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Re: Neutron from Thailand~!!!

Posted: Wed Jul 30, 2014 7:24 pm
by Richard Hull
No need for further discussion. You are doing fusion! Congratulations. You can now fine tune your fusor system from here and maybe widen that count background versus neutrons. You got a 200% increase over background. That is solid.

I told you the span was tight on the GE tube, but you spent the time needed and found its sweet spot. What was it? There was no closeup of the bias meter, but it looked like 550 or 600 volts. I think mine was around 640 volts, if I remember

You now have a working neutron and cosmic ray counter.


I will now add your name to the neutron club. Good work.

Richard Hull

Re: Neutron from Thailand~!!!

Posted: Wed Jul 30, 2014 7:41 pm
by Jack Puntawong
Richard,

fore me, the sweet spot is 730. I am really surprise that the "window" for a working neutron detector is really tight. When I tried 750, the background count shoot up to 300 cpm. When I tried 720, the detector does have any background count. =D Thanks for adding me to the Neutron Club.

Cheers!

Kunakorn (Jack) Puntawong

Re: Neutron from Thailand~!!!

Posted: Wed Jul 30, 2014 8:08 pm
by Richard Hull
Yes, those old GE tubes are really nice once you are in that tiny narrow range. I find it interesting they allow for a possible working window of 600-800 volts, but the useful working span within that wide range is often only a tricky to adjust 20 volts or so. No working amateur neutron counter that is supposed to count neutrons, only, would normally ever read over 2 to 10 cpm as a back ground, end of story. If your background reading is more, you are not counting neutrons at all.

Note: Giant volume, high pressure, multi-tube, parallel connected and recording neutron detector tubes of the BF3 and 3He types can indeed have 100-200 or more CPM as background. However nothing that typically winds up in amateur hands can ever have backgrounds approaching even 10 cpm when properly adjusted in a moderator.

Richard Hull

Re: Neutron from Thailand~!!!

Posted: Thu Jul 31, 2014 1:25 am
by Tyler Christensen
I've always calibrated those GE tubes by placing ore next to it, turn the bias up until it detects the ore (confirm it's the ore by then removing it and checking that the count rate drops again). Then, turn it down 50V and it's a great neutron detector.

Certainly still have to do moderator checks to confirm it's not some other energy particle triggering a geiger mode, but I've never had it fail. Takes a minute and very repeatable and robust. Have to do it for every tube to get the unique voltage, since those are so old that the neutron voltage varies by hundreds of volts tube-to-tube in my experience.

Re: Neutron from Thailand~!!!

Posted: Thu Jul 31, 2014 3:44 pm
by Richard Hull
I have only set up two tubes, but no two are even close, as you note Tyler. These used to appear frequently on E-bay really cheap and might represent the least expensive, yet quite servicable, ready to roll, neutron counter that the average amateur might stumble across.

Richard Hull