Definition of radioactivity
Radioactivity means that elements spontaneously emit rays from unstable nuclei (such as alpha rays, beta rays, gamma rays, etc.) and decay to form stable elements and stop radiation (decay products). This phenomenon is called radioactivity. The energy released during decay is called decay energy. Elements with an atomic number of 83 (bismuth) or above are radioactive, but some elements with an atomic number of less than 83 (such as technetium) are also radioactive.