In the XRF spectra of differents light matrices (lignocellulosic biomass) the sulphur K-alpha peak (2.30-2.31 keV) is wider than normal. At the right of this peak (about 2.4 keV) it seems as if there is a hidden peak overlapping the sulphur . However, no relevant chemical element generates this peak (K or L) and can not be explained by escape peak. PyMca also finds nothing in that area.
What can cause it?
Hi Ricardo,
what is about Pb M alpha 1&2 (~2,34keV)? Do you have Pb nearby, e.g. as shielding material ?
.... and Mo L beta 1 (2,4 keV)? what is your excitation source ? (Mo based x-ray tube?); or Mo as shielding, sample support ....?
You may share a bit more about your set up.
Dear Gerhard,
Thank you for your reponse.
My anticathode is of rhodium. The lead fluorescence seemed to me a plausible hypothesis. I putted a 1.5mm thick of Pb-sheet just above the sample holder (receiving the beam transmitted through 1cm of biomass). The spectra were the same with or without a sheet of lead (21 kV- 40 uA, without any filter).
Maybe some lead elsewhere around?
Tube shielding ?
What is about that peak when using a polymere ( just low Z atoms) e.g. PMMA or polycarbonate or Nylon, PET etc.: I think on Compton scatter from your sample when a lot of Pb radiation is coming from outside.....(just brain storm like thoughts...).
Shielding of detector input port against such radiation is a night mare. However for your low energy photons the situation is quite more relaxed.
When recording spectra without sample and without shielding on almost there is no signal in the zone. But when I recording backscatter with a 100% Teflon cilinder, a very small peak appears around position of Pb. When the fluorescence is recorded on pure Pb-sheet, a wide peak appears covering the entire area from 2.25 to 2.52 keV. I have no doubt that there is a bit of Pb in the measuring head either at the tube outlet and/or at the arrival to the detector (handheld equipment). The only problem is that a nonzero intersection coefficient appears on the calibration curve. All my attempts to correct the sulphur peak by subtracting proportions of the Pb signal have been unsuccessful, I believe that it is best to leave as is, assuming a peak over the sulphur K-zone even though its concentration is almost null.
I also have a similar problem, have got peaks 1.78KeV, 3.29KeV and 15.03KeV which I can figure out corresponds to which specific elements.
Help
Dear Wellington Tauya ,
please have a look at my detailed answer here:
https://www.researchgate.net/post/How_do_I_assign_peaks_from_a_given_XRF_Spectrum
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