When the heaviest element, uranium was bombarded with neutrons, it was discovered that instead of inducing radioactivity as did other elements, something different happened. This process was named fission. When fission occurred, not only were two lighter elements and a lot of radiation produced, but also more neutrons. It was clear that these neutrons could in turn also cause fission, producing more neutrons and developing a chain reaction which might spread throughout all the uranium present.
In the fission of uranium 235 nucleus, the amount of energy released is about 60,000,000 times as much as when a carbon atom burns. Most of the energy from fission appears as kinetic energy as the fission products shoot apart and quickly share their energy with their surroundings, thus producing heat. The first reactors to produce a usable amount of power were built at Calder hall in England.
With pure fissionable material, atomic bombs can be made. Of the two bombs dropped on Japan to end the World War 2, one contained plutonium and the other very highly enriched uranium 235.
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