Home Made Near real time Neutron Detector

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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John Futter
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Home Made Near real time Neutron Detector

Post by John Futter » Tue Dec 15, 2009 12:43 am

Edit
An idea to use very tightly coupled silver with a phosphor to measure neutrons by Ag:N activation

Well the Gamma camera has given up one of its PMT's an RCA 4524/VI. I couldn't find any data on this beast but the only 3"head on type, in my RCA book = 8054 an S11 type response. My guess is that the 4524 is a wavelength extended version of the 8054 probably a bialkali photo cathode.
So now for the neutron detector using one of the above PMTs I coated a 3"quartz wafer on the nonpolished side with TEM grade Phosphor. Photo 1 shows a phosphor coated wafer alongside a new one.
I then mounted the wafer in our sputter coater, phosphor side towards a new Ag grade 6 target ---Photo2

Photo three shows all the bits so far including the tube base with the correct resistor chain installed, the silver coated phosphor on the Q wafer, the PMT and a block of UMWPE that will be turned to act as a cap over the PMT giving 3cm of thickness of PE to moderate the neutrons.
The Q wafer will put onto the face of the PMT with Dow corning 200 fluid for good optical coupling. A thin sponge rubber pad will help keep pressure on the wafer to keep it against the PMT window.
The whole assembly will then be rolled in copper foil and then in lead foil, with the whole shooting match protected by some plastic plumbing fittings.

I will reply to this post when more progress has been made
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Doug Coulter
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Re: Home Made Near real time Neutron Detector

Post by Doug Coulter » Tue Dec 15, 2009 3:29 pm

Definitely an interesting approach, and IMO, almost anything is better than a BTI if it's faster and more reliable. For us, neutron detectors have certainly been a critical-path-limit issue, finally somewhat solved, and it's important to everyone doing this work to have some way of knowing when it's working!

In my opinion, the faster the better -- a BTI is far too slow, this won't be super fast, but will still be a lot better than bubbles. Also in my opinion, relative readings are fine for all but that final report paper too. All you need to perfect a fusor is information on "did this make it better", preferably *as* you make the adjustment. Once you've made it as "better" as you can, then is the time to figure out what the absolute Q was, and so on.

So, John, please keep us up to date on this -- and best wishes for success!
Why guess when you can know? Measure!

John Futter
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Re: Home Made Near real time Neutron Detector

Post by John Futter » Thu Jan 14, 2010 8:59 pm

Its been awhile with Xmas getting in the way. But the detector is finished

Pic1 all bits ready for final assembly including the optical coupling fluid

Pic2 polyethylene moderator installed and copper shield in place

pic3 lead cover wound on note ground wire to copper shield

pic4 finished

4" diameter 10" long weight approx 2.5 pounds
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Steven Sesselmann
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Re: Home Made Near real time Neutron Detector

Post by Steven Sesselmann » Fri Jan 15, 2010 12:06 am

Nice work John,

Look forward to see how sensitive it is.

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG

John Futter
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Re: Home Made Near real time Neutron Detector

Post by John Futter » Fri Jan 15, 2010 1:04 am

Thanks Steven
Presently trying a cal on it
background = 36-38counts per hour
Sitting next to our calibrated neutron dtector head in the magnet room it giving 460 counts per hour @ 0.3mrem/hr on the calibrated detector. This on a 0.9MeV deuteron beam 20nA on target

John Futter
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Re: Home Made Near real time Neutron Detector

Post by John Futter » Fri Jan 15, 2010 2:57 am

Cal setup
Nim modules to amplify and count, nim Hvpsu on top set at 1600volts
four hours into cal 2000 odd counts.

On monday i'll do another 4 hour run when the accelerator is not running to get the background at this position with all settings the same
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Richard Hull
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Re: Home Made Near real time Neutron Detector

Post by Richard Hull » Fri Jan 15, 2010 4:05 pm

Good man! Not trusting the data until it has been double blind verified in a fixed location.

Very nice and interesting setup. Reminds me of my early efforts with the PMT/BT Bicron setup back in 1997-98. Not very sensitive but very serviceable and gave my first solid, undeniable, indications of real fusion.

Keep us posted.

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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Doug Coulter
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Re: Home Made Near real time Neutron Detector

Post by Doug Coulter » Sun Jan 17, 2010 9:47 pm

Just a lazy question to toss out there for those who may know offhand and save me from a few hours of looking in books that have the data, just not organized for this sort of question.

Is there something maybe better than silver for this? Eg real good activation cross section and really short half life would be primary goals. In fact, maybe not even activation as such, but simply a N to gamma (or anything else) converter that the phosphor would pick up on for the phototube or night vision camera type thing. I already have the tech in hand to put phosphor down on thin clear screens just so -- took awhile, but it's now solved, and have used to to make charged particle pinhole cameras that work great.

My interest here is somewhat other than this -- I have good neutron detectors now. But I don't have a *camera* which a neutron to light converting screen is likely a necessary element of (along with a lot of other unsolved problems, I know, but hey, one thing at a time gets you there).

Doug
Why guess when you can know? Measure!

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