Nuclear fusion

Nuclear fusion is the process of making a single heavy nucleus (part of an atom) from two lighter nuclei in a process is called a nuclear reaction. It releases a large amount of energy.

The nucleus made by fusion is heavier than either of the starting nuclei. However, it is not as heavy as the combination of the original mass of the starting nuclei (atoms). This lost mass is changed into lots of energy, which is shown in Albert Einstein's famous E=mc² equation.

Fusion happens inside stars like our Sun, where Hydrogen atoms are joined together to make Helium atoms. This can release a lot of energy and heat, which is why the Sun feels warm and bright. Over time, stars can slowly make even heavier elements like iron, the heaviest element a star can make because of its high nuclear binding energy. Once all the Hydrogen atoms are fused to make Helium, the star can not give out heat or light, and it eventually cools down until it dies.

On Earth it is very difficult to start nuclear fusion reactions that release more energy than is needed to start the reaction. The reason is that fusion reactions only happen at high temperature and pressure, like in the Sun, because both nuclei have a positive charge, and positive repels positive. The only way to stop the repulsion is to make the nuclei hit each other at very high speeds. They only do that at high pressure and temperature. The only successful approach so far has been in nuclear weapons. The hydrogen bomb uses an atomic (fission) bomb to start fusion reactions. Scientists and engineers have been trying for decades to find a safe and working way of controlling and containing fusion reactions to generate electricity. They still have many challenges to overcome before fusion power can be used as a clean source of energy.

Related pages

• Fusion power
• Stellar nucleosynthesis
• Supernova
• Tritium

Wikimedia Commons has media related to Nuclear fusion.

Notes