Shields are devices of various types designed to keep ionising radiation away from people and the environment or to attenuate it.

Depending on the type and intensity of the radiation to be shielded, different materials and material thicknesses are required. For alpha radiation, a sheet of paper is sufficient; beta radiation can be shielded by a baking tray, for example. For electromagnetic radiation such as gamma and X-rays, on the other hand, solid walls are needed, made e.g. of lead.