Wavelength-based neutron/gamma ray discrimination in CLYC

We investigated the optical components of Cs₂LiYCl₆:Ce (CLYC) as a possible path to particle discrimination by measuring the effects of optical filters on the shape of the waveform and comparing filtered waveforms to unfiltered ones. Crystals packaged with two optical windows were viewed by two photomultiplier tubes operated in coincidence to be certain that the signals from the same event were analyzed. We applied long-pass optical filters with cut-off wavelengths from 280 to 455 nm, and bandpass filters with cut-off wavelengths at 313, 350, 385, and 425 nm. Waveforms from gamma rays were significantly sharpened by the 313 nm bandpass filter because this filter cut out self-trapped exciton luminescence, while neutron waveforms were largely unaffected by filtering. Cumulative distribution functions generated from average filtered waveforms indicate that the neutron/gamma assignment can be made 44 ns by applying a Kolmogorov-Smirnov test comparing an acquired waveform to the average filtered waveforms.