A radioactive source emits beta particles. Describe how a beta particle is produced in the nucleus and state two properties of beta particles that are different from those of gamma rays.

Cambridge International IGCSE Physics (0625) — 5.2 Radioactivity · Describe · 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 produced when a neutron in the nucleus undergoes β⁻ decay, converting into a proton while emitting an electron (the beta particle) and an antineutrino.

Two properties that differ from gamma rays are:
1. Beta particles carry a negative electric charge, whereas gamma rays are uncharged.
2. Beta particles have rest mass (they are electrons), while gamma rays are mass‑free photons.

Additionally, beta particles are only moderately penetrating – they can be stopped by a thin sheet of aluminium – whereas gamma rays are highly penetrating and require several centimetres of lead to be effectively absorbed.

Examiner tips

  • Use the term ‘β⁻ decay’ and mention the neutron→proton conversion. Include the electron’s charge and mass. Mention the relative penetration to secure the extra mark.

Common mistakes

  • Confusing beta decay with gamma emission. Forgetting to state the charge or mass difference. Using vague terms like ‘small’ or ‘large’ without specifying penetration.

Mark scheme (4 marks)

  1. A beta particle is produced when a neutron in the nucleus converts/splits into a proton and an electron
  2. Beta particles have (negative) charge / gamma rays have no charge
  3. Beta particles have (rest) mass / gamma rays have no mass
  4. Beta particles are moderately penetrating (stopped by thin aluminium) whereas gamma rays are highly penetrating (require several centimetres of lead to stop them)

Key terms in this question

beta particle · gamma ray

Related

More Radioactivity questions

▶ Try answering this question with AI marking (free) →