# A patient is given a radioactive tracer to help doctors identify the location of cancerous cells inside the body. The tracer used is a gamma emitter with a half-life of 6 hours. Explain why a gamma-emitting tracer with this half-life is well suited for use inside the human body, and explain one risk associated with using gamma radiation in this way.

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

> Medical imaging techniques use radioactive tracers that are injected or swallowed by the patient. Detectors outside the body are used to track where the tracer travels. The choice of isotope — including its type of emission and its half-life — is critical to the safety and effectiveness of the procedure.

## Mark scheme (5 marks)

1. Gamma radiation is the most penetrating type of nuclear radiation, so it can pass through body tissue and be detected outside the body.
2. Gamma radiation has the least ionising power of the three types, so it causes less damage to healthy body tissue/cells than alpha or beta radiation would.
3. A half-life of 6 hours is long enough for the tracer to travel through the body and be detected before it decays.
4. A half-life of 6 hours means the tracer decays to a safe level / becomes much less radioactive relatively quickly, reducing the long-term radiation dose to the patient.
5. One risk: gamma radiation can irradiate and damage healthy cells surrounding the target area, as it is difficult to confine the radiation to only the cancerous tissue.

## 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 A (H556)](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-patient-is-given-a-radioactive-eef4002b) · Published by Druglandscape Ltd.