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radiation :
The giving off of energy in the form of rays or waves. The radiation of light and heat by the sun warms the planets. Also, the kind of energy radiated in the form of rays or waves. Heat, light, and radio waves are types of radiation. Also, a stream of particles or waves given off by the atoms and molecules in a radioactive substance such as uranium. This kind of nuclear radiation includes alpha and beta particles, gamma rays, and neutrons. Nuclear radiation is often harmful to living tissue.
