Novel technologies for future applications of nuclear reactor monitoring using antineutrinos

Nuclear reactors produce copious number of antineutrinos as a result of the nuclear fission process.
This antineutrino emission can be used to monitor the nuclear reactor, providing important information regarding its operating state, power level, and fissile content in the core.
Efforts are underway to construct a large-scale water-based antineutrino detector that is able to detect and monitor a nuclear reactor at distance-scales of tens of kilometres.
The baseline conceptual design is a kilotonne-scale water-Cherenkov detector doped with gadolinium that detects the ``double flash'' of a positron and a neutron resulting from the inverse beta decay process.
However, novel detection technologies are being actively studied to improve performance or extract more information from antineutrino interactions.

One such technology is water-based liquid scintillator, a highly scalable detection medium with improved light yield compared to pure water.
Detector simulations utilising water and water-based liquid scintillator detector fills suggests that such detectors would be sensitive to a nuclear reactor complex at a distance of around \SI{150}{\kilo\metre}.
Water-based liquid scintillator performs better in general, although despite the improved light yield from the addition of scintillator, gadolinium is still required to boost the neutron capture signal and suppress backgrounds.

Another key technology is the Large Area Picosecond PhotoDetector (LAPPD), a microchannel plate photosensor that offers millimetre-scale positional resolution and timing resolution of tens of picoseconds.
The LAPPD performance is characterised and verified using a custom-designed laser test stand.
In order to perform vertex reconstruction using LAPPDs, an algorithm to disambiguate photon hits on the LAPPD is developed allowing for the isolation of individual photon hits from hit clusters and the determination of the position and timing of these individual photons.

To achieve the goal of a large-scale demonstration of an antineutrino detector for nuclear security, smaller scale technology testbeds are being developed.
One such testbed is the BUTTON detector at Boulby, which aims to deploy both water-based liquid scintillator and LAPPDs.
The LAPPD characterisation and multiphoton disambiguation work detailed in this thesis will contribute directly to the deployment and operation of LAPPDs in BUTTON.