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Wednesday, November 23, 2011

Caesium-137 - Wikipedia, the free encyclopedia

Caesium-137 - Wikipedia, the free encyclopedia

Caesium-137

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For the band, see Cesium 137 (band).
Caesium-137
General
Name, symbolCaesium-137,137Cs
Neutrons82
Protons55
Nuclide data
Natural abundance0 (artificial element)
Half-life30.17 y[1] ± 0.03 y
Parent isotopes137Xe (β−)
Decay products137mBa
Isotope mass136.907 u
Spin11⁄2−
Decay modeDecay energy
beta, gamma1.176 [2] MeV
Cs-137 Decay Scheme
Caesium-137 (137
55Cs, Cs-137) is a radioactive isotope of caesium which is formed as a fission product by nuclear fission.
It has a half-life of about 30.17 years,[3] 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 153 seconds, 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).[4]
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

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[edit] Uses

Caesium-137 has a small number of practical uses. In small amounts, it is used to calibrate radiation-detection equipment. It is used as a gamma emitter for oilfield wireline density measurements. 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.[5]

[edit] Radioactive caesium in the environment

The ten highest deposits of caesium-137 from U.S. nuclear testing at the Nevada Test Site. Test explosions "Simon" and "Harry" were both from Operation Upshot-Knothole in 1953, while the test explosions "George" and "How" were from Operation Tumbler-Snapper in 1952
Cs-137 γ-spectrum: 661.7 keV γ- and 32 keV Ba K-lines.
Small amounts of caesium-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 caesium-134, iodine-131, and strontium-90, caesium-137 was among the isotopes, distributed by the reactor explosion, which constitute the greatest risk to health.
As of April 2011, it was also being found in the plumes emanating from the continuing leakage at the Fukushima reactors in Japan. In July 2011, meat from 11 cows shipped to Tokyo from Fukushima prefecture was found to have 3 to 6 times the legal limit of 500 becquerels per kilogram of radioactive caesium.[6]
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.[citation needed]
All caesium-137 existing today is unique in that it is totally anthropogenic (man-made). Unlike most other radioisotopes, caesium-137 is not produced from its non-radioactive isotope but from uranium,[7] meaning that until now, it has not occurred on Earth for billions of years. 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". [8]

[edit] Health risk of radioactive caesium

ActinidesHalf-lifeFission products
244Cm241Pu f250Cf243Cmf10–30 y137Cs90Sr85Kr
232U  f238Puf is for
fissile		69–90 y151Sm nc➔
4n249Cf  f242Amf141–351No fission product
has half-life 102to 2×105 years
241Am251Cf  f431–898
240Pu229Th246Cm243Am5–7 ky
4n245Cmf250Cm239Pu f8–24 ky
233U    f230Th231Pa32–160
4n+1234U4n+3211–29099Tc126Sn79Se
248Cm242Pu340–373Long-lived fission products
237Np4n+21–2 My93Zr135Cs nc➔
236U4n+1247Cmf6–23 My107Pd129I
244Pu80 My>7%>5%>1%>.1%
232Th238U235U    f0.7–12 Tyfission product yield
Caesium-137 reacts with water producing a water-soluble compound (caesium hydroxide), and the biological behavior of caesium is similar to that of potassium and rubidium. After entering the body, caesium gets more or less uniformly distributed throughout 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.[9] Experiments with dogs showed that a single dose of 3800 μCi/kg (140 MBq/kg, or approximately 44 μg/kg) is lethal within three weeks.[10]
Accidental ingestion of caesium-137 can be treated with Prussian blue, which binds to it chemically and then speeds its expulsion from the body.[11]

[edit] Incidents

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 of 1985, 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 four deaths and 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.[12]
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.[13]
In 2009, a Chinese cement company (in Tongchuan, Shaanxi Province) was demolishing an old, unused cement plant and did not follow standards for handling radioactive materials. This caused some caesium-137 from a measuring instrument to be included with eight truckloads of scrap metal on its way to a steel mill, where the radioactive caesium was melted down into the steel.[14]

[edit] See also

Medium-lived fission products
Prop:
Unit:		t½
a		Yield
%		Q *
keV		βγ
*
155Eu4.76.0803252βγ
85Kr10.76.2180687βγ
113mCd14.1.0008316β
90Sr28.94.5052826β
137Cs30.236.3371176βγ
121mSn43.9.00005390βγ
151Sm90.531477β

[edit] References

  1. ^ National Institute of Standards and Technology. "Radionuclide Half-Life Measurements". http://www.nist.gov/pml/data/halflife-html.cfm. Retrieved 2011-11-07. 
  2. ^ The Lund/LBNL Nuclear Data Search. "Nuclide Table". http://nucleardata.nuclear.lu.se/NuclearData/toi/nuclide.asp?iZA=550137. Retrieved 2009-03-14. 
  3. ^ National Institute of Standards and Technology. "Radionuclide Half-Life Measurements". http://www.nist.gov/pml/data/halflife-html.cfm. Retrieved 2011-11-07. 
  4. ^ "NIST Nuclide Half-Life Measurements". NIST. Retrieved 13 March 2011. http://www.nist.gov/pml/data/halflife.cfm. 
  5. ^ http://www.bt.cdc.gov/radiation/isotopes/cesium.asp
  6. ^ "High levels of caesium in Fukushima beef". Independent Online. 9 July 2011. http://www.iol.co.za/news/world/high-levels-of-caesium-in-fukushima-beef-1.1096205. 
  7. ^ Takeshi Okumura (October 21, 2003). "The material flow of radioactive cesium-137 in the U.S. 2000". http://www.epa.gov/. US Environmental Protection Agency. http://www.epa.gov/rpdweb00/docs/source-management/csfinallongtakeshi.pdf. 
  8. ^ http://www.winespectator.com/webfeature/show/id/42436
  9. ^ R. Nave. "Biological Half-life". Hyperphysics. http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/biohalf.html. 
  10. ^ 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. 
  11. ^ http://www.bt.cdc.gov/radiation/prussianblue.asp
  12. ^ "Radioactive Scrap Metal". NuclearPolicy.com. Nuclear Free Local Authorities. October 2000. http://www.nuclearpolicy.info/publications/scrapmetal.php. 
  13. ^ 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. 
  14. ^ "Chinese 'find' radioactive ball". BBC News. 27 March 2009. http://news.bbc.co.uk/2/hi/asia-pacific/7967285.stm. 

[edit] External links

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