Radiation Shielding Materials Containing H, B, and N

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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Endersworld
Posts: 19
Joined: Sun Jan 22, 2012 10:25 am

Postby Endersworld » Wed May 02, 2012 11:37 pm

Why don't we just spatter transfer the interior walls with tungsten, its a fairly good neutron reflector and temperature resistant.

DeltaV
Posts: 2245
Joined: Mon Oct 12, 2009 5:05 am

Postby DeltaV » Thu May 03, 2012 5:01 am

The problem may be gammas, more than neutrons, for p-11B.

Need suppressed Navy data to be sure.

Endersworld
Posts: 19
Joined: Sun Jan 22, 2012 10:25 am

Postby Endersworld » Fri May 04, 2012 5:09 am

so the gammas are basicly high energy xrays, or hard xrays, a surface with high enough density should be capable of deflecting them, a multi layer system would probably eliminate all of it. xrays have enough trouble going through hardened steel.

D Tibbets
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Joined: Thu Jun 26, 2008 6:52 am

Postby D Tibbets » Fri May 04, 2012 5:58 am

Penetration of gamma rays depends on it's energy. Steel will stop 50,000 eV gammas or x-rays with only thin layers. A million eV gamma is a different story. Lead, tungsten or uranium would do better per thickness, unit of weitht, but the number of gammas to absorb where perhaps 1 part in 10,000 to 50,000 of the fusion energy is huge. In a 100 Megawatt output, that would be
~ 2,000 Watts of gamma energy. That is enough to quickly fry anybody near a non shielded machine. Without looking it up , I think a few second exposure may be lethal.

Dan Tibbets
To error is human... and I'm very human.

93143
Posts: 1130
Joined: Fri Oct 19, 2007 7:51 pm

Postby 93143 » Fri May 04, 2012 8:57 pm

I calculated somewhere that for a reactor to be safe to work near for long periods, you'd want roughly a foot of lead shielding. These gammas are 4, 12, and 16 MeV, occurring due to gamma decay of excited ¹²C (excess energy of 16 MeV) once in every ~10,000 p-¹¹B reactions.

This is not a particularly well-documented reaction branch, though, and it's possible (if unlikely) that it won't turn out to be a problem...

RERT
Posts: 106
Joined: Mon Jun 02, 2014 9:10 pm

Re: Radiation Shielding Materials Containing H, B, and N

Postby RERT » Thu Dec 28, 2017 3:53 pm

I've been fiddling with data from Wikipedia on p11B fusion, which suggests that the side reaction

p+11B->12C+Gamma (16MeV) occurs with a 0.1 % branching probability.

Given this, I think a 10MW (Th) reactor would be a source of kilowatts of 16MeV gammas, and I agree with the last post that a foot of lead is about what is needed to stay healthy a couple of metres from such a thing.

However, there is no definitive reference, and looking at tables of excited states 12C* I can't see such a decay mentioned.

Does anyone have a definitive reference, or a suggestion where to search for such a thing?

As far as I can see this is very important to any p11B system.

RERT
Posts: 106
Joined: Mon Jun 02, 2014 9:10 pm

Re: Radiation Shielding Materials Containing H, B, and N

Postby RERT » Fri Dec 29, 2017 7:33 pm

I found this, seems to corroborate the above, around page 65 onwards

http://www.iaea.org/inis/collection/NCL ... 090626.pdf


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