A global shortage of helium-3 has left many neutron detectors—used to monitor nuclear reactors, safeguard nuclear materials, and check radiotherapy beams—without a reliable, affordable replacement. This project aims to optimise a silicon-based detector coated with a thin layer of lithium fluoride (⁶LiF) that can capture thermal neutrons and produce two charged fragments whose coincidence signal suppresses false alarms from gamma rays. The problem is practical: helium-3 gas counters are expensive and scarce, and alternative detectors often lack the spatial resolution needed for neutron imaging or the efficiency to compete in high-flux environments. The researchers will refine the deposition process for the converter layer, apply it to segmented silicon detectors (pixels and strips), and test these devices in neutron beams and clinical radiotherapy settings. If successful, this work could deliver low-cost, large-area neutron detectors that maintain high efficiency and offer intrinsic spatial resolution—useful for nuclear safety, accelerator monitoring, and medical physics. It may also improve neutron imaging capabilities, a technique used in materials science and security scanning. The project is applied, not fundamental: it directly addresses a supply-chain bottleneck in a technology that quietly underpins energy security and healthcare.
View original technical description
Detection of thermal neutrons is necessary in a wide range of contexts from nuclear energy and safeguarding to monitoring of accelerators and radiotherapy treatments. The most popular method of measuring thermal neutron fluxes has historically been the He-3 gas proportional counter. However, due to the global shortage of He-3 there is a need for lower cost, large area thermal neutron detectors which still maintain high efficiency (https://doi.org/10.2172/956899). In addition to this, there is also a need to have detectors with intrinsic spatial resolution that could be used for neutron imaging. Application of converter layers to silicon (e.g. 10B, 6Li) and other solid state detectors in order to make them sensitive to thermal neutrons has long been investigated as an alternative to He-3 detectors. Use of a stable, enriched Lithium fluoride layer (6LiF) uniformly deposited to a thickness of a few microns on silicon has been carried out by Micron Semiconductor Ltd and the characterisation of these devices carried out at Liverpool using an AmBe neutron source located on campus. The benefit of this (Si-6LiF) configuration, is not only the large cross section for thermal neutron detection on 6Li (940b) but the production of two charged fragments with >2 MeV of kinetic energy in the resulting fission reaction after neutron capture (n + 6Li ? a(2.05MeV ) + 3H(2.73MeV)). Since these two charged fragments are produced with sufficient kinetic energy to exit a thin converter layer and reach the neighbouring silicon layer(s), this gives a greater opportunity to register the presence of a neutron. This is an advantage compared with converter layers that only produce a single charged particle with sufficient range (kinetic energy) for detection e.g 10B. Moreover, detecting a coincidence between the alpha and the triton reaction products from 6Li allows suppression of backgrounds, in particular the high fluxes of gamma rays often present with neutron production that cause false events to be registered as neutrons. The aims of the CASE award proposal outlined here will be to build on previous work (doi: 10.1117/12.2236752) carried out with Micron sensors and converters to deliver the following results: Optimisation of the converter deposition process on silicon to obtain a thermal neutron converter layer that maximises sensitivity to thermal neutrons Application of the above converter layer to segmented detectors such as pixels and strip detectors. Characterisation of these detectors in the lab and also in neutron sources and neutron beams Investigation of how temporal and spatial resolution can improve detection efficiency for single and for multiple layers to better compete with He-3 Investigation, (via simulation and/or measurement) into the application of this technology to neutron monitoring in clinical radiotherapy beams
Plain English summaries and category classifications on this site are generated by AI and may not perfectly reflect the original research.
Is something wrong? Let us know