From NIAC 2012 Symposium.
Radiation Shielding Materials Containing Hydrogen, Boron, and Nitrogen: Systematic Computational and Experimental Study
Radiation Shielding Materials Containing H, B, and N
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- Posts: 19
- Joined: Sun Jan 22, 2012 10:25 am
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- Posts: 19
- Joined: Sun Jan 22, 2012 10:25 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
~ 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.
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...
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...
Re: Radiation Shielding Materials Containing H, B, and N
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.
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.
Re: Radiation Shielding Materials Containing H, B, and N
I found this, seems to corroborate the above, around page 65 onwards
http://www.iaea.org/inis/collection/NCL ... 090626.pdf
http://www.iaea.org/inis/collection/NCL ... 090626.pdf