Strontium-90
| General | |
|---|---|
| Symbol | 90Sr |
| Names | strontium-90, 90Sr, Sr-90 |
| Protons (Z) | 38 |
| Neutrons (N) | 52 |
| Nuclide data | |
| Natural abundance | syn |
| Half-life (t1/2) | 28.79 years |
| Decay products | 90Y |
| Decay modes | |
| Decay mode | Decay energy (MeV) |
| Beta decay | 0.546 |
| Isotopes of strontium Complete table of nuclides | |
Strontium-90 (90
Sr
) 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]
Radioactivity
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.
| t½ (year) |
Yield (%) |
Q (keV) |
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
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
Biological activity
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. Strontium-90 is probably the most dangerous component of the radioactive fallout from a nuclear weapon.[citation needed]
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]
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.[11]
Medical applications
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
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 through the 1950s and early 1960s. The study's final results showed that children born 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.[12]
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.[13]
Industrial and aerospace applications
90Sr finds use in industry as a radioactive source for thickness gauges.
Heat source for radioisotope thermoelectric generators
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[14] 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.[15] It was also used in the US Sentinel series of RTGs.[16]
Dispersal hazards
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]
References
- ^ a b "Nuclear Fission Fragments". HyperPhysics. Retrieved 18 June 2012.
- ^ "Strontium | Radiation Protection | US EPA". EPA. 24 April 2012. Retrieved 18 June 2012.
- ^ Decay data from National Nuclear Data Center at the Brookhaven National Laboratory in the US.
- ^ Tiller, B. L. (2001), "4.5 Fish and Wildlife Surveillance", Hanford Site 2001 Environmental Report (PDF), DOE, retrieved 2014-01-14
- ^ Driver, C.J. (1994), Ecotoxicity Literature Review of Selected Hanford Site Contaminants (PDF), DOE, doi:10.2172/10136486, retrieved 2014-01-14
- ^ "Freshwater Ecology and Human Influence". Area IV Envirothon. Retrieved 2014-01-14.
- ^ "Radioisotopes That May Impact Food Resources" (PDF). Epidemiology, Health and Social Services, State of Alaska. Retrieved 2014-01-14.
- ^ "Human Health Fact Sheet: Strontium" (PDF). Argonne National Laboratory. October 2001. Retrieved 2014-01-14.
- ^ "Biological Half-life". HyperPhysics. Retrieved 2014-01-14.
- ^ Glasstone, Samuel; Dolan, Philip J. (1977). "XII: Biological Effects". The effects of Nuclear Weapons (PDF). p. 605. Retrieved 2014-01-14.
- ^ Boehm, Bernhard O. (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.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Schneir, Walter (April 25, 1959). "Strontium-90 in U.S. Children". The Nation. 188 (17): 355–357.
- ^ Hevesi, Dennis. "Dr. Louise Reiss, Who Helped Ban Atomic Testing, Dies at 90", The New York Times, January 10, 2011. Accessed January 10, 2011.
- ^ Harris, Dale; Epstein, Joseph (1968), Properties of Selected Radioisotopes (PDF), NASA
- ^ 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
- ^ "Power Sources for Remote Arctic Applications" (PDF). Washington, DC: U.S. Congress, Office of Technology Assessment. June 1994. OTA-BP-ETI-129.