Gayo 2021 Update

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Joe Gayo
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Re: Gayo 2021 Update

Post by Joe Gayo »

I've decided on something similar. A wall of 5 gallon buckets (2 rows staggered) filled with Borax dissolved in water. The wall is placed in front of my lead sheets.
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Joe Gayo
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Re: Gayo 2021 Update

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I've been able to reduce the neutron rate measured at the operator station with water jugs, but as the overall numbers continue to climb, I need a more aggressive approach.

- Moving the operator station another 10ft (35ft total)
- Adding another staggered row of stackable 5gal Jerry cans

My general though has been to place shielding as close to the operator and far from the source as possible.
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Richard Hull
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Re: Gayo 2021 Update

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This is the best method. I recommended a shadow cone shield years ago and detailed it. By letting everything around you at range get blasted by inverse square law reduced radiation make stopping that much weakened blast easier to shield the operator. The shadow cone was designed to protect an operator at 7 foot ranges by a 18X18 box with an 18X18 sheet of 3/8 inch thick lead plate on exterior of the of the box facing the fusor. Inside the box whose internal interior width is 4 inches, a piece of HDPE sheeting 18x18x1" thick is placed inside the box and the remaining 3" width has borax mixed with molten paraffin is cast in the box.

Jammed up close to the fusor, the lead would limit the x-rays and the interior would absorb and scatter the bulk of the fast neutron flux as thermals. This was for what was then an 85kv fusor design. The cone on the other side of the shield would allow for a 7 foot distant operator to be in the vast shadow cone cast by this shield.

In your case, a bit of both near heavy cone shielding and light distant shielding might be a good idea. X-rays are a major issue, but easily shielded close in by the lead and the paraffin/borax would really kill the bulk of the fast neutrons resulting in heavily scattered thermals, resulting in frontal, rearwards and sideways scattering of the original fast flux. Scatter, close-in, with the shield what is effectively a projected impacting onslaught of fast neuts will turn into a 360 degree sphere of thermal neuts. At distance, within the cone of the close-in shield further shielding should a snap, if an issue at all, due to the inverse square law.

Do your best shielding up close and live in the shadow cone.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
JoeBallantyne
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Re: Gayo 2021 Update

Post by JoeBallantyne »

I agree with Richard. Shield as close to the source as possible.

When I proposed using a single 275 gallon 4' x 4' tote for neutron shielding, my thought was to place it as close to the fusor as reasonably possible so that the fusor was centered on one face of the cube. Depending on the height of your fusor, centering the tote might very well require raising it a foot or so off the floor. On a short stack of pallets for example.

Then place the operator station as far away as possible on the same line that runs through the center of the fusor and the centerpoint of the face of that cube.

If you want to put even more shielding right in front of the operator station, fine, but I think you will get the most bang for your shielding buck by stopping as many neutrons as close to the fusor as possible.

To be clear, I don't think anyone else on fusor.net needs to be messing around with 275 gallon totes for shielding, but you are in a class by yourself at the moment, and the less irradiated you get, the longer you can keep doing your thing, making even more neutrons. The nasty thing about radiation doses is that they are cumulative, and every dose you get reduces your total remaining radiation handling capacity by that amount. Once your remaining handling capacity hits zero. Game over. No respawn.

Joe.
Last edited by JoeBallantyne on Tue Jul 06, 2021 2:13 am, edited 2 times in total.
JoeBallantyne
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Re: Gayo 2021 Update

Post by JoeBallantyne »

One issue with that kind of neutron shielding up close to the fusor, is that it will likely affect your counts, because some of the neutrons will be reflected back and get counted with the shielding up close. You should probably run some experiments to determine if neutron shielding up close does indeed impact your numbers. I think it will artificially inflate them somewhat depending on the exact geometry of the fusor, shielding, and neutron detection equipment.

Joe.
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Joe Gayo
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Re: Gayo 2021 Update

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I've been very reluctant to add neutron shielding "close" to the device since I have an array of neutron detectors (at various angles and distances) to better characterize total output and any distribution bias. These detectors have been calibrated with a point source and I don't want excessive moderators changing the distribution of neutrons. In addition, I can't place any detector closer than 100cm or the counts are overwhelming and x-ray pile-up becomes a risk (the latest runs are at 10mA+).
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Joe Gayo
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Re: Gayo 2021 Update

Post by Joe Gayo »

In other news, after a short run I decided to bring my Geiger counter to check to see if I activated any material near the moderated detector tubes. The aluminum plates that electronically shield the detector assembly give about 10k cpm! It fades fairly quickly in agreement with the 2.2min half life of aluminum.
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Richard Hull
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Re: Gayo 2021 Update

Post by Richard Hull »

It's nice to see that the 5 folks who bought my 5 copies of the table of the isotopes at HEAS 31-2020 have been using them. That glorious aid and reference is a must have item for those doing any activation.

Yes, any form of neutron shielding will scatter like a big bear. That is the beauty of the shield!.... To turn any direct fast neutrons heading for a human bag of water, operator into a big sphere of thermals. It does screw with critical neutron counting trying to determine any beaming. Of course wooden structures, building materials, etc., will also send neutrons a-flying in tortured directions if the flux is high enough.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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