Fast Neutron Detection With ${\rm Cs}_{2} {\rm LiYCl}_{6}$

This paper discusses our initial investigation of fast neutron detection with a Cs 2 LiYCl 6 (CLYC) scintillator. CLYC has been already developed for dual mode detectors (thermal neutrons and gamma rays). Described are results collected under mono-energetic irradiation from a Van de Graaff generator and a continuous irradiation from a 252 Cf source. There are two reactions in which fast neutrons are captured 35 Cl(n,p) 35 S and 6 Li(n,t)α; both have been observed. They produce a proton and a pair of α/t particles, respectively. The response to mono-energetic fast neutrons due to the 35 Cl(n,p) reaction produces a peak and due to the 6 Li(n,t) reaction a continuum in the energy spectra. The relation between the peak (continuum) position and the excitation energy is linear within evaluated energy range. This allows for fast neutron spectroscopy. The α/β ratios for both reactions were found to be different and somewhat dependent on the excitation energy. The decay times under the proton excitation slightly differ from these under the α/t excitation, while both are significantly different from the gamma ray excited curves. This is important for pulse shape discrimination. Using continuous excitation from 252 Cf initial efficiency was estimated for the 35 Cl(n,p) reaction. For a 1-inch right cylinder crystal the measured intrinsic efficiency is at least 0.06%, while calculated is 0.5%. The discrepancy is due to experimental inaccuracies. The relative detection efficiency scales linearly with the volume. A convolution of the theoretical 252 Cf fast neutron distribution and the 35 Cl(n,p) cross-section curve was found to match the experimental data.