Isotopes of arsenic

Arsenic (As) has 33 known isotopes and at least 10 isomers. Only one of these isotopes, ⁷⁵As, is stable; as such, it is considered a monoisotopic element. The longest-lived radioisotope is ⁷³As has a half-life of 80 days. Arsenic has been proposed as a "salting" material for nuclear weapons (cobalt is another, better-known salting material). A jacket of ⁷⁵As, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope ⁷⁶As with a half-life of 1.0778 days and produce approximately 1.13 MeV of gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several hours. Such a weapon is not known to have ever been built, tested, or used.

Standard atomic mass: 74.92160(2) u.

Table

nuclide symbol	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)	daughter isotope(s)	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
60As	33	27	59.99313(64)#		p	59Ge	5+#
61As	33	28	60.98062(64)#		p	60Ge	3/2-#
62As	33	29	61.97320(32)#		p	61Ge	1+#
63As	33	30	62.96369(54)#		p	62Ge	(3/2-)#
64As	33	31	63.95757(38)#	40(30) ms [18(+43-7) ms]	β+	64Ge	0+#
65As	33	32	64.94956(32)#	170(30) ms	β+	65Ge	3/2-#
66As	33	33	65.94471(73)	95.77(23) ms	β+	66Ge	(0+)
66m1As	1356.70(17) keV			1.1(1) µs			(5+)
66m2As	3023.9(3) keV			8.2(5) µs			(9+)
67As	33	34	66.93919(11)	42.5(12) s	β+	67Ge	(5/2-)
68As	33	35	67.93677(5)	151.6(8) s	β+	68Ge	3+
68mAs	425.21(16) keV			111(20) ns [?107(+23-16) ns]			1+
69As	33	36	68.93227(3)	15.2(2) min	β+	69Ge	5/2-
70As	33	37	69.93092(5)	52.6(3) min	β+	70Ge	4(+#)
70mAs	32.008(23) keV			96(3) µs			2(+)
71As	33	38	70.927112(5)	65.28(15) h	β+	71Ge	5/2-
72As	33	39	71.926752(5)	26.0(1) h	β+	72Ge	2-
73As	33	40	72.923825(4)	80.30(6) d	EC	73Ge	3/2-
74As	33	41	73.9239287(25)	17.77(2) d	β+ (66%)	74Ge	2-
					β- (34%)	74Se
75As	33	42	74.9215965(20)	Stable			3/2-	1.0000
75mAs	303.9241(7) keV			17.62(23) ms			9/2+
76As	33	43	75.922394(2)	1.0942(7) d	β- (99.98%)	76Se	2-
					EC (.02%)	76Ge
76mAs	44.425(1) keV			1.84(6) µs			(1)+
77As	33	44	76.9206473(25)	38.83(5) h	β-	77mSe	3/2-
77mAs	475.443(16) keV			114.0(25) µs			9/2+
78As	33	45	77.921827(11)	90.7(2) min	β-	78Se	2-
79As	33	46	78.920948(6)	9.01(15) min	β-	79mSe	3/2-
79mAs	772.81(6) keV			1.21(1) µs			(9/2)+
80As	33	47	79.922534(25)	15.2(2) s	β-	80Se	1+
81As	33	48	80.922132(6)	33.3(8) s	β-	81mSe	3/2-
82As	33	49	81.92450(21)	19.1(5) s	β-	82Se	(1+)
82mAs	250(200) keV			13.6(4) s	β-	82Se	(5-)
83As	33	50	82.92498(24)	13.4(3) s	β-	83mSe	3/2-#
84As	33	51	83.92906(32)#	4.02(3) s	β- (99.721%)	84Se	(3)(+#)
					β-, n (.029%)	83Se
84mAs	0(100)# keV			650(150) ms
85As	33	52	84.93202(21)#	2.021(10) s	β-, n (59.4%)	84Se	(3/2-)#
					β- (40.6%)	85Se
86As	33	53	85.93650(32)#	0.945(8) s	β- (67%)	86Se
					β-, n (33%)	85Se
87As	33	54	86.93990(32)#	0.56(8) s	β- (84.6%)	87Se	3/2-#
					β-, n (15.4%)	86Se
88As	33	55	87.94494(54)#	300# ms [>300 ns]	β-	88Se
					β-, n	87Se
89As	33	56	88.94939(54)#	200# ms [>300 ns]	β-	89Se	3/2-#
90As	33	57	89.95550(86)#	80# ms [>300 ns]
91As	33	58	90.96043(97)#	50# ms [>300 ns]			3/2-#
92As	33	59	91.96680(97)#	30# ms [>300 ns]

Notes

• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

References

• Isotope masses from:
  • G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• Isotopic compositions and standard atomic masses from:
  • J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. {{cite journal}}: Unknown parameter |laysummary= ignored (help)
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
  • G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties" (PDF). Nuclear Physics A. 729: 3–128. Bibcode:2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  • National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. Retrieved September 2005. {{cite web}}: Check date values in: |accessdate= (help)
  • N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide (ed.). CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0-8493-0485-9. {{cite book}}: Unknown parameter |nopp= ignored (|no-pp= suggested) (help)

• A.Shore, A. Fritsch, M. Heim, A. Schuh, M. Thoennessen. Discovery of the Arsenic Isotopes. arXiv:0902.4361.