Efficient and Accurate Computation of Non-Negative Anisotropic Group Scattering Cross Sections for Discrete Ordinates and Monte Carlo Radiation Transport

A new method for approximating anisotropic, multi-group scatter cross sections for use in discretized and Monte Carlo multi-group neutron transport is presented. The new method eliminates unphysical artifacts such as negative group scatter cross sections and falsely positive cross sections. Additionally, when combined with the discrete elements angular quadrature method, the new cross sections eliminate the lack of angular support in the discrete ordinates quadrature method. The new method generates piecewise-average group-to-group scatter cross sections. The accuracy and efficiency for calculating the discrete elements cross sections has improved by many orders of magnitude compared to DelGrande and Mathews previous implementation. The new cross sections have extended the discrete elements method to all neutron-producing representations in the Evaluated Nuclear Data Files. The new cross section method has been validated and tested with the cross section generation code, NJOY. Results of transport calculations using discrete elements, discrete ordinates, and Monte Carlo methods for two, one-dimensional slab geometry problems are compared

Characterization of the Double Scatter Spectrum in Multiplexed Compton Scatter Tomography

The Multiplexed Compton Scatter Tomograph (MCST) uses single back-scattered photons to image electron density in aluminum. A source of error in this imaging technique is the presence of multiple scatters. This thesis studies the double scatter spectrum as an approximation of the multiple scatter spectrum. A deterministic code called Monte Carlo Double Scatter (MOCADS) was developed to investigate the double scatter spectrum. The code includes calculations of the Rayleigh scatter, Compton scatter, Doppler broadening effects of the spectrum, and polarization effects following the Compton scatter. The Doppler broadening portion of the code was validated by a deterministic code called Scatgram. The mechanics of double scatter were validated by a Monte Carlo transport code. And all included features in the code were validated by a laboratory experiment. The MOCADS code was used to simulate an experiment where a void was present in the sample and compared to a solid sample. The simulation showed that the shape of the double scatter spectrum did not depend of the presence of the void. Another simulation examined the effects of polarization and Doppler broadening. These two effects were shown to significantly influence the shape of the spectrum. Finally, a laboratory experiment was examined where the single scatter estimate was improved by the removal of the double scatter spectrum from the total spectrum