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 will be studied with beam energies near the Coulomb barrier and about 40-MeV per nucleon. Studies will concentrate on neutron-rich nuclei near the N=50 and N=82 neutron shell closures and light nuclei important to understand nucleosynthesis in stars. These studies will be carried out with accelerated beams of rare isotopes at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University, the Argonne Tandem Linac Accelerator System (ATLAS) at Argonne National Laboratory and the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. One focus is to extract spectroscopic strengths with reduced dependence on theoretical model parameters.
Another challenge in nuclear structure physics is to understand the balance between a microscopic description of the nuclear wave function and a model based on collective motions of the nucleons within the nucleus. This balance changes as a function of excitation energy and angular momentum and may be quite different in nuclei away from the valley of stability from the observed behavior of nuclei near stability. The focus of the second component of this proposal addresses, via measurements of the magnetic moments of excited states, the interplay of single-particle configurations with an underlying spherical or deformed core. The technique of Coulomb excitation in inverse kinematics is well established and has been tested on radioactive beams (RIBs). However, recent high statistics experiments carried out with heavier nuclei than in the past, and with higher energy beams, have uncovered several issues that need to be addressed before the methods are tried at the new RIB facilities. Semi-magic Tin-126 will be studied at HRIBF. A new program of research to be established at the ATLAS facility will focus initially on the low-lying states of Samarium-150 and Gadolinium-152 and on the efficacy of alpha transfer reactions.
The structure of the proposed activities is designed to have as large an impact as possible on the education and training of graduate and undergraduate students, as well as 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.
The anticipated nuclear physics results are also of importance in astronomy, to understand the abundance of elements observed in the cosmos; in condensed matter physics, to understand the microscopic components of the transient hyperfine field; and for nuclear energy and national security, to understand properties of and reactions on fission fragments.