Below are some general categories that make up our natural background exposure. All figures are averages for the United States. 200 mrem Radon is a radioactive gas that is the decay product of naturally occurring isotopes in the earth's soil and rocks.
Radon is the largest contributor to our natural background radioactive exposure.
All living things contain trace amounts of radioactive materials, including radioactive carbon and potassium. Certain foods that we eat also contain trace amounts of radioactive materials, including bananas and brazil nuts. In addition to radon, we also receive background exposure from the rocks in the earth's crust. Remember that most building materials, including bricks and concrete, are made from natural products. These materials contain small amounts of natural uranium and thorium.