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Properties of Co-60 radiation

Radioactive 60Co can be generated by irradiating the stable element 59Co with neutrons inside a reactor. 60Co decays to 60Ni with a half-life of T½ = 1925.5 d. The decay of a 60Co nucleus releases one electron with 317.9 keV energy and two gamma quanta with energies of 1.173 MeV and 1.332 MeV.

The 60Co radiation sources used in the irradiation facility usually consist of activated discs or small pellets of metallic cobalt welded into cylindrical stainless steel containers. As the beta radiation (electrons) generated during the decay of 60Co very strongly interacts with matter, it is absorbed already inside the source or in its cladding so that only the two gamma quanta reach the outside. However, these quanta, too, may interact inside the radiation source or cladding (in particular by Compton scattering), and this may lead to a decrease in their energy. As a result, not only the two lines at the energies of 1.173 MeV and 1.332 MeV are observed in the gamma radiation spectrum emitted by a typical 60Co radiation source, but also a portion of low-energy radiation. The figure shows a typical spectrum of a 60Co radiation source.

Design principle of a typical 60Co radiation source

The two strong peaks at the energies of 1.173 MeV and 1.332 MeV and the smaller portion of low-energy radiation can be clearly seen. As the kind of interaction of the gamma radiation strongly depends on the structure of the radiation source (and of the whole irradiation facility), the spectra obtained for different 60Co radiation sources may differ.