International
Tables for Crystallography Volume C Mathematical, physical and chemical tables Edited by E. Prince © International Union of Crystallography 2006 
International Tables for Crystallography (2006). Vol. C, ch. 7.4, p. 657


Figure 7.4.3.1
Schematic diagram of the inelastic scattering interactions, ΔE = E_{1} − E_{2} is the energy transferred from the photon and K the momentum transfer. The valence electrons are characterized by the Fermi energy, E_{F}, and momentum, k_{F} ( being taken as unity). The core electrons are characterized by their binding energy E_{B}. The dipole approximation is valid when Ka < 1, where a is the orbital radius of the scattering electron. 