High count rate performance of NE213 scintillation detectors with associated pulse shape discrimination electronics

During deuterium-tritium plasma discharges in the Joint European Torus (JET), Link Analytical 5020 pulse shape discrimination (PSD) units failed to discriminate correctly neutron and gamma-ray induced pulses from NE213 scintillation detectors. In this paper the discrimination failure is detailed as well as the subsequent experiments that were aimed at identifying the reason for the failure. The neutron/gamma-ray pulse misinterpretation was found to be related to rapid and significant changes in count rate which perturbed the PSD unit on a time scale faster than the response time of its DC stabilisation mechanism; operation at high but steady count rates did not lead to neutron/gamma-ray pulse misinterpretation. After increasing the frequency at which the stabilisation mechanism is triggered and the magnitude of the stabilisation signals, the 5020 PSD unit has been shown to be more responsive to a rapid change in count rate so that the degree of neutron/gamma-ray pulse misinterpretation is greatly reduced.