Hard radiation is a term used to describe high-energy electromagnetic radiation, typically high energy X-rays or gamma rays. The term refers to the ability of the rays to penetrate a given thickness of material, typically a lead shield.
Hard radiation is able to cross 167 gcm−2 of lead (composed by p with energy greater than 1 GeV, m with E>300 MeV and e and g with E>10 GeV) [1]