Recent material advancements in plastic scintillators enable marked increases in material light yield, detection efficiency, pulse-shape discrimination, and array production rates. These advances may resolve significant capability gaps for lowcost, portable, and durable dual-particle imaging (DPI) systems for nuclear safety, security and safeguard purposes. Two such materials, both 21% bismuth-loaded plastics utilizing iridium complex fluorophores (Ir-Bi-Plastic) were experimentally evaluated for DPI purposes as a small, pixelated radiographic array and compared to similar arrays made from EJ-200 and EJ-256 (5 wt% Pb). Experimentation involved separate exposures to 370 kVp x-rays and 14.1 MeV neutrons when paired with a digital radiographic panel, and array performance was evaluated using ASTM methods for dSNRn determination. Additionally, the development of fast-curing plastic scintillator (FCPS) formulations is highly attractive because it facilitates the 3D-printing of complete pixelated plastic scintillator arrays for radiation detection and localization. Future advancements in this area will significantly reduce the time and costs associated with current array manufacturing techniques. Some early investigations of FCPS samples sensitized with 5 wt% Bi is discussed herein, with their gamma detection efficiencies and associated light yields compared to an equivalent sample of EJ-256. These early unoptimized samples provided similar but not superior performance to EJ-256, and this is an ongoing area of research at the Air Force Institute of Technology.
The multi-institution Single-Volume Scatter Camera (SVSC) collaboration led by Sandia National Laboratories (SNL) is developing a compact, high-efficiency double-scatter neutron imaging system. Kinematic emission imaging of fission-energy neutrons can be used to detect, locate, and spatially characterize special nuclear material. Neutron-scatter cameras, analogous to Compton imagers for gamma ray detection, have a wide field of view, good event-by-event angular resolution, and spectral sensitivity. Existing systems, however, suffer from large size and/or poor efficiency. We are developing high-efficiency scatter cameras with small form factors by detecting both neutron scatters in a compact active volume. This effort requires development and characterization of individual system components, namely fast organic scintillators, photodetectors, electronics, and reconstruction algorithms. In this presentation, we will focus on characterization measurements of several SVSC candidate scintillators. The SVSC collaboration is investigating two system concepts: the monolithic design in which isotropically emitted photons are detected on the sides of the volume, and the optically segmented design in which scintillation light is channeled along scintillator bars to segmented photodetector readout. For each of these approaches, we will describe the construction and performance of prototype systems. We will conclude by summarizing lessons learned, comparing and contrasting the two system designs, and outlining plans for the next iteration of prototype design and construction.
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