Effects of rain and soil moisture on background neutron measurements with the SuperMISTI neutron array

Background neutron measurements were recorded for approximately two months at Camp Blanding, FL, with a large array of moderated gas proportional detectors and EJ-309 liquid scintillator detectors. The variations in the local neutron background rate were on the order of 10% and were observed to be primarily due to the changing level of moisture in the local soil due to precipitation and evaporation. Simple models were constructed based only on very basic climatological information and were able to reproduce the major variations in our measured neutron counts with time. These simple models compare favorably to the more-complex modified Penman equation developed for the California Irrigation Management Information System. An accurate model to describe local neutron background variations based on easily measured climatological data would be invaluable to provide corrections for stationary neutron monitors.