Neutron detection moderator embedded activation!

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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Richard Hull
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Neutron detection moderator embedded activation!

Post by Richard Hull »

I debated reporting this effort in my new fusor V posting as it bears on the fusor V work and an idea I have had rolling around in my head for some time. The foregoing being said, there are good ideas and bad ideas. This, I feel, is a great idea, but in my lab and with my highly variable, high level of background radiation, the results will not allow for lower level activation detection with ease.

I will give the epitome of the process here. I am still musing over this effort and will continue the work.

I refer all to the superb moderator I used in the recent rebuild of fusor V in the Construction forum. (URL given below) I noticed that the total envelopment of the large 3He tube in HDPE far exceeded the results over the older water moderator used in Fusor IV. I also noted that indium foil placed on a plastic coupon and inserted in the new HDPE moderator. really allowed for the total replacement of the old "Neutron Oven" used with Fusor IV and was an improvement at the lower end of activation.

Both indium and silver have good activation levels for strong beta emitters which, unfortunately, have half-lives of under 25 seconds. In the past I have shut down the fusor, grabbed the activated specimen, and raced for my 2" pancake NIM based, GM counter to place the specimen smashed onto the face of the GM detector. This process took on the order of 10 seconds at best.

Due to the efficiency of my current larger HDPE moderator, I thought, "Why not take one of my many slender Russian Beta-Gamma tubes, used in my homemade GM counters, wrap it in the foil to be activated and place it in the counter moderator?"....But how to do this??

The Process

I noted the long slender 1-inch by 1-inch by 18-inch HDPE rod needed for the moderator, (see my detailed moderator posting...URL below), might provide the answer. I proceeded to mill out the section of this rod that would contain the foil covered tube and a slot for the connecting BNC cable. (see photos). The tube and BNC cable assembly within the rod were place in the central cavity just over the 3He detector.

A special counter was needed for this effort. It was made up using an Arduino Uno micro controller as its core component. It was realized that a running counter would just read the torrent of x-rays while running the fusor. Thus a "start count" push button was needed to start the counter the instant the fusor was turned of after an activation run. Also, it would be nice if after every ten seconds of counting, the count could be stored in the Arduino's EEPROM. The count is then zero'd and resumed for another 10 seconds and the EEPROM storage cell incremented by one to have the next count stored again. This process is to be repeated for 60 - 10 second periods to generate the exponential decay chain of measurements. I felt this was a fabulous opportunity. to eliminate the "running of the bulls" to the NIM counter to maximize the initial seconds of decay. A second push button was needed. ("memory dump") Once all the smoke cleared and data taken, at any point, later on, one could hook the device to a PC and dump a comma delimited string of numerically ordered counts from the Arduino's EEPROM to the Serial monitor screen on the PC and using the Control A and control C keys to paste to a notepad file. This stored file could be waltzed over to EXCEL and generate a graph! This type of automated counting and storage was right in the Arduino's wheelhouse! The counter and program were completed in a no sleep 30 hour period.

It worked!!....Kinda'...

My rather huge variable background fouled the entire process. Sure, the first three ten second countes were large and obvious to the meanest intelligence, but after that, the whole thing went to hell and back. The subsequent counts had the variable background added in and by six to ten, 10 second periods there was no semblance of a decay! I am confident that in a much lower background, this system would shine like the sun!

I submit the following "catch-up URLs for reference and the numerous photos of the steps in the process.

Fusion V build - viewtopic.php?f=6&t=13501
Moderator build - viewtopic.php?f=13&t=13553


As always click ion images to enlarge..........
Attachments
This old mill has been used a lot to create all foils.
This old mill has been used a lot to create all foils.
first composite image of probe construction.
first composite image of probe construction.
Last composite image of embedded probe.  Note silver around GM tube
Last composite image of embedded probe. Note silver around GM tube
Guts of counter.  Arduino, HV supply for tube, readout and push button board
Guts of counter. Arduino, HV supply for tube, readout and push button board
Final setup in use for activation
Final setup in use for activation
counting after activation
counting after activation
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 detection moderator embedded activation!

Post by Dennis P Brown »

First, great pics and set up, of course. Your experiments are well thougth out.

That rolling mill is the exact one I have - my unit, I will be converting to high temperature rolling.
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Re: Neutron detection moderator embedded activation!

Post by Frank Sanns »

The larger the detection area, the more the counts. Double the area doubles the background counts as well as the signal counts.

It is the signal to noise ratio that needs to be improved. Put half an inch of lead around that tube or a standard pancake probe element and you will be in heaven. Filter out most of your background gammas and let the neutrons stream right on through. Of course the moderator must still surround the lead and the probe but you will probably improve the signal to noise ratio a couple orders of magnitude.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: Neutron detection moderator embedded activation!

Post by Richard Hull »

Great minds think in similar circles, Frank. I have already done that a day ago, but have yet to test it as I have spent a good deal of time on a revision to the program. The issue is the Gammas in the lab. The moderator plastic shields against 100% of the extant betas, the tube stops all alphas (thin metal shell). This means it is only a pure higher energy background of gamma. I will report on the background drop soon as I have a number of chores and honey-dos which I have ignored in the rush to get this activation effort going to my satisfaction.

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 detection moderator embedded activation!

Post by Richard Hull »

A great success this morning! Yes, I am still up at 4:33 AM. I ran the fusor for a record run this evening (see data in the new fusor V construction posting)

I had placed the lead, as noted in my post just above, on top of and to the side of the moderator on Wednesday, but only got around to testing it this AM. The 1/16" of lead seen in the attached image really cut down on the background and leveled it out a bit. Still many wild fluctuations. I'll have to massage the attached graphs a bit. Unfortunately, even though there are a lot of data points taken, 10 second counts are only going to get a few counts and any variation is going to be just terrible. We are dealing with some fast decay times so that we can enjoy some fast activation. Thus, the 60, 10 second samplings started instantly at removal of fusor HV from an activation run. Maybe only a one second delay to push the "count begin" button.....No more wasted seconds dashing to the NIM bin setup in the middle of the lab and fiddling with the pancake elevation probe prior to hitting the count start button there.

I attach an image of the lead shield which proved most helpful. Also, I attach 3 Excel plots of the data taken over 60 ten second samplings pulled from the Arduino's EEPROM following the count-and-store period after the run from activating the silver. The plots are 1. unshielded embedded GM background run. 2. Lead shield in place with new background run 3. The graph proving neutron activation of the 24.5 second isotope. At the end of 2 minutes there might be a barely detectable signature of the longer isotope. Just too much noise.

You guys be the judge. I will continue to work the numbers. The lead was not even noticed by the fast neutrons, it was the HDPE that tamed them for counting. Note: the lead positioning was based on the nearby "shed" and some material up above. It worked out OK, I think. I might try more lead, but I think I got the medium energy gammas snuffed out a bit.

Richard Hull
Attachments
lead bkgd shield.Anno.jpg
unshieldedGMBKGD.JPG
ShieldedGMBKGD.JPG
NeutronActivationAG 8 Aug 20  TIER.jpg
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 detection moderator embedded activation!

Post by Frank Sanns »

Looks like the limited shielding dropped your background from 15 counts down to around 12. Not a very big change but not much lead either.

No matter as your graph is showing a great activation of 82 counts (per minute?). This is a big jump over the 12 and clearly due to activation.

It appears that you are switching off the fusor once the foil is activated and measuring the decay times. While this is good to identify the half lives, it is not necessary to see how the fusor neutron output is running.

Would it not be better to measure the steady state activation numbers with the fusor running full out? After three or so half lives of run time, there will be an equilibrium. It is that equilibrium plateau that is giving you all isotope decay contributions no matter how short or long they are. Taking a background before and after the run will give the numbers you seek for the level of activation. Of course when the fusor is switched off finally after all of the measurements, you get your decay time curve like your #3 graph so nothing is lost. Only gained.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: Neutron detection moderator embedded activation!

Post by Richard Hull »

The background never changes much and is irrelevant, of course, if you want to see proof of activation. In this case, with an averaged back ground of 13-15 counts, the 82 count first peak and subsequent counts are definitive and shows an over 5 times background activation level! This is what I wanted to see show up. My neutron counter is the sole arbiter of how my fusor is doing in a solid quantitative, though un-calibrated manner.

Activation is for "grins and googlers" to demonstrate how you can, indeed, make things radioactive with neutrons, (neutrons being the ultimate proof of D-D fusion)....A cool demo thingy, but it has to be super convincing to a critical audience. As a long time shower of my fusors, the audience is the thing, here. I have run my fusors for reporters, idiots, the idle curious, as well as the fully capable and fusion savvy people. Activation, for most, is just another "show and tell" during fusor operation, but for the adroit and trained in the art, it is the real proof of the pudding, regardless of some counter roaring in the background that the operator is "claiming" are real neutron counts.

I realize that...
1. With enough lead, I could run the activation counting system constantly and take readings. I can piddle with that at any future time. I would also have to alter the software to store thousands of ten second count intervals. (Easily done in a single line of code on the Arduino). However, by shutting off any source of radiation, (shutting down the fusor), all the more impressive that you have made silver radioactive....
2. I also realize that the full activation time for the 24.5 second half-life, Ag activation product at any given, fixed flux level, is only 2.45 minutes. This is why I shut the system down and took the count after finally obtaining 68k CPM on the neutron counter for about 3 minutes. I had been running the system for 20 minutes at 40k CPM, then inching it to 50k CPM, and then finally bumped over 60k CPM, ( a record on fusor V, to date), thus, I realized this was a peak and took several one minute counts on the neutron counter well over 60k CPM. At the point of 68k CPM, I shut the system down and instantly started the counting.

The 40 k CPM for some minutes was not going to do it for me, nor was the 50k CPM for subsequent minutes. All they were doing is lightly activating the long lived product over this long period of varying, yet ever increasing flux, and ever peaking the short lived one, but only to those levels of fluxing. It was the short lived product coupled with the over 60 k CPM, for the required 3 minutes, that I was after and I got it.

I will look into more lead, but only from the perspective of killing more background noise levels. All familiar with PMT castles, know that more lead can mean a limit to background levels where the lead becomes a contributor to background, due to the following points.

I also wonder if some of the noise is related to gamma, Compton scattering in the silver and the even the fusor, for that matter, due to the harder gammas. Remember, some of the gammas are up to 2.8 MeV. I doubt there is much pair production though as photoelectric electron scattering and Compton scattering would predominate for the far more prevalent under 1 MeV gammas.

Nice to talk these issues out.

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 detection moderator embedded activation!

Post by Richard Hull »

I just came in from the lab running the badckground count with 10 times the original thickness of lead. 5/8-inch thick plates of lead were used. This might have knocked the background down a point or two, if that. However, I noticed a lot of higher peaks. In lead this thick, Compton scattering and pair production and photo electrons are possible, Bumping the counts up in the extreme count range. make of this what you will.
Attached image. You just can't get this thing quiet in my background of gammas.

Richard Hull
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Heavy lead shield bkgd.JPG
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 detection moderator embedded activation!

Post by Frank Sanns »

Something is not right Richard. Think about how much the tungsten backed geiger probe blocks spurious background radiation. You counts should have been cut down at least by a factor of 10. Are you sure you are not getting noise in your tube or electronics? Even new lead would not be contributing hardly any extra counts compared to your lab background.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: Neutron detection moderator embedded activation!

Post by Frank Sanns »

I just took my Ludlum low energy gamma probe and tested a hot radium source at 1 inch. The counts were cut by a factor of 10 with just 0.25" of lead.

Also, there is an unusual amount of variability for in your background data for that length of count times. look at your higher counts. They are making a straight line with good correlation one data point to the next. But when it get down closer to the noise floor, it becomes extremely variable.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Re: Neutron detection moderator embedded activation!

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I have scoped the tube during my assembly as I adjusted the proper GM tube voltage. An immaculate scope trace resulted no noise, a flat, zero volt base line save for the huge 5 volt detect pulse sent to the Arduino interrupt pin. Finally, the tube has zero tungsten in it. The shell is pure, very thin aluminum to let in the betas to which it is most sensitive along with very low energy gammas. High energy gammas arriving at the tube would zip right through undetected. An Am241 source makes it scream as those are only 60 keV gammas and are easily detected due to photo electrons from the Aluminum shell. So, there is zero noise in the electronics and zero tungsten present in the tube. This is why I refuse to even take a count with any fusor power applied or the supply even turned on at zero variac position. I have a total power kill switch to the HV control variac before I press the count begin button. The entire area is EMF free during the count.

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 detection moderator embedded activation!

Post by Richard Hull »

Still battling the background. Lots of suggestion from Bill Kolb as well as Frank. I just can't kill background even with 5/8 thick lead plate due to gamma P.E. and Compton radiation.

Due to dispersed storage issues, I have gamma coming in at this setup over a 2 pi situation and just can't shield the moderator over that range. I can only shield for my most intense direction gamma. Add to this the Compton scattering and Photo electrons from the GM tube walls, it is just not merely a case of a whole bunch of lead unless I could attempt to shield over that 2 pi range. My current setup will not really allow that, so I hit the hot directed gamma with shielding and it is what it is.

Enjoy, mumble, muse and cogitate. I think I will just go with the 1/16th inch sheeting and carry on. I was rather unimpressed with the external 5/8 thick lead. It covered only about .4 pi from the most intense direction. It is that uncovered 1.6 pi that made the 5/8 inch thick reduction unimpressive

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 detection moderator embedded activation!

Post by Richard Hull »

To beat the background back a bit in the resultant Ag activation effort, I will increase the surface area of activation by 800%! See image below.
The beauty of the variable and movable components of the "toy block" built up moderator is showing its value. I have already tested the tube in its assembly for background in the moderator. It is just a tiny bit lower on average than the old setup. The old setup will be kept in reserve of course.

I will cover the new rectangular form in the next day of two and test it out. I will keep all abreast of how it does.

Richard Hull
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Large GM Anno.jpg
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 detection moderator embedded activation!

Post by Richard Hull »

Another great activation this evening. I was able to hit 3He numbers of 93,000 cpm for about 3 minutes after 6 or 7 minutes at rates over 40,000 cpm on the climb past 60,000 and 70,000 to 80,000. I find that skipping just one day of operation the system is difficult to push above 60,000 cpm. However after two days of rest, I have to run the system and struggle to get to 50,000 counts, however if I shut down and let the fusor chamber cool and start back up 3 hours later, I have no problem hitting 80,000. I dare not experiment and leave the system off for 2 weeks. I will prep the system prior to the big HEAS event in early October as folks will expect it to function well.

I attach the graph of the Excell file.
Attachments
Hit 110 counts in the first 10 sec count! (660 cpm)  I can start the count within 2 seconds of the shutdown of fusor power.
Hit 110 counts in the first 10 sec count! (660 cpm) I can start the count within 2 seconds of the shutdown of fusor power.
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 detection moderator embedded activation!

Post by ChristofferBraestrup »

Very intersting progress! There is one problem that have been nagging me ever since you made this thread: The STS-5/SBM-20 tubes are aluminium-cased, they will undoubtedly activate as well. For aluminium activation this might be of no consequence but for silver, shouldn't the corresponding decay be two superimposed decay functions? And given the aluminium casing, couldn't the tube by itself function as a complete assembly for Al-activation?

I think it would be interesting to try out a similar concept with a flat-plate plastic scintillator coupled to a PMT with a long-ish acryllic light pipe.
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Richard Hull
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Re: Neutron detection moderator embedded activation!

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A non-issue for sure. Aluminum requires a lot of neuts delivered over a much longer period to activate to any measurable degree compared to Silver. Fusors are operated over rather short periods. As such, the aluminum has no figure in this case. How could the tube of the GM boost the silver activation?? It will not emit neutrons as it is activated. The silver would absorb most of the thermal neutrons that try to reach the aluminum due to the cross sectional figures. In short, the silver would act as a neutron absorber, protecting the aluminum to a degree from activation.

Of note, there are indeed two simultaneous decays going on with Silver! There are two that can fully activate rather for any given flux within 600 seconds of exposure. This is why I chose to set the Arduino up to collect data for only 600 seconds. (see graph)

Ag110 will fully activate from activation time, t=0 and be in "activation equilibrium" in 130 seconds! Ag108 will fully activate to activation equilibrium from T=0 within ~600 seconds. The instant neutrons go away, (fusor turned off), both nuclides start to decay from decay time, T=0. Thus a complex curve results plotted by solving simultaneous, dual exponential decay equations. My friend Bill Kolb has joined me in this effort and I submit his efforts on my behalf in the image below.

Aluminum has no place in any of this unless one has access to a steady 10e5 neutron flux over the normal 600 second activation period as Al27 has an atrocious cross section of 0.2 compared to either of the silver nuclides, the worst of which is 150 times more likely to capture a neutron than the aluminum shell of the GM counter! Add to this, the fact that full activation of the aluminum would require an exposure time in any flux of 10,100 seconds 17 times longer than I expose the silver for....Figuring further.... at my peak first 10 second count, (see graph), I detect 10 bq of total silver activation radiation. The aluminum by comparison would contribute but .0006 bq to that count over the 600 second neutron activation period. I now consider Bill Kolb as a partner in this endeavor. As such, the graph is 100% attributable to my old pal,William Kolb.

Richard Hull
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Bill Kolbs best fit 8-16 and 8-30 activation.JPG
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 detection moderator embedded activation!

Post by Richard Hull »

I have, since HEAS, been busy with my activation efforts following a degree of calibration for my system due to Bob Reite bringing his remball system to HEAS. (my remball system has a defective indicator electronics box). Many of the preceding images in this post have been made with my Arduino data logging box. This box took 60 successive reading of 10 second counts. This comma delimited data was placed in Xcel to generate all the graphs seen in all the preceding posts. Bill Kolb has assisted with his work on generating a computed best fit for the dual silver decay paths which agree very well with the data collected in the graphs.

As the silver 110 decays with a half life of only ~24 seconds, the first ten second count is a smear of counts taken over almost a quarter of the half life, I have changed two values in only two lines of code in the Arduino program to alter the count interval to only 5 seconds taken over 120 counts. (Still a 10 minute data collection period.). It is realized that statistically halving of the count, doubles the error. However, I feel that the long 10 second count will smear, by a large amount, the first half-life's peak of Ag108. It is unfortunate that the background is so high, yet, also halved along with the total interval's count. It is hoped that the peak of the AG110 will be more representative of the first 10 count intervals.

Note: If this shorter interval of 5 seconds proves too noisy I will return to the 10 sec count interval. This may be the case once I get the Rhodium.

I submit my new background graph over the total 10 minute count interval. I also contribute the decay graph of a super run of fusor five with a peak TIER of 825,000 n/s run with a peak neutron count in my detector of 140,000 CPS.

Richard Hull
Attachments
NeutACT 11-4-20.JPG
Background 11-1-20 5 sec.JPG
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 detection moderator embedded activation!

Post by Richard Hull »

To go with the above post, Bill Kolbs best fit for the Ag110 and Ag108. The run on the 4th was really great.
While the scatter is amplified due to the 5 second counts, the trend line clustering is obvious.

Richard Hull
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Bill Kolbs best fit 11-4-20 activation.JPG
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 detection moderator embedded activation!

Post by Richard Hull »

There be Rhodium!

Yes, I bit the bullet, spent the long buck and the image is contained below. It cost exactly what I recently paid for the large 6" - 6 way conflat cross!!
I hope to set this up in my enclosed moderator activation scheme in some fashion soon. More later. Yes, the sting of $500 still hurts a bit, but the die is cast.

Edit 11/20: What a difference a day or two makes! Rhodium hit $13,800 per troy ounce!
Edit #2 11/23: Rh hit $15,300 today for a while.

Richard Hull
Attachments
Rhodium.anno.jpg
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 detection moderator embedded activation!

Post by Richard Hull »

I finally ran the rhodium activation effort. I attach images of the probe modification and of a 20 minute comparison, activation run of silver versus rhodium.

A bit of background. I have not done any activation since a week of two after HEAS. As some may remember I did fantastic activation at HEAS with over 120,000 peak CPM neutrons in an activation run. Laying fallow for two months, the wall loading was zero. I spent about three days of running fusor V to just get the fusor back up into the 80k CPM range, at best! I have shortened the count to 5 seconds per data point in the Xcel graphs, to better capture the fast decays. Nonetheless, with fusor V producing less than optimum results and the lab getting colder, I decided to try the effort of comparison runs.

As some know, the Ag 110 has a half-life of 24 seconds and decays very rapidly. It has a neutron capture cross section of ~80. Rhodium has almost double the half-life with a cross section of ~145 These two characteristics make it the ideal fast activation metal with the highest cross section of its one isotope composing 100% of the metal. Silver 109, the fast activator to Ag 110 is only 50% of the metal. Rhodium is king, for sure.

I went into these runs worried that rhodium due to a number of factors would be crippled due to the factors listed below.

1. The old silver probe is seen to have 100% coverage of the activated metal as a nice cylinder of silver of 9999 purity completely covers the GM tube. The rhodium covers only two sides not even 50% coverage.
2. The old silver probe had 100% of it active detection length exposed to the activated metal. The rhodium strips do not cover the entire active detection length of the GM tube.
3. Worse still, was the fact that the silver run on the 24th had a fusor conditioned over its 3 day prior runs so that on the 24th, ~90,000 CPM neutron counts were obtained. I skipped the 25th not running the fusor at all and in just the 36 hours lost, the Rhodium run struggled to hit 74,000 CPM ( slight loss of wall loading.)

YET! The rhodium run beat the results of the silver run in spite of all the above handicaps! I love the longer single isotope decay time that spreads the decay out over time.

Net Results

Rhodium obtained 22% more activation with only 81% of the peak neutron activation that silver had and with only 45% of the tube counting versus 100% of the tube counting the silver....Wow!

Check out the photos and graphs. Rhodium is the the cat's pajamas!

Richard Hull
Attachments
Rhodium 1.jpg
Rhodium 2.jpg
Rhodium 3.jpg
Silver, silver, silver above  for comparison as noted in the above test.
Silver, silver, silver above for comparison as noted in the above test.
Rhodium, Rhodium  "Less is more with rhodium"  speaking in the Orwellian
Rhodium, Rhodium "Less is more with rhodium" speaking in the Orwellian
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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Mark Rowley
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Re: Neutron detection moderator embedded activation!

Post by Mark Rowley »

Excellent results Richard. Now you have me wondering if there’s an inexpensive and easily obtainable rhodium alloy that could be used for activation.

Mark Rowley
Last edited by Mark Rowley on Fri Nov 27, 2020 3:12 pm, edited 2 times in total.
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Richard Hull
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Re: Neutron detection moderator embedded activation!

Post by Richard Hull »

Rhodium plating was often used in the past on cheap junk jewelry as it provided a had and bright overcoat that would not leave a green of colored remnant on the wearer's skin. Rhodium was often sold in solution by atomic weight for plating. Needless to say any rhodium alloy or chemical compound would be priced based on the market spot of the current $14,700 per troy ounce by its atomic percent weight.

Technical stuff

I will, in future, retain the 5 second count data point grabs recently replacing the original 10 second data points in the silver Xcel graphs. In future Rhodium graphs, only the first 300 seconds of decay will be grabbed at end of run counting. This means only 60 - 5 second count periods, instead of the old 120 - 5 second count counts with silver. This is due to the single Rh104 half-life of 44 seconds. (6 X 44) = 264 seconds. The extra time is to assure total decay. I will only have to change two lines of code in the Arduino Uno controller in my "count box" at fusor V. A real snap to change and blow into the Arduino via the USB port

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 detection moderator embedded activation!

Post by Richard Hull »

Keeping fusor V busy and blasting rhodium up a bit. I attach the graph of today's run. Got over 100kcpm neutron counts.
Yellow bars are 1 sigma limits

Richard Hull
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RhodiumActivation 11-29-20 1 Sigma.jpg
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 detection moderator embedded activation!

Post by Richard Hull »

I feel I must explain the red line in the graphs fully to those not so well heeled in statistics.

1. The Red line is the arithmetic mean, "average", of a full 10 minute long series of 5 sec readings from the un-activated metal probe. A total of 120 individual readings. This is often called "background".
2. To a statistics person, they want to know the standard deviation about the average or "mean" This is the square root of the mean or average value. It is represented by the Greek letter Sigma
3. A one sigma confidence level in the average of a data set. Tells the statistician that the range of values above or below the mean will all fall within plus or minus 67% of the mean or average value of the data set.

I have attached an excel graph of my latest background test, let us look at it. I had the Xcel spread sheet compute the mean by adding all the 120 data point counts to a large number and then divide it by 120. I got the result of the mean or average to be 6.5 counts every 5 second count. However the Sigma is the square root of the mean which is 2.4. Thus 67% of all background measurements will lie between about ~4 and ~9 counts for every 5 second count result. these limits are shown to lie between the two yellow lines.

You can see the span above and below the mean allows for a lot of what was actually measured to one Sigma confidence level. This is reflected in the jumpiness of the data over the entire graph.
This indicates 5 second counts in an already high background area is not really all that great, but does allow a highly visible, if jumpy, indication of the natural exponential decay of the activated Rhodium.

As an example, scroll to the post just above this post. I have added the 1 sigma yellow bars to the result of my 11/29/20 Rhodium activation results This give a better view of when the activation counting ended at about (60 on the graph), 5 second intervals totaling 300 seconds or about after 6 full half lives of the activated rhodium. I will endeavor to continue the one sigma bars in future.

Richard Hull
Attachments
Background 11-27-20 5 sec1sigma.jpg
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 detection moderator embedded activation!

Post by Richard Hull »

Wow! This is a rolling post....I think I think too much after thinking and posting. (if you can decipher that sentence, you may need help)

Bill Kolb and I have been musing about my charts and graphs. I first noticed, during our discussions the intrinsic wild high count gyrations always seen during the first half life data grab be it Silver or Rhodium. These gyrations were way outside of the 5-6 six count wobble due to the one sigma background range. This is optically visible to the meanest intelligence. Bill mused over it as well. To put off any effort to deal with this to distraction, we left it to "it's what radiation does". It does random real well. It left me a bit uneasy, but we moved on to more pressing issues.

Alas, I was getting a soda after the above posting and a flash came to me. Beta recoil double counting!! I will explain below and in a diagram.

Beta recoil???

I have always loved this and include it in many radiation tutelages which I often I give. See diagram #1.... You can do this yourself. Grab a mica windowed GM counter and hopefully a beta only emitter Tl204 or Sr90 set up the scenario in the diagram and set two lead plates, ( I use tungsten), as shown. Remove plate #1 take a count, then put the plate back in place. Count again. Wow! cool, huh? Given betas of sufficient energy, they will recoil and create soft x-rays that will shine into the detector after impacting a super dense metal. This is beta recoil and bremsstrahlung.

Diagram #2 is the manner in which I think the huge peak variations occur during the first and part of the second half-life of these hot, short-lived, beta isotopes work to do this double counting of the same beta particle! It is partly due to the method of setup in my case.

The reasoning

1. Both silver110 and Rh104 have powerful peak beta energies, (2.87 meV and 2.44 meV respectively). As we know from the beta energy curves, they are not the bulk of the emitted betas but only a small fraction. Most beta energies gather around 0.3 to 0.6 the peak value.
2. Betas can easily travel through thin aluminum, like the shell of my Russian STS-5 tubes. Only the very weakest are lost to counting. Regardless, energy is lost as a beta electron moves through any solid matter
3. Acute angles of impact boost beta recoil as head on impacts with dense matter tend to just stop the beta particle....unless it penetrates the target at reduced energy.
4. From a materials science standpoint, both silver and rhodium are dense metals. These can both readily absorb and reflect beta particles.

I have tried to make the diagram and some of the ray trace keys fairly obvious. I have not covered every possible path, but more to show how double counting might take place.

The upshot is that the blisteringly hot betas that stand a chance of beta recoil, (few), are more likely to be numerous at the T zero in the decay scheme. As the activated material decays the number of hot betas naturally decrease. As the isotope "cools", the normal Sigma of background starts to become more prevalent. For double counting in the silver scenario the hot betas must leave the cylinder penetrate the GM aluminum make a count then re-penetrate the aluminum tube then recoil off the silver again and get through the aluminum again to trigger the second count.

The mass of active silver110 is only 1/2 the activity of the silver by mass. Not so for the Rhodium as 100% of it stands to be activated at its much higher cross section, so double counting is boosted in spite of the two possible unguarded escapes on the sides of the tube without a metal reflector of Rhodium.

I hope Bill likes this idea. Two heads are always better than one and that is a good thing. Anyone else's head have a better explanation?? Debate? Experimenting with radiation and numerous test instruments coupled with reading up on it a lot and often expanding on what you already possess is always to advantage.

Oh, as always, click on the diagram to enlarge it.

Richard Hull
Attachments
Beta recoil big.jpg
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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