First search for α decays of naturally occurring Hf nuclides with emission of γ quanta

The first ever search for α decays to the first excited state in Yb was performed for six isotopes of hafnium (174, 176, 177, 178, 179, 180) using a high purity Hf sample of natural isotopic abundance with a mass of 179.8 g. For 179Hf, also α decay to the ground state of 175Yb was searched for thanks to the β-instability of the daughter nuclide 175Yb. The measurements were conducted using an ultra-low-background HPGe-detector system located 225 m underground. After 75 days of data taking no decays were detected but lower bounds for the half-lives of the decays were derived on the level of limT1/2∼1015−1018 a. The decay with the shortest half-life based on theoretical calculation is the decay of 174Hf to the first 2+ 84.3 keV excited level of 170Yb. The experimental lower bound was found to be T1/2≥3.3×1015 a. ; JRC.G.2 - Standards for Nuclear Safety, Security and Safeguards