Strontium SR-89 is a radioactive isotope of strontium. Strontium-89 decays by beta emission with a half-life of 50.5 days. Beta-particles produced by radioactive decay penetrate tissues at a range of approximately 8 mm. Strontium SR-89 is used in medicine for the relief of bone pain in patients with painful skeletal metastases. Following intravenous injection, soluble strontium compounds behave like their calcium analogs, clearing rapidly from the blood and selectively localizing in bone mineral. Uptake of strontium by bone occurs preferentially in sites of active osteogenesis; thus primary bone tumors and areas of metastatic involvement (blastic lesions) can accumulate significantly greater concentrations of strontium than surrounding normal bone.