Nuclear Structure Studies of Medium-Mass Nuclei: from Stability to Afar

Mississippi State University, Mississippi State MS

Investigators

Abstract

This award focuses on obtaining a better understanding of the structure of the atomic nucleus and working towards a predictive model of the atomic nucleus as a function of proton number, neutron number, and energy. The objective of the research program is to determine properties of medium-mass nuclei (mass numbers from ~30 to ~80) and ranging from stable nuclear systems to exotic, neutron-rich nuclear systems. Each of the nuclei to be studied has predictions of exhibiting multiple shapes, long-lived nuclear states called isomers, and/or they are relevant to other rare nuclear phenomena such as neutrinoless double-beta decay or double-gamma decay. Through experimentally quantifying nuclear properties directly related to these phenomena, the research addresses the question, “How do the rich patterns observed in the structure and reactions of nuclei emerge from the interactions between neutrons and protons?”, as outlined by the broader nuclear physics community in “A New Era of Discovery: The 2023 Long Range Plan for Nuclear Science.” The PI and graduate students in the group will perform experiments at US based facilities such as the Facility for Rare Isotope Beams, the High Intensity Gamma-Ray Source, and John D. Fox Laboratory at Florida State University, and build on the PI’s experience with experimental nuclear physics techniques and detection systems employed at each laboratory. The objective of this project is to determine properties of excited nuclear states and their decays, such as excitation energies, lifetimes, branching ratios, and transition strengths, in medium mass nuclei ranging from stability to extremely exotic. This information is targeted for nuclei that are predicted to exhibit multiple shapes, i.e., so-called shape coexistence, and/or show effects of shell evolution caused by the emergence of effects from intruder orbitals, altered shell gaps, and cross-shell excitations. Comparisons of results with modern shell-model calculations will aid in the determination of the underlying nuclear configurations and serve as a stringent test of theoretical predictions. By studying 72Ge, 72Ga, and a host of neutron-rich nuclei approaching N = 28 and N = 50 using state of the art nuclear detection systems, a thorough approach is taken to characterizing this region of medium-mass nuclei where shape coexistence and intruder orbital effects are predicted to occur yet remain to be fully quantified. This research will also have an important impact on the education of young scientific researchers. 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.