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Strontium-90, 90Sr
Namesstrontium-90, Sr-90
Nuclide data
Natural abundancesyn
Half-life28.79 years
Decay products90Y
Decay modes
Decay modeDecay energy (MeV)
Beta decay0.546
Isotopes of strontium
Complete table of nuclides

Strontium-90 (90
) is a radioactive isotope of strontium produced by nuclear fission, with a half-life of 28.8 years. It undergoes β decay into yttrium-90, with a decay energy of 0.546 MeV.[1] Strontium-90 has applications in medicine and industry and is an isotope of concern in fallout from nuclear weapons and nuclear accidents.[2]


Naturally occurring strontium is nonradioactive and nontoxic at levels normally found in the environment, but 90Sr is a radiation hazard.[3] 90Sr undergoes β decay with a half-life of 28.79 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 hours and a decay energy of 2.28 MeV distributed to an electron, an antineutrino, and 90Zr (zirconium), which is stable.[4] Note that 90Sr/Y is almost a pure beta particle source; the gamma photon emission from the decay of 90Y is so infrequent that it can normally be ignored.

90Sr has a specific activity of 5.21 TBq/g.[5]

fission products
Q *
βγ *
155Eu 4.76 0.0803 252 βγ
85Kr 10.76 0.2180 687 βγ
113mCd 14.1 0.0008 316 β
90Sr 28.9 4.505 2826 β
137Cs 30.23 6.337 1176 βγ
121mSn 43.9 0.00005 390 βγ
151Sm 88.8 0.5314 77 β

Fission product[edit]

90Sr is a product of nuclear fission. It is present in significant amount in spent nuclear fuel and 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 U-235 is 5.7%, from U-233 6.6%, but from Pu-239 only 2.0%.[6]

Nuclear waste[edit]

Strontium-90 is classified as high-level waste. The half life is long, around 30 years. 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.[7]


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 quanitity and also present in nuclear waste.[7]

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.[8]

A study of the pond alga Closterium moniliferum using non-radioactive strontium found that varying the ratio of barium to strontium in water improved strontium selectivity.[7]

Biological effects[edit]

Biological activity[edit]

Strontium-90 is a "bone seeker" that exhibits biochemical behavior similar to calcium, the next lighter group 2 element.[3][9] After entering the organism, most often by ingestion with contaminated food or water, about 70–80% of the dose gets excreted.[2] Virtually all remaining strontium-90 is deposited in bones and bone marrow, with the remaining 1% remaining in blood and soft tissues.[2] Its presence in bones can cause bone cancer, cancer of nearby tissues, and leukemia.[10] Exposure to 90Sr can be tested by a bioassay, most commonly by urinalysis.[3]

The biological half-life of strontium-90 in humans has variously been reported as from 14 to 600 days,[11][12] 1000 days,[13] 18 years,[14] 30 years[15] and, at an upper limit, 49 years.[16] The wide-ranging published biological half life figures are explained by strontium's complex metabolism within the body. However, by averaging all excretion paths, the overall biological half life is estimated to be about 18 years.[17]

The elimination rate of strontium-90 is strongly affected by age and sex, due to differences in bone metabolism.[18]

Together with the caesium isotopes 134Cs, 137Cs, and iodine isotope 131I, it was among the most important isotopes regarding health impacts after the Chernobyl disaster. As strontium has an affinity to the calcium-sensing receptor of parathyroid cells that is similar to that of calcium, the increased risk of liquidators of the Chernobyl power plant to suffer from primary hyperparathyroidism could be explained by binding of strontium-90.[19]


Radioisotope thermoelectric generators (RTGs)[edit]

The radioactive decay of strontium-90 generates a significant amount of heat, 0.536 W/g in the form of pure strontium metal or approximately 0.256 W/g as strontium titanate[20] and is cheaper than the alternative 238Pu. It is used as a heat source in many Russian/Soviet radioisotope thermoelectric generators, usually in the form of strontium titanate.[21] It was also used in the US "Sentinel" series of RTGs.[22]

Industrial applications[edit]

90Sr finds use in industry as a radioactive source for thickness gauges.[2]

Medical applications[edit]

90Sr finds extensive use in medicine as a radioactive source for superficial radiotherapy of some cancers. Controlled amounts of 90Sr and 89Sr can be used in treatment of bone cancer, and to treat coronary restenosis via vascular brachytherapy. It is also used as a radioactive tracer in medicine and agriculture.[2]

Aerospace applications[edit]

90Sr is used as a blade inspection method in some helicopters with hollow blade spars to indicate if a crack has formed.[23]

90Sr contamination in the environment[edit]

Strontium-90 is not quite as likely as caesium-137 to be released as a part of a nuclear reactor accident because it is much less volatile, but is probably the most dangerous component of the radioactive fallout from a nuclear weapon.[24]

A study of hundreds of thousands of deciduous teeth, collected by Dr. Louise Reiss and her colleagues as part of the Baby Tooth Survey, found a large increase in 90Sr levels through the 1950s and early 1960s. The study's final results showed that children born in St. Louis, Missouri, in 1963 had levels of 90Sr in their deciduous teeth that was 50 times higher than that found in children born in 1950, before the advent of large-scale atomic testing. Reviewers of the study predicted that the fallout would cause increased incidence of disease in those who absorbed strontium-90 into their bones.[25] However, no follow up studies of the subjects have been performed, so the claim is untested.

An article with the study's initial findings was circulated to U.S. President John F. Kennedy in 1961, and helped convince him to sign the Partial Nuclear Test Ban Treaty with the United Kingdom and Soviet Union, ending the above-ground nuclear weapons testing that placed the greatest amounts of nuclear fallout into the atmosphere.[26]

The Chernobyl disaster released roughly 10 PBq, or about 5% of the core inventory, of strontium-90 into the environment.[27] The Fukushima Daiichi disaster released 0.1 to 1 PBq of strontium-90 in the form of contaminated cooling water into the Pacific Ocean.[28]


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  4. ^ Decay data from National Nuclear Data Center at the Brookhaven National Laboratory in the US.
  5. ^ Delacroix, D.; Guerre, J. P.; Leblanc, P.; Hickman, C. (2002). Radionuclide and Radiation Protection Data Handbook 2002 (2nd ed.). Nuclear Technology Publishing. ISBN 978-1-870965-87-3.
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  8. ^ "Biosorption of Strontium from Simulated Nuclear Wastewater by Scenedesmus spinosus under Culture Conditions: Adsorption and Bioaccumulation Processes and Models". Int J Environ Res Public Health. 2014. doi:10.3390/ijerph110606099.
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  20. ^ Harris, Dale; Epstein, Joseph (1968), Properties of Selected Radioisotopes (PDF), NASA
  21. ^ Standring, WJF; Selnæs, ØG; Sneve, M; Finne, IE; Hosseini, A; Amundsen, I; Strand, P (2005), Assessment of environmental, health and safety consequences of decommissioning radioisotope thermal generators (RTGs) in Northwest Russia (PDF), Østerås: Norwegian Radiation Protection Authority
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