Fast Neutron Spectroscopy at FRIB: Neutron Scattering Dynamics and Multi-Neutron Detection

Abstract:  Detection of fast neutrons using plastic scintillator provides a valuable tool for the study of neutron- unbound nuclear states at or beyond the dripline. The upcoming FRIB facility will enable experiments to explore neutron-unbound states much farther up the neutron dripline, and to explore multi-neutron decay systems in higher mass regions. Two current goals for the MoNA Collaboration are 1) to design and ultimately construct the next generation neutron detector array for use in the upcoming FRIB HRS hall, and 2) to improve our ability to detect and filter multi-neutron decay events with high efficiency. To this end we conducted an experiment at the LANSCE facility at Los Alamos National Lab using 16 MoNA detector bars to observe in better detail how neutrons scatter in the scintillator volume. Results revealed some disparities in Monte Carlo predictions, especially at higher FRIB energies. Along with recent measurements of detector waveform non-linearities, these observations provide helpful input into the design of the next generation HRS array. We have also developed, based in part on these observations, a neutron hit-pattern algorithm to optimize our multi-neutron detection capability. Results from these studies, and a few ideas for next generation designs, will be presented.