[Ifeffit] Basic question in normalization and background removal

Bruce Ravel bravel at bnl.gov
Fri Feb 8 07:44:50 CST 2013


On Friday, February 08, 2013 01:22:14 PM Bajamundi Cyril wrote:
> My first naïve approach to the approximation  of the normalization range is
> to choose a range such that the post-edge line is parallel with pre-edge
> line, this in my novice eyes this seems to be the case between these line
> two lines, at least in the XANES range. This observation came from playing
> with some spectra in the databases I found online. May I know the pitfalls
> of this approach?

Pre- and post-edge lines are sometimes parallel, but not in general.
As I said, the details of the sample and the method of measurement
have a lot to do with what the data look like.

I really cannot answer your question in general.  What you suggest may
work for you, it may not.  At the end of the day, the defensibility of
an analysis is the bottom line.  Can you convince your reader (or
thesis advisor or potential boss in a job interview or whatever) that
your intepretation of the analysis of your data is correct?

In the context of linear combination fitting, you have another tool at
your disposal.  You can prepare defined mixtures of your standards and
measure those the same way youmeasure your actual data.  If your
normalization procedure and LCF analysis works on the defined mixtures
and gives an answer that is consistent within its uncertainty with how
you made the mixtures, that gives you confidence that you can
correctly analyze the unknowns.

Of course that means spending an hour or two at the beamline measuring
those defined mixtures.  That takes time away from measuring the real
samples.  But if you end up in a better position to interpret the real
data, that seems like a win to me.

B


-- 

 Bruce Ravel  ------------------------------------ bravel at bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
 Building 535A
 Upton NY, 11973

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