Isotopes of osmium

Osmium (₇₆Os) has seven naturally occurring isotopes, five of which are stable: ¹⁸⁷Os, ¹⁸⁸Os, ¹⁸⁹Os, ¹⁹⁰Os, and (most abundant) ¹⁹²Os. The other natural isotopes, ¹⁸⁴Os, and ¹⁸⁶Os, have extremely long half-lives (1.12×10¹³ years and 2.0×10¹⁵ years, respectively) and for practical purposes can be considered to be stable as well. ¹⁸⁷Os is the daughter of ¹⁸⁷Re (half-life 4.12×10¹⁰ years) and is most often measured by the ¹⁸⁷Os/¹⁸⁸Os ratio. This ratio, as well as the ¹⁸⁷Re/¹⁸⁸Os ratio, have been used extensively in dating terrestrial as well as meteoric rocks. It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons.

There are also 31 artificial radioisotopes,^[4] the longest-lived of which are ¹⁹⁴Os with a half-life of 6.0 years, ¹⁸⁵Os with 92.95 days, and ¹⁹¹Os with 14.99 days; others are under 30 hours, with most under seven minutes. There are also 19 listed nuclear isomers, the longest-lived of which is ^191mOs with a half-life of 13.10 hours. All isotopes and nuclear isomers of osmium are either radioactive or observationally stable, meaning that they are predicted to be radioactive but no actual decay has been observed.