Year
2013
Abstract
Nuclear Resonance Fluorescence (NRF) is a photon absorption interaction in which the absorbing nuclei de-excite post-absorption by emission of photons at isotope-specific energies. Some potential exists for exploitation of this interaction in the realm of nuclear safeguards. Applications might include Non-Destructive Assay (NDA) for isotopic inventory during inspection, treaty verification, or detection of Special Nuclear Material (SNM) at border crossings. NRF has already been applied with good accuracy to isotope detection as demonstrated by a cargo scanning system designed by Passport Systems, Inc. The logical next step would be to utilize NRF in detection of isotope concentrations within the interrogated volume. Complicating NRF experiments is the fact that resonances from NRF, while strong, are very narrow. State of the art quasi-monoenergetic photon beams based on Compton backscattering of light have been achieved using particle accelerators. Such beams offer the ideal light source for NRF measurements given their high flux and narrow energy width. However, even these narrow-width beams are quite broad compared to the widths of NRF resonances. Consequently, clean detection of NRF transitions has been quite difficult and thus questions can be raised as to the accuracy of measured cross sections in the current data library. Additionally, known NRF transitions occur in the 2-3 MeV energy range for SNM materials U and Pu. This range is the same as that of other elastic photon scattering processes, namely Delbrück scattering, for these materials, thus further complicating clean detection. In this work, simple photon scattering experiments have been simulated in the Monte Carlo radiation transport code MCNPX in order to assess the detection of NRF signatures of U and Pu above the background using the current cross section data libraries.