Questions about CHM-12 B10 Detector Tube

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Miles Duncan
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Joined: Thu Feb 06, 2020 6:53 pm
Real name: Miles Duncan

Questions about CHM-12 B10 Detector Tube

Post by Miles Duncan »

Here are some pictures for context:
Tube
Tube
End Piece
End Piece
Cathode with End Piece unscrewed
Cathode with End Piece unscrewed
The long metal piece on the inside of the tube I am going to assume is the cathode, so I will refer to it as the cathode in this post. Please correct me if I am wrong.

I recently received a CHM 12 tube to use for detection in my upcoming reactor project. However, I have a couple of questions about how it is built. In the images I included, there is an unscrewable end piece and a white plastic insulator (at least I think it's an insulator) between the cathode and the surrounding anode tube. When I remove the end piece, I can see the cathode clearly protruding from the tube.

I have a Ludlum model 12 which I plan to connect to the tube and calibrate using a polonium-beryllium neutron source. In between the detector and tube, I plan to have a 100 megaohm resistor and 100pf capacitor. I plan to solder an insulated wire directly to the cathode to then connect to the BNC cable. I know neither if this is a good idea, nor if it will actually work. Do I have to connect the tube's anode to anything, or do I only need to connect the cathode to the counter?

Any help would be great.

- Miles
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Richard Hull
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Real name: Richard Hull

Re: Questions about CHM-12 B10 Detector Tube

Post by Richard Hull »

The tube body is the Cathode and the central pin is the Anode.

All nuclear detection tubes, regardless of type, demand to be in a closed electrical circuit (two connections).
Neutron detection is not easy for the person looking to assemble their own electronics. No easy walk in the park here.

The main post on utilizing these Russian tubes can be found at...

viewtopic.php?t=12474

For the person new to electronics and especially new to neutron detection, the above post might be confusing, but it is probably one of the best on the Russian tubes. Note: this recommended post was posted before major issues arose with changing to Go Daddy as our provider. Many posts prior to 2019 lost many or all of their highly valuable images, circuit diagrams, etc. They are mostly lost forever. The reason being that many of the posters are no longer here, coupled with the fact that all posters cannot edit their old posts without special permission.

You will discover, if successful, background counts of real neutrons and some cosmic rays in even the biggest and best tubes are on the order of 5-10 counts per minute. If you count more than that, your neutron counter is not counting neutrons. It is either defective or not setup electronically in a correct manner to count only neutrons.

The smaller the neutron detection tube, the lower the background count. Never try and set up a neutron counter using a neutron source until you have first obtained an ultra-low background count. Small tubes like yours, when placed in a suitable moderator, might produce only one good background count in 2 minutes. Naturally, with a good neutron source this will go up proportionally and be the key indicator that you are, indeed, counting only neutrons.

All the above I have posted here is based on what I have picked up via osmosis as I have never used or relied on any Russian neutron detection tube.
I have been deeply involved in successful neutron detection and counting for the past 23 years here. My experience is with only U.S. made BF3 and 3He high pressure tubes of 75% or better efficiency. My large 23 inch long, one inch diameter 4 atmosphere 3He tube in its large moderator has a normal background count of 6-10 CPM. (See photos attached. Click on image to enlarge.)

Finally, a number of adroit and capable people here have turned these Russian tubes into very reliable neutron detection systems. Many others of lesser abilities have never succeeded in obtaining more than very dubious results that were not accepted as being viable neutrons counting results based on the base knowledge of other very critical, experienced and jaundiced eyes here. No one will accept any neutron counts that do not make sense.

As the British are fond of saying "mind how you go, mate."

Richard Hull
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