Strontium-90 is a synthetic radioactive isotope of strontium produced primarily as a fission product in reactors and nuclear detonations. It undergoes beta decay and transforms into yttrium-90 before reaching the stable isotope zirconium-90. Because of its decay mode and chemistry it behaves differently from many gamma-emitting radionuclides and presents specific biological and radiological concerns.

Physical and chemical characteristics

Sr-90 has a radioactive half-life of approximately 28.8 years, making it persistent on timescales relevant to environmental contamination. It emits energetic beta particles rather than significant gamma radiation, and its daughter, yttrium-90, is itself a high-energy beta emitter with a much shorter half-life. Chemically strontium is similar to calcium, so Sr-90 tends to accumulate in bones and teeth when ingested or inhaled, increasing long-term dose to bone marrow and nearby tissues.

History and environmental occurrence

Strontium-90 was first identified in fallout from atmospheric nuclear weapons testing in the mid‑20th century and later in releases from reactor accidents and some reprocessing events. Its presence in soil, forage and the food chain prompted monitoring programs because of its tendency to concentrate in bones of humans and animals. Detection typically involves radiochemical separation followed by beta counting or spectrometric techniques.

Uses and applications

  • Medicine: Sr-90 and related isotopes have been used in external and surface radiotherapy such as ophthalmic applicators and treatment of superficial lesions; other strontium isotopes (for example Sr-89) are used for bone pain palliation. See clinical guidance on radiation therapy.
  • Power and heat sources: As a long‑lived beta emitter that produces heat during decay, Sr-90 has been used in radioisotope thermoelectric generators (RTGs) as an alternative where plutonium sources were unavailable; historically it has been substituted for plutonium compounds in some remote power applications and small nuclear heat sources.
  • Industry and research: Sr-90 provides a stable beta source for calibration, thickness gauging and scientific experiments because its emissions and decay chain are well characterized.

Health, safety and regulation

Ingestion or inhalation of Sr-90 poses a radiological health risk due to bone-seeking behavior and sustained dose to marrow; long-term exposure increases the risk of bone cancers and leukemia. Beta particles can be shielded effectively with low‑density materials such as acrylic, but bremsstrahlung X-rays from high-energy betas may require additional shielding. Regulatory bodies control production, transport and disposal of Sr-90 sources and monitor environmental levels following releases.

Notable distinctions include its role as a fission product and environmental tracer, its primarily beta emission unlike many medical gamma sources, and its dual character as both a useful industrial/medical tool and a persistent contaminant that requires careful handling and long-term remediation planning. For further technical references and safety standards see authoritative sources and regulatory guidance via technical summaries and monitoring reports (isotope data, element profiles, decay tables).