Caesium-137

Caesium-137 (also spelled cesium) is a radioactive isotope which is formed mainly by nuclear fission. It has a half-life of 30.23 years, and decays by pure beta decay to a metastable nuclear isomer of barium-137 (Ba-137m). Barium-137m has a half-life of 2.55 minutes and is responsible for all of the gamma ray emission. The ground state of barium-137 is stable.

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Caesium-137 is water-soluble and extremely toxic in minute amounts. Once released into the environment, it remains present for many years as its radiological half-life is 30.23 years. It can cause cancer 10, 20 or 30 years from the time of ingestion, inhalation or absorption providing sufficient material enters the body. ^[1]

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 as other isotopes offer higher gamma activities given volume. It can be found in some moisture and density gauges, flow meters, and other sensor equipment.

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 ^[2].

Small amounts of Cs-134 and Cs-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 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.

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 Goiania accident, when a radiation therapy machine from an abandoned clinic in Goiania, 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;^[3] a notable example is the case from 1998, when Recycler Acerinox in Cadiz, Spain accidentally melted a source. Many abandoned sources are scattered over the area of the former Soviet Union.

See also

• Commonly used gamma emitting isotopes

References