A radioactive source emits beta particles. Describe the nature of a beta particle and explain why beta particles are less ionising than alpha particles.

WJEC GCSE Physics (Wales) — 2.7 Types of radiation · 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)

A beta particle is a fast‑moving electron emitted from the nucleus.

Beta particles have a much smaller mass than alpha particles.

Because of its smaller mass (and charge), a beta particle interacts less strongly with the atoms it passes through.

Therefore beta particles cause fewer ionisations per unit length (per centimetre of path) than alpha particles.

Examiner tips

  • Use the exact terms ‘beta particle’, ‘fast‑moving electron’, ‘smaller mass’, ‘fewer ionisations per unit length’
  • Show the logical link: small mass → weaker interaction → less ionising
  • Keep the answer concise – 4 points only

Common mistakes

  • Confusing beta particles with gamma rays or alpha particles
  • Failing to mention the mass difference or the resulting weaker interaction
  • Using vague phrases like ‘less energetic’ instead of ‘less ionising per unit length’

Mark scheme (4 marks)

  1. A beta particle is a fast-moving electron (emitted from the nucleus).
  2. A beta particle has a much smaller mass than an alpha particle.
  3. Because of its smaller mass (and charge), a beta particle interacts less strongly with atoms it passes through.
  4. So beta particles cause fewer ionisations per unit length / per centimetre of path compared to alpha particles.

Key terms in this question

beta particle · ionising · alpha particle

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