Explain why gamma radiation is used to sterilise medical equipment rather than alpha or beta radiation.

Edexcel GCSE Physics (1PH0) — 6.1 Radioactivity · Explain · 4 marks · View as Markdown

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

Hospitals use radioactive sources to sterilise surgical instruments. The radiation must be able to penetrate the sealed packaging surrounding the instruments and kill microbes on the surfaces inside.

Model answer (4 marks)

Gamma radiation is highly penetrating, so it can pass through the sealed packaging and reach the instruments inside. Alpha radiation is weakly penetrating and would be stopped by a few centimetres of air or a thin sheet of material, so it cannot reach the instruments. Beta radiation has only medium penetration and would not reliably penetrate thick packaging as effectively as gamma.

Examiner tips

  • Use the word ‘penetrating’ to link to the requirement of reaching inside the packaging
  • Mention that alpha is stopped by a few centimetres of air, beta by a thin sheet, and gamma can go through

Common mistakes

  • Confusing alpha with beta as the more penetrating type
  • Failing to state that gamma can reach inside the sealed packaging

Mark scheme (4 marks)

  1. Gamma radiation is highly penetrating
  2. So gamma can pass through the sealed packaging to reach the instruments inside
  3. Alpha radiation is weakly penetrating / stopped by a few centimetres of air or thin materials
  4. Beta radiation has only medium penetration / would not reliably penetrate thick packaging as effectively as gamma

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