Multiparticle Imaging of Weapons-Grade Plutonium
Metal Using an Organic Glass-Based System

Material control and accountability is a vital aspect of the modern nuclear safeguards regime. Special nuclear materials are among the most important substances to track and monitor, leading to various procedures in use today that are specifically meant to localize the materials in a timely manner. Generally, particle imaging systems, like gamma ray Compton cameras or neutron scatter cameras, can assist in these efforts by providing users with angular information that can be used to localize sources. Advanced imaging systems are engineered to simultaneously be sensitive to both gamma rays and neutrons, a beneficial function for scenarios where either particle type’s signature is small or nonexistent. This is important due to several materials of interest emitting both fast neutrons and gamma rays, with shielding often being present along with the source. The University of Michigan has recently redesigned our dual-particle imager to feature organic glass scintillators, which were created and obtained from collaborators at Sandia National Laboratories. The composition of this relatively new detector material was designed to enable particle discrimination capabilities and has already shown promise in early imaging experiments. This work will present the first gamma ray and fast neutron images created with the system when measuring kg quantities of plutonium metal. Gamma spectrometry information resulting from single counts in the CeBr3 and double scatter coincident events within the imager will also be reported. These results will demonstrate the capabilities of the new system in conditions more closely resembling monitoring or verification scenarios and will indicate how viable organic glass is for this specific application use.