Isotopes of arsenic

Arsenic occurs naturally as one stable isotope, ⁷⁵As, so is monoisotopic and mononuclidic. Synthetic radioisotopes are known from ⁶⁴As to ⁹⁵As, as well as at least 11 isomers.

Quick facts Main isotopes, Decay ...

Isotopes of arsenic (₃₃As)

Main isotopes^[1]			Decay
Isotope	abundance	half-life (t_1/2)	mode	product
⁷³As	synth	80.30 d	ε	⁷³Ge
⁷⁴As	synth	17.77 d	β⁺66%	⁷⁴Ge
⁷⁴As	synth	17.77 d	β⁻34%	⁷⁴Se
⁷⁵As	100%	stable

Standard atomic weight A_r°(As)

74.921595±0.000006^[2]
74.922±0.001 (abridged)^[3]

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The most stable of these are ⁷³As with a half-life of 80.30 days and ⁷⁴As with a half-life of 17.77 days, followed by ⁷¹As (65.30 hours), ⁷⁷As (38.79 hours), ⁷⁶As (26.24 hours), and ⁷²As (26.0 hours). All others outside this range of mass number 71-77 have half-lives under 100 minutes and most under one minute. The longest-lived of the isomers is ^82mAs at 13.6 seconds.

Isotopes lighter than the stable one generally decay by positron emission or electron capture to germanium isotopes, while those heavier beta decay to selenium isotopes. A notable exception is that ⁷⁴As decays both ways.

List of isotopes

More information Nuclide, Z ...

Nuclide ^{[n 1]}	Z	N	Isotopic mass (Da)^[4] ^{[n 2]}^{[n 3]}	Discovery year^[5]^[6]	Half-life^[1]	Decay mode^[1] ^{[n 4]}	Daughter isotope ^{[n 5]}^{[n 6]}	Spin and parity^[1] ^{[n 7]}^{[n 8]}	Isotopic abundance
Nuclide ^{[n 1]}	Excitation energy^{[n 8]}			Discovery year^[5]^[6]	Half-life^[1]	Decay mode^[1] ^{[n 4]}	Daughter isotope ^{[n 5]}^{[n 6]}	Spin and parity^[1] ^{[n 7]}^{[n 8]}	Isotopic abundance
⁶⁴As	33	31	63.95756(22)#	1995	69.0(14) ms	β⁺	⁶⁴Ge	0+#
⁶⁴As	33	31	63.95756(22)#	1995	69.0(14) ms	β⁺, p?	⁶³Ga	0+#
⁶⁵As	33	32	64.949611(91)	1991	130.3(6) ms	β⁺	⁶⁵Ge	3/2−#
⁶⁵As	33	32	64.949611(91)	1991	130.3(6) ms	β⁺, p?	⁶⁴Ga	3/2−#
⁶⁶As	33	33	65.9441488(61)	1978	95.77(23) ms	β⁺	⁶⁶Ge	0+
^66m1As	1356.63(17) keV			1998	1.14(4) μs	IT	⁶⁶As	5+
^66m2As	3023.(3) keV			1998	7.98(26) μs	IT	⁶⁶As	9+
⁶⁷As	33	34	66.93925111(48)	1980	42.5(12) s	β⁺	⁶⁷Ge	(5/2−)
⁶⁸As	33	35	67.9367741(20)	1971	151.6(8) s	β⁺	⁶⁸Ge	3+
^68mAs	425.1(2) keV			1994	111(20) ns	IT	⁶⁸As	1+
⁶⁹As	33	36	68.932246(34)	1955	15.2(2) min	β⁺	⁶⁹Ge	5/2−
⁷⁰As	33	37	69.9309346(15)	1950	52.6(3) min	β⁺	⁷⁰Ge	4+
^70mAs	32.046(23) keV			1979	96(3) μs	IT	⁷⁰As	2+
⁷¹As	33	38	70.9271136(45)	1939	65.30(7) h	β⁺	⁷¹Ge	5/2−
⁷²As	33	39	71.9267523(44)	1947	26.0(1) h	β⁺	⁷²Ge	2−
⁷³As	33	40	72.9238291(41)	1948	80.30(6) d	EC	⁷³Ge	3/2−
^73mAs	427.902(21) keV			1956	5.7(2) μs	IT	⁷³As	9/2+
⁷⁴As	33	41	73.9239286(18)	1938	17.77(2) d	β⁺ (66%)	⁷⁴Ge	2−
⁷⁴As	33	41	73.9239286(18)	1938	17.77(2) d	β⁻ (34%)	⁷⁴Se	2−
⁷⁵As	33	42	74.92159456(95)	1920	Stable			3/2−	1.0000
^75mAs	303.9243(8) keV			1957	17.62(23) ms	IT	⁷⁵As	9/2+
⁷⁶As	33	43	75.92239201(95)	1934	1.0933(38) d	β⁻	⁷⁶Se	2−
^76mAs	44.425(1) keV			1968	1.84(6) μs	IT	⁷⁶As	(1)+
⁷⁷As^{[n 9]}	33	44	76.9206476(18)	1951	38.79(5) h	β⁻	⁷⁷Se	3/2−
^77mAs	475.48(4) keV			1957	114.0(25) μs	IT	⁷⁷As	9/2+
⁷⁸As	33	45	77.921828(10)	1937	90.7(2) min	β⁻	⁷⁸Se	2−
⁷⁹As	33	46	78.9209484(57)	1950	9.01(15) min	β⁻	⁷⁹Se	3/2−
^79mAs	772.81(6) keV			1998	1.21(1) μs	IT	⁷⁹As	(9/2)+
⁸⁰As	33	47	79.9224744(36)	1959	15.2(2) s	β⁻	⁸⁰Se	1+
⁸¹As	33	48	80.9221323(28)	1960	33.3(8) s	β⁻	⁸¹Se	3/2−
⁸²As	33	49	81.9247387(40)	1968	19.1(5) s	β⁻	⁸²Se	(2−)
^82mAs	131.6(5) keV			1970	13.6(4) s	β⁻	⁸²Se	(5-)
⁸³As	33	50	82.9252069(30)	1968	13.4(4) s	β⁻	⁸³Se	5/2−#
⁸⁴As	33	51	83.9293033(34)	1968	3.16(58) s	β⁻ (99.72%)	⁸⁴Se	(2−)
⁸⁴As	33	51	83.9293033(34)	1968	3.16(58) s	β⁻, n (.28%)	⁸³Se	(2−)
⁸⁵As	33	52	84.9321637(33)	1967	2.022(7) s	β⁻, n (62.6%)	⁸⁴Se	(5/2−)
⁸⁵As	33	52	84.9321637(33)	1967	2.022(7) s	β⁻ (37.4%)	⁸⁵Se	(5/2−)
⁸⁶As	33	53	85.9367015(37)	1973	945(8) ms	β⁻ (64.5%)	⁸⁶Se	(1−,2−)
						β⁻, n (35.5%)	⁸⁵Se
						β⁻, 2n?	⁸⁴Se
⁸⁷As	33	54	86.9402917(32)	1970	492(25) ms	β⁻ (84.6%)	⁸⁷Se	(5/2−,3/2−)
						β⁻, n (15.4%)	⁸⁶Se
						β⁻, 2n?	⁸⁵Se
⁸⁸As	33	55	87.94584(22)#	1994	270(150) ms	β⁻	⁸⁸Se
⁸⁸As	33	55	87.94584(22)#	1994	270(150) ms	β⁻, n?	⁸⁷Se
⁸⁹As	33	56	88.95005(32)#	1994	220# ms [>150 ns]	β⁻?	⁸⁹Se	5/2−#
						β⁻, n?	⁸⁸Se
						β⁻, 2n?	⁸⁷Se
⁹⁰As	33	57	89.95600(43)#	1997	70# ms [>300 ns]	β⁻?	⁹⁰Se
						β⁻, n?	⁸⁹Se
						β⁻, 2n?	⁸⁸Se
^90mAs	124.5(5) keV			2012	220(100) ns	IT	⁹⁰As
⁹¹As	33	58	90.96082(43)#	1997	100# ms [>300 ns]	β⁻?	⁹¹Se	5/2−#
						β⁻, n?	⁹⁰Se
						β⁻, 2n?	⁸⁹Se
⁹²As	33	59	91.96739(54)#	1997	45# ms [>300 ns]	β⁻?	⁹²Se
						β⁻, n?	⁹¹Se
						β⁻, 2n?	⁹⁰Se
⁹³As^[7]	33	60		2024
⁹⁴As^[7]	33	61		2024
⁹⁵As^[7]	33	62		2024
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[1]
^mAs – 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]
Modes of decay:

EC: Electron capture

n: Neutron emission

p: Proton emission
[5]
Bold italics symbol as daughter – Daughter product is nearly stable.
[6]
Bold symbol as daughter – Daughter product is stable.
[7]
( ) spin value – Indicates spin with weak assignment arguments.
[8]
# – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
[9]
Fission product

Isotopes of arsenic

List of isotopes

See also

References

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