Re: [Ifeffit] Self absorption Correction

Hi, In the "J. Phys. III (France)" paper you have the expression to calculate the "information depth"-magnitude. Self absorption will take place if this magnitude is smaller than your fine powder size. Typically, for a non-diluted material "information depth"-magnitude is (in microns) equal to one tenth of the measured edge energy (in keV) that should be compared to your powder grain size. Carlos Prieto At 08:51 03/02/2009, you wrote:

Hi, Thanks Richard and Carlos for the the links. But is the "Fluo"-Algorithm for self absorption correction also valid if I have the concentrated sample (standard) applied as a fine powder to a carbon tape or is it only valid for much much thicker samples?

thanks, Jens

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Message: 4 Date: Mon, 2 Feb 2009 09:51:10 -0500 From: Richard Mayes Subject: Re: [Ifeffit] Self absorption Correction To: XAFS Analysis using Ifeffit Message-ID: <5a2a54820902020651nfaf1af7q4ec435fc207fc38a@mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1"

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 wrote:

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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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