Sr90

Strontium-90 (Sr-90) is a radioactive isotope of strontium with a mass number of 90. It is produced as a fission product in the splitting of uranium-235 and plutonium-239 and is a notable component of nuclear fallout and spent reactor fuel. Sr-90 has a half-life of about 28.8 years, allowing it to persist in the environment for decades after release.

Sr-90 decays by beta emission to yttrium-90 (Y-90). Y-90, with a half-life of about 64 hours, subsequently beta-decays to stable zirconium-90 (Zr-90). The beta emissions come with maximum energies around 0.546 MeV for Sr-90 and 2.28 MeV for Y-90, contributing to the radiological dose from the decay chain.

Biological behavior is strongly influenced by chemistry: strontium behaves like calcium and tends to accumulate in bone tissue when ingested or inhaled, delivering radiation to bone marrow and nearby tissues. This can increase the risk of bone cancer and leukemia, especially with internal exposure. Environmental and occupational safety measures aim to limit ingestion and inhalation and to manage contamination in the event of releases.

Applications and regulation: Sr-90 is subject to strict regulatory control as a radioactive material. It is not widely used directly in medicine or industry today; its decay product Y-90 is employed in certain radiopharmaceutical therapies, and Sr-89 is used for palliation of bone pain in metastases. In many contexts, Sr-90 is studied primarily as a concern in nuclear safety, waste management, and environmental monitoring rather than as a routine therapeutic agent.