ABSTRACT
Naturally radioactive elements in soil and rock such as uranium, thorium, radium, and potassium-40 contribute to the natural radiation exposure of humans. Gamma radiation from these sources irradiates humans with external radiation. Natural radioactivity is ingested and inhaled and results in internal radiation dose. A special case of internal radiation is the inhalation of airborne radon decay products which decay in the human lung giving an alpha radiation dose to the cells of the bronchial epithelium. Ionizing radiation can be divided into four broad categories: electromagnetic radiation, energetic electrons, energetic heavy ions, and neutrons. Beta radiation consists of high-energy electrons emitted from the nucleus during radioactive beta decay. Beta radiation can be negatively charged electrons or positively charged electrons. Fission occurs when an atomic nucleus of high atomic weight absorbs a neutron and splits into two fission fragments with the release of energy.
