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Concept
Cobalt-60
Summary
Cobalt-60 (60Co) is a synthetic radioactive isotope of cobalt with a half-life of 5.2714 years. It is produced artificially in nuclear reactors. Deliberate industrial production depends on neutron activation of bulk samples of the monoisotopic and mononuclidic cobalt isotope . Measurable quantities are also produced as a by-product of typical nuclear power plant operation and may be detected externally when leaks occur. In the latter case (in the absence of added cobalt) the incidentally produced is largely the result of multiple stages of neutron activation of iron isotopes in the reactor's steel structures via the creation of its precursor. The simplest case of the latter would result from the activation of . undergoes beta decay to the stable isotope nickel-60 (). The activated nickel nucleus emits two gamma rays with energies of 1.17 and 1.33 MeV, hence the overall equation of the nuclear reaction (activation and decay) is: + n → → + e− +
Corresponding to its half-life, the radioactive activity of one gram of is . The absorbed dose constant is related to the decay energy and time. For it is equal to 0.35 mSv/(GBq h) at one meter from the source. This allows calculation of the equivalent dose, which depends on distance and activity.
For example, a source with an activity of 2.8 GBq, which is equivalent to 60 μg of pure , generates a dose of 1 mSv at one meter distance within one hour. The swallowing of reduces the distance to a few millimeters, and the same dose is achieved within seconds.
Test sources, such as those used for school experiments, have an activity of
Official source
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