MCNP Characterization of 239 1 Pu with PGAA for Minimum Detection Limits

As safeguards verification becomes a more pressing concern, with the increase in global special nuclear material production, enhanced nondestructive methods of detection are necessary. Prompt Gamma Activation Analysis (PGAA) is an effective process to generate, detect and measure characteristic gamma rays at high energies. These gamma rays are unlikely to be attenuated through glove boxes and therefore radionuclides would not need to be removed from the process line for quantification. While intense prompt gamma rays can be readily detected for PGAA using a high purity germanium detector, low intensity emissions may be lost in high background radiation due to the Compton continuum in the collected spectrum. When combined with Compton suppression to reduce the continuum, low intensity prompt gamma rays can be more easily identified. PGAA has only recently been applied for 239 Pu characterization experimentally at the University of Texas at Austin, but has not as yet been modelled in MCNP. This lack of characterization extends to the MCNP databases, as there are no tabulated prompt gamma rays for 239 Pu that can be referenced when running simulations. For verification purposes, an MCNP model of the Compton suppression system at the Nuclear Engineering Teaching Lab was created. The experimental system was a combined Compton suppression and PGAA setup. Therefore, the MCNP model was first created to model the decay gammas of 239 Pu with Compton suppression. Once this simulation matched the experimental results, the previously identified PGAA gammas were input instead of the 239 Pu decay gamma rays. With these results, it was possible to determine the minimum time required to detect the characteristic PGAA gamma rays for a 1.81E6 Bq 0.789 mg 239 Pu foil electrodeposited on nickel. The data produced from this simulation could be utilized to compare to experimental glovebox verifications to determine 239 32 Pu quantities in nuclear facilities. PGAA can also be used to detect very low levels of 239 Pu for on-site verification to determine whether the radionuclide is being produced.