> 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
I beg to differ again with regard to our selenium crystal: there is a normal
diffraction pattern arising from the unbound [majority of] electrons
(imagine the crystal below the K-edge, for example--no resonant scattering,
right?), but then there is also another signal arising from the resonant
scattering, which has a definite phase lag with respect to the
elastically-scattered wave. Is there something I am missing?
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