COBALT-57

HISTORY

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JPNM Physics Isotopes

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Cobalt (kobald, from the German, goblin or evil spirit, cobalos, Greek, mine) with an atomic weight of 58.93, was discovered by Brandt about 1735. Cobalt occurs in the minerals cobalite, smaltite, and erythrite. It is a brittle, hard metal, closely resembling iron and nickel in appearance. The metal is used in electroplating because of its appearance, hardness, and resistance to oxidation. The salts have been used for centuries for the production of brilliant and permanent blue colors in porcelain, glass, pottery, and enamels. Cobalt carefully used in the form of chloride, sulfate, acetate, or nitrate has been found effective in correcting certain mineral deficiency diseases in animals. If cobalt ion is given orally it is only partially absorbed in the gut. The portion that is absorbed is rapidly excreted, 90% by the kidneys and 10% through the biliary tree.

Two radionuclides of cobalt, Co-60 and Co-57, have been useful in nuclear medicine. Originally, Co-60 was used for medical tracer studies, but it has gamma energies in excess of 1 MeV, a physical half-life of 5.2 years, and decays by beta (minus) emission. Co-57 has a half-life of 270.9 days, gamma photons of 122 and 136 keV, and decays by electron capture. For all the above reasons, Co-57 is the preferred nuclide for clinical use.

Prepared by Luis E. Diaz, M.D.

References

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Douglas J. Wagenaar, Ph.D., wagenaar@nucmed.bih.harvard.edu