The word radiation comes from the Latin for “ray of light,” and 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 be in the form of a spray of subatomic particles, like miniature bullets from a machine gun, or in the form of electromagnetic waves, which are nothing but pure energy and which include light itself, as well as radio waves and several other kinds.
The word radiation is also sometimes used to describe the transfer of heat from a hot object to a cooler one that it is not touching; a hot object is said to radiate heat. You can “feel the heat” on your face when standing near a red-hot furnace, even if there is no movement of hot air between the furnace and you. What you are feeling is infrared radiation, a form of electromagnetic energy that makes molecules move faster, and therefore behave hotter, when it strikes them.
When many people hear the word “radiation,” they think of the radiations that come from radioactive materials. These radiations, some of which are particles and some of which are electromagnetic waves, are harmful because they are of such high energy that they damage materials through which they pass. This is in contrast to light, for example, which has no lasting effect on, say, a pane of glass through which it passes.
The higher energies of radiation are called ionizing radiations because when they tear apart atoms they leave behind a trail of ions, or atoms that have had some of their electrons removed. Ionizing radiations include x rays, alpha particles, beta particles, and gamma rays.
Many kinds of lower-energy radiations are quite common and are harmless in reasonable amounts. They include all colors of visible light, ultraviolet and infrared light, microwaves and radio waves, including radar, TV and FM, short wave and AM. All of these radiations are electromagnetic radiations.
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