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
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?
