Fusion Message Board

In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.

Subject: Re: p + B11 reaction
Date: Feb 22, 6:40 pm
Poster: Pierce Nichols

On Feb 22, 6:40 pm, Pierce Nichols wrote:

>>While initially attractive because it is "a-neutronic" (that is, it doesn't give up neutrons which cause all sorts of problems), it has a very low cross section (which means it is hard to make it work), and, there are other reactions that will inevitably occur in the same reaction vessel that DO yield neutrons, so you haven't actually saved much hassle.
>I take it the low cross section means that getting a proton to hit a boron nucleus and split it is difficult?. Also, what are the neutron generating side reactions?

Ok, we've actually kicked this one around repeatedly. While Jim Lux is correct about both the low cross-section and the presence of neutron generating side reactions, he is incorrect about how incredibly useful the reaction is, because of two things: The neutronic side reactions are much lower in cross section than the main reaction, and the emitted alpha particles fit into tight energy bands. This second fact is the real advantage, b/c it means you can extract electrical power directly by decelerating those alphas through a 1.5 megavolt potential. This is much more efficient than the thermal energy extraction otherwise available.

That said, the cross-section problem kicks it out of all but the most well-funded and powerful amateur fusors. According to http://silver.neep.wisc.edu/~neep602/lecture26.html, slide 26, the x-section for p-B11 reaction has an anomalous spike around 55 kV (anyone got an explanation for this?? I'm thinking it looks like an experimental error), higher than D-D at the same voltage, passes D-D for good at about 90 kV, and peaks around 200 kV, at which point it beats out D-T and D-He3 (which are both declining from their peaks at that point). In summary, I don't think it's worth it unless you are set up to go to at least 100 kV. I would look into putting your paws on some He3 instead, which peaks at about 100 kV, on par with D-T at the same voltage and way above everything else.