(Dr. Nolan Hertel, advisor)
"An Illicit Nuclear Material Detection System Based on Photoneutron & Photofission Interactions"
An unquestionable need exists for robust systems to detect illicit nuclear materials at border crossings and seaports throughout the United States. These vulnerable locations provide the potential for terrorist organizations to smuggle nuclear materials that could be used in a radiological dispersal device (RDD) or even a nuclear (fissionable) device. Further motivated by the events of September 11, 2001, a study was conducted into the feasibility of using an electron-based, cargo imaging system to detect illicit nuclear materials. This system utilizes a linear accelerator to create bremsstrahlung photons from the acceleration of 5-15 MeV electrons incident on a tungsten/copper target. These high energy photons are used to image containers and trucks in order to determine their contents. Since transuranic elements will undergo photonuclear/photofission reactions when the incident photon energy exceeds an interaction threshold energy, a resultant neutron spectrum can be observed. Utilizing the Los Alamos National Laboratory Extended N-Particle Transport Code MCNPX version 2.5, several models were developed to simulate this system. These models replicate the imaging system as well as an ISO sealand container housing various types and quantities of cargo and transuranic materials. Using incident electron energies ranging from 5-15 MeV, the resulting neutron spectrum is evaluated to determine if minimum detectable limits are exceeded.