A radionuclide's an atom with an unstable nucleus, which's a nucleus characterized by excess energy which's available to be imparted either to a newly-created radiation particle within the nucleus, or else to an atomic electron (see internal conversion) . The radionuclide, in this process, undergoes radioactive decay, and emits a gamma ray(s) and/or subatomic particles. These particles constitute ionizing radiation. Radionuclides may occur naturally, but can also be artificially produced. Radi… (More on Radionuclide)