Homebrew X-ray fluorescence (XRF)

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Brian McDermott
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Homebrew X-ray fluorescence (XRF)

Post by Brian McDermott »

There has been some talk of x-ray fluorescence in past posts, but no real primer on techniques to use in the home laboratory. Can you use a simple NaI detector and MCA or is there not enough resolving power at the low energies involved?

As for irradiation of the sample under analysis, what is typically used? In professional setups, a low energy x-ray tube (~20KeV) is used to irradiate the sample. What have others here used as an irradiation source?
3l
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Re: Homebrew X-ray fluorescence

Post by 3l »

Hi Brian:

I used a radio tube to be over driven... plenty of xrays.
rectifier tubes work best 2X2 or 1BT3.
Burning rays as the voltage was around 20 kv.
My detector was a geiger tube encased in a lead case with a collimating pin hole.
Used a meter stick and large wooden protracter to measure angles.
it was a go or no go set up.
I used mineral samples and metal crystals .
I measured the brag angle deflection in the crystal lattice.
The Xray tube was also coated in lead with a matching pinhole.
Crude as it was it did the job.
A photograpic plate behind the mineral would reveal a pattern as the xray was diffracted you could measure that pattern and get a pretty accurate measurement of the crystalline lattice.

Happy Fusoring!
Larry Leins
Fusor Tech
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Brian McDermott
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Re: Homebrew X-ray fluorescence

Post by Brian McDermott »

This is somewhat unrelated, but where does one get photograpic plates? Are they even made anymore? Is there a modern substitute?
Jon Rosenstiel
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Re: Homebrew X-ray fluorescence

Post by Jon Rosenstiel »

In case you haven't seen R. Hull's post on this subject, follow this link. Good info.

viewtopic.php?f=13&t=5330#p33774

As Richard mentions, Cd-109 and/or Fe-55 disc sources make good "exciters". I use a Cd-109 source.

Good source for sources:

http://www.spectrumtechniques.com/

They're very friendly folks. Give them a call and have your credit card handy. $40.00 for most 1uC source discs. $80.00 for 10uC discs.

Jon Rosenstiel
3l
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Re: Homebrew X-ray fluorescence

Post by 3l »

Hi Jon:

I remember reading about that post a while back.
What detector do you use for the X-ray fluorescence
spectroscopy?
If it's the bicron ...how low can you go with it.

Happy Fusoring!
Larry Leins
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Jon Rosenstiel
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Re: Homebrew X-ray fluorescence

Post by Jon Rosenstiel »

Larry,

My Bicron 2x2 detector will with certainty go down to 22.2keV (silver).
I haven't pushed the infamous eBay Bicron 2x1 detector into the lower energies yet, but it should go a tad lower because of the thinner xtal.

I also have a FIDLER detector (5" diameter by 0.040" thickness) that will go down to around 10keV. It doesn't work so swell on weak x-rays because it also picks up lotsa' background. (It'll pick up a chunk of uranium ore 12 feet away)!

Jon Rosenstiel
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Re: Homebrew X-ray fluorescence

Post by pkuiper »

I use polaroid film. Polapan 57 (3000 ASA) works well, but it seems that
production has been discontinued :-(
For developing you need a Polaroid cassette (545).

It works fine for x-rays of dead birds etcetera. And also for Laue pictures, of
course. Steffen Weber has a nice applet to help with interpretattion of all the
spots: http://jcrystal.com/steffenweber/JAVA/jlaue/jlaue.html .
3l
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Re: Homebrew X-ray fluorescence

Post by 3l »

Hi Jon:

How is the short xtal Bicron working out?
I've yet to use mine.
The Mca needs fixin and my shop is under renovation to fit all
stuff to do precise pulse measurements.
I hope to have it all done before the rainy season hits Mississippi.

Happy Fusoring!
Larry Leins
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Brian McDermott
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Re: Homebrew X-ray fluorescence

Post by Brian McDermott »

I have one of the Ebay Bicron detectors as well. Is it possible to swap out the crystal and put in one that has a Beryllium window to facilitate the passage of x-rays?
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Richard Hull
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Re: Homebrew X-ray fluorescence

Post by Richard Hull »

lots of stuff to answer.

If you go to the Amptek site URL given in my original posts so admirably put up by Jon you will see what the ideal xrf detector is.

NaI:Tl detectors can be used, but they are crappy at best and have close to zero resolution demanded to play in this narrow bandwidth region.

No you cannot change the xtal in the Bicron heads found on E-bay. They are set in stone......Thank goodness.

Photographic plates are still available to professional astronomers for big bucks. But you can't effectively get them. Polaroid film packs are the best you can do beyond buying common 4X5 cut sheet film and developing it yourself.

Jon has done about the best possible work that can be done in XRF with a NaI setup. You can identify a few lines in the most dense elements, but a lot are lost due to the lack of sharpness in the detection crystal.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Homebrew X-ray fluorescence

Post by Jon Rosenstiel »

Larry:

The eBay short xtal Bicron works quite well. (Especially considering the cost) Its sensitivity isn't as good as my 2" x 2" Bicron (particularly in the high energy range). But at very low energies (22keV x-ray of Ag) its resolution is about 2% better.
The ol' give and take.

Jon Rosenstiel
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Richard Hull
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Re: Homebrew X-ray fluorescence

Post by Richard Hull »

The Cadmium Teluride detectors rule here in the sub 100kev range where 180ev resolutions are demanded. A very good NaI would be doing good to hit 1 or 2 kev over the 100kev spread. many elements have lines so close that even 100ev resolution is not too sharp.

So while a good mca in the hands of an accomplished user with a superb NAI head can play in XRF it is not to be considered good enough to do serious XRF Work. NaI is for 80kev to about 1.5 mev with a stretch to 2.5mev on big 5" crystals. The GeLi is the king of 'em all though.

Richard Hull

Note** I appended (XRF) to Brian's original post title and my older post's title to make these interesting threads searchable in future with just the XRF letters.
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Homebrew X-ray fluorescence

Post by ChrisSmolinski »

I've used the Amptek detectors in a previous life. It was quite amazing to be
able to fluoresce a piece of stainless, and see all the K-alpha (and even
some K-beta) lines stand out, right where they should be. Used it to
characterize low energy (20 and 40 keV) x-ray sources. I also had one of the
CZT based detectors for higher energy x-ray sources, we used it up to 240
keV, and also to look at scatter from Cs137.
JohnCuthbert
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Re: Homebrew X-ray fluorescence (XRF)

Post by JohnCuthbert »

A little late in the day, but if anyone is interested, there is an XRF machine on ebay (uk) at the moment.
(I'm not the seller, nor am I that interested in buying)
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Carl Willis
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Re: Homebrew X-ray fluorescence (XRF)

Post by Carl Willis »

I think XRF using a NaI(Tl) detector of any kind is a real stretch.

Theoretical maximum resolution (FWHM) in a scintillation detector of any kind is dictated by Poisson statistics of electron emission from the PMT photocathode. Low-energy events make few photoelectrons, and hence have low resolution. The resolution scales as 1/SQRT (E). So if you have a NaI(Tl) detector with a FWHM (full-width half maximum) resolution of 7% at 661 keV (Cs-137) you have about 40% at 20 keV!

Now, as Jon has probably alluded to in his last post, you CAN locate the peak centroid of your 20 keV x-ray with better precision than +/- 40%. What the resolution really tells you is whether or not you can distinguish two peaks that are close, for example 20 keV and 13 keV. In this case, you cannot. You'll get just one big wide peak.

If you want to look at x-rays with a scintillator, consider a low-noise charge-sensitive preamp. Even though NaI(Tl) is extremely bright as a scintillator, at x-ray energies there can be some electronic noise. Bicron's website has a great little article on socket assemblies and preamps, and they have designed a preamp just for the purpose of x-ray analysis using NaI(Tl). I built the circuit and it's decent and cheap. Cannot be used for high-energy gamma spectroscopy though, unless I really crank down the PMT high voltage. It saturates at high energies.

-Carl
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