Criticize my neutron detection setup

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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Silviu Tamasdan
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Criticize my neutron detection setup

Post by Silviu Tamasdan »

I'm nowhere near having a fusion-producing fusor, but getting there little by little. I've found it more productive to concentrate on one particular subsystem at a time, so lately I've been working on the neutron detection.
I have now what I consider a reasonable setup for detecting neutrons, and I'd love to have comments or criticisms. It's not in the final configuration yet (still need some stuff to make a more convenient and mobile moderator because right now it's a pile of things that need to be taken apart and rebuilt when I make a change).
I did not build the system, I purchased it. I have a pretty good idea how it's built, but can't really answer very detailed questions about its components.

1. Detector. It's a Russian SNM-32 3He corona tube. AFAIK it's one of the biggest they made, at 332x18mm. Datasheet says 700V for initiation of corona discharge, plateau at 1500V and above. In practice however I've found that the tube cannot be used at any voltage above 1275V. At higher voltages the tube oscillates giving high frequency/high amplitude pulses (over -100mV at 1000000-2000000cpm). The builder of the system says that is typical of many of the SNM-32 tubes he has worked with and recommended to keep the voltage below 1200V. I will attach some test results below, but essentially I have found that the tube can be used as a counter at voltages between 700 and 1200V.

2. High voltage source. It is USB-powered, software-controlled (has no physical controls - I would have preferred it otherwise, but oh well). Can deliver up to 3000V, and have tested it up to 1500V with various other detectors (photomultiplier-based scintillation gamma detectors, Geiger tubes). One disadvantage is that I cannot modify the voltage while a count is running. I have to stop the running count, change the voltage, and then restart.

3. Detection electronics. Biasing resistor, coupling capacitor and probably a charge-sensitive amplifier based on Bob Higgins' design, but I don't know the details. The acquisition part is a USB oscilloscope (Picoscope 2000 series). The front-end is a custom program that combines acquisition and control of the voltage source. I can set the voltage, and the trigger amplitude of the detected pulses. I can present the output in cpm or cps, it does some basic statistics automatically, and can record and save the shape of every single pulse it counts. I have found that latter feature very useful for tweaking voltages and trigger values. It cannot filter pulses by pulse duration.

4. Home-made moderator. As I said above it's not complete (I have some HDPE blocks on order) but I've improvised something that works already fairly well. I had a 15x20 block of HDPE, 1 inch thick. I cut it in 4 pieces 5x15x1inch and stacked them together to make a 4x5x15inch block. By itself that worked to some extent, either with the neutron source (see below) on one side of it and the detector on the other, or with both on the same side. But it definitely could use improvement. I don't have any other HDPE yet, but I thought about moderators and found that I did have something that in practice I found suitable. Both HDPE and paraffin are comprised of carbon and hydrogen at approx 1:2 molar ratio. Another thing that has carbon and hydrogen at the same ratio is mineral oil. More specifically, motor oil. Which conveniently comes in brick-shaped bottles, 2x4x8inches. I took 12 of these bottles (unopened, so no leaks), laid them flat in layers of 2x2 bottles, 3 layers high. I put the HDPE block at the top. The detector tube is inserted between the 2nd and 3rd layer. The check source, if used for a particular experiment, is inserted in the same place, close to the middle of the tube and in direct contact with it. This way both detector and source are surrounded by at least 10cm of moderator in all directions. I will aattach results below.

5. Neutron source. It's made with a 5mCi polonium static eliminator, less than 2 weeks old so it should be still close to its stated initial activity. The beryllium came from some irregular cuts from a 1mm thick sheet. I have broken them in pieces and managed to arrange the pieces in the source window above the grate to get >90% coverage of the window, and held in place with tape. Picture attached.

6. Gamma rejection. Was checked using a 10uCi cesium disc source.

I have done many tests, with various voltages, trigger levels and moderator configurations. I'm attaching the most recent and relevant ones. They each comprise a background check with no source nearby, a gamma rejection check with the cesium source in contact with the detector tube, and a test source check with the neutron generator in contact with the tube. All tests were done with moderator in the configuration I described above surrounding the detector. Picture of the working configuration attached.

Tests were done counting pulses for 10 minutes in the given configuration. All the tests were done last night in the same location, in a contiguous 90-minute period. The voltages and trigger values are noted in the name of the file. Basically, one test was done at 1200V and a trigger value of -14mV, one at 700V and trigger of -24mV, and one at 700V and -22mV.

Each file contains the raw output from the software for the given experiment. They contain text files with parameters and basic statistics, and .png images with the shape of every single pulse counted, some graphs and temporal distribution of pulses.
Attachments
test10-700V-22mV-enhancedmod.zip
neutron test source, 700V and -22mV trigger
(4.24 MiB) Downloaded 347 times
test9-700V-24mV-enhancedmod.zip
neutron test source, 700V and -24mV trigger
(3.12 MiB) Downloaded 337 times
test8-1200V-14mV-enhancedmod.zip
neutron test source, 1200V and -14mV trigger
(4.4 MiB) Downloaded 344 times
gamma10-700V-22mV-enhancedmod.zip
gamma rejection, 700V and -22mV trigger
(321.1 KiB) Downloaded 332 times
gamma9-700V-24mV-enhancedmod.zip
gamma rejection, 700V and -24mV trigger
(120.76 KiB) Downloaded 340 times
gamma8-1200V-14mV-enhancedmod.zip
gamma rejection, 1200V and -14mV trigger
(139.34 KiB) Downloaded 342 times
background10-700V-22mV-enhancedmod.zip
background, 700V and -22mV trigger
(261.99 KiB) Downloaded 341 times
background9-700V-24mV-enhancedmod.zip
background, 700V and -24mV trigger
(64.07 KiB) Downloaded 351 times
background8-1200V-14mV-enhancedmod.zip
background, 1200V and -14mV trigger
(132.17 KiB) Downloaded 338 times
"enhanced" moderator
"enhanced" moderator
"enhanced" moderator
"enhanced" moderator
"enhanced" moderator
"enhanced" moderator
HDPE moderator block
HDPE moderator block
polonium-beryllium source
polonium-beryllium source
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Nnnnnnn
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Re: Criticize my neutron detection setup

Post by Nnnnnnn »

I can say a few things about moderators. Moderators are used to turn fast neutrons into thermal (slow) neutrons. This means that you only want a moderator if you expect to have more fast neutrons than thermal neutrons, like in a fusor. For your source you can look at this report http://digitalscholarship.unlv.edu/cgi/ ... sertations
I only skimmed it but it seems that your source emits just as many thermal neutrons as fast neutrons. So I am not sure if you need a moderator. Keep in mind that thermal neutrons are more likely to be absorbed than fast neutrons.

There are 3 things that can happen to a neutron in a moderator. (1) It can scatter (probability related to scattering x-section) (2) be absorbed (absorption x-section) (3) Nothing. Depending on the scattering and absorption x-section you can calculate the distance till absorption for your material.

You can now hopefully see that designing a moderator is task dependent. Look up Neutron X-Sections the calculations you need to do are very simple and look a lot like the calculations you do for radioactive decay.

Also I don't know why so many people like HDPE. What's wrong with water? Easily available and there is a lot of documentation on it.
Silviu Tamasdan
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Re: Criticize my neutron detection setup

Post by Silviu Tamasdan »

Thanks for the comment.
My task is not to determine how many fast vs thermal neutrons the source emits, but rather to determine the appropriateness of my system for detecting neutrons (thermal, or fast after moderation). As long as it can detect neutrons from a relatively weak source like the one I made, I'm happy. In my opinion it does that.

I did run a few count series without moderator (not shown here). The counts I got this way were practicably indistinguishible from the background over 10 minutes. Perhaps with counting times of a few hours I could have seen a difference. I do not think that this source by itself generates many thermal neutrons.

I do plan on running a few more experiments, in particular counting with the neutron source shielded vs unshielded by lead to eliminate any contribution from possible intrinsic gammas.

Regarding water: apart from its undesirable interaction with high voltages in case of spills, nothing wrong with it. In fact one of my first ideas about an improvised moderator involved empty half-gallon cartons of juice or milk, rinsed and filled with tap water. Then I had the idea about mineral oil and it seemed much better. This way in case of a spill all I have to worry about is cleaning up the oil, rather than replacing the damaged HV source. (other fantasies involved surrounding the source and detector with cans of Coke...). The oil does contribute significantly to the moderation and detectability of neutrons. When using only the HDPE block as moderator, the counts are on the order of 4-5 cpm only.

(edit) I also have a SMN-11 boron-lined corona tube; I have just finished attaching a BNC connector to it and did some quick preliminary tests. Seems to work pretty well, doesn't balk at the voltage until 1650V. The baseline appears cleaner, but the sensitivity is somewhat less.
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Dennis P Brown
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Re: Criticize my neutron detection setup

Post by Dennis P Brown »

Randomly opened one of your data sets - rather a (very!) large set of data per file. This isn't something I'd think anyone here would want to go through - especially since there is no clear information on what you think the given file is displaying (or did I miss that?) You might want to find relevant data sets, smooth them (remove noise compared to signals), process as needed, analyse and present a few selected (relevant) sets that both show a clear neutron signal from your source with and without moderator with enough support information so we can offer an informed opinion. Until that is done, I'd not worry at all about testing with and without lead; one knows that without lead, one will have a lot of false signals. That is best a run after you prove you are seeing some neutrons via the moderator/non-moderator test.

If you are getting clear signals using that small source, a properly operating fusor will be a cake-walk for you.

You are following a very good methodology for your fusor effort. Building the required and separate components is an outstanding procedure. Getting a working detector is one of THE difficulties that cause far too many people from proving they have a working fusor (fusion.) Looks like you are well on your way in this aspect.
Silviu Tamasdan
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Re: Criticize my neutron detection setup

Post by Silviu Tamasdan »

Thanks for the comment.
To keep track of things I tend to put the experimental conditions in the name of the file (that is set in the GUI before running an experiment).
For example the file you opened is part of my 10th series of experiments (that's irrelevant for anyone but me, helps me organize data), using the test neutron source, 700V on the tube, trigger -22mV and using the "enhanced" moderator pictured above.
Yes there is a lot of extra data in each file. You can safely ignore the pulse shapes if you want, the counts for each minute in text form etc. The two most relevant files in each set are stats.txt and the counts vs time image (called History.png).
At some point I will do some real data processing in Sigmaplot probably, but for now since all I'm doing is exploring the best detector parameters using my two small sources (not real fusor work) I didn't feel it necessary.
Perhaps a better way to present these test results in a simple way would be a screenshot of my GUI at the end of each run. It shows me most of the relevant information (counts vs time, basic stats and pulse shapes) together in one place.

BTW as an addendum, since yesterday I've been concentrating on using the boron-lined tube SNM-11in this setup instead of the helium one. I have had this morning even better results than in the files attached above. Very clean baseline with almost no noise, allowing me to decrease the trigger value considerably, and not much worse sensitivity to neutrons compared with the SNM-32. All combined with very low background counts and parasitic gamma pulses from the check source. I've also ran some counts with the neutron source and no moderator, and they're the same basically as the background counts (if you want numbers, 30cpm with moderated source vs 32cpm for the SNM-32; the background/gamma/unmoderated source is between 0.2 and 0.5cpm)
Last edited by Silviu Tamasdan on Sat Oct 21, 2017 7:10 pm, edited 1 time in total.
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Silviu Tamasdan
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Re: Criticize my neutron detection setup

Post by Silviu Tamasdan »

I'm attaching the results from the best run with the SNM-11 tube. Just the relevant files, no pulse shapes etc. I did not run a plain background count, the counts with the gamma source and the unmoderated Po/Be source were so low. Overall, I got 4 counts in 10 minutes with the 10uCi 137-Cs source, 5 counts in 10 minutes with the fast neutrons from the Po/Be source without moderator, and 282 counts in 10 minutes with the Po/Be source plus moderator. The operating parameters were: tube voltage 700V, pulse trigger value -12mV.
Attachments
SNM-11 best run results.zip
(19.1 KiB) Downloaded 338 times
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Richard Hull
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Re: Criticize my neutron detection setup

Post by Richard Hull »

First off, a millicurie Po source with Be is no small source of fast neutrons. It is a fabulous source! Second a good neutron source testing a well tuned neutron counter with its tube, outside of a moderator, should not detect hardly any neutrons beyond background of any significance! A Po-Be source is a vast source of fast neutrons only! This is seen in this report as Silviu noted, and that was reassuring in the reports here. Silviu, in my opinion, has done it all correctly and double checked his work. This is one of the finest reports on one these often mis-applied Russian Corona tubes that has been published here. I have no crticisms of this effort.

I was particularly impressed that it was noted that at higher voltages the noise picked up as it should. Past credible reports have noted this with these tubes. Refining of the circuit and other corrective actions have helped raise the voltage a bit, but these are corona tubes and the very word corona means electrical noise. This is why this tube and many boron lined neutron tubes are real bears to turn into good neutron counters. At some HV point they become good GM counters and leave neutron detection behind as they start to count everything.

Silviu recognizes the rather heroic effort and experiment needed to turn a corona tube into a neutron counter. Just as I realize that anyone using one of these tubes and claiming fusion is always a candidate for possible self-deception through ill-application of the tube.

As a general rule, anyone claiming fusion using a Corona tube or a Boron lined tube should have a neutron source to bring the tube into reliable adjustment showing it is counting only neutrons.

I will not have to worry about Silvui if he claims fusion due to his fine report issued 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
Silviu Tamasdan
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Re: Criticize my neutron detection setup

Post by Silviu Tamasdan »

Richard -

I see you found my thread. I saw your reply first in the new user forum, and was going to point here, but no need now.
Thanks for your confidence. I do have a long way to go though. I need a fusor chamber, and my voltage supply is at best in the planning stages. I have almost given up trying to find an Xray transformer, and have started thinking more often about making my own high frequency supply with ferrite transformer from scratch. But that's another story.

FWIW I'm attaching the full datasets from my "best run" with the SNM-11 tube at 700V and -12mV trigger. If you compare the waveforms with the ones from the SNM-32, you will see they are much cleaner.

I'm also attaching a picture of my 3 current detectors which I use. From top to bottom, SNM-32 with SHV connector (bought with the system), SNM-11 (from sovtube on ebay) with my homemade BNC coupling (made from 1mm copper sheet, originally intended to be roof shingles, insulated with several layers of teflon tape and electrical tape; the reason for the teflon tape is to act as moisture barrier; for the next tube I plan on 3D printing a proper adapter from PETG, but this one seems to work quite well) and a 3inch Bicron BC-412 scintillation detector. I have on order a 1.5inch photomultiplier to which I will attach a LYSO crystal matrix and hopefully have something usable for gamma spectroscopy and activation experiments.

One lesson I've learned in working with these corona tubes is that more voltage does not equal better signal. In fact I get the best signals at the lowest end of their usable voltage range, i.e. 700V. I have run tests (not shown here but I have the data if there's interest in it) with the SNM-11 up to 1600V, and the noise increases to a point where it becomes troublesome, and signal decreases proportionally. Above 1650V the tube will oscillate at high frequency as does the SNM-32 at over 1275V.
Attachments
SNM-32, SNM-11 and 3-inch BC412
SNM-32, SNM-11 and 3-inch BC412
test28unmoderated-SNM11-700V-12mV.zip
same as test28 but without moderator.
(111.9 KiB) Downloaded 333 times
test28-SNM11-700V-12mV.zip
neutron counts for SNM-11 tube at 700V, -12mV trigger, 5mCi Po/Be source, moderator 4x5x15inch block of HDPE and 12 quarts of mineral oil
(4.8 MiB) Downloaded 342 times
gamma28-SNM11-700V-12mV.zip
gamma rejection for SNM-11 tube, 700V, -12mV trigger, 10uCi 137Cs source
(100.33 KiB) Downloaded 355 times
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Finn Hammer
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Re: Criticize my neutron detection setup

Post by Finn Hammer »

Silviu Tamasdan wrote: Sun Oct 22, 2017 6:16 pm I have almost given up trying to find an Xray transformer, and have started thinking more often about making my own high frequency supply with ferrite transformer from scratch. But that's another story.

Silvio,

If you live in the states, you could get in contact with The Geek Group, they have offered X-ray transformers for sale recently. Chris Boden is their leader.

Hope this helps.

Cheers, Finn Hammer
Silviu Tamasdan
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Re: Criticize my neutron detection setup

Post by Silviu Tamasdan »

Finn Hammer wrote: Mon Oct 23, 2017 8:45 am

If you live in the states, you could get in contact with The Geek Group, they have offered X-ray transformers for sale recently. Chris Boden is their leader.

Hope this helps.

Cheers, Finn Hammer
Thanks for the tip. I had never heard of The Geek Group. I don't see anything HV-related for sale on their web site or their ebay store, but I'm going to leave a message through their contact form and see what comes out of it. To be frank, all my recent buying of vacuum and detection parts has kinda depleted my finances for now but we'll see.
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Silviu Tamasdan
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Re: Criticize my neutron detection setup

Post by Silviu Tamasdan »

Oh. I don't use Facebook so I can't see that page. :(
(or any other 'social networking'; I may have a Google+ account, comes compulsory of using gmail and/or an Android phone, but I don't know for sure and I've never tried using it).
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Richard Hull
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Re: Criticize my neutron detection setup

Post by Richard Hull »

Likewise here. I have never used any of the common forms of social media. I fear it is a mixed bag of "here, look at me and what I am doing now" and also some valuable info., I am sure. I have chosen not to jump into the mixing bowl. I don't need to be bouyed by 5,432 likes or have 20,604 friend me's.

Fusor net is about the extent of my on line presence. My life is truly lived off-line, doing things. But enough philosophy.

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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: Criticize my neutron detection setup

Post by Rex Allers »

Silviu,

This reply was stimulated by your post about TIER for one of these tubes.
Exercise TIER calculation for SNM-11 tube
viewtopic.php?f=13&t=11983

Richard replied that he would expect to see more counts from the test set-up you have.

Earlier I made a reply to your BNC connector post.
Making a BNC adapter for SNM-11 boron neutron counters
viewtopic.php?f=18&t=11971

In that, I mentioned the excellent paper by Bob Higgins about using these Corona Neutron Detector tubes. It is the best reference I have seen on the subject. You said you had read it in great detail, but then you said some things about voltages that make me wonder if you really follow how these tubes are intended to be used. You said,
"However the SNM-11 works best at 700V. In fact I've had one test where the tube worked correctly at 670V. I didn't try lower voltages.
...
In fact even other corona tubes such as the SNM-32 which are also said to work at 1500-1700V; my experience is that they are unusable at voltages above 1275V because they start oscillating at high frequency (and I've had independent confirmation from somewhere else that it's indeed their normal and expected behavior based on a sizeable sample of them). But they work well at 700V. "
The ~100 Mohm resistor in series with these tubes is critical. I was trying to point that out in the BNC thread.

Here's a table with specs for a good number of these Russian tubes.
Translated specs.pdf
(21.85 KiB) Downloaded 484 times
This was google-translated from Russian. The places where it says "crown" should be "corona". It has listings for both the SNM-11 and SNM-32. The SNM-11 is a Boron tube while the SNM-32 is 3He but both are expected to be run in corona mode. The letters SNM are westernized from Russian, I've seen CHM, CNM, etc. all seem to be equivalent.

These corona tubes are intended to have an internal light corona discharge all the time they are operating. The normal configuration has a 100 Mohm resistor (or maybe a bit more) in series with the anode (center conductor) of the tube. The supply voltage goes through this resistor, not directly to the tube.

The pdf table above has 3 key columns of values: Nominal operating voltage, Starting voltage, and discharge current max. The nominal voltage is the HV that is applied across the series connected tube and 100 Mohm resistor. Per the table, for the SNM-11 or 32 this should be in the 1500 to 3000 V range.

As this voltage is first applied, the tube appears as an open connection, drawing no current, so the tube will see the whole voltage. This starts the corona discharge in the tube, causing it to draw current. The current through the 100 Mohm resistor causes voltage drop across it making the tube see a lower voltage. The system finds a stable operating point with 600 to 700 V across the tube and the corona discharge drawing about 10 to 20 uA current. In the table, the Starting Voltage column gives the voltage across the tube in corona mode and the discharge current max column is the highest current that the tube should be allowed to draw in its idle mode.

The 100 Mohm resistor in series with the HV supply effectively makes a constant current supply for the tube in the 10-20 uA range. In his paper Bob did some calculations. He assumed the corona voltage would settle to the midpoint of its start voltage range or 650 V. He picked a supply voltage of 1800 V, so the voltage across the 100 M resistor is 1800-650 = 1150V, so the current through the resistor (and tube) calculates to 11.5 uA which seems OK and well below the max current. This is a ballpark calculation. The tube will find its own operating point but it should be close to this.

The 100 M in series also helps to quench the tube after a neutron pulse. The pulse draws more current making the drop across the big resistor greater and lowering the voltage across the tube a bit.

I think you said you bought your solution from someone else. The circuit feeding the tube needs to be roughly constant current, either via the 100 Mohm or some other method. If I was you I would try to figure out the circuit and ensure you have a very large resistor (~ 100 Mohm) from the HV supply. The specified operating voltage of 1500 to 3000 V is into this series resistor, so the voltage across the tube should settle to around 600-700V. If you want to measure this directly bear in mind that the effective impedance of the tube is around 650/12u or about 55 Mohm, so your meter should have an input impedance of 500 Mohm or more to not shift the reading much from what just the tube sees.

Here's Bob's simple diagram of the detector.
Corona block.png
He is coupling the neutron detection pulses from the anode through a DC-blocking 27 pF capacitor to the amplifier and comparator. He put the battery-operated detection and HV supply circuitry very close to the corona tube. Bob feeds the resulting pulses through a coax to some kind of counter.

If I understand your configuration, you may have the same general circuits but you are planning to run a coax from the tube to the circuits to carry both the high voltage and signal. It would look like this.
with cable.png
This may work OK but it puts the capacitance of the cable from the anode to ground. This may make it harder to get a clean pulse and might make the whole set-up more likely to oscillate. The connections to the cable here are high impedance so more susceptible to noise. I think you'll do better if you can put the front end circuit close to the tube and send the processed pulses from a low impedance driver through the cable as Bob did.

Bob Higgins' paper covers all this in more detail than I have provided, but your mention that 700V works better than >1200V makes me think you might not be seeing the distinction between the supply voltage and the corona voltage across the tube.
Rex Allers
Silviu Tamasdan
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Re: Criticize my neutron detection setup

Post by Silviu Tamasdan »

I understand perfectly well what you're saying, and I had much of the same concerns from the beginning. I plan on investigating exactly how the inner connections are made in the MCA I use - it is built like a tank though and I think it will be difficult to open. Nonetheless I'll find a way to do it non-destructively. I think that the voltage I'm setting in the software is the voltage across the tube only, not tube+resistor, and that would be in line with the tube specs and your post.
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Richard Hull
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Re: Criticize my neutron detection setup

Post by Richard Hull »

I will say that I wonder at the max count rate of such a setup. Rex did a great job of explaining the purpose and need for the 100 meg resistor and its action in establishing the corona.

The reason for the wonder at the max rate is that this tube may have the same problem of early GM tubes prior to quench agents. The earliest of GM system demanded a 100meg resistor or better to achieve "quench", (end the conduction once the gas had broken down). Just as Rex noted, once the gas fully conducts, (creates a pulse), to end the pulse the increased voltage drop across the resistor kills the corona and the tube shuts down. Basically, the power supply voltage to the tube buckles once it conducts. This action creates an effective, fixed, recovery time before the next count based on the net RC time constant of the system. 100meg with any capacitance will slow the recovery time consant, limiting the upper level rate of counting.

With GM tubes, an alcohol quench was used in the earliest internally quenched tubes to stop the conduction, this allowed the ballast resistor in series with the tube to be reduced to under 10 meg with a nearly 100 fold increase in count rate. Unfortunately, the alcohol was chemically bound up and thus, used up, limiting the life of such early quenched tubes to about a billion counts. Modern tubes, since the 50's have a Halogen quench agent which molecularly, uncouples after quench and can live forever. Today only about a 3 meg resistor is needed in series with the best GM tubes.

Even if a quench gas is used in the Russian tubes here. The rate will forever be limited by the RC time constant. This should not matter in fusor neutron counting as the rates are low in all but the finest of fusors that go over the mega neutron/sec class.

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: Criticize my neutron detection setup

Post by Silviu Tamasdan »

I think I read somewhere that a halogen is used in the corona boron-lined tubes. Don't ask me for a quote becaise I don't remember where that came from; I have read so much in so many places about them. OTOH I don't think a quenching agent is used in the helium corona tubes.
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Richard Hull
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Re: Criticize my neutron detection setup

Post by Richard Hull »

Like I said, even with quench gas the time constant will limit the rate with the 100 meg resistor as it is used as a ballast much like the 1920's GM tubes.
Chemical quench in the GM tubes was used to get rid of the early 50-200 meg quench resistor that limited the count rate.

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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Finn Hammer
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Joined: Sat Mar 05, 2016 7:21 am
Real name: Finn Hammer
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Re: Criticize my neutron detection setup

Post by Finn Hammer »

Silviu,

One thing about your data puzzels me, because they are a couple orders of magnitude away from my own data. I seem to have an output in the 1-3 volt range, whereas your setup appears to output in the 10 - 30mV range.
So you trigger in the low tens of millivolt, whereas I would be comfortable to set a trigger level around 1.5V.
Operating in a noisy environment, a high signal level is an asset, so I would like to ask you this:
Do you have any explanation of the low output from your tube? This low output could be caused by the resistor and capacitor network that is connected directly to the end of the tube, it looks like it is covered by just alluminum tape, any chance you want to have a peek under it?

Cheers, Finn Hammer
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