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 (90Sr) is a radioactive isotope of strontium produced in nuclear explosions or by nuclear reactors Strontium-90 is not quite as likely as cesium-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] Strontium-90 undergoes beta decay, emitting electrons with energy 0.546 MeV with a half-life of 28.8 years. The decay product is yttrium-90. [2]
Radioactivity
Natural strontium is nonradioactive and nontoxic, but 90Sr is a radioactivity hazard. 90Sr undergoes β− decay with 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 perfectly pure beta source; the gamma photon emission from the decay of 90Y is so weak 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.
Together with 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.[4]
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
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. 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.[5]
Industrial and Aerospace Applications
90Sr finds use in industry as a radioactive source for thickness gauges. 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/Soviet radioisotope thermoelectric generators, usually in the form of strontium fluoride.
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.
References
- ^ http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/fisfrag.html#c5
- ^ http://www.epa.gov/rpdweb00/radionuclides/strontium.html#environment
- ^ Decay data from National Nuclear Data Center at the Brookhaven National Laboratory in the US.
- ^ Boehm, Bernhard O. (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); Unknown parameter|month=ignored (help) - ^ Hevesi, Dennis. "Dr. Louise Reiss, Who Helped Ban Atomic Testing, Dies at 90", The New York Times, January 10, 2011. Accessed January 10, 2011.