[Ifeffit] Self absorption questions

[Bruce Ravel]

Hi gang,

I started a new page at xafs.org devoted to this topic.  Please add
new information, relevant literature references, and other resources
to the wiki page.

   http://xafs.org/Experiment/OverAbsorption

B



On Wednesday 07 November 2007 20:56:54 Anatoly Frenkel wrote:
> 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
> >
> > _______________________________________________
> > Ifeffit mailing list
> > Ifeffit at millenia.cars.aps.anl.gov
> > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>
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-- 
 Bruce Ravel  ----------------------------------- bravel at bnl.gov

 National Institute of Standards and Technology
 Building 535A, Room M7
 c/o Brookhaven National Laboratory
 Upton NY, 11973, USA

 My homepage:    http://xafs.org/BruceRavel
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/