An atomic bomb is a weapon of mass destruction which uses nuclear fission to produce vast amounts of energy. Its basic principle is assembling a critical mass of a radioactive element with properties to spark a swift chain reaction. Its devastating effect is twofold: first, from the heat of the thermonuclear reaction, and second, from the radioactive fallout which continues after the bomb has been deployed.

The difference between an atomic bomb and a nuclear reactor is in the speed and control of the release of energy. It is precisely those features which are undesirable in a nuclear reactor that are vital in an atomic weapon. An atomic weapon must chain react swiftly enough that the entire reaction happens in a matter of minutes. Uranium-235 and plutonium are generally used for atomic bombs because of their ability to fission when hit by "slow" neutrons. That is...