Nuclear fission is the process in which:

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A heavy nucleus splits into two or more lighter nuclei, releasing energy. Nuclear fission is the process in which a heavy atomic nucleus (such as uranium-235 or plutonium-239) splits into two or more smaller, lighter nuclei, along with several neutrons and a large amount of energy. This energy comes from the conversion of a small amount of mass into energy according to Einstein's equation E = mc². Nuclear fission is the process used in nuclear power plants to generate electricity and was used in the atomic bombs dropped on Hiroshima and Nagasaki.

Light nuclei combining to form a heavier nucleus describes nuclear fusion, the opposite process, which powers the Sun and other stars. Fusion also releases enormous energy but requires extremely high temperatures and pressures to overcome the electrostatic repulsion between positively charged nuclei. Stripping electrons from atoms by high-energy radiation describes ionization, a chemical process rather than a nuclear one. Breaking and reforming chemical bonds between atoms describes ordinary chemical reactions, which involve electron interactions rather than nuclear transformations.

In nuclear fission, the neutrons released by the splitting of one nucleus can trigger the fission of nearby nuclei, creating a chain reaction. In nuclear power plants, this chain reaction is carefully controlled to produce steady energy output. In nuclear weapons, the chain reaction is uncontrolled, releasing enormous energy in a very short time. Understanding the difference between fission and fusion, and between nuclear and chemical reactions, is important for the CLEP Natural Sciences exam.

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