Isotopes of selenium

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 of 327,000 years,^[4][5] 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.

Isotopes of selenium (₃₄Se)

Main isotopes[1] 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[2] 78.971±0.008 (abridged)[3]
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List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da)[6] [n 2][n 3]	Half-life[1] [n 4][n 5]	Decay mode[1] [n 6]	Daughter isotope [n 7]	Spin and parity[1] [n 8][n 5]	Natural abundance (mole fraction)
	Excitation energy							Normal proportion[1]	Range of variation
63Se	34	29	62.98191(54)#	13.2(39) ms	β+, p (89%)	62Ge	3/2−#
					β+ (11%)	63As
					2p? (<0.5%)	61Ge
64Se	34	30	63.97117(54)#	22.6(2) ms	β+?	64As	0+
					β+, p?	63Ge
65Se	34	31	64.96455(32)#	34.2(7) ms	β+, p (87%)	64Ge	3/2−#
					β+ (13%)	65As
66Se	34	32	65.95528(22)#	54(4) ms	β+	66As	0+
					β+, p?	65Ge
67Se	34	33	66.949994(72)	133(4) ms	β+ (99.5%)	67As	5/2−#
					β+, p (0.5%)	66Ge
68Se	34	34	67.94182524(53)	35.5(7) s	β+	68As	0+
69Se	34	35	68.9394148(16)	27.4(2) s	β+ (99.95%)	69As	1/2−
					β+, p (.052%)	68Ge
69m1Se	38.85(22) keV			2.0(2) μs	IT	69Se	5/2−
69m2Se	574.0(4) keV			955(16) ns	IT	69Se	9/2+
70Se	34	36	69.9335155(17)	41.1(3) min	β+	70As	0+
71Se	34	37	70.9322094(30)	4.74(5) min	β+	71As	(5/2−)
71m1Se	48.79(5) keV			5.6(7) μs	IT	71Se	(1/2−)
71m2Se	260.48(10) keV			19.0(5) μs	IT	71Se	(9/2+)
72Se	34	38	71.9271405(21)	8.40(8) d	EC	72As	0+
73Se	34	39	72.9267549(80)	7.15(9) h	β+	73As	9/2+
73mSe	25.71(4) keV			39.8(17) min	IT (72.6%)	73Se	3/2−
					β+ (27.4%)	73As
74Se	34	40	73.922475933(15)	Observationally Stable[n 9]			0+	0.0086(3)
75Se	34	41	74.922522870(78)	119.78(3) d	EC	75As	5/2+
76Se	34	42	75.919213702(17)	Stable			0+	0.0923(7)
77Se	34	43	76.919914150(67)	Stable			1/2−	0.0760(7)
77mSe	161.9223(10) keV			17.36(5) s	IT	77Se	7/2+
78Se	34	44	77.91730924(19)	Stable			0+	0.2369 (22)
79Se[n 10]	34	45	78.91849925(24)	3.27(28)×105 y	β−	79Br	7/2+
79mSe	95.77(3) keV			3.900(18) min	IT (99.94%)	79Se	1/2−
					β− (0.056%)	79Br
80Se	34	46	79.9165218(10)	Observationally Stable[n 11]			0+	0.4980(36)
81Se	34	47	80.9179930(10)	18.45(12) min	β−	81Br	1/2−
81mSe	103.00(6) keV			57.28(2) min	IT (99.95%)	81Se	7/2+
					β− (.051%)	81Br
82Se[n 12]	34	48	81.91669953(50)	8.76(15)×1019 y	β−β−	82Kr	0+	0.0882(15)
83Se	34	49	82.9191186(33)	22.25(4) min	β−	83Br	9/2+
83mSe	228.92(7) keV			70.1(4) s	β−	83Br	1/2−
84Se	34	50	83.9184668(21)	3.26(10) min	β−	84Br	0+
85Se	34	51	84.9222608(28)	32.9(3) s	β−	85Br	(5/2)+
86Se	34	52	85.9243117(27)	14.3(3) s	β−	86Br	0+
					β−, n?	85Br
87Se	34	53	86.9286886(24)	5.50(6) s	β− (99.50%)	87Br	(3/2+)
					β−, n (0.60%)	86Br
88Se	34	54	87.9314175(36)	1.53(6) s	β− (99.01%)	88Br	0+
					β−, n (0.99%)	87Br
89Se	34	55	88.9366691(40)	430(50) ms	β− (92.2%)	89Br	5/2+#
					β−, n (7.8%)	88Br
90Se	34	56	89.94010(35)	210(80) ms	β−	90Br	0+
					β−, n?	89Br
91Se	34	57	90.94570(47)	270(50) ms	β− (79%)	91Br	1/2+#
					β−, n (21%)	90Br
					β−, 2n?	89Br
92Se	34	58	91.94984(43)#	90# ms [>300 ns]	β−?	92Br	0+
					β−, n?	91Br
					β−, 2n?	90Br
92mSe	3072(2) keV			15.7(7) μs	IT	92Se	(9−)
93Se	34	59	92.95614(43)#	130# ms [>300 ns]	β−?	93Br	1/2+#
					β−, n?	92Br
					β−, 2n?	91Br
93mSe	678.2(7) keV			420(100) ns	IT	93Se
94Se	34	60	93.96049(54)#	50# ms [>300 ns]	β−?	94Br	0+
					β−, n?	93Br
					β−, 2n?	92Br
94mSe	2430.0(6) keV			680(50) ns	IT	94Se	(7−)
95Se	34	61	94.96730(54)#	70# ms [>400 ns]	β−?	95Br	3/2+#
					β−, n?	94Br
					β−, 2n?	93Br
96Se[7]	34	62
97Se[7]	34	63
This table header & footer: view

1. ^mSe – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. Bold half-life – nearly stable, half-life longer than age of universe.
5. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
6. Modes of decay:

   EC:	Electron capture
   IT:	Isomeric transition
   n:	Neutron emission
   p:	Proton emission

7. Bold symbol as daughter – Daughter product is stable.
8. ( ) spin value – Indicates spin with weak assignment arguments.
9. Believed to decay by β⁺β⁺ to ⁷⁴Ge with a half-life over 2.3×10¹⁸ y.
10. Long-lived fission product
11. Believed to decay by β⁻β⁻ to ⁸⁰Kr
12. Primordial radionuclide

Use 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.^[8]

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.^[9][10]