Natural radioactivity

Abstract

Natural radioactivity originates from two primary sources: cosmic radiation and radioactive elements in the earth’s crust. Natural radionuclides are ubiquitous in the environment and make a major contribution to background radiation. The level of natural background radiation varies depending on location. 238U is the most abundant uranium isotope and its decay products account for the largest proportion of human exposure to ionizing radiation, primarily due to radon gas (222Rn). Terrestrial gamma rays originate chiefly from the radioactive decay of natural K, U, and Th which are widely distributed in terrestrial materials including rocks, soils, and building materials extracted from the earth. In general, the gamma radiation dose at any location is proportional to the amount of K, U, and Th in the ground and in building materials. Industrial processes can concentrate naturally occurring radioactive materials, which can enhance the ionizing radiation exposure to workers or exposed populations.