Improvements of Background Neutron Estimation for Mobile Radiological Search Systems by the Exclusion of Fission Events

Abstract

Accurately quantifying the neutron background is a crucial task for interpreting the presence of illicit nuclear material when responding to potential terrorist threats. This research focused on improving the Mobile Radiological Search System’s (MRSS) neutron background response by exploiting detectable muons in NaI detectors to estimate the neutron background count rate. The method devised by Wagner et al. utilized an assumption that all counts above 4 MeV were muons. During the experimental stage of this previous project, this assumption led to an increase in the estimated mean neutron count rate in the presence of a fission source, rendering the method incapable of differentiating background in those events. The research presented here determined the cause of increased muon count rate and indicated that an energy threshold of 11.5 MeV eliminates the inability to differentiate background from man-made sources during such anomalies.