ionizing radiation, high-energy electromagnetic waves (such as x-rays and gamma rays) and particles (such as alpha and beta particles, neutrons, protons, and heavy nuclei) that cause substances in their paths to dissociate into ions. The spatial distribution of the ionization depends on the kind of radiation, its penetrating power, the location of the source, and the nature of the irradiated material. High-energy x-rays penetrate deeply, most beta particles penetrate only a few millimeters, and alpha particles penetrate only a fraction of a millimeter. However, all three produce intense ionization along their tracks. Ionizing radiation directly affects living organisms by killing cells or slowing their development and by producing gene mutations and chromosome breaks. Tissues containing elements with relatively high atomic masses, such as calcium in bones and teeth, absorb much higher doses of ionizing radiation than do soft tissues.
