One of the major problems of the $D$-$T$ fusion reaction is that it releases a 14MEV neutron. In large numbers, these neutrons irradiate the chamber walls and wreak havoc on the metallic lattice, introducing numerous technical problems.

What if we introduced a neutron poison into the plasma, such as Xe135 or B10, to capture these neutrons, rather than allowing them to slam into the chamber walls? The neutron poisons would be heated, and while it would be difficult to extract power from the heated neutron poisons, it seems more convenient than allowing for neutrons to destroy the tokamak.

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    $\begingroup$ The 10B(n,$\gamma$)11B cross section at 14MeV is roughly 5 orders of magnitude lower than at thermal neutron energies - it just isn't good at capturing neutrons. $\endgroup$
    – Jon Custer
    Jan 22, 2020 at 20:55
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    $\begingroup$ You don't want to get rid of those neutrons - for D-T fusion they carry all the excess energy that you want to harvest! Also if you put some neutron poison all over the tokamak, it's going to get hard to get the poison from diffusing into the reaction volume - even considering the lower diffusion coefficients in the pedestial region. People have tried to inject impurities into only the divertor region for other reasons - and only injected there, it's hard to keep the impurities from diffusing in. $\endgroup$ Jan 22, 2020 at 21:57

1 Answer 1


What if we introduced a neutron poison into the plasma, such as Xe135 or B10

The amount of energy lost from the plasma varies with the mass of the particles within it. This is why the divertor and scrape-off systems are so important, otherwise heavier atoms spalled off the reactor walls murder your energy balance by increasing the x-ray emission.

So, adding something to the plasma, especially like Xe, is a Very Bad Idea.


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