# A patient has been injected with a radioactive tracer that emits beta particles. A second patient has been injected with a different tracer that emits gamma rays. A doctor wants to detect the radiation from outside the body to form an image of an internal organ. Explain why the gamma-emitting tracer is more suitable for this purpose than the beta-emitting tracer.

> OCR A-Level Physics A (H556) — 6.2 Electric and magnetic fields · Explain · 5 marks

> Radioactive tracers are used in medicine to image internal organs. The tracer is injected into or swallowed by the patient, and detectors placed outside the body record the radiation emitted.

## Mark scheme (5 marks)

1. Gamma radiation has the greatest penetrating power (of the three types of radiation)
2. Gamma radiation can pass through body tissue to reach the detector outside the body
3. Beta radiation has medium penetrating power and would be absorbed by body tissue before reaching the external detector
4. Gamma radiation has the least ionising power, so it causes less damage to body tissue as it passes through
5. Beta radiation is more ionising than gamma, so using a beta tracer would cause more harm / damage to healthy tissue

## Key terms

- [gamma ray](https://www.gradenine.co.uk/glossary/gamma-ray)
- [beta particle](https://www.gradenine.co.uk/glossary/beta-particle)
- [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)
- [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-has-been-injected-with-9a0df9b9) · Published by Druglandscape Ltd.