Nuclear Fusion

This lesson covers nuclear fusion — the joining of light nuclei to release energy — as required by the Edexcel GCSE Physics specification (1PH0), Topic 6: Radioactivity. You need to understand what fusion is, where it occurs naturally, why it is difficult to achieve on Earth, and how it compares to fission.

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What Is Nuclear Fusion?

Nuclear fusion is the process in which two light nuclei join (fuse) together to form a single, heavier nucleus, releasing a large amount of energy.

Key Points

• Fusion involves light nuclei — typically isotopes of hydrogen:
  • Deuterium (²₁H) — hydrogen with 1 proton and 1 neutron
  • Tritium (³₁H) — hydrogen with 1 proton and 2 neutrons
• The combined mass of the products is slightly less than the total mass of the original nuclei — this "missing mass" has been converted into energy.
• Fusion releases a very large amount of energy — even more per kilogram of fuel than fission.

Example Fusion Reaction

When deuterium and tritium fuse:

²₁H + ³₁H → ⁴₂He + ¹₀n + energy