Neutron Silver Activation Demo Cell

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Jim Kovalchick
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Re: Neutron Silver Activation Demo Cell

Post by Jim Kovalchick »

Ah yes. Of course you are right about the Rh 104 product. I was looking at a chart in an activation analysis text and found that there is a Rh 104m product with a 51 keV gamma and a 4.3 min half life. The cross section is 12 barns for that reaction. My Geiger will see that energy. If only looking at beta, you are correct, only the the Rh 104 is relevant.
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Jim Kovalchick
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Re: Neutron Silver Activation Demo Cell

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Tonight I ran the fusor twice. I terminated the first run after a total time of about 12 minutes when counts started to drop presumably from heat. I fan cooled the chamber and started a second run that ended with a run at near peak flux that varied no more than +/- 10% for seven minutes.

I collected data from my activation cell and plotted together with data from the run on 2/23. I need to think a little bit about the shape of the latest curve and the difference in how steady the latter part of the curve.

Jim K
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Richard Hull
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Re: Neutron Silver Activation Demo Cell

Post by Richard Hull »

When doing 10 sec or 5 sec collection times to generate a curve, which is the right thing to do, the background always plays havoc near the 3rd or fourth half-life count. Cosmics and natural Rn and local U glass, U or Th ore and so many other factors really clutter up the low end in 5 to 10 sec data gathering periods. Bill and I both expressed extreme frustration due to my uncommonly high background readings. I am sure you do not have my back ground levels and are a bit more lucky in this respect. Still, even with a background, good data can be sifted out in the form of good overall, representative decay curves.

Here is a test I recommend to everyone. Insulate a 6" length of #22 bare (naked wire). place it in your lab. Attach it to the negative hot terminal of a 1 kv DC supply and ground to your AC mains the positive 5kv terminal. turn it on and walk away for at least 4 hours. Return and turn off the supply, remove the wire and using only a mica windowed GM counter, preferably hooked to a digital counter, and measure what you have collected due to Radon gas in the air.

Key to the success of this is and un-internally grounded 1KV DC power supply! Also critical is the ownership of a true alpha counting mica windowed GM counter. (preferably a 2" pancake type probe.
Needless to say, no kids or curious pets allowed in the room with the naked high voltage wire looming like a cobra in air ready to strike and kill.

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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Jim Kovalchick
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Re: Neutron Silver Activation Demo Cell

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I reviewed my data from last night's run. I have the ability to recreate bin sizes on the existing data from the PRA software. In the first second after I shut off the fusor 26 counts were recorded on the silver faced GM. That's an initial count rate of 1560 cpm. The next handful of seconds were close to this, so in pretty I'm pretty confident in the numbers. Now taking some liberty and will assumptions, I presume to estimate what this would be on a two inch pancake probe and silver disk. Assuming similar detector efficiency and that counts would be multiplied by the ration of the difference of surface are between my one inch probe and a two inch standard, the initial count rate would be 6240 cpm!
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Richard Hull
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Re: Neutron Silver Activation Demo Cell

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There is no doubt about it; when counting betas the gold standard is and always will be the 2" pancake mica windowed GM tube. I may wind up modifying my moderator imbedded GM tube from the Famos Russian SBM-20 to one of my 7311 LND 2" pancake tubes. I would have to change out my small 450 volt supply in the Arduino box to the same board that I designed to be a doubler circuit to get the 900 volts needed. I had designed the little PC board whipped up by express PCB to handle the 350-450 V Russian tubes or my 750V-900V 5979, 1B85, and 7311 tubes with the addition of one more capacitor and diode to be the doubler.

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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Richard Hull
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Re: Neutron Silver Activation Demo Cell

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I ultimately decided against the 2" pancake as its gamma sensitivity is too high due to the steel backing doing compton scattering, making it far more sensitive to gammas of all energies. Most of my lab gammas are in the 500kev to 1.5mev range. This would increase my background. The intimate contact Russian STS-5 is nearly perfect for beta and x-ray counting of rhodium and silver. I have and also tested as good, 40 STS-5 tubes on hand.

I have run the counting Arduino while operating the fusor at 35kv in neutron production and the average 5 second count is 658 counts of 658X12= 7896 cpm This is due to the weak but peak fusor x-rays penetrating the shell.
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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Jim Kovalchick
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Re: Neutron Silver Activation Demo Cell

Post by Jim Kovalchick »

Richard,
I think if there were a way to only detect betas, it would be ideal for the gamma cell. Another issue with gammas is s variable efficiency with energy. Perhaps that Russian tube of yours makes predicting the decay curve easier, but I haven't looked at the sts's relative ability with gammas as closely as you.

Jim K
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Richard Hull
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Re: Neutron Silver Activation Demo Cell

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We are told that GM tubes are poor detectors of gamma rays. Gamma rays have vast range of energies as does a shell based x-ray spectrum. Low energy photons can liberate electrons in their encounter with matter. The higher Z metals will exhibit more electrons per unit mass for any given photon energy. The two types of photonic scattering or absorption that are relevant to the GM tube are photo production and Compton scattering production of electrons. Metals of all atomic numbers and densities will photo and Compton produce electrons. The lower Z elements produce more photo electrons than Compton electrons at any given x-ray energy under 10kev. Between 10 and 100 KeV thick low Z elements produce fewer photo electrons and more Compton electrons both entering and exiting the metal.

A thin, light aluminum shell for a GM tube just will not see many gamma detections above 100kev energies. The thin shell will allow betas to pass through and be detected. However weak x-rays in the 20kev to 80kev range will penetrate and can be photo and Compton electron releasing electrons into the counting volume of gas, if not on first penetration then on internal impact with the opposite wall, thus, counting some fraction of the x-rays of lower energy.

The solid steel mica windowed 2" pancake is much more efficient if that is the word at counting all gamma out to nearly 1mev! This is due mainly to Compton electron release due to the very high Z steel case. The photo release is obviously high as well. So, for 80kev to nearly 1 MeV the mica windowed counter has a decent, perhaps 3%-5% effectiveness for counting the higher span of gamma energies.

This is why I use the small thin walled aluminum Russian tube. (background reduction) my 2" pancake in the lab has a 300 cpm gamma only count vs. the 58-70 cpm count on the Russian tube.

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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Jim Kovalchick
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Re: Neutron Silver Activation Demo Cell

Post by Jim Kovalchick »

I did a personal record silver activation today. 10 second bins so the first 10 seconds averaged over 1000 cpm.
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Re: Neutron Silver Activation Demo Cell

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Continuing on with my silver activation, my little one inch cell confirmed what my neutron detectors were telling me. I had another personal best fusor run. I cannot confirm my TIER but I am confident of mega neutrons per second.

Unfortunately, I fiddled with the detector monitoring my silver cell when it went to alarm causing me to lose the first 20 seconds of data, but the 10 second bin starting at 20 had more counts than even my best numbers at zero seconds.

My activation time was about 10 minutes.
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Re: Neutron Silver Activation Demo Cell

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Great work Jim! Somewhat leaky fusors, like ours, keep getting better as long as rather continuous operation persists. I hit 500,000 n/s TIER last night at 44kv. I just need more voltage to do better. I have up to 60kvDC sitting just outside the lab in a 60hz old XRF supply contained in a 700lb steel, oil filled box, but it would require a total, ground-up, rebuild of my entire system area in the back of the lab.

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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