Caesium-137
| Caesium-137 | |
|---|---|
| General | |
| Name, symbol | Caesium-137,137Cs |
| Neutrons | 82 |
| Protons | 55 |
| Nuclide data | |
| Natural abundance | 0 (artificial element) |
| Half-life | about 30.1 years |
| Isotope mass | 136.907 u |
| Spin | 11⁄2− |
| Decay mode | Decay energy |
| beta, gamma | 0.662 [1] MeV |
Caesium-137 (137
55Cs, 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 about 30.1 years, and decays by beta emission to a metastable nuclear isomer of barium-137: barium-137m (137mBa, Ba-137m). (About 95 percent of the nuclear decay leads to this isomer. The other 5.0 percent directly populates the ground state, which is stable.) Ba-137m has a half-life of about 2.55 minutes, and it is responsible for all of the emissions of gamma rays. One gram of caesium-137 has an activity of 3.215 terabecquerel (TBq)[2].
The photon energy of Ba-137m is 662 keV. These photons can be useful in food irradiation and in the radiotherapy of cancer. Caesium-137 is not widely-used for industrial radiography because it is quite chemically reactive, and hence, difficult to handle. Also the salts of caesium are very soluble in water, and this complicates the safe handling of caesium. Cobalt-60, 60
27Co, is preferred for radiography, since it is chemically a rather nonreactive metal offering higher energy gamma-ray photons. Caesium-137 can be found in some moisture and density gauges, flow meters, and related sensors.
Contents |
[edit] Uses
Caesium-137 has a small number of practical uses. In small amounts, it is used to calibrate radiation-detection equipment. It is also sometimes used in cancer treatment, and it is also used industrially in gauges for measuring liquid flows and the thickness of materials.[3]
[edit] Radioactive caesium in the environment
Small amounts of cesium-134 and caesium-137 were released into the environment during nearly all nuclear weapon tests and some nuclear accidents, most notably the Chernobyl disaster. As of 2005, caesium-137 is the principal source of radiation in the zone of alienation around the Chernobyl nuclear power plant. Together with cesium-134, iodine-131, and strontium-90, caesium-137 was among the isotopes with greatest health impact distributed by the reactor explosion.
The mean contamination of caesium-137 in Germany following the Chernobyl disaster was 2000 to 4000 Bq/m2. This corresponds to a contamination of 1 mg/km2 of caesium-137, totaling about 500 grams deposited over all of Germany.
Due to caesium-137 mostly being a product of artificial nuclear fission, it did not occur in nature to any significant degree before nuclear weapons testing began. By observing the characteristic gamma rays emitted by this isotope, it is possible to determine whether the contents of a given sealed container were made before or after the advent of atomic bomb explosions. This procedure has been used by researchers to check the authenticity of certain rare wines, most notably the purported "Jefferson bottles".
[edit] Health risk of radioactive caesium
| Actinides | Half-life | Fission products | ||||||
|---|---|---|---|---|---|---|---|---|
| 244Cm | 241Pu f | 250Cf | 243Cmf | 10–30 y | 137Cs | 90Sr | 85Kr | |
| 232U f | 238Pu | f is for fissile |
69–90 y | 151Sm nc➔ | ||||
| 4n | 249Cf f | 242Amf | 141–351 | No fission product has half-life 102 to 2×105 years |
||||
| 241Am | 251Cf f | 431–898 | ||||||
| 240Pu | 229Th | 246Cm | 243Am | 5–7 ky | ||||
| 4n | 245Cmf | 250Cm | 239Pu f | 8–24 ky | ||||
| 233U f | 230Th | 231Pa | 32–160 | |||||
| 4n+1 | 234U | 4n+3 | 211–290 | 99Tc | 126Sn | 79Se | ||
| 248Cm | 242Pu | 340–373 | Long-lived fission products | |||||
| 237Np | 4n+2 | 1–2 my | 93Zr | 135Cs nc➔ | ||||
| 236U | 4n+1 | 247Cmf | 6–23 | 107Pd | 129I | |||
| 244Pu | 80 my | >7% | >5% | >1% | >.1% | |||
| 232Th | 238U | 235U f | 0.7–12by | fission product yield | ||||
Caesium-137 is water-soluble and chemically toxic in small amounts. The biological behavior of caesium-137 is similar to that of potassium and rubidium. After entering the body, caesium gets more or less uniformly distributed through the body, with higher concentration in muscle tissues and lower in bones. The biological half-life of caesium is rather short at about 70 days.[4] Experiments with dogs showed that a single dose of 3800 μCi/kg (approx. 44 μg/kg of caesium-137) is lethal within three weeks.[5]
Accidental ingestion of caesium-137 can be treated with the chemical Prussian blue, which binds to it chemically and then speeds its expulsion from the body.[6]
The improper handling of caesium-137 gamma ray sources can lead to release of this radio-isotope and radiation injuries. Perhaps the best-known case is the Goiânia accident, in which an improperly-disposed-of radiation therapy system from an abandoned clinic in the city of Goiânia, Brazil, was scavenged from a junkyard, and the glowing caesium salt sold to curious, uneducated buyers. This led to multiple serious injuries from radiation exposure.
Caesium gamma-ray sources that have been encased in metallic housings can be mixed-in with scrap metal on its way to smelters, resulting in production of steel contaminated with radioactivity.[7]
One notable example was the Acerinox accident of 1998, when the Spanish recycling company Acerinox accidentally melted down a mass of radioactive caesium-137 that came from a gamma-ray generator.[8]
In 2009, a Chinese cement company in China (the Shaanxi Province) was demolishing an old, unused cement plant and it did not follow the standards for handling radioactive materials. This caused some caesium-137 from a measuring instrument to be melted down along with eight truckloads scrap metal on its way to a steel mill. Hence, the radioactive caesium got melted down into the steel.[9]
[edit] See also
| Prop: Unit: |
t½ a |
Yield % |
Q * KeV |
βγ * |
|---|---|---|---|---|
| 155Eu | 4.76 | .0803 | 252 | βγ |
| 85Kr | 10.76 | .2180 | 687 | βγ |
| 113mCd | 14.1 | .0008 | 316 | β |
| 90Sr | 28.9 | 4.505 | 2826 | β |
| 137Cs | 30.23 | 6.337 | 1176 | βγ |
| 121mSn | 43.9 | .00005 | 390 | βγ |
| 151Sm | 90 | .5314 | 77 | β |
[edit] References
- ^ The Lund/LBNL Nuclear Data Search. "Nuclide Table". http://nucleardata.nuclear.lu.se/NuclearData/toi/nuclide.asp?iZA=550137. Retrieved 2009-03-14.
- ^ "Properties of Caesium-137 isotope". Wolfram Alpha LLC. Retrieved 10 September 2010. http://www.wolframalpha.com/entities/isotopes/cesium_137/le/qm/t8/.
- ^ http://www.bt.cdc.gov/radiation/isotopes/cesium.asp
- ^ R. Nave. "Biological Half-life". Hyperphysics. http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/biohalf.html.
- ^ 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. PMID 5030090. http://www.jstor.org/stable/3573559.
- ^ http://www.bt.cdc.gov/radiation/prussianblue.asp
- ^ "Radioactive Scrap Metal". NuclearPolicy.com. Nuclear Free Local Authorities. October 2000. http://www.nuclearpolicy.info/publications/scrapmetal.php.
- ^ J.M. LaForge (1999). "Radioactive Caesium Spill Cooks Europe". Earth Island Journal (Earth Island Institute) 14 (1). http://www.earthislandprojects.org/EIJOURNAL/winter99/wr_winter99cesium.html.
- ^ "Chinese 'find' radioactive ball". BBC News. 27 March 2009. http://news.bbc.co.uk/2/hi/asia-pacific/7967285.stm.
