Search for $α$ decay of naturally occurring Hf-nuclides using a Cs$_2$HfCl$_6$ scintillator

Abstract

Residual radioactive contaminants of a caesium hafnium chloride (Cs 2 HfCl 6 ) 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 174 Hf was observed with T 1/2 = (7.0 ± 1.2) × 10 16 y.Keywords: rare alpha decay; 174 Hf; 176 Hf; 177 Hf; 178 Hf; 179 Hf; 180 Hf; crystal scintillator; Cs 2 HfCl 6 ; HP-Ge γ spectrometer; source = detector approach; low background experiment; hafnium.