The elementary theory of the scattering of X-rays by atoms, leading to the real atomic scattering factor fo, applies only for X-radiation whose
The real and imaginary terms, , in the atomic scattering factor are independent of sin(θ)/λ and in
In the older literature the term anomalous dispersion was used for resonant scattering. In macromolecular crystallography the term anomalous scattering is used widely in place of resonant scattering.
The resonant scattering of X-rays was theoretically predicted by Waller (Waller, I., 1928, Über eine verallgemeinerte Streuungsformel. Z. Phys. 51, 213-231.) and first calculated by Hönl (Hönl, H., 1933, Zur Dispersionstheorie der Röntgenstrahlen. Z. Phys. 84, 1-16; Hönl, H., 1933, Atomfactor für Röntgenstrahlen als