Blair, Noah Jeffrey, authorBrandl, Alexander, advisorSudowe, Ralf, committee memberJeckel, Kimberly, committee member2024-05-272024-05-272024https://hdl.handle.net/10217/238393At ports of entry into the country, at high security events such as political or athletic gatherings of crowds, and at high risk locations, portal monitors are used to detect the presence of ionizing radiation and ensure radiological/nuclear materials do not fall out of regulatory control or are utilized with malicious intent. This work uses computer models to determine the probability of photon radiation being detected in polyvinyl toluene, a plastic scintillator material, for a range of source energies, truck positions relative to the detector, and cargo materials. These results are used to develop models for operators of portal monitors to predict the activity of a radioactive source given the measured count rate and integrated count measurements. A linear model of the detection efficiency produces an analytic expression of the measured count rate given the emission spectrum of a source which allows for calculation of net counts between two points on the truck's trajectory and the time derivative of the count rate. The time derivative of the count rate has a similar characteristic behavior along the truck's trajectory and has the potential to be an indicator of weak radiological sources. A MARS model allows for accurate prediction of the net count rate for truck positions and source energies not directly modeled. These models best predict detection efficiency for higher energy photons and are primarily useful for the prediction of detection of fission and activation products.born digitalmasters thesesengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.Monte Carloportal monitoringphotondetection efficiencyText