A radioactive nucleus emits a beta particle during nuclear decay. Explain what a beta particle is, describe what happens to the nucleus when it is emitted, and explain why the nucleus changes into a different element.

WJEC A-Level Physics (Wales) — 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 beta particle is a fast‑moving electron.
When it is emitted the nucleus undergoes a neutron → proton conversion.
The proton number (atomic number) increases by one.
The mass number (total nucleons) remains unchanged.
Because the element is defined by its proton number, the increase means the nucleus is now a different element.

Examiner tips

  • Use the exact phrase "fast‑moving electron" for a beta particle. Show the neutron → proton change and state the atomic number increases. Remember the mass number stays the same. Link the change in Z to a different element.
  • common_mistakes
  • :
  • Calling the beta particle a positron or a gamma ray. Saying the mass number increases or that the element stays the same. Forgetting to mention the neutron‑to‑proton conversion.

Mark scheme (5 marks)

  1. A beta particle is a fast-moving electron
  2. The beta particle is emitted from the nucleus when a neutron changes into a proton
  3. The proton number (atomic number) increases by one
  4. The mass number (nucleon number) stays the same / is unchanged
  5. Because the proton number determines the element, a higher proton number means it is a different element

Key terms in this question

beta particle · nuclear decay

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