All-Electronic Gamma Rejection Method in Neutron Detection

Neutron-sensitive microchannel Plates (MCPs) are now providing state-of-the-art user-based, high spatial resolution neutron imaging systems at several US government neutron research facilities as well as university research reactors. Using enriched 10B, thermalized neutron detection efficiencies exceeding 50% have been demonstrated, and cold neutron detection efficiencies of up to 70% have been documented. Although NOVA Scientific already has already been successful in uniquely providing highly effective MCP neutron detectors for thermal and cold neutrons, with exceptional and simultaneous spatial (~20 µm) and timing (~0.1 µs) resolution, the main goal of this Phase I program is to achieve dramatically reduced gamma ray sensitivity as well – by orders of magnitude - to expand the number of applications in neutron research and nuclear physics. This will enable the neutron-sensitive MCP detection approach to become a more highly competitive alternative to the ‘gold standard’ 3He neutron detector - as well as its alternative replacement detector technologies - many of which already offer exceptionally low gamma ray sensitivity. Until now, there has really been no truly effective method to discriminate neutrons from gamma rays with NOVA’s neutron-sensitive MCPs. Over the years, several attempts have been made by multiple researchers, including NOVA, to solve the MCP gamma sensitivity problem. However, such attempts have always had significant drawbacks – in terms of complexity and performance. In some nuclear physics applications and in neutron scattering and diffraction, as well as very low count rate neutron detection applications (for security), gamma ray interference with the neutron signal can be a serious problem indeed. We now believe there is a solution to the MCP gamma sensitivity problem, based upon a bulk semiconductor phenomenon existing inside the MCP structure itself. This new approach to the problem, comparatively simple and truly ‘all-electronic’, does not require ancillary hardware but can instead be implemented with relatively simple pulse analysis firmware or software, to discriminate opposite pulse polarities at MHz rates. The approach exploits a remarkable polarity reversal of very fast pulses picked off the MCP contact electrodes themselves, which are normally only used as DC high voltage bias contacts. This opens up the potential to separately distinguish neutrons and gamma rays, as well as time-tag them with sub microsecond precision - thus providing a measure of particle identification, and which may provide an option to segment gammas vs. neutrons. This promises to provide a several order of magnitude improvement in neutron-gamma discrimination in neutron-sensitive MCPs as compared to what is currently feasible.