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.

Isotopes of arsenic (₃₃As)

Main isotopes Decay Isotope abun­dance half-life (t1/2) mode pro­duct ^73As synth 80.30 d ε ^73Ge ^74As synth 17.77 d β^+66% ^74Ge β^−34% ^74Se ^75As 100% stable
Standard atomic weight Ar°(As)
	74.921595±0.000006 74.922±0.001 (abridged)
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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

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

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

See also

Daughter products other than arsenic

• Isotopes of selenium
• Isotopes of germanium
• Isotopes of gallium

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