Naturally occurring radiation – or so-called “background radiation” – on average accounts for approximately 50% of our exposure. It’s found in the food we eat, the water we drink and the construction materials used in our buildings, while terrestrial radiation also comes from soils enriched in naturally occurring uranium and natural forms of energy such as oil and gas. All of this influences our exposure to radiation.
In addition to terrestrial radiation, we are also exposed to radiation from space or “cosmic radiation” which increases with altitude. The higher you are above sea level, the greater the exposure to cosmic radiation. People living in La Paz, Bolivia, for example – 3,650 m or 11,975 ft above sea level – are exposed to much more cosmic radiation than residents of Amsterdam in the Netherlands, which is at sea level.
Most of our exposure to ionizing radiation comes from a naturally occurring radioactive gas called radon. It’s formed from the radioactive decay of uranium, which has been present since the earth was formed and has a half-life of 4.5 billion years. As a result, radon will continue to exist almost indefinitely at about the same levels as it does today.1 Radon can accumulate in buildings, especially in confined areas, and most of our exposure is received indoors. Its concentration varies according to location but no one can escape exposure to it.2