Radioactivity Facts



  • Radioactivity is when a certain kind of atom disintegrates spontaneously and sends out little bursts of radiation from its nucleus (center).
  • Isotopes are slightly different versions of an atom, with either more or less neutrons. With stable elements, such as carbon, only certain isotopes called radio-isotopes are radioactive.
  • Some large atoms, such as radium and uranium, are so unstable that all their isotopes are radio-isotopes.
  • Radioactive isotopes emit three kinds of radiation: alpha, beta and gamma rays.
  • When the nucleus of an atom emits alpha or beta rays it changes and becomes the atom of a different element. This is called radioactive decay.
  • Alpha rays are streams of alpha particles. These are made from two protons and two neutrons — basically the nucleus of a helium atom. They travel only a few centimeters and can be stopped by a sheet of paper.
  • Beta rays are beta particles. Beta particles are electrons (or their opposite, positrons) emitted as a neutron decays into a proton. They can travel up to 1 m and can penetrate aluminum foil.
  • Gamma rays are an energetic, short-wave form of electromagnetic radiation. They penetrate most materials but not lead.
  • The half-life of a radioactive substance is the time it takes for its radioactivity to drop by half. This is much easier to assess than the time for the radioactivity to disappear altogether.