Explain why alpha radiation is considered more hazardous than gamma radiation when a radioactive source is swallowed or inhaled, but less hazardous than gamma radiation when the source is outside the body.

OCR GCSE Physics A: Gateway Science (J249) — P4.4 Uses and hazards of radiation · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Radioactive materials can enter the body through ingestion or inhalation. The type of radiation emitted affects how dangerous the source is, depending on whether it is inside or outside the body.

Model answer (4 marks)

Alpha radiation has a very short range in air and cannot penetrate skin, so an external alpha source cannot reach internal organs.
When a radioactive source is swallowed or inhaled, alpha particles are heavily ionising and deposit all of their energy in the surrounding tissue, causing significant damage to cells.
Gamma radiation is weakly ionising and passes through the body, so it causes less damage to internal tissue per unit length.
An external gamma source is hazardous because gamma radiation is highly penetrating and can reach and ionise internal organs from outside the body.

Examiner tips

  • Use the word ‘short range’ for alpha and ‘highly penetrating’ for gamma.
  • Explain ionising ability and energy deposition for each case.
  • Show the difference between external and internal exposure.
  • Keep the answer concise and use the exact terminology from the mark scheme.

Common mistakes

  • Confusing the effects of alpha and gamma radiation inside the body.
  • Claiming alpha can penetrate skin when it cannot.
  • Over‑generalising that gamma is always more dangerous without noting penetration differences.

Mark scheme (4 marks)

  1. Alpha radiation has a very short range in air / cannot penetrate skin, so an external alpha source cannot reach internal organs.
  2. When inside the body, alpha radiation is heavily ionising / deposits all its energy in surrounding tissue, causing significant damage to cells.
  3. Gamma radiation is weakly ionising / passes through the body, so it causes less damage to internal tissue per unit length.
  4. An external gamma source is hazardous because gamma radiation is highly penetrating and can reach and ionise internal organs from outside the body.

Key terms in this question

alpha radiation · gamma radiation · hazardous

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