X-Ray and Fast Neutron Radiographic Performance of an Ir-Bi-Plastic Array

Organic plastic scintillators offer the potential for exciting improvements in particle interaction efficiency, light yield (LY), and pulse shape discrimination (PSD). An area of particular application for select plastics exists in portable dual-particle imaging (DPI) systems supporting nuclear safety, security, and safeguards missions. One promising material, an Ir-Bi-Plastic, is experimentally evaluated within separate 370 kVp X-ray and 14.1 MeV neutron fields in the form of a pixelated array, which was fabricated by Lawrence Livermore National Laboratory (LLNL). Ir-Bi-Plastics pair high bismuth loadings with iridium-complex fluorophores to provide high intrinsic efficiencies for both photoelectric absorption and fast neutron detection, as well as improved LYs from the triplet-harvesting capabilities of the iridium-complex. These attributes make Ir-Bi-Plastics ideal candidates for DPI applications. Radiographic performance results for the Ir-Bi-Plastic array are compared against similar evaluations of smaller arrays made from EJ-200 and EJ-256, both industry standard materials. Measurements were recorded by pressure-coupling the three arrays to a commercial a-Si digital radiographic panel, and ASTM standard test methods and practices were utilized to calculate the modulation transfer function (MTF) and limits of spatial resolution for all three arrays. The results suggest the Ir-Bi-Plastic array, despite its larger pixel pitch, provides significantly improved performance over equivalent arrays made from either EJ-200 or EJ-256 for all X-ray and fast neutron environments practical for portable DPI.