# A patient has been referred for a medical scan to investigate a suspected blockage in their digestive system. The medical team is considering injecting a radioactive tracer into the patient. Explain why a gamma-emitting isotope with a short half-life is most suitable for use as a radioactive tracer in this procedure.

> OCR A-Level Physics A (H556) — 6.4 Medical imaging · Explain · 5 marks

> Radioactive tracers are used in hospitals to produce images of the inside of the body. The tracer travels through the body and is detected externally by specialist equipment.

## Mark scheme (5 marks)

1. Gamma radiation is the most penetrating type of radiation
2. This allows the gamma radiation to be detected outside the body
3. Alpha or beta radiation would be absorbed before leaving the body / would not reach the external detector
4. A short half-life means the isotope does not remain strongly radioactive in the body for long / the activity quickly decreases after the scan
5. The half-life must be long enough for the tracer to travel through the body and be detected before it decays away

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics A (H556)](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-patient-has-been-referred-for-3174e4ab) · Published by Druglandscape Ltd.