charged-particle detector, an array of up to 72 CsI detectors, has been coupled with the AFRODITE gamma-ray spectrometer through collaboration between ATOMKI and ithemba LABS under a bilateral agreement between Hungary and South Africa. The intention is to request for an extension of the collaboration beyond

23 In the present arrangement, the full DIAMANT detector and its electronics have to be routinely shipped between GANIL and ithemba LABS in order to enable measurements to be carried out at both laboratories. This results in extra shipping costs, exposes the equipment to possible damage during shipment, and makes scheduling of experiments extremely difficult. Hence, it is proposed here that ithemba LABS obtains its own CsI array with the necessary electronics in order for the very successful collaborative research programme to continue and develop during the next five years. A full array of CsI detectors and VXI (or alternative) electronics can be built up in a modular fashion. For the study of superdeformed nuclei, a powerful array of clover detectors would be needed to give sufficient charged-particle/gamma-ray detection efficiency. A major step forward would be to obtain highly segmented clover detectors, similar to those used in EXOGAM at GANIL and TIGRESS at ISAC-TRIUMF. Not only would this maximize the detection efficiency of AFRODITE and hence allow the array to perform beyond its original specifications, it will enable the opportunities that will arise from the new high current ECR source to be fully realized. Time Frame: First 18 months Search for superdeformation in 70 Zn with AFRODITE-DIAMANT. Order highly segmented clover detectors from Canberra-Eurisys Order CsI crystals, photo-diodes, electronics; assembly and construction through collaboration with ATOMKI. Install three clover detectors on loan from ATOMKI and KVI during continuation of Hungarian- South Africa agreement. Time Frame: Second 18 months Investigate incomplete fusion reactions with light cluster-type beams produced from the present ECR source since new ECR source will be available. Install segmented clover detectors in AFRODITE as they become available. Installation of complete charged-particle detector with AFRODITE. Time Frame: Third 18 months Full operation of segmented clover detectors in AFRODITE. Operation of fully fledged highefficiency charged-particle/gamma-ray system. Resources: Existing and Required Existing The AFRODITE array with up to 9 (possibly 12 with three loaned from ATOMKI/KVI) escape suppressed clover and 8 segmented planar Ge detectors. The DIAMANT array of CsI particle detectors for particle-γ coincidence measurements. Required High intensity stable heavy-ion beams from the new ECR source. 5 extra standard clover systems Light cluster type beams (e.g. 7 Li, 9 Be) from the existing ECR source. In-house charged-particle detector system. Eight segmented clover detectors plus escape-suppression shields to allow 4 at 35, 8 at 90 and 4 at

24 Research Topic 1.7: Scattering of Radioactive ion beams off hydrogen Rational and Motivation: The purpose of scattering radioactive ion beams (RIBs) off hydrogen at intermediate energies (30A 200A MeV) is to probe the density of the radioactive ion. In the inverse kinematics such scattering equates to proton scattering off the exotic nucleus. By probing the density of the target one may elicit properties of the exotic nucleus not encountered in the valley of stability. For example, the very weak binding energy of nuclei near the drip lines allows for the formation of halos and skins. While scattering off heavy ions may probe some details of the surface of nuclei, it does not probe into the interior. The effects of the halo changes the density in the core of the nucleus [1] and this may be studied directly using proton scattering. Analysis of data coming from such scattering experiments, especially those involved exotic structures, requires a model of scattering which is entirely predictive in order to probe details of nuclear structure: all inputs of the model (structure of the target, interaction, etc.) must be preset and no a posteriori adjustment of parameters may be allowed. Such a model is the g- folding model of the Melbourne Group [2]. It is based on a coordinate-space representation of the g matrices of the nucleon-nucleon interaction in-medium. That energy- and densitydependent effective interaction is folded with the one-body density matrix elements defining the structure of the target nucleus to give the intermediate energy microscopic optical potential describing the scattering. That optical potential is nonlocal by construction: the exchange terms giving rise to the nonlocality come naturally in the model by requiring an antisymmetric initial state between the projectile nucleon and the bound state nucleon, leading to terms describing the knockout process, where the incident nucleon is not the emergent one. The g matrices are solutions of the Brueckner-Bethe-Goldstone equation in momentum space, for a projectile interacting with infinite nuclear matter [2]. It incorporates Pauli blocking, as well as the effects of the mean field. That is done in an average way by acknowledging that above 30 MeV incident energy the density of states in the nucleus is large enough such that the intermediate coupling over excited states in elastic scattering may be done implicitly by the averaging process. In that regard, the model has been extensively tested in the energy range 50 to 300 MeV, with the optimal energy range MeV. A suitable RIB-hydrogen scattering facility would need to have energies within the range 50A-200A MeV. Also, the effect of the halo or skin is observed in the differential cross section beyond the first diffraction minimum, at large momentum transfer [1], while the central maximum relates primarily to the rms radius of the nucleus. It is important, therefore to be able to define the region of the first diffraction minimum, hence a good angular resolution is needed (in the centre of mass). The structure of the differential cross section is important in this respect. The Melbourne g-folding model has had much success in the prediction of elastic scattering data (differential cross sections and spin observables), and has been used as a test for structure of exotic nuclei. (For a complete review, see Ref. [2].) Inelastic scattering may also be described in the Distorted Wave Approximation (DWA) using the effective interaction as the transition operator. There has been good agreement between theory and experiment also 24

25 for such data [2], including inelastic scattering leading to excited states in exotic nuclei ( 6 He [3], for example). Elastic scattering probes the bulk density of the nuclear medium and, at intermediate energies, particularly the core in the case of halo nuclei. As the NN interaction at these energies is dominated by the V_{pn} term, proton scattering primarily, though not exclusively, probes the neutron density and vice versa. Hence, scattering from neutron rich nuclei can be done, and much information is still needed on the nature of the core in 11Li, in light of the shake-off mechanism in scattering [4]. Other scattering experiments may be done on neutron rich p- and sd- shell nuclei towards the drip lines. Inelastic scattering may probe different facets of the structure, depending on the transition. In particular, inelastic E2 scattering probes the surface of the nucleus [3]. In that case, such would be sensitive directly to the details of the halo, as was demonstrated in the case of 6 He [3]. Along those lines, a measurement of the inelastic scattering to the states around 1.3 MeV in 11 Li [4] is needed to resolve the discrepancy between various models and unambiguously establish the spectrum. As the core of 11 Li is 9 Li, measurements on 9 Li should be done also. References [1] S. Karataglidis, P. J. Dortmans, K. Amos, and C. Bennhold, Phys. Rev. C 61, (2000). [2] K. Amos, P. J. Dortmans, H. V. von Geramb, S. Karataglidis, and J. Raynal, Adv. Nucl. Phys. 25, 275 (2000). [3] A. Lagoyannis et al., Phys. Lett. B518, 27 (2001); S. V. Stepantsov et al., Phys. Lett. B542, 35 (2002). [4] S. Karataglidis et al., Phys. Rev. Lett. 79, 1447 (1997). 25

26 Research Topic 2.1: Giant Resonances Hadronic scattering and reactions at intermediate energies of a few 100 MeV per nucleon serve as a classical tool for the investigation of giant resonances. There are various topics of current interest: The investigation of the fine structure of giant resonances to help with the identification of the excitation and decay modes of giant resonances. The study of the magnetic dipole and the related GT resonance response in nuclei remains a field at the heart of nuclear structure physics. It is driven by a subtle interplay of single-particle and collective degrees of freedom and thus serves as an ideal testing ground for microscopic nuclear structure models. Benchmark tests of modern microscopic nuclear theory GT Strengths in Nuclei and Supernova Physics Determine late pre-collapse stages of massive stars Explosive nucleosynthesis during the supernova shock wave Goal: extract GTo from (p,p ) M s 2 Rationale and Motivation The ithemba LABS K600 magnetic spectrometer is the only light ion spectrometer in the world that can be used to make high energy-resolution measurements in the proton energy region up to 200 MeV. A firm collaboration between ithemba LABS, Wits, UCT, and the Institut für Kernphysik, Technical University Darmstadt, has grown around using the K600 magnetic spectrometer to investigate the phenomenon of Giant Resonances in nuclei, producing amongst others the first article published in Physical Review Letter from work done at ithemba LABS. This collaboration has recently grown to include the users of the Grand Raiden spectrometer of RCNP, Osaka University who can also study spin flip resonances with the (3He,t) reaction. Specific topics of interest to this collaboration include the following: Fine Structure of Giant Resonances Fine structure in the energy region of the ISGQR (Isoscalar Giant Quadropole Resonance) in heavy nuclei was observed in high energy-resolution proton scattering experiments performed at ithemba LABS. A novel method based on wavelet transforms was introduced for the extraction of scales characterizing the fine structure. Comparisons of these scales with microscopic model calculations enable the identification of the excitation and decay modes of giant resonances. The systematic investigation of the fine structure of giant resonances with the emphasis on the ISGQR will be extended from the heavy mass region 58<A<208 to the low mass region 12<A<40. This will open up the question as to the role of the escape width, which becomes more important for the lighter nuclei, and will establish the global nature of fine structure in the ISGQR from very light to very heavy nuclei. The fine structure in other giant resonances such as Spin-Dipole resonance is also to be studied. 26

27 The Electric and Magnetic Dipole Resonances Inelastic proton scattering with very high resolution at extremely forward angles, including zero degrees, is a very powerful tool for studying E1 and M1 excitations in nuclei. Such experiments are very difficult, and for this reason there are still many important measurements that are outstanding. In order to extract the E1 strengths from measured data, it is vital to measure the energy dependence of the cross section, which in the case of E1 excitations depends strongly on the incident beam energy. The physics motivation is explained by relating the dipole transitions to the nucleosynthesis and other aspects in supernovae. Model calculations show that the amount of E1 strength significantly affects the nucleosynthesis scenario in the Type-II supernovae. The M1 resonances are strongly related to neutrino-induced reactions in the supernova. These processes are relevant to the energy flow during supernova nucleosynthesis by neutral currents, and dynamic simulations of the evolution of a supernova. While our partner laboratory in Japan, RCNP, concentrates on experiments at higher proton beam energies up to 400MeV, measurements at ithemba LABS up to the maximum proton beam energy of 200MeV, is seen to complement many of these studies at the lower energies. Isospin Structure of the PDR (Pygmy Dipole Resonance) from (α,α γ) Coincidence Experiments The coincident measurement of the γ-decay of nuclei excited in inelastic hadron scattering reactions is an exciting prospect that would require the use of the AFRODITE gamma-array in coincidence with the K600 magnetic spectrometer. The AFRODITE clover detectors have relatively good efficiencies for the high energy γ-rays that are expected to be observed. Such a measurement will typically allow excitations with energies very close to one another to be resolved, multipolarities to be assigned, branching ratios to be determined and the isospin character of bound excitations to be studied. As an example one should consider the study of the isospin structure of the PDR from (α,α γ) coincidence measurements. Measurement of polarization transfer observables to help understand nuclear structure The addition of a focal plane polarimeter (FPP) to the K600 magnetic spectrometer will open up a new range of possible measurements e.g. the measurement of spin-flip probabilities for single excitations... Work plan High-resolution measurements of charged particles emitted at angles > 7 can be performed fairly routinely with the K600 magnetic spectrometer at ithemba LABS. However, making high-resolution measurements of charged particles emitted at zero degrees is difficult because one has to separate out the reaction products from the beam producing the reactions. For this magnetic spectrometers are invaluable. 27

28 The K600 Zero Degree Facility is already in an advanced stage of development. The Zero Degree beamdump has been successfully commissioned, and various changes to the beamline and scattering chamber are being implemented. In order to run an experiment at zero degrees the focal plane detectors have to have both good horizontal- and vertical position-resolution in the focal plane. Since the existing detectors cannot provide good vertical resolution, new detectors were designed and are currently being manufactured. The extra wires to be read out have also meant that more electronics is required, but the existing modules were manufactured some 20 years ago by a now defunct company, necessitating the total replacement of the readout. This is now currently underway. Changing over to modern electronics also coincides with the phasing out of the computers that have up till now been used for data acquisition, with the result that a new data acquisition system is also required for future experiments. This holds true for all future experiments. Time Frame: First 18 months The systematic investigation of the fine structure of giant resonances with the emphasis on the ISGQR will be extended from the heavy mass region 58<A<208 to the low mass region 12<A<40. This can be achieved with the existing K600 setup, using the existing focal plane detector system at scattering angles of 7 and more. The K600 Zero Degree Facility will be commissioned and tested within the first eighteen months. Investigations into running (α,α γ) coincident measurements on the K600 will begin. Time Frame: Second 18 months The fine structure in ISGQR has been studied and there are plans to extend this sort of study to Spin-Dipole resonances. The first (p,p ) and (p,t) experiments with the full K600 Zero Degree Facility will be performed and preparations for running (α,α γ) with parts of the AFRODITE array in coincidence with the K600 will be completed and towards the end of this period or the beginning of the next these experiments will start in earnest. Time Frame: Third 18 months The M1 states and (α,α γ) experimental program at zero degree as well as the fine structure studies will continue during this period. In order to achieve extremely high energy resolution of 15keV or better, investigation into changes to the P and S beamlines are required which will be investigated in this period. Planning for the focal plane polarimeter should start. Resources : existing and required Existing The K600 magnetic spectrometer using the medium dispersion focal plane detector system. Required The K600 Zero Degree facility, which includes the new focal plane detector system and new data acquisition system. In order to measure more observables we need a focal plane polarimeter. Start with planning phases, but money and especially extra technical support personnel will be required to undertake this project. To be able to mount several of the AFRODITE clovers around the K600 scattering chamber will also require a significant amount of technical support to designing and building structures to house them. 28

29 Outcomes Publications, Conference presentations, M.Sc. and Ph.D. graduate training. 29

30 Research Topic 2.2: Level structure of exotic nuclei: Application in Type I X-ray bursts in astronomy The level structure of exotic nuclei is to be studied, using the two neutron pick-up (p,t) reaction. Rationale and Motivation Since their discovery more than seventy type I X-ray bursts have been observed. Type I X- ray bursts have been explained as emissions from runaway thermonuclear explosions in the atmosphere of accreting neutron stars. The runaway explosion is triggered by the break-out from the hot CNO cycles and is driven by a subsequent p- and rp-process converting the initial CNO material into 56 Ni with a few seconds. The exact rise time and the structure of the light-curve of the runaway explosion depend on the nuclear timescale associated with the p- and rp-process reaction rates. Several X-ray burst sources have been observed with a pronounced double peak structure in the bolometric luminosity. The separation between the two peaks is of the order of a few seconds. This indicates a nuclear waiting point impedance in the thermo-nuclear reaction flow associated with the p-process. The p-process is identified as a sequence of (α,p) and (p,γ) reactions, channelling the reaction flow from the 14 O and 18 Ne waiting point nuclei towards higher masses. Waiting points have been identified as even-even nuclei along the reaction path which cannot be depleted by proton capture reactions. They are either prohibited by the negative Q-values or substantially quenched by inverse photodisintegration at the burst temperature because of a very low Q-value. The two main waiting point nuclei, 14 O and 18 Ne, in the CNO cycles are bypassed by the 14 O(α,p) 17 F(p,γ) 18 Ne(α,p) 21 Na(p,γ) 22 Mg reaction sequence triggering the p- process. The timescale for the subsequent p-process flow 22 Mg(α,p) 25 Al(p,γ) 26 Si(α,p) 29 P(p,γ) 30 S(α,p) 33 Cl(p,γ) 34 Ar(α,p) 37 K(p,γ) 38 Ca and the switch-over to the classical rp-process is determined by the associated reaction rates. It has recently been shown that the experimentally unknown 30 S(α,p) 33 Cl and 34 Ar(α,p) 37 K reaction rates are critical for determining the timescale of the thermonuclear runaway explosion. No experimental information is available for the 30 S(α,p) 33 Cl and 34 Ar(α,p) 37 K reaction cross sections. Present simulations of the p-process are based on Hauser Feshbach predictions for the cross sections which rely on the assumption of a high level density in the associated compound nuclei 34 Ar and 38 Ca. Resonant contributions are however limited to natural parity states only, which may significantly reduce the effective level density in 34 Ar and 38 Ca. The (α,p) reaction rates are determined by the number of resonances, the resonance energies and α-partial widths of the α-unbound states within about 2 MeV above the threshold of Q = and MeV, respectively. The reaction rates depend exponentially on the resonance energies which are therefore particularly important to measure as precisely as possible. We will study the level structure of 30 S, 34 Ar, and 38 Ca using the two neutron pick-up reactions 32 S(p,t) 30 S, 36 Ar(p,t) 34 Ar, and 40 Ca(p,t) 38 Ca, respectively. High resolution spectrometer studies are planned to probe in particular α-unbound resonant states in these nuclei to determine the resonance energy with high accuracy. 30

31 Work plan High-resolution measurements of charged particles emitted at angles > 7 can be performed routinely with the K600 magnetic spectrometer at ithemba LABS. However, making high-resolution measurements of charged particles emitted at zero degrees is difficult because one has to separate out the reaction products from the beam producing the reactions. For this magnetic spectrometers are invaluable. The K600 Zero Degree Facility is already in an advanced stage of development. The Zero Degree beam dump has been successfully commissioned, and various changes to the beamline and scattering chamber are being implemented. In order to run an experiment at zero degrees the focal plane detectors has to have good horizontal- and vertical positionresolution in the focal plane. Since the existing detectors cannot provide good vertical resolution new detectors were designed and are currently being manufactured. Time Frame: First 18 months The K600 Zero Degree Facility will be commissioned and tested. Additionally a new beamstop, the so-called triton beamstop, will be designed and installed inside the magnetic spectrometer to enable the zero degree measurement of (p,t) reactions. An argon gas target must be designed, installed and tested. Time Frame: Second 18 months The first experiments with the full K600 Zero Degree Facility will be performed. Time Frame: Third eighteen months Continuation of the experimental program, studying different targets. Resources : existing and required Existing The K600 magnetic spectrometer with medium dispersion focal plane detector system Required The K600 Zero Degree facility, which includes the new focal plane detector system and new data acquisition system. A new beamstop for the (p,t) mode at zero degrees which fits in the vacuum chamber between the two dipoles of the K600. Outcomes Publications, Conference presentations, M.Sc. and Ph.D. graduate training. 31

32 Research Topic 2.4: Studies of exotic nuclear shapes and symmetries Rational and Motivation: Spectroscopy of Actinide region (Hyperdeformation) The study of the actinide region is motivated by a search to find gamma-ray transitions from the third well - the hyperdeformed well. Hyperdeformation is one of the hottest topics in spectroscopy, with over eight weeks of beam time devoted to the search in the mass 130 region, at the world's largest detector arrays, Gammasphere and Euroball IV. In the actinide region, the transitions within the hyperdeformed band are expected to decay through E1 transitions with an average energy of about 100 kev. In this regime AFRODITE is the most efficient array in the world and is thus ideally placed to search for hyperdeformation in this region. A difficulty with all searches for hyperdeformation is that such shapes occur only at high spin where competition from fission decay is strong. Tetrahedral shapes Tetrahedral shapes in atomic nuclei have been predicted by Dudek et al[1] to occur in selected mass regions. A particularly favourable region occurs at N=90 and Z=70, corresponding to the nucleus 160 Yb, which is currently being made at ithemba LABS to look for evidence of tetrahedal shapes. Also under study at ithemba are the nuclei 152,154 Gd, which, having N 90 are also favourable cases. In a recent article Dudek et al[1] examined the decay properties of negative parity bands and suggested that the strong E1 transitions to the ground state bands could be a signature of tetrahedral shape. The analysis of the ithemba data is still being finalized, but further measurements to directly measure B(E1) strengths are planned. This is possible using Coulomb excitation of the Gd isotopes. We intend to put in a proposal to study 160 Yb at a radioactive beam facility when such a beam becomes available. A useful by-product of such an experiment would be to gain experience with using radioactive beams, especially in preparation for possible radioactive beams at ithemba LABS. [1] Dudek et al, Phys.Rev.Lett. 88, (2002); Phys.Rev.Lett. 97, (2006) Chiral Bands in mass 180 region A topic of considerable interest in nuclear spectroscopy is the observation of chirality in atomic nuclei. It is a dynamical effect expected in triaxial nuclei when the core, proton and neutron angular momenta are mutually perpendicular. These conditions are relatively rare - being found only in selected region of the nuclear chart. The best evidence for chirality has been the πh 11/2 νh 11/2 bands of the 130 region, but recent measurements of lifetimes have proved that the proposed chiral bands are in fact manifestations of shape coexistence. Thus the existence of nuclear chirality remains an open question. 32