4.4.2

• Why do unstable nuclei give out radiation?

  Unstable nuclei undergo decay to become more stable
• What is the name of the process in which an unstable nucleus gives out radiation to become more stable?

  Radioactive decay
• Define the activity of an unstable nucleus.

  Activity is the rate of decay of a source of unstable nuclei
• What is the unit of radioactive activity?

  Becquerel (Bq)
• What is count-rate?

  The number of radioactive decays per second for a radioactive source
• Give an example of a detector that may be used to measure count-rate.

  Geiger-Muller tube
• State four types of nuclear radiation.

  1. Alpha particles
  2. Beta particles
  3. Gamma rays
  4. Neutrons
• What are the constituents of an alpha particle?

  Two protons and two neutrons
• What is the range of an alpha particle through air?

  A few centimetres (normally in the range of 2-10 cm)
• What will stop beta radiation from passing through a point?

  A thin sheet of aluminium or several metres of air
• What will stop gamma radiation from passing through a point?

  Several centimetres of lead or a few metres of concrete
• Which type of radiation is most ionising?

  Alpha radiation
• Which type of radiation is least ionising?

  Gamma radiation
• State any changes to mass or charge that occur due to the emission of a gamma ray.

  Both mass and charge remain unchanged
• Describe the nature of radioactive decay.

  • Random
  • Which nuclei decays and when is determined only by chance
  • It is impossible to predict which nuclei will decay and when
• Define the half-life of a radioactive isotope.

  The time it takes for the number of unstable nuclei in a substance to halve
• What is radioactive contamination?

  The presence of unwanted radioactive nuclei on other materials
• What is irradiation?

  The process of exposing a material to nuclear radiation without making it radioactive
• Why is it 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
  • This is known as peer review