Arsenic-72

Main isotopes of arsenic

iso NA half-life DM DE (MeV) DP 73As syn 80.3 d ε – 73Ge γ 0.05D, 0.01D, e – 74As syn 17.8 d ε – 74Ge β+ 0.941 74Ge γ 0.595, 0.634 – β− 1.35, 0.717 74Se 75As 100% is stable with 42 neutrons
Standard atomic weight (Ar)	7001749215950000000♠74.921595(6)

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.

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