[Ifeffit] Self-Absorption Corrections

[Francois Farges]

>Hi all,
>
>>Corwin Booth (at LBL lab, Berkeley) presented a very nice procedure
>>for making these corrections for EXAFS at the conference, improving
>>the work of L. Troger, et al from the mid 1990's.
>
>>I'd be interested in hearing others opinions on this topic, and
>>whether this should be included in Ifeffit.
>
>
>Corwin Booths approach to selfabsorption correction seems to be very 
>nice. I think that especially its possibility to give up the 
>"infinite sample thickness" limitation could be an important 
>improvement over the previous approaches.
>Still, it makes two (more or less implicit) assumptions:
>* the detector surface has to be parallel to the x-ray beam (phi + 
>theta = 90 deg)
>* the detector has to have a neglectable solid angle
>
>I'm not sure if these two assumptions hold for most fluorescence experiments?
surely no !  (cf ID21 at ESRF) and most future expeirments won't be 
that "ideal" for sure.


>When I collected my last fluorescence data a couple of years ago, 
>large solid angle detectors (like Lytle-detectors) were still in 
>use. I have shown that Troegers approach to selfabsorption 
>correction can be generalized for large detector surfaces (Phys. 
>Rev. B 60, 9335 (1999)). In principle this should be also possible 
>for Corwin Booths formula.

except for cations above than Zr.

>But when integrating over large solid angles, the exact geometry of 
>the experimental setup plays a crucial role in determining the 
>selfabsorption correction and I doubt that a useful implementation 
>into iFeffit would be possible.

yes but if you say so nothing will ever work. one has to start. I 
would be amazed to see that one day, the perfect self absorption 
correction code will work.


>If, however, everyone is using solid state detectors now, I would 
>say that implementing Corwin Booths code into iFeffit could be worth 
>the effort.

the most important to me is to expand it to XANES (as in FLUO by 
Haskel) where self-absorption effects are relatively more important 
as compared to the EXAFS, and going opposite ways depending if you 
considering the pre-edge or the main edge regions (because of the 
collapsing mu0 near E0).


FF
-- 
Francois FARGES

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