Cesium hafnium chloride scintillator coupled with an avalanche photodiode photodetector

Optical and scintillation properties of pure Cs₂HfCl₆ (CHC) single crystals were investigated. In particular, light output and energy resolution were measured using a Si avalanche photodiode (Si-APD), since the Si-APD has sufficient quantum efficiency of around 70 % at emission wavelength region of CHC around 420 nm. This CHC single crystal grown using the vertical Bridgeman method showed light output of 37,000± 2,000 photons/MeV . The FWHM energy resolution was determined to be 3.7± 0.5× ( E /662 keV)^{−0.85± 0.03}[%], where E [keV] is the gamma-ray energy. Moreover, the temperature dependence of the light output was stable from −5 to 30 ^oC, while the light output increased below −10 ^oC.