Isomeric transition is a radioactive decay process that occurs in an atom where the nucleus is in an excited meta state (e.g. following the emission of an alpha or beta particle). The extra energy in the nucleus is released by the emission of a gamma ray, returning the nucleus to the ground state. This process is therefore similar to a gamma emission but differs in that it involves excited meta-states.
The gamma-ray may transfer its energy directly to one of the most tightly bound electrons causing it to be ejected from the atom, a process termed internal conversion.
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