Radioactive half-life

When an unstable nucleus gives out an alpha or beta particle, the nucleus turns into the nucleus of a new element. This process is called radioactive decay. Although radioactive decay is a random process, statistically, over a time called the half-life , half of the parent radioactive nuclei will have decayed.

A diagram where green squares represent the parent unstable nuclei decaying into daughter nuclei represented by red squares. They decay from 16 radioactive atoms to 1 in 4 half-lives.

Working out the half-life allows us to calculate when a will become stable.

Look at the diagram.

In this decay model, the green squares represent the parent unstable nuclei. They decay into the red squares – the .

The process is random. You can’t tell when a green will turn into a red, or which green will decay, but after every half-life, half of the green parents will have decayed into red daughters.

Diagram showing the parent atoms only. There are 16 at the start and they halve after each half-life until there is 1 left. Each decay is shown by an arrow and the label T half.

This diagram shows the parent atoms only. Notice that they halve after every half-life.

This graph shows the pattern of the decay.

Graph titled radioactive decay, plotting Number of parent atoms left against Number of half-lives. The number of atoms go from 16 to 1. The number of half-lives go from 0 to 4.

The graph starts at 16 atoms and shows the number of halving every half-life.

All radioactive isotopes have a decay curve that looks like the one in the graph, however the half-life times can vary from seconds to millions of years.

The half-life of a radioactive element is the time taken for:

  • the to halve
  • the number of parent nuclei to halve
  • the mass of the parent nuclei to halve
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Half-lives of isotopes used in GCSE questions

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