Caesium-137: Difference between revisions
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Revision as of 13:30, 8 April 2010
| General | |
|---|---|
| Symbol | 137Cs |
| Names | caesium-137, 137Cs, Cs-137 |
| Protons (Z) | 55 |
| Neutrons (N) | 82 |
| Nuclide data | |
| Natural abundance | 0 (artificial element) |
| Half-life (t1/2) | 30.07 years |
| Isotope mass | 136.907 Da |
| Spin | 11⁄2− |
| Decay modes | |
| Decay mode | Decay energy (MeV) |
| Beta, Gamma | 1.174[1] |
| Isotopes of caesium Complete table of nuclides | |
Caesium-137 (137Cs, Cs-137) is a radioactive isotope of caesium which is formed mainly as a fission product by nuclear fission. It has a half-life of 30.07 years, and beta decays to a metastable nuclear isomer of barium-137: barium-137m (137mBa, Ba-137m). (95% of the decay leads to this isomer; the other 5% directly populates the ground state, which is stable.) Ba-137m has a half-life of 2.55 minutes and is responsible for all of the gamma ray emission. 1 gram of Cs-137 has an activity of 3.4 Terabecquerel (TBq).
Caesium-137 is water-soluble and extremely toxic even in small amounts. Once released in the environment, it remains present for many years as its radiological half-life is 30.07 years. It can cause cancer 10, 20 or 30 years from the time of ingestion, inhalation or absorption provided a sufficient quantity enters the body.[2]
The photon energy of Ba-137m is 662 keV. These photons can be used in food irradiation, or in radiotherapy of cancers. Cs-137 is not widely used for industrial radiography because it is chemically unstable. For example, its salts are easily soluble in water which complicates safe handling. Cobalt-60 (60Co, Co-60) is preferred for radiography, as it is a chemically stable metal offering higher gamma energies and higher activities. Cs-137 can be found in some moisture and density gauges, flow meters, and other sensor equipment.
Caesium in environment
Small amounts of caesium-134 and caesium-137 were released into the environment during nuclear weapon tests and some nuclear accidents, most notably the Chernobyl disaster. As of 2005, Cs-137 is the principal source of radiation in the zone of alienation around the Chernobyl nuclear power plant. Together with caesium-134, iodine-131, and strontium-90, it was among the isotopes with greatest health impact distributed by the reactor explosion.
The mean contamination of Cs-137 in Germany after Chernobyl was 2000–4000 Bq/m2, some parts in the south even 10 times higher. This corresponds to a contamination of 1 mg/km2 of Cs-137, totalling around 500 g deposited all over Germany.
Health risk
| Actinides[3] by decay chain | Half-life range (a) |
Fission products of 235U by yield[4] | ||||||
|---|---|---|---|---|---|---|---|---|
| 4n | 4n + 1 | 4n + 2 | 4n + 3 | 4.5–7% | 0.04–1.25% | <0.001% | ||
| 228Ra№ | 4–6 a | 155Euþ | ||||||
| 244Cmƒ | 241Puƒ | 250Cf | 227Ac№ | 10–29 a | 90Sr | 85Kr | 113mCdþ | |
| 232Uƒ | 238Puƒ | 243Cmƒ | 29–97 a | 137Cs | 151Smþ | 121mSn | ||
| 248Bk[5] | 249Cfƒ | 242mAmƒ | 141–351 a |
No fission products have a half-life | ||||
| 241Amƒ | 251Cfƒ[6] | 430–900 a | ||||||
| 226Ra№ | 247Bk | 1.3–1.6 ka | ||||||
| 240Pu | 229Th | 246Cmƒ | 243Amƒ | 4.7–7.4 ka | ||||
| 245Cmƒ | 250Cm | 8.3–8.5 ka | ||||||
| 239Puƒ | 24.1 ka | |||||||
| 230Th№ | 231Pa№ | 32–76 ka | ||||||
| 236Npƒ | 233Uƒ | 234U№ | 150–250 ka | 99Tc₡ | 126Sn | |||
| 248Cm | 242Pu | 327–375 ka | 79Se₡ | |||||
| 1.53 Ma | 93Zr | |||||||
| 237Npƒ | 2.1–6.5 Ma | 135Cs₡ | 107Pd | |||||
| 236U | 247Cmƒ | 15–24 Ma | 129I₡ | |||||
| 244Pu | 80 Ma |
... nor beyond 15.7 Ma[7] | ||||||
| 232Th№ | 238U№ | 235Uƒ№ | 0.7–14.1 Ga | |||||
| ||||||||
Biological behavior of Cs-137 is similar to potassium. After entering the organism, all caesium gets more or less uniformly distributed through the body, with higher concentration in muscle tissue and lower in bones. The biological half-life of caesium is short at 70 days.[8] Experiments with dogs showed that a single dose of 3800 μCi/kg (4.1 μg of caesium-137) is lethal within three weeks,[9]
Improper handling of Cs-137 sources can lead to release of the isotope and radiation contamination and injuries. Perhaps the best known case is the Goiânia accident, when a radiation therapy machine from an abandoned clinic in Goiânia, Brazil, was scavenged and the glowing caesium salt sold to curious buyers. Metallic caesium sources can be also accidentally mixed with scrap metal, resulting in production of contaminated steel;[10] a notable example is the Acerinox accident in 1998, when the Spanish recycling company Acerinox accidentally melted a source.[2] In 2009, a Chinese demolition company in north-western Shaanxi province did not follow environmental standards, causing some Cs-137 from a measuring instrument to be melted down with other pieces of scrap into slag.[11]
See also
| 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 |
References
- ^ The Lund/LBNL Nuclear Data Search. "Nuclide Table". Retrieved 2009-03-14.
- ^ a b J.M. LaForge (1999). "Radioactive Cesium Spill Cooks Europe". Earth Island Journal. 14 (1). Earth Island Institute.
- ^ Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
- ^ Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
- ^ Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4.
"The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk248 with a half-life greater than 9 [years]. No growth of Cf248 was detected, and a lower limit for the β− half-life can be set at about 104 [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]." - ^ This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
- ^ Excluding those "classically stable" nuclides with half-lives significantly in excess of 232Th; e.g., while 113mCd has a half-life of only fourteen years, that of 113Cd is eight quadrillion years.
- ^ R. Nave. "Biological Half-life". Hyperphysics.
- ^
H.C. Redman; et al. (1972). "Toxicity of 137-CsCl in the Beagle. Early Biological Effects". Radiation Research. 50 (3): 629–648. doi:10.2307/3573559. JSTOR 3573559.
{{cite journal}}: Explicit use of et al. in:|author=(help) - ^ "Radioactive Scrap Metal". NuclearPolicy.com. Nuclear Free Local Authorities. October 2000.
- ^ "Chinese 'find' radioactive ball". BBC News. 27 March 2009.