Isotopes of selenium

Isotopes of selenium (₃₄Se)

Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 72Se synth 8.4 d ε 72As γ – 74Se 0.860% stable 75Se synth 119.8 d ε 75As γ – 76Se 9.23% stable 77Se 7.60% stable 78Se 23.7% stable 79Se trace 3.27×105 y β− 79Br 80Se 49.8% stable 82Se 8.82% 8.76×1019 y β−β− 82Kr
Standard atomic weight Ar°(Se)
	78.971±0.008 78.971±0.008 (abridged)

The chemical element selenium (₃₄Se) has six naturally occurring isotopes, five of which are stable: ⁷⁴Se, ⁷⁶Se, ⁷⁷Se, ⁷⁸Se, and ⁸⁰Se. The last three also occur as fission products, along with ⁷⁹Se, which has a half-life of 327,000 years, and ⁸²Se, which has a very long half-life (~10²⁰ years, decaying via double beta decay to ⁸²Kr) and for practical purposes can be considered to be stable. There are 23 other unstable isotopes that have been characterized, the longest-lived being ⁷⁹Se with a half-life 327,000 years, ⁷⁵Se with a half-life of 120 days, and ⁷²Se with a half-life of 8.40 days. Of the other isotopes, ⁷³Se has the longest half-life, 7.15 hours; most others have half-lives not exceeding 38 seconds.

List of isotopes

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)	daughter isotope(s)	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
65Se	34	31	64.96466(64)#	<50 ms	β+ (>99.9%)	65As	3/2−#
					β+, p (<.1%)	64Ge
66Se	34	32	65.95521(32)#	33(12) ms	β+	66As	0+
67Se	34	33	66.95009(21)#	133(11) ms	β+ (99.5%)	67As	5/2−#
					β+, p (.5%)	66Ge
68Se	34	34	67.94180(4)	35.5(7) s	β+	68As	0+
69Se	34	35	68.93956(4)	27.4(2) s	β+ (99.955%)	69As	(1/2−)
					β+, p (.045%)	68Ge
69m1Se	39.4(1) keV			2.0(2) µs			5/2−
69m2Se	573.9(10) keV			955(16) ns			9/2+
70Se	34	36	69.93339(7)	41.1(3) min	β+	70As	0+
71Se	34	37	70.93224(3)	4.74(5) min	β+	71As	5/2−
71m1Se	48.79(5) keV			5.6(7) µs			1/2− to 9/2−
71m2Se	260.48(10) keV			19.0(5) µs			(9/2)+
72Se	34	38	71.927112(13)	8.40(8) d	EC	72As	0+
73Se	34	39	72.926765(11)	7.15(8) h	β+	73As	9/2+
73mSe	25.71(4) keV			39.8(13) min	IT	73Se	3/2−
					β+	73As
74Se	34	40	73.9224764(18)	Observationally Stable			0+	0.0089(4)
75Se	34	41	74.9225234(18)	119.779(4) d	EC	75As	5/2+
76Se	34	42	75.9192136(18)	Stable			0+	0.0937(29)
77Se	34	43	76.9199140(18)	Stable			1/2−	0.0763(16)
77mSe	161.9223(7) keV			17.36(5) s	IT	77Se	7/2+
78Se	34	44	77.9173091(18)	Stable			0+	0.2377(28)
79Se	34	45	78.9184991(18)	3.27(8)×105 y	β−	79Br	7/2+
79mSe	95.77(3) keV			3.92(1) min	IT (99.944%)	79Se	1/2−
					β− (.056%)	79Br
80Se	34	46	79.9165213(21)	Observationally Stable			0+	0.4961(41)
81Se	34	47	80.9179925(22)	18.45(12) min	β−	81Br	1/2−
81mSe	102.99(6) keV			57.28(2) min	IT (99.948%)	81Se	7/2+
					β− (.052%)	81Br
82Se	34	48	81.9166994(22)	0.97(5)×1020 y	β−β−	82Kr	0+	0.0873(22)
83Se	34	49	82.919118(4)	22.3(3) min	β−	83Br	9/2+
83mSe	228.50(20) keV			70.1(4) s	β−	83Br	1/2−
84Se	34	50	83.918462(16)	3.1(1) min	β−	84Br	0+
85Se	34	51	84.92225(3)	31.7(9) s	β−	85Br	(5/2+)#
86Se	34	52	85.924272(17)	15.3(9) s	β−	86Br	0+
87Se	34	53	86.92852(4)	5.50(12) s	β− (99.64%)	87Br	(5/2+)#
					β−, n (.36%)	86Br
88Se	34	54	87.93142(5)	1.53(6) s	β− (99.01%)	88Br	0+
					β−, n (.99%)	88Br
89Se	34	55	88.93645(32)#	0.41(4) s	β− (92.2%)	89Br	(5/2+)#
					β−, n (7.8%)	88Br
90Se	34	56	89.93996(43)#	300# ms [>300 ns]	β−, n	89Br	0+
					β−	90Br
91Se	34	57	90.94596(54)#	270(50) ms	β− (79%)	91Br	1/2+#
					β−, n	90Br
92Se	34	58	91.94992(64)#	100# ms [>300 ns]	β−	92Br	0+
93Se	34	59	92.95629(86)#	50# ms [>300 ns]			1/2+#
94Se	34	60	93.96049(86)#	20# ms [>300 ns]			0+

Notes

• The precision of the isotope abundances and atomic mass is limited through variations. The given ranges should be applicable to any normal terrestrial material.
• 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.

See also

• Selenium
• Selenium-79

References

• 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. Archived from the original (PDF) on 2008-09-23. {{cite journal}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
• 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. {{cite journal}}: Unknown parameter |laysummary= ignored (help)
• 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. Archived from the original (PDF) on 2008-09-23. {{cite journal}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005. {{cite web}}: Check date values in: |accessdate= (help)
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide (ed.). CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9. {{cite book}}: Unknown parameter |nopp= ignored (|no-pp= suggested) (help)