A radioactive nucleus undergoes beta decay. Explain what happens inside the nucleus during beta decay and describe the properties of the beta particle that is emitted.

Eduqas A-Level Physics — 3.5 Nuclear decay · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

A neutron in the nucleus converts into a proton by emitting a beta particle. The beta particle is an electron, carrying a negative charge. It is emitted from the nucleus. The electron has a range of a few metres in air (or is stopped by a few millimetres of aluminium). The atomic number of the nucleus increases by one after the decay.

Examiner tips

  • Use the word "neutron" and "proton" to show the conversion; mention the electron explicitly. Include the charge and the range/stop distance. End with the change in atomic number. Keep each point short and to the point.

Common mistakes

  • Confusing the beta particle with a positron; describing it as a positron instead of an electron. Not mentioning the negative charge or the range in air. Writing the conversion as a proton turning into a neutron instead of the reverse.

Mark scheme (5 marks)

  1. A neutron changes into a proton (inside the nucleus)
  2. The beta particle is an electron (emitted from the nucleus)
  3. The beta particle has a negative charge
  4. Beta particles have a range of a few metres in air (or are stopped by a few mm of aluminium)
  5. The proton number (atomic number) of the nucleus increases by one (after beta decay)

Key terms in this question

beta decay · beta particle

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