[Ifeffit] Peaks in MCA spectra

[George Sterbinsky]

Hello,

I am writing with a general XAS question. It does not necessarily pertain
to Ifeffit, however, I think the topic is something some, maybe most, list
members will be knowledgeable about. So it seems like this list is a good
place to post this question.

On to the question. I have attached a plot of a MCA spectrum collected with
a vortex silicon drift detector. The spectrum is actually the average of
several spectra, all collected in the post edge region of the Co L-edge.
The spectra were averaged to reduce noise. The three peaks result from
fluorescence from carbon, oxygen, and cobalt. Low-energy shoulders on the
Co and O peaks are also observed. These can be seen as the regions of the
spectrum that are not well reproduced by the fit. The main reason I
included the fit in the plot is to illustrate the presence of these
shoulders, particularly in the oxygen florescence, where the additional
intensity is not so obvious.

I am writing to see if anyone has any suggestion as to what the origins of
these peaks might be. They are not due to additional elements, as they
appear at the same incident energies as the main florescence peaks, i.e.
the Co shoulder appears at the same incident energies as the main Co peak,
and the O shoulder appears at the same incident energies as the main O
peak. It is possible that the peaks result form other transitions.
Considering Co, the main peak is due to L3/L2-M4 transitions, and the
shoulder is in a position that could be consistent with L3/L2-M1
transitions. However, by fitting the peaks with Gaussians, one finds an
area for the shoulder that is about 25% of the area of the main peak. This
is significantly larger than what one might expect from tabulated
transition strengths like those given in Hephaestus.

To summarize, does anyone know what these shoulders might result from if
not lower energy transitions? If they are low energy transitions, why would
the relative transition strengths differ from tabulated values?

Thank you,
George
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