A geologist discovers a rock sample that is radioactive. Tests show the sample emits all three types of nuclear radiation: alpha, beta, and gamma. Explain why gamma radiation is the most difficult type of radiation to shield against.

OCR GCSE Physics A: Gateway Science (J249) — P4.3 Radioactive emissions · Explain · 4 marks · View as Markdown

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

A geologist discovers a rock sample that is radioactive. Tests show the sample emits all three types of nuclear radiation: alpha, beta, and gamma.

Model answer (4 marks)

Gamma radiation has very high penetrating power.
Gamma radiation is an electromagnetic wave, so it has no mass and no charge.
Because it has no charge it interacts very weakly with matter and ionises poorly.
Therefore several centimetres of lead or metres of concrete are required to significantly reduce gamma radiation.

Examiner tips

  • Use the word ‘penetrating power’ to show understanding of why shielding is difficult.
  • Mention that gamma is electromagnetic, no mass/charge, weak interaction with matter.
  • Give a realistic shielding example (lead or concrete).

Common mistakes

  • Confusing alpha or beta radiation as the most difficult to shield.
  • Omitting the fact that gamma is electromagnetic and has no charge.
  • Not giving a concrete shielding example.

Mark scheme (4 marks)

  1. Gamma radiation has very high penetrating power
  2. Gamma radiation is an electromagnetic wave / has no mass and no charge
  3. Because gamma radiation has no charge it interacts very weakly with matter / ionises poorly
  4. Several centimetres of lead or metres of concrete are needed to significantly reduce gamma radiation

Key terms in this question

gamma radiation

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