Evaluation of novel bismuth-loaded plastic arrays for fast neutron radiography

Plastic scintillators utilizing iridium complex fluorophores offer substantial improvements in light yield, and their light yield is not significantly quenched in compositions with bismuth metalorganic loading, at a loading level of 21 wt% bismuth metal. This new bismuth plastic (Ir-Bi-Plastic) offers improved detection efficiency over commercial plastic scintillators. One application for Ir-Bi-Plastic is in low-cost, portable, and durable dual-particle imaging (DPI) systems supporting nuclear safety, security, and safeguards. However, new materials must undergo investigation using industry standards to quantify their capabilities. In this work, an Ir-Bi-Plastic was experimentally evaluated as a small, pixelated radiographic array in a fast neutron environment, with individual pixel dimensions of 2×2×19 mm. For comparison, identical evaluations were conducted for two similarly sized arrays made from EJ-200 and EJ-256. A separate Ir-Bi-Plastic array with 5×5×20 mm pixels was also evaluated. ASTM methods were leveraged to determine the modulation transfer function and spatial resolution for each array. Edge response measurements of a 2-in thick tungsten block were recorded by pressure coupling all four arrays to a commercial a-Si digital radiographic panel. Experimental results were then compared for all four arrays, and the results demonstrated that the Ir-Bi-Plastic outperforms similar arrays made from EJ-200 and EJ-256 (5 wt% Pb). These findings suggest that DPI systems utilizing Ir-Bi-Plastic hold promise for continued development over older, more traditional, alternatives.