[Ifeffit] Origin of terminology "self-absorption"

[Scott Calvin]

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