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This article is about the chemical isotope. For the band, see Strontium 90 (band).
Name, symbol Strontium-90,90Sr
Neutrons 52
Protons 38
Nuclide data
Natural abundance syn
Half-life 28.79 years
Decay products 90Y
Decay mode Decay energy
Beta decay 0.546 MeV

Strontium-90 (90Sr) 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]


Natural strontium is nonradioactive and nontoxic, but 90Sr is a radioactivity hazard. 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 anti-neutrino, and the yttrium isotope 90Y, which in turn undergoes β decay with half-life of 64 hours and decay energy 2.28 MeV distributed to an electron, an anti-neutrino, and 90Zr (zirconium), which is stable.[3] 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.

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 96.6 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 5.8%, from U-233 6.8%, but from Pu-239 only 2.1%.

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. 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 might possibly cause bone cancer, cancer of nearby tissues, and leukemia. Nonetheless, Strontium which deposits in bone, substituting for Calcium, remains extra-cellular (outside the cell), in crystals of hydroxylapatite Ca10(PO4)6(OH)2 or SrCa9(PO4)6(OH)2. As such, Strontium is a couple of orders of magnitude further removed from the DNA in space than the intra-cellular electrolytes, Potassium and Magnesium. Exposure to 90Sr can be tested by a bioassay, most commonly by urinalysis. It has been argued that Strontium-90 is potentially the most dangerous component of the radioactive fallout from a nuclear weapon, although the physical structure of Bone#Bone structure markedly diminishes any risk compared to Potassium-40.

The biological half life of strontium-90 in humans has variously been reported as from 14 to 600 days,[4][5] 1000 days,[6] 18 years,[7] 30 years[8] and, at an upper limit, 49 years.[9] The wide ranging published biological half life figures are explained by the isotope's complex metabolism within the body. However, by averaging all excretion paths, the overall biological half life is estimated to be about 18 years.[10]

Strontium-90 released by a nuclear event enters an environment where there is many orders of magnitude more natural Strontium. The level of Strontium is not measurably altered by such an event. Bioaccumulation is the process by which an element is concentrated by chemical processes in bodily tissues.[11] Thus the level of Strontium in the environment is not measurably increased by such an event, and the level of Strontium in bone will not change. Strontium-90 will accumulate in bone until it reaches equilibrium with the other (non-radioactive) Strontium in the environment. The release of Sr-90 into the Pacific Ocean from the Fukushima incident in Japan in 2011 has been estimated at 0.1-1PBq.[12] 1 PBq is equal to 150gm of Sr-90. Strontium is present in seawater at a level of 8 mg/l or 1.05 x 1019.[13] Sr-90 therefore constitutes of 7 x 10−16 of the total Strontium. Should the approximately 1gm of Strontium in a human body be replaced by Strontium from the oceans, this person would contain approximately 10550 Sr-90 nuclei or 10−4 Bq.

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.[14]

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. It is also used as a radioactive tracer in medicine and agriculture.

90Sr in fallout[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.[1]

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 in 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. Commentators on the study said that the fallout was likely to cause increased cases of diseases in those who absorb strontium-90 into their bones.[15]

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.[16]

Industrial and aerospace applications[edit]

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

Heat source for radioisotope thermoelectric generators[edit]

The radioactive decay of strontium-90 generates a significant amount of heat, 0.95 W/g in the form of pure strontium metal or approximately 0.23 W/g as strontium titanate[17] 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.[18] It was also used in the US Sentinel series of RTGs.[19]

Dispersal hazards[edit]

Accidental mixing of radioactive sources containing strontium with metal scrap can result in production of radioactive steel. Discarded radioisotope thermoelectric generators are a major source of 90Sr contamination in the area of the former Soviet Union.[citation needed]


  1. ^ a b "Nuclear Fission Fragments". HyperPhysics. Retrieved 18 June 2012. 
  2. ^ "Strontium | Radiation Protection | US EPA". EPA. 24 April 2012. Retrieved 18 June 2012. 
  3. ^ Decay data from National Nuclear Data Center at the Brookhaven National Laboratory in the US.
  4. ^ Tiller, B. L. (2001), "4.5 Fish and Wildlife Surveillance", Hanford Site 2001 Environmental Report, DOE, retrieved 2014-01-14 
  5. ^ Driver, C.J. (1994), Ecotoxicity Literature Review of Selected Hanford Site Contaminants, DOE, doi:10.2172/10136486, retrieved 2014-01-14 
  6. ^ "Freshwater Ecology and Human Influence". Area IV Envirothon. Retrieved 2014-01-14. 
  7. ^ "Radioisotopes That May Impact Food Resources". Epidemiology, Health and Social Services, State of Alaska. Retrieved 2014-01-14. 
  8. ^ "Human Health Fact Sheet: Strontium". Argonne National Laboratory. October 2001. Retrieved 2014-01-14. 
  9. ^ "Biological Half-life". HyperPhysics. Retrieved 2014-01-14. 
  10. ^ Glasstone, Samuel; Dolan, Philip J. (1977). "XII: Biological Effects". The effects of Nuclear Weapons. p. 605. Retrieved 2014-01-14. 
  11. ^ "Bioaccumulation". 
  12. ^ "Biogeosciences". 
  13. ^ grams for the ocean as a whole"Strontium". 
  14. ^ Boehm, Bernhard O.; Rosinger, Silke, Belyi, David, Dietrich, Johannes W. (August 2011). "The Parathyroid as a Target for Radiation Damage". New England Journal of Medicine 365 (7): 676–678. doi:10.1056/NEJMc1104982. PMID 21848480. Retrieved 19 August 2011. 
  15. ^ Schneir, Walter (April 25, 1959). "Strontium-90 in U.S. Children". The Nation 188 (17): 355–357. 
  16. ^ Hevesi, Dennis. "Dr. Louise Reiss, Who Helped Ban Atomic Testing, Dies at 90", The New York Times, January 10, 2011. Accessed January 10, 2011.
  17. ^ Harris, Dale; Epstein, Joseph (1968), Properties of Selected Radioisotopes, NASA 
  18. ^ 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 (StrålevernRapport 2005:4), Østerås: Norwegian Radiation Protection Authority 
  19. ^ "Power Sources for Remote Arctic Applications". Washington, DC: U.S. Congress, Office of Technology Assessment. June 1994. OTA-BP-ETI-129. 

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