GCSE Combined Science (AQA)

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Measuring Half-Life

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Atomic structure Atoms and nuclear radiation

Measuring Half-Life

4:53 Half-Life
Spec 4.4.2.3
Previous Half-Life Next Half-Life Calculations
  • As nuclei in a radioactive source decay, the activity decreases.
  • Activity is the rate at which decays occur in a sample of unstable nuclei.
  • Over time, as nuclei decay, fewer are left to decay, reducing activity.
  • Half-life is the time it takes for the activity of a radioactive isotope to halve.
  • Half-life also describes the time it takes for the number of undecayed nuclei to halve.
  • Activity is proportional to the number of undecayed nuclei.
  • To measure half-life, calculate the count rate over time using a Geiger-M��ller tube.
  • The Geiger-M��ller tube detects radiation directed towards it, clicking for each decay.
  • Measure count rate at even time intervals and plot on a graph.
  • The graph shows a downward curve as count rate decreases over time.
  • Half-life is determined by the time it takes for the count rate to halve from any value.
  • Example: If count rate starts at 20, it halves to 10 in 1.5 minutes, then to 5 in 3 minutes, and to 2.5 in 4.5 minutes.
  • The half-life of the sample is 1.5 minutes.
  • Be confident in calculating half-lives from graphs for exams.

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