Nuclear Reactors

Uranium is the main element used in nuclear reactors and certain types of nuclear bombs. The specific isotope used for reactors and bombs is uranium-235. When a neutron strikes uranium-235 it is first absorbed making uranium-236, and then it becomes unstable causing the atom to fission. The fissioning of uranium-236 can create many new products such as: 235U + 1 neutron ---> 2 neutrons + 92Kr+ 142Ba +Energy 235U + 1 neutron ---> 2 neutrons + 92Sr + 142Xe +Energy In both of these reactions the neutron splits the atom and when the atom splits another neutron is released. This is how a chain reaction may occur, because if there was more uranium-235 present those two neutrons could cause two more atoms to split. Each of those two atoms will release an additional neutron, resulting in a total of four neutrons. These four neutrons would strike more uranium-235 atoms releasing even more neutrons which causes a chain reaction to continue until all uranium-235 is gone.

Water Nuclear Reactors

Water Nuclear Reactor The typical pressurized water nuclear reactor has a core of fissionable material in which the chain reaction takes place. The energy that is released during the fission process heats the water. The chain reactions are controlled by rods inserted into the core that absorbs the neutrons. The water moderates the neutrons by slowing them down during fission which changes the fission neutrons' energy from kinetic energy to thermal energy. The thermal energy is then removed from the core by the water to an external thermal-energy converter. In the external water reactor the thermal energy produces steam for the turbine to drive the generator which produces electricity. The energy contained from the water nuclear reactors is mostly used to power ships.

Nuclear Weapons

Nuclear fission can be used to generate large amounts of energy for destructive purposes. When an atom of 235U is bombarded by a neutron it releases a large amount of energy. If additional neutrons are not controlled they can cause a chain reaction which could result in a nuclear explosion (A-bomb). Only a small amount of uranium, about the size of a baseball, is needed to produce an explosion as powerful as 20 kilotons of TNT.

Nuclear Fission Stimulator

Check out this website to view a Nuclear Fission Stimulator that you can interact with.
http://michele.usc.edu/java/fission/nuclear.html

History of Nuclear Fission

Enrico Fermi and his collaborators were the first to study elements that have been bombarded by neutrons resulting in new radioactive elements being formed. However this process was not interpreted as fission until several years later.
Fermi had predicted that the neutron would be a useful nuclear projectile. He thought this because neutrons are uncharged and receive no electric forces from the nucleus when reaching the nuclear surface. Fermi's prediction was proven correct later on by other physicists.

Otto Hahn and Fritz Strassman tested uranium salts by bombarding these solutions with neutrons. Later through chemical analysis they found a number of new radioactive elements present. Hahn and Strassman conducted repeated tests to prove that barium was produced during this process.

Otto Frisch was able to show that a uranium nucleus, which had absorbed a neutron could split into roughly two equal parts one of which was barium. During this process there were large amounts of energy being released. Frisch named this the process of fission.

What is Nuclear Fission?

Nuclear energy is the energy trapped inside of an atom. Nuclear fission is when an atom's nucleus is split apart releasing an tremendous amount of energy. The energy released is both light and heat energy.
When a nucleus of an atom fissions it splits into several smaller fragments, usually two different fragments or fission products. The fission products are equal or half the mass of the original mass of the atom. During the process of fission two or three neutrons are emitted, large quantities of energy is released and radioactive products are formed.
Fission can occur spontaneously or when a nucleus of a heavy atom captures a neutron.
Fissile isotopes are isotopes of an element that can be split through fission. There are only certain isotopes that are fissile (able to fission). An important factor that will determine whether or not isotopes will fission, is the speed of the bombarding neutron. Some isotopes such as thorium-232 requires a very fast moving neutron for fission, where as uranium-235 needs a slow moving neutron to fission. If a neutron is too fast it will pass right through the atom which will not affect the isotope at all.