Nuclear Resonance Fluorescence Simulation Techniques Using MCNP

Nuclear resonance fluorescence (NRF) is of particular interest to the detection of special nuclear material where isotopic characterization is paramount. NRF allows for specific isotope identification by exploiting the nuclear structure of atoms, and has the potential to be a powerful active interrogation technique. This paper will focus on the development of two NRF simulation methods. Both methods will use MCNPX and variance reduction methods to reproduce the results of an experiment performed by Bertozzi et al [1]. The measurement was simulated with both methods and the number of counts in the detector from each nuclear resonance is compared to the measurement data. The first technique was developed without including the NRF cross sections for 235U in the MCNPX photonuclear libraries. The NRF reaction rate was calculated analytically based on cross section measurements from reference [1]. The second technique involves an update to the ENDF/B-VII NRF photonuclear libraries, which now include the NRF cross sections for 235U. Both simulation techniques produce relatively consistent results, given the uncertainty in the measured cross sections. However, the simulation results over predict the integrals of the photo peaks from the measurement data.