cesium-137

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cesium-137 (137Cs)

a radioactive material with a half-life of 30.2 years that is used in radiotherapy as a sealed source of gamma rays intended for application to various malignancies that are treated by brachytherapy. Cesium has replaced radium for such applications. See also brachytherapy.

cesium

a chemical element, atomic number 55, atomic weight 132.905, symbol Cs. See Table 6.

cesium-137
a product of atomic fission by explosion or breakdown of a reactor. It is feared as a pollutant because of its very long half-life.