Novel Scintillator Development for High Rate Capability Neutron Scattering Detectors

Abstract

As flux at neutron scattering facilities increases, the development of affordable, large area neutron detectors with high count rate capability is a growing priority. The current state-of-the-art ZnS:Ag/⁶LiF scintillation detectors are count rate limited by fundamental luminescence mechanisms. In this work two novel scintillators for high count rate capability neutron detection applications are explored: ZnO:Zn/⁶LiF and nanoparticle ZnS:Ag/⁶LiF.
Analysis of ZnO:Zn/⁶LiF scintillation and the optical properties of detector components was performed, and the first position sensitive ZnO:Zn/⁶LiF neutron detector subsequently developed. The fundamental lack of afterglow in ZnO:Zn/⁶LiF was exploited to achieve count rate capabilities 2.5 times greater than ZnS:Ag/⁶LiF detectors. ZnO:Zn/6LiF wavelength shifting fibre detectors were, however, found to have poor efficiency due to low light output and inhomogeneous scintillator composition. Detection efficiency problems were mitigated by utilising high light collection configurations suited for disordered material diffraction. As a result, ZnO:Zn/⁶LiF was shown for the first time to be a viable alternative to ZnS:Ag/⁶LiF in high light collection geometries.
Nanoparticle ZnS:Ag/⁶LiF based scintillators were found to possess the characteristics needed for dramatic improvements to count rate capability. Nanoparticles of ZnS and ZnS:Ag were hydrothermally synthesised with different precursors and doping concentrations, and physical, optical, and scintillation properties were explored. ZnS:Ag nanoparticles were discovered to have primary scintillation decay under 8ns and no long term afterglow. The first neutron detector employing ZnS:Ag nanoparticles was created to capitalise on these improved timing properties. Novel signal processing techniques were developed to achieve excellent gamma rejection and count rate capabilities over 10⁶ counts per second, approximately 70 times greater than ZnS:Ag/⁶LiF based detectors. Areas for improvement including low detection efficiency (∼14% at 1.8Å) are discussed, and possible solutions explored. Overall, this work proves that nanoparticle ZnS:Ag/⁶LiF scintillation detectors could be developed into the next generation of high count rate capability neutron scattering detectors.

Date of Award	10 Dec 2024
Original language	English
Awarding Institution	University of Bristol
Sponsors	UKRI STFC ISIS
Supervisor	G. Jeff Sykora (Supervisor), Lilly Liu (Supervisor), James W Pomeroy (Supervisor) & Martin H H Kuball (Supervisor)