Detonation of Atomic Bombs

Gun Method

Various systems were devised to detonate the prototype atomic bombs. The simplest system is the gun-type weapon, in which a projectile made of fissile material is fired at a target of the same material so that the two weld together into a supercritical assembly. The atomic bomb exploded by the United States over Hiroshima, Japan, on August 6, 1945, was a gun-type weapon. It had the energy equivalent of about 13 kilotons of TNT.

Implosion Method

A more complex method, known as implosion, is utilized in a spherically shaped weapon. The outer part of the sphere consists of a layer of closely fitted and specially shaped lenses, which are composed of high explosive and designed to concentrate the blast towards the centre of the bomb. Each segment of the high explosive is equipped with a detonator, which in turn is wired to all other segments. An electrical impulse explodes all the chunks of high explosive simultaneously, resulting in a detonation wave that converges towards the core of the weapon. At the core is a sphere of fissile material, which is compressed by the powerful, inwardly directed pressure, or implosion. The density of the metal is increased, and a supercritical assembly is produced. The Trinity test bomb exploded near Alamogordo, as well as the one dropped by the United States on Nagasaki, Japan, on August 9, 1945, was of the implosion type. Each was equivalent to about 20 kilotons of TNT.

Regardless of the method used to attain a supercritical assembly, the chain reaction proceeds for about a millionth of a second, liberating vast amounts of heat energy. The extremely fast release of a very large amount of energy in a relatively small volume causes the temperature to rise to tens of millions of degrees. The resulting rapid expansion and vaporization of the bomb material causes the explosion.