Isotopes of osmium

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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)×1015 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. ↑ 6.0 6.1 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

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  • Isotope masses from:
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  • Isotopic compositions and standard atomic masses from:
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  • Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
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Isotopes of rhenium Isotopes of osmium Isotopes of iridium
Table of nuclides
Isotopes of the chemical elements
1
H		 2
He
3
Li		 4
Be		 5
B		 6
C		 7
N		 8
O		 9
F		 10
Ne
11
Na		 12
Mg		 13
Al		 14
Si		 15
P		 16
S		 17
Cl		 18
Ar
19
K		 20
Ca		 21
Sc		 22
Ti		 23
V		 24
Cr		 25
Mn		 26
Fe		 27
Co		 28
Ni		 29
Cu		 30
Zn		 31
Ga		 32
Ge		 33
As		 34
Se		 35
Br		 36
Kr
37
Rb		 38
Sr		 39
Y		 40
Zr		 41
Nb		 42
Mo		 43
Tc		 44
Ru		 45
Rh		 46
Pd		 47
Ag		 48
Cd		 49
In		 50
Sn		 51
Sb		 52
Te		 53
I		 54
Xe
55
Cs		 56
Ba		 1 asterisk 72
Hf		 73
Ta		 74
W		 75
Re		 76
Os		 77
Ir		 78
Pt		 79
Au		 80
Hg		 81
Tl		 82
Pb		 83
Bi		 84
Po		 85
At		 86
Rn
87
Fr		 88
Ra		 2 asterisks 104
Rf		 105
Db		 106
Sg		 107
Bh		 108
Hs		 109
Mt		 110
Ds		 111
Rg		 112
Cn		 113
Uut		 114
Fl		 115
Uup		 116
Lv		 117
Uus		 118
Uuo
1 asterisk 57
La		 58
Ce		 59
Pr		 60
Nd		 61
Pm		 62
Sm		 63
Eu		 64
Gd		 65
Tb		 66
Dy		 67
Ho		 68
Er		 69
Tm		 70
Yb		 71
Lu
2 asterisks 89
Ac		 90
Th		 91
Pa		 92
U		 93
Np		 94
Pu		 95
Am		 96
Cm		 97
Bk		 98
Cf		 99
Es		 100
Fm		 101
Md		 102
No		 103
Lr
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