This article describes sources of ionizing radiation and gives some reasons for the variations in radiation exposure received. It also presents the multiple uses of radiation sources in different socio-economic sectors and the basic principles of radiation protection.

Throughout the history of life on earth, organisms continuously have been exposed to cosmic rays, radionuclides produced by cosmic ray interactions in the atmosphere, and radiation from naturally occurring substances (terrestrial) which are ubiquitously distributed in all living and nonliving components of the environment. The largest natural source of radiation exposure to humans is radon gas. While radon gas has always been in the environment, awareness of its contribution to human radiation exposure has increased in recent years. It is clear that contemporary life have adjusted or are doing so to all features and limitations of the environment, including the natural radiation background. Although high levels of radiation are definitely harmful to organisms, some environmental radiation is of importance to life.

Over the last few decades man has “artificially” produced several hundred radionuclides. And he has learned to use the power of the atom for a wide variety of purposes, from medicine to weapons, from the production of energy to the detection of fires, from illuminating watches to prospecting for minerals. With regard to sources of artificial exposure, is the use of radiation in medicine which dominates other uses of radiation.