A student is investigating the penetrating power of three types of nuclear radiation: alpha, beta and gamma. The student passes each type of radiation through different materials and records whether the radiation is stopped. Describe how the penetrating power of alpha, beta and gamma radiation differs, and explain these differences in terms of the nature of each type of radiation.

Eduqas GCSE Physics — 2.4 The atom, the nucleus and radioactivity · Describe and Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Alpha radiation has the least penetrating power – it is stopped by a few centimetres of air or a thin sheet of paper.
Beta radiation has intermediate penetrating power – it is stopped by a few millimetres of aluminium.
Gamma radiation has the greatest penetrating power – it requires several centimetres of lead or thick concrete to reduce its intensity significantly.
The differences arise from the nature of each type of radiation. Alpha particles are large, consisting of 2 protons and 2 neutrons, so they have a high charge and mass and interact strongly with matter, ionising heavily and losing energy quickly. Beta particles are fast‑moving electrons, much smaller and lighter, so they interact less strongly and penetrate further. Gamma rays are electromagnetic radiation with no mass or charge, so they interact very weakly with matter and penetrate the greatest distance.

Examiner tips

  • Use the exact wording from the mark scheme – e.g. ‘stopped by a few centimetres of air’. Show the order of penetration clearly. Explain each type in terms of size, charge and mass. Mention ionisation for alpha and beta, and lack of charge for gamma.

Common mistakes

  • Confusing the order of penetration (e.g. saying gamma is least penetrating). Using vague terms like ‘stronger’ or ‘weaker’ without linking to charge/mass. Omitting the specific stopping materials (paper, aluminium, lead).

Mark scheme (4 marks)

  1. Alpha radiation has the least penetrating power / is stopped by a few centimetres of air or a thin sheet of paper
  2. Beta radiation has intermediate penetrating power / is stopped by a few millimetres of aluminium
  3. Gamma radiation has the greatest penetrating power / requires several centimetres of lead or thick concrete to reduce its intensity significantly
  4. The difference in penetrating power is related to the nature of each radiation: alpha particles are large / consist of 2 protons and 2 neutrons so they interact strongly with matter / ionise heavily and lose energy quickly; beta particles are fast-moving electrons / smaller and interact less strongly; gamma is electromagnetic radiation / has no mass or charge so it interacts very weakly with matter

Key terms in this question

gamma radiation · penetrating power

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