Improved neutron detection using zinc sulfide with boron

Thesis

Phosphor screens designed to detect neutrons by producing light are used in many applications to detect thermal neutrons including the SoLid antineutrino detection experiment. These screens are formed by binding powders of zinc sulfide and lithium-6 fluoride with an epoxy. Due to poor transparency, these screens have limited neutron detection efficiency. The current study proposes an alternate material with the potential for higher neutron detection efficiency based on sintering zinc sulfide and boron compounds to form a polycrystalline composite ceramic. A model was developed to predict neutron detection efficiency of ceramics and screens based on modifying parameters such as composition and grain size. By varying these design parameters, an optimal ceramic design was found that increased the neutron capture rate by 45% (using enriched boron) and increased the signal per neutron by 18% compared to a model of the phosphor screen used in the SoLid experiment. These design parameters were then used to fabricate ceramics by sintering commercial powders of unenriched BN and ZnS(Ag) using the FAST sintering technique. The ceramics retained the luminescent properties of ZnS(Ag) and demonstrated improved translucency. Drawbacks of this methodology include apparent carbon migration into the ceramic and difficulty reproducing the ceramics. The ceramics and a phosphor screen used in the SoLid experiment were exposed to neutrons in a custom test apparatus that collected light from either side. The results of these experiments were used to compare the neutron detection efficiency of the ceramics and the screen and compare the experimental results to the model predictions. The rate of neutrons detected and the signal produced per neutron by the ceramics were respectively 10% and 40% that of the rate and signal of the phosphor screens (the model predicted a rate roughly 35% of the phosphor screen using unenriched boron). While the experimental results did not confirm the model predictions, the effort demonstrated the feasibility of the concept and showed promise of success with further development.

Authors: Castle, B

• DOI: 10.5287/ora-zbggo4dbw
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford