neutron bomb: see hydrogen bomb.

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 would result in the suggested neutron bomb, which would have a minimum trigger and a nonfissionable tamper; there would be blast effects and a hail of lethal neutrons but almost no radioactive fallout; this theoretically would cause minimal physical damage to buildings and equipment but kill most living things. 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.

cobalt bomb: see hydrogen bomb.

atomic bomb or A-bomb, weapon deriving its explosive force from the release of atomic energy through the fission (splitting) of heavy nuclei (see nuclear energy). The first atomic bomb was produced at the Los Alamos, N.Mex., laboratory and successfully tested on July 16, 1945. This was the culmination of a large U.S. army program that was part of the Manhattan Project, led by Dr. Robert Oppenheimer. It began in 1940, two years after the German scientists Otto Hahn and Fritz Strassman discovered nuclear fission. On Aug. 6, 1945, an atomic bomb was dropped on Hiroshima with an estimated equivalent explosive force of 12,500 tons of TNT, followed three days later by a second, more powerful, bomb on Nagasaki. Both bombs caused widespread death, injury, and destruction, and there is still considerable debate about the need to have used them.

Atomic bombs were subsequently developed by the USSR (1949; now Russia), Great Britain (1952), France (1960), and China (1964). A number of other nations, particularly India, Pakistan, Israel, and North Korea now have atomic bombs or the capability to produce them; South Africa formerly possessed a small arsenal. The three smaller Soviet successor states that inherited nuclear arsenals (Ukraine, Kazakhstan, and Belarus) relinquished all nuclear warheads, which have been removed to Russia.

Atomic bombs have been designed by students, but their actual construction is a complex industrial process. Practical fissionable nuclei for atomic bombs are the isotopes uranium-235 and plutonium-239, which are capable of undergoing chain reaction. If the mass of the fissionable material exceeds the critical mass (a few pounds), the chain reaction multiplies rapidly into an uncontrollable release of energy. An atomic bomb is detonated by bringing together very rapidly (e.g., by means of a chemical explosive) two subcritical masses of fissionable material, the combined mass exceeding the critical mass. An atomic bomb explosion produces, in addition to the shock wave accompanying any explosion, intense neutron and gamma radiation, both of which are very damaging to living tissue. The neighborhood of the explosion becomes contaminated with radioactive fission products. Some radioactive products are borne into the upper atmosphere as dust or gas and may subsequently be deposited partially decayed as radioactive fallout far from the site of the explosion.

See disarmament, nuclear; hydrogen bomb; nuclear strategy; and nuclear weapons; see also nuclear energy.

or H-bomb or thermonuclear bomb

Weapon whose enormous explosive power is generated by the nuclear fusion of hydrogen isotopes. The high temperatures required for the fusion reaction are produced by detonating an atomic bomb (which draws its energy from nuclear fission). The bomb's explosion produces a blast that can destroy structures within a radius of several miles, an intense white light that can cause blindness, and heat fierce enough to set off firestorms. It also creates radioactive fallout that can poison living creatures and contaminate air, water, and soil. Hydrogen bombs, which may be thousands of times more powerful than atomic bombs, can be made small enough to fit in the warhead of a ballistic missile (see ICBM) or even in an artillery shell (see neutron bomb). Edward Teller and other U.S. scientists developed the first H-bomb and tested it at Enewetak atoll (Nov. 1, 1952). The Soviet Union first tested an H-bomb in 1953, followed by Britain (1957), China (1967), and France (1968). Most modern nuclear weapons employ both fusion and fission.

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Bomb with a guidance system that directs its path toward a target. It is steered by fins or wings on the bomb that move in response to guidance commands. Guidance systems may be electro-optical, laser, infrared, or inertial. Electro-optical systems send pictures of the area so that the bomb can be guided onto the target. Laser-guided bombs follow the reflections of a laser beam trained onto the target by an aircraft or a spotter on the ground. Infrared guidance responds to radiation generated by warm areas of the target. Inertial navigation is based on inputting coordinates derived from radar systems or from Global Positioning System satellites into the bomb's gyroscopes. Smart bombs, initially used in the Vietnam War, offer far greater accuracy than traditional gravity, or “dumb,” bombs.

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or enhanced radiation warhead

Small thermonuclear weapon that produces minimal blast and heat but releases large amounts of lethal radiation. The blast and heat are confined to a radius of only a few hundred yards; within a somewhat larger area, the bomb throws off a massive wave of neutron and gamma radiation, which is extremely destructive to living tissue. Such a bomb could be used with deadly efficiency against tank and infantry formations on the battlefield without endangering towns or cities only a few miles away. It can be carried in a missile or delivered by a howitzer or even an attack aircraft.

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or flying bomb or buzz bomb

German missile of World War II. The forerunner of modern cruise missiles, it was about 25 ft (8 m) long and had a wingspan of about 18 ft (5.5 m). It was launched from catapult ramps or sometimes from aircraft; it carried an explosive warhead of almost 1,900 lbs (850 kg) and had an average range of 150 mi (240 km). More than 8,000 V-1s were launched against London in 1944–45, and a smaller number against Belgium. Seealso V-2 missile.

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In volcanology, any unconsolidated volcanic material that has a diameter greater than 1.25 in. (32 mm). Bombs form from clots of wholly or partly liquid lava ejected during a volcanic explosion; they solidify and become rounded during flight. The final shape is determined by the initial size, viscosity, and flight velocity of the magma.

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Weapon whose great explosive power results from the sudden release of energy upon the splitting, or fission, of the nuclei of heavy elements such as plutonium or uranium (see nuclear fission). With only 11–33 lb (5–15 kg) of highly enriched uranium, a modern atomic bomb could generate a 15-kiloton explosion, creating a huge fireball, a large shock wave, and lethal radioactive fallout. The first atomic bomb, developed by the Manhattan Project during World War II, was set off on July 16, 1945, in the New Mexico desert. The only atomic bombs used in war were dropped by the U.S. on Hiroshima on Aug. 6, 1945, and on Nagasaki three days later. In 1949 the Soviet Union tested its first atomic bomb, followed by Britain (1952), France (1960), China (1964), India (1974), and Pakistan (1998). Israel and South Africa were suspected of testing atomic weapons in 1979. Seealso hydrogen bomb; Nuclear Non-proliferation Treaty; nuclear weapon.

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