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

This paper discusses our initial investigation of fast neutron detection with a Cs₂LiYCl₆ (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 ²⁵²Cf source. There are two reactions in which fast neutrons are captured ³⁵Cl(n,p)³⁵S and ⁶Li(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 ³⁵Cl(n,p) reaction produces a peak and due to the ⁶Li(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 ²⁵²Cf initial efficiency was estimated for the ³⁵Cl(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 ²⁵²Cf fast neutron distribution and the ³⁵Cl(n,p) cross-section curve was found to match the experimental data.