Multi-mode Polymer Organic Glass Scintillators for Next Generation Radiation Portal Monitors

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 Radiation Portal Monitor’s (RPMs) that scan vehicles and cargo containers across U.S. points of entry for radiation signatures. The current RPMs predominantly consist of polyvinyltoluene (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 its low cost and scalability. 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. RMD in collaboration with Sandia National Laboratories (SNL) propose tin-loaded Polymer Organic Glass Scintillators (POGS) for use in next generation RPMs. Pure OGS would not be scalable to large detection volumes, due to concerns for cracking. For this reason, we propose OGS blended with a polymer such as polystyrene (PS). We will incorporate organotin compounds to impart gamma-ray spectroscopic capabilities to POGS. Thus, the ultimate goal of the proposed work is to fabricate tin-loaded POGS for RPMs. In the Phase I project, we optimized the composition of small (2” x 2”) tin-loaded POGS by varying the amount of OGS in the polymer, as well as changing the organotin concentration. Samples were characterized for their mechanical and scintillation properties. GEANT4 simulations were performed to estimate and compare the neutron and gamma-ray detection efficiencies of the tinloaded POGS and compare these to standard RPM scintillators such as EJ200. The primary goal of the Phase-II is to scale up the tin-loaded POGS to 6”x6”x2” and 8”x8”x3” slab sizes. Additionally, we will investigate fusing of two smaller slabs into one larger slab. We will continue GEANT4 simulations to investigate the detector response of tin-loaded POGS in a multisource, mixed field. Finally, we investigate light transport and readout schemes to produce a detector. This work will consider the trade-off between using one or multiple PMT’s at different locations along the scintillator. An important task of the Phase-II will be field testing of the tin-loaded POGS at SNL using modified GADRAS algorithms for RPMs. The results will be compared to PVT-based RPM detectors. We will conduct accredited testing of the tin-loaded POGS at the Technical Test and Analysis Center (TTAC) at Oak Ridge National Laboratory (ORNL). This would be an important step towards commercialization. The potential applications for the proposed OGS include nuclear security and non-proliferation - RPMs, high energy and particle physics research, nuclear waste characterization, industrial nondestructive evaluation, space, and health physics.