AFRODITE | Fast Neutron Beam Facility | H-line | K600
Since its commissioning in 1986, the iThemba LABS K=200 separated sector cyclotron (SSC) has played a critical role in advancing nuclear physics, particle therapy, and radioisotope production. However, the equal division of beam time across these programs has historically limited the full potential of nuclear physics research. That’s about to change.
With a strategic focus on increasing beam time for nuclear physics, particularly beyond weekend slots, iThemba LABS is positioning itself for a significant boost in its research capacity. This shift, supported by enhanced infrastructure and human resource development, is set to transform the lab's contribution to global subatomic physics research over the next decade. By 2030, iThemba LABS aims to double both its research staff and user base, reinforcing its reputation as a world-class center for nuclear innovation and training.
The SSC accelerates protons to a maximum energy of 200 MeV, making it a highly adaptable tool for advanced research. This capability is supported by two injector cyclotrons, SPC1 and SPC2, which pre-accelerate particles to 8 MeV/nucleon and 10 MeV/nucleon, respectively. Equipped with cutting-edge ion sources—an Electron Cyclotron Resonance (ECR) source in SPC1 and a Penning Induction Gauge (PIG) source in SPC2—this system ensures precision in the acceleration process.
With its diverse functionality, the cyclotron contributes to a broad spectrum of research. It is instrumental in nuclear studies that investigate the structure, reactions, and origins of matter in the universe, while also serving applied research in metrology, detector calibration, and radiation biophysics. Additionally, its role in producing radiopharmaceuticals significantly impacts medical science, particularly in diagnostics and therapeutic applications. This combination of fundamental and applied research underscores the cyclotron's vital role in pushing the boundaries of both nuclear science and its real-world applications.
The competitive nature of the research programme is informed by the range of available particle beams and the detection capabilities at iThemba LABS.
iThemba LABS has a wide range of gamma-ray detectors available, and the
list is growing through investment and collaborations with international facilities. These include background-shielded single-crystal high-purity germanium (HPGe) detectors for activation or environmental radiation studies, segmented Clover detectors, eight HPGe low-energy photon detectors (LEPS), eight fast-timing
2” x 2” LaBr3:Ce detectors, and the AFRODITE and ALBA detector arrays. In addition, a range of ancillary detectors are available, which include:
the refurbished Siegbahn-Kleinheinz electron spectrometer with a field of Bmax ~0.15 T and Si(Li) detectors of 5–6 mm thickness
(African Omni-purpose Detector for Innovative Techniques and Experiments) is a gamma-ray array consisting of 17 Compton suppressed HPGe Clover detectors. The array provides experimentalists with improved detection efficiency and resolution.
(African LaBr3:Ce Array) consists of 21 high-efficiency large-volume
(89 x 203 mm) LaBr3:Ce detectors. This array provides the high-efficiencies for the studies of gamma-ray decay of resonances at high excitation energies or photon strength function measurements.
May be run stand-alone or combined in any of the two new frames, namely Soccer- ball and Dandelion. The new frames have been designed to accommodate the detectors at variable distances from the target position.
(Gamma-ray AsymMetric spectrometer for Knowledge in Africa) provides a unique array that combines detector elements from ALBA and AFRODITE. GAMKA
was built by a consortium of iThemba LABS and several SA universities, and
was supported by an NRF grant. In addition to the new frames, an investment
was made in an on-site liquid nitrogen production plant capable of producing 260l/day. GAMKA is supported by the National Research Foundation of South Africa (Strategic Research Equipment Grant Number: 114668), and by contributions from iThemba LABS, Stellenbosch University, University of the Western Cape, University of the Witwatersrand and the University of Zululand.
The K=600 magnetic spectrometer is a high-resolution kinematically corrected magnetic spectrometer for light ions. It is capable of measuring inelastically scattered particles and reactions at extreme forward angles that include 0°, making it one of only two facilities worldwide (the other being at RCNP, Japan) where high- energy resolution is combined with 0° measurements at medium-beam energies. The advantage of such measurements is the selectivity it provides to excitations with low angular momentum transfer.
A new scattering chamber was designed and manufactured to accommodate
the Coincidence Array for K=600 Experiments (CAKE). CAKE, shown on the left, consists of up to six wedge-shaped double-sided silicon strip detectors, placed in a lampshade configuration upstream from the target ladder. It enables coincidence spectroscopy of charged-particle decays following inelastic scattering and transfer reactions detected by the focal-plane detectors of the K=600.
Coincident γ-ray detection capability was recently added to the K=600 repertoire through the installation of a frame which allows for interchangeable configurations of up to 30 gamma-ray detectors, including AFRODITE-PLUS, ALBA and fast- timing detectors. The efficiency and granularity of the new set-up, and also the
fact that K=600 measurements can be performed at zero degrees, all combine to make this set-up a unique experimental tool. Over the next years, a new focal-plane detector will be installed which will eliminate particles having to traverse air and will allow for the detection of heavier-mass particles or lower-excitation energies.
The Low-energy Nuclear Astrophysics Beamline at the Tandetron facility, iThemba LABS, is designed to study indirectly radiative capture reactions through measurements of statistical properties. These reactions involve the capture of a charged particle, either a proton or an α-particle, by the nucleus, resulting in the emission of gamma-ray photons. This process plays a pivotal role in stellar nucleosynthesis, contributing to the formation of heavier elements in the universe.
The IAEA database on Photon Strength Functions has identified only 22 nuclei (with Z=22−40) that have been experimentally measured using (p,γ) reactions. Extracting the photon strength function from these measurements is crucial for not only calculating nucleosynthesis reaction rates but also for studying the underlying nuclear structure. The scarcity of such data underlines the challenges in obtaining experimental results and emphasizes the need to measure proton or alpha capture rates.
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