Isotopes of arsenic

Arsenic (33As) 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 with 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. Such a weapon is not known to have ever been built, tested, or used.

Isotopes of arsenic (33As)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
73As synth 80.3 d ε 73Ge
γ
74As synth 17.8 d ε 74Ge
β+ 74Ge
γ
β 74Se
75As 100% stable
Standard atomic weight Ar°(As)
  • 74.921595±0.000006
  • 74.922±0.001 (abridged)[2][3]

Transmutation of arsenic to much less toxic selenium could prevent cycling of arsenic, from groundwater to waterways to oceans and back via Sargassum seaweeds. Bioremediation can provide a large supply of arsenic and rid aquifers of persistent poisoning issues.

List of isotopes

Nuclide
[n 1]
Z N Isotopic mass (Da)
[n 2][n 3]
Half-life
Decay
mode

[n 4]
Daughter
isotope

[n 5][n 6]
Spin and
parity
[n 7][n 8]
Natural abundance (mole fraction)
Excitation energy[n 8] Normal proportion Range of variation
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 (.279%) 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]
This table header & footer:
  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).

References

  1. Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  2. "Standard Atomic Weights: Arsenic". CIAAW. 2013.
  3. Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; et al. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
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