Radioactive tracers are used in medicine to investigate how well organs are functioning. Explain why a radioactive tracer used inside the human body should emit gamma radiation rather than alpha radiation.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Alpha particles have a very short range and are absorbed quickly inside the body, so they cannot penetrate body tissue to reach a detector outside. Gamma rays have a long range and can pass through body tissue, allowing them to exit the body. Therefore gamma radiation can be detected externally, enabling imaging or measurement. Alpha radiation is more ionising and causes more damage to body cells, whereas gamma radiation causes less ionisation and is therefore less harmful to the patient.
Examiner tips
- Use the word ‘penetrate’ to link gamma rays to external detection.
- Mention both the short range of alpha particles and the long range of gamma rays.
- Highlight the lower ionising damage of gamma compared to alpha.
- Keep the answer concise – 4 points can be covered in 3–4 short sentences.
Common mistakes
- Confusing alpha with beta radiation; alpha is the short‑range particle.
- Failing to state that gamma rays can exit the body and be detected externally.
- Over‑emphasising ionisation without linking it to safety for the patient.
Mark scheme (4 marks)
- Alpha radiation has a very short range / is absorbed quickly inside the body / cannot penetrate through body tissue to reach a detector outside
- Gamma radiation can penetrate through body tissue / has a long range and can pass out of the body
- So gamma radiation can be detected outside the body / allows an image or reading to be taken externally
- Alpha radiation is more ionising than gamma / alpha causes more damage to body cells / gamma causes less ionisation so is less harmful to the patient
Key terms in this question
radioactive tracer · gamma radiation · alpha radiation
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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