General English


  • Particles and radiation emitted by the fission of unstable atomic nuclei


  • The spontaneous disintegration of unstable atomic nuclei, such as those of uranium or curium, mainly through the emission of alpha, beta, or gamma rays. Also called decay (2).
  • A specific instance of radioactivity (1), such as that occurring when an atom of uranium-238 emits an alpha particle to form an atom of thorium-234. Also called decay (3).
  • The reduction over time of the radioactivity of a substance, due to radioactivity (1). Also called decay (4).
  • synonymradioactive decay
  • synonymradioactive disintegration


  • noun energy in the form of radiation emitted by a radioactive substance


  • noun radiation given off by a radioactive substance

General Science

  • noun a gradual disintegration of the nucleus of radioactive matter