histoire du nucléaire

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The discovery of the process occurred in the late 1930s, the result of a long sequence of nuclear physics studies. The German scientists Otto HAHN and Fritz Strassmann reported on an experiment involving neutron irradiation of uranium in early 1939. Subsequently, Otto Frisch and interpreted the experiment as the fissioning of uranium into lighter elements.

The possibility of a chain reaction was apparent, and provided added impetus for accelerated research.

Secret government research into the military applications of nuclear fission began with World War II ( PROJECT). The development of a weapon required that a self-sustaining fission reaction could be created and, further, that an adequate amount of fissionable material could be produced for use in a weapon.

On December 2, 1942, at the University of , a team under the direction of successfully brought the world's first reactor to a self-sustaining, or "critical," state. The reactor was fueled with natural uranium imbedded in blocks. The fissioning occurred in the isotope of uranium, .

Natural uranium contains only 0.7% of , while the remaining 99.3% of the uranium is , which does not fission except with very high energy neutrons not available from the fission process. In making a bomb, it was necessary to provide much higher concentrations of U-235, or "," and ultimately, a form of gaseous was used to separate U-235 from U-238. A significant part of the Manhattan Project was devoted to developing a processing technology to separate
U-235 from U-238. Ultimately, the solution was found in a form of gaseous diffusion that was used to separate the two materials.
On July 16,1945, however, the work of the U.S. MANHATTAN PROJECT came to fruition when an ATOMIC BOMB was successfully tested at . From on July 26, Truman, Churchill, Stalin and Chiang Kai-shek issued an ultimatum demanding the unconditional surrender of Japan.

On Aug. 6, 1945, an atomic bomb with an explosive force greater than 20,000 U.S. tons of TNT was dropped on the Japanese city of , with a population of about 300,000.
At least 78,000 people were killed outright, 10,000 were never found, and more than 70,000 were injured. Almost two-thirds of the city was destroyed. On August 9, an atomic bomb was dropped on .

The concept of an energy source that promised extended naval voyages without refueling was obviously worth investigation. Under the direction of Hyman RICKOVER, a naval reactor program began in the late 1940s and the first nuclear submarine, the , was launched in 1954.

An outstanding success, the Nautilus proved the merits of nuclear propulsion for naval vessels. Its reactor was the prototype for the first commercial nuclear power plant, built in Shippingport, Pennsylvania, in 1957.

The decision to declassify much nuclear-related information in order to foster peaceful applications was made by President Dwight D. and announced in his "Atoms for Peace" speech at the United Nations in December 1953. Other nations joined in the search for peaceful uses for the atom, and the first international conference on nuclear energy was held in Geneva in 1955. In the United States the Atomic