Using decay time to discriminate neutron and gamma ray pulses from a CLYC detector

The reduced availability of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He is a motivation for developing alternative neutron detectors. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> Li-enriched CLYC (Cs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> LiYCl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> ), a scintillator, is a promising candidate to replace <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> He. The neutron and gamma ray signals from CLYC have different shapes due to the slower decay of neutron pulses. The long decay time associated with the scintillation emission of CLYC often results in pulse pileup for event rates exceeding 100 kHz. Discriminating neutrons in a mixed field of gamma rays and neutrons is a challenging task especially when the event rate is high. There have been other methods that successfully distinguish neutrons at less than 100 kHz event rates, but separating them at higher event rates has not been satisfactory. In this work, we propose an algorithm that discriminates the neutron events directly based on their decay time and energy spectral density (ESD). The approach is assessed with data collected for different event rates (13 kHz to 1660 kHz) for an average data record length of about 750 ms in each case, providing more than 100,000 events to analyze. The results show accurate clusters of neutron events in the pulse shape discrimination (PSD) plot even during high event rates, and the approach gives a uniform figure of merit (FOM) ranging between 1.28-1.35 for all event rates.

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