WikipediaExtracts:Thermonuclear weapon
Extracted from Wikipedia --
A thermonuclear weapon, fusion weapon or hydrogen bomb (H-bomb) is a second-generation nuclear weapon design. Its greater sophistication affords it vastly greater destructive power than first-generation nuclear bombs, a more compact size, a lower mass, or a combination of these benefits. Characteristics of nuclear fusion reactions make possible the use of non-fissile depleted uranium as the weapon's main fuel, thus allowing more efficient use of scarce fissile material. Its multi-stage design is distinct from the usage of fusion in simpler boosted fission weapons. The first full-scale thermonuclear test (Ivy Mike) was carried out by the United States in 1952, and the concept has since been employed by at least the five recognized nuclear-weapon states and UNSC permanent members: the United States, Russia, the United Kingdom, China, and France.
The design of all thermonuclear weapons is believed to be the Teller–Ulam configuration, in which a fission bomb primary stage's energy is channelled into implosion of a separate fusion secondary stage containing thermonuclear fuel, usually lithium-6 deuteride. During detonation, neutrons convert lithium-6 to helium-4 plus tritium. The heavy isotopes of hydrogen, deuterium and tritium, then undergo an energetic reaction. For this reason, thermonuclear weapons are often colloquially called hydrogen bombs or H-bombs.
The weapon firing begins with the detonation of the fission primary. Its temperature soars past 100 million kelvin, emitting X-rays via inverse Compton scattering. These flood the radiation case, allowing compression of the separately located secondary. A neutron shield blocks the predetonation of the secondary, which completes detonation before destruction by the primary's fireball.
The secondary stage consists of the outer pusher/tamper, fusion fuel, and central fissile sparkplug. The primary's X-rays intensely ionize and ablate the tamper surface, imploding the secondary. This triggers a fission explosion in the sparkplug. These forces combine to begin fusion ignition in the fusion fuel, around 300 million kelvin. The Jetter cycle produces the crucial tritium fuel from neutron-lithium-6 reactions.
Additionally, most weapons use a natural or depleted uranium tamper and case. This undergoes fast fission from fast fusion neutrons and is the main contribution to the total yield and radioactive fission product fallout.
Before Ivy Mike, the US Operation Greenhouse in 1951 was the first nuclear test series investigating thermonuclear principles. Shot George tested radiation implosion and the first artificial thermonuclear fusion while shot Item tested the boosted fission principle. The Teller-Ulam configuration was named for its two chief contributors, Edward Teller and Stanisław Ulam, who developed it in 1951 for the United States, with certain concepts developed with the contribution of physicist John von Neumann.
Multi-stage devices were independently developed and tested by the Soviet Union (1955), the United Kingdom (1957), China (1966), and France (1968). There is not enough public information to determine whether India, Israel, or North Korea possess multi-stage weapons. Pakistan is not considered to have developed them. After the 1991 collapse of the Soviet Union, Ukraine, Belarus, and Kazakhstan became the first and only countries to relinquish their thermonuclear weapons, although these had never left the operational control of Russian forces.
Thermonuclear weapons are the only artificial source of explosions above one megaton TNT. The Tsar Bomba was the most powerful bomb ever detonated at 50 megatons TNT. As they are the most efficient design for yields above 50 kilotons of TNT (210 TJ), and with decreased relevance of tactical nuclear weapons, virtually all the nuclear weapons deployed by the five recognized nuclear-weapons states today use the Teller–Ulam design. Their ability to miniaturize high yields, such as in MIRV warheads, plays an important role in nuclear deterrence. While some have been developed into clean bombs, most thermonuclear weapons designed, including all current US and UK nuclear warheads, derive most of their energy from fast fission, causing high fallout.
