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Radioactivity (A-level only)

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Question 10

During the nucleosynthesis in a red giant star, helium-4 and carbon-12 fuse to form oxygen-16. The equation for this reaction is:

24He+612C→816O {}^{4}_{2}\text{He} + {}^{12}_{6}\text{C} \rightarrow {}^{16}_{8}\text{O} 24​He+612​C→816​O

Data for these nuclei are given in the table below:

NucleusMass / u
24He{}^{4}_{2}\text{He}24​He4.00260
612C{}^{12}_{6}\text{C}612​C12.00000
816O{}^{16}_{8}\text{O}816​O15.99491

Constants:

  • Unified atomic mass unit, 1 u=1.661×10−27 kg1\text{ u} = 1.661 \times 10^{-27}\text{ kg}1 u=1.661×10−27 kg
  • Speed of light, c=3.00×108 m s−1c = 3.00 \times 10^8\text{ m s}^{-1}c=3.00×108 m s−1
  • Permittivity of free space, ε0=8.85×10−12 F m−1\varepsilon_0 = 8.85 \times 10^{-12}\text{ F m}^{-1}ε0​=8.85×10−12 F m−1
  • Elementary charge, e=1.60×10−19 Ce = 1.60 \times 10^{-19}\text{ C}e=1.60×10−19 C
1.

Calculate, in J, the energy released when this reaction occurs.

[3]
2.

One model of nuclear fusion suggests that fusion happens when nuclei touch. Initially, the helium nucleus and carbon nucleus are separated so that the electrostatic force between them is negligible. They move towards each other until they fuse. Fusion occurs when their centres are separated by a distance of 4.6 × 10-15 m.

Calculate the total change in electrostatic potential energy, in J, between the initial positions and final positions of the nuclei.

[4]
Markscheme

Radioactivity (A-level only) Questions

  1. A Level
  2. /Physics
  3. /Radioactivity (A-level only)

128 exam-style questions on AQA A Level Physics Radioactivity (A-level only), covering Rutherford scattering (A-level only), $\alpha$ , $\beta$ and $\gamma$ radiation (A-level only), Radioactive decay (A-level only), Nuclear instability (A-level only), Nuclear radius (A-level only), Mass and energy (A-level only), Induced fission (A-level only), and Safety aspects (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.

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