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Isotopes of sodium


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 relative atomic mass: 22.98976928(2). 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 shortest-lived is 18
Na
, with a half-life of 1.3(4)×10−21 seconds.

Acute neutron radiation exposure (e.g., from a nuclear criticality accident) converts some of the stable 23
Na
in human blood plasma to 24
Na
. By measuring the concentration of this isotope, the neutron radiation dosage to the victim can be computed.


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