Tuesday, March 7, 2023

Complete DIY XRF Setup

My DIY XRF setup is finally complete - it is comprised of an Amptek X-123 detector using the proprietary Amptek 25 mm2 / 500 μm Si-PIN X-Ray detector element (model FSJ32MD-G3SP), Amptek Pre-Amplifier and DP5 DPP /MCA.

Details about the detector are in THIS post.

On the exciter side, in the past, I have used X-Rays from an Am-241 source (59.54keV). Unfortunately, there is no exempt quantity or a way to obtain high activity, pure Am-241. The ones used in modern household smoke detectors are only 0.9 uCi (unless obtained from the old Pyrotronics industrial smoke detectors with up to 80uCi) but still have the Am-241 mixed and pressed into Gold and Silver foil which has parasitic emissions of the said metals in addition to the Am-241 decay product - usually a fairly strong Np La line emission (from Np-237 decay product). The Neptunium La-line is observed even with recently created Am-241) La at 13.95keV.

I decided to switch over to an X-Xay Tube where the emission can be controlled precisely, the spectrum is uniform with the exception of the XRF emissions from the target material (Tungsten in my case) but this is normally a single element and easy to remove from the spectra.

 I am using Moxtek Magnum series transmission X-Ray tube with Tungsten target - 10W total electrical power (-50kV / 200 uA) controlled by an X-ray source controller of my own design my own design.

The X-Ray tube is placed inside a Lead shield. The aluminum box on the right-top in this picture is the detector enclosure, housing the detector element, preamp, power supply and the Amptek DP5 Digital Pulse Processor.

This is my test setup while doing XRF on a piece of copper foil for initial Energy Calibration.

The aluminum box in the center of the picture is the X-Ray tube's high-voltage power supply module. It is a high-frequency switching supply with a very easy to work interface - 3 output channels (2 analog and 1 digital) and 3 input channels (2 analog and 1 digital) + 12V main power. The supply is very efficient and the current draw is around 1.5A at maximum power.

The X-Ray source aperture and detector at almost 90 degrees so the X-Rays are skimming the surface of the specimen.

This is the first XRF of Copper foil with the new source - the Ka line is at 8.05keV and to the right the Kb-line is at 8.90keV. 
I still need to adjust the detector Peaking Time and Flat Top Time as well as the Slow and Fast detector thresholds - currently I have over 99% of Dead time due to the current settings intended for low X-Ray flux source and too much of primary beam getting into the detector. Revising the geometry of the setup - the placement of the detector, exciter and sample should resolve this issue.

My X-Ray Source Controller works flawlessly, and I am really happy with the end-result.