This award supports a novel approach of making targeted measurements of the excited states or resonances of heavy neutron-rich nuclei to better understand the properties and behavior of neutron stars. This is because the pressure that pushes neutrons across the nucleus to form a thick neutron skin is the same pressure which supports a neutron star collapsing against the pull of gravity. Furthermore, at boundaries between the liquid core and solid crust of a neutron star, quantities such as the transition density and the pressure depend on the properties of the neutron rich matter. The collaborative environment supported by this award will enable recruitment and retention of African American students to STEM education by providing opportunities in mentored research experiences. The skills acquired during the training will prepare these students for advanced degrees and experience appropriate for careers to mitigate the scarcity of underrepresented minorities in national laboratory STEM professions and will contribute positively to the production of an overall diverse and competitive scientific workforce.
Recent theoretical studies show that resonance parameters can be used to establish the necessary constraints on symmetry-energy terms in the Equation of State (EoS). One of the big challenges is relating properties of the EoS to nuclear observables. Promising nuclear observables include the measurement of neutron-skin thickness and properties of nuclear excitations arising from collective motion of protons and neutrons, for example, the Isovector Giant Quadrupole Resonance (IVGQR). The IVGQR is a collective mode of the nucleus characterized by the out-of-phase oscillation of protons against neutrons. The restoring force is due to the symmetry energy term which appears in the nuclear EoS. Therefore, the systematic determination of the IVGQR parameters supported by this award will provide important constraints on the symmetry energy term in the EoS. The supported activities will produce polarization asymmetry data with uncertainties of 1% or better for the Sn-112 and Sn-114 isotopes. These data will allow extraction of the mass dependencies of the IVGQR energy, the resonance width, and the depletion of the energy-weighted sum rule with uncertainties considerably lower than any previous measurement. These resonance parameters will improve theoretical models with further constraints on the symmetry energy in the equation of state for neutron rich matter.
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.
