Our environment is made up of the air we breathe, the food we eat and drink, and the places where we live and work. Radioactivity from both natural and artificial sources is present throughout the environment. Natural sources include radon in the home and radioactivity in the earth’s crust present since the formation of the Earth, while artificial sources include medical exposures and releases of radioactivity into the environment from nuclear facilities and as a result of accidents such as that at Chernobyl. 

Some sources of radiation expose every member of the population while, in other cases, only certain members of the population may be exposed. For example, natural radioactivity is found in soils everywhere and therefore everyone receives some exposure from this source. On the other hand, in the case of radon, those who have high levels of radon in their home receive the greatest exposure.