Isotopes of cobalt


Naturally occurring cobalt, Co, consists of a single stable isotope, Co. Twenty-eight radioisotopes have been characterized; the most stable are Co with a half-life of 5.2714 years, Co, Co, and Co. All other isotopes have half-lives of less than 18 hours and most of these have half-lives of less than 1 second. This element also has 19 meta states, of which the most stable is 58m1Co with a half-life of 8.85 hours.
The isotopes of cobalt range in atomic weight from Co to Co. The main decay mode for isotopes with atomic mass less than that of the stable isotope, Co, is electron capture to iron isotopes, and the main mode of decay for those with greater mass is beta decay to nickel isotopes.

List of isotopes

Stellar nucleosynthesis of cobalt-56

One of the terminal nuclear reactions in stars prior to supernova produces Ni. Ni then decays to Co, which then decays to Fe. These decays power the luminosity displayed in light decay curves. Both the light decay and radioactive decay curves are expected to be exponential. Therefore, the light decay curve should give an indication of the nuclear reactions powering it. This has been confirmed by observation of bolometric light decay curves for SN 1987A. Between 600 and 800 days after SN1987A occurred, the bolometric light curve decreased at an exponential rate with half-life values from 68.6 days to 69.6 days. The rate at which the luminosity decreased closely matched that expected of exponential decay of Co.

Cobalt-57

Cobalt-57 is used in medical tests; it is used as a radiolabel for vitamin B uptake. It is useful for the Schilling test.
Co is used as a source in Mössbauer spectroscopy of iron-containing samples. Electron capture by Co forms an excited state of the Fe nucleus, which in turn decays to the ground state with the 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-60

is used in radiotherapy. It produces two gamma rays with energies of 1.17 MeV and 1.33 MeV. The Co source is about 2 cm in diameter and as a result produces a geometric penumbra, making the edge of the radiation field fuzzy. The metal has the unfortunate habit of producing fine dust, causing problems with radiation protection. The Co source is useful for about 5 years but even after this point is still very radioactive, and so cobalt machines have fallen from favor in the Western world where linacs are more usual.
Cobalt-60 is useful as an industrial gamma ray source also: uses for industrial cobalt include