Especially, the crystallographers are interested in everything concerning resonance scattering, which is indeed a valid terminus technicus in natural sciences. The question of Jacob is very interesting. We have to distinguish between absorption cross section and scattering cross section and relate them, say, by Kramers Kronig. As I see it: The total scattering cross section of an electron depends on the eigenfrequency and the constant of friction of the electron bound to the nucleus. Near resonance the total scattering cross section increases dramatically and the proability to scatter an X-ray is much larger than remote from the edge. However, this scattering process is elastic: it means that the wavelength is NOT altered. However, a phase shift of the scattered photon occurs which is different from the 180 deg usually expected for Thompson scattering. We have to correct for this (Hönl-correction) and this gives us also the opportunity to determine phase.
If really absorption occurs, of course we have fluorescence which has lost all the phase relation relative to the incident photon and is indeed not scattered in reflections anymore, EXCEPT when there are collective processes as for example observed in "nuclear resonance scattering" of Mössbauer radiation. Marius > Dear Crystallographers, > > I have been wondering recently whether the anomalous component of a > diffraction pattern is of a > different wavelength from the regular diffraction pattern. It seems > reasonable as resonant > scattering seems to be akin to fluorescence, although as I understand > it, is not exactly the same. > Does anybody know here for sure, or at least where to look or whom to > ask? > > All the best, > > Jacob Keller > > *********************************** > Jacob Keller > Northwestern University > 6541 N. Francisco #3 > Chicago IL 60645 > (847)467-4049 > [EMAIL PROTECTED] > *********************************** PD Dr. habil. Marius Schmidt Physikdepartment E17 Technische Universitaet Muenchen James Franck Strasse 85747 Garching/Germany email: [EMAIL PROTECTED] http://users.physik.tu-muenchen.de/marius/ phone: +49-(0)89-2891-2550 fax: +49-(0)89-2891-2548
