Radionuclides (radioactive materials)

Radionuclides (or radioactive materials) are a class of chemicals where the nucleus of the atom is unstable. They achieve stability through changes in the nucleus (spontaneous fission, emission of alpha particles, or conversion of neutrons to protons or the reverse). This process is called radioactive decay or transformation, and often is followed by the release of ionizing radiation (beta particles, neutrons, or gamma rays).