Internal contamination of the Cs2HfCl6 crystal scintillator

The internal contamination (radio-purity) of a cesium hafnium chloride (Cs2HfCl6) crystal scintillator and its starting material (CsCl, HfCl4 initial and after 3-fold static sublimation purification) was studied by HR-ICP-MS and with an ultra-low-background high purity germanium (ULB-HPGe) detector deep underground. This study was conducted for the purpose of assessing the feasibility of using CHC as a potential detector to the search for rare α decay occurring in Hafnium isotopes. Despite the low radio-purity of starting material, the resulting analysis concluded that the grown CHC crystal is free of nuclides of the U/Th natural decay chain. Only a limit was set on their activities to a few mBq/kg. However, the crystal was found to contain artificial and cosmogenic radionuclides: 137Cs at 0.8 Bq/kg, 132Cs at 25 mBq/kg, 134Cs at 52 mBq/kg and 181Hf at 14 mBq/kg.