Rod-shaped pulse shape discrimination plastic scintillation detectors applied for neutron source direction survey

A fast neutron detector system that can figure out neutron source direction is developed. The system consists of two rod-shaped fast neutron detectors and one polyethylene moderator. Pulse shape discrimination plastic scintillators are applied for reduced gamma-ray background and improved system sensitivity for fast neutron detection. The neutron detectors are placed on the back and front sides of the moderator facing a neutron source. Experiments are conducted for a single rod-shaped detector and the system changing the PuBe neutron source direction. Simulation-based studies are also performed using the Monte Carlo simulation code, PHITS (Particle and Heavy ion Transport code System). Taking the ratio of counts of the front and back system detectors, linear change with an increased detector angle is observed, except for near 0° and 90°. This enables us to deduce neutron source direction from several measurements. The method is probably useful for a quick and efficient survey of neutron sources or special nuclear materials.