4.4.4.2 - Nuclear Fusion

What nuclear fusion is

The nucleus is the tiny central part of an atom that contains protons and neutrons. Nuclear fusion happens when two light nuclei join together. The product is a heavier nucleus.

The word light means the starting nuclei have relatively low mass numbers. At GCSE, the most common context is hydrogen nuclei joining in stars to form heavier nuclei such as helium. You do not need a detailed fusion equation for this specification point.

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Do not describe fusion as two complete atoms sticking together. The important change is in the nuclei, not in the electrons outside the nucleus.

Mass and radiation energy

Fusion is a nuclear process, so it can involve much larger energy changes than ordinary chemical reactions. During fusion, the total mass after the reaction may be slightly less than the total mass before the reaction. The missing mass is not simply lost; it may be converted into the energy of radiation.

For this lesson, the specification is qualitative. You should be able to say that some of the mass may be converted into radiation energy. You do not need to calculate the energy from the mass change.

Radiation energy means energy carried away from the nuclear reaction as radiation. In a star, this energy is part of the reason the star gives out light and other electromagnetic radiation.