Nuclear fission is the process of taking a large nucleus
and dividing it into smaller nuclei. Commercial power
plants and nuclear weapons depend on the fission process.
Uranium-235, Uranium-233 and Plutonium-239 undergo fission
when struck by a slow moving neutron. A heavy nucleus
can split in many different ways. Two different ways
that the uranium-235 nucleus splits are shown below:
The extra neutrons that are produced by the fission of
uranium-235 can then cause additional uranium-235 to go
through the fission process. This is called a chain
reaction. If the reaction is allowed to proceed
unchecked, then a nuclear explosion can result. If the
process is moderated or slowed down then the process can be
used as a fuel source in a nuclear reactor. In a nuclear
reactor, control rods are lowered between fuel rods to slow
the fission process by capturing excess neutrons.