7.98 Feature
A basic nuclear primer...The world entered the nuclear age on December 2, 1942, beneath a gymnasium at the University of Chicago, when a team headed by Enrico Fermi succeeded in creating the first controlled "chain reaction." This led, in turn, to the creation of the Manhattan Project, headed by General Leslie Groves and directed by J. Robert Oppenheimer. The Manhattan Project culminated, on 16 July, 1945, in the first successful detonation of a fission bomb at Alamogordo, New Mexico. Less than a month later, on August 6, 1945, the weapon was employed for the first time at Hiroshima, Japan. Three days later, a slightly different bomb was dropped on Nagasaki. In the face of this unprecedented demonstration of power, Imperial Japan capitulated, thus ending the blood bath begun by the Japanese on December 7, 1941, with the bombing of Pearl Harbor.There are two kinds of bombs, fission (the older) and fusion (thermonuclear devices). Fission devices get their energy from the splitting of atomic nuclei, while fusion devices derive their energy by forcing atomic nuclei to join together in an uncontrolled nuclear fusion. How powerful are these weapons? The fission devices, or atomic bombs, are about one million times more powerful than a comparably sized conventional bomb, and the fusion weapons, or hydrogen bombs, are about a thousand times more powerful than the A-bomb. How are these bombs built? Fission devices are fueled by Uranium 235, an isotope of the more commonly occurring Uranium 238. U-235 was originally produced by a process known as "gasseous diffusion," invented at the Oak Ridge National Laboratory. The invention of the "cascade" gaseous diffusion method of enriching U-238 was dependent on development of a porous barrier which allowed the progressive enrichment of U-238 as it passed through a series of these barriers, with unenriched uranium being passed backward at each stage to be reprocessed. The final "cascade" barrier produced U-235 of sufficient density to produce the "chain reaction" that is the guts of the explosion. Thermonuclear devices are fueled by Plutonium, the product of "enrichment" by exposure to the ongoing reactions inside a conventional reactor. "Fast-breeding" reactors actually produce more fuel than they consume. "Critical mass" is the level of fuel concentration at which fission or fusion is self-sustaining. The atomic fuel must be compressed sufficiently to insure that the escaping neutrons from fission are sure to strike the nucleus of surrounding isotopes, causing further fission. This is the function of the nuclear "trigger." "Triggering" the explosion of nuclear devices is accomplished either by implosion, in which the nuclear material is surrounded on all sides by conventional explosives that are detonated simultaneously, forcing the nuclear material into a critical mass, or by a "gun-type" trigger, in which two pieces of nuclear material are "fired" at one another, forcing the two materials into a single, supercritical mass, thereby "triggering" the explosion.
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