A hospital uses a radioactive source to sterilise medical equipment. The source emits alpha particles, beta particles and gamma rays. Explain why gamma rays are chosen for this purpose rather than alpha particles or beta particles, referring to the properties of each type of radiation.

WJEC A-Level Physics (Wales) — 6.1 Radioactivity · Explain · 5 marks · View as Markdown

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

Radioactive sources emit ionising radiation that can be used in a variety of medical and industrial applications. The type of radiation chosen for a particular use depends on its penetrating power and its ionising ability.

Model answer (5 marks)

Gamma rays are chosen because they have the greatest penetrating power. Alpha particles are stopped by a few centimetres of air or a sheet of paper, so they would not reach the inside of the equipment or its packaging. Beta particles have moderate penetration and are stopped by a few millimetres of aluminium, which is insufficient to penetrate the bulk of the equipment. Gamma rays, being highly penetrating, can pass through thick materials, including the equipment and its packaging, and therefore can reach and kill bacteria or other microorganisms inside. This makes gamma radiation suitable for sterilisation.

Examiner tips

  • Use the term ‘penetrating power’ to link to the mark scheme.
  • Explain why alpha and beta are insufficient before stating gamma’s advantage.
  • Keep each point brief and to the point.

Common mistakes

  • Confusing ionising ability with penetration; both alpha and beta are highly ionising but poorly penetrating.
  • Failing to mention that gamma rays are electromagnetic and can penetrate thick materials.

Mark scheme (5 marks)

  1. Alpha particles have very low penetrating power / are stopped by a few centimetres of air or a sheet of paper
  2. Alpha particles would not penetrate the medical equipment / packaging to sterilise it
  3. Beta particles have moderate penetrating power / are stopped by a few millimetres of aluminium
  4. Gamma rays have the greatest penetrating power / can penetrate thick materials including the equipment and packaging
  5. Gamma rays can therefore reach and kill bacteria / microorganisms inside the packaging, making it suitable for sterilisation

Key terms in this question

alpha particles · beta particles · gamma rays · sterilise

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