radiation

Definition 1

Direct transmission of heat or electromagnetic energy through space or another medium. It is the 'non-ionizing' type of radiation that does not affect chemical bonds and thus is usually harmless. Also called radiant energy.

Definition 2

Particulate emanation of unstable or split atomic nuclei, such as protons or helium nuclei (alpha radiation), high-energy electrons (beta radiation), and neutrons (from fission). It is the 'ionizing' type of radiation that directly breaks down chemical bonds and is likely to be harmful.