radioactive nuclide
Radionuclides are also called unstable nuclides, as opposed to stable nuclides. It refers to an unstable atomic nucleus that can spontaneously emit rays (such as alpha rays, beta rays, etc.) and form stable nuclide through decay. The energy released during decay is called decay energy, and the time required for decay to half of the original number becomes the decay half-life, which ranges widely from 1015 to 10-12 seconds.