On the Fabrication and Characterization of Heterogeneous Composite Neutron Detectors with Triple-Pulse-shape-discrimination Capability

This paper describes the fabrication and characterization of a novel triple-pulse-shape-discrimination (PSD) capable heterogeneous composite neutron detector that utilizes fast neutron-sensitive scintillating polyvinyl toluene (PVT) and Li-6-glass rods. The objective of this study was twofold: 1) Assess the effect of PPO (primary dopant) loading on the mechanical properties of the PVT, and 2) fabricate a triple PSD-capable composite detector using PPO-doped PVT and Li-6-glass rods. Thermal and mechanical characterization reveals that, as the weight content of the PPO in PVT increases, the glass transition temperature (T-g) of the PVT decreases. This decrease in T-g leads to a mechanically soft polymer which is undesirable for machining and susceptible to damage and deformation. Therefore, a crosslinking agent (divinylbenzene, DVB) was introduced to control the mechanical properties while still exploiting the PSD capabilities of the high PPO content PVT. The composite was then fabricated using the crosslinked PVT as the fast neutron and gamma sensitive material and Li-6-glass rods as the thermal neutron sensitive material. The final fabricated composite sample has a glass weight content of 6% and dimensions of 2.5 cm x 2.5 cm. A UV/Vis spectrometer was used to characterize the optical properties of the composite sample. A Cf-252 source was used to test the PSD capabilities and intrinsic efficiency of the sample. The figure of merit for the fast neutron and gamma rays was measured to be similar to 1, while the thermal neutrons and gamma rays exhibit a figure of merit of similar to 3. A Co-60 source was used to measure the gamma rejection of the sample, which was found to be 10(-5). The capture efficiency of the small prototype sample for unmoderated neutrons was measured to be 0.09%, closely matching the result of simulation (0.11%).