Osmium (₇₆Os) has seven naturally occurring

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numb ...

s, 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 Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable at ...

(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 ¹⁸⁷ Re (

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

rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wales ...

s. 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

craton A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging an ...

s. However, the most notable application of Os in dating has been in conjunction with

iridium Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of ...

, to analyze the layer of

shocked quartz Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure (but limited temperature), the crystalline structure of quartz is deformed along planes inside the crystal. These pl ...

along the Cretaceous–Paleogene boundary that marks the extinction of the

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s 66 million years ago. There are also 30 artificial

radioisotope A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...

s, the longest-lived of which is ¹⁹⁴Os with a half-life of six years; all others have half-lives under 94 days. There are also nine known

nuclear isomer A nuclear isomer is a metastable state of an atomic nucleus, in which one or more nucleons (protons or neutrons) occupy higher energy levels than in the ground state of the same nucleus. "Metastable" describes nuclei whose excited states have ...

s, 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 Stable nuclides are nuclides that are not radioactive and so (unlike radionuclides) do not spontaneously undergo radioactive decay. When such nuclides are referred to in relation to specific elements, they are usually termed stable isotopes. Th ...

, meaning that they are predicted to be radioactive but no actual decay has been observed.

Uses of osmium isotopes

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 derived 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. Being a descendent of ¹⁸⁷Re, ¹⁸⁷Os can be

radiogenic A radiogenic nuclide is a nuclide that is produced by a process of radioactive decay. It may itself be radioactive (a radionuclide) or stable (a stable nuclide). Radiogenic nuclides (more commonly referred to as radiogenic isotopes) form some ...

ally formed by beta decay. This decay has actually pushed the ¹⁸⁷Os/¹⁸⁸Os ratio of the Bulk silicate earth (Earth minus the

core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...

) 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. Within the mantle however, the uneven response of Re and Os results in these mantle, and melted materials being depleted in Re, and do not allow for them to accumulate ¹⁸⁷Os like the continental material. The input of both materials in the marine environment results in the observed ¹⁸⁷Os/¹⁸⁸Os of the oceans and has fluctuated greatly over the history of our planet. 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 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. 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 NO_x and CO₂, 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) which is heavily depleted (3, 7). The effect of anthropogenic Os can be seen best by comparing aquatic Os ratios and local sediments or deeper waters. Impacted surface waters tend to have depleted values compared to deep ocean and sediments beyond the limit of what is expected from cosmic inputs. This increase in effect is thought to be due to the introduction of anthropogenic airborne Os into precipitation. The long half-life of ¹⁸⁴Os with respect to alpha decay to ¹⁸⁰W has been proposed as a

radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares ...

method for osmium-rich rocks or for differentiation of a planetary core.

List of isotopes

, - , ¹⁶¹Os , style="text-align:right" , 76 , style="text-align:right" , 85 , , 0.64(6) ms , α , ¹⁵⁷W , , , , - , ¹⁶²Os , style="text-align:right" , 76 , style="text-align:right" , 86 , 161.98443(54)# , 1.87(18) ms , α , ¹⁵⁸W , 0+ , , , - , rowspan=3, ¹⁶³Os , rowspan=3 style="text-align:right" , 76 , rowspan=3 style="text-align:right" , 87 , rowspan=3, 162.98269(43)# , rowspan=3, 5.5(6) ms , α , ¹⁵⁹W , rowspan=3, 7/2−# , rowspan=3, , rowspan=3, , - , β⁺, p (rare) , ¹⁶²W , - , β⁺ (rare) , ¹⁶³Re , - , rowspan=2, ¹⁶⁴Os , rowspan=2 style="text-align:right" , 76 , rowspan=2 style="text-align:right" , 88 , rowspan=2, 163.97804(22) , rowspan=2, 21(1) ms , α (98%) , ¹⁶⁰W , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁺ (2%) , ¹⁶⁴Re , - , rowspan=2, ¹⁶⁵Os , rowspan=2 style="text-align:right" , 76 , rowspan=2 style="text-align:right" , 89 , rowspan=2, 164.97676(22)# , rowspan=2, 71(3) ms , α (60%) , ¹⁶¹W , rowspan=2, (7/2−) , rowspan=2, , rowspan=2, , - , β⁺ (40%) , ¹⁶⁵Re , - , rowspan=2, ¹⁶⁶Os , rowspan=2 style="text-align:right" , 76 , rowspan=2 style="text-align:right" , 90 , rowspan=2, 165.972691(20) , rowspan=2, 216(9) ms , α (72%) , ¹⁶²W , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , β⁺ (28%) , ¹⁶⁶Re , - , rowspan=2, ¹⁶⁷Os , rowspan=2 style="text-align:right" , 76 , rowspan=2 style="text-align:right" , 91 , rowspan=2, 166.97155(8) , rowspan=2, 810(60) ms , α (67%) , ¹⁶³W , rowspan=2, 3/2−# , rowspan=2, , rowspan=2, , - , β⁺ (33%) , ¹⁶⁷Re , - , rowspan=2, ¹⁶⁸Os , rowspan=2 style="text-align:right" , 76 , rowspan=2 style="text-align:right" , 92 , rowspan=2, 167.967804(13) , rowspan=2, 2.06(6) s , β⁺ (51%) , ¹⁶⁸Re , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , α (49%) , ¹⁶⁴W , - , rowspan=2, ¹⁶⁹Os , rowspan=2 style="text-align:right" , 76 , rowspan=2 style="text-align:right" , 93 , rowspan=2, 168.967019(27) , rowspan=2, 3.40(9) s , β⁺ (89%) , ¹⁶⁹Re , rowspan=2, 3/2−# , rowspan=2, , rowspan=2, , - , α (11%) , ¹⁶⁵W , - , rowspan=2, ¹⁷⁰Os , rowspan=2 style="text-align:right" , 76 , rowspan=2 style="text-align:right" , 94 , rowspan=2, 169.963577(12) , rowspan=2, 7.46(23) s , β⁺ (91.4%) , ¹⁷⁰Re , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , α (8.6%) , ¹⁶⁶W , - , rowspan=2, ¹⁷¹Os , rowspan=2 style="text-align:right" , 76 , rowspan=2 style="text-align:right" , 95 , rowspan=2, 170.963185(20) , rowspan=2, 8.3(2) s , β⁺ (98.3%) , ¹⁷¹Re , rowspan=2, (5/2−) , rowspan=2, , rowspan=2, , - , α (1.7%) , ¹⁶⁷W , - , rowspan=2, ¹⁷²Os , rowspan=2 style="text-align:right" , 76 , rowspan=2 style="text-align:right" , 96 , rowspan=2, 171.960023(16) , rowspan=2, 19.2(5) s , β⁺ (98.9%) , ¹⁷²Re , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , α (1.1%) , ¹⁶⁸W , - , rowspan=2, ¹⁷³Os , rowspan=2 style="text-align:right" , 76 , rowspan=2 style="text-align:right" , 97 , rowspan=2, 172.959808(16) , rowspan=2, 22.4(9) s , β⁺ (99.6%) , ¹⁷³Re , rowspan=2, (5/2−) , rowspan=2, , rowspan=2, , - , α (.4%) , ¹⁶⁹W , - , rowspan=2, ¹⁷⁴Os , rowspan=2 style="text-align:right" , 76 , rowspan=2 style="text-align:right" , 98 , rowspan=2, 173.957062(12) , rowspan=2, 44(4) s , β⁺ (99.97%) , ¹⁷⁴Re , rowspan=2, 0+ , rowspan=2, , rowspan=2, , - , α (.024%) , ¹⁷⁰W , - , ¹⁷⁵Os , style="text-align:right" , 76 , style="text-align:right" , 99 , 174.956946(15) , 1.4(1) min , β⁺ , ¹⁷⁵Re , (5/2−) , , , - , ¹⁷⁶Os , style="text-align:right" , 76 , style="text-align:right" , 100 , 175.95481(3) , 3.6(5) min , β⁺ , ¹⁷⁶Re , 0+ , , , - , ¹⁷⁷Os , style="text-align:right" , 76 , style="text-align:right" , 101 , 176.954965(17) , 3.0(2) min , β⁺ , ¹⁷⁷Re , 1/2− , , , - , ¹⁷⁸Os , style="text-align:right" , 76 , style="text-align:right" , 102 , 177.953251(18) , 5.0(4) min , β⁺ , ¹⁷⁸Re , 0+ , , , - , ¹⁷⁹Os , style="text-align:right" , 76 , style="text-align:right" , 103 , 178.953816(19) , 6.5(3) min , β⁺ , ¹⁷⁹Re , (1/2−) , , , - , ¹⁸⁰Os , style="text-align:right" , 76 , style="text-align:right" , 104 , 179.952379(22) , 21.5(4) min , β⁺ , ¹⁸⁰Re , 0+ , , , - , ¹⁸¹Os , style="text-align:right" , 76 , style="text-align:right" , 105 , 180.95324(3) , 105(3) min , β⁺ , ¹⁸¹Re , 1/2− , , , - , style="text-indent:1em" , ^181m1Os , colspan="3" style="text-indent:2em" , 48.9(2) keV , 2.7(1) min , β⁺ , ¹⁸¹Re , (7/2)− , , , - , style="text-indent:1em" , ^181m2Os , colspan="3" style="text-indent:2em" , 156.5(7) keV , 316(18) ns , , , (9/2)+ , , , - , ¹⁸²Os , style="text-align:right" , 76 , style="text-align:right" , 106 , 181.952110(23) , 22.10(25) h , EC , ¹⁸²Re , 0+ , , , - , ¹⁸³Os , style="text-align:right" , 76 , style="text-align:right" , 107 , 182.95313(5) , 13.0(5) h , β⁺ , ¹⁸³Re , 9/2+ , , , - , rowspan=2 style="text-indent:1em" , ^183mOs , rowspan=2 colspan="3" style="text-indent:2em" , 170.71(5) keV , rowspan=2, 9.9(3) h , β⁺ (85%) , ¹⁸³Re , rowspan=2, 1/2− , rowspan=2, , rowspan=2, , - , IT (15%) , ¹⁸³Os , - , ¹⁸⁴Os , style="text-align:right" , 76 , style="text-align:right" , 108 , 183.9524891(14) , 1.12(23)×10¹³ y , αTheorized to also undergo β⁺β⁺ decay to ¹⁸⁴W , ''¹⁸⁰W'' , 0+ , 2(1)×10⁻⁴ , , - , ¹⁸⁵Os , style="text-align:right" , 76 , style="text-align:right" , 109 , 184.9540423(14) , 93.6(5) d , EC , ¹⁸⁵Re , 1/2− , , , - , style="text-indent:1em" , ^185m1Os , colspan="3" style="text-indent:2em" , 102.3(7) keV , 3.0(4) μs , , , (7/2−)# , , , - , style="text-indent:1em" , ^185m2Os , colspan="3" style="text-indent:2em" , 275.7(8) keV , 0.78(5) μs , , , (11/2+) , , , - , ¹⁸⁶Os primordial radionuclide , style="text-align:right" , 76 , style="text-align:right" , 110 , 185.9538382(15) , 2.0(11)×10¹⁵ y , α , ¹⁸²W , 0+ , 0.0159(3) , , - , ¹⁸⁷OsUsed in rhenium-osmium dating , style="text-align:right" , 76 , style="text-align:right" , 111 , 186.9557505(15) , colspan=3 align=center, Observationally StableBelieved to undergo α decay to ¹⁸³W , 1/2− , 0.0196(2) , , - , ¹⁸⁸Os , style="text-align:right" , 76 , style="text-align:right" , 112 , 187.9558382(15) , colspan=3 align=center, Observationally StableBelieved to undergo α decay to ¹⁸⁴W , 0+ , 0.1324(8) , , - , ¹⁸⁹Os , style="text-align:right" , 76 , style="text-align:right" , 113 , 188.9581475(16) , colspan=3 align=center, Observationally StableBelieved to undergo α decay to ¹⁸⁵W , 3/2− , 0.1615(5) , , - , style="text-indent:1em" , ^189mOs , colspan="3" style="text-indent:2em" , 30.812(15) keV , 5.81(6) h , IT , ¹⁸⁹Os , 9/2− , , , - , ¹⁹⁰Os , style="text-align:right" , 76 , style="text-align:right" , 114 , 189.9584470(16) , colspan=3 align=center, Observationally StableBelieved to undergo α decay to ¹⁸⁶W , 0+ , 0.2626(2) , , - , style="text-indent:1em" , ^190mOs , colspan="3" style="text-indent:2em" , 1705.4(2) keV , 9.9(1) min , IT , ¹⁹⁰Os , (10)− , , , - , ¹⁹¹Os , style="text-align:right" , 76 , style="text-align:right" , 115 , 190.9609297(16) , 15.4(1) d , β⁻ , ¹⁹¹Ir , 9/2− , , , - , style="text-indent:1em" , ^191mOs , colspan="3" style="text-indent:2em" , 74.382(3) keV , 13.10(5) h , IT , ¹⁹¹Os , 3/2− , , , - , ¹⁹²Os , style="text-align:right" , 76 , style="text-align:right" , 116 , 191.9614807(27) , colspan=3 align=center, Observationally StableBelieved to undergo α decay to ¹⁸⁸W or β⁻β⁻ decay to ¹⁹²Pt with a half-life over 9.8×10¹² years , 0+ , 0.4078(19) , , - , rowspan=2 style="text-indent:1em" , ^192mOs , rowspan=2 colspan="3" style="text-indent:2em" , 2015.40(11) keV , rowspan=2, 5.9(1) s , IT (87%) , ¹⁹²Os , rowspan=2, (10−) , rowspan=2, , rowspan=2, , - , β⁻ (13%) , ¹⁹²Ir , - , ¹⁹³Os , style="text-align:right" , 76 , style="text-align:right" , 117 , 192.9641516(27) , 30.11(1) h , β⁻ , ¹⁹³Ir , 3/2− , , , - , ¹⁹⁴Os , style="text-align:right" , 76 , style="text-align:right" , 118 , 193.9651821(28) , 6.0(2) y , β⁻ , ¹⁹⁴Ir , 0+ , , , - , ¹⁹⁵Os , style="text-align:right" , 76 , style="text-align:right" , 119 , 194.96813(54) , 6.5 min , β⁻ , ¹⁹⁵Ir , 3/2−# , , , - , ¹⁹⁶Os , style="text-align:right" , 76 , style="text-align:right" , 120 , 195.96964(4) , 34.9(2) min , β⁻ , ¹⁹⁶Ir , 0+ , , , - , ¹⁹⁷Os , style="text-align:right" , 76 , style="text-align:right" , 121 , , 2.8(6) min , , , , ,

References

* Isotope masses from: ** * Isotopic compositions and standard atomic masses from: ** ** * Half-life, spin, and isomer data selected from the following sources. ** ** ** {{Navbox element isotopes Osmium Osmium