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a chemical element, atomic number 27, atomic weight 58.933. (See Appendix 6.)
cobalt 57 a radioisotope of cobalt, atomic mass 57, having a half-life of 270 days; used as a label for cyanocobalamin. Symbol 57Co.
cobalt 60 a radioisotope of cobalt, atomic mass 60, having a half-life of 5.27 years and a principal gamma ray energy of 1.33 MeV; used as a radiation therapy source. Symbol 60Co.
co·balt 57 (57Co),(kō'bawlt),
Half-life, 271.8 days; decays by electron capture with emission of a medium energy (122.06 keV) gamma ray. Used as a diagnostic aid with some metabolic disorders.