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59Co is the only stable cobalt isotope and the only isotope that exists naturally on Earth. Twenty-two radioisotopes have been characterized: the most stable, 60Co, has a half-life of 5.2714 years; 57Co has a half-life of 271.8 days; 56Co has a half-life of 77.27 days; and 58Co has a half-life of 70.86 days. All the other radioactive isotopes of cobalt have half-lives shorter than 18 hours, and in most cases shorter than 1 second.

Cobalt-57 is used as a source in Mössbauer spectroscopy of iron-containing samples. Electron capture by 57Co forms an excited state of the 57Fe nucleus, which in turn decays to the ground state with emission of a gamma ray. Measurement of the gamma ray spectrum provides information about the chemical state of the iron atom in the sample.

Cobalt-57 is also used in medical tests; it is used as a radiolabel for vitamin B12 uptake.

Spectrum (Fullscreen)

5 minute measurement with a High Purity Germanium (HPGe) radiation detector.


Isotope: Cobalt
Mass number: 57
Atomic number: 27
Neutron number: 30

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