Radioactive fallout does take time to clear. Masks would help prevent you from inhaling contamination (contamination is the particles that decay, releasing radiation. Very bad internally, less bad external) but it would just collect the contamination on your face creating a wonderful Radioactive face covering much like for the virus you're just collecting filth.

If you want to survive the radiation, you've got to avoid it. To avoid it, you've gotta hide from it. Being inside helps, being in a basement is better. But the contamination will make it into the water and air anyway, so if you don't have each already isolated you're fucked.

None of it matters anyway because people have zero understanding of the evil + incompetence of government or things like radiation