Re: [Ifeffit] Self absorption questions

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@millenia.cars.aps.anl.gov [mailto:ifeffit-bounces@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" To: "XAFS Analysis using Ifeffit" 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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-- Bruce Ravel ----------------------------------- bravel@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/