[Ifeffit] Peaks in MCA spectra

Matt Newville newville at cars.uchicago.edu
Tue Apr 1 12:26:18 CDT 2014

Hi George,

On Tue, Apr 1, 2014 at 11:56 AM, George Sterbinsky
<GeorgeSterbinsky at u.northwestern.edu> wrote:
> Hi Matthew,
> Hephaestus shows the strength of the Ll emission to be about 10% of the La2
> emission. When fitting the spectrum as a sum of Gaussians, I find that the
> area of of the Gaussian used to fit the Ll is 24% of that used to fit the
> La2. What would cause the ratio determined from tabulated data to differ
> from that found in the data I collected? Am I misunderstanding the meaning
> of the "strength" value in Hephaestus?
> Thanks,
> George

Strength here means "fraction of the X-rays emitted from the decay of
the initial level".  So, well above L3 edge, Ll should be ~10% of
La1,2.  Well above L2 edge, Ln should be ~10% of Lb1,2.

Those values of branching could be somewhat approximate.  It's also
possible that they don't properly account for the Coster-Kronig
process (inter-shell transitions, known to be important for L shells,
especially low energy lines where Auger transitions dominate).  I
thought they did take this into account, but perhaps that's not
correct. of the correction is

It wasn't completely clear what your incident energy is, but there are
also elastic and Compton peaks to consider.  I think the elastic line
being folded into your main peak would tend to make the ratio of La1,2
to Ll (Lb1,2 and Ln)  bigger, which seems to be the wrong way.  It
seems the incident energy was below the L1 edge (925 eV), because the
Lb3,4 peaks (~855 eV) are missing...    Then again, if the detector
was at 90deg in the horizontal plane from a synchrotron source, the
elastic peak may be tiny.

Compton scattering might appear to increase the low energy side of the
peak.   I think you'd have  to do a more careful analysis with the
energy well above all Co L edges with a well-resolved Compton peak
separated from the L lines to do a more quantitative analysis.

Finally, it's known (perhaps not well-known) that the peaks are
slightly asymmetric, with a low energy tail.   This is usually a small
effect, but perhaps it's part of what you're seeing.

All that said, I don't have a lot of experience working at such low energies.


More information about the Ifeffit mailing list