hydrogen bomb

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hydrogen bomb or H-bomb, weapon deriving a large portion of its energy from the nuclear fusion of hydrogen isotopes. In an atomic bomb, uranium or plutonium is split into lighter elements that together weigh less than the original atoms, the remainder of the mass appearing as energy. Unlike this fission bomb, the hydrogen bomb functions by the fusion, or joining together, of lighter elements into heavier elements. The end product again weighs less than its components, the difference once more appearing as energy. Because extremely high temperatures are required in order to initiate fusion reactions, the hydrogen bomb is also known as a thermonuclear bomb.

The first thermonuclear bomb was exploded in 1952 at Enewetak by the United States, the second in 1953 by Russia (then the USSR). Great Britain, France, and China have also exploded thermonuclear bombs, and these five nations comprise the so-called nuclear club—nations that have the capability to produce nuclear weapons and admit to maintaining an inventory of them. The three smaller Soviet successor states that inherited nuclear arsenals (Ukraine, Kazakhstan, and Belarus) relinquished all nuclear warheads, which have been removed to Russia. Several other nations either have tested thermonuclear devices or claim to have the capability to produce them, but officially state that they do not maintain a stockpile of such weapons; among these are India, Israel, and Pakistan. South Africa's apartheid regime built six nuclear bombs but dismantled them later.

The presumable structure of a thermonuclear bomb is as follows: at its center is an atomic bomb; surrounding it is a layer of lithium deuteride (a compound of lithium and deuterium, the isotope of hydrogen with mass number 2); around it is a tamper, a thick outer layer, frequently of fissionable material, that holds the contents together in order to obtain a larger explosion. Neutrons from the atomic explosion cause the lithium to fission into helium, tritium (the isotope of hydrogen with mass number 3), and energy. The atomic explosion also supplies the temperatures needed for the subsequent fusion of deuterium with tritium, and of tritium with tritium (50,000,000°C and 400,000,000°C, respectively). Enough neutrons are produced in the fusion reactions to produce further fission in the core and to initiate fission in the tamper.

Since the fusion reaction produces mostly neutrons and very little that is radioactive, the concept of a "clean" bomb has resulted: one having a small atomic trigger, a less fissionable tamper, and therefore less radioactive fallout. Carrying this progression further results in the neutron bomb, which has a minimum trigger and a nonfissionable tamper; it produces blast effects and a hail of lethal neutrons but almost no radioactive fallout and little long-term contamination. This theoretically would cause minimal physical damage to buildings and equipment but kill most living things. Developed in 1958 by the United States and successfully tested, a number of countries are believed to have included such weapons in their nuclear arsenals; the United States built several hundred neutron bombs in the 1980s but did not deploy them.

The theorized cobalt bomb is, on the contrary, a radioactively "dirty" bomb having a cobalt tamper. Instead of generating additional explosive force from fission of the uranium, the cobalt is transmuted into cobalt-60, which has a half-life of 5.26 years and produces energetic (and thus penetrating) gamma rays. The half-life of Co-60 is just long enough so that airborne particles will settle and coat the earth's surface before significant decay has occurred, thus making it impractical to hide in shelters. This prompted physicist Leo Szilard to call it a "doomsday device" since it was capable of wiping out life on earth.

Like other types of nuclear explosion, the explosion of a hydrogen bomb creates an extremely hot zone near its center. In this zone, because of the high temperature, nearly all of the matter present is vaporized to form a gas at extremely high pressure. A sudden overpressure, i.e., a pressure far in excess of atmospheric pressure, propagates away from the center of the explosion as a shock wave, decreasing in strength as it travels. It is this wave, containing most of the energy released, that is responsible for the major part of the destructive mechanical effects of a nuclear explosion. The details of shock wave propagation and its effects vary depending on whether the burst is in the air, underwater, or underground.

See disarmament, nuclear and nuclear weapons; see also nuclear energy.

See R. Rhodes, Dark Sun: The Making of the Hydrogen Bomb (1995).

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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."


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.

Richard G.Hewlett


See alsoArms Race and Disarmament ; Nuclear Weapons .

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hydrogen bomb (H-bomb) Nuclear weapon developed by the USA in the late 1940s, and first exploded in 1952 in the Pacific. The explosion results from nuclear fusion when hydrogen nuclei are joined to form helium nuclei, releasing great destructive energy and radioactive fallout. An atomic bomb is used as the trigger.

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hy·dro·gen bomb • n. an immensely powerful bomb whose destructive power comes from the rapid release of energy during the nuclear fusion of isotopes of hydrogen (deuterium and tritium), using an atom bomb as a trigger. Compare with atom bomb.

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Hydrogen Bomb. See Nuclear Weapons.

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hydrogen bomb. See nuclear energy.