# Explain why the half-life of a radioactive isotope is an important factor when choosing a suitable isotope for use as a medical tracer inside the human body.

> AQA GCSE Physics (8463) — 4.4.2 Atoms and nuclear radiation · Explain · 4 marks

## Mark scheme (4 marks)

1. The half-life must be short enough that the isotope does not remain in the body for a long time / to minimise the radiation dose received by the patient
2. The half-life must be long enough for the tracer to travel through the body and be detected before it decays away
3. Activity / count-rate must remain high enough during the procedure for a detector (e.g. Geiger-Muller tube) to measure the radiation / locate the tracer
4. After the procedure, a short half-life means the isotope quickly becomes stable / decays to a safe level, reducing long-term risk to the patient

## Key terms

- [half-life](https://www.gradenine.co.uk/glossary/half-life)
- [tracer](https://www.gradenine.co.uk/glossary/tracer)

## Related

- [Revision notes for AQA GCSE Physics (8463)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-half-life-of-a-18b1a6bf) · Published by Druglandscape Ltd.