About Nuclear Fission

When an atom is spit this is called nuclear fission. Fission happens naturally but can also be produced under controlled situations. When you see a nuclear power plant it is using nuclear fission. During World War II nuclear fission bombs were developed. The power plant has a controlled reaction that determines how many atoms are split at a time while the bomb is uncontrolled. Fission is studied by scientists to understand the nature of atoms.

History

Two German chemists, Otto Hahn (1879 to 1960) and Fritz Strassmann (1902 to 1980) discovered fission when bombarding uranium with neutrons. In 1939 they published the results of their work. Lise Meitner and her nephew Otto Frisch verified that Hahn and Strassmann had split uranium nuclei into two smaller fragments.
In 1934 Italian physicist Enrico Fermi (1901 to 1954) and colleagues found that neutrons with lower speed, or "energy" were more effective in starting nuclear reactions (reactions involving particles and nuclei in which energy is released or absorbed) when they entered a nucleus. They stayed in the nuclear area longer and reacted better.
Uranium, the heaviest known nuclei known at the time, was used. It was thought that if uranium was bombarded with neutrons a new nucleus might be created, or element. What happened was fission. The experimental results weren't checked well enough to know what had happened. In 1942 Fermi helped to build the first nuclear reactor, where heat is produced from controlled nuclear fission, at the University of Chicago.

Function

A uranium 235 (U235) atom is split by sending a low energy neutron into a U 235 atom. This slow moving neutron hits and is absorbed by the uranium nucleus. The atom then becomes uranium 236 which is not stable. This new uranium nucleus starts to shake very quickly and is forced out of shape. The shaking continues until the atom splits or "fissions."
The uranium 236 breaks apart into barium and krypton nuclei and three neutrons. Along with the fission there is a large amount of energy released. This energy is about one hundred million times greater than the energy released by gas or coal.
This kind of reaction is just one type. There are many possible reactions that can occur in nuclear fission. Some fissions produce up to 5 neutrons, though the average number is 2.5 neutrons.

Identification

Because of its average release of 2.5 neutrons uranium can be used to create a series of self sustained fissions. Every single neutron released can start another fission episode. These react to start more neutron emissions, which then react to make more fissions and it repeats from there. This is what is known as a chain reaction.

Features

During an uncontrolled chain reaction, the number of fissions can increase thousands of times within a few millionths of a second. Unrestrained chain reactions can result in an astounding amount of energy in a small amount of time. This is the fission that happens in a nuclear bomb.
Controlled nuclear fission chain reactions are used in nuclear power plants. By limiting the number of neutrons in a contained area then every fission occurrence lends only one neutron to fission just one nucleus. Done in this way, the chain reaction and energy production are controllable.

Significance

Natural fission occurs with U-235. But at only 0.72% of all natural uranium it is a very small amount. While in laboratories fission is studied by nuclear physicists. By looking at fission and the results of it more is learned of the physical nature of things and how everything is interrelated.

Resources

• Fermi Lab Education Office