As asked, I'm trying to understand the origin of Gaussian shape of characteristic x-ray peaks in EDS. Mostly, these peaks are in a Gaussian shape.
Ideally, the peak should be a Delta-function, is that right? Why there are signals with higher or lower energies laying around the maximum peak? Is there a physical picture of this?
Dear Huaping Sheng,
you know that the peak in EDS is due to the sum of charges electrons and holes created by the incoming x-ray.
The statistical variation of the numbers of collected charges by the electronic circuit of the detectors is the reason for the peak broadening.
Statistical variations are caused by the stochastic recombination processes of the electron and holes charges on their way to the detector electrodes. Even the primary numbers of electrons and holes is a statistical number due to fact that they are the result of a huge number of scatter processes.
However some deviations from Gaussian peak profile also occur:
http://www.globalsino.com/EM/page1755.html
http://www.globalsino.com/EM/page1757.html
Gerhard Martens
Hi Gerhard,
Thank for answering me:)
Here is my interpretation of your explaination. Correct me if wrong.
The energy displayed in the final result, i.e., the spectrum, does not directly reflect the energy of the x-ray. Instead, it shows the number of electron-hole pairs created /collected by the circuit. Since this number is a statistic value, it can be either a little higher or lower for a single x-ray pulse (imagined as partilces). And this caused the gaussian curve like distribution of the peak. Is this right?
And yes, I have also found the webpage you referred. It is indeed a good place to go for us.
Thank you again!
Yes, your conclusions are right.
You do not 'see' the energy of the x-rays but only the numbers of electron hole pairs created by the x-rays and reaching the electrodes of the detector. Depending on the detector material the energy needed for the creation of an electron hole pair is different. So Si and Ge detectors will have different numbers of primary electron hole pairs per incident x-ray photon of same energy.
For details please see for example:
http://www.desy.de/~niebuhr/Vorlesung/Detektor/Vorlesung_4.pdf
Gerhard Martens
Now I understand it. This is very much different from eels, where the edge position is a direct reflection of the energy loss. And thank you for the document. It helps.
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