radioactivity

• Radioactive decay


  The process where some isotopes have an unstable nucleus and give up radiation to become stable
• Types of nuclear radiation

  • Alpha particle
  • Beta particle
  • Gamma ray
  • Neutron
• Alpha particle


  Consists of two protons and two neutrons, same as the nucleus of a helium atom
• Beta particle


  An electron ejected from the nucleus at high speed, formed when a neutron changes into a proton and an electron
• Gamma ray


  A type of electromagnetic radiation from the nucleus, not a particle
• Neutron


  Can be given up by an unstable nucleus
• Radioactive decay is a completely random process, scientists cannot predict when a nucleus will decay
• Activity


  The rate at which unstable nuclei decay, measured in Becquerels (Bq)
• Count rate


  The number of decays recorded each second by a detector like a Geiger-Muller tube, not the same as activity
• Radioactivity and radiation topics will be found in the physics revision workbook
• Isotopes


  Different forms of an element, with the same number of protons but different numbers of neutrons
• Only one or two of an element's isotopes are stable, while the rest are unstable and undergo radioactive decay</b>
• Radioactive


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

  • Alpha particles
  • Beta particles
  • Gamma rays
  • Neutrons
• 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 centimetres 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 metres of air or 5mm 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, so tend to pass straight through materials
  • Only weakly ionizing, can penetrate far into materials 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 by a thin sheet of aluminium, and gamma rays require a thick piece of lead to stop them