Effectiveness of water (H2O) on fast neutrons?

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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Tony Lai
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Effectiveness of water (H2O) on fast neutrons?

Post by Tony Lai » Fri Sep 11, 2020 7:59 am

Hi there
A bit of research shows me that water is a common material used for neutron shielding, and on some papers it actually does the job of slowing down fast neutrons well. So it arouses the question for me, is it possible to just stack a few of those brick-like large packaged drinking water (4-5L) around the fusor for additional protection? I'm actually pretty intimated by the price of HDPE blocks and wouldn't want to purchase any more of those after spending a fortune on thirty 5cm cubes. It would be fantastic if water can handle this job, instead of stacking loads of paraffin around the fusor.

Dan Knapp
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Re: Effectiveness of water (H2O) on fast neutrons?

Post by Dan Knapp » Fri Sep 11, 2020 12:37 pm

This has been discussed previously at length. Search “water as a neutron shield.”

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Dennis P Brown
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Re: Effectiveness of water (H2O) on fast neutrons?

Post by Dennis P Brown » Fri Sep 11, 2020 3:35 pm

I bought paraffin which isn't very expensive (just wax!) and is easy to melt, drill, cut so as to make shields into tube like structures to fit a detector. Putting a detector inside a water container could be difficult.

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Richard Hull
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Re: Effectiveness of water (H2O) on fast neutrons?

Post by Richard Hull » Fri Sep 11, 2020 7:56 pm

As mentioned in many posts on a shadow shield, neutrons are never an issue unless you are planning of operating for 6 hours each day for 200 days out of the year and are producing 3 million neutrons per second TIER during that full 6 hours each day. Be realistic!! follow the real rules of radiation...........Inverse square law.............time of actual exposure to a serious "dose rate" No need to freak out. Much ado about nothing whatsoever regarding neutrons.

If your entire work area in in a clothes closet with a fusor producing 3 mega-neuts TIER at 60kv.... Be very conscious of X-radiation FIRST.....Neutrons LAST!

We all know that an acute dose of 300 -500 Roentgens is LD50 for radiation among normal healthy people..... A normally deadly source of radiation.

You could pick up and throw a 500R source of radiation over a cliff in 3 seconds without any real fear! Use your noodle and a bit of mathematics. You received a dose of about only 400 mrem tossing that deadly source over the cliff. Your net dose is equivalent of about 1 year of normal life on earth. The only issue is the dose was acute and not the much more preferred chronic dosing over that yearly period like we all suffer as we work, play and live on this planet. Just eat your Wheaties with no real effect, provided the norm for you is not tossing 500R sources over cliffs for a living.

As the quoted inscription on the base of the statue of Emil Faber founder of Faber College during the opening credits of the movie Animal House", reads, ........."knowledge is good".

There is an old post here with an image of a fellow's fusor who mounded up paraffin blocks with many stacked up boxes of 20 mule team borax. A wasted effort. I wonder if he is still here or even made the neutron club. Regardless, it was gross overkill for a total non-issue.

X-rays are the deadly issue over 40kv, as long before neutrons are even to be considered, long exposures to hot x-radiation on your way to producing neutrons is the big issue.

I do not know why I even bother to write the FAQs!

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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