What kind of radiation?
ALL metal (or even paper and cardboard) will absorb "some" radiation, the question is "how much" losses of radiation (of what kind) can your system tolerate?
Even a thin sheet of plastic will stop all alpha particles, most beta's.
Some of the incident Gamma rays will get through even tons of lead.
Neutrons will pass through some materials, be completely absorbed by other metals, be slowed down by some, be ignored by others.
Will activate some metals, be ignored by others.
Lighter density metals will absorb less gamma and xrays than heavier metals of the same thickness.