Collaborative Research: RUI: Study of Exotic Nuclei and Neutron Detector Response

Indiana Wesleyan University, Marion IN

Investigators

Abstract

The main goal of this experimental program is to advance understanding of the nature of exotic atomic nuclei, with undergraduate student participation as an integral component. Experiments will be conducted at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU) using the Modular Neutron Array (MoNA) and the Large-area multi-Institutional Scintillator Array (LISA), both constructed and tested by undergraduate students from several institutions in the MoNA collaboration. The PIs of this award and their team of undergraduate students will investigate the structure of light neutron-rich nuclei near the limits of stability, which will provide data to test current theoretical models of nuclear structure. As the nuclear mass-to-charge ratio for isotopes of an element increases, the isotopes become weakly-bound or unbound, and they exhibit significantly different structure compared with their stable counterparts. These unstable nuclei are produced by collisions of an accelerated nuclear beam with a stable target, and accurate computer simulations of neutron scattering in the MoNA-LISA plastic scintillator detectors are critical for extracting physics results from the breakup of these short-lived nuclei. Analysis of recent neutron-scattering experiments conducted at Los Alamos National Laboratory will improve accuracy of these simulations in preparation for higher energy experiments soon to be conducted at the Facility for Rare Isotope Beams (FRIB) at MSU. Broader impacts of the proposed work include formative research opportunities for undergraduate students and investing in the MoNA Collaboration in terms of equipment development and leadership. Research supported by this award will consist of conducting two new experiments, analyzing recent and future data, and contributing to the development of the next generation fast neutron detector for use with the High-Rigidity Spectrometer at FRIB. Two final MoNA experiments at the NSCL will be performed in 2020 to study neutron-unbound states in neutron-rich nuclei. The nuclei of interest are 13Be and 28F. These experiments will resolve the longstanding issue of the level structure of 13Be, which is in the N=8 region of the nuclear chart known for structural changes, and measurements of unbound 28F states combined with previously determined two-body matrix elements from 28F will help place limits on the one-neutron separation energy of 28O. To prepare for experiments at the upcoming FRIB facility, an experiment was performed at the Los Alamos Neutron Science Center (LANSCE) in November 2019 to measure neutron scattering and secondary neutron production during the interaction of fast neutrons with plastic scintillator detectors. This work will add to the recent neutron scattering work from the PIs which exposed some failures of current GEANT4-based Monte Carlo simulation packages. The goal is to improve the modeling of neutron interactions with these detectors, which will be crucial for improving detector resolution and filtering of data for FRIB experiments. The work also serves a broader community since plastic scintillators are widely used for neutron detection in nuclear physics and related applications. 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.