X-ray spectral lines generated by the transition of electrons between '
inner orbitals'. The term '
inner orbital' serves to designate the sharp, not degenerate electronic levels of atoms in a solid
and therefore is a general term for all orbitals except the
valence band.
Source:
PAC, 1983, 55, 2023
(Nomenclature, symbols and units recommended for in situ microanalysis (Provisional))
on page 2026