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Quoting Jacob Keller <[log in to unmask]>: > 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