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Hard radiation is a colloquial term given to ionizing radiation which is at the higher end of the energy spectrum. It has general usage in the physics, health physics and radiation instrument community to provide a shorthand description of a general energy range of radiation without rigidly defining it.

Such radiation is capable of penetrating a thicker mass of material than "soft" radiation. A reference to cosmic rays suggest typically a shield 167 g·cm−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]

However, the term is also used for gamma rays, X-rays and beta particles.