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
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