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