X-Ray Florescence With Am 241

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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George Schmermund
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Joined: Tue Aug 15, 2006 8:51 pm
Real name: George Schmermund
Location: Carlsbad, CA

X-Ray Florescence With Am 241

Post by George Schmermund »

I was attempting to make some room on one of my experiment benches today and ran across a box of loose sources. Included in the collection were some of the ~ 1 uCi Am 241 sources that I'm sure most of you have floating around the lab, too. Recognizing an opportunity to avoid further efforts at organization, I decided to distract myself with them.

I needed to find a interesting direction to wander off in, so I did a Google image search for the radiation spectrum of Am 241. What caught my eye was the low energy x-ray florescence lines generated by the decay products. They are bunched nicely below 30 Kev and looked like a good substitute for a low energy, low power x-ray tube. The ~ 59 Kev line looked helpful, too. It's interesting to see how many versions of the spectrum there are depending on the type of detector used. I've included a spectrum of my detector's interpretation.

Since I'd recently purchased one of the Russian proportional counting tubes from eBay, this seemed as good a time as any to test it. It works, but not very well. It will resolve some of the lower energy peaks, but really isn't up to the job. An earlier purchase of a double windowed proportional tube turned out to be a complete dud. The Be windows can still be salvaged, though. As long as the experiment was set up, I switched the Russian tube out for a tried and true GE 10-SPG tube. I could have used one of the Si(Li) detectors in the lab, but they take too long to cool down and I was after quick results.

Anyhow, since this experiment was lashed together in a couple of hours with no intention of being quantitative, I'll spare you guys the details of the measurements and just post a few of the images. They show the basic arrangement of the 2 sources pointing away from the Be windowed detector and aimed at the target. The images indicate that ~ 2 uCi of Am 241 can be used as an x-ray source for making a crude XRF system.

I may reconstruct the sources for a more efficient geometry and fix them into a Delrin holder. This will allow for a reproducible irradiating source that can be use with a wide assortment of other detectors. The current set-up is only a proof of concept quickie.

So, what does all this have to do with fusors? Not much.... I just thought that it might give other experimenters an idea on how to make radiation measurements with detectors other than GM tubes, NaI(Tl)/PMTs, and He3 proportional counters. As beam-on-target experiments become more popular here, it will be useful for builders to know much more about how to detect and measure an assortment of ionizing and particle radiation sources.
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1-AM241 3.jpg
1-AM241 4.jpg
1-AM241 1.jpg
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Anything obvious in high vacuum is probably wrong.
David Mitchell
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Re: X-Ray Fluorescence With Am-241

Post by David Mitchell »

Interesting observations, George. I also did some XRF experiments, using a 7.5 uCi Am-241 excitation source. My detector was room-temperature CdZnTe, biased at about 700V, and encased in 1.6mm aluminium.
My MCA was a Ortec 2K Trump card, and Ortec spectrum analysis software. I didn't record the plots, but I recall a significant response from lead - the Am source was located inside a lead pig.
I was searching for low energy peaks from various elements, without success, and I note that the proportional tube used in your investigations uses a beryllium window. I was thinking of modifying the CZT casing to include a beryllium foil window, so that I can access low energy peaks.
George Schmermund
Posts: 262
Joined: Tue Aug 15, 2006 8:51 pm
Real name: George Schmermund
Location: Carlsbad, CA

Re: X-Ray Florescence With Am 241

Post by George Schmermund »

David - Thanks for the reply. What you have described is the primary reason that I started this thread. There are many pitfalls in the use of sources and detectors that reside outside of those typically found in fusor work. As BoT projects increase in popularity here a higher level of understanding will be necessary to do meaningful radiation detection and measurement. Hopefully there will be more and more people here that do advanced experiments and not just construction projects.

Now, before the reactionary comments start, let me state that this post is merely an observation and not in any way a critique.
Anything obvious in high vacuum is probably wrong.
David Mitchell
Posts: 11
Joined: Fri Dec 28, 2012 8:29 pm
Real name: David Mitchell
Location: Victoria, Australia

Re: X-Ray Florescence With Am 241

Post by David Mitchell »

George - I mistakenly said in my comment that I'd used an Am-241 source to excite lead, whereas it was actually a Cs-137 source. I did save a plot, which shows Pb peaks at around 75KeV and 86KeV.
The americium source is intended as an excitation source for lower energy work below the 59KeV Am peak, as you've demonstrated.
Availability of inexpensive surplus parts and online research literature allows exciting possibilities regarding sources and detectors. Something I never thought possible in my younger days.
Another type of detector for LE X-Rays, which I'm interested in assembling is a peltier-cooled optical PIN diode, which should give energy resolution approaching the Amptek devices.
A compact X-Ray/neutron source using a pyroelectric lithium titanate crystal operated under low pressure (again used by Amptek in one of their products) is another possible project.

Cheers
George Schmermund
Posts: 262
Joined: Tue Aug 15, 2006 8:51 pm
Real name: George Schmermund
Location: Carlsbad, CA

Re: X-Ray Florescence With Am 241

Post by George Schmermund »

David - I did a quick test with a piece of solder to see what the K and L series lines for lead and tin would look like with the current setup. The two L alpha and beta lines for Pb show up well along with the L lines of the Sn. Due to the low resolution of the detector, the lower energy Sn lines are mixed with other lines that would be expected in the sample. The K lines of the Sn are at the limit of detection for the proportional tube and show low sensitivity and very broad peaks.

This current experiment is barely useful, but does demonstrate that the Am 241 source is good choice for excitation. These sources are cheap, readily available, and safe (as long as you don't eat them or stick them up your nose). In the past I've used 10 uCi Cd 109 sources for these type of experiments with good results. They are also readily available, but they're much more expensive and have a relatively short half life.

There's not much sense in spending time to improve the proportional tube resolution. I have some other ideas for better detectors and your cooled PIN diode is on the list. Si(Li) detectors are hard to beat for XRF, but they're very expensive which puts them pretty much out of reach for the average hacker.
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Anything obvious in high vacuum is probably wrong.
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