Absorbers of α, β, and γ radiation.
An absorber is any material that is efficient at stopping ionizing radiation from passing through. Alpha particles are totally absorbed by a sheet of paper. Beta particles are absorbed by a few centimeters of plastic material or 1 cm of aluminum. Materials with a high atomic number and high density (e.g., lead, steel, and concrete) are used as absorbers of gamma rays. Neutron absorbers such as boron, hafnium, and cadmium are used in control rods for reactors.