GCSE Different half lives of radioactive isotopes

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.