Strontium-90 (90Sr) is a radioactive isotope of strontium produced by nuclear fission with a half-life of 28.8 years. It undergoes β− decay into yttrium-90, with a decay energy of 0.546 MeV. Strontium-90 has applications in medicine and industry and is an isotope of concern in fallout from nuclear weapons and nuclear accidents.

Read more about Strontium-90:  Radioactivity, Fission Product