Coincidence-based reconstruction and analysis for remote reactor monitoring with antineutrinos

Antineutrinos from a nuclear reactor comprise an unshieldable signal which carries information about the core. Their interaction via inverse beta decay (IBD), in a gadolinium-doped water medium, produces a positron-neutron pair coincident in time and space. NEO (Neutrino Experiment One), a gadolinium-doped water-based Cherenkov detector, is planned to demonstrate remote reactor monitoring for nuclear non-proliferation. Such a monitor would, by its very nature, operate at the limit of its sensitivity, detecting low-energy antineutrinos, from a distance, in a complex nuclear landscape. In this thesis, I investigate ways to achieve optimal sensitivity to a reactor signal.

I implement a reconstruction which uses the combined light from both events in an IBD pair to accurately reconstruct the interaction vertex. I also develop a powerful analysis to reject coincident backgrounds and find the maximal sensitivity of a detector to a reactor signal. Finally, I evaluate the sensitivity of NEO detector designs to reactor signals at the planned site in Boulby Mine.

I find that the combined reconstruction improves vertex resolution for IBD positrons by up to a factor of two. IBD-neutron vertex resolution is found to improve by more than 20% at most energies. The coincidence analysis shows that a 22 m gadolinium-doped water-based liquid scintillator detector would be sensitive to the signal from the Heysham 2 nuclear reactor complex 149 km away within 22 months and could detect the dual-site signal from the reactors at the Heysham 2 and Torness complexes in just over 6 months.

A detector at Boulby Mine could detect signals from reactor complexes within the time constraints of the current schedule for reactor decommissioning in the UK. As a remote reactor monitoring prototype, NEO would be the first ever neutrino physics application.