Isotopes of sodium

There are 21 known isotopes of sodium (₁₁Na), ranging from
Na to
Na (except for Na and Na), and five isomers.
Na is the only stable (and the only primordial) isotope, making sodium a monoisotopic (and mononuclidic) element. Sodium has two radioactivecosmogenic isotopes (
Na, with a half-life of 2.6019 years and
Na, with a half-life of 14.956 hours). With the exception of those two isotopes, all other isotopes have half-lives under a minute, most under a second.

Acute neutron radiation exposure (e.g., from a nuclear criticality accident) converts some of the stable
Na in human blood plasma to
Na. The neutron radiation dose absorbed by the patient can be assessed by measuring the concentration of the radioisotope.

Na is a positron-emitting isotope with a relatively long half-life, about 2.6 years. It is used to create test-objects and point-sources for positron emission tomography.