FF is probably going to need some neutron shielding. The alpha particles will generate some neutrons and there isn’t much to stop it. I don’t remember the number but I know Zapkitty commented on it a while back. I think the number was something like 0.2% of the energy output. If my memory is even so-so, that is 10 kW of neutrons is a big deal. The neutron yield is enough to be a concern from a regulatory stand point. I’m sure the activation decay is fast depending on the surrounding materials. No energy source is perfect but some are far better than others….if they work.
