The proposed activities are designed to have as large as possible an impact on the education and training of graduate and undergraduate students and postdoctoral associates. The project will also serve to enhance the diversity of the nuclear science workforce by including early career scientists who are women or come from other under-represented backgrounds. The participation of these early career scholars in the forefront research would prepare them for careers in higher education and basic and applied research, in national laboratories and industry.
Intellectual Merit One of the frontier areas of nuclear physics is the study of the structure of atomic nuclei far from the valley of stability. In atomic nuclei the single-particle orbitals are expected to change as a function of neutron and proton number, and in addition are very sensitive to the presence of deformation. Single-particle characteristics can be probed in single-particle transfer reactions. Light-ion transfer reactions have been studied with beams of rare isotopes near the Coulomb barrier at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. Studies concentrated on neutron-rich nuclei near the N=82 neutron shell closure and light nuclei important to understand nucleosynthesis in stars. The purity of the single-neutron excitations in 133Sn, with spectroscopic factors consistent with unity, highlights 132Sn (N=82, Z=50) as one of the best examples of a doubly-magic nucleus, with closed shells of both neutrons and protons. Similar structure was observed in 131Sn, which impacts the rapid neutron capture process of nucleosynthesis in stars. Elastic deuteron scattering with 7Be rare isotope beams was used to search for a resonance in the 7Be+d system; no strong resonance was observed. Therefore, a solution outside of nuclear physics is needed to resolve the discrepancy between calculations and observations for 7Li abundances. Another challenge in nuclear structure physics is to understand the microscopic components of the nuclear wave function, as a function of excitation energy and angular momentum and in nuclei away from stability. The focus of the second component of this project was to address, via measurements of the magnetic moments or g factors of excited states, the microscopic components of the nuclear wave function of these states. The technique of Coulomb excitation in inverse kinematics is well established and has been tested on radioactive beams. The method was used at HRIBF to measure the sign and magnitude of the g factor of the first excited state of the unstable 126Sn. In addition, the precision of the experiments carried out by this technique allows measurements of higher excited states in stable nuclei and permits accurate measurements of states near closed shell nuclei. Studies were completed in even-mass isotopes of Zn, Sr, Zr, Pd, and Ru, probing details of the interplay between collective and single-particle structures. Broader Impacts The project’s activities had considerable impact on the education and training of graduate and undergraduate students, as well as postdoctoral associates. The project served to enhance the diversity of the nuclear science workforce by including early career scientists who are women or come from other under-represented backgrounds. The participation of these early career scholars in the forefront research has prepared them for careers in higher education and basic and applied research, in national laboratories and industry. The nuclear physics results are of importance to astronomy, in understanding the abundance of elements observed in the cosmos; to condensed matter physics, in understanding the microscopic components of the transient hyperfine field; and for national security, in understanding properties of and reactions on fission fragments.
