Alpha, Beta, Gamma

• Isotopes

  Different forms of an element, with the same number of protons but different numbers of neutrons
• Radioactive

  Consisting of unstable isotopes that can decay
• Types of nuclear radiation

  • Alpha particles
  • Beta particles
  • Gamma rays

  Emitted from unstable nuclei
• Alpha particles

  • Made up of two protons and two neutrons, the same as a helium nucleus
  • Have an overall charge of two plus
  • Easily stopped by collisions, can only travel a few centimeters in air and are absorbed by a single sheet of paper
  • Strongly ionizing, can easily knock electrons off atoms they collide with
• Beta particles

  • Just electrons
  • Emitted when a neutron in the nucleus decays into a proton and an electron
  • Have a charge of -1 and virtually no mass
  • Moderately ionizing and penetrate moderately far, stopped by several meters of air or about 5 millimeters of aluminium
• Gamma rays

  • Waves of electromagnetic radiation, not particles
  • Often emitted after alpha or beta radiation to get rid of extra energy
  • Have no mass or charge, tend to pass straight through materials
  • Weakly ionizing, can penetrate long distances through air and require thick lead or concrete to stop
• Neutron emission


  • Occurs when a nucleus contains too many neutrons, making it unstable
• Alpha particles are stopped by a single sheet of paper

  Beta particles are stopped by a thin sheet of aluminium

  Gamma rays require a thick piece of lead to stop them