XRF part II


After two days of working on my XRF (X-ray fluorescence) system, I’ve finally understood the following:

  1. My preamp was inadequate. I achieved a 14% FWHM (Full Width at Half Maximum) at the Cs-137 line with a 7% crystal.
  2. The Ba (Barium) shielding is ineffective. I’ve discarded it.
  3. I need to adjust the geometry between the Am-241 source and the detector.
  4. I require a proper X-ray collimator that shields the CsI(Tl) (Cesium Iodide doped with Thallium) detector from direct Am-241 gamma rays, allowing only X-ray fluorescence to enter. I’ve ordered some pure Bismuth metal to sand cast an appropriate one.

While waiting for the Bismuth, I’ve tested the arrangement of the Am-241 sources and found that they should be placed parallel to each other to minimize unwanted interactions. I’ve also discovered that the stronger the Am-241 source, the better the results. Currently, I’m conducting experiments with 3 sources, but I plan to increase this number to 6-8, totaling 6.4 microcuries (uCi).


I’m using a NIM system made out of:


CsI(Tl) FWHM @ 59keV

I’ve tested the FWHM (Full Width at Half Maximum) of my crystal at 59 keV from Am-241: it’s 18.1%. This is almost the best performance I can achieve with CsI(Tl) (Cesium Iodide doped with Thallium) material. I suspect that NaI(Tl) (Sodium Iodide doped with Thallium) could provide an improvement of two to three FWHM points, but I don’t have the capability to cut and prepare such material in my lab.


As I mentioned earlier, my old equipment was inadequate. However, this new one I’ve developed works exceptionally well. It’s also very durable and reliable!

My new preamp


A picture says more than a thousand words.


It seems that I can distinguish between copper and gold… not bad! I should try to further improve my system!