GCSE Physics (AQA)

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Hazards & Half Lives

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Atomic structure Hazards and uses of radioactive emissions and of background radiation

Hazards & Half Lives

2:31 Radiation in Medicine
Spec 4.4.3.2
Previous Background Radiation Dose Next Radioactive Tracers
  • Half-life determines the activity and stability duration of a radioactive source.
  • Half-life is the time it takes for half of the radioactive nuclei in a sample to decay.
  • Iodine-131 and Cesium-137 contaminated the environment after Chernobyl and Fukushima disasters.
  • Iodine-131 has a short half-life of 8 days; Cesium-137 has a long half-life of 30 years.
  • Half-life affects the nature of the hazard presented by radioactive sources.
  • Sources with short half-lives have high activities, giving high radiation doses in a short time.
  • These sources become safe after 99% of atoms decay, typically after seven half-lives.
  • Iodine-131 becomes safe quickly, in about two months.
  • Sources with long half-lives have low activities, giving low doses over a short time.
  • Long half-life sources contaminate surroundings for a long time, taking longer to become stable.
  • Cesium-137 remains unstable for over 100 years, emitting radiation for a long time.
  • In exams, you may need to compare risks of different radiation sources based on their half-lives.

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