Breakable wrote: Is the neutron output energy not a probabilistic distribution? If so does that mean the high energy neutrons are just a negligible fraction?

They are .1% of reactions, .2% of total energy…

“These neutrons come primarily from the reaction
11B + α → 14N + n + 157 keV
The reaction itself produces only 157 keV, but the neutron will carry a large fraction of the alpha energy, which will be close to Efusion/3 = 2.9 MeV.” — http://en.wikipedia.org/wiki/Aneutronic_fusion