Investigating Correlated Neutrons from Pulsed Photonuclear Interrogation for Treaty Verification Applications

The treaty verification field is of renewed importance as continued nuclear weapons disarmament is prioritized nationally in partnership with other nuclear weapons states. This interest has led to research and development on technologies that could support future U.S. verification missions. A technology employing pulses of high-energy photons from an electron linear accelerator is one technique under consideration. High-energy photons are advantageous as an interrogation source because they penetrate thick shielding and can generate neutrons inside a measurement object. The neutrons would then multiply when presented with an object containing fissile material and allow for detection in a time domain immediately after the pulse. The purpose of this work was to develop an understanding of neutron behavior following a high-energy photon pulse and then develop a tool set to analyze data from this region to determine if a measurement object contains multiplying material, the mass of that material if present, and the moderation in the measurement object. Results indicate the tool sets developed were able to determine multiplication was present accurately in 3 out of 4 realistic verification objects. Additionally the state of the moderation in each object was able to be determined, and the mass could potentially be determined by calibrating to representative samples.