Atom & Nuclear radiation

• Why is it important to warn people that a radiation source is being used?

  Radiation damages cells
• Why are some atoms radioactive?

  Unstable
• Explain why radiation is dangerous to humans.

  Damages cells causing cancer
• Explain why the alpha particles are less dangerous than the beta particles and gamma rays.

  alphas will be stopped by skin which can reach cells
• Explain why gamma radiation is not suitable for detecting changes to the thickness of the cardboard.

  Changing thickness won’t change count rate
• State one way in which the process of nuclear fusion differs from the process of nuclear fission.

  nuclei are joined
• Describe the process of nuclear fission.

  Neutron absorbed by nucleus which forms a larger unstable nucleus which splits into 2 releasing 3 neutrons and energy
• What is a beta particle and from what part of an atom is it emitted?

  An electron from the nucleus
• Beta decay does not cause the mass number of an atom to change. Explain why not.

  number of neutrons decreases by one and the number of protons increases by one
• 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)