Osmium-186

Main isotopes of osmium

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct 184Os 0.02% stable 185Os syn 93.6 d ε 185Re 186Os 1.59% 2.0×1015 y α 182W 187Os 1.96% stable 188Os 13.24% stable 189Os 16.15% stable 190Os 26.26% stable 191Os syn 15.4 d β− 191Ir 192Os 40.78% stable 193Os syn 30.11 d β− 193Ir 194Os syn 6 y β− 194Ir
Standard atomic weight (Ar, standard)	190.23(3)

Osmium (₇₆Os) has seven naturally occurring isotopes, 6 of which are stable: ¹⁸⁴Os, ¹⁸⁷Os, ¹⁸⁸Os, ¹⁸⁹Os, ¹⁹⁰Os, and (most abundant) ¹⁹²Os. The other natural isotope, ¹⁸⁶Os, has an extremely long half-life (2×10¹⁵ years) and for practical purposes can be considered to be stable as well. ¹⁸⁷Os is the daughter of ¹⁸⁷Re (half-life 4.56×10¹⁰ years) and is most often measured in an 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. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the dinosaurs 66 million years ago.

There are also 30 artificial radioisotopes, the longest-lived of which is ¹⁹⁴Os with a half-life of 6 years, all others have half-lives under 94 days. There are also 9 known nuclear isomers, the longest-lived of which is ^191mOs with a half-life of 13.10 hours.

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