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 (05 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 6979129999999999999♠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.

22
Na is a positron-emitting isotope with a remarkably long half-life. It is used to create test-objects and point-sources for positron emission tomography.

Table