Production of a switchable fission-like neutron flux using a monoenergetic 14 MeV neutron generator and a depleted uranium reflector for vehicle borne improvised explosive device detection

A remotely controlled prototype has been built to detect explosives in vehicles. The inspection time is between 2 to 5 minutes. The system utilizes a neutron generator and a ²³⁸U reflector as the neutron source and high-purity germanium (HPGe) detectors housed in moving components that scan the entire vehicle. The design and performance of a switchable neutron source utilizing a D-T neutron generator and a depleted uranium reflector are presented. Approximately half the generator's 14 MeV neutron flux is used to produce a fission-like neutron spectrum similar to ²⁵²Cf. For every 14 MeV neutron entering the reflector, more than one fission-like neutron is reflected back across the surface of the reflector. The source has pulsed mode capability, because delayed neutron production is two orders of magnitude below prompt neutron production. The source simultaneously emits 14 MeV neutrons optimal to excite fast neutron-induced gamma-ray signals, such as from carbon and oxygen, and fission-like neutrons optimal to induce neutron capture gamma-ray signals, such as from hydrogen, nitrogen, and chlorine. Experiments were performed, which compare well to Monte Carlo simulations, showing that the uranium reflector enhances thermal signals by a factor of 15 compared to the absence of a reflector.