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 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 highenergy 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.

Main isotopes of arsenic (33As)
Iso­tope Decay
abun­dance half-life (t1/2) mode pro­duct
73As syn 80.3 d ε 73Ge
74As syn 17.8 d ε 74Ge
β+ 74Ge
β 74Se
75As 100% stable
Standard atomic weight Ar, standard(As)
  • 74.921595(6)[1]

List of isotopes

Z(p) N(n)  
isotopic mass (u)
half-life decay
mode(s)[2][n 1]
isotope(s)[n 2]
spin and
(mole fraction)
range of natural
(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]
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]
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)


  • 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.


  1. ^ Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
  2. ^ "Universal Nuclide Chart". nucleonica. (Registration required (help)). Cite uses deprecated parameter |registration= (help)



Arsenic is a chemical element with symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but only the gray form, which has a metallic appearance, is important to industry.

The primary use of arsenic is in alloys of lead (for example, in car batteries and ammunition). Arsenic is a common n-type dopant in semiconductor electronic devices, and the optoelectronic compound gallium arsenide is the second most commonly used semiconductor after doped silicon. Arsenic and its compounds, especially the trioxide, are used in the production of pesticides, treated wood products, herbicides, and insecticides. These applications are declining due to the toxicity of arsenic and its compounds.A few species of bacteria are able to use arsenic compounds as respiratory metabolites. Trace quantities of arsenic are an essential dietary element in rats, hamsters, goats, chickens, and presumably other species. A role in human metabolism is not known. However, arsenic poisoning occurs in multicellular life if quantities are larger than needed. Arsenic contamination of groundwater is a problem that affects millions of people across the world.

The United States' Environmental Protection Agency states that all forms of arsenic are a serious risk to human health. The United States' Agency for Toxic Substances and Disease Registry ranked arsenic as number 1 in its 2001 Priority List of Hazardous Substances at Superfund sites. Arsenic is classified as a Group-A carcinogen.

Arsenic (disambiguation)

Arsenic is the chemical element with symbol As and atomic number 33.

Arsenic may also refer to:

Arsenic trioxide, a poison commonly referred to as simply as "arsenic"

Arsenic acid, a chemical compound with the formula H3AsO4

Arsenic Lake, a lake in Ontario, Canada

Ärsenik, a French rap group

Mr. Arsenic, an America anthology television series


Selenium is a chemical element with symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, and also has similarities to arsenic. It rarely occurs in its elemental state or as pure ore compounds in the Earth's crust. Selenium (from Ancient Greek σελήνη (selḗnē) "Moon") was discovered in 1817 by Jöns Jacob Berzelius, who noted the similarity of the new element to the previously discovered tellurium (named for the Earth).

Selenium is found in metal sulfide ores, where it partially replaces the sulfur. Commercially, selenium is produced as a byproduct in the refining of these ores, most often during production. Minerals that are pure selenide or selenate compounds are known but rare. The chief commercial uses for selenium today are glassmaking and pigments. Selenium is a semiconductor and is used in photocells. Applications in electronics, once important, have been mostly replaced with silicon semiconductor devices. Selenium is still used in a few types of DC power surge protectors and one type of fluorescent quantum dot.

Selenium salts are toxic in large amounts, but trace amounts are necessary for cellular function in many organisms, including all animals. Selenium is an ingredient in many multivitamins and other dietary supplements, including infant formula. It is a component of the antioxidant enzymes glutathione peroxidase and thioredoxin reductase (which indirectly reduce certain oxidized molecules in animals and some plants). It is also found in three deiodinase enzymes, which convert one thyroid hormone to another. Selenium requirements in plants differ by species, with some plants requiring relatively large amounts and others apparently requiring none.

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.