The word "radiation" refers to energy that emanates, or radiates, from a source and travels through space with the possibility of depositing a fraction of its energy in any matter it encounters.

There are many kinds of radiation. Familiar ones are radio waves that allow us to communicate long distances via phones, televisions, and satellites. Microwaves are used in communications as well as in microwave ovens. Visible light waves are those we can see reflected by matter, including raindrops that reflect the colors of a rainbow.

These and similar types of radiation belong to the category known as nonionizing radiation. They are considered nonionizing because the individual waves have too little energy to cause ionization (the stripping of electrons from atoms, which breaks the chemical bonds of molecules, which give matter structure).

Ionizing radiation, on the other hand, is capable of stripping electrons from atoms and breaking chemical bonds, creating highly reactive ions (atoms or molecules that have an electric charge). Radioactive materials, those that contain atoms that have unstable nuclei, occur naturally and emit ionizing radiation in a process known as radioactive decay.

The most common types of ionizing radiation are alpha particles, beta particles, gamma rays, and x-rays. The particles and rays cannot be seen, heard, tasted, smelled, or felt, which is why ionizing radiation remained undiscovered until the late 1800s even though many ordinary materials emit small amounts.

Natural sources include the soil, water, air, food, and building materials. Man-made devices such as x-ray machines also produce ionizing radiation. Potential sources include nuclear accidents involving medical or industrial nuclear material or terrorist actions involving nuclear devices.

To learn more about ionizing radiation, see the U.S. Nuclear Regulatory Commission fact sheet and additional information at the NRC Web site.

Information developed by AFRRI staff, 5/4/09