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• Electromagnetic radiation
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The word radiation comes from a Latin term that means "ray of light." It is used in a general sense to cover all forms of energy that travel through space from one place to another as "rays." Radiation may occur in the form of a spray of subatomic particles, like miniature bullets from a machine gun, or in the form of electromagnetic waves. Subatomic particles are the basic units of matter and energy (electrons, neutrons, protons, neutrinos, and positrons), which are even smaller than atoms. Electromagnetic waves are a form of energy that includes light itself, as well as other forms of energy such as X rays, gamma rays, radio waves, and radar.

In addition, the word radiation is sometimes used to describe the transfer of...