CXXII. A search for natural radioactivity in neodymium, rhenium and osmium

The element neodymium and the naturally occurring isobaric pair Rhenium 187 and Osmium 187 are investigated, as internally mounted sources in a well-shielded proportional counter, for evidence of natural radioactivity. The β-decay probability of Neodymium 150 corresponds to a half-life of not less than 1016 yr. No beta instability of rhenium is observed and 1015yr. is suggested as the minimum possible half-life for the isotope 187Re. The emission of L x-rays from osmium is observed, but it is found that dense materials show similar emission, and it is attributed to the photoelectric absorption of γ-fays (residual background) in the materials. It is concluded that there is no evidence of decay in osmium and the estimated minimum possible half-life by electron capture exceeds 1015 yr.