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 g/cm-2 of lead (composed by p with energy greater than 1 GeV, μ with E>300 MeV and e and γ with E>10 GeV)