# A patient requires a medical scan to investigate blood flow through the heart. A radioactive tracer containing technetium is considered, but a doctor also considers using an alpha-emitting tracer instead. Explain why technetium is a more suitable choice as a medical tracer than an alpha-emitting isotope for this purpose.

> OCR A-Level Physics B: Advancing Physics (H557) — 6.4 Medical imaging · Explain · 5 marks

> Technetium has a half-life of 6 hours and is a gamma emitter. It is injected into the bloodstream and detected by external sensors placed outside the body. The scan takes approximately 2–3 hours to complete.

## Mark scheme (5 marks)

1. Technetium is a gamma emitter, which is the most penetrating type of radiation
2. Gamma radiation can pass through body tissue to be detected by sensors outside the body
3. Alpha radiation is stopped within a few centimetres of air / cannot penetrate body tissue
4. Alpha radiation is highly ionising, which would damage healthy cells / tissue inside the body
5. Technetium's half-life of 6 hours is long enough to complete the scan but short enough to decay away quickly, reducing long-term radiation exposure to the patient

## Key terms

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

## Related

- [Revision notes for OCR A-Level Physics B: Advancing Physics (H557)](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/a-patient-requires-a-medical-scan-f513642a) · Published by Druglandscape Ltd.