# A doctor suspects that a patient has a bone tumour. The patient is given a radioactive tracer that accumulates in areas of high bone activity. A gamma camera placed outside the body detects the radiation and builds up an image showing where the tracer has collected. Explain why a gamma-emitting tracer with a half-life of several hours is suitable for this procedure, rather than an alpha-emitting tracer with a half-life of several years.

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

> A doctor suspects that a patient has a bone tumour. The patient is given a radioactive tracer that accumulates in areas of high bone activity. A gamma camera placed outside the body detects the radiation and builds up an image showing where the tracer has collected.

## Mark scheme (5 marks)

1. Gamma radiation is the most penetrating type of radiation, so it can pass out through body tissue to reach the detector outside the body.
2. Alpha radiation is the least penetrating type of radiation and would be absorbed by body tissue before reaching the detector.
3. Alpha radiation is highly ionising, so an alpha-emitting tracer inside the body would cause significant damage to healthy cells / internal tissue.
4. A half-life of several hours means the tracer remains active long enough to travel through the body and be detected, but then decays away quickly so the patient is not exposed to radiation for a long time.
5. A half-life of several years would mean the tracer stays radioactive inside the patient for a very long time, causing prolonged irradiation and increased risk of harm.

## Key terms

- [half-life](https://www.gradenine.co.uk/glossary/half-life)
- [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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-doctor-suspects-that-a-patient-5a38c174) · Published by Druglandscape Ltd.