A sample of radioactive material emits alpha particles. Describe the nature of an alpha particle and explain what happens to the nucleus of an atom when it emits an alpha particle.

WJEC A-Level Physics (Wales) — 3.5 Nuclear decay · Describe and Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

An alpha particle is a helium nucleus, consisting of 2 protons and 2 neutrons, and carries a charge of +2e.
When a nucleus emits an alpha particle:
1. The mass number decreases by 4 (A → A‑4).
2. The atomic number decreases by 2 (Z → Z‑2).
3. Because the proton number changes, the atom becomes a different element.

Examiner tips

  • Use the phrase "helium nucleus" to show knowledge of the particle’s composition. Show the two changes (A and Z) and link the Z change to a new element. Keep the answer concise – 5 marks are awarded for the five points listed.

Common mistakes

  • Saying the alpha particle has a charge of +1 instead of +2. Failing to mention that the element changes. Using vague terms like "a small particle" without specifying 2p+2n.

Mark scheme (5 marks)

  1. An alpha particle consists of 2 protons and 2 neutrons
  2. An alpha particle has a relative charge of +2 (positively charged)
  3. The mass number (nucleon number) of the nucleus decreases by 4
  4. The atomic number (proton number) of the nucleus decreases by 2
  5. A new (different) element is formed because the number of protons has changed

Key terms in this question

alpha particle · nucleus

Related

More Nuclear decay questions

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