Year
2007
Abstract
Conventional neutron-multiplicity counters (NMCs) employ 3He tubes embedded in polyethylene for the nondestructive assay (NDA) of plutonium-bearing items. This approach is centered on the detection of neutrons simultaneously emitted from spontaneous fission. The presence of lightelement impurities leads to a large single-neutron rate from (a,n) reactions that can give rise to an increased number of accidental coincidences because of the relatively slow response time of 3He tubes. To address the difficulties of assaying such impure items, we are developing a liquidscintillator multiplicity counter (LSMC). Liquid scintillator (LS) has a response time that is faster than 3He by several orders of magnitude, thereby allowing for data acquisition to occur with a much more narrow coincidence gate that will virtually eliminate accidental coincidences. In addition to the assay of impure plutonium items, LS-based detectors are suited to the active interrogation of highly enriched uranium (HEU). Recent advances in the development of our GEANT4 Monte Carlo (MC) model have been made, and comparisons between gamma-ray data and MC results will be presented. Additionally, initial pulse-shape discrimination results illustrating neutron-gamma separation in 252Cf data will be shown.