Neutron Silver Activation Demo Cell

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Jim Kovalchick
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Neutron Silver Activation Demo Cell

Post by Jim Kovalchick »

Now that my cross fusor is reliably producing neutrons, I am now doing some basic activation. In order to quantify my work, I have built an activation demo cell similar in concept to Richard Hull's silver foil wrapped Geiger with data recording at the moment activation is stopped.

My cell starts with a Philips ZP 1452 mica windowed GM tube that is a little more than one inch in diameter. I covered most of the face with 0.013" sterling (90% Ag). The detector was then buried in a 4 inch diameter poly tube filled with hdpe granules. The fill facing the fusor is 1.75" before the silver.

The detector is driven by a Ludlum Model 177 operating at 625 +VDC. The 177 has a db 9 output jack, but rather than fiddle with that, I installed a bnc jack tied to pin 5 of the db 9, to grab a negative 5 volt pulse for each detector count.

I put the output pulses through a 20 dB attenuator and a 3.5 phono plug. The plug was fed to the mic jack of a laptop.

I ran PRA soundcard mca software to record the pulses seen by the mic. There is an excellent count rate vs time function that has easily changed time bins. The bins can be adjusted at any time.

For the first demo run, I ran a background count for a while. I suspended PRA counting when I started the fusor because I did not want irrelevant xrays in my measurement. As soon as I shut the voltage off, I restarted the PRA counting where it left off. I am attaching a 20 second bin plot where you can easily see the spike in the right hand of the plot where the count restarted. I have not yet analyzed the data, but the decay appears to be consistent with activated silver. PRA can export the data to txt files.

I think my method has potential use for individuals who don't have Richard's arduino skills.

I'm not sure that I haven't done much more than slap some silver foil between some plastic to paraphrase a long time, respected fusioneer, but I am pretty happy with this arrangement because it makes one of my primary fusor purposes easier.

Jim K
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Result
Result
Cell by fusor
Cell by fusor
Filling cell with hdpe
Filling cell with hdpe
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Output pulse
Model 177 modification
Model 177 modification
ZP 1452 GM tube
ZP 1452 GM tube
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Jim Kovalchick
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Re: Neutron Silver Activation Demo Cell

Post by Jim Kovalchick »

Here is a 10 second bin plot.
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Richard Hull
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Re: Neutron Silver Activation Demo Cell

Post by Richard Hull »

Jim you are now listed as an elite fusioneer having activated silver as an already extant neutron club member.

About silver........... Standard "coin" silver in all US coins 1790s to 1964 = 90% silver...... All hallmarked and stamped "Sterling" silver = 92.5% silver...... "Fine" or pure silver = 99.9% or better silver
Both coin and Sterling silver contain added copper to make up the missing 10% and 7.5%, respectively. Copper increases hardness and wear characteristics.
Gold U.S. coin is also dealt with at the 90% purity level with 10% copper.
All precious metals are sold and traded in troy weight, traditionally.

Good work on cobbling up the detection system.

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: Neutron Silver Activation Demo Cell

Post by Jim Kovalchick »

I wanted see how theoretical decay looked against my most recent decay data.

I assumed that both Ag 108 and Ag 110 had built to saturation. This meant that the ratio of the initial activity of the two isotopes was equal to the ratios of there relative masses times the ratio of their cross sections. This gave me a start on the multiplier for each decay component. I still needed to correct for particulars of my detector efficiency, background etc. The background is just a constant added in the equation and the other stuff is a multiplier. I assumed that my arrangement saw decay products for both isotopes with the same efficiency.

To draw the theoretical curve I just derived the constant multiplier through my first point at ten seconds. I plotted the curve as if it started at 0 seconds.

Attached is the graphical result.

Jim K
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Richard Hull
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Re: Neutron Silver Activation Demo Cell

Post by Richard Hull »

Great work and clean decay data Jim!!

If you will remember and refer back to my moderator embedded work on silver done in Aug-Oct last year, (2020), found in a group of 4 page postings at ...

viewtopic.php?f=13&t=13568&start=10

You will see my Xcel graphs were submitted to my pal Bill Kolb who did best fits which included his two simultaneous equations for the decay of both silver isotopes on the log-lin graph straight lines he added. He had to assume or figure a constant, as well. I stopped using the silver and switched to Rhodium of which there is only one isotope. 100% rhodium activates to only one radioactive product. It turns out I bought that little $500 .04 troy ounce rhodium foil strip cheap! The current price is $22,500 per try oz. but it goes as low as $18,000 and then dances back above $20,000....Ouch!

Activation is the ultimate, noiseless proof of the fusion pudding. No one can say you had noise in your data with activation on a well thought out data capture scheme over the decay of the resultant product isotope. You have done a great job here.

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: Neutron Silver Activation Demo Cell

Post by Jim Kovalchick »

Richard,
Thanks for the feedback. I contacted Bill Kolb yesterday before I calculated my curve. He calculated the constants using least squares where I calculated them based on saturated activation. Our ratios differ by a factor of two as a result. Bill thinks I am adding uncertainty by running it this way and tying it to the time zero result. He may be right, though there is less detection uncertainty in the earlier part of the curve as you know. Today I will be pondering how my assumptions affect the curve and if I come up with something important I will report back.

Bill echoed your comment about Rhodium. Several years ago I had a chunk of it that I activated with an earlier version of my fusor, but that was before I emulated your embedded activation cell method and developed data collection. How I came to have the Rhodium and better yet, how I no longer have it is a story for another day. I will be on the look out for another piece, but it's not likely I will be paying for a piece anytime soon.

Jim K
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Re: Neutron Silver Activation Demo Cell

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Richard,
I pondered some more about curve derivation, and I believe the difference between where Bill and I landed is related to my assumption about saturation. I think the past, folks have said that silver activation saturation happens in just a few minutes. That's fine is you are just looking to catch the decay of the longer lived Ag 108, but Ag 110 will take longer to get into saturation. This means my ratio of initial activity factors of 110 to 108 was lower than what Bill derived empirically from your data. This makes sense if you only did runs of a few minutes. To see the impact of activation time, I am including in this post a table of both Ag 110 to 108 initial activity ratios and saturation factors all versus time in seconds.

Note: this post was revised on 2/26 to correct the column headers of the table of silver isotope calibration factors.

Jim K
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Re: Neutron Silver Activation Demo Cell

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A lot of good discussion has taken place between Bill and I and now you and Bill on Silver activation. In general, due to the length of time we can maintain max neutron count, we will, in a short run, never saturate the long lived isotope as your chart suggests. Yes, we will activate it but only at a reduced level. However the short lived product we can activate to a saturation easily in a short run.

My activation of both Silver and Rhodium was a well planned adventure. There was a long period of activation as I worked up to maximum neutron output. Activation was going on all the time, but I would only stop and count after I was able to get 5 similar peak one minute high readings in a row. This warranted maximum activation of the short half life-isotope. With silver, this let the long half-life isotope fall where it would, wherever that was. To avoid the mixed decay detections of the two isotopes, I spent the big bucks to buy the rhodium foil. In spite of the high price tag, I am glad I did. (Rh hit $23,000 per troy oz today.)

Due to the short half life of either silver or rhodium, I had to devise my little Arduino counter setup with silver/rhodium/GM moderator embedment. This nice setup allowed only a 1 second delay from fusor shutdown to activation count start of the 5 second interval counts. This lost little of the decay curve peak value. As I noted and others like yourself have witnessed at HEAS in the past, I would waste about 10 seconds on removing the activated silver from the neutron oven, racing to the digital counter around the other side of the fusor table, placing the silver under the 2" pancake in near contact and hitting the count start button. Doing this, I only recorded a single, total one minute count with 10 seconds of the hot peak shaved off the count.

Enrico Fermi used a Ra:Be source in his early activation work as a neutron source and used Rhodium as his favorite N source calibration standard. He did his extensive activation work in the late thirties following the discovery of the neutron.

Rhodium is the only element that is a 100% single isotopic mass with only one single short half-life activation product which can be easily read when presented with low N source flux conditions.

update and mea culpa 7/27/21:
It seems that rhodium has two cross sections for two different activations in spite of its 100% isotopic abundance of Rh103. Thus like silver it has a dual co-joint activation decay curve to the expected Rh104 beta emitter to saturation in just 220 seconds and an Rh104m which is an x-ray emitter which can be GM counted. Rh104m saturates in 750 seconds. Again both are still 100% isotopic activations and not activations of two different isotopes of Rhodium.

I attach my latest plot showing the Rhodium 104m still active above the background long after the Rh104 is dead.


Richard Hull
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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: Neutron Silver Activation Demo Cell

Post by Jim Kovalchick »

Richard,
I'm not sure I agree with your statement that the longer lived silver activation product will never be activated to saturation. At 900 second (15 minutes) activation time, it is saturated to over 98 percent. I believe it is within reach of a fusor to maintain that. In fact, I think it is easier to get that isotope into saturation than it is to get the Rhodium product into saturation. At a 900 second activation time, the Rhodium product is still only at 91 percent. Rhodium has a great cross section and it's slower decay makes it easier to collect data, but if one wants to use it for as a flux measurement for comparison purposes in a fusor, a greater run time is required.

Jim K
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Re: Neutron Silver Activation Demo Cell

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What!! Rhodium activation isotope has only a 43 second half-life!!! That is why both Enrico and I recommend it! In about 4 minutes or a bit over a 200 second exposure Rhodium is pretty max'd out. 900 seconds for the long silver at peak is bit long to maintain a rather uniform high neutron output in my fusor. I can run my neutron producing fusor for 20 minutes, 1200 seconds, if I want to maintain an even 200k neutrons/sec TIER, to fully activate the long silver to absolutely disappointing levels. It is important for Rhodium that if in and amongst 5 one minute counts you record 300k N in minute one and subsequently count 425 minute 2, 400 in minute 3, 550 in minute 4, and 580 in minute 5, the low 300, two 400 and 425 minutes cost you a lot of activation via decay in those low periods that was ruinous to the later 500k+ counts. It is cumulative activation sure, but variable low periods cause the decays to hurt the highs, lowering the final activation count. As such, it is imperative to use the term "fully activated" to mean over the full 5 or 6 half life period of neutron exposure that the flux be maintained at some rather uniform high level.(provided you are seeking maximum count due to full activation at the end of a "uniform" exposure period.)

Rhodium in(5) 43 second periods 1=330k 2=390k 3= 470k 4=410k 5= 590k done! The 590k period is nothing and will never add much to the activation as the total period is dominated by long decay periods and low N counts from the early periods. Thus, to say we fully activated rhodium is misleading and disappointing as opposed to having each and every period be in the 500k n/s range which would give a true full activation in a more of less uniform bombardment in the moderator and a much higher peak count at decay start time following activation.

Even a bulk mean or average of the five periods of 438k n/s means nothing as over each and every period the growth and interim decays are geometric in nature. ( a complex calculation) Regardless of complexity, a 900 second count on silver over varying neutron outputs over that long period would wind up being what ever it is. It will not represent a uniform full activation based on the highest or the lowest output of neutrons over the period.

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: 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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Re: Neutron Silver Activation Demo Cell

Post by Jim Kovalchick »

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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Re: Neutron Silver Activation Demo Cell

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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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Re: Neutron Silver Activation Demo Cell

Post by Jim Kovalchick »

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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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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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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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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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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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

Post by Jim Kovalchick »

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

Post by Richard Hull »

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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