Improvements in thermal neutron scintillation detectors for time-of-flight studies

Abstract

Scintillation methods of detecting thermal neutrons are reviewed and ways of preparing and using the organic borate/zincsulphide scintillator are described which lead to a marked improvement in efficiency. In particular, a method of pulse-shape discrimination is described, based on a pronounced difference in pulse sha[es from ZnS(Ag) excited by alpha-particles and electrons. Methods of measuring detector efficiency or neutron flux are reviewed and a simple method is shown to be satisfactory to 1 2 % accuracy. Using these techniques a thermal neutron efficiency of 42% is observed in the presence of 5mR/h gamma radiation, or 52% in the absence of gamma background. Some tests have been carried out on lithium glass scintillators showing that with small area detectors in applications where the gamma background is low, high efficiencies can be achieved, but where gamma backgrounds are high the zincsulphide type is preferable.