- Strontium-90
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 =
decay_product =isotopes of yttrium#90
decay_symbol =Y
decay_mass =90
decay_mode1 =Beta decay
decay_energy1 =0.546
decay_mode2 =
decay_energy2 =
decay_mode3 =
decay_energy3 =
decay_mode4 =
decay_energy4 =
parent =
parent_symbol =
parent_mass =
parent_decay =
parent2 =
parent2_symbol =
parent2_mass =
parent2_decay =
spin =
excess_energy =
error1 =
binding_energy =
error2 =Strontium-90 (90Sr) is a
radioactive isotope ofstrontium , with ahalf life of 28.8 years. 90Sr undergoesbeta decay withdecay energy of 0.546 MeV to theyttrium isotope 90Y, which in turn undergoesbeta decay withhalf life of 64 hours and decay energy 2.28 MeV for beta particles to 90Zr (zirconium), which is stable [Decay data from [http://www.nndc.bnl.gov National Nuclear Data Center] at the Brookhaven National Laboratory in the US.] . Note that 90Sr/Y is almost a perfectly pure beta source; thegamma photon emission from the decay of 90Y is so weak that it can normally be ignored.90Sr finds extensive use in medicine and industry, as a radioactive source for thickness gauges and for superficial
radiotherapy of some cancers. Controlled amounts of 90Sr and 89Sr can be used in treatment ofbone cancer . As the radioactive decay of strontium-90 generates significant amount of heat, and is cheaper than the alternative 238Pu, it is used as a heat source in many Russian/Sovietradioisotope thermoelectric generator s, usually in the form ofstrontium fluoride . It is also used as aradioactive tracer in medicine and agriculture. It is obtained duringnuclear reprocessing ofspent nuclear fuel .90Sr is a product of
nuclear fission . It is present in significant amount in spentnuclear fuel and inradioactive waste fromnuclear reactor s and innuclear fallout fromnuclear test s. Forthermal neutron fission as in today's nuclear power plants, thefission product yield fromU-235 is 5.8%, fromU-233 6.8%, but fromPu-239 only 2.1%.Together with caesium isotopes 134Cs, 137Cs, and iodine isotope 131I it was between the most important isotopes regarding health impacts after the
Chernobyl disaster . Slightly elevated levels of 90Sr may be present in the vicinity ofnuclear 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 inbone s andbone marrow , with the remaining 1% remaining in blood and soft tissues. Its presence in bones can causebone cancer , cancer of nearby tissues, andleukemia . Exposition to 90Sr can be tested by abioassay , most commonly byurinalysis .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 chamisa growing in
Bayo Canyon , nearLos 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" 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] .] . The same happens with thetumbleweed plants at theHanford Site ; "crews armed with pitchforks" are employed to prevent the contaminated plants from spreading .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.
References
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]
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