Nuclear Fusion (Edexcel International A Level Physics)

Revision Note

Katie M


Katie M



Nuclear Fusion

  • Fusion is defined as:

Small nuclides that combine together to make larger nuclei, releasing energy

  • Low mass nuclei (such as hydrogen and helium) can undergo fusion and release energy

The fusion of deuterium and tritium to form helium with the release of energy

Conditions for Nuclear Fusion

  • For two nuclei to fuse;
  • Both must have high kinetic energy, to overcome the electrostatic repulsion between protons
    • This can only be achieved in an extremely high-energy environment, such as star’s core
    • To achieve high enough kinetic energy the temperature must be on the scale of 100 × 106 Kelvin
  • Very high density is also required

Fusion Products

  • When two protons fuse, the element deuterium is produced
  • In the centre of stars, the deuterium combines with a tritium  nucleus to form a helium nucleus, plus the release of energy, which provides fuel for the star to continue burning


Exam Tip

In the fusion process, the mass of the new heavier nucleus is less than the mass of the constituent parts of the nuclei fused together, as some mass is converted into energy. 

Not all of this energy is used as binding energy for the new larger nucleus, so energy will be released from this reaction. The binding energy per nucleon afterwards is higher than at the start. 

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Katie M

Author: Katie M

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