ABSTRACT
Cosmic radiation contributes to a great extent to the total radiation exposure of human beings. Radioactivity in air due to cosmic radiation is a source of external irradiation of human beings as well as internal irradiation. Radionuclides that have a terrestrial origin are present at various levels in every kind of matter in nature. Natural radionuclides can be and are released to the atmosphere as a result of the industrial processing of various raw materials. Mineral processing and the combustion of fossil fuels are the most important processes that contribute to the emission of uranium and thorium series radionuclides to the environment, increasing their air volume activities and causing exposure of human beings. Radionuclides released to the atmosphere can be transmitted over large distances or can be released in the form of dust or fly ash in the vicinity of the industrial plant.
