The name “cesium” derives from Latin word for “sky” (caelum). Gustav Kirchhoff and Robert Bunsen first identified cesium spectrophotometrically in the mineral water of Dürkheim, Germany in 1860.81 Cesium (Cs) is among the most rare and reactive alkali metals. Elemental cesium (Cs0) is silvery white, soft, and malleable. It has a relatively low melting point of 82.4°F (28°C) and thus may exist as both solid and liquid at room temperature. Cs0 ignites violently when exposed to moist air or water but forms stable salt complexes. The greatest concentration of naturally occurring cesium (32%), the compound cesium oxide (Cs2O), is found in the ore pollucite.1,78,80 Since Cs0 is so highly reactive and short lived, the name “cesium” will refer to cesium salts in the following discussion, unless specifically noted otherwise.
Radionuclides of cesium were identified in the 1940s by the American scientist and Nobel Prize winner Glenn Seaborg and his student Margaret Melhase.60 Radioactive cesium isotopes are products of nuclear fission of uranium and plutonium.81 Both 134Cs and 137Cs decay via β particle emission; however, only 137Cs emits γ rays.78 137Cs has a long half-life of 30 years, and it serves not only as an “atomic clock” but also poses potential radiological hazard as it deposits and complexes in earth and water. Of the numerous cesium radioisotopes have been identified to date, only 133Cs is stable.9
Several releases of radioactive cesium have occurred in the past century, resulting in large-scale contamination and human exposure. Examples include the nuclear weapons use in Hiroshima and Nagasaki, nuclear weapons testing in Bikini Atoll11 and Republic of Georgia,27 poor nuclear waste management in Goiânia,36,57,65 Tammiku,37 and Camp Lilo27 in the Republic of Georgia, as well as critical nuclear power plant malfunctions in Chernobyl68 and Fukushima Daiichi.
Whereas nuclear disasters are associated with release of numerous radioactive isotopes, isolated exposure to 137Cs was implicated in the events that took place in Goiânia, Tammiku, and Camp Lilo. In September 1987, two men removed a large cylinder that contained 137Cs from an abandoned apparatus in Goiânia Institute of Radiotherapy. Several weeks passed between the incident and discovery of the source, with resultant 137Cs contamination of the community. Approximately 112,000 people required monitoring and 249 people suffered from internal and external contamination.36,65
On October 21, 1994, three brothers entered a waste repository in Tammiku, Estonia. One of the brothers picked up a metal vessel that unknowingly contained 137Cs. Although he died of a syndrome similar to radiation-induced illness, acute radiation contamination was not recognized until his stepson was hospitalized with radiation-induced hand burns a month later.37