On Friday 24 April 2009 11:53:27 Jacob Keller wrote:
> Aha, so I have re-invented the wheel! But I never made sense of why f' is
> negative--this is beautiful! Just to make sure: you are saying that the real
> part of the anomalous scattering goes negative because those photons are
> sneaking out of the diffraction pattern through absorption-->fluorescence?
I am not sure about that "because". Let's not confuse correlation with
causality. The negative f' is adequately explained by the Kramers-Kronig
equation as being a result of the resonance interaction.
http://www.rp-photonics.com/kramers_kronig_relations.html
The maximum resonance is at the absorption energy, which is also the
maximum for the fluorescence. Both effects are "because of" the match
between incident photon energy and the energy required to kick an electron
out of its current orbital state. I am uneasy saying that one effect
causes the other effect.
Ethan
> Jacob
>
> *******************************************
> Jacob Pearson Keller
> Northwestern University
> Medical Scientist Training Program
> Dallos Laboratory
> F. Searle 1-240
> 2240 Campus Drive
> Evanston IL 60208
> lab: 847.491.2438
> cel: 773.608.9185
> email: j-kell...@northwestern.edu
> *******************************************
>
> ----- Original Message -----
> From: "Ethan Merritt" <merr...@u.washington.edu>
> To: "Jacob Keller" <j-kell...@md.northwestern.edu>; <CCP4BB@jiscmail.ac.uk>
> Sent: Friday, April 24, 2009 1:40 PM
> Subject: Re: [ccp4bb] Reason for Neglected X-ray Fluorescence
>
>
> > On Friday 24 April 2009 11:28:16 Jacob Keller wrote:
> >> Dear Dr. Holton and CCP4BBers,
> >>
> >> Are you saying that a resonant event is always accompanied by a
> >> fluorescence
> >> event? If that were true, wouldn't the resonant event end up manifesting
> >> as
> >> *negative* scattering component from the resonant atom, due to the
> >> elimination of an otherwise-scattered photon, this making the resonant
> >> atom
> >> "darker" than would be expected?
> >
> > Yes.
> > That is why the real component of the scattering factor, f', is negative.
> >
> >
> > --
> > Ethan A Merritt
> > Biomolecular Structure Center
> > University of Washington, Seattle 98195-7742
> >
>
>
>
--
Ethan A Merritt
Biomolecular Structure Center
University of Washington, Seattle 98195-7742
