Finally in 1942, Fermi, who had immigrated to the United States to avoid Mussolini�s control over Italy, constructed the world�s first nuclear reactor, or as it was called then, nuclear pile. The pile used Cadmium rods as controls and was surrounded by graphite, both of which (Cadmium and graphite) absorb neutrons and would then control the reaction. The pile was built in secret under the racquet ball courts at the University of Chicago where Fermi was teaching. Along with building the world�s first nuclear reactor, Fermi came up with and equation 235/92-U + 1/0 n ? 139/56-Ba + 94/36-Kr + 3 1/0 n which is the formula for the nuclear reaction, fission, and was used in the making of the atomic bomb.
During this time, many chemists and physicists worried about the power of the chain reaction and about fission itself. They convinced Einstein to write a letter to the President of the United States, Franklin D. Roosevelt, saying �� it may become possible to set up a nuclear chain reaction in a large mass of uranium, by which vast amounts of power and large quantities of new radium-like elements would be generated�. It appears almost certain that this could be achieved in the immediate future. This new phenomenon would also lead to the construction of bombs, and it is conceivable�though much less certain�that extremely powerful bombs of a new type may thus be constructed�� (Matter. Lapp, Ralph E. 1963). This was the start of the arms race between the two superpowers: the United States of America and the Soviet Union. President Roosevelt knew that if the U.S. could figure out how to make a nuclear bomb then the Soviet Union knew how to, also. Roosevelt started the �Manhattan project�. This group of scientist learned how to make two kinds of nuclear bombs. They created a fission bomb and a fusion bomb. The latter bomb's power comes from the energy released by the fusing of two atoms. These two bombs were dropped on Japan ending World War two.
