Cluster Production in MoNA Through Charge Exchange*

The Modular Neutron Array (MoNA) is a neutron detector composed of 144 plastic scintillator bars with 10 x 10 x 200 cm dimensions. One neutron scattering possibility in MoNA is the np charge exchange interaction where an incoming neutron swaps identities with a H proton, producing a high energy proton. These protons create additional light in adjacent bars, producing hit-clusters in the data set. A filter is currently in use that reduces the single-neutron scattering background, based on identifying and reducing these proton-induced clusters, and then checking the causal relationship of all remaining hits in an event. When a gap between detectors is introduced into the array, protons traveling across the gap can be identified by a distinct band in a plot of energy deposited vs. velocity. This event can then be used as a multi-neutron filter by vetoing events with scattering angles at 90 degrees relative to the proton's trajectory (where the scattered neutron would be detected) and then looking for additional hits across the gap which are likely separate neutrons. In our 2019 experiment investigating neutron scattering at Los Alamos National Laboratory, we clearly identified these charge exchange protons, and are using those observations to help design the future MoNA array.