Everyone is exposed to radiation every day. People are continuously exposed to low-level radiation found in food, soils, building materials, and the air and from outer space. All of this radiation originates from naturally occurring sources. For example, bananas contain naturally occurring radioactive potassium-40 and air contains radon, a radio- active gas. Your average natural background radiation dose* is about 3.0 mSv (300 mrem) each year (millisieverts and millirem are units of radiation dose, much like a gram or an ounce is a unit of weight).