Calibration and Characterisation of a Novel BN:ZnS Neutron Detector for CRNS Applications

Project Description: 

Cosmic Ray Neutron Sensing (CRNS) is a ground-based technique that exploits the interaction between secondary cosmic ray neutrons and environmental hydrogen to non-invasively estimate soil moisture content over field scales. As high-energy cosmic ray particles enter the atmosphere, they initiate cascades of secondary particles, including fast and epithermal neutrons that reach the Earth's surface. These neutrons are highly sensitive to hydrogen-rich materials in the near-surface environment — most notably liquid water in the soil — and their count rate at the surface is inversely related to soil water content. By continuously monitoring epithermal neutron flux, CRNS systems can infer volumetric soil moisture over a sensing footprint of approximately 150–300 metres in radius and 20–40 centimetres in depth, bridging the spatial gap between point-scale in-situ sensors and coarse satellite remote sensing products. The detection of epithermal neutrons has historically relied on helium-3 (He-3) proportional counters, which offer high efficiency and well-characterised response functions. However, the global scarcity and increasing cost of He-3 gas have driven interest in alternative detector technologies. Boron-10/Zinc Sulphide (BN:ZnS) scintillator detectors represent one of the most promising alternatives, operating on the principle that thermal and epithermal neutrons are captured by boron-10 nuclei, producing charged secondary particles that in turn excite ZnS scintillator material to produce measurable light pulses. Despite this potential, the deployment of BN:ZnS detectors in operational CRNS systems requires a thorough understanding of their detection efficiency, energy response, pulse height characteristics, and sensitivity to environmental hydrogen — properties that must be established through controlled laboratory characterisation before field deployment can be justified. Laboratory calibration and characterisation of radiation detectors involves exposing the detector to known radiation fields and systematically varying the measurement conditions to map out the detector's response. For neutron detectors, this includes measurements using radioactive neutron sources of known activity, moderated and unmoderated source configurations to probe different neutron energy ranges, and comparison against reference detectors with well-established response functions. Statistical analysis of the resulting count rate distributions, combined with pulse height spectroscopy, allows optimal operating parameters such as high voltage settings and discriminator thresholds to be determined. Benchmarking against existing instrumentation — such as GM-tube-based systems already in use within the research group — provides an additional validation layer and allows direct performance comparisons to be drawn. This project will conduct a systematic laboratory characterisation of the BN:ZnS neutron detector currently under development within the group. The student will measure detection efficiency as a function of neutron moderation geometry, characterise the pulse height spectrum and establish discriminator settings, and quantify the detector's sensitivity to environmental hydrogen by varying moderator configurations. Results will be benchmarked against reference detectors available in the laboratory. The outcomes will directly inform the integration of this detector into the group's operational CRNS network and contribute to the broader development of cost-effective, He-3-free neutron sensing technology for environmental monitoring applications.(NWU)

Supervisor

North-West University (NWU)

Co-Supervisor