[Ifeffit] Self-Absorption Corrections

[Peter Pfalzer]

Francois,

> Here is a gif of Nb2O5 at Nb K-edge  and TiO2 at Ti K-edge. Both 
> collected withb same geometry and detectors and same BL (SSRL 11-2).
>  Fluo was collected at 90° to the beam (while transmission data was 
> collected on the exact same sample).
> 
> both spectra are normalized. Is there not any remaining
> self-absorption in the fluo spectrum for Nb2O5, despite data
> collected at 90° ?? (while TiO2 sounds fine, as Troeger predicted ?).

Clearly - like you say -, for Nb2O5, the amplitude of the fluorescence 
scan is reduced compared to the transmission data. Nevertheless I'm more 
surprised that the TiO2 scans match even near the absorption edge.
Although I find it hard to discuss your experiments without knowing the 
details here are two ideas that came to my mind:

* You can't get an exit angle of exactly 90 deg, it's always a bit 
smaller. Therefore selfabsorption won't vanish completely
* The amplitude damping, even at identical geometries, depends on which 
fraction of the overall absorption coefficient comes from the absorber. 
(The damping is something like 
mu_absorber(E)/(mu_tot(E)+g*mu_tot(E_fl)) .) I would expect this 
fraction to be larger and the selfabsorption to be worse for Ni.

> and anyway one needs a code with all the angles allowed to vary.

As far as I understand the mathematics in Corwin's paper, phi and theta 
can be varied independently. The phi+theta=90 condition seems to be only 
a limitation of the "sabcor" program that only asks for phi in its input 
file.

Peter


-- 
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Peter Pfalzer
Universitaet Augsburg                    Tel: +49-821-598-3215
Lehrstuhl fuer Experimentalphysik II     Fax: +49-821-598-3411
Universitaetsstr. 1
D-86135 Augsburg
Germany                   Peter.Pfalzer at physik.uni-augsburg.de
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