What is Nuclear Fusion?

Nuclear fusion is a reaction between two nuclei that combine together to form a heavier nuclei. The sun shines thanks to fusion reactions that turn hydrogen nuclei into helium.

Because nuclei are all positively charged, fusion typically happens only at very hot temperatures of millions of degrees Fahrenheit, where nuclear collisions are energetic enough to overcome the repulsive electric force between two nuclei.

Due to these high temperature requirements, a nuclear fusion reactor has never been built, but current experimental work is focused on confining extremely hot, ionized hydrogen gas with strong magnetic fields or powerful lasers.

As a side note, two chemists claimed in 1989 to have observed fusion in room temperature water. The results were never verified, which is why "cold fusion" has become nearly synonymous with scientific hoax.

What is Nuclear Fission?