Where does the natural background radiation come from?
Of the average total radiation received by each American every year (360 mrem), 82% comes from Natural Sources. Of these, the largest contribution (55% or 200 mrem) comes from radon gas, a natural decay product of uranium and thorium in the soil. Another 8% (27mrem) come from above, from cosmic sources & solar flares, and 8% (28 mrem) come from the natural radioactive isotopes of uranium, thorium and potassium in the Earth below us (terrestrial radiation). Because our environment is naturally radioactive, our own bodies are a source of radiation (11%, or 40 mrem), primarily because of a long-lived natural radioactive isotope of potassium, K-40 and cosmogenically generated carbon-14. (We know about C-14 because of it’s usefulness in determining the age of organic fossils through carbon dating.) Remember these percentages are averages and can vary with location (altitude, soil composition), housing construction (radon) and health habits (smoking). For example: Radiation levels can be 2 o
