Alexander, Abigail Mary;
(2024)
Characterisation and Modelling of High Purity Germanium Detectors for the LEGEND Experiment and Beyond.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
The search for neutrinoless double beta (0νββ) decay provides one of the most promising experimental portals to new physics, with a discovery set to uncover the nature of the neutrino, probe the absolute neutrino mass, and reveal the existence of lepton number violating processes. Among many experiments searching for 0νββ, LEGEND boasts an excellent energy resolution and ultra-low background, both necessary prerequisites for achieving its world-leading target half-life sensitivity of beyond 10²⁸ yr in ⁷⁶Ge across two experimental phases. The first phase, LEGEND-200, is currently taking first data at the Gran Sasso National Laboratory with ∼200 kg of High Purity Germanium (HPGe) detectors enriched in ⁷⁶Ge. An accurate understanding of these HPGe detectors is paramount to LEGEND’s success and achieved through dedicated characterisation measurements. This thesis is composed of three distinct research projects, the first two of which deal with the active volume (AV) characterisation of LEGEND detectors, while the third comprises the R&D for a novel high-mass HPGe detector. Firstly, the AV of 29 LEGEND-200 HPGe detectors is determined through a method based in γ-line spectroscopy and the comparison of characterisation data (individual detectors exposed to low-energy sources) to equivalent Monte Carlo simulations. The AV is an important quantity which directly impacts the detection efficiency required for the 0νββ discovery sensitivity. Secondly, a novel machine learning based approach to AV characterisation (involving a recurrent neural network trained on simulated energy spectra) is explored for a single LEGEND-200 detector. Finally, a new HPGe detector design is investigated through electric field and pulse shape simulations. The unique geometry of this proposed detector enables larger detector masses to be achieved while preserving the superb energy resolution, making it a suitable candidate for future LEGEND phases and beyond.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Characterisation and Modelling of High Purity Germanium Detectors for the LEGEND Experiment and Beyond |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10193530 |
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