Isotopes of strontium

The alkaline earth metalstrontium (₃₈Sr) has four stable, naturally occurring isotopes: Sr (0.56%), Sr (9.86%), Sr (7.0%) and Sr (82.58%), giving it a standard atomic weight of 87.62.

Only Sr is radiogenic; it is produced by decay from the radioactive alkali metal Rb, which has a half-life of 4.97 × 10 years (i.e. more than three times longer than the current age of the universe). Thus, there are two sources of Sr in any material: primordial, formed during nucleosynthesis along with Sr, Sr and Sr; and that formed by radioactive decay of Rb. The ratio Sr/Sr is the parameter typically reported in geologic investigations; ratios in minerals and rocks have values ranging from about 0.7 to greater than 4.0 (see rubidium–strontium dating). Because strontium has an electron configuration similar to that of calcium, it readily substitutes for calcium in minerals.

In addition to the four stable isotopes, thirty-two unstable isotopes of strontium are known to exist, ranging from Sr to Sr. Radioactive isotopes of strontium primarily decay into the neighbouring elements yttrium (Sr and heavier isotopes, via beta minus decay) and rubidium (Sr, Sr and lighter isotopes, via positron emission or electron capture). The longest-lived of these isotopes, are Sr with a half-life of 28.91 years, Sr at 64.846 days, Sr at 50.56 days, and Sr at 25.35 days. All other strontium isotopes have half-lives shorter than 10 hours, most under 10 minutes.

Strontium-89 is an artificial radioisotope used in treatment of bone cancer; this application utilizes its chemical similarity to calcium, which allows it to substitute calcium in bone structures. In circumstances where cancer patients have widespread and painful bony metastases, the administration of Sr results in the delivery of beta particles directly to the cancerous portions of the bone, where calcium turnover is greatest.

Strontium-90 is a by-product of nuclear fission, present in nuclear fallout. The 1986 Chernobyl nuclear accident contaminated a vast area with Sr. It causes health problems, as it substitutes for calcium in bone, giving it a long lifetime in the body. Because it is a long-lived high-energy beta emitter, it is used in SNAP (Systems for Nuclear Auxiliary Power) devices. These devices hold promise for use in spacecraft, remote weather stations, navigational buoys, etc., where a lightweight, long-lived, nuclear-electric power source is required.

In 2020, researchers have found that mirror nuclides Sr and Br were found to not behave identically to each other as expected.