MCNPX-PoliMi Simulation of Radioxenon Detection for Treaty Verification

Radioxenon monitoring is one component of the verification regime for the Comprehensive Nuclear-Test-Ban Treaty Organization. A model in MCNPX-PoliMi has been developed to simulate radioxenon decay and detector response to analyze alternative detector assemblies. The detection of radioxenon is typically measured in coincidence mode, where the xenon concentrated gas sample is contained in a plastic scintillator that is the electron detector. The plastic scintillator is placed inside of a well NaI(Tl) detector that is the photon detector. A new MCNPX-PoliMi model was created to ensure proper source production of electron-photon coincidence particles from the decay of radioxenon. MCNPX-PoliMi was used instead of other simulations programs because of its speed and output file structure, which is compact and allows for a variety of analyses. Validation of the model is presented through comparisons of experimental and simulated data from the coincidence setup using plastic and NaI(Tl) detectors. The sources simulated were Cs-137, Xe-131m, Xe-133, Xe-133m and Xe-135.