Investigating Nuclear Matter Radii Extraction with the MoNA-LISA-Sweeper Setup at FRIB

Understanding how matter is distributed inside nuclei is essential for improving theoretical models describing the nuclear structure and reactions. In this project, we investigate the potential to extract nuclear matter radii from angular distributions using the MoNA-LISA-Sweeper setup at the Facility for Rare Isotope Beams (FRIB) of Michigan State University.



An 88.8 MeV/nucleon secondary beam of 33Mg impinged on a segmented target composed of alternating silicon detectors and beryllium targets. Upon interaction, unbound neutron rich nuclei are formed that subsequently decay by emitting charged fragments and one or more neutrons. Unreacted 33Mg, along with other beam contaminants, were deflected by the Sweeper magnet onto a suite of detectors for tracking and particle identification. Neutrons, unaffected by the magnetic field, continued forward through the magnet gap and were detected by the MoNA-LISA array. An optical matrix modeling the Sweeper magnet allows to reconstruct the kinematics of each isotope at the reaction target and subsequently the angular distribution of their nuclear form factors. As a first step toward extracting matter radii, we modeled the collisions as elastic interactions between spherical nuclei. By applying an inverse Fourier transform to the form factor, we estimated the spatial matter distribution. The results were then compared to simulated angular distributions generated using the São Paulo Potential version 2 (SPP2), which models the nucleus-nucleus interaction through a double-folding potential.

This project also connects with the BECOLA collaboration at FRIB, which studies charge radii using laser spectroscopy. By comparing matter and charge radii of isotopes of common interest, we aim to gain new insight into neutron distributions in both stable and unstable nuclei. Preliminary results from this study will be presented and discussed.