Basic aspects of natural radioactivity

The chapter deals with basic aspects related to natural ionizing radioactivity and focuses on the main parameters to be controlled in building products. The definitions of ionizing radioactivity in general, parent and daughter nuclides, different types of ionizing radiation (i.e., alpha, beta, gamma, and X-rays), external and internal radiation, naturally occurring radioactive materials (NORM), and naturally occurring radionuclides (NOR), are introduced and explained. The structure of radiation dose is discussed. It is shown that 80% of the dose has natural origin and besides medicine, only about 1% comes from artificial radioactivity, while the major segment of the natural radiation comes from the exposure to radon (including thoron).It is concluded that the main parameter characterizing the external radiation dose, created solely by building materials of mineral origin, is the activity concentration of the three main natural radionuclides: ²³²Th, ²²⁶Ra (in a state of radioactive equilibrium with the short-lived radon decay products), and ⁴⁰K, while the main parameters characterizing radon emanation and exhalation rate from building products are the radon emanation coefficient and the radon exhalation rate. Additional parameters characterizing the rate of radon release from the material are the radium activity concentration, the radon diffusion coefficient, product thickness, and density.