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Selenium-75

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Selenium-75

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Main isotopes			Decay
	abundance	half-life (t_1/2)	mode	product
⁷²Se	synth	8.4 d	ε	⁷²As
⁷²Se	synth	8.4 d	γ	–
⁷⁴Se	0.860%	stable
⁷⁵Se	synth	119.8 d	ε	⁷⁵As
⁷⁵Se	synth	119.8 d	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%	1.08×10²⁰ y	β⁻β⁻	⁸²Kr

Standard atomic weight A_r°(Se)

78.971±0.008
78.971±0.008 (abridged)

Selenium (₃₄Se) 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, 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	Z	N	Isotopic mass (Da)	Half-life	Decay mode	Daughter isotope	Spin and parity	Natural abundance (mole fraction)
Nuclide	Excitation energy			Half-life	Decay mode	Daughter isotope	Spin and parity	Normal proportion	Range of variation
⁶⁵Se	34	31	64.96466(64)#	<50 ms	β⁺ (>99.9%)	⁶⁵As	3/2−#
⁶⁵Se	34	31	64.96466(64)#	<50 ms	β⁺, p (<.1%)	⁶⁴Ge	3/2−#
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−#
⁶⁷Se	34	33	66.95009(21)#	133(11) ms	β⁺, p (.5%)	⁶⁶Ge	5/2−#
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−)
⁶⁹Se	34	35	68.93956(4)	27.4(2) s	β⁺, p (.045%)	⁶⁸Ge	(1/2−)
^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−
^73mSe	25.71(4) keV			39.8(13) min	β⁺	⁷³As	3/2−
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−
^79mSe	95.77(3) keV			3.92(1) min	β⁻ (.056%)	⁷⁹Br	1/2−
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+
^81mSe	102.99(6) keV			57.28(2) min	β⁻ (.052%)	⁸¹Br	7/2+
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+)#
⁸⁷Se	34	53	86.92852(4)	5.50(12) s	β⁻, n (.36%)	⁸⁶Br	(5/2+)#
⁸⁸Se	34	54	87.93142(5)	1.53(6) s	β⁻ (99.01%)	⁸⁸Br	0+
⁸⁸Se	34	54	87.93142(5)	1.53(6) s	β⁻, n (.99%)	⁸⁷Br	0+
⁸⁹Se	34	55	88.93645(32)#	0.41(4) s	β⁻ (92.2%)	⁸⁹Br	(5/2+)#
⁸⁹Se	34	55	88.93645(32)#	0.41(4) s	β⁻, n (7.8%)	⁸⁸Br	(5/2+)#
⁹⁰Se	34	56	89.93996(43)#	300# ms [>300 ns]	β⁻, n	⁸⁹Br	0+
⁹⁰Se	34	56	89.93996(43)#	300# ms [>300 ns]	β⁻	⁹⁰Br	0+
⁹¹Se	34	57	90.94596(54)#	270(50) ms	β⁻ (79%)	⁹¹Br	1/2+#
⁹¹Se	34	57	90.94596(54)#	270(50) ms	β⁻, n	⁹⁰Br	1/2+#
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+
This table header & footer: view

Selenium-75

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

Isotope masses from:
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
Isotopic compositions and standard atomic masses from:
- de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
- Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051.
"News & Notices: Standard Atomic Weights Revised". International Union of Pure and Applied Chemistry. 19 October 2005.
Half-life, spin, and isomer data selected from the following sources.
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
- National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
- Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.