PROMPT GAMMA RESPONSE SIMULATIONS FOR NUCLEAR FORENSIC
APPLICATIONS

A simulation package has been developed to aid in the characterization and identification of unique nuclear material signatures throughout the nuclear fuel cycle. This work is focused on predicting a sample response to neutron activation analysis (NAA), which will be performed using the mechanical time-of-flight (TOF) system that has been designed for the Pennsylvania State Breazeale Reactor. This TOF system will use epithermal neutrons for NAA and allow for isotopic material analysis with significantly greater sensitivity than conventionally used NAA based on thermal neutrons. This project aims at predicting the prompt gamma response of samples interrogated with epithermal neutrons. A prompt gamma response can be correlated with a delayed gamma response resulting from an irradiation of a sample and will complement the non-destructive analysis capabilities afforded by epithermal NAA. Simulations of prompt gamma responses are performed with DICEBOX, an open-source Monte Carlo code, which simulates gamma cascades from a nucleus using statistical models of level density and photon strength functions. The purpose of the simulation package is to create an easy-to-use interface for a user to input material information of a given sample and assemble a DICEBOX input file. The package extracts necessary information such as internal conversion coefficients from external databases, selects the appropriate level density and photon strength function models, and runs the file to simulate the prompt gamma response. The resulting gamma signatures may be used to make inferences about samples’ material processing history or provenance for nuclear forensics characterization. Detection of rare-Earth elements and analysis of radiochronometric signatures are of particular interest and the use of epithermal neutrons in NAA will utilize elevated isotopically sensitive cross sections at resonance energies and allow for detection of trace signatures.