Search for α and 2β decays of naturally occurring osmium nuclides accompanied by γ quanta

A search for α and ββ decays of naturally occurring osmium isotopes to the excited levels of daughter nuclei has been performed using an ultra-low-background broad-energy germanium γ detector and an ultrapure osmium sample at the Gran Sasso National Laboratory of the INFN (Italy). The isotopic composition of the osmium sample has been measured with high precision by using negative thermal ionization mass spectrometry. During the data taking with the γ detector, no effect has been detected, and lower limits for the half-life of α and ββ decays were set at the level of 1015−1020 yr. In the case of α decays of 184Os and 186Os to the first excited levels of daughter nuclei, the limits substantially exceed the present theoretical estimates of the decays probabilities. This gives hope to the possibility to detect such transitions in the ongoing data taking. The present work will describe a review of recent new measurements and new experimental perspectives.