Quoting Jacob Keller <j-kell...@md.northwestern.edu>:
Also, in your selenium crystal example, I think there would still be an anomalous signal, because there would always be regular scattering as well as the anomalous effect. Isn't that true?
It is certainly not correct to state that there is no anomalous scattering in elemental Se. There is anomalous scattering: the atomic form factors f' and f" have the specific wavelength-dependence, which can be measured from the diffraction data (by collecting data at different wavelengths); you can collect a fluorescence scan over the absorption edge etc. However, because there is only one type of scatterer (the f' + if" for all atoms are the same), Friedel's law remains valid, i.e. I(+h) and I(-h) remain the same. And even this is only true as long as we consider that the atoms are spherical and neglect anisotropy of anomalous scattering etc.
Marc
