Comparison of Fast Neutron Imaging Using a Gamma-Sensitive Scintillator with an Iron Converter versus Polypropylene (PP)-ZnS Screens

We evaluated fast-neutron detection and imaging using gamma sensitive scintillators and neutron-to-gamma convertor materials to boost fast neutron detection efficiency for nuclear security applications. Two gamma-sensitive crystals, gadolinium aluminum gallium garnet (GAGG:Ce) and cadmium tungstate (CdWO₄), were coupled to iron converters and compared with zinc sulfide (ZnS) screens dispersed in polypropylene (PP) under reactor and deuterium-tritium (D-T) neutron-generator conditions. Reactor-based measurements showed that 10-millimeter iron converters provided optimal signal enhancement, increasing counts per pixel by 14.8% compared to that of bare scintillators. In one of the experiments using a 14.1 MeV D-T neutron generator, the uncollimated geometries suppress radiographic contrast for high-density objects and expose the camera to radiation-induced artifacts. CdWO₄ with iron shows the most robust transmission performance but exhibits a baseline offset suggesting secondary signal components unaffected by 20 cm of lead in the beam. Furthermore, the rapid initial drop in signal with 5 cm of lead in the beam suggests a significant contribution from source-generated gammas. Overall, iron-converted gamma-sensitive scintillators are a promising path for fast-neutron imaging where penetration and contrast through dense materials are necessary, but further optimization is required.