A-Level Physics October/November 2024 Q10(b)(i): Describe the differences between nuclear fission and nuclear fusion.

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  Nuclear fission and nuclear fusion are different in the following ways:

  1. Type of Nuclei: Fission involves the splitting of a single large, heavy nucleus (e.g., Uranium-235). In contrast, fusion involves the joining of two small, light nuclei (e.g., isotopes of hydrogen).

  2. Process: In fission, one nucleus splits into two or more smaller daughter nuclei, often releasing neutrons. In fusion, two nuclei combine or 'fuse' together to form a single, larger nucleus.

  3. Initiation Conditions: Fission is typically induced by the absorption of a slow-moving neutron. Fusion, however, requires extremely high temperatures (on the order of $10^7$ K) and pressures to overcome the electrostatic repulsion between the positive nuclei and allow them to get close enough for the strong nuclear force to take effect.

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  How the marks are awarded

  • B1 — Correctly identifying that fission involves large/heavy nuclei whereas fusion involves small/light nuclei.
  • B1 — Describing the process of fission as one nucleus splitting into two (or more) smaller nuclei.
  • B1 — Describing the process of fusion as two nuclei joining to form one larger nucleus, OR stating the initiation condition for fission (neutron bombardment) or fusion (very high temperatures).

  Common mistakes

  • Confusing the two processes, for example, stating that fission is the joining of nuclei.
  • Giving vague descriptions like 'fission is splitting and fusion is joining' without specifying the number and type of nuclei involved (e.g., one large nucleus splitting, two small nuclei joining).
  • Stating that both processes release energy, which is a similarity, not a difference as requested by the question.
  • Incorrectly describing the products, for example, saying fission produces two identical nuclei.

  Examiner tip: For 'describe differences' questions, use comparative words like 'whereas' or 'in contrast' and structure your answer as a point-by-point comparison to ensure you address both concepts for each difference.

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