ished the Manhattan Project. Physicists from 1939 onward conducted much research to find answers to such questions as how many neutrons were emitted in each fission, which elements would not capture the neutrons but would moderate or reduce their velocity , and whether only the lighter and scarcer isotope of uranium (U-235) fissioned or the common isotope (U-238) could be used. They learned that each fission releases a few neutrons. A chain reaction, therefore, was theoretically possible, if not too many neutrons escaped from the mass or were captured by impurities. To create this chain reaction and turn it into a usable weapon was the ultimate goal of the Manhattan Project. In 1942 General Leslie Groves was chosen to lead the project, and he immediately purchased a site at Oak Ridge, Tenn., for facilities to separate the necessary uranium-235 from the much more common uranium-238. Uranium 235 was an optimal choice for the bomb because of its unusually unstable composition. Thus, the race to separate the two began. During that time, the work to perfect the firing mechanism and structure of the bomb was also swiftly underway. General Groves' initial task had been to select a scientific director for th
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