Neutrinos for Non-Proliferation

Technical paper presented at the 2018 Defence and Security Doctoral Symposium.Identifying the existence of a clandestine reactor in a complex nuclear landscape for nuclear threat reduction is challenging. WATCHMAN will demonstrate for the first time the feasibility of detecting the signal from a hidden reactor against the background of a second reactor. A kilotonne-scale detector to be built underground in the Boulby Mine in North Yorkshire, WATCHMAN will detect antineutrinos - the unshieldable by-product of radioactive decay in a nuclear reactor.A WATCHMAN-style detector could be used remotely as part of a non-proliferation agreement and WATCHMAN offers a unique opportunity to develop reactor antineutrino detection technology for non-proliferation and beyond.Such a detector will out of necessity operate at long range, often at the very limit of its sensitivity, and so minimising backgrounds is essential. Photomultipliers (PMTs) detect light from antineutrino interactions in the detector however accidental coincidences from the decay of radioactive isotopes in PMT glass mimic the antineutrino signal and are one of the principle sources of backgrounds for the experiment.This paper presents an analytical method for optimising the signal-to-background ratio in the experimental results and uses it to compare the relative benefits of different PMT types. It is found that while the optimal detector design uses 10” low radioactivity glass PMTs, the potentially stronger and more readily available 12” standard-glass PMTs can give comparable results due to the improvement in the precision with which we can identify exactly where in the detector an event has occurred. This result is sensitively dependent on the dark noise rate in the tubes due to its effect on reconstruction at lower energies