The Collaborative International Dictionary
radiostrontium
Strontium-90 \Strontium-90\ A radioactive isotope of strontium produced by certain nuclear reactions, and constituting one of the prominent harmful components of radioactive fallout from nuclear explosions; also called radiostrontium. It has a half-life of 28 years.
Wiktionary
radiostrontium
n. any radioactive isotope of strontium, especially (nuclide 90 38 Sr)