Hazards of Contamination & Irradiation (OCR Gateway GCSE Physics)

Half-Life and the Hazards from Radioactive Material

• The half-life is the time it takes for the activity of a radioactive source to decrease to half of its original value
• Different radioactive isotopes can have very different half-lives
• For example:
  • Francium-218 has a half-life of only 1 millisecond (0.001 seconds)
  • Polonium-210 has a half-life of about 140 days
  • Uranium-235 has a half-life of about 700 million years

Short Half-Life Values

• If an isotope has a short half-life, the nuclei will decay very quickly
  • This means that the isotope will emit a lot of radiation in a short amount of time

• If only a small amount of the isotope is used, having a short half-life can be advantageous, as the material will quickly lose its radioactivity
  • It is therefore commonly use in medical tracers
• If a large amount is used, however, the levels of radiation emitted could make handling the isotope extremely dangerous
  • This is because the isotope will have a large activity
  • The person will be exposed to a lot of radiation in a short period of time

Long Half-Life Values

• If an isotope has a long half-life then a sample of it will decay slowly
  • Although it may not emit a lot of radiation, it will remain radioactive for a very long time

• Sources with long half-life values present a risk of contamination for a much longer time
• Radioactive waste with a long half-life is buried underground to prevent it from being released into the environment

Depending on the activity of radioactive waste, it is buried in different ways

Part (a)

• • A short half-life means a source has a high activity
  • This means there is a high rate of radioactive emissions, compared to a source with a long half-life

Part (b)

• • Sources with long half-lives will remain radioactive for longer
  • They need to be controlled for longer, to prevent them spreading
  • Shielding and storage may be required