Fusor 2020 Activation Experiments

For posts specifically relating to fusor design, construction, and operation.
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Mark Rowley
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Re: Fusor 2020 Activation Experiments

Post by Mark Rowley » Thu Nov 19, 2020 8:41 am

Thanks Richard. Fusoring and gamma spec is quite the mix!

After repairing the power supply I elected to try activating Vanadium. Figured it’d be better to go for a new element in the case I had another unexpected power supply issue. Happy to report that wasn't the case.

The vanadium sample was a 9.5g 5x10cm sheet at 99.98% purity.

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This sample was fluxed at roughly 2E+06 n/s TIER for 12 minutes. Far cry from the numbers I had last week but I’m not going to press my luck. Best to take it easy. Spacing from the grid was 17cm.

Once it hit the spectrometer it registered 15.1 cps.
200 seconds: 12.1 cps
1000 seconds: 6.9 cps
2000 seconds: 5.1 cps

The expected photopeak at 1434keV was immediately apparent once the spectrometer started its run.

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Since the fusor was down for repairs most of my wall loading had gone away. However, I’ll try building it back up again for a couple days in hopes of getting a better gamma spec of iodine. The 528keV photopeak was missing but I think a good 15 minute exposure at higher numbers should remedy that.

Mark Rowley

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Jim Kovalchick
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Re: Fusor 2020 Activation Experiments

Post by Jim Kovalchick » Thu Nov 19, 2020 11:37 am

I bought a piece of that vanadium on ebay a month ago. You beat me to the activation! As always, nice work Mark.

Jim K

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Richard Hull
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Re: Fusor 2020 Activation Experiments

Post by Richard Hull » Thu Nov 19, 2020 4:21 pm

Indeed, fabulous work! I have added you to the elite fusioneers touting your multi-element continuous activation. Great work and a seeming non-stop effort.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Mark Rowley
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Re: Fusor 2020 Activation Experiments

Post by Mark Rowley » Fri Nov 20, 2020 9:42 am

I’m running out of things to activate! lol. Gadolinium seems like something fun to experiment with, at least in the neutron detector department.

Tonight’s run was a 15 minute Iodine activation at roughly 2.8E+06 n/s TIER. Compared to the ill fated first attempt (Nov 12th) which was abruptly stopped after the first couple minutes, this one resulted with a much stronger peak at 441keV. The peak at 528keV is still elusive, however when background was subtracted a small peak (or possibly noise) was near the 528keV region. Fwiw, after another 1000 seconds in the spectrometer the peak had decayed to zero but I’m still not really convinced.

It’s also likely that my spectrometer resolution is not good enough to isolate such a small photopeak so close to the wide base of the 411keV photopeak. As pointed out by Carl Willis in his Iodine activation report from years earlier, the 528keV accounts for a minuscule 1.5% of decays while the 411keV a whopping 14%. That’s a tiny blip to isolate with a crude NaI(TI) spectrometer. This actually highlights my concern with attempting a Molybdenum activation. Any hint of TC99m (140keV) will be very small and nudged up against or enveloped by the the wide base of the natural lead XRF peak at around 90kev. Background subtraction on Theremino MCA has a tendency to leave a bunch of xrf noise.

Regarding the iodine, maybe it just needs more neuts thrown at it! I may revisit this one again in the future.

Mark Rowley

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