The Manhattan Project

The Manhattan Project

On the morning of August 6, 1945, a B-29 bomber named Enola Gay flew over the industrial city of Hiroshima, Japan and dropped the first atomic bomb ever. The city went up in flames caused by the immense power equal to about 20,000 tons of TNT. The project was a success. The people who were responsible were civilian, military scientific brain power-brilliant, intense, and young people. Unknowingly, they came to an isolated mountain setting, known as Los Alamos, New Mexico, to design and build the bomb that would end World War 2, but begin serious controversies concerning its sheer power and destruction.

The Manhattan Project was the code name for the US effort during World War II to produce the atomic bomb. It was appropriately named for the Manhattan Engineer District of the US Army Corps of Engineers, because much of the early research was done in New York City (Badash 238). Sparked by refugee physicists in the United States, the program was slowly organized after nuclear fission was discovered by German scientists in 1938, and many US scientists expressed the fear that Hitler would attempt to build a fission bomb. Frustrated with the idea that Germany might produce an atomic bomb first, Leo Szilard and other scientists asked Albert Einstein, a famous scientist during that time, to use his influence and write a letter to president FDR, pleading for support to further research the power of nuclear fission (Badash 237). His letters were a success, and President Roosevelt established 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 the bomb project. His first two choices, Ernest O. Lawrence, director of the electromagnetic separation project, and Arthur H. Compton, director of Chicago Metallurgical Laboratory, were not available. Groves had some doubts regarding the next best candidate, J. Robert Oppenheimer (Wood 2). Finally, Groves gambled on Oppenheimer, a theoretical mathematician, as director of the weapons laboratory, built on an isolated mesa (flat land area) at Los Alamos, New Mexico.

After much difficulty, an absorbent barrier suitable for separating isotopes of uranium was developed and installed in the Oak Ridge gaseous diffusion plant. Finally, in 1945, uranium-235 of bomb purity was shipped to Los Alamos, where it was fashioned into a gun-type weapon. In a barrel, one piece of uranium was fired at another, together forming a supercritical, explosive mass. To achieve chain-reaction fission, a certain amount of fissile material, called critical mass, is necessary. The fissile material used in the Hiroshima model was uranium 235. In the bomb, the uranium was divided into two parts, both of which were below critical mass. The bomb was designed so that one part would be slammed into the other by an explosive device to achieve critical mass instantaneously (Badash 238). When critical mass is achieved, continuous fission (a chain reaction) takes place in an extremely short period of time, and far more energy is released than in the case of a gun-powder explosion (Badash 238). On December 2, 1942, the first self-sustaining chain reaction with cadmium took place, overseen by Enrico Fermi, in the University of Chicago squash fields (Asimov 783).

Another type of atomic bomb was also constructed using the synthetic element plutonium. Fermi built a reactor at Chicago in late 1942, the prototype of five production reactors erected at Hanford, Wash. These reactors manufactured plutonium by bombarding uranium-238 with neutrons. At Los Alamos the plutonium was surrounded with high explosives to compress it into a super dense, super critical mass far faster than could be done in a gun barrel.