hydrogen bomb

An explosive weapon of enormous destructive power caused by the fusion of the nuclei of various hydrogen isotopes in the formation of helium nuclei.

A device in which an uncontrolled, self-sustaining, thermonuclear fusion reaction is carried out in heavy hydrogen (deuterium or tritium) to produce an explosion. In a fusion reaction, the collision of two energy-rich nuclei results in a mutual rearrangement of their protons and neutrons to produce two or more reaction products, together with a release of energy of amount E given by A. Einstein's formula E = mc², where m is the mass difference between the original and produced nuclei, and c is the velocity of light. See also Nuclear fusion.

For the hydrogen bomb reaction to become self-sustaining, a so-called critical temperature of about 3.5 × 10⁷ K (6.3 × 10⁷°F) must be attained with the aid of the enormous temperature created by a fission explosive. Once this temperature is achieved, the energy released in the initial reaction maintains the temperature, and the chain proceeds either until the supply of fusionable material is exhausted or until sufficient expansion has taken place that the material is cooled below the critical temperature. See also Atomic bomb.

There are two ways to use fusion: boosting of fission explosive yields or generating multistage thermonuclear reactions.

In a fusion-boosted warhead, when the sphere of fissile materials is compressed (imploded) by the chemical explosion, an uncontrolled fission chain reaction begins. If there is fusionable material inside the device, thermonuclear reactions will boost the fission yield. The fusion reactions do not directly contribute very much to the explosive energy, but instead enhance the fission rate, due to the release of a large number of additional neutrons. See also Atomic bomb.

Multistage thermonuclear weapons contain three physically separated components: a small fission or fusion-boosted explosive called a primary or trigger, an assembly of lithium-deuteride fusion material called the secondary, and a massive casing surrounding the primary and secondary. Explosive detonation is generated in three phases: ignition caused by the fission-explosive primary stage, coupling of x-radiation to the secondary fusion stage, and secondary-stage implosion induced by fission x-rays, which compresses the lithium-deuteride.

As neutrons from the primary traverse the compressed lithium-deuteride compound, they are absorbed in enriched lithium-6, which immediately decomposes into tritium and an alpha particle. If the tritium thus created fuses with deuterium, an energetic alpha particle and a 14-MeV neutron are released. Soon the fusion materials reach densities and temperatures where thermonuclear ignition occurs, liberating many times more energy than that which came originally from the trigger. See also Heat radiation.

If the massive casing is made mostly of uranium-238 (natural or depleted uranium), neutrons from the thermonuclear reactions will cause the uranium nuclei to undergo fission, giving off still more energy. A device of this sort can be regarded as a three-stage fission-fusion-fission bomb.

The yield, or total energy, of a hydrogen bomb is expressed in megatons (1 megaton equals 10¹⁵ calories or 4.18 × 10¹⁵ joules). Typical fusion-boosted weapons yield hundreds of kilotons (tenths of megatons), and typical multistage weapons yield megatons. See also Nuclear explosion.

An immensely powerful bomb in which hydrogen nuclei combine to form helium nuclei and release energy in an uncontrolled self-sustaining fusion reaction.

See the Introduction, Abbreviations and Pronunciation for further details.

For more information on hydrogen bomb, visit Britannica.com.

Hydrogen Bomb, a type of nuclear weapon, also known as the "superbomb," that derives some of its energy from the fusion of the nuclei of light elements, typically isotopes of hydrogen. Physicists recognized the fusion or thermonuclear reaction as the source of the sun's energy as early as 1938.During World War II, scientists of the Manhattan Project saw the possibility of creating a thermonuclear weapon, but they decided to concentrate first on building a fission or atomic bomb because any fusion bomb would likely require a fission device to initiate its thermonuclear "burning."

Although by 1945 the United States had developed and used the atomic bomb, only modest theoretical re-search on fusion was done before the first Soviet atomic test of August 1949. Many of the scientists of the U.S. Atomic Energy Commission and its General Advisory Committee opposed development of the hydrogen bomb on both practical and moral grounds, but advocates within Congress, the military, and elsewhere argued that any restraint shown by the United States in the matter would not be reciprocated by a Soviet Union still ruled by Joseph Stalin. Following a theoretical design breakthrough in February 1951 by Stanislaw Ulamand Edward Teller, the United States conducted the world's first thermonuclear test in November 1952. The device exploded with a force equivalent to more than 10 million tons of TNT, approximately seven hundred times the power of the fission bomb at Hiroshima. Within hours of the blast, the resulting mushroom cloud had spread across one hundred miles of sky, its stem alone measuring thirty miles across. In August 1953 the Soviet Union detonated its first boosted fission weapon, a bomb that used thermo-nuclear fuel to increase in a limited way its explosive yield, and in November 1955 the Soviet Union tested its first "true" thermonuclear weapon. By the 1960s, largely due to the hydrogen bomb, both superpowers had acquired the ability to obliterate as much of the other as they wished in a matter of hours. The world had entered the era of "mutual assured destruction."

Bibliography

Federation of American Scientists. "The High Energy Weapons Archive: A Guide to Nuclear Weapons." Available at http://nuketesting.enviroweb.org/hew/.

Hewlett, Richard G., and Francis Duncan. A History of the United States Atomic Energy Commission. Volume 2: Atomic Shield, 1947–1952. Washington, D.C.: U.S. Atomic Energy Commission, 1972. Comprehensive official history.

Rhodes, Richard. Dark Sun: The Making of the Hydrogen Bomb. New York: Simon and Schuster, 1995.

See thermonuclear weapon.

A nuclear weapon with enormous explosive power, fueled by nuclear fusion, in which atoms of hydrogen combine to form atoms of helium.