Strontium-90 ( 90 < br> Sr
) is a strontium radioactive isotope produced by nuclear fission, with a half-life of 28.8 years. This experience? - decomposes to yttrium-90, with a decaying energy of 0.546 MeV. Strontium-90 has applications in medicine and industry and is an isotope of concern in the fall of nuclear weapons and nuclear accidents.
Video Strontium-90
Radioactivity
Naturally occurring strontium is not radioactive and non-toxic at levels normally found in the environment, but 90 Sr is the radiation hazard. 90 Sr experience? - decomposes with a half-life of 28.79 years and the decay energy of 0.546 MeV is distributed to electrons, anti-neutrino and yttrium isotope 90 Y , which in turn experience? - decomposes with a half-life of 64 hours and decomposes 2.28 MeV of energy distributed to an electron, a stable anti-neutrino, and 90 Zr (zirconium). Notice that 90 Sr/Y is almost a source of pure beta particles; the emission of gamma photons from decay 90 Y is so rare that it can usually be ignored.
90 Sr has a specific activity of 5.21Ã, TBq/g.
Maps Strontium-90
Product fission
90 Sr is the product of nuclear fission. It is present in significant amounts in spent fuel and in radioactive waste from nuclear reactors and in nuclear fallout from nuclear tests. For thermal neutron fission as in current nuclear power plants, the fission product yield of U-235 is 5.7%, of U-233 6.6%, but from Pu-239 only 2.0%.
Biological effects
Biological activity
Strontium-90 is a "bone seeker" that exhibits a biochemical behavior similar to calcium, the next mild group 2 element. After entering the organism, most often by swallowing with contaminated food or water, about 70-80% of the dose is excreted. Nearly all remaining strontium-90 is stored in bone and bone marrow, with the remaining 1% remaining in the blood and soft tissues. Its presence in bone can cause bone cancer, nearby tissue cancer, and leukemia. Exposure to 90 Sr can be tested by bioassay, most often with urinalysis.
The biological half-life of strontium-90 in humans has been reported from 14 to 600 days, 1000 days, 18 years, 30 years and, at the upper limit, 49 years. The biologically published half-life number is explained by the metabolism of the strontium complex in the body. However, with an average of all excretory pathways, the overall biological half-life is estimated to be about 18 years.
The level of strontium-90 elimination is strongly influenced by age and sex, due to differences in bone metabolism.
Together with the cesium isotope 134 Cs, 137 Cs, and the iodine isotope 131 I it is one of the most important isotopes of health impact after Chernobyl disaster. Since strontium has an affinity for receptors of calcium-sensing parathyroid cells similar to calcium, an increased risk of liquidators from Chernobyl power plants for primary hyperparathyroidism can be explained by the binding of strontium-90.
Usage
Thermoelectric Radioisotope (RTG) Generator
The radioactive decay of strontium-90 produces large amounts of heat, 0.536 W/g in pure strontium metal or about 0.256 W/g as strontium titanate and cheaper than the 238 pu alternative. It is used as a heat source in many Russian/Soviet radio thermoelectric generators, usually in the form of strontium titanates. It was also used in the US "Sentinel" RTG series.
Industrial applications
90 Sr. finds use in industry as a radioactive source for thickness gauges.
Sr90 medical applications find widespread use in medicine as a radioactive source for superficial radiotherapy of some cancers. Controlled amounts of 90 Sr and 89 Sr can be used in the treatment of bone cancer. It is also used as a radioactive tracer in medicine and agriculture.
Aerospace application
90 Sr is used as a knife inspection method in several helicopters with hollow sparring to indicate whether a crack has been formed.
90 Sr contamination in the environment
Strontium-90 is not as simple as cesium-137 to be released as part of nuclear reactor accidents because it is much more unstable, but is probably the most dangerous component of the radioactive impact of nuclear weapons.
A study of hundreds of thousands of deciduous teeth, collected by Dr. Louise Reiss and her colleagues as part of the Baby Dental Survey, found a large increase in levels of 90 Sr throughout the 1950s and early 1960s. The final results of this study show that children born at St. Louis, Missouri, in 1963 had a level of 90 Sr on their first tooth that was 50 times higher than that found in children born in 1950, before the advent of large-scale atomic testing. Commentators in the study say that the fall is likely to cause an increase in cases of disease in those who absorb strontium-90 into their bones.
An article with preliminary findings of this study was circulated to US President John F. Kennedy in 1961, and helped convince him to sign the Partial Nuclear Trial Ban Treaty with Britain and the Soviet Union, ending a nuclear weapons test on land that places the greatest number of fallout nuclear to the atmosphere.
The Chernobyl disaster releases about 10 PBq, or about 5% of the core inventory, from strontium-90 to the environment. Fukushima Daiichi Disaster releases 0.1-1Ã, PBq strontium-90 in the form of contaminated cooling water into the Pacific Ocean.
References
External links
- NLM Hazardous Substances Databank - Strontium, Radioactive
Source of the article : Wikipedia
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