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| An '''atomic bomb''' is the name given to a device designed to produce an enormous explosion by harnessing [[nuclear energy]].
| | '''Atomic bomb''' (''aka'' '''atom bomb''') was the name given to the first explosive device to derive its destructive power from, as defined by the ''[[Oxford English Dictionary]]'', "the rapid release of energy by fission of heavy atomic nuclei".<ref>OED 2004, Eleventh Edition, p. 83.</ref> |
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| The [[United States of America]] was the first nation to produce atomic bombs. | | Three atomic bombs were detonated by the United States during World War II. The first was a test explosion at [[Alamogordo]], [[New Mexico (U.S. state)|New Mexico]], on 16 July 1945. That was the culmination of the [[Manhattan Project]]. The bomb was then deployed by the [[United States Air Force]] in a bid to end the [[Pacific War]] against Japan without the need for an invasion of the Japanese mainland. On 6 August, a bomb codenamed [[Little Boy (atomic bomb)|Little Boy]] was dropped on [[Hiroshima (city)|Hiroshima]]. There was a second strike against [[Nagasaki (city)|Nagasaki]] three days later and Japan surrended on 14 August. |
| So far, two bombs the United States dropped on the [[Japan]]ese cities of [[Hiroshima]] and [[Nagasaki]], in the closing days of [[World War 2]], have been the only military uses of atomic weapons.
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| The first atomic bombs, like the two dropped on Japan, relied on producing a [[chain reaction]] of [[nuclear fission|fissioning]] [[radioactive]] [[atomic nuclei|nuclei]]. Atoms of the heaviest elements found in nature, like [[Uranium]] and [[Thorium]], have no stable [[isotopes]]. All isotopes are radioactive.
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| The radioactive isotopes of Uranium and Thorium have relatively long [[half-lives]], measured in the millions of years. However, as [[Leo Szilard]] was the first to note, an atom of [[Uranium 235]] could be stimulated to fission, if it was struck by a slow neutron. This fission of the Uranium nuclei into two smaller atoms releases a very large amount of energy - and another neutron. Szilard suggested that, if a large enough mass of relatively pure Uranium 235, were gathered in a single place, neutrons released by the fission of some atoms would stimulate the fissioning of other atoms. He called this a "[[critical mass]]".
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| He described how, if this fissioning could be controlled, it could be an extremely useful source of energy. The mechanism for harnessing this kind of energy is now called a [[nuclear reactor]].
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| And, when a critical mass is brought together suddenly, forcing a very large fraction of the unstable radioactive nuclei to fission, almost simultaneously, it would result in a massive explosion.
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| Up until the test of the first atomic bomb, in [[Los Alamos]], the largest man-made explosion had been the explosion of several thousand tons that were all on single ship, in [[Halifax]], during [[World War I]]. That explosion flattened much of the city center and caused about 500 deaths.
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| Estimates of the yields of the USA's first simple fission bombs were the equivalent of 10-20,000 tons of [[TNT]].
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| Following victory in World War 2 some nations continued to develop and test atomic bombs that harnessed both fission and [[Hydrogen Fusion]] that were the equivalent of millions of tons of TNT.
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| The yields of the most commonly fielded nuclear weapons are in the 400 kiloton range.
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| ==The non-proliferation treaty==
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| The [[Soviet Union]] was the second nation to successfully test an atomic weapon, in 1949. The [[United Kingdom]], [[France]] and [[China]] each developed atomic weapons, before most nations signed the non-proliferation treaty]].
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| In the treaty those nations that did not yet possess nuclear weapons agreed they would not develop them. The treaty called this the prevention fo "horizontal proliferation".
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| In return the nations that had developed weapons agreed to share the benefits of the peaceful use of atomic energy with those other nations, and they promised that they would not expand the number or sophistication of their nuclear arsenals - "vertical proliferation".
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| Nuclear armed nations ignored their promise, and both continued to increase the size of their arsenals, and the sophistication of their weapons.
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| Other than building nuclear reactors, for profit, in foreign countries, little effort was made to share the benefits of the peaceful use of atomic energy. At one time the United States had proposals to use atomic explosions for excavation - as an instance of peacefully sharing the benefits of atomic energy. One plan was to bury a string of hundreds of nuclear bombs across [[Panama]], and then detonate them all at once. This would result in a single deep trench. This was described as a benefit as it could build a second [[Panama Canal]] - this time at [[sea level]], so ships passing through the canal would not need to go through locks. However, proponents forgot this plan would have released as much radioactive fallout as a full-scale nuclear war.
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