Fission, in physics, is the splitting of the nucleus of an atom into two nearly equal lighter nuclei. This process occurs most readily in such heavy elements as uranium and plutonium. Fission can take place naturally or it can be produced artificially by striking a fissionable nucleus with a neutron or some other nuclear particle. Neutrons and gamma-ray photons are also often released during fission.
When a nucleus splits into two fission fragments, a large amount of energy is released. This energy comes from a decrease in the mass of the original fissionable nucleus. The energy can be calculated using Einstein’s equation E = mc-squared (also written E = mc 2). The equation states that energy (E) equals mass (m) multiplied by the speed of light squared (c-squared). To calculate the energy released, m equals the difference in mass between the original nucleus and the mass of the fission fragments. The fission of 2.2 pounds (1 kilogram) of uranium releases more energy than the burning of 6.6 million pounds (3 million kilograms) of coal.
A fissioning nucleus also releases several neutrons. These free neutrons may strike other nuclei and cause them to fission. A continuous series of such fissions, called a chain reaction, produces the energy in atomic bombs and nuclear reactors.
See also Nuclear energy; Plutonium; Uranium.
