Isotopes of osmium

Osmium (Os) 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,^[1] 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.

Relative atomic mass: 190.23(3).

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life[n 1]	decay mode(s)[2][n 2]	daughter isotope(s)[n 3]	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
^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%)	^176W
^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 4]			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 5]	76	110	185.9538382(15)	2.0(11)×10^15 y	α	^182W	0+	0.0159(3)
^187Os[n 6]	76	111	186.9557505(15)	Observationally Stable[n 7]			1/2−	0.0196(2)
^188Os[n 6]	76	112	187.9558382(15)	Observationally Stable[n 8]			0+	0.1324(8)
^189Os	76	113	188.9581475(16)	Observationally Stable[n 9]			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 10]			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 11]			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. Bold for isotopes with half-lives longer than the age of the universe (nearly stable)
2. Abbreviations:
   EC: Electron capture
   IT: Isomeric transition
3. Bold for stable isotopes, bold italics for nearly stable isotopes (half-life longer than the age of the universe)
4. Believed to undergo α decay to ¹⁸⁰W or β⁺β⁺ decay to ¹⁸⁴W with a half-life over 56×10¹² years
5. primordial radionuclide
6. Used in rhenium-osmium dating
7. Believed to undergo α decay to ¹⁸³W
8. Believed to undergo α decay to ¹⁸⁴W
9. Believed to undergo α decay to ¹⁸⁵W
10. Believed to undergo α decay to ¹⁸⁶W
11. Believed to undergo α decay to ¹⁸⁸W or β⁻β⁻ decay to ¹⁹²Pt with a half-life over 9.8×10¹² years

Notes

• Evaluated isotopic composition is for most but not all commercial samples.
• The precision of the isotope abundances and atomic mass is limited through variations. The given ranges should be applicable to any normal terrestrial material.
• Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.

References

1. Flegenheimer, Juan (2014). "The mystery of the disappearing isotope" (PDF). Revista Virtual de Química 6 (4): 1139–1142.
2. "Universal Nuclide Chart". nucleonica. (registration required (help)).

• Isotope masses from:
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). 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:
  • J. R. de Laeter; J. K. Böhlke; P. De Bièvre; H. Hidaka; H. S. Peiser; K. J. R. Rosman; P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry 75 (6): 683–800. doi:10.1351/pac200375060683.
  • M. E. Wieser (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. See editing notes on this article's talk page.
  • G. Audi; A. H. Wapstra; C. Thibault; J. Blachot; O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005.
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9.