Strontium, like calcium, is an alkaline earth. It has the symbol Sr and the mass number 38. It has 35 known isotopes with a mass number ranging between 73 and 107, and nine nuclear isomers. Among them, four isotopes are stable and represent the totality of natural strontium: Sr-84, Sr-86, Sr-87 and Sr-88 (largely the majority).

Of the 31 artificial isotopes, the most stable are strontium 90 (Sr-90) with a half-life of 28.9 years, strontium 85 (Sr-85) with 64.8 days and strontium 82 (Sr-82 ) With 25.36 days. All other isotopes have half-lives of less than 33 hours and most of them less than 100 minutes.

The lighter isotopes than the stable isotopes disintegrate mainly by positron emission (β +), with the exception of strontium 82, which like strontium 85 disintegrate mainly by electronic capture. All disintegrate mainly in rubidium isotopes. Heavier radioisotopes disintegrate into yttrium isotopes.

Strontium 85 disintegrates by capturing an electron into rubidium 85, followed by the emission of a photon.

Strontium 85 is used in medicine and biology research. Given these properties close to calcium it is used in particular for the imaging of bones and the study of calcium metabolism. It can also be used for the estimation of strontium 89 therapy.