Dear Julie,

Thank you for sharing this issue.
I have reviewed the test.mu file, which contains the normalized spectrum, and would like to share a couple of observations:

In the pre-edge region (2400–2440 eV):
The spectrum exhibits NEGATIVE intensity values and a noticeable increase in intensity across this energy range.

In the EXAFS region (from ~2557 eV onward):
The spectrum shows a monotonic decrease in intensity, which contrasts with the increasing trend seen in the pre-edge region. This pattern suggests that the normalization may not have sufficiently flattened the post-edge portion of the data.

I recommend the following steps to improve the processing:
Truncate the data between 2400–2440 eV before normalization or fitting, as the negative values and rising trend in this pre-edge region might be disrupting the scaling and background correction. Additionally, redo the normalization in Athena, and set the “Normalization order” to 3. This higher-order polynomial fit is better suited for flattening the post-edge region, especially in cases where a residual slope is present.

I hope these adjustments help resolve the issue you're encountering with Linear Combination Fitting. Wishing you success with the rest of your analysis!

Warm regards,
Bokky, D.C. Nguyen
ALBA Synchrotron

On 2025-07-24 22:28, 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

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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

 

 

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