Search for alpha and double-alpha decays of naturally occurring europium isotopes with HPGe gamma spectrometry

An experimental search for α and 2 α decays of naturally occurring europium isotopes, 151 Eu and 153 Eu, was carried out at the Gran Sasso underground laboratory using a 313.8 g highly radiopure sample of europium oxide and a 118 cm 3 broad-energy HPGe detector. In the spectrum measured over 4211 h, no γ peaks expected from the processes of interest were observed. Improved partial half-life limits were set for the α decays of 151 Eu to the 91.1-keV daughter level and 153 Eu to all energetically allowed levels: > 4.0 × 10 18 y and > 1.6 × 10 18 y, respectively, at 90% C.L. The first experimental limits were obtained for 2 α decay of 151 Eu ( > 5.0 × 10 11 y) and 153 Eu ( > 2.6 × 10 17 y).