[Ifeffit] Peaks in MCA spectra
Matthew Marcus
mamarcus at lbl.gov
Tue Apr 1 17:07:14 CDT 2014
I don't think so. This may be a better question for M. Newville, or whoever wrote the program.
mam
On 4/1/2014 9:56 AM, George Sterbinsky 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
>
>
> On Tue, Apr 1, 2014 at 11:45 AM, Matthew Marcus <mamarcus at lbl.gov <mailto:mamarcus at lbl.gov>> wrote:
>
> OK, I think the "other Matt" has solved it - it's the L1 peak. I was confused by an inaccurate attempt at reading the energy scale.
> Also, I somehow didn't read correctly the branching ratio from Hephaestus.
> mam
>
>
> On 3/31/2014 8:57 PM, George Sterbinsky wrote:
>
> Hi Matt,
>
> Thanks for your reply. Please see below.
>
> On Mon, Mar 31, 2014 at 8:10 PM, Matt Newville <newville at cars.uchicago.edu <mailto:newville at cars.uchicago.edu> <mailto:newville at cars.__uchicago.edu <mailto:newville at cars.uchicago.edu>>> wrote:
>
> Hi George,
>
> Calibrated spectra would help, but if we guess the calibration is 0.56
> bins/ eV, then we'd have
>
>
> I've attached a plot of the data showing the x-axis in keV. Also, as requested by Zack, I've attached a two column data file.
>
>
> line E (eV) bin #
> ------------------------------__---------------
> Co La1,2 775 434
> O Ka1,2 525 294
> C Ka1,2 277 155
>
> which looks pretty good. This puts the the unknown peak near
> 380/0.56 which is 678 eV. Tthat's very close to Co Ll (M1->L3),
> which is at 677 eV, and should be a bit less than 10% of Co La1 and
> La2, which is roughly right.
>
>
> Based on fitting the spectrum with Gaussians, the Co LI is 24% of the La2. As you mention, a value of roughly 10% is expected. What could cause such a discrepancy?
>
>
> So, I think it's Co Ll. That says the sample is just Co, C, and O.
> Is that reasonable?
>
>
> Yes, it is. I think maybe a little fluorine too, but it is very weak as I mention in my response to Matthew.
>
>
> What surprises me is that there is no signal from the elastic peak.
> Was that somehow filtered out?
>
>
> No, if there is an elastic peak it is probably lost under the Co La2.
>
>
> Thanks,
> George
>
> The fact that the counts don't go to
> zero between C and O could be many factors, including incomplete
> charge collection. This (and Compton scattering) generally make peaks
> have a slightly non-Gaussian shape, with a low-energy tail.
>
>
>
>
>
>
> Cheers,
>
> --Matt
>
> On Mon, Mar 31, 2014 at 5:01 PM, George Sterbinsky
> <GeorgeSterbinsky at u.__northwestern.edu <mailto:GeorgeSterbinsky at u.northwestern.edu> <mailto:GeorgeSterbinsky at u.__northwestern.edu <mailto:GeorgeSterbinsky at u.northwestern.edu>>> 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
> >
> >
> >
> >
> > _________________________________________________
> > Ifeffit mailing list
> > Ifeffit at millenia.cars.aps.anl.__gov <mailto:Ifeffit at millenia.cars.aps.anl.gov> <mailto:Ifeffit at millenia.cars.__aps.anl.gov <mailto:Ifeffit at millenia.cars.aps.anl.gov>>
> > http://millenia.cars.aps.anl.__gov/mailman/listinfo/ifeffit <http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit>
> >
>
>
>
> --
> --Matt Newville <newville at cars.uchicago.edu <http://cars.uchicago.edu> <http://cars.uchicago.edu>> 630-252-0431 <tel:630-252-0431> <tel:630-252-0431 <tel:630-252-0431>>
> _________________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.__gov <mailto:Ifeffit at millenia.cars.aps.anl.gov> <mailto:Ifeffit at millenia.cars.__aps.anl.gov <mailto:Ifeffit at millenia.cars.aps.anl.gov>>
> http://millenia.cars.aps.anl.__gov/mailman/listinfo/ifeffit <http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit>
>
>
>
>
>
> _________________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.__gov <mailto:Ifeffit at millenia.cars.aps.anl.gov>
> http://millenia.cars.aps.anl.__gov/mailman/listinfo/ifeffit <http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit>
>
> _________________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.__gov <mailto:Ifeffit at millenia.cars.aps.anl.gov>
> http://millenia.cars.aps.anl.__gov/mailman/listinfo/ifeffit <http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit>
>
>
>
>
> _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>
More information about the Ifeffit
mailing list