Different half-lives of radioactive isotopes

Radioactive isotopes have a very wide range of half-life values.

Half-Life & Risk

• 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

• If a large amount is used, however, the levels of radiation emitted could make handling the isotope extremely dangerous

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

Question: Summarise the difference in the risk posed by radioactive sources with very short and very long half-lives with regards to:

(a) Irradiation.

(b) Contamination.

\n Part (a)

• A short half-life means a source has a high activity

  1. 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

  1. They need to be controlled for longer, to prevent them spreading
  2. Shielding and storage may be required