Radioactive decay and nuclear radiation

• • Some atomic nuclei are unstable.
  • The nucleus gives out radiation as it changes to become more stable
  • this is a random process called radioactive decay
• • Activity is the rate at which a source of unstable nuclei decays.
  • activity is measured in becquerel (Bq)
• Count-rate is the number of decays recorded each second by a detector (eg Geiger-Muller tube)
• The nuclear radiation emitted may be:

  • an alpha particle
  • a beta particle
  • a gamma ray
  • a neutron
• Alpha particle

  • Consists of 2 neutrons and 2 protons
  • the same as a helium nucleus
  • a range of a few centimetres through air (2-10cm)
  • doesn’t penetrate far, absorbed by a sheet of paper
  • highly ionising
• Beta particle

  • A high speed electron ejected from the nucleus as a neutron turns into a proton
  • A range in air of a few metres
  • Moderately penetrating - absorbed by a sheet of aluminium (around 5mm thick)
  • moderately ionising
• Gamma ray

  • electromagnetic radiation from the nucleus
  • Travel a long distance through air
  • Highly penetrating - absorbed by thick sheets of lead or concrete
  • weakly ionising