[Ifeffit] Self absorption questions

[Anatoly Frenkel]

Matthew:
 
It is a beautiful summary. Thanks for putting it together.
 
Here is another reference, for your collection:
 
A. Ryazhkin, Y. Babanov, M. Takafumi
"Thickness inhomogeneity and fluorescence effects in EXAFS spectroscopy
for powder samples: solution of the inverse problem".
J. Synchrotron Rad. (2001), 8, 291-293.
 
as well as the earlier one:
 
D. L. Brewe, D. M. Pease, J. I. Budnick, 
"Corrections of residual fluorescence distortions for a
glancing-emergence-angle x-ray-absorption technique "
Phys. Rev. B 50, 9025-9030 (1994).
 
and the later one:
 
A. I. Frenkel, D. M. Pease, J. I. Budnick, P. Shanthakumar, T. Huang 
Application of Glancing Emergent Angle Flourescence for Polarized XAFS
Studies of Single Crystals 
J. Synchrotron Rad. 14, 272-275 (2007)

 
Anatoly
 
 

  

-----Original Message-----
From: ifeffit-bounces at millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of Matthew
Marcus
Sent: Wednesday, November 07, 2007 11:31 AM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] Self absorption questions



You can find a writeup which explains overabsorption in great and gory
detail at
http://xraysweb.lbl.gov/uxas/Beamline/Operation/Operation.htm .
    mam
----- Original Message -----
From: "Richard Mayes" <mayes at ion.chem.utk.edu>
To: "XAFS Analysis using Ifeffit" <ifeffit at millenia.cars.aps.anl.gov>
Sent: Wednesday, November 07, 2007 7:39 AM
Subject: [Ifeffit] Self absorption questions


>
> Greetings all!
>
> I'm trying to explain self absorption for our group's guide to EXAFS
and I
> need some help understanding some of the finer details of self
absorption.
> In the realm of fluorescence EXAFS, am I correct in that at a given
> energy there is a certain penetration depth of the X-rays that is
expected
> (in a thick, dilute sample), but in a thick, concentrated sample, the
> penetration depth is actually less than the expected depth in thick,
> dilute samples (causing the decrease in the amplitude of the
oscillation
> peak in Bruce's "wiggle up" of the XAFS oscillation)?  Then, in the
> "wiggle down" of the XAFS oscillation, the penetration depth is
actually
> more than what would be expected so the depth of the oscillation
valley
> decreases.  As a result, for thick concentrated samples like a metal
foil,
> in the "wiggle up," the fluorescence accounts for fewer than expected
> absorbing atoms and in the "wiggle down" the fluorescence accounts for
> more than expected absorbing atoms.
>
> Next, in our amorphous silicates (doped with Ti, V, Cr, W, or Sn), is
the
> self absorption effect greater in the lower Z elements (like titanium)
> than in the higher Z elements (like tin)?  Does the high background
due to
> the silicon at the lower energies (4.9 keV) in relation to the higher
> energies (29.2 keV) have an effect or is it just an underlying,
> independent issue that is more pronounced with the lower Z elements
when
> self absorption occurs?
>
> Thanks!
>
> -Richard
>
> --
> Richard Mayes
>
> Graduate Research Assistant
> Barnes Group
> 450/452 Buehler Hall
> Department of Chemistry
> University of Tennessee
> Knoxville, TN 37996
>
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