# A hospital uses a radioactive tracer to help diagnose a patient's condition. The tracer contains a gamma-emitting isotope. Explain why a gamma-emitting isotope is used as a tracer rather than an alpha-emitting isotope, and why an isotope with a short half-life is chosen for this purpose.

> Edexcel A-Level Physics (9PH0) — 6.1 Circular motion and momentum · Explain · 5 marks

> Radioactive tracers are injected into patients and detected outside the body using specialist equipment. The choice of isotope used in a tracer is important for both effectiveness and patient safety.

## Mark scheme (5 marks)

1. Gamma radiation is highly penetrating / can pass through body tissue to reach an external detector
2. Alpha radiation is weakly penetrating / would be absorbed by body tissue before reaching an external detector
3. Alpha radiation is highly ionising, which would cause damage to the patient's cells / body tissue
4. A short half-life means the activity / count rate of the tracer decreases rapidly after use
5. This reduces the patient's exposure to radiation / reduces the risk of harm to the patient after the procedure is complete

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Physics (9PH0)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-hospital-uses-a-radioactive-tracer-db6108de) · Published by Druglandscape Ltd.