Radioactive materials can be used as tracers in medicine. A doctor injects a patient with a radioactive tracer that emits gamma radiation. Explain why gamma-emitting isotopes are chosen for use inside the body as medical tracers, rather than isotopes that emit alpha or beta radiation.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Gamma radiation can penetrate body tissue and be detected externally.
Alpha particles have a very short range, are stopped by a few centimetres of air or skin and would not be detected outside the body.
Alpha particles cause the most ionisation inside the body, so they would damage body cells and tissues.
Beta particles have greater penetration than alpha but are still largely absorbed by body tissue and do not penetrate as well as gamma.
Gamma radiation has the lowest ionising power, causing the least ionisation damage to body cells, making it the safest option inside the body.
Alpha particles have a very short range, are stopped by a few centimetres of air or skin and would not be detected outside the body.
Alpha particles cause the most ionisation inside the body, so they would damage body cells and tissues.
Beta particles have greater penetration than alpha but are still largely absorbed by body tissue and do not penetrate as well as gamma.
Gamma radiation has the lowest ionising power, causing the least ionisation damage to body cells, making it the safest option inside the body.
Examiner tips
- Use the exact phrases from the mark scheme – e.g. ‘penetrate body tissue’, ‘short range’, ‘most ionisation’.
- Show the order of safety: alpha > beta > gamma, and explain why gamma is chosen.
- Keep each point brief and to the point, matching the 5 marks.
Common mistakes
- Confusing beta and gamma penetration; writing that beta penetrates as well as gamma.
- Failing to mention the ionisation damage caused by alpha particles.
- Using vague terms like ‘safe’ without linking to ionisation power.
Mark scheme (5 marks)
- Gamma radiation can penetrate through body tissue / organs to be detected outside the body
- Alpha radiation has very short range / is stopped by a few centimetres of air or skin and would not be detected outside the body
- Alpha radiation causes the most ionisation (inside the body) / would cause the most damage to body cells / tissues
- Beta radiation has greater penetration than alpha but is still largely absorbed by body tissue / does not penetrate as well as gamma
- Gamma radiation has the lowest ionising power / causes the least ionisation damage to body cells, making it the safest option inside the body
Key terms in this question
gamma radiation · beta radiation · tracer
Related
- All Eduqas A-Level Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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