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Nuclear fusion

is when two small, light join together to make one heavy nucleus. Fusion reactions occur in stars where two hydrogen nuclei fuse together under high temperatures and pressure to form a nucleus of a helium .

Process of nuclear fusion, with different isotopes of hydrogen colliding and fusing to make helium.

There are a number of different nuclear fusion reactions happening in the Sun. The simplest is when four hydrogen nuclei become one helium nuclei.

\(4_{1}^{1} H \rightarrow _{2}^{4}He\)

The combined mass of four hydrogen nuclei is 6.693 Ă— 10-27 kilograms (kg). The mass of one helium nucleus is 6.645 Ă— 10-27 kg. This means that there is a missing amount of mass equalling 0.048 Ă— 10-27 kg.

The missing mass is converted to energy, which away. This is seen happening in the Sun. In all a small amount of the mass changes to energy.

However, the issue with fusion is that it requires the fusing of nuclei, which are positive particles. As two nuclei approach each other, they will because they have the same . The fusion of the nuclei has to happen quickly so that the repulsion of the charges does not have time to stop it from happening.

A way that particles can travel that quickly is by being in a hot gas or in , like in the Sun.