Enhancing pixelated fast-neutron block detector performance using a slotted light guide

The first fast-neutron scintillation block detector has been developed for use in neutron imaging applications. The low-cost, large field of view (FOV) block detector consists of a 10 x 10 array of plastic scintillator crystals, each with a size of approximately 1x1x5 cm³. To achieve both low cost and fast response time, the detector uses a 2 x 2 array of photomultiplier tubes (2-in. Photonis XP20D0) optically coupled to the array of scintillation crystals through a custom-made light guide. The light guide is segmented in such a way that all scintillator crystals can be resolved, including the edge crystals, to fully utilize the entire FOV of the detector. The thickness and depth of the light-guide segments were also optimized to maintain nearly uniform linearity between the true pixel locations and the reconstructed positions. Flood images from simulation and experiment show that each of the 100 pixels is resolved with an average peak-to-valley ratio for 14 MeV neutrons of 9:1. A mean deviation of 3.3 mm is obtained between the resolved image peaks and the respective true positions demonstrating good linearity. A coincidence measurement performed using a deuterium-tritium neutron generator, in which the neutrons were measured with the block detector and the corresponding alpha particles were measured with another scintillation detector revealed a total time resolution of 1.3 ns full width at half maximum.