Strontium-90
Strontium-90
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Strontium-90

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Strontium-90

Strontium-90 (90
Sr
) is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.91 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, nuclear weapons testing, and nuclear accidents.

Naturally occurring strontium is nonradioactive and nontoxic at levels normally found in the environment, but 90Sr is a radiation hazard. 90Sr undergoes β decay with a half-life of 28.91 years and a decay energy of 0.546 MeV distributed to an electron, an antineutrino, and the yttrium isotope 90Y, which in turn undergoes β decay with a half-life of 64.05 hours and a decay energy of 2.28 MeV distributed to an electron, an antineutrino, and occasionally a gamma ray, leaving stable 90Zr. The gamma-emitting branches are so weak that for most purposes 90Sr/Y can be considered a pure beta particle source.

90Sr is a product of nuclear fission. It is present in significant amount in spent nuclear fuel, in radioactive waste from nuclear reactors and in nuclear fallout from nuclear tests. For thermal neutron fission as in today's nuclear power plants, the fission product yield from uranium-235 is 5.7%, from uranium-233 6.6%, but from plutonium-239, only 2.0%. (Commercial reactors derive energy both from uranium-235 and plutonium-239 in comparable amounts.)

Strontium-90 is classified as high-level waste. Its 29-year half-life means that it can take hundreds of years to decay to negligible levels. Exposure from contaminated water and food may increase the risk of leukemia and bone cancer. Reportedly, thousands of capsules of radioactive strontium containing millions of curies are stored at Hanford Site's Waste Encapsulation and Storage Facility.

Algae has shown selectivity for strontium in studies, where most plants used in bioremediation have not shown selectivity between calcium and strontium, often becoming saturated with calcium, which is greater in quantity and also present in nuclear waste.

Researchers have looked at the bioaccumulation of strontium by Scenedesmus spinosus (algae) in simulated wastewater. The study claims a highly selective biosorption capacity for strontium of S. spinosus, suggesting that it may be appropriate for use of nuclear wastewater.

A study of the pond alga Closterium moniliferum using stable strontium found that varying the ratio of barium to strontium in water improved strontium selectivity.

Strontium-90 is a "bone seeker" that exhibits biochemical behavior similar to calcium, the next lighter group 2 element. After entering the organism, most often by ingestion with contaminated food or water, about 70–80% of the dose gets excreted. Virtually all remaining strontium-90 is deposited in bones and bone marrow, with the remaining 1% remaining in blood and soft tissues. Its presence in bones can cause bone cancer, cancer of nearby tissues, and leukemia. Exposure to 90Sr can be tested by a bioassay, most commonly by urinalysis.

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