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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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