# Explain why the half-life of a radioactive isotope used as a medical tracer must be neither too long nor too short.

> AQA GCSE Physics (8463) — 4.4.3 Hazards and uses of radioactive emissions and of background radiation (Phys only) · Explain · 4 marks

> Technetium-99m is a gamma-emitting isotope with a half-life of six hours. It is injected into patients so that doctors can monitor organs and detect disease.

## Mark scheme (4 marks)

1. A half-life that is too short means the isotope decays before it can travel through the body and be detected
2. A half-life that is too long means the patient is exposed to radiation / irradiated for an unnecessarily long period of time
3. The isotope must be a gamma emitter so that the radiation can penetrate out of the body and be detected externally
4. A suitable half-life means the isotope decays to a safe / stable product after the procedure, minimising long-term harm 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-half-life-of-a-c56a3c84) · Published by Druglandscape Ltd.