XRF on a gamma spectrometer!

[kotarak]

Hi Boris,
I have a proper XRF spectrometer (Amptek) which covers 1keV to approx 60keV (max efficiency up to 13keV). In my setup i am also using Am-241 (30uCi) exciter.
The lowest Z element I am able to reliably detect is Sc.
Any lower and the Ka and Kb lines are simply absorbed in the air gap. If your CsI crystal is encapsulated in Al - this will only add to the absorbtion of low energy x-rays.
The air gap between the sample and detector must be minimal. Also keep in mind that Am-241 source emits parasitic K and L lines of Np (decay product) as well as Au and Ag used in manufacturing the Am-241 foil.

Check out my blog - blog. kotarak.net -i have a few posts on XRF.

[luuk]

Hi guys,
It took a little longer than prommised but I was very busy.
Here is a simple CsI(Tl) low energie probe test,
please read the pdf
Luuk

[Sparky]

Luuk,
I am impressed how quickly you put together such a good low energy probe. If you change your y scale to log and scan a little longer, you can probably see the 26 keV gamma of Am241 with your new probe. Of course, a big goal for amateur xrf is to put together an exciter that produces as little of this Am241 in your spectrum as possible, but looking directly at Am241 is a good way to check the low energy performance of your probe. Even with a perfect exciter design some of the low energy photons from Am241 are “reflected” directly from the target as coherent Raleigh scattering and down shifted Compton scattering. All you can do is discount this interference with your xrf spectrum and know where it will be.

Boris
In re-reading the University of Malaysia paper that I referenced earlier, I found that they did not see the “difference” scattering peaks as you described. All their target spectrums show a Compton peak around 49 keV. My own scattering experiments with Aluminum, Copper and water targets show there is some sort of shifting of the Compton peak (around 50) upward with higher Z. ???? Anyone have an explanation? A couple of useful calculators are below and my scattering spectrums are attached.
References:

https://web-docs.gsi.de/~stoe_exp/web_p ... /index.php
http://www.sciencecalculators.org/nucle ... cattering/

[luuk]

Hello Boris,
My goal was not to make a working xrf detector I just wanted to show that it is possible to make a simple but good working low energy detector with a low noise level, much lower than on the spectra showed in this thread.
And I think this type of detector can be used for xrf and can be build with out spending lots of money for it.
And I hope that it will stimulate others to try to make such a detector or try to improve there own detector, and try to get similar results.
If there is any interest I have some 2” CsI(Tl) ± 2-4mm thick discs for sale to experiment with.
Luuk