He3 Neutron Detector HDPE moderator

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russssellcrow
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He3 Neutron Detector HDPE moderator

Post by russssellcrow » Sat Feb 27, 2021 5:25 pm

2-21-2021

Lawrence Brent Rees, Ph.D. and J. Bart Czirr, Ph.D., of Brigham Young University report their best results in moderating neutrons from a 252-Cf source are acquired using a HDPE moderator 5-7cm thick between the source and He3 tubes (they used 2, we have only 1). The block we built is 6cm thick at the thinnest point. https://www.osti.gov/servlets/purl/1178530

We obtained 6 blocks of High Density Polyethylene, measuring 12 x 6 x 1 inches for $106.71 In the DallasMakerSpace Woodshop, we set a regular round wood 5/8 inch router bit, set the fence, and made 3 passes down the length of each of 2 of the HDPE blocks to form a domed channel for the He3 tube. We then used regular shrink wrap to bind the 1 inch slabs into a block. Voila, a neutron moderator!

We'll employ our ESP32 WiFi OLED data logger platform to web enable the detector, as we did with our Geiger Counter, Scintillator, Mass Flow Controller, and Peltier Gas Dryer. We plan to publish the Arduino IDE code for the ESP32 platform, and Java PC receiver when we have finished alpha testing.

He3_HDPE_routing.jpg
He3_HDPE_block.jpg

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Jim Kovalchick
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Re: He3 Neutron Detector HDPE moderator

Post by Jim Kovalchick » Sat Feb 27, 2021 6:39 pm

That will surely count neutrons for you. The construction looks good.

You probably don't need as much hdpe to moderate d d fusion neutrons as you would for a Californium source because d d neutrons are only 2.45 MeV. I'm not suggesting you change your design, Carl Willis did some work someone back that showed that 1.5" is good. The down side to having too much is that it increases the chance that a thermal neutron is absorbed by something other than your detector and thicker moderator is that much further away your detector is held. I think your setup will work just fine.

Jim K

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Re: He3 Neutron Detector HDPE moderator

Post by russssellcrow » Sat Feb 27, 2021 10:41 pm

Thanks for the heads up!

We made this from 1 inch sheets, so we could pull or place different thicknesses in front of the tube. Then we can rotate the block axially to fine tune the HDPE thickness, so we can vary from 1-9 cm of HDPE.

We still haven't fired the tube, but from what I've read we'll need to be able to range from 1300-1800 Vdc. Does that sound about right?

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Jim Kovalchick
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Re: He3 Neutron Detector HDPE moderator

Post by Jim Kovalchick » Sat Feb 27, 2021 11:27 pm

A lot will depend on whether it is a proportional tube or corona tube. I personally prefer proportional because it is more straight forward. Many of the Russian tubes are corona but not all. Some folks have had good luck with both, and there is good info on the forum.

1300 to 1500 sounds like a typical tube but it varies. The Russian CHM 11 tubes do fine 750 V and my current Nancy Wood BF3 tube is 2100 V.

You may also need a preamp depending on your setup.

I wish neutron detection was easier but what fun would that be?

Jim K

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Richard Hull
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Re: He3 Neutron Detector HDPE moderator

Post by Richard Hull » Sat Feb 27, 2021 11:57 pm

With a neutron source like Californium, you will have no trouble honing and discriminating out pulses that are not neutrons. This is the number one buga-boo facing those making a neutron counter. (getting it to count only neutrons.) Carl Willis put out a great video on setting up a neutron counter properly. (provided you have a reliable neutron source)

It is incredibly easy if you have all the right materials. Virtually 100% of folks who want to count neutrons do not have the right stuff. A good preamp is important for a proportional tube like a BF3 or 3He.

https://www.youtube.com/watch?v=skP3SWWR9Kw&t=6s

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
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russssellcrow
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Re: He3 Neutron Detector HDPE moderator

Post by russssellcrow » Wed Mar 10, 2021 2:31 am

We have some Cs-132 tokens, some Americium samples, and some Uranium rocks. I hope these will suffice.

The Maths are straightforward, but the risks are not. We hope to contain risk while expanding knowledge at our site.

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