What Is Radiation?

Since radiation was discovered in the late 19th century, scientists have studied it extensively.

In simple terms, radiation is energy emitted from a source. Radiation is generated either from unstable atoms that undergo radioactive decay or from machines. Radiation is transmitted from its source in the form of energy waves or energized particles.

All of us are exposed to radiation every day from a variety of sources, both natural and human-made. The NCRP estimates that the average annual radiation dose per person in the United States is 620 millirem. Most of the average annual dose comes from natural background radiation sources, including the following:

• Radon and thoron (radioactive gases that are created when naturally occurring elements undergo radioactive decay)
• Space (cosmic radiation)
• Naturally occurring radioactive minerals in our bodies (internal)
• Naturally occurring radioactive minerals in the ground (terrestrial)

The average American also receives 48% of his or her annual dose of radiation from medical procedures. That percentage becomes many times larger when radiation therapy, used in the treatment of cancer, is factored into the equation.

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