Internal conversion is the act of returning from an excited state by an atom or molecule.

This is an alternative to gamma-ray emission, which is the usual method for an excited nucleus to return to the ground state. In internal conversion, the excited nucleus transfers its energy directly to one of the most tightly bound electrons causing it to be ejected from the atom. After the ejection of the internal conversion electron the vacancy is filled by another shell electron and the atom ejects one or several x-rays or Auger electrons.