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Half-life – WJECUsing a decay curve to find the half-life

Radioactive isotopes are used for blood flow monitoring, cancer treatment, paper mills, carbon dating and smoke alarms. Each isotope used in these applications has a characteristic half-life.

Part of Physics (Single Science)Forces, space and radioactivity

Using a decay curve to find the half-life of a radioactive element

Follow these steps to find the half-life from a .

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  1. Graph plotting Counts per minute against Time (days). The counts per minute go from 0 to 80. The time goes from 0 to 10 days. 80 counts per minute has been circled on the y-axis.

    In this example, the starting activity is 80 counts per minute.

Following these steps, try and answer the following questions.

Question

What is the half-life of this isotope?

Graph plotting Activity (counts/minute) against Time (days). The activity goes from 0 to 80. The time goes from 0 to 25 days.

Question

What is the half-life of this isotope?

Graph plotting Percentage Element X against Time (billion years). The percentage goes from 0 to 100. The time goes from 0 to 6.5 billion years.

Question

Can you estimate the half-life of this isotope?

Graph plotting Number of radioactive nuclei against Time (hours). The Number of radioactive nuclei goes from 0 to 1,000. The time goes from 0 to 7 hours.

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Half-lives of isotopes used in GCSE questions

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