Selenium

Selenium

Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

(Se) has six naturally occurring isotope

Isotope

Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

s, five of which are stable: ⁷⁴Se, ⁷⁶Se, ⁷⁷Se, ⁷⁸Se, and ⁸⁰Se. The last three also occur as fission products, along with ⁷⁹Se

Selenium-79

Selenium-79 is a radioisotope of selenium present in spent nuclear fuel and the wastes resulting from reprocessing this fuel. It is one of only 7 long-lived fission products. Its yield is low as it is near the lower end of the mass range for fission products...

 which has a half-life

Half-life

Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...

 of 327,000 years, and ⁸²Se which has a very long half-life (~10²⁰ yr, decaying via double beta decay

Double beta decay

Double beta decay is a radioactive decay process where a nucleus releases two beta rays as a single process.In double-beta decay, two neutrons in the nucleus are converted to protons, and two electrons and two electron antineutrinos are emitted...

 to ⁸²Kr

Krypton

Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...

) and for practical purposes can be considered to be stable. 23 other unstable isotopes 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. All other isotopes have half-lives less than 8 hours, most less than 38 seconds, which of these, ⁷³Se is the most stable, with a half-life of 7.15 hours.

Standard atomic mass: 78.96(3) u

Table

nuclide symbol	Z(p Proton The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number.... )	N(n Neutron The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of... )	isotopic mass (u)	half-lifeBold for isotopes with half-lives longer than the age of the universe (nearly stable)	decay mode(s)Abbreviations: EC: Electron capture Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... IT: Isomeric transition Isomeric transition An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer....	daughter isotope(s)Bold for stable isotopes	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
65Se	34	31	64.96466(64)#	<50 ms	β+ Beta decay In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...  (>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 Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino...	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 Isomeric transition An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer....	73Se	3/2-
					β+	73As
74Se	34	40	73.9224764(18)	Observationally Stable Believed to decay by β+β+ to 74Ge			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 Selenium-79 Selenium-79 is a radioisotope of selenium present in spent nuclear fuel and the wastes resulting from reprocessing this fuel. It is one of only 7 long-lived fission products. Its yield is low as it is near the lower end of the mass range for fission products... Long-lived fission product Long-lived fission product Long-lived fission products are radioactive materials with a long half-life produced by nuclear fission.-Evolution of radioactivity in nuclear waste:...	34	45	78.9184991(18)	3.27(8)×105 a	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 StableBelieved to decay by β-β- to 80Kr			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
82SePrimordial Primordial nuclide In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known...  radionuclide Radionuclide A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...	34	48	81.9166994(22)	97(5)×1018 a	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 Neutron emission Neutron emission is a type of radioactive decay of atoms containing excess neutrons, in which a neutron is simply ejected from the nucleus. Two examples of isotopes which emit neutrons are helium-5 and beryllium-13... (.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+

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