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. The beamline specifications include an array capable of handling proton beam with energies up to 6 MeV and alpha beam with energies up to 9 MeV, with intensities reaching up to 10 micro Amperes. The array includes a half-AFRODITE detector frame on one side, which can accommodate up to 6 High Purity Germanium (HPGe) detectors or 6 large-volume LaBr detectors (or a combination of both), and a dedicated table on the other, supporting a maximum of three (3) HPGe detectors at multiple angles. The setup can, therefore, accommodate a total of 9 detectors (with the possibility of including 4 small-volume LaBr detectors) for high-resolution, high-efficiency measurements. The beamline not only contributes to scientific knowledge but also emphasizes capacity development by focusing on training the next generation of researchers and fostering local and international collaborations.
The beam spot at the target position exhibits a 2 mm diameter for 5.5 MeV protons, 3 mm for 0.5 MeV protons, and up to 6 mm at the beam dump with quadrupole magnets turned off. An adjustable collimator, approximately 3-4 mm wide, allows for additional fine-tuning of the beam profile. Applications of the beamline range from measuring photon strength functions to exploring nuclear structures through gamma-gamma coincident studies. Successful proof-of-principle experiments, such as the study of 50Cr(p,γ)51Mn, showcase the capabilities of the beamline (Netshiya et al., J. Phys. Conf. Ser. 2586, 012111, 2023). In 2023, two experiments were successfully conducted. These experiments were titled “Testing the Brink-Axel Hypothesis using the 60Ni(p,γ) reaction” and “Testing conventional explanations of the X17” – led by a team of international researchers. The beamline not only contributes to scientific knowledge but also emphasizes capacity development by focusing on training the next generation of researchers and fostering local and international collaborations.
