Neutron Time Projection Chamber for Nuclear Security and Verification Applications

Detection of fast neutrons produced by fission is a powerful method for discovering, verifying the presence, or monitoring significant quantities of special nuclear material (SNM) at up to moderate distances. Fast neutrons are relatively rare in the natural background and can be very penetrating, even in situations when the energetic gamma-rays are well shielded. Fast neutrons point in the direction of their source and can thus be considered for use in imaging, a feature desirable for rapid, high-signal-to-noise detection of concealed SNM and for nuclear verification. We describe the development and performance of a prototype neutron time projection chamber (nTPC) and its use for directional neutron detection and high-resolution neutron imaging. The nTPC is based on similar to 0.025 m(3) of a hydrogen-methane mixture and utilizes a readout system with low channel count and is optimized for low event rates. We experimentally demonstrate robust operation, reliable particle identification, event-by-event directional reconstruction over the entire 4 pi solid angle, and insensitivity to gamma-rays. High-efficiency and high-resolution modes of operation based on single and double neutron scatters, respectively, have also been demonstrated.