A hospital uses gamma radiation from a radioactive source to treat a patient with a tumour. Explain why gamma radiation is chosen for this treatment and describe one hazard associated with this use of radiation, linking your answer to the properties of gamma radiation and the concept of half-life.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Gamma-emitting radioactive isotopes are used in cancer treatment to target and destroy cancerous cells inside the body. The half-life of the isotope chosen, and the penetrating power of the radiation it emits, are both important factors in deciding whether an isotope is suitable.
Model answer (5 marks)
Gamma radiation has the greatest penetrating power of the three types of nuclear radiation, so it can reach cancerous cells deep inside the body without being absorbed by surrounding tissue.
The high energy photons transfer energy to the cancerous cells, damaging their DNA and killing them.
However, healthy cells surrounding the tumour may also be irradiated and destroyed, causing harmful side effects.
An isotope with a short half‑life is preferable because it decays quickly, reducing the long‑term radiation dose to the patient.
The high energy photons transfer energy to the cancerous cells, damaging their DNA and killing them.
However, healthy cells surrounding the tumour may also be irradiated and destroyed, causing harmful side effects.
An isotope with a short half‑life is preferable because it decays quickly, reducing the long‑term radiation dose to the patient.
Examiner tips
- Use the keyword ‘penetrating power’ to justify the choice of gamma radiation.
- Mention both the therapeutic effect (killing cancer cells) and the risk (damage to healthy cells).
- Explain why a short half‑life is advantageous – quick decay limits exposure.
- Keep the answer concise and use the exact terms from the mark scheme.
Mark scheme (5 marks)
- Gamma radiation has the greatest penetrating power (of the three types of nuclear radiation)
- Gamma radiation can therefore reach the cancerous cells deep inside the body without being absorbed by surrounding tissue
- The gamma radiation transfers energy to the cancerous cells, killing them
- Healthy cells surrounding the tumour may also be irradiated and destroyed, causing harmful side effects
- An isotope with a short half-life is preferable because it decays quickly, reducing the long-term radiation dose to the patient
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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