Radioactive Na

特許 係属中 There are twenty recognized isotopes of sodium, ranging from 18 Na to 37 Na and two isomers (22m Na and 24m Na). 23 Na is the only stable (and the only primordial) isotope. As such, it is considered a monoisotopic element and it has a standard atomic mass: 22.98976928(2) u. Sodium has two radioactive cosmogenic isotopes (22 Na, half-life = 2.605 years; and 24 Na, half-life ≈ 15 hours). With the exception of those two, all other isotopes have half-lives under a minute, most under a second. The least stable is 18 Na, with a half-life of 1.3(4)×10−21 seconds.