Naturally occurring rhenium (75Re) is 37.4% 185Re, which is stable (although it is predicted to decay), and 62.6% 187Re, which is unstable but has a very long half-life (4.12×1010 years).
[4] Among elements with a known stable isotope, only indium and tellurium similarly occur with a stable isotope in lower abundance than the long-lived radioactive isotope.
There are 36 other unstable isotopes recognized, the longest-lived of which are 183Re with a half-life of 70 days, 184Re with a half-life of 38 days, 186Re with a half-life of 3.7186 days, 182Re with a half-life of 64.0 hours, and 189Re with a half-life of 24.3 hours.
There are also numerous isomers, the longest-lived of which are 186mRe with a half-life of 200,000 years and 184mRe with a half-life of 177.25 days.
Rhenium-186 is a beta emitter and radiopharmaceutical that is used to treat glioblastoma,[10] is used in theranostic medicine[11] and has been reported to be used in synoviorthesis.