Nuclear Fission
Definition
Splitting a heavy nucleus into lighter ones, releasing enormous energy: the process powering nuclear reactors and atomic bombs.
Technical definition
Nuclear fission is the splitting of a heavy nucleus, such as U-235, into lighter nuclei plus neutrons and energy, triggered by neutron capture. Each fission releases about 200 MeV and extra neutrons, enabling a self-sustaining chain reaction when critical mass geometry is achieved.
Example
One kilogram of U-235 releases about 24 million kWh through fission: roughly 3 million times the energy of burning 1 kg of coal.
Common confusion
Fission and fusion are opposites. Fission SPLITS heavy nuclei (reactors, atomic bombs) while fusion JOINS light nuclei (the Sun, hydrogen bombs): both release energy through the mass defect.