Search for α decay of naturally occurring Hf-nuclides using a Cs2HfCl6 scintillator

Residual radioactive contaminants of a caesium hafnium chloride (Cs₂HfCl₆) crystal scintillator have been measured in a low background setup at the Gran Sasso National Laboratory of the INFN, Italy. The total alpha activity of the detector is at the level of 7.8(3) mBq/kg. The results of direct studies of the α decay of naturally occurring Hf isotopes that have been performed using the "source=detector" approach are presented. In 2848 h of data taking, the α decay of ¹⁷⁴Hf was observed with ^1/2T = (7.0 ± 1.2) ×10¹⁶ y.