Осмий изотоптары: массалық саны әртүрлі ядролық түрлер

Nuclides with atomic number of 76 but with different mass numbers

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 life (1.12×1013 years and 2×1015 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 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 31 artificial radioisotopes, the longest lived of which is 194Os with a half life of six years; all others have half lives under 93 days. There are also ten known 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.

The isotopic ratio of osmium 187 and osmium 188 (187Os/188Os) can be used as a window into geochemical changes throughout the ocean's history. The average marine 187Os/188Os ratio in oceans is 1.06. This decay has actually pushed the 187Os/188Os ratio of the Bulk silicate earth (Earth minus the core) by 33%. This is what drives the difference in the 187Os/188Os ratio we see between continental materials and mantle material. Crustal rocks have a much higher level of Re, which slowly degrades into 187Os driving up the ratio. This allows for researchers to make estimates on weathering fluxes, identifying flood basalt volcanism, and impact events that may have caused some of our largest mass extinctions. The marine sediment Os isotope record has been used to identify and corroborate the impact of the K T boundary for example. The impact of this ~10 km asteroid massively altered the 187Os/188Os signature of marine sediments at that time. With the average extraterrestrial 187Os/188Os of ~0.13 and the huge amount of Os this impact contributed (equivalent to 600,000 years of present day riverine inputs) lowered the global marine 187Os/188Os value of ~0.45 to ~0.2. The same 187Os/188Os ratios that are common in geological settings may be used to gauge the addition of anthropogenic Os through things like catalytic converters.