JimmyT wrote:
We are talking airplane design here. Right?

Neutron shielding is always going to be bulky (from the moderator/absorber part) and heavy (from the gamma shield), especially for the high energy neutrons from D+D or D+T. That’s the beauty of p+B11, the few neutrons you do get from side reactions are much lower energy. So you only need a relatively thin layer of borated polyethylene to slow & absorb them. After this you still need some heavy metal shielding to capture the gamma-rays produced in the neutron absorption reactions. The gamma shield will also partly double as a neutron reflector, as described above.

I’m sure if the DPF was in the tail or out on the wings it would be viable to put them in an airplane. The radiation levels would be down to below what pilots are getting from cosmic rays anyway. (cargo planes at least – passengers may take a little more convincing)