Isotopes of arsenic

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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 gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several hours.[citation needed] Such a weapon is not known to have ever been built, tested, or used.

Standard atomic mass: 74.92160(2) u.

Table[edit]

nuclide
symbol
Z(p) N(n)  
isotopic mass (u)
 
half-life decay
mode(s)[1][n 1]
daughter
isotope(s)[n 2]
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]
  1. ^ Abbreviations:
    EC: Electron capture
  2. ^ Bold for stable isotopes, bold italic for nearly-stable isotopes (half-life longer than the age of the universe)

Notes[edit]

  • 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.

Notes[edit]

References[edit]

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


Isotopes of germanium Isotopes of arsenic Isotopes of selenium
Table of nuclides