Perhaps a thick shell of water suffices. In the order of meters, perhaps one to four meters. Perhaps combine it with lead, in the order of centimeters, perhaps ten centimeters, then one meter of water would suffice.
Numerous long-duration spacecraft designs incorporate water storage in the outer structure, or a high-radiation shelter within a water storage structure, for just this purpose.
Water attenuates radiation quite rapidly. And has other uses.
Water attenuates radiation quite rapidly. And has other uses.
<https://news.ycombinator.com/item?id=41646990>
<https://isoe-network.net/publications/pub-proceedings/sympos...>