Radiation is energy given off in the form of waves or small particles of matter. Radiation is found throughout the universe and comes in many forms. Most people have heard of X rays, gamma rays, and radiation from nuclear reactors. These types of radiation are often mentioned as possible health hazards, though X rays and gamma rays also have valuable uses in medicine. But there are many other forms of radiation as well. The most familiar is probably the light we see, such as the light from the sun or a flashlight. The sun's ultraviolet rays, which cause suntan and sunburn, are another form of radiation. Heat from a fireplace, radio signals bringing music, the intense light from a laser, and the microwaves used to cook food are still others.
Radiation is present whenever energy moves from one place to another. Atoms and molecules give off radiation to dispose of excess energy. When the radiation strikes a substance, it may transfer some or all of its energy to the substance. Often, the energy takes the form of heat, raising the temperature of the material. Except for light, most kinds of radiation are invisible.
There are two chief types of radiation. One type, called electromagnetic radiation, consists only of energy. The other type, known as particle radiation or particulate radiation, consists of tiny bits of matter.
There are many sources of electromagnetic radiation. All materials that have been heated act as sources of such radiation. The sun produces electromagnetic radiation from nuclear reactions in its core. This energy heats the sun's outer layer until the hot gases glow, giving off light and other radiation. This solar radiation travels through space to the earth and other planets.
Particle radiation comes from radioactive substances. Radium, uranium, and many other heavy elements found in rocks and soil are naturally radioactive. In addition, scientists can create radioactive forms of any element in a laboratory by bombarding the element with atomic particles, the tiny bits of matter that make up atoms.
All life on earth depends on radiation, but some forms of radiation can be dangerous if not handled properly. X rays, for example, allow doctors to locate and diagnose hidden diseases. But X rays also can damage cells, causing them to become cancerous or die. Light from the sun enables plants to grow and warms the earth, but it also causes sunburn and skin cancer. Gamma radiation is used to treat disease by killing cancer cells, but it also can cause birth defects. Nuclear power plants produce electric energy, but the same facilities create radioactive waste that can kill living things.
