Veto detectors for neutrino measurements at nuclear reactors

Nuclear energy has great value for reducing carbon emissions, which is a goal of great importance to create a sustainable human society. However, nuclear technology poses certain safety and security risks, which have hindered it’s deployment across the world. Neutrinos have the potential to allow us to decrease the risk of these dangers being actualised, by providing a separate channel of measurement, allowing for independent verification of several operating parameters of nuclear reactors, and their byproducts. However, neutrino detection is a complex procedure, and the more proven types of detectors able to conduct such measurements are extremely large, in the scale of tonne to kilotonne. The Coherent Elastic ν (Neutrino) Nucleus Scattering (CEνNS) interaction however has a cross-section larger than the more commonly used processes by orders of magnitude. Hence, detectors able to detect such an interaction have the potential to be able to achieve much more with far less target mass. That said, the interaction is largely unexplored, with no confirmed detection of such an interaction by neutrinos in the energy range of reactor antineutrinos. This thesis develops in contribution to two promising low energy experiments: the NUCLEUS experiment, which specifically intends to detect CEνNS from the two 4.25 GWth reactors cores of the Chooz-B nuclear power plant in France, and the BULLKID experiment, which plans to port its technology to create a CEνNS detection experiment in the future, but is currently in the process of developing a dark matter direct detection experiment. It explores the development and commissioning of veto detectors, detectors intended to exclude background events from the experimental dataset through an anti-coincidence filter, a strategy common to most experiments conducting rare event searches. Firstly, within the context of the NUCLEUS experiment, this thesis relays the commissioning process of the High Purity Germanium (HPGe) semiconductor detectors forming the NUCLEUS Cryogenic Outer Veto (COV), specifically the installation and commissioning of their readout system, reaching a base, and the proposal of a new procedure allowing to decrease the impact on the rest of the experiment of the long term operation of the detectors. Secondly, within the BULLKID collaboration, this thesis follows the development of a new veto architecture, based on the combination of very sensitive calorimetric detectors using the same technology as the target detectors, but for the readout of scintillation from a much more easily scalable scintillating crystal. A proof-of-concept detector, based on the architecture, has been assembled and characterised, demonstrating performance near the target for the final detector, despite several clear technical improvements having yet to be implemented due to time constraints.