Easy $150 Neutron Detection System

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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Jim Kovalchick
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Re: Easy $150 Neutron Detection System

Post by Jim Kovalchick » Sun May 24, 2020 12:50 pm

Thanks Mark. I tried a couple iterations of threshold adjustments and found that another tenth of a ten-turn got my background down to 1 to 2 cpm. Because there is no preamp, I'm afraid to move the threshold to far. A proportional tube dip will be too small to see otherwise I think. Fusor run later to test with known neutrons.

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Jim Kovalchick
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Re: Easy $150 Neutron Detection System

Post by Jim Kovalchick » Sat Jun 06, 2020 3:08 pm

My Ludlum 2200 threshold is set at 0.8 on the ten-turn, and voltage is 750. Background is around 1 cpm.

Today I packed the CHM 11 into a piece of 4 inch poly drain pipe with HDPE granules. Parked up next to my fusor running at -37.5 kV and 8 mA, the detector read 2000 cpm on the rate meter. I think with some adjustments to geometry it could improve, but at this point I really just need to set a consistent benchmark that i can use as a gauge of fusor performance.

These Soviet tubes seem to be immune to xrays when set up the way Mark advises. Performance, cost, and size make these tubes an easy choice for permanent fusor neutron detection.

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Richard Hull
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Re: Easy $150 Neutron Detection System

Post by Richard Hull » Sun Jun 07, 2020 4:19 am

I am glad to here you have it working. Good going. The higher a neutron count you can get versus background, the better. (more efficient neutron detection) This allows for detecting very small neutron counts from very weak neutron sources as well as small differentials in small, weak sources.

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.

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Jim Kovalchick
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Re: Easy $150 Neutron Detection System

Post by Jim Kovalchick » Sun Jun 07, 2020 12:03 pm

Richard,
I doubt the CHM 11 tubes will be very useful for low neutron counts. Maybe I will try some low voltage, low current ops to find out. I'm not real keen on running my fusor too low voltages because with deuterium the pressure is hard on the turbo. I may just shut it off.

I was really thinking of using the CHM 11 tube as more of a 'speedometer' if you will. I will permanently affix it to the fusor such that at the high end I will have a measure of performance and benchmark for experiments like activation.

For much lower neutron counts I intend to use my lithium 6 paddle. That detector was intended to rival a whole bank of He 3 tubes. I have yet to fully explore it's full capabilities. I think it may even be able to pick up low count rate alpha-n reactions from non-fusor experiments I'm interested in doing. For fusor work I found that it's size made it a little impractical and more importantly, it was very sensitive to pile up of the numerous xrays even when I shielded.

Jim K

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