Development and validation of the discrete prompt and delayed gamma-ray source term and detector response calculation technique

A newly developed photon assay modeling technique, capable of calculating complex discrete gamma-ray source terms and detector responses is introduced in this paper. This method integrates modified versions of existing Monte Carlo-based transport (MCNPX) and analytical decay/depletion (CINDER) codes with a Discrete Gamma-ray Source Definition (DGSDEF) code specifically developed for this application. The resulting hybrid simulation scheme provides robust calculations for time- and spatially-dependent passive and actively induced gamma-ray signatures. The code package uses latest data libraries containing multigroup neutron cross-sections, fission yield sets, decay constants and branching ratios obtained from a variety of sources, including international data libraries and evaluation codes. The performance of this modeling technique was benchmarked and validated in an extensive experimental campaign aimed at reproducing empirically acquired passive and delayed gamma-ray spectra. Delayed gamma-ray activation tests involved accelerator-driven neutron sources and samples of fissile and fertile materials and their combinations with a variety of interrogation setups. The code development was performed as a part of the UC Berkeley, Los Alamos National Laboratory, and Idaho Accelerator Center collaborative research and design effort focused on the advanced instruments and methods for non-destructive quantification of plutonium content in spent fuel assemblies. Based on good benchmark performance, the modeling technique is currently utilized for the research and design of delayed gamma, passive prompt gamma, and xray fluorescence assay instruments. (author)