Author Topic: uranium Ma Mb  (Read 330 times)


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uranium Ma Mb
« on: August 11, 2021, 01:11:50 AM »
Hi all,
sorry for my silly question - I´m beginner, but I would like to explain, why in WDS intensity of Mb line of U is higher than Ma? I thought that all elements have intensity of Ka, La, Ma line 100 and other lines are much lower (moreover table values in Jeol software also show that Ma has 100 and Mb has 60). Why reality is different from theory? Is there some covering with another line? 
Thank you very much


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Re: uranium Ma Mb
« Reply #1 on: August 11, 2021, 02:32:57 AM »
The short answer is: U Mβ is not higher than U Mα. It is spectroscopic nuance of P10 (90 % of Ar) based gas proportional counters. (If You will look to EDS You will see that U Ma on Uranium standard is higher than U Mb). It happens that Ar K absorption edge is in between U Ma and U Mb. There are few overlapping processes which makes that difference of measurement present.
First U Ma is at lower energy than Ar K edge, and is better absorbed by Ar K shell, thus the X-ray of that energy ionizes less of Ar (this is actually questionable for me too, where the absorbed energy go? does P10 emit non-ionizating radiation?).
Second process is that higher energy than Ar K shell will cause secondary xray fluorescence of Ar, which will creat additional ionisation of gas chamber, which is known as "Ar escape peak" in PHA. If You would filter Argon escape peak at PHA, and would do WDS scan You would see, that U Ma is actually higher than U Mb.

Last but not least, You should not look only to absolute height of peaks, but for intensity comparison you should normalize peak height with background height (I_peak/I_bkgd), without any PHA filtering You will see that actually even on P10 gas proportional counters U Ma is more intense peak than U Mb, as Bremstrahlung background is buffed-up at lower theta (higher energy) than Ar K edge too.
« Last Edit: August 11, 2021, 05:02:36 AM by sem-geologist »


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Re: uranium Ma Mb
« Reply #2 on: August 11, 2021, 08:25:43 AM »
SEM geologist is exactly correct.

In fact there is already a topic on this issue here:
The only stupid question is the one not asked!