![]() Because the helium nucleus is tightly bound (has a large binding energy), the reaction produces a great deal of energy. Here the two rare isotopes of hydrogen combine to form 4 2He, the common isotope of helium plus a free neutron. This is a process, in a sense the opposite of fission, in which two light nuclei are brought together in a reaction which produces a heavier nucleus. There is no doubt, however, that the Soviets would have obtained the bomb not too many years after the war in any case.īefore the fission bomb was even completed there was discussion at Los Alamos about the possibility of another kind of bomb based on fusion. It was also the secret obtained by the Soviet Union through espionage, which accelerated their development of the bomb. Implosion was a crucial and difficult engineering problem, overcome by the scientists at Los Alamos, where the bomb was built during the 1940s. (Scientists were so sure of the gun-type device, that it was not tested before its use at Hiroshima.) The bomb set off over Nagasaki, which ended the world war, was an implosion plutonium device. ![]() (Implosion can be used with either plutonium or uranium.) The first atomic bomb ever exploded was a plutonium bomb tested in the New Mexico desert before the bombs were used in war. The sphere is surrounding with high explosives in such a way that, when they are set off, the plutonium is compressed to a high density it then becomes critical and explodes. A sphere of plutonium that is less than a critical mass can be made critical by compressing it to high density. Instead the method of "implosion" is used. This method was used in the atomic bomb that destroyed Hiroshima at the close of World War II.įor technical reasons, the gun-type assembly cannot be used in a plutonium bomb. When the critical mass (the full sphere) is formed, and a small influx of neutrons is introduced at the right time, a fission explosion occurs. Chemical explosions at two ends of the bomb drive the two hemispheres together. ![]() The simplest method of assembling a critical mass is to begin with two hemispheres, each containing half of a critical mass, and drive them together rapidly. Plutonium, some combination of 239Pu and 240Pu, critical mass about 16 kg.Uranium-235 ( 235U), the rare isotope of.Two types of fissile material have been used in atomic bombs up to the present type: ![]() An atomic bomb must contain a critical mass of fissile material, that is, material that can undergo fission. ![]()
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