English: Main sources of natural radioactivity stem from Uranium, Thorium and Potassium in the ground (bottom) and cosmic particle showers that break down in the upper atmosphere, above the altitude of passenger airplanes (top). Common artificial sources are medical applications (left) and nuclear power plants (right).

For alpha and beta radiation, the relevant particle decay equations are stated in the top left corner. The greek gamma letter represents photons of high energy (= ionizing radiation) from gamma decays or X-rays.

This work includes other CC-licensed pictograms depicting a hospital, nuclear power plant and airplane.