Teller–Ulam design

A thermonuclear weapon is a nuclear weapon that uses the energy from a primary nuclear fission reaction to compress and ignite a secondary nuclear fusion reaction. The result is greatly increased explosive power when compared to single-stage fission weapons. It is colloquially referred to as a hydrogen bomb or an H-bomb because it employs the fusion of isotopes of hydrogen.

The first full scale thermonuclear test was carried out by the United States in 1952; the concept has since been employed by most of the world's nuclear powers in the design of their weapons. The modern design of all thermonuclear weapons in the United States is known as the Teller–Ulam configuration for its two chief contributors, Edward Teller and Stanislaw Ulam, who developed it in 1951 for the United States, with certain concepts developed with the contribution of John von Neumann. Similar devices were developed by the Soviet Union, United Kingdom, China, and France.

As thermonuclear weapons represent the most efficient design for weapon energy yield in weapons with yields above 50 kilotons of TNT (210 TJ), virtually all the nuclear weapons deployed by the five nuclear-weapon states under the NPT today are thermonuclear weapons using the Teller–Ulam design.

The radiation implosion mechanism is a heat engine that exploits the temperature difference between the secondary stage's hot, surrounding radiation channel and its relatively cool interior. This temperature difference is briefly maintained by a massive heat barrier called the "pusher", which also serves as an implosion tamper, increasing and prolonging the compression of the secondary. If made of uranium, as is almost always the case, it can capture neutrons produced by the fusion reaction and undergo fission itself, increasing the overall explosive yield. In many Teller–Ulam weapons, fission of the pusher dominates the explosion and produces radioactive fission product fallout.

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