Spontaneous decay of some isotopes in nuclei.
Radiation resulting from radioactive decay; SYN. activity.
Spontaneous alteration of the nuclei of radioactive atoms, accompanied by the emission of radiation. It is the property exhibited by the radioactive isotopes of stable elements and all isotopes of radioactive elements, and can be either natural or induced. See radioactive decay.
Radioactivity establishes an equilibrium in parts of the nuclei of unstable radioactive substances, ultimately to form a stable arrangement of nucleons (protons and neutrons); that is, a non-radioactive (stable) element. This is most frequently accomplished by the emission of alpha particles (helium nuclei); beta particles (electrons and positrons); or gamma radiation (electromagnetic waves of very high frequency). It takes place either directly, through a one-step decay, or indirectly, through a number of decays that transmute one element into another. This is called a decay series or chain, and sometimes produces an element more radioactive than its predecessor.
The instability of the particle arrangements in the nucleus of a radioactive atom (the ratio of neutrons to protons and/or the total number of both) determines the lengths of the half-lives of the isotopes of that atom, which can range from fractions of a second to billions of years. All isotopes of atomic weight 210 and greater are radioactive. Alpha, beta, and gamma radiation are ionizing in their effect and are therefore dangerous to body tissues, especially if a radioactive substanceis ingested or inhaled.
Svojstvo elemenata da svojim zracima pocrne fotografsku ploču, da jonizuju vazduh, da prodiru kroz tvari svake vrste; sem urana i radijuma to svojstvo imaju torijum, aktinijum, polonijum (prirodna radioaktivnost); veštačka radioaktivnost je radioaktivnost koja je izazvana najpre kod aluminijuma. (lat.)