Principle of internal conversion
An excited nucleus emits a gamma ray (a). This gamma interacts with one of the inner electrons of the atom (b), most likely with an electron of the K layer The electron is ejected from the atom. Absorbed by the electron, the gamma is absorbed and vanishes. The ejection creates a void in the layer where the electron was. The atom reorganizes : a more externel electron, here belonging to layer L, comes to occupy the void (c). An X-ray is emitted.