State and explain two safety precautions a laboratory technician should take when handling a radioactive source, relating each precaution to the properties of ionising radiation.

Cambridge International IGCSE Physics (0625) — 5.2 Radioactivity · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

1. Keep the source at a safe distance and use tongs or forceps to handle it.
– Because the count rate of ionising radiation falls rapidly with distance (inverse square law), keeping the source away reduces the dose received by the technician.

2. Store the source in a lead‑lined container and use shielding.
– Lead absorbs gamma rays; several centimetres of lead are required to stop them, so shielding prevents ionising radiation from reaching living tissues.

Examiner tips

  • Use the exact phrase "keep the source at a safe distance" and explain the inverse square law.
  • Mention that lead is the shielding material and that gamma rays need centimetres of lead to be stopped.

Common mistakes

  • Writing "use gloves" instead of specifying distance or tongs. Using a material other than lead for shielding (e.g., aluminium) which does not stop gamma rays effectively.

Mark scheme (4 marks)

  1. Keep source at a distance / use tongs or forceps to handle the source
  2. Because count rate decreases with distance / reducing exposure to ionising radiation which can remove electrons from atoms (forming ions) and cause mutations in DNA
  3. Use shielding / store the source in a lead-lined container
  4. Because shielding absorbs the radiation / gamma rays require several centimetres of lead to stop them, so lead shielding prevents ionising radiation reaching living tissues

Key terms in this question

ionising radiation

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