radiation Emission of any rays from either natural or man-made origins, such as radio waves, the sun's rays, medical X-rays and the fall-out and nuclear wastes produced by nuclear weapons and nuclear energy production. Radiation is usually divided between non-ionizing radiation, such as thermal radiation (heat) and light, and nuclear radiation. Non-ionizing radiation includes ultraviolet radiation from the sun which, although it can damage cells and tissues, does not involve the ionization events of nuclear radiation['reɪdɪ'eɪʃ(ə)n]сущ.
