A radiographer is considering which type of radioactive source to use when treating a patient who has a tumour deep inside their body. Explain why a gamma-emitting source with a short half-life is more suitable for this treatment than an alpha-emitting source with a long half-life.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Gamma radiation can be directed at cancerous cells to destroy them. However, the choice of isotope affects both the effectiveness of treatment and the level of risk to the patient.
Model answer (5 marks)
Gamma radiation has the greatest penetrating power, so it can pass through body tissue to reach the deep tumour.
Alpha radiation has very low penetrating power and would be absorbed/stopped before reaching the deep tumour.
A short half‑life means the source does not remain strongly radioactive for long, reducing the long‑term radiation dose to the patient.
A long half‑life source remains weakly radioactive for a very long time, so it would continue to irradiate healthy cells and cause damage over an extended period.
Gamma radiation can destroy cancerous cells (the cells absorb the energy and are killed), which is the purpose of the treatment.
Alpha radiation has very low penetrating power and would be absorbed/stopped before reaching the deep tumour.
A short half‑life means the source does not remain strongly radioactive for long, reducing the long‑term radiation dose to the patient.
A long half‑life source remains weakly radioactive for a very long time, so it would continue to irradiate healthy cells and cause damage over an extended period.
Gamma radiation can destroy cancerous cells (the cells absorb the energy and are killed), which is the purpose of the treatment.
Examiner tips
- Use the command word ‘Explain’ to give a clear, logical sequence of reasons. Mention both physical penetration and dose‑rate considerations. Show the link between half‑life and patient safety.
- Include all five points in separate sentences to match the 5‑mark structure.
Common mistakes
- Confusing the roles of alpha and gamma radiation; e.g. saying alpha has high penetration. Forgetting to mention the half‑life effect on long‑term dose. Using vague phrases like ‘more suitable’ without explaining why.
Mark scheme (5 marks)
- Gamma radiation has the greatest penetrating power, so it can pass through body tissue to reach the deep tumour.
- Alpha radiation has very low penetrating power and would be absorbed/stopped before reaching the deep tumour.
- A short half-life means the source does not remain strongly radioactive for long, reducing the long-term radiation dose to the patient.
- A long half-life source remains weakly radioactive for a very long time, so it would continue to irradiate healthy cells and cause damage over an extended period.
- Gamma radiation can destroy cancerous cells (the cells absorb the energy and are killed), which is the purpose of the treatment.
Key terms in this question
Related
- All OCR A-Level Physics B: Advancing Physics (H557) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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