Nuclear Fusion

Nuclear fusion is a process in which two atoms combine into a single larger atom, releasing large amounts of energy. Because it occurs only at excessively high temperatures and pressures such as those found in the core of the sun, where hydrogen fuses into helium, controlling fusion on earth is exceedingly difficult. The basis for the H-bomb is the "Teller-Ulam" configuration, which uses the huge energy released by nuclear fission to create the conditions necessary to ignite fusion in a secondary stage of the bomb. Fission is a process roughly the opposite of fusion: It releases energy through the physical smashing of an atomic nucleus into smaller parts. In addition to these two stages, an H-bomb might have a third stage consisting of depleted uranium or other fissile material.