Development of a boron-10 based Multi-Grid detector for neutron spectroscopy

Backis, Alexander (2023) Development of a boron-10 based Multi-Grid detector for neutron spectroscopy. PhD thesis, University of Glasgow.

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This work presents the continued development of the Multi-Grid, a boron-10-based cold to epithermal neutron detector technology. The Multi-Grid is a large area detector, tens of square meters, intended for time-of-flight neutron spectroscopy. The detector development started around 2010, and its first application is intended at the upcoming European Spallation Source, currently under construction in Lund, Sweden. This is to address the expected high flux at the upcoming facility, which is beyond the rate capabilities of current state-of-the-art detectors, and to substitute the large area helium-3 tube arrays commonly used for neutron spectroscopy, which have become prohibitively expensive at high He-3 gas pressures.

Here, the latest developments are shown, based on measurements with the most recent implementations of the Multi-Grid, which are the MG.SEQ and MG.LET prototypes. This includes the characterisation of different detector properties – such as neutron detection efficiency, signal-to-background ratio and energy resolution – as well as an investigation on how to properly select an internal shielding design. It also includes a detailed account of the effects of internal neutron scattering and how it can be reduced. This is a general step-by-step guide on how to compare and evaluate different neutron shielding candidates and it is relevant for all neutron detectors, not just the Multi-Grid.

The characterisation work is primarily based on data collected during two beamtimes: one at the ESS Test Beamline V20 at the Helmholtz-Zentrum Berlin, Germany, and one at the cold neutron spectrometer LET at the ISIS neutron and muon source, United Kingdom. For the internal shielding investigations, Geant4 was used together with the newly developed NCrystal library. Using these code packages, various shielding materials were modeled and simulations were performed of how neutrons interact with them.

From the results, a signal-to-background ratio of approximately 10[sup]4 was shown together with an improvement in energy lineshape, which was broadly comparable to the LET helium-3 tubes and had a reduced energy smearing compared to that observed during a previous test at the CNCS instrument at the Spallation Neutron Source. Important information was obtained on how the effects on internal neutron scattering can be attenuated, and a direct comparison was made with state-of-the-art helium-3 detectors in the LET instrument. The energy resolution was also studied in detail and the detection efficiency was re-confirmed. These contributions bring the development of the detector towards its finalisation and use at neutron scattering facilities.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: Q Science > QC Physics
Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
Supervisor's Name: Hamilton, Dr. David and Livingston, Dr. Kenneth
Date of Award: 2023
Depositing User: Theses Team
Unique ID: glathesis:2023-83756
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 03 Aug 2023 14:11
Last Modified: 08 Aug 2023 10:46
Thesis DOI: 10.5525/gla.thesis.83756
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