[Ifeffit] Self absorption Correction

[Richard Mayes]

Jens,

Since no one has answered yet, I'll chime in.  First let me direct you to a
discussion of self-absorption and other sample-related distortions:
http://www.xafs.org/Experiment/OverAbsorption  (this is a link from the
tutorials page of www.xafs.org).

As for your questions:

I think that you should use the non-normalized XANES data to perform the SA
correction.

for the angle-in and angle-out meanings, see Grant Bunker's paper on
self-absorption here:
http://gbxafs.iit.edu/training/Self_Absorption_effects.pdf

Now, how do you determine if you have self-absorption effects?  I have to
defer here to those with more experience.  What you suggest sounds
appropriate, but I'm not sure how you could determine this without studying
multiple concentrations of your absorber and watch the signals, i.e. does a
10% increase in absorber concentration translate to a 10% increase in
fluorescence yield (similar to what Matthew Marcus and Alain Manceau
describe in their paper, from the over-absorption link above).

HTH,
-Rich

On Fri, Jan 30, 2009 at 11:49 AM, Jens Kruse <jens.kruse at uni-rostock.de>wrote:

> Hi there,
>
> I have measured a pure reference compound with high absorber
> concentration in fluorescence mode (P K-edge XANES).  I tried to use the
> Self absorption correction  included in Athena but I don't really
> understand the results.
> Fist: Do I have to use the edge step normalized spectrum or the spectrum
> without normalization ? I tried both and the results  of course a quite
> different. I would rather use the not normalized spectrum.
> Second: the value "Angel in"  is this the angle between the incident
> beam and the sample surface" and "Angle out"  the angle between the
> sample surface and the detector position?
> Third: More general- How can I identify a spectrum suffering self
> absorption? Just comparing the relative peak intensities of total
> electron yield signal with the fluorescence yield signal ?
>
> thanks a lot for your comments,
> cheers,
>  Jens
>
> --
> Jens Kruse
> Institute for Land Use
> Faculty for Agricultural and Environmental Sciences
> Rostock University
> Justus-von-Liebig-Weg 6
> 18059 Rostock GERMANY
> Phone: +49(0)381-498 3190
>
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