Explain why gamma radiation is more hazardous to living cells than alpha radiation when a radioactive source is located inside the human body.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Nuclear medicine uses radioactive sources placed inside the body to treat certain cancers. Doctors must carefully choose which type of radiation the source emits to minimise unintended harm to healthy tissue.
Model answer (4 marks)
1. Alpha particles have a high ionising power, so they ionise cells strongly.
2. Alpha particles have a very short range; they are stopped by a few centimetres of air or by soft tissue, so the damage is concentrated locally.
3. Gamma rays have a low ionising power, so they ionise cells weakly.
4. Gamma rays are highly penetrating and pass through the whole body, irradiating a much larger volume of healthy tissue and organs.
2. Alpha particles have a very short range; they are stopped by a few centimetres of air or by soft tissue, so the damage is concentrated locally.
3. Gamma rays have a low ionising power, so they ionise cells weakly.
4. Gamma rays are highly penetrating and pass through the whole body, irradiating a much larger volume of healthy tissue and organs.
Examiner tips
- Use the word "ionising power" for alpha and gamma; mention range for alpha and penetration for gamma.
- Show the contrast: high ionising power + short range vs low ionising power + high penetration.
- Keep each point concise and directly linked to the hazard.
Common mistakes
- Confusing the ionising power of gamma with that of alpha; students often say gamma has high ionising power. Failing to mention the short range of alpha particles. Using vague phrases like "more harmful" without explaining the mechanism.
Mark scheme (4 marks)
- Alpha radiation has high ionising power / ionises cells strongly
- Alpha radiation has a very short range / is stopped by a few centimetres of air or by soft tissue, so causes concentrated damage locally
- Gamma radiation has low ionising power / ionises cells weakly
- Gamma radiation is highly penetrating and passes through the whole body, so it can irradiate and damage a much larger volume of healthy tissue / organs
Key terms in this question
gamma radiation · alpha radiation
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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