Isotopes of osmium

Osmium (₇₆Os) has seven naturally occurring isotopes, six 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.

Main isotopes of osmium (₇₆Os)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct ^184Os 0.02% stable ^185Os syn 93.6 d ε ^185Re ^186Os 1.59% 2.0×10^15 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(Os)	190.23(3)[1]

There are also 30 artificial radioisotopes,[2] 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 isomers, the longest-lived of which is ^191mOs with a half-life of 13.10 hours.

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.[3] The average marine ¹⁸⁷Os/¹⁸⁸Os ratio in oceans is 1.06.[3] 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.[3] Being a descendent of ¹⁸⁷Re, ¹⁸⁷Os can be radiogenically formed by beta decay.[4] This decay has actually pushed the ¹⁸⁷Os/¹⁸⁸Os ratio of the Bulk silicate earth (Earth minus the core) by 33%.[5] 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.[4] 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.[4] 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 cab observed in the marine sediment that is deposited, and eventually lithified in that time period.[6] 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.[7] 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.[3]

Os isotope ratios may also be used as a signal of anthropogenic impact.[8] 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.[8] 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.[8] 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.[8] This increase in effect is thought to be due to the introduction of anthropogenic airborne Os into precipitation.

Os isotope ratios may also be used as a signal of anthropogenic impact.[8] 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 (3). 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.[8] 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.[8] This increase in effect is thought to be due to the introduction of anthropogenic airborne Os into precipitation.

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da) [n 2][n 3]	Half-life [n 4]	Decay mode [n 5]	Daughter isotope [n 6]	Spin and parity [n 7][n 8]	Natural abundance (mole fraction)
	Excitation energy							Normal proportion	Range of variation
^161Os	76	85		0.64(6) ms	α	^157W
^162Os	76	86	161.98443(54)#	1.87(18) ms	α	^158W	0+
^163Os	76	87	162.98269(43)#	5.5(6) ms	α	^159W	7/2−#
					β^+, p (rare)	^162W
					β^+ (rare)	^163Re
^164Os	76	88	163.97804(22)	21(1) ms	α (98%)	^160W	0+
					β^+ (2%)	^164Re
^165Os	76	89	164.97676(22)#	71(3) ms	α (60%)	^161W	(7/2−)
					β^+ (40%)	^165Re
^166Os	76	90	165.972691(20)	216(9) ms	α (72%)	^162W	0+
					β^+ (28%)	^166Re
^167Os	76	91	166.97155(8)	810(60) ms	α (67%)	^163W	3/2−#
					β^+ (33%)	^167Re
^168Os	76	92	167.967804(13)	2.06(6) s	β^+ (51%)	^168Re	0+
					α (49%)	^164W
^169Os	76	93	168.967019(27)	3.40(9) s	β^+ (89%)	^169Re	3/2−#
					α (11%)	^165W
^170Os	76	94	169.963577(12)	7.46(23) s	β^+ (91.4%)	^170Re	0+
					α (8.6%)	^166W
^171Os	76	95	170.963185(20)	8.3(2) s	β^+ (98.3%)	^171Re	(5/2−)
					α (1.7%)	^167W
^172Os	76	96	171.960023(16)	19.2(5) s	β^+ (98.9%)	^172Re	0+
					α (1.1%)	^168W
^173Os	76	97	172.959808(16)	22.4(9) s	β^+ (99.6%)	^173Re	(5/2−)
					α (.4%)	^169W
^174Os	76	98	173.957062(12)	44(4) s	β^+ (99.97%)	^174Re	0+
					α (.024%)	^170W
^175Os	76	99	174.956946(15)	1.4(1) min	β^+	^175Re	(5/2−)
^176Os	76	100	175.95481(3)	3.6(5) min	β^+	^176Re	0+
^177Os	76	101	176.954965(17)	3.0(2) min	β^+	^177Re	1/2−
^178Os	76	102	177.953251(18)	5.0(4) min	β^+	^178Re	0+
^179Os	76	103	178.953816(19)	6.5(3) min	β^+	^179Re	(1/2−)
^180Os	76	104	179.952379(22)	21.5(4) min	β^+	^180Re	0+
^181Os	76	105	180.95324(3)	105(3) min	β^+	^181Re	1/2−
^181m1Os	48.9(2) keV			2.7(1) min	β^+	^181Re	(7/2)−
^181m2Os	156.5(7) keV			316(18) ns			(9/2)+
^182Os	76	106	181.952110(23)	22.10(25) h	EC	^182Re	0+
^183Os	76	107	182.95313(5)	13.0(5) h	β^+	^183Re	9/2+
^183mOs	170.71(5) keV			9.9(3) h	β^+ (85%)	^183Re	1/2−
					IT (15%)	^183Os
^184Os	76	108	183.9524891(14)	Observationally Stable[n 9]			0+	2(1)×10^−4
^185Os	76	109	184.9540423(14)	93.6(5) d	EC	^185Re	1/2−
^185m1Os	102.3(7) keV			3.0(4) μs			(7/2−)#
^185m2Os	275.7(8) keV			0.78(5) μs			(11/2+)
^186Os[n 10]	76	110	185.9538382(15)	2.0(11)×10^15 y	α	^182W	0+	0.0159(3)
^187Os[n 11]	76	111	186.9557505(15)	Observationally Stable[n 12]			1/2−	0.0196(2)
^188Os[n 11]	76	112	187.9558382(15)	Observationally Stable[n 13]			0+	0.1324(8)
^189Os	76	113	188.9581475(16)	Observationally Stable[n 14]			3/2−	0.1615(5)
^189mOs	30.812(15) keV			5.81(6) h	IT	^189Os	9/2−
^190Os	76	114	189.9584470(16)	Observationally Stable[n 15]			0+	0.2626(2)
^190mOs	1705.4(2) keV			9.9(1) min	IT	^190Os	(10)−
^191Os	76	115	190.9609297(16)	15.4(1) d	β^−	^191Ir	9/2−
^191mOs	74.382(3) keV			13.10(5) h	IT	^191Os	3/2−
^192Os	76	116	191.9614807(27)	Observationally Stable[n 16]			0+	0.4078(19)
^192mOs	2015.40(11) keV			5.9(1) s	IT (87%)	^192Os	(10−)
					β^− (13%)	^192Ir
^193Os	76	117	192.9641516(27)	30.11(1) h	β^−	^193Ir	3/2−
^194Os	76	118	193.9651821(28)	6.0(2) y	β^−	^194Ir	0+
^195Os	76	119	194.96813(54)	6.5 min	β^−	^195Ir	3/2−#
^196Os	76	120	195.96964(4)	34.9(2) min	β^−	^196Ir	0+
^197Os	76	121		2.8(6) min

1. ^mOs – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. Bold half-life – nearly stable, half-life longer than age of universe.
5. Modes of decay:

   EC:	Electron capture
   IT:	Isomeric transition
   p:	Proton emission

6. Bold symbol as daughter – Daughter product is stable.
7. ( ) spin value – Indicates spin with weak assignment arguments.
8. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
9. Believed to undergo α decay to ¹⁸⁰W or β⁺β⁺ decay to ¹⁸⁴W with a half-life over 56×10¹² years
10. primordial radionuclide
11. Used in rhenium-osmium dating
12. Believed to undergo α decay to ¹⁸³W
13. Believed to undergo α decay to ¹⁸⁴W
14. Believed to undergo α decay to ¹⁸⁵W
15. Believed to undergo α decay to ¹⁸⁶W
16. Believed to undergo α decay to ¹⁸⁸W or β⁻β⁻ decay to ¹⁹²Pt with a half-life over 9.8×10¹² years

References

1. Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
2. Flegenheimer, Juan (2014). "The mystery of the disappearing isotope". Revista Virtual de Química. 6 (4): 1139–1142. doi:10.5935/1984-6835.20140073. Archived from the original (PDF) on 2015-06-19. Retrieved 2014-06-13.
3. Peucker-Ehrenbrink, B.; Ravizza, G. (2000). "The marine osmium isotope record". Terra Nova. 12 (5): 205–219. Bibcode:2000TeNov..12..205P. doi:10.1046/j.1365-3121.2000.00295.x.
4. Esser, Bradley K.; Turekian, Karl K. (1993). "The osmium isotopic composition of the continental crust". Geochimica et Cosmochimica Acta. 57 (13): 3093–3104. Bibcode:1993GeCoA..57.3093E. doi:10.1016/0016-7037(93)90296-9.
5. Hauri, Erik H. (2002). "Osmium Isotopes and Mantle Convection" (PDF). Philosophical Transactions: Mathematical, Physical and Engineering Sciences. 360 (1800): 2371–2382. Bibcode:2002RSPTA.360.2371H. doi:10.1098/rsta.2002.1073. JSTOR 3558902. PMID 12460472. S2CID 18451805.
6. Lowery, Chistopher; Morgan, Joanna; Gulick, Sean; Bralower, Timothy; Christeson, Gail (2019). "Ocean Drilling Perspectives on Meteorite Impacts". Oceanography. 32: 120–134. doi:10.5670/oceanog.2019.133.
7. Selby, D.; Creaser, R. A. (2005). "Direct Radiometric Dating of Hydrocarbon Deposits Using Rhenium-Osmium Isotopes". Science. 308 (5726): 1293–1295. Bibcode:2005Sci...308.1293S. doi:10.1126/science.1111081. PMID 15919988. S2CID 41419594.
8. Chen, C.; Sedwick, P. N.; Sharma, M. (2009). "Anthropogenic osmium in rain and snow reveals global-scale atmospheric contamination". Proceedings of the National Academy of Sciences. 106 (19): 7724–7728. Bibcode:2009PNAS..106.7724C. doi:10.1073/pnas.0811803106. PMC 2683094. PMID 19416862.

• Isotope masses from:
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
• Isotopic compositions and standard atomic masses from:
  • de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
  • Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary.
• Half-life, spin, and isomer data selected from the following sources.
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
  • National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
  • Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.