We’re generally not troubled by galactic cosmic rays (CR) here on Terra Firma.
It’s when you emerge out from the protection provided by Earth’s magnetic field when the real trouble with cosmic rays starts.
Talk about energetic—CRs are brutal, unrelenting, and, so far, and for all practical purposes—unstoppable. Collectively, they are the implacable enemy of biological life. Shielding them? How much lead do you think it will take, if lead will even do the trick? This is going to take a scientific miracle.
It is going to require a totally new artificial metamaterial created at the molecular level (nanotechnology).
Lead is way too heavy.
Since the material does not exist I cannot characterize it further at this point.