Strontium-90
5700197
202031166
2008-03-30T11:51:47Z
Element16
6666894
sp
{{otheruses4|the chemical isotope|the band|Strontium 90 (band)}}
{{Infobox isotope
| alternate_names =
| symbol =Sr
| mass_number =90
| mass =
| num_neutrons =52
| num_protons =38
| abundance =
| halflife =28.8 years
| error_halflife =
| background =#7F7
| text_color =
| image =
| decay_product =isotopes of yttrium#90
| decay_symbol =Y
| decay_mass =90
| decay_mode1 =[[Beta decay]]
| decay_energy1 =0.546
| decay_mode2 =
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| parent =
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{{Medium-lived fission products}}
'''Strontium-90 (<sup>90</sup>Sr)''' is a [[radioactive]] [[isotope]] of [[strontium]], with a [[half life]] of 28.8 years. <sup>90</sup>Sr undergoes [[beta decay]] with [[decay energy]] of 0.546 [[electronvolt|MeV]] to the [[yttrium]] isotope '''[[isotopes of yttrium#90|<sup>90</sup>Y]]''', which in turn undergoes [[beta decay]] with [[half life]] of 64 hours and decay energy 2.28 MeV for beta particles to [[zirconium|<sup>90</sup>Zr]] (zirconium), which is stable<ref>Decay data from [http://www.nndc.bnl.gov National Nuclear Data Center] at the Brookhaven National Laboratory in the US.</ref>. Note that <sup>90</sup>Sr/Y is almost a perfectly pure [[beta particle|beta]] source, the [[gamma photon]] emission from the decay of <sup>90</sup>Y is so weak that it can normally be ignored.
<sup>90</sup>Sr finds extensive use in medicine and industry, as a radioactive source for thickness gauges and for superficial [[radiotherapy]] of some cancers. Controlled amounts of <sup>90</sup>Sr and [[strontium-89|<sup>89</sup>Sr]] can be used in treatment of [[bone cancer]]. As the radioactive decay of strontium-90 generates significant amount of heat, and is cheaper than the alternative [[plutonium-238|<sup>238</sup>Pu]], it is used as a heat source in many Russian/Soviet [[radioisotope thermoelectric generator]]s, usually in the form of [[strontium fluoride]]. It is also used as a [[radioactive tracer]] in medicine and agriculture. It is obtained during [[nuclear reprocessing]] of [[spent nuclear fuel]].
<sup>90</sup>Sr is a product of [[nuclear fission]]. It is present in significant amount in spent [[nuclear fuel]] and in [[radioactive waste]] from [[nuclear reactor]]s and in [[nuclear fallout]] from [[nuclear test]]s.
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%.
Together with caesium isotopes [[caesium|<sup>134</sup>Cs]], [[caesium-137|<sup>137</sup>Cs]], and iodine isotope [[iodine-131|<sup>131</sup>I]] it was between the most important isotopes regarding health impacts after the [[Chernobyl disaster]]. Slightly elevated levels of <sup>90</sup>Sr may be present in the vicinity of [[nuclear power plant]]s.
Strontium has biochemical behavior similar to [[calcium]]. 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 is deposited in [[bone]]s 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]]. Exposition to <sup>90</sup>Sr can be tested by a [[bioassay]], most commonly by [[urinalysis]].
In the vicinity of nuclear waste and nuclear test sites, strontium also enters the metabolism of plants in lieu of calcium. For example, specimens of [[Chrysothamnus nauseosus|chamisa]] growing in [[Bayo Canyon]], near [[Los Alamos]], [[New Mexico]], exhibit a concentration of radioactive strontium 300,000 times higher than normal plants. Their roots reach into a nuclear waste treatment area that has been closed since 1963; the radioactive shrubs are "indistinguishable from other shrubs without a Geiger counter" <ref name="masco">Masco, Joseph. ''The Nuclear Borderlands: The Manhattan Project in Post-Cold War New Mexico''. [http://press.princeton.edu/titles/8185.html Princeton University Press, 2006].</ref>. The same happens with the [[tumbleweed]] plants at the [[Hanford Site]]; "crews armed with pitchforks" are employed to prevent the contaminated plants from spreading <ref name="masco"/>.
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 <sup>90</sup>Sr contamination in the area of the former Soviet Union.
==References==
{{reflist}}
==External links==
*[http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@na+@rel+strontium,+radioactive NLM Hazardous Substances Databank – Strontium, Radioactive]
[[Category:Isotopes]]
[[Category:Strontium]]
[[Category:Fission products]]
[[Category:Radioisotope fuels]]