Investigating further, it seems that the problem might instead be that 
you are putting too much faith in the default values for the various 
parameters used to process the data.  I mean this in the sense of the 
third paragraph of this page:

https://urldefense.us/v3/__https://bruceravel.github.io/demeter/documents/Athena/bkg/index.html__;!!G_uCfscf7eWS!ZV4G3Tv0ADAF_XfsXPi7jp09Cy7uP90mAc50zVhsg5W6sWIUoUfT5EXKbLzmKOeDR5JshShN8zoyLHLiNB-XnQc-0reA8Q$

In short, you need to be more mindful of the values of the various 
processing parameters.  I am skeptical of the value of E0.  The values 
of the normalization parameters are certainly incorrect for this 
measurement, as is clear from the green and purple lines.  And when I 
click the orange normalization button, sure enough ... it plots the data 
inverted.

Playing around just a bit with the parameters explained here:

  https://urldefense.us/v3/__https://bruceravel.github.io/demeter/documents/Athena/bkg/norm.html__;!!G_uCfscf7eWS!ZV4G3Tv0ADAF_XfsXPi7jp09Cy7uP90mAc50zVhsg5W6sWIUoUfT5EXKbLzmKOeDR5JshShN8zoyLHLiNB-XnQcAXQmnXw$

and setting them to sensible values for your data completely fixes the 
problem.

Professorial advice: don't just trust things, make sure you understand 
what is happening with your data.

B

On 7/24/25 16:28, Muretta, Julie via Ifeffit wrote:
> Hello, First of all, thank you all so very much for offering this 
> platform to address XAS data processing!! It is wonderful to know it is 
> available. I am having a problem using Athena "Linear Combination 
> Fitting" with x-ray fluorescence
> ZjQcmQRYFpfptBannerStart
> This Message Is From an External Sender
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> Hello,
> 
> First of all, thank you all so very much for offering this platform to 
> address XAS data processing!! It is wonderful to know it is available.
> 
> I am having a problem using Athena "Linear Combination Fitting" with x- 
> ray fluorescence data from SSRL. Last year, we collected sulfur K-edge 
> XANES data at SSRL, beamline 4-3 and processed them using SixPack 
> (averaging 5 sweeps and normalization) and then used Athena to conduct 
> linear combination fitting of the XANES region. It worked great!
> 
> This year's data are presenting a problem when I get to the LCF step, 
> however.  When I import the sample data .mu file into Athena and plot it 
> by pressing the orange "E" button, the normalized spectrum looks like it 
> should (albeit noisy and sometimes not the best data, but that is not 
> Athena's fault). When I attempt to apply the Linear Combination Fitting 
> algorithm, fitting a number of spectra from reference samples also 
> collected _last year and this year_, Athena inverts the sample.mu 
> spectrum (between -1 and 0 rather than 0 and 1). It does not invert old 
> or new reference sample spectra. When I try this with old data, using 
> old and new reference sample spectra, I do not have this problem. With 
> the inverted sample spectrum, it often does not find a fit, but 
> sometimes it does.
> 
> Attached is an example Athena project file, the .mu file, and a plot of 
> the output of a test fit, for your reference.
> 
> I am hoping someone can please help me figure out why this is happening. 
> I cannot see anything wrong, based on my limited experience, but 
> hopefully it is something I have done wrong that can be easily corrected.
> 
> Thank you in advance,
> Julie
> 
> *Julie Muretta, Ph.D.*
> 
> /Materials Testing Laboratory Manager/
> 
> /Center for Advanced Materials Processing (CAMP)/
> 
> _(406) 496-4808_ | jmuretta@mtech.edu
> 
> _Montana Technological University <https://urldefense.com/v3/__https://  
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-- 
  Bruce Ravel  ------------------------------------ bravel@bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS-II
  Lead Beamline Scientist, 6BM (BMM)
  Building 743, Room 114
  Upton NY, 11973

  Homepage:    https://urldefense.us/v3/__http://bruceravel.github.io/home/__;!!G_uCfscf7eWS!ZV4G3Tv0ADAF_XfsXPi7jp09Cy7uP90mAc50zVhsg5W6sWIUoUfT5EXKbLzmKOeDR5JshShN8zoyLHLiNB-XnQdhkgZxlg$
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