Topic 8 - Half-Life

• Define the half-life of a radioactive isotope.

  • 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.
• Why are isotopes with long half-lives particularly harmful?

  • They remain radioactive for much longer periods of time.
  • They must be stored in specific ways to avoid humans and the environment from being exposed to radiation for too long.
• State two uses of nuclear radiation in the field of medicine.

  1. Examining of internal organs
  2. Controlling and destroying unwanted tissue
• 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
• Explain how to determine and verify half-life from a decay curve.

  • Read off the time axis the time it takes for the unstable nuclei to half.
  • To verify, check that the time it takes for that number to half again is the same.
• Explain the basic idea behind carbon dating.

  • All living things contain the same relative amount of carbon-12.
  • When they die, the carbon decays at a known rate.
  • By measuring the amount of carbon remaining, the age can be calculated.
• Explain how a medical radioactive tracer is used.

  • The tracer is inserted in the body (often through the bloodstream).
  • The tracer is radioactive so decays.
  • A detector outside the body can detect this radiation and locate the tracer.
• What can be said about the half-life of a given radioactive isotope?

  It is constant.
• Define the activity of an unstable nucleus.

  Activity is the rate at which a source of unstable nuclei decays.
• What is the unit of radioactive activity?

  Becquerel (Bq)