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 Gamka: Proposal Description

Proposal Description 

This proposal is for a fundamental acquisition of a state of the art research equipment for gamma-ray spectroscopy research into the Structure of Atomic Nuclei and Nuclear Astrophysics, in line with the demands, sophistication and quality of research needed in the 21st century and beyond. This proposal is in strong synergy with national priorities such as the Square Kilometre Array (SKA) and the South African (SA) nuclear energy build. It is put forward by a consortium composed by the University of the Western Cape (UWC), Stellenbosch University (SUN), University of Zululand (UniZulu), University of the Witwatersrand (Wits) and iThemba LABS. Thus it is truly a user driven proposal involving a number of historically disadvantaged universities. The proposal is led by UWC as the largest nuclear physics group of the SA Universities, with over 50 members composed primarily by black SA students from Historically Disadvantaged Institutions (HDIs). Moreover, UWC leads the first African physics experiment at CERN (spokesperson: Nico Orce) and has the first SarChi Chair in Nuclear Science (Co-applicant Smarajit Triambak). UWC, together with UniZulu and iThemba LABS, has one of the most successful Honours/Masters programs in the country, the MaNus/MatSci, bringing up about 25 SA students from HDIs every year. You can find more information about UWC's Nuclear Physics and GAMKA at:

iThemba LABS is the Host Institution, as the only facility in Africa where competitive experimental nuclear structure and nuclear astrophysics research can be undertaken from the level of Masters through PhD and beyond. This NRF Facility has been contributing to equity and redress by training postgraduates in nuclear sciences (80% of post graduates are black South Africans). Since the available beam time is fixed we can only expand the training by improving the efficiency of our detector systems. 

Our proposal asks for resources to acquire new radiation detectors that will complete the gamma-ray array at iThemba LABS to the full original design of 16 escape-suppressed High Purity Germanium (HPGe) detectors of the “clover” type that each consist of 4 Ge crystals in a close geometry, contained in a single cryostat. This constitutes the maximum number of detectors that can be accommodated in the present geometry and would give the largest possible coverage of the full 4pi solid angle. The present AFRODITE array consists of 9 clover detectors. Clover HPGe detectors and BGO shields together form a Compton suppressed gamma-ray spectrometer. HPGe detectors are still the only option for high resolution gamma-ray spectroscopy. For gamma-ray spectroscopy with high intensity stable heavy-ion beams an array of clover detectors remain a competitive solution at a reasonable cost. Since iThemba LABS views the completion of the array as a very high priority, funding from the Strategic Research Infrastructure programme for National Facilities was requested and received for an additional 3 clover detectors. This proposal thus asks for 4 Ge clover detectors to complete the array as well as for one additional detector as a spare in order to ensure that full capacity can be maintained when a detector has to undergo annealing or repair. 

Gamma spectrometers are by no means off-the-shelf instruments. Both the clover and BGO detectors require high-voltage supply. A single system with different cards can supply the different requirements of these (high voltage, low current for clovers and lower voltage, high current for BGO). Additional data acquisition electronics of the same type as presently in use are required to accommodate the additional detectors. Each PIXIE 16 card can accommodate 2 clovers. The annealing system, a vacuum fitting and heater with temperature control, and a liquid nitrogen generator are a essential tools to allow regular maintenance and optimum functioning. The infrastructure required to mount the additional detectors already exists, and the new elements can be used to do research as soon as they arrive. However, a support structure to house detectors in an asymmetric configuration will be designed and constructed. The GAMKA request is thus for: 

1) 3 HPGe clover detectors + 3 BGO (Bismuth Germinate) Compton suppression shields for collection of high-resolution                gamma rays. 

2) 23 large-volume LaBr3 detectors for collection of high-efficiency gamma rays,  

3) 3 XIA PIXIE 16 digital data acquisition cards (12 bit 500Mz digitization) with a crate, 

4) a high voltage system for 4kV at low current (clovers) and for 2kV at high current (BGO), 

5) 1 annealing system for clover detectors, 

6) support frames to accommodate up to 30 detectors, 

7) liquid nitrogen liquefier. 

The increased efficiency of GAMKA will allow more students to be trained and will enhance our international competitiveness by ensuring that the training and research remain internationally relevant.​


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