Rare Isotope Reaction Studies for Nuclear Structure and Astrophysics

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This award will support the principal investigator and her group of early career scientists to advance our understanding of the structure of atomic nuclei as well as their reactions and synthesis in exploding stars. Nearly all elements heavier than iron are made in stars and stellar explosions through processes that involve the capture of neutrons. To learn more about those processes the PI will lead experiments using beams of rare isotopes, concentrating on neutron-rich nuclei. This research program will use state-of-the-art instruments and accelerator facilities in the U.S. The project will also serve to enhance the diversity of the nuclear science workforce. The participation of these early career scientists in forefront research and the development of scientific instruments will prepare them for careers in higher education and fundamental and applied research at national laboratories and in industry. Light-ion transfer reactions will be studied with beams of rare isotopes with energies near the Coulomb barrier and about 45-MeV per nucleon. Studies will concentrate on neutron-rich nuclei near the N=50 neutron shell closure and light nuclei important for understanding the synthesis of nuclei in stars and their explosions. These studies will be carried out with accelerated beams of rare isotopes at Michigan State University, first with the ReAccelerated (ReA) beam capability and starting in 2022 with the Facility for Rare Isotopes Beams (FRIB). Additional experiments will be performed at the ATLAS accelerator facility at Argonne National Laboratory. At FRIB the focus is to constrain the shape of the potential that binds neutrons in a neutron-rich nucleus and, therefore, extract spectroscopic strengths and direct neutron capture rates with reduced dependence on theoretical model parameters. The neutron-transfer reaction with deuterated targets has been validated as a surrogate for neutron capture when reaction products are measured in coincidence with gamma rays. Therefore, both charged particles and coincident gamma radiation will be measured with Gamma-array ORRUBA: Dual Detectors for Experimental Structure Studies (GODDESS), where the Oak Ridge Rutgers University Barrel Array (ORRUBA) is coupled to large, highly segmented arrays of high-purity germanium gamma-ray detectors. The results will be compared with theoretical predictions of nuclear structure and reactions away from stability and disseminated as input into calculations of nucleosynthesis in stars and their explosions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.