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Isotopes of selenium

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Source updated June 17, 2026

Selenium has six natural isotopes that occur in significant quantities, along with the trace isotope ⁷⁹Se, which occurs in minute quantities in uranium ores. Five of these isotopes are stable: ⁷⁴Se, ⁷⁶Se, ⁷⁷Se, ⁷⁸Se, and ⁸⁰Se. The last three also occur as fission products, along with ⁷⁹Se, which has a half-life about 330,000 years, and ⁸²Se, which has the very long half-life of 8.76×10¹⁹ years as it decays via double beta decay to krypton-82 and for practical purposes can be considered to be stable. There are 23 other unstable isotopes that have been characterized, the longest-lived after ⁷⁹Se being ⁷⁵Se with its half-life 119.78 days, ⁷²Se at 8.40 days, and ⁷³Se at 7.15 hours. The others are all under an hour and most do not exceed 38 seconds.

01List of isotopes

Nuclide	Z	N	Isotopic mass (Da)	Discovery year	Half-life	Decay mode	Daughter isotope	Spin and parity	Natural abundance (mole fraction)
Nuclide	Excitation energy			Discovery year	Half-life	Decay mode	Daughter isotope	Spin and parity	Normal proportion	Range of variation
⁶³Se	34	29	62.98191(54)#	2016	13.2(39) ms	β⁺, p	⁶²Ge	3/2−#
⁶³Se	34	29	62.98191(54)#	2016	13.2(39) ms	2p? (<0.5%)	⁶¹Ge	3/2−#
⁶⁴Se	34	30	63.97117(54)#	2005	22.6(2) ms	β⁺?	⁶⁴As	0+
⁶⁴Se	34	30	63.97117(54)#	2005	22.6(2) ms	β⁺, p?	⁶³Ge	0+
⁶⁵Se	34	31	64.96455(32)#	1993	34.2(7) ms	β⁺, p (87%)	⁶⁴Ge	3/2−#
⁶⁵Se	34	31	64.96455(32)#	1993	34.2(7) ms	β⁺ (13%)	⁶⁵As	3/2−#
⁶⁶Se	34	32	65.95528(22)#	1993	54(4) ms	β⁺	⁶⁶As	0+
⁶⁶Se	34	32	65.95528(22)#	1993	54(4) ms	β⁺, p?	⁶⁵Ge	0+
⁶⁷Se	34	33	66.949994(72)	1991	133(4) ms	β⁺ (99.5%)	⁶⁷As	5/2−#
⁶⁷Se	34	33	66.949994(72)	1991	133(4) ms	β⁺, p (0.5%)	⁶⁶Ge	5/2−#
⁶⁸Se	34	34	67.94182524(53)	1990	35.5(7) s	β⁺	⁶⁸As	0+
⁶⁹Se	34	35	68.9394148(16)	1974	27.4(2) s	β⁺ (99.95%)	⁶⁹As	1/2−
⁶⁹Se	34	35	68.9394148(16)	1974	27.4(2) s	β⁺, p (.052%)	⁶⁸Ge	1/2−
^69m1Se	38.85(22) keV			1988	2.0(2) μs	IT	⁶⁹Se	5/2−
^69m2Se	574.0(4) keV			1988	955(16) ns	IT	⁶⁹Se	9/2+
⁷⁰Se	34	36	69.9335155(17)	1950	41.1(3) min	β⁺	⁷⁰As	0+
⁷¹Se	34	37	70.9322094(30)	1957	4.74(5) min	β⁺	⁷¹As	(5/2−)
^71m1Se	48.79(5) keV			1982	5.6(7) μs	IT	⁷¹Se	(1/2−)
^71m2Se	260.48(10) keV			1982	19.0(5) μs	IT	⁷¹Se	(9/2+)
⁷²Se	34	38	71.9271405(21)	1948	8.40(8) d	EC	⁷²As	0+
⁷³Se	34	39	72.9267549(80)	1948	7.15(9) h	β⁺	⁷³As	9/2+
^73mSe	25.71(4) keV			1953	39.8(17) min	IT (72.6%)	⁷³Se	3/2−
^73mSe	25.71(4) keV			1953	39.8(17) min	β⁺ (27.4%)	⁷³As	3/2−
⁷⁴Se	34	40	73.922475933(15)	1922	Observationally Stable			0+	0.0086(3)
⁷⁵Se	34	41	74.922522870(78)	1947	119.78(3) d	EC	⁷⁵As	5/2+
⁷⁶Se	34	42	75.919213702(17)	1922	Stable			0+	0.0923(7)
⁷⁷Se	34	43	76.919914150(67)	1922	Stable			1/2−	0.0760(7)
^77mSe	161.9223(10) keV			1947	17.36(5) s	IT	⁷⁷Se	7/2+
⁷⁸Se	34	44	77.91730924(19)	1922	Stable			0+	0.2369 (22)
⁷⁹Se	34	45	78.91849925(24)	1950	3.27(28)×10⁵ y	β⁻	⁷⁹Br	7/2+
^79mSe	95.77(3) keV			1950	3.900(18) min	IT (99.94%)	⁷⁹Se	1/2−
^79mSe	95.77(3) keV			1950	3.900(18) min	β⁻ (0.056%)	⁷⁹Br	1/2−
⁸⁰Se	34	46	79.9165218(10)	1922	Observationally Stable			0+	0.4980(36)
⁸¹Se	34	47	80.9179930(10)	1949	18.45(12) min	β⁻	⁸¹Br	1/2−
^81mSe	103.00(6) keV			1949	57.28(2) min	IT (99.95%)	⁸¹Se	7/2+
^81mSe	103.00(6) keV			1949	57.28(2) min	β⁻ (0.051%)	⁸¹Br	7/2+
⁸²Se	34	48	81.91669953(50)	1922	8.76(15)×10¹⁹ y	β⁻β⁻	⁸²Kr	0+	0.0882(15)
⁸³Se	34	49	82.9191186(33)	1937	22.25(4) min	β⁻	⁸³Br	9/2+
^83mSe	228.92(7) keV			1947	70.1(4) s	β⁻	⁸³Br	1/2−
⁸⁴Se	34	50	83.9184668(21)	1960	3.26(10) min	β⁻	⁸⁴Br	0+
⁸⁵Se	34	51	84.9222608(28)	1960	32.9(3) s	β⁻	⁸⁵Br	(5/2)+
⁸⁶Se	34	52	85.9243117(27)	1973	14.3(3) s	β⁻	⁸⁶Br	0+
⁸⁶Se	34	52	85.9243117(27)	1973	14.3(3) s	β⁻, n?	⁸⁵Br	0+
⁸⁷Se	34	53	86.9286886(24)	1968	5.50(6) s	β⁻ (99.50%)	⁸⁷Br	(3/2+)
⁸⁷Se	34	53	86.9286886(24)	1968	5.50(6) s	β⁻, n (0.60%)	⁸⁶Br	(3/2+)
⁸⁸Se	34	54	87.9314175(36)	1970	1.53(6) s	β⁻ (99.01%)	⁸⁸Br	0+
⁸⁸Se	34	54	87.9314175(36)	1970	1.53(6) s	β⁻, n (0.99%)	⁸⁷Br	0+
⁸⁹Se	34	55	88.9366691(40)	1971	430(50) ms	β⁻ (92.2%)	⁸⁹Br	5/2+#
⁸⁹Se	34	55	88.9366691(40)	1971	430(50) ms	β⁻, n (7.8%)	⁸⁸Br	5/2+#
⁹⁰Se	34	56	89.94010(35)	1994	210(80) ms	β⁻	⁹⁰Br	0+
⁹⁰Se	34	56	89.94010(35)	1994	210(80) ms	β⁻, n?	⁸⁹Br	0+
⁹¹Se	34	57	90.94570(47)	1975	270(50) ms	β⁻ (79%)	⁹¹Br	1/2+#
						β⁻, n (21%)	⁹⁰Br
						β⁻, 2n?	⁸⁹Br
⁹²Se	34	58	91.94984(43)#	1997	90# ms [>300 ns]	β⁻?	⁹²Br	0+
						β⁻, n?	⁹¹Br
						β⁻, 2n?	⁹⁰Br
^92mSe	3072(2) keV			2012	15.7(7) μs	IT	⁹²Se	(9−)
⁹³Se	34	59	92.95614(43)#	1997	130# ms [>300 ns]	β⁻?	⁹³Br	1/2+#
						β⁻, n?	⁹²Br
						β⁻, 2n?	⁹¹Br
^93mSe	678.2(7) keV			2012	420(100) ns	IT	⁹³Se
⁹⁴Se	34	60	93.96049(54)#	1997	50# ms [>300 ns]	β⁻?	⁹⁴Br	0+
						β⁻, n?	⁹³Br
						β⁻, 2n?	⁹²Br
^94mSe	2430.0(6) keV			2020	680(50) ns	IT	⁹⁴Se	(7−)
⁹⁵Se	34	61	94.96730(54)#	2010	70# ms [>400 ns]	β⁻?	⁹⁵Br	3/2+#
						β⁻, n?	⁹⁴Br
						β⁻, 2n?	⁹³Br
⁹⁶Se	34	62		2024
⁹⁷Se	34	63		2024
This table header & footer:

02Use of radioisotopes

The isotope selenium-75 has radiopharmaceutical uses. For example, it is used in high-dose-rate endorectal brachytherapy, as an alternative to iridium-192.

In paleobiogeochemistry, the ratio in amount of selenium-82 to selenium-76 (i.e, the value of δ^82/76Se) can be used to track down the redox conditions on Earth during the Neoproterozoic era in order to gain a deeper understanding of the rapid oxygenation that trigger the emergence of complex organisms.

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Sources and credits

This article is adapted from the Wikipedia article “Isotopes of selenium”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

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Isotopes of selenium

01List of isotopes

02Use of radioisotopes

Sources and credits

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