SNM-11 He3 tube with the SNM-32 circuit detailed in the FAQs

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Grigory_Heaton
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SNM-11 He3 tube with the SNM-32 circuit detailed in the FAQs

Post by Grigory_Heaton » Thu Dec 01, 2016 5:54 am

I'm looking to try and construct a neutron detector using the method and schematic outlined in this very informative post: viewtopic.php?f=31&t=10971

Unfortunately SNM-32 tubes seem to be nowhere to be found on Ebay, Sovtube, or anywhere else. The SNM-11, on the other hand, is in numerous places for pretty decent prices. I am looking at the specs between the two types of tubes and I'm not seeing much of a difference, both can operate on 1600-1800 V (1500-3000 V limits) (1800 V is used in the linked paper), both even have the same dimensions and plateau characteristics. I really can't find much of a difference between the two at all, but since they are different He3 tube variants I assume there has to be a difference.

With that in mind:

- Has anyone successfully used a SNM-11 tube with the circuit outlined in the above paper?

- If not, is it just that nobody has tried, or that there is some reason I am missing that it won't work without modification? What is the difference between these tubes? I haven't been able to find any major differences so far.

Thanks in advance for any assistance.

Rex Allers
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Re: SNM-11 He3 tube with the SNM-32 circuit detailed in the

Post by Rex Allers » Thu Dec 01, 2016 8:01 am

I would not be surprised if the same circuit in the paper would work with your SNM-11. I think all the Russian corona neutron detector tubes work with about the same drive and detection circuitry, though the operating voltage may be different. I do believe your tube is a different technology, though. Pretty sure your SNM-11 tube is B10 based while the SNM-32, as described in the article, is He3 based.

To my knowledge, for these tubes, the nomenclature SNM, CHM, and CNM, that you may see listed are the same (SNM-11 = CHM-11). Here's a list I saved from somewhere around 2013 that is the reason I think the SNM-11 is a B10 tube.
b10_data.jpg
Russian B10 corona neutron detector tubes.
Several years back, there was a lot of discussion about these various tubes on this forum and Doug Coulter's. Here's one thread I found:
Operating Parameters for Corona Neutron Counters
viewtopic.php?f=13&t=6210&p=41190

Let's see if anyone else has an opinion.
So I'd be really surprised if anyone has used an SNM-11 tube with the circuit in the recent article, but it very well could work, in my opinion. Maybe comparing some of the older posts will give you an idea if you want to try.
Rex Allers

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Richard Hull
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Re: SNM-11 He3 tube with the SNM-32 circuit detailed in the

Post by Richard Hull » Thu Dec 01, 2016 7:12 pm

Regardless of tube,be it a BF3 tube, a 3 He tube or a boron lined tube, it is all about conditioning and filtering of the tube's output that determines whether it is detecting only neutrons! This simplifies to voltage across the tube and dicrimination of the output signal. All of this has been discussed in some detail in the FAQs. Just having a good neutron detector tube in hand means little in relation to the actual reliability in any supposedly finished neutron counter to the actual detection of only neutrons.

The ideal is to have,on hand, a good hot source of gamma rays and at least a decent small source of neutrons. Carl Willis' series of videos really give superb details on tackling the critical discrimination process.

Richard Hull
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Fusion is the energy of the future....and it always will be
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Silviu Tamasdan
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Re: SNM-11 He3 tube with the SNM-32 circuit detailed in the FAQs

Post by Silviu Tamasdan » Sat Oct 21, 2017 12:19 pm

I have one of these tubes, and have begun using it with the system I described in my other thread viewtopic.php?f=13&t=11954 The system came originally with a SNM-32 tube, so I can directly compare the two. I can run a series of tests if there's interest and post the results.

As a first impression (I have used the SNM-11 for less than 24h), the tube I have is quieter than the SNM-32 (the baseline has less noise) at similar voltages, but has somewhat lower sensitivity. The same experimental conditions that give me 32cpm with my polonium/beryllium test source and moderator on the SNM-32, give 22-25cpm on the SNM-11 - with the background and the gamma source rejection tests being 0.5cpm or less. I am still tweaking the operation point of the tube to achieve better counts. The fact that the tube is quieter allows me to decrease the trigger value more compared to the SNM-32. This tweaking takes time, and I haven't yet reached the point where gamma detection becomes significant. I run at least 10-minute counts, so a full operation point check (test source counts, background counts and gamma source counts) takes at least 30 minutes. The SNM-11 has a slightly smaller overall volume than the SNM-32, but not by much (only about 6%) because it's shorter.

I have noted an interesting fact about these corona tubes. I can't speak for other setups, but with my system I tend to get occasionally outlying counts (significantly too high) in the first minute after voltage is applied across the tube, compared to the average of the following minutes of the count. This applies both to the SNM-32 and to the SNM-11. It may not be a characteristic of the tubes but of my system (HV stabilization, etc) - however it does not happen with my system for other types of detectors (photomultiplier based ones for instance). That is the reason for running at least 10-minute counts each time.

Again, my preliminary results so far seem to point that it's a decent alternative to a 3He tube; and the fact that it still can be had at decent prices is a definite plus. In fact, I have just ordered a few more.
There _is_ madness to my method.

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Richard Hull
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Re: SNM-11 He3 tube with the SNM-32 circuit detailed in the FAQs

Post by Richard Hull » Sun Oct 22, 2017 6:16 pm

You sound like you know what you are doing and can put forth valuable data. Your technique also sounds very good.

Please do post data on these tubes as a lot of folks use, but mostly misuse them. Guidance on how to test and use these often found tubes would be good for those working on counters using them.

Please post a data reduction with details on your work in the Radiation and neutron detection forum once you feel you have a handled on how to apply them electronically.

Let us know your sources for both the neutrons and the gamma level testing.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

Silviu Tamasdan
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Re: SNM-11 He3 tube with the SNM-32 circuit detailed in the FAQs

Post by Silviu Tamasdan » Sun Oct 22, 2017 9:41 pm

Richard -

I've already posted in the thread I linked above almost all the work that I've done in the past couple of days with the SNM-11. The only thing that I realize I didn't add are some waveforms, but that's easily corrected. There's data there about the sources I use (with pictures), the voltage supply, the acquisition system (as much as I know about it because it wasn't made by me), as well as some complete datasets from experiments with the SNM-32 helium tube. And some results from SNM-11 testing.

But I see you have found it already...
There _is_ madness to my method.

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