Isotopes of osmium

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Osmium (Os) has seven naturally-occurring isotopes, 5 of which are stable: ¹⁸⁷Os, ¹⁸⁸Os, ¹⁸⁹Os, ¹⁹⁰Os, and (most abundant) ¹⁹²Os. The other two, ¹⁸⁴Os and ¹⁸⁶Os, have enormously long half-lives and for practical purposes can be considered to be stable as well. ¹⁸⁷Os is the daughter of ¹⁸⁷Re (half-life 4.56 x 10¹⁰ years) and is most often measured in an ¹⁸⁷Os/¹⁸⁸Os ratio. This ratio, as well as the ¹⁸⁷Re/¹⁸⁷Os 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 K-T boundary that marks the extinction of the dinosaurs 65 million years ago.
Standard atomic mass: 190.23(3) u

[edit] Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
nuclide symbol	excitation energy			half-life	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
¹⁶²Os	76	86	161.98443(54)#	1.87(18) ms	0+
¹⁶³Os	76	87	162.98269(43)#	5.5(6) ms	7/2-#
¹⁶⁴Os	76	88	163.97804(22)	21(1) ms	0+
¹⁶⁵Os	76	89	164.97676(22)#	71(3) ms	(7/2-)
¹⁶⁶Os	76	90	165.972691(20)	216(9) ms	0+
¹⁶⁷Os	76	91	166.97155(8)	810(60) ms	3/2-#
¹⁶⁸Os	76	92	167.967804(13)	2.06(6) s	0+
¹⁶⁹Os	76	93	168.967019(27)	3.40(9) s	3/2-#
¹⁷⁰Os	76	94	169.963577(12)	7.46(23) s	0+
¹⁷¹Os	76	95	170.963185(20)	8.3(2) s	(5/2-)
¹⁷²Os	76	96	171.960023(16)	19.2(5) s	0+
¹⁷³Os	76	97	172.959808(16)	22.4(9) s	(5/2-)
¹⁷⁴Os	76	98	173.957062(12)	44(4) s	0+
¹⁷⁵Os	76	99	174.956946(15)	1.4(1) min	(5/2-)
¹⁷⁶Os	76	100	175.95481(3)	3.6(5) min	0+
¹⁷⁷Os	76	101	176.954965(17)	3.0(2) min	1/2-
¹⁷⁸Os	76	102	177.953251(18)	5.0(4) min	0+
¹⁷⁹Os	76	103	178.953816(19)	6.5(3) min	(1/2-)
¹⁸⁰Os	76	104	179.952379(22)	21.5(4) min	0+
¹⁸¹Os	76	105	180.95324(3)	105(3) min	1/2-
^181m1Os	48.9(2) keV			2.7(1) min	(7/2)-
^181m2Os	156.5(7) keV			316(18) ns	(9/2)+
¹⁸²Os	76	106	181.952110(23)	22.10(25) h	0+
¹⁸³Os	76	107	182.95313(5)	13.0(5) h	9/2+
^183mOs	170.71(5) keV			9.9(3) h	1/2-
¹⁸⁴Os	76	108	183.9524891(14)	STABLE [>56E+12 a]	0+	0.0002(1)
¹⁸⁵Os	76	109	184.9540423(14)	93.6(5) d	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	76	110	185.9538382(15)	2.0(11)E+15 a	0+	0.0159(3)
¹⁸⁷Os	76	111	186.9557505(15)	STABLE	1/2-	0.0196(2)
¹⁸⁸Os	76	112	187.9558382(15)	STABLE	0+	0.1324(8)
¹⁸⁹Os	76	113	188.9581475(16)	STABLE	3/2-	0.1615(5)
^189mOs	30.812(15) keV			5.81(6) h	9/2-
¹⁹⁰Os	76	114	189.9584470(16)	STABLE	0+	0.2626(2)
^190mOs	1705.4(2) keV			9.9(1) min	(10)-
¹⁹¹Os	76	115	190.9609297(16)	15.4(1) d	9/2-
^191mOs	74.382(3) keV			13.10(5) h	3/2-
¹⁹²Os	76	116	191.9614807(27)	STABLE [>9.8E+12 a]	0+	0.4078(19)
^192mOs	2015.40(11) keV			5.9(1) s	(10-)
¹⁹³Os	76	117	192.9641516(27)	30.11(1) h	3/2-
¹⁹⁴Os	76	118	193.9651821(28)	6.0(2) a	0+
¹⁹⁵Os	76	119	194.96813(54)	6.5 min	3/2-#
¹⁹⁶Os	76	120	195.96964(4)	34.9(2) min	0+
¹⁹⁷Os	76	121		2.8(6) min

[edit] 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.

[edit] References

Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683-800, (2003) and Atomic Weights Revised (2005).
Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
- Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3-128 (2003).
- National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).
- David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.