Nuclear energy from fission and fusion

Nuclear power is generated either through fusion or through fission. Fission is the splitting of a heavy nucleus into light nuclei that are more energetically favorable. Since Iron-56 is the most energetically favorable nucleus, both the fission of heavy nuclei and the fusion of light nuclei can release energy.

Fission is the process used in the first nuclear weapons and in power plants. One drawback to its use as a power source is that among the heavy nuclear fragments it produces are radioactive elements with long half-lives.

Fission is set off by bringing together a critical mass of an element such as Uranium-235. If a sufficient amount of Uranium is brought together an emitted neutron will most likely be captured, changing the Uranium to U-236, rather than escaping from the surface. Since U-236 decays and produces 2 neutrons, the number of neutrons grows exponentially, and practically all the U-235 nuclei decay in short order. This is called a chain reaction. In a power plant the chain reaction is modified with neutron absorbing rods.

Fusion is the source of the sun's energy and is the source of energy in hydrogen bombs. Fusion is an inherently cleaner source of energy, but igniting it in a controlled way has proved problematic. (Fusion "hydrogen" bombs are set off by fission "atomic" bombs which produce a sufficiently high temperature to overcome the Coulomb barrier.)

Nuclear physics index      examples        Lecture index