Date(s) - 06/20/2013
The shortage of 3He has created a need to identify alternative neutron detection options for a variety of nuclear nonproliferation applications. One application which is currently under study for a 3He replacement technology is that of mass accountancy, which utilizes coincidence and multiplicity counters to verify special nuclear material declarations. A Monte Carlo N-Particle eXtended (MCNPX) study was conducted to evaluate candidate alternatives which could have comparable neutron detection efficiencies and die away times (average lifetime of a neutron in the coincidence or multiplicity counter) to He-3 proportional counters in a multiplicity counter configuration. Of the technologies evaluated, the properties determined for 6LiF/ZnS scintillating sheets were the most promising. A small-scale test unit using these sheets was constructed and experimentally characterized. These data were also used to validate the MCNPX model predictions, and adjust for model-data inconsistencies. The measurements demonstrated that the test unit has a higher gamma ray sensitivity than 3He filled proportional counters. The effect of gamma ray detections on the assay results was considered by including the gamma ray moments in the multiplicity equations.