Definition of internal conversion in English:

internal conversion

noun

  • 1Physics
    The conversion of energy from one form to another within a particular system; especially (in later use) a process in which the energy of a gamma-ray photon emitted by a decaying nucleus is given up to an orbital electron, causing the electron to be emitted from the atom.

  • 2Chemistry
    The radiationless transition of a molecule or atom from one state to another of lower energy but the same multiplicity.

Origin

Early 20th century.