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Isotopes of osmium
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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, 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.
Osmium isotopes in radiometric dating
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 value represents a balance of the continental riverine inputs of Os with a 187Os/188Os ratio of ~1.3, and the mantle/extraterrestrial inputs with a 187Os/188Os ratio of ~0.13. The lighter isotope, 187Os, is produced by beta decay of 187Re. This decay has actually increased the 187Os/188Os ratio of the bulk silicate earth (Earth less the core) by 33%. The difference between crust and mantle ratios is explained this way: crustal rocks have a much higher level of rhenium, which produces an excess of 187Os. The combined input of the two sources to the marine environment results in the observed ratio in the oceans, and has fluctuated over the geologic history. These changes in the isotopic values of marine Os can be observed in the marine sediment that is deposited, and eventually lithified in that time period. This allows for researchers to estimate weathering fluxes, flood basalt volcanism, and impact events that may have caused some of our largest mass extinctions. The marine sediment Os isotope record has corroborated the K-T boundary impact, for example. The impact of this ~10 km asteroid massively altered the 187Os/188Os signature of marine sediments at that time - 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 a minimum of ~0.2.
Os isotope ratios may also be used as a signal of anthropogenic impact. 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. While catalytic converters have been shown to drastically reduce the emission of NOx and CO, they are introducing platinum group elements (PGE) such as Os, to the environment. Other sources of anthropogenic Os include combustion of fossil fuels, smelting chromium ore, and smelting of some sulfide ores. In one study, the effect of automobile exhaust on the marine Os system was evaluated. Automobile exhaust 187Os/188Os has been recorded to be ~0.2 (similar to extraterrestrial and mantle derived inputs). The effect of anthropogenic Os can be seen best by comparing aquatic Os ratios and local sediments or deeper waters. Surface waters thought to be affected have depleted values compared to deep ocean and sediments by a ratio larger than can be explained by cosmic inputs.
The alpha decay of 184Os into 180W (with a rate perhaps large enough for detection) has been proposed as a radiometric dating method for osmium-rich rocks or for differentiation of a planetary core.
List of isotopes
Osmium-197m |-id=Osmium-160 | 160Os | | | α | 156W | 0+ | | |-id=Osmium-160m | | α | 156W | 8+ | | |-id=Osmium-161 | 161Os | 160.98905(43)# | | α | 157W | (7/2–) | | |-id=Osmium-162 | 162Os | 161.98443(32)# | | α | 158W | 0+ | | |-id=Osmium-163 | α
| 159W |
|---|
| β+ ? |
| 163Re |
| -id=Osmium-164 |
| α (96%) |
| 160W |
| - |
| β+ (4%) |
| 164Re |
| -id=Osmium-165 |
| α (90%) |
| 161W |
| - |
| β+ (10%) |
| 165Re |
| -id=Osmium-166 |
| α (83%) |
| 162W |
| - |
| β+ (17%) |
| 166Re |
| -id=Osmium-167 |
| α (51%) |
| 163W |
| - |
| β+ (49%) |
| 167Re |
| -id=Osmium-167m |
| | IT | 167Os | 13/2+ | | |-id=Osmium-168 | β+ (57%)
| 168Re |
|---|
| α (43%) |
| 164W |
| -id=Osmium-169 |
| β+ (86.3%) |
| 169Re |
| - |
| α (13.7%) |
| 165W |
| -id=Osmium-170 |
| β+ (90.5%) |
| 170Re |
| - |
| α (9.5%) |
| 166W |
| -id=Osmium-171 |
| β+ (98.20%) |
| 171Re |
| - |
| α (1.80%) |
| 167W |
| -id=Osmium-172 |
| β+ (98.81%) |
| 172Re |
| - |
| α (1.19%) |
| 168W |
| -id=Osmium-173 |
| β+ (99.6%) |
| 173Re |
| - |
| α (0.4%) |
| 169W |
| -id=Osmium-174 |
| β+ (99.976%) |
| 174Re |
| - |
| α (0.024%) |
| 170W |
| -id=Osmium-175 |
| 175Os |
| 174.956945(13) |
| | β+ | 175Re | (5/2−) | | |-id=Osmium-176 | 176Os | 175.954770(12) | | β+ | 176Re | 0+ | | |-id=Osmium-177 | 177Os | 176.954958(16) | | β+ | 177Re | 1/2− | | |-id=Osmium-178 | 178Os | 177.953253(15) | | β+ | 178Re | 0+ | | |-id=Osmium-179 | 179Os | 178.953816(17) | | β+ | 179Re | 1/2– | | |-id=Osmium-179m1 | | IT | 179Os | (7/2)– | | |-id=Osmium-179m2 | | IT | 179Os | (9/2)+ | | |-id=Osmium-180 | 180Os | 179.952382(17) | | β+ | 180Re | 0+ | | |-id=Osmium-181 | 181Os | 180.953247(27) | | β+ | 181Re | 1/2− | | |-id=Osmium-181m1 | | β+ | 181Re | 7/2− | | |-id=Osmium-181m2 | | IT | 181Os | 9/2+ | | |-id=Osmium-182 | 182Os | 181.952110(23) | | EC | 182Re | 0+ | | |-id=Osmium-182m1 | | IT | 182Os | 8– | | |-id=Osmium-182m2 | | IT | 182Os | 25+ | | |-id=Osmium-183 | 183Os | 182.953125(53) | | β+ | 183Re | 9/2+ | | |-id=Osmium-183m | β+ (85%)
| 183Re |
|---|
| IT (15%) |
| 183Os |
| -id=Osmium-184 |
| 184Osprimordial radionuclide |
| 183.95249292(89) |
| **** |
| αTheorized to also undergo β+β+ decay to 184W |
| 180W |
| 0+ |
| 2(2)×10−4 |
| |-id=Osmium-185 | 185Os | 184.95404597(89) | | EC | 185Re | 1/2− | | |-id=Osmium-185m1 | | IT | 185Os | 7/2− | | |-id=Osmium-185m2 | | IT | 185Os | 11/2+ | | |-id=Osmium-186 | 186Os | 185.95383757(82) | **** | α | 182W | 0+ | 0.0159(64) | |-id=Osmium-187 | 187OsUsed in rhenium-osmium dating | 186.95574957(79) | 1/2− | 0.0196(17) | |-id=Osmium-187m1 | | IT | 187Os | 7/2− | | |-id=Osmium-187m2 | | IT | 187Os | 11/2+ | | |-id=Osmium-188 | 188Os | 187.95583729(79) | 0+ | 0.1324(27) | |-id=Osmium-189 | 189Os | 188.95814595(72) | 3/2− | 0.1615(23) | |-id=Osmium-189m | | IT | 189Os | 9/2− | | |-id=Osmium-190 | 190Os | 189.95844544(70) | 0+ | 0.2626(20) | |-id=Osmium-190m | | IT | 190Os | 10− | | |-id=Osmium-191 | 191Os | 190.96092811(71) | | β− | 191Ir | 9/2− | | |-id=Osmium-191m | | IT | 191Os | 3/2− | | |-id=Osmium-192 | 192Os | 191.9614788(25) | 0+ | 0.4078(32) | |-id=Osmium-192m1 | IT
| 192Os |
|---|
| β−? |
| 192Ir |
| -id=Osmium-192m2 |
| | IT | 192Os | (20+) | | |-id=Osmium-193 | 193Os | 192.9641496(25) | | β− | 193Ir | 3/2− | | |-id=Osmium-193m | | IT | 193Os | (9/2−) | | |-id=Osmium-194 | 194Os | 193.9651794(26) | | β− | 194Ir | 0+ | | |-id=Osmium-195 | 195Os | 194.968318(60) | | β− | 195Ir | (3/2−) | | |-id=Osmium-195m | IT
| 195Os |
|---|
| β−? |
| 195Ir |
| -id=Osmium-196 |
| 196Os |
| 195.969643(43) |
| | β− | 196Ir | 0+ | | |-id=Osmium-197 | 197Os | 196.97308(22)# | | β− | 197Ir | 5/2−# | | |-id=Osmium-198 | 198Os | 197.97466(22)# | | β− | 198Ir | 0+ | | |-id=Osmium-199 | 199Os | 198.97824(22)# | | β− | 199Ir | 5/2−# | | |-id=Osmium-200 | 200Os | 199.98009(32)# | | β− | 200Ir | 0+ | | |-id=Osmium-201 | 201Os | 200.98407(32)# | [300ns] | β−? | 201Ir | 1/2−# | | |-id=Osmium-202 | 202Os | 201.98655(43)# | [300ns] | β−? | 202Ir | 0+ | | |-id=Osmium-203 | β−?
| 203Ir |
|---|
| β− n? |
| 202Ir |
References
Isotope masses from:
Isotopic compositions and standard atomic masses from:
Half-life, spin, and isomer data selected from the following sources.
References
- Flegenheimer, Juan. (2014). "The mystery of the disappearing isotope". Revista Virtual de Química.
- (2000). "The marine osmium isotope record". Terra Nova.
- (1993). "The osmium isotopic composition of the continental crust". Geochimica et Cosmochimica Acta.
- (2002). "Osmium Isotopes and Mantle Convection". Philosophical Transactions: Mathematical, Physical and Engineering Sciences.
- (2019). "Ocean Drilling Perspectives on Meteorite Impacts". Oceanography.
- (2005). "Direct Radiometric Dating of Hydrocarbon Deposits Using Rhenium-Osmium Isotopes". Science.
- (2009). "Anthropogenic osmium in rain and snow reveals global-scale atmospheric contamination". Proceedings of the National Academy of Sciences.
- (April 2014). "Alpha-decay of 184Os revealed by radiogenic 180W in meteorites: Half life determination and viability as geochronometer". Earth and Planetary Science Letters.
- (September 2014). "Cosmogenic 180W variations in meteorites and re-assessment of a possible 184Os–180W decay system". Geochimica et Cosmochimica Acta.
- (September 2018). "Excess 180W in IIAB iron meteorites: Identification of cosmogenic, radiogenic, and nucleosynthetic components". Earth Planet Sci Lett.
- (2023). "Decay spectroscopy at the two-proton drip line: Radioactivity of the new nuclides 160Os and 156W". Physics Letters B.
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