Caesium 137

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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, and decays by beta emission to a metastable nuclear isomerof barium-137barium-137m (137mBa, Ba-137m). (About 95 percent of the nuclear decayleads 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 ofgamma rays. One gram of caesium-137 has an activity of 3.215 terabecquerel(TBq).[2]

 

Health risk of radioactive caesium

Caesium-137 reacts with water producing a water-soluble compound (caesium hydroxide), and the biological behavior of caesium is similar to that of potassiumand 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.[7] Experiments with dogs showed that a single dose of 3800 ?Ci/kg (140 MBq/kg, or approximately 44 ?g/kg) is lethal within three weeks.[8]

Accidental ingestion of caesium-137 can be treated with Prussian blue, which binds to it chemically and then speeds its expulsion from the body.[9]

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 theGoiânia accident, in which an improperly-disposed-of radiation therapy system from an abandoned clinic in the city of GoiâniaBrazil, was scavenged from a junkyard, and the glowing caesium salt sold to curious, uneducated buyers. This led to multiple 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.[10]

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.[11]

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 was melted down into the steel.[12]

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