The trafficking of special-nuclear material (SNM) and radiological sources remains a serious threat to the security of the United States. To counter nuclear trafficking, the Department of Homeland Security (DHS) relies on a fleet of Radiation Portal Monitors (RPMs) that continuously scan inbound vehicles and cargo containers across all U.S. points of entry for radiation signatures. RPMs face an enormous technical challenge to identify nuclear and radiological threats quickly and accurately despite the high volume of inbound crossings, their aging technology, and inherent performance limitations. The current RPMs predominantly consist of large poly-vinyl-toluene (PVT) scintillator slabs. Apart from their low light yield, PVT can only provide gross gamma-ray counting due to their low density and low effective atomic number. Despite this limitation, PVT is used in RPMs because of their low cost and scalability allowing for the construction of large slabs. Inorganic scintillators are expensive and cannot be scaled up to RPM sizes. Therefore, an alternative technology is needed that is scalable, cost-effective, and can also provide spectroscopic information with higher light yield. How the Problem is Addressed: RMD in collaboration with Sandia National Laboratories (SNL) propose a metal-loaded Polymer Organic Glass Scintillator (POGS) for use in the next generation RPMs. Pure OGS would not be scalable to the large detection volume required by an RPM, due to concerns for cracking. For this reason, we propose OGS blended with a polymer such as polystyrene (PS). We will incorporate organotin compounds and explore sterically-encumbered lanthanide compounds to impart gamma-ray spectroscopic capabilities to POGS. Thus, the ultimate goal of the proposed work is production of metal-loaded (spectroscopic) POGS for RPMs, leveraging the knowledge present at RMD and SNL in areas of metal-loaded OGS and polymer-blend OGS. Plans for Phase I: In the Phase I project, we plan to optimize composition of a novel metal-loaded POGS by varying amount of OGS in polymer, as well as changing concentrations of metal loading in POGS. 2 x 2 samples will be fabricated at RMD and SNL and characterized for mechanical and scintillation properties. One of the key tasks in Phase-I will be GEANT4 simulations to estimate and compare the neutron and gamma-ray detection efficiencies of the metal-loaded POGS and compare it to standard RPM scintillators such as EJ200. Commercial and Scientific Potential: The potential applications for the proposed OGS include nuclear security and non-proliferation - RPMs, high energy and particle physics research, nuclear waste characterization, industrial non-destructive evaluation, space, and health physics.
