Nuclear weapon - Wikipedia. A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion (thermonuclear weapon). Both reactions release large quantities of energy from relatively small amounts of matter. The first test of a fission (. The first thermonuclear (. Nuclear weapons are weapons of mass destruction, and their use and control have been a major focus of international relations policy since their debut. Nuclear weapons have been used twice in war, both times by the United States against Japan near the end of World War II. On August 6, 1. 94. U. S. Army Air Forces detonated a uranium gun- type fission bomb nicknamed . Army Air Forces detonated a plutonium implosion- type fission bomb codenamed . The bombings resulted in the deaths of approximately 2. Only a few nations possess such weapons or are suspected of seeking them. 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The only countries known to have detonated nuclear weapons—and acknowledge possessing them—are (chronologically by date of first test) the United States, the Soviet Union (succeeded as a nuclear power by Russia), the United Kingdom, France, the People's Republic of China, India, Pakistan, and North Korea. Israel is also believed to possess nuclear weapons, though, in a policy of deliberate ambiguity, it does not acknowledge having them. Germany, Italy, Turkey, Belgium and the Netherlands are nuclear weapons sharing states. Modernisation of weapons continues to occur. Weapons whose explosive output is exclusively from fission reactions are commonly referred to as atomic bombs or atom bombs (abbreviated as A- bombs). This has long been noted as something of a misnomer, as their energy comes from the nucleus of the atom, just as it does with fusion weapons. In fission weapons, a mass of fissile material (enriched uranium or plutonium) is assembled into a supercritical mass—the amount of material needed to start an exponentially growingnuclear chain reaction—either by shooting one piece of sub- critical material into another (the . The latter approach is considered more sophisticated than the former, and only the latter approach can be used if the fissile material is plutonium. A major challenge in all nuclear weapon designs is to ensure that a significant fraction of the fuel is consumed before the weapon destroys itself. The amount of energy released by fission bombs can range from the equivalent of just under a ton to upwards of 5. TNT (4. 2 to 2. 1. Many fission products are either highly radioactive (but short- lived) or moderately radioactive (but long- lived) and as such are a serious form of radioactive contamination if not fully contained. Fission products are the principal radioactive component of nuclear fallout. The most commonly used fissile materials for nuclear weapons applications have been uranium- 2. Less commonly used has been uranium- 2. Neptunium- 2. 37 and some isotopes of americium may be usable for nuclear explosives as well, but it is not clear that this has ever been implemented, and even their plausible use in nuclear weapons is a matter of scientific dispute. Such fusion weapons are generally referred to as thermonuclear weapons or more colloquially as hydrogen bombs (abbreviated as H- bombs), as they rely on fusion reactions between isotopes of hydrogen (deuterium and tritium). All such weapons derive a significant portion, and sometimes a majority, of their energy from fission. This is because a fission reaction is required as a . Almost all of the nuclear weapons deployed today use the thermonuclear design because it is more efficient. In the Teller- Ulam design, which accounts for all multi- megaton yield hydrogen bombs, this is accomplished by placing a fission bomb and fusion fuel (tritium, deuterium, or lithium deuteride) in proximity within a special, radiation- reflecting container. When the fission bomb is detonated, gamma rays and X- rays emitted first compress the fusion fuel, then heat it to thermonuclear temperatures. The ensuing fusion reaction creates enormous numbers of high- speed neutrons, which can then induce fission in materials not normally prone to it, such as depleted uranium. Each of these components is known as a . In large, megaton- range hydrogen bombs, about half of the yield comes from the final fissioning of depleted uranium. This technique can be used to construct thermonuclear weapons of arbitrarily large yield, in contrast to fission bombs, which are limited in their explosive force. The largest nuclear weapon ever detonated, the Tsar Bomba of the USSR, which released an energy equivalent of over 5. TNT (2. 10 PJ), was a three- stage weapon. Most thermonuclear weapons are considerably smaller than this, due to practical constraints from missile warhead space and weight requirements. For example, a boosted fission weapon is a fission bomb that increases its explosive yield through a small amount of fusion reactions, but it is not a fusion bomb. In the boosted bomb, the neutrons produced by the fusion reactions serve primarily to increase the efficiency of the fission bomb. There are two types of boosted fission bomb: internally boosted, in which a deuterium- tritium mixture is injected into the bomb core, and externally boosted, in which concentric shells of lithium- deuteride and depleted uranium are layered on the outside of the fission bomb core. Some weapons are designed for special purposes; a neutron bomb is a thermonuclear weapon that yields a relatively small explosion but a relatively large amount of neutron radiation; such a device could theoretically be used to cause massive casualties while leaving infrastructure mostly intact and creating a minimal amount of fallout. The detonation of any nuclear weapon is accompanied by a blast of neutron radiation. Surrounding a nuclear weapon with suitable materials (such as cobalt or gold) creates a weapon known as a salted bomb. This device can produce exceptionally large quantities of long- lived radioactive contamination. It has been conjectured that such a device could serve as a . The concept involves the tapping of the energy of an exploding nuclear bomb to power a single- shot laser which is directed at a distant target. During the Starfish Prime high- altitude nuclear test in 1. Nuclear electromagnetic pulse. This is an intense flash of electromagnetic energy produced by a rain of high energy electrons which in turn are produced by a nuclear bomb's gamma rays. This flash of energy can permanently destroy or disrupt electronic equipment if insufficiently shielded. It has been proposed to use this effect to disable an enemy's military and civilian infrastructure as an adjunct to other nuclear or conventional military operations against that enemy. Because the effect is produced by very high altitude nuclear detonations, it can produce damage to electronics over a very wide, even continental, geographical area. Research has been done into the possibility of pure fusion bombs: nuclear weapons that consist of fusion reactions without requiring a fission bomb to initiate them. Such a device might provide a simpler path to thermonuclear weapons than one that required development of fission weapons first, and pure fusion weapons would create significantly less nuclear fallout than other thermonuclear weapons, because they would not disperse fission products. In 1. 99. 8, the United States Department of Energy divulged that the United States had, . Air Force funded studies of the physics of antimatter in the Cold War, and began considering its possible use in weapons, not just as a trigger, but as the explosive itself. Additionally, development and maintenance of delivery options are among the most resource- intensive aspects of a nuclear weapons program: according to one estimate, deployment costs accounted for 5. United States in relation to nuclear weapons since 1. This method places few restrictions on the size of the weapon. It does, however, limit attack range, response time to an impending attack, and the number of weapons that a country can field at the same time. With miniaturization, nuclear bombs can be delivered by both strategic bombers and tactical fighter- bombers. This method is the primary means of nuclear weapons delivery; the majority of U. S. Although even short- range missiles allow for a faster and less vulnerable attack, the development of long- range intercontinental ballistic missiles (ICBMs) and submarine- launched ballistic missiles (SLBMs) has given some nations the ability to plausibly deliver missiles anywhere on the globe with a high likelihood of success. More advanced systems, such as multiple independently targetable reentry vehicles (MIRVs), can launch multiple warheads at different targets from one missile, reducing the chance of a successful missile defense. Today, missiles are most common among systems designed for delivery of nuclear weapons. Making a warhead small enough to fit onto a missile, though, can be difficult. An atomic mortar was also tested at one time by the United States. Small, two- man portable tactical weapons (somewhat misleadingly referred to as suitcase bombs), such as the Special Atomic Demolition Munition, have been developed, although the difficulty of combining sufficient yield with portability limits their military utility. The policy of trying to prevent an attack by a nuclear weapon from another country by threatening nuclear retaliation is known as the strategy of nuclear deterrence. The goal in deterrence is to always maintain a second strike capability (the ability of a country to respond to a nuclear attack with one of its own) and potentially to strive for first strike status (the ability to completely destroy an enemy's nuclear forces before they could retaliate). An error occurred while setting your user cookie. Please set your. browser to accept cookies to continue. 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