Radioactivity is the phenomenon of emissions of neutral or charged particles or electromagnetic radiations from unstable atomic nuclei. œe more common types of radiations are listed in Table 80.1. Several naturally occurring (primordial) radionuclides and some produced by cosmic rays in the Earth’s atmosphere are given in Table 80.2. Methods of producing other unstable nuclei are discussed as follows. Radioactive isotopes from man-made sources and from naturally occurring nuclides are widely used in health sciences, industry, and academic research.