Atoms and nuclear radiation

• Radioactive decay


  The process in which an unstable nucleus gives out radiation to become more stable
• Unstable nuclei


  • They undergo decay to become more stable
  • As they release radiation their stability increases
• Activity


  The rate of decay of a source of unstable nuclei
• Unit of radioactive activity

  Becquerel (Bq)
• Count-rate


  The number of radioactive decays per second for a radioactive source
• Detector used to measure count-rate

  • Geiger-Muller tube
• Types of nuclear radiation

  • Alpha particles
  • Beta particles
  • Gamma rays
  • Neutrons
• Alpha particle


  Two protons and two neutrons, the same as a helium nucleus
• Range of alpha particle through air

  A few centimetres (normally in the range of 2-10cm)
• What stops beta radiation

  • A thin sheet of aluminium
  • Several metres of air
• What stops gamma radiation

  • Several centimetres of lead
  • A few metres of concrete
• Most ionising radiation


  Alpha radiation
• Least ionising radiation


  Gamma radiation
• Emission of a gamma ray does not change mass or charge
• Radioactive decay


  • Random
  • Which nuclei decays and when is determined only by chance
  • It is impossible to predict which nuclei will decay and when
• Half-life


  • The time it takes for the number of unstable nuclei in a substance to halve
  • The time it takes for the count rate from a sample to fall to half its initial level
• Radioactive contamination


  The presence of unwanted radioactive nuclei on other materials
• Irradiation


  • The process of exposing a material to nuclear radiation
  • The material does not become radioactive
• It is important for the results of studies on the effects of radiation to be published and shared with other scientists to allow the findings to be independently checked (peer review)