AQA GCSE Different half lives of radioactive isotopes(Physics)
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Different half lives of radioactive isotopes
There are two possible definitions, either is suitable:
The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve.
The time it takes for the count rate (or activity) from a sample containing the isotope to fall to half its initial level.
The half life for this radioactive isotope is 4 minutes. This is because every 4 minutes the activity will halve.
However, different radioactive isotopes have different half lives.
| Radioactive isotope | Half life |
|---|---|
| Iodine-131 | 8 days |
| Cobalt-60 | 5.3 years |
| Uranium-238 | 4.5 billion years |
Length of the half life
The length of the half life can indicate the hazard.
If the half life is very short, it can mean that a lot of radiation is emitted in a short time period, which can be hazardous. However, the material will decay quickly.
If the half life is very long, then the material takes a long time to decay, but it will emit the radiation over a longer time period.
When using radioactive sources, we need to consider the length of the half life, so it is long enough for our needs, but that it poses a minimum hazard to our health.
Practice Questions
1. Define the term half life
2. Which radioactive source Iodine-131 or Cobalt-60 is likely to emit more radiation over a 1 day time period?
3. Radioactive waste stays radioactive for tens of thousands of years, suggest why.
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