Irradiation, << ih `ray` dee AY shuhn, >> is the exposing of matter to radiation, often for the purpose of producing a specific biological, chemical, or physical change. Accidental exposure to low doses of artificial radiation is common. However, a large dose of high-energy radiation is harmful to living things. Radiation consists of particles or electromagnetic waves (related patterns of electric and magnetic force). The particles include individual alpha particles, electrons and neutrons released by radioactive substances, and beams of particles expelled from particle accelerators (see Particle accelerator). High-energy electromagnetic waves include gamma rays, ultraviolet rays, and X rays.
When high-energy particles or rays penetrate matter, they ionize it. The resulting electrically charged atoms, or ions, combine to form new chemical compounds or altered molecular structures. For example, complex compounds, such as ethane (C2H6) and propane (C3H8), are produced from the simple gas methane (CH4) by exposing it to high-energy electrons or gamma rays. Subjecting living cells to ionizing radiation can disrupt their normal chemical activity and kill them.
Irradiation has many practical applications. It can be used to prepare industrial chemicals and to cure certain paints that would be damaged by ordinary heat treatment. Irradiation is effective in killing bacteria. Thus, it is used in food preservation and for sterilizing surgical supplies. Cancer cells can be destroyed by carefully controlled irradiation. But serious biological damage and even death can result from excessive exposure to radiation. Also, genes damaged by radiation may transmit undesirable traits to offspring.
