Characterization of the Double Scatter Spectrum in Multiplexed Compton Scatter Tomography

摘要

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.