Re: [Ifeffit] Origin of terminology "self-absorption"

But the effect commonly known by that name not only has nothing to do with the re-absorption of the fluorescent light by the sample, it can be reduced by increasing such absorption, for instance by doing grazing-exit detection. mam ----- Original Message ----- From: "Matt Newville" To: "XAFS Analysis using Ifeffit" Sent: Tuesday, November 16, 2010 11:23 AM Subject: Re: [Ifeffit] Origin of terminology "self-absorption" It's a term taken from x-ray fluorescence spectroscopy, or probably really any fluorescence spectroscopy, where it has very sensible meaning: the attenuation of the fluorescence signal by the sample itself. I would even say it is used "mostly correctly" in XAFS, or at least with a similar intent as the original term, much as the term Debye-Waller Factor is used. --Matt On Tue, Nov 16, 2010 at 1:01 PM, Scott Calvin wrote:

I tried a few searches, but rapidly get lost in other uses of the term. My guess is we borrowed it from some other spectroscopy, much the way we borrowed "Debye-Waller factor" from XRD, and then proceeded to change its meaning. But it would be nice to be able to track that down.

--Scott Calvin Faculty at Sarah Lawrence College Currently on sabbatical at Stanford Synchrotron Radiation Laboratory

On Nov 16, 2010, at 10:54 AM, Matthew Marcus wrote:

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It's definitely a misnomer. I use "overabsorption" and encourage others to do so. I suppose to track it down would require going back over the seminal papers on the subject. mam

On 11/16/2010 10:19 AM, Scott Calvin wrote:

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Hi all,

As some of you know, I'm currently working on a textbook on XAFS analysis. Because of that, I'm going to occasionally pose some questions for the list that may seem a bit random. I hope none of you mind me using the list in this way; the questions may seem to come out of left field, but I think they will still be of interest to many.

With that said, here's my question for today:

What is the origin of the use of "self-absorption" to describe the suppression of fine-structure observed in thick, concentrated samples measured in fluorescence? I understand the physics of the effect itself, my question is the curious wording. Compared to a thin concentrated sample, the effect might better be described as "saturation," while compared to a thick dilute sample, it's actually related to a lack of absorption by other elements.

--Scott Calvin Faculty at Sarah Lawrence College Currently on sabbatical at Stanford Synchrotron Radiation Laboratory _______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit

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