[Ifeffit] Peaks in MCA spectra

[Matthew Marcus]

Hmmm.  An interesting brain-teaser.  Scaling very roughly from the graph, the mystery peak shows up at about 715eV.  This is consistent with Fe.
Could there be a background from Fe somewhere in the detection systen?  The intensity between the O and Co peaks doesn't really look like
a peak, but just like a background tail, perhaps from the strong Co peak.  It seems to be a little to the right of where N (from, for instance,
a kapton window) would be.  I could be wrong, in which case my Fe theory goes away.  Now, I thought about an escape peak from Si, but I suspect that
this is really small down here and anyway, the Si L-fluorescence energy is 92eV or so, and the extra peak is about 55eV below the main peak.

Did you duck below the Fe edge to see if the peak to the L of Co goes away?

The peaks in the fit seem to be consistently to the left of the ones in the data.  Any idea why?  Was the energy scale not a fit parameter?
In order to analyze the 'extra' peaks, it may be useful to optimize the fit to the main peaks, then subtract to get the residual, including
the 'extras'.  What would happen if you added Fe and maybe N to the fit?

I admit that I've never done soft X-ray fluorescence, so my ideas come from hard X-ray experience, which may not totally apply.
	mam

On 3/31/2014 3:01 PM, George Sterbinsky wrote:
> 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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