Nuclear fission

Nuclear fission diagram shows a neutron being absorbed by a uranium nucleus which then becomes unstable and splits into two new atoms with release of energy and some more neutrons.

Nuclear fission is when an atom splits apart into smaller atoms. It gives off a lot of energy, and is used in nuclear weapons and nuclear reactors. This process was discovered in December 1938 by the German nuclear chemist Otto Hahn and his assistant Fritz Strassmann in Berlin.

Introductory video clip on nuclear fission.

Certain types of the elements including uranium and plutonium can be made to fission. While all atoms are small, atoms of uranium and plutonium are very large and heavy compared to most atoms. At their center is a very heavy ball called a nucleus, which is made of protons and neutrons. If a very large nucleus is hit by a neutron, it will sometimes become unstable and break into two pieces. When the nucleus breaks apart (or fissions) it releases a lot of energy and it also causes some more neutrons to be released. If those neutrons then hit other atoms, they will make the other atoms split. This can happen again and again. This is called a nuclear chain-reaction, and it can release huge amounts of energy very quickly. The amount of energy released by a nuclear chain reaction is measured in kilotons. One kiloton is the same as the explosive force of one thousand tons of TNT (trinitrotoluene).

In a nuclear bomb, this must happen very quickly to make a very big explosion. In a nuclear reactor, this must happen very slowly to create heat. In a reactor, the heat created by the uranium or plutonium atoms when they fission (or break apart) boils water into steam. This can be used to power a generator to create electricity.

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Nuclear fission

Other websites

• Annotated bibliography for nuclear fission from the Alsos Digital Library