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.
Rejection of Gamma Background Radiation Pulses in Hornyak Buttons
The nature of pulses resulting from alpha, beta, gamma, and neutron irradiation of Hornyak buttons has been examined under various conditions, including the use of light filters and both fast and slow electronics. Tentative conclusions about the mechanism of their origin are reached. Pulses from Compton recoils originate in the matrix and light transmitting media of the Hornyak button and phototube. Such pulses are of short duration, being similar in shape to photomultiplier noise pulses, in contrast to the 70-nanosecond decay of the fastest component of ZnS(Ag) fluorescence. A relatively simple, passive anticoincidence network is described which allows fast cancellation of the gamma-induced short pulses while passing the zinc sulfide scintillation with adequate efficiency. Rise time of the pulses emerging from the background suppression circuit is about 7 nsec. This network, in conjunction with a distributed amplifier, tunnel diode discriminator, and other fast electronic equipment is usel to select fission neutrons in coincidence with fission events.
Bridgman growth of Cs2LiYCl6:Ce and 6Li-enriched Cs26LiYCl6:Ce crystals for high resolution gamma ray and neutron spectrometers
Abstract Single crystals of small and large diameter Cs 2 LiYCl 6 :Ce and 6 Li-enriched Cs 2 6 LiYCl 6 :Ce have been grown by the vertical Bridgman technique. These scintillator crystals are used in the fabrication of high resolution, gamma ray and neutron spectrometers. The Cs 2 LiYCl 6 :Ce and 6 Li-enriched Cs 2 6 LiYCl 6 :Ce crystals we have grown have high light outputs of up to ∼22,000 photons/MeV. The emission wavelength for the Cs 2 LiYCl 6 :Ce and 6 Li-enriched Cs 2 6 LiYCl 6 :Ce is λ =373 nm. This material has an excellent energy resolution at room temperature of ∼4% FWHM for 662 keV photons (using a super bialkali photomultiplier). Cs 2 LiYCl 6 :Ce exhibits different temporal responses to gamma and neutron radiation. This difference results in effective pulse shape discrimination. In this paper, we will report on our results to date for vertical Bridgman crystal growth and characterization of Ce-doped Cs 2 LiYCl 6 :Ce and 6 Li-enriched Cs 2 6 LiYCl 6 :Ce crystals.