الرئيسية
1. The Chain Reaction
The University of Chicago is not only the site of the world's first self-sustaining nuclear reaction, but also one of the earliest and most influential centers of the atomic scientists' movement.
On December 2, 1942, scientists at the University of Chicago produced the world's first self-sustaining nuclear chain reaction in a nuclear pile constructed in a squash court beneath the West Stands of Stagg Field, the University's athletic stadium. This experiment, crucial to the control of nuclear fission, was one of several research projects at sites around the country, each concentrating on some task critical to production of an atomic bomb. All were administered by the U.S. Army under the code name of Manhattan Engineer District, or Manhattan Project.
After the discovery of nuclear fission in 1938 by German chemists Otto Hahn and Fritz Strassman, theorizing and experimentation in this country had proceeded rapidly at Columbia, Princeton, Berkeley, Chicago, and elsewhere. Enrico Fermi, who had defected from Italy while accepting the Nobel Prize in physics, arrived at Columbia in 1939 where he theorized that the neutrons emitted in fission might induce fission reactions. Fermi further concluded that it should be possible to sustain a chain reaction in uranium which, under the right conditions, might multiply fast enough to cause a nuclear explosion. Fermi and Columbia physicist Leo Szilard proposed placing uranium in a matrix of graphite, forming a cubical lattice of uranium with potential for inducing a self-sustaining controlled reaction.
Amid fears that German scientists might already be well on their way to constructing an atomic weapon, President Roosevelt in the fall of 1941 approved a full-scale effort to translate these theories into the construction of the bomb. Arthur Holly Compton, professor of physics at the University of Chicago and a Nobel laureate, was placed in charge of the program with work on a reactor to be concentrated in Chicago under the code name Metallurgical Laboratory. Consequently, early in 1942 groups of scientists from Princeton and Columbia arrived at Chicago to combine their efforts.
In November 1942 construction began on the reactor in the West Stands. Layers of graphite blocks containing slugs of uranium metal and uranium oxide alternated with layers of solid graphite blocks, in a roughly spherical shape supported by a wood framework. A square balloon-cloth bag encased the reactor to reduce absorption of neautrons by nitrogen in the air. Higher grades of uranium became available as work progressed, and the pile was redesigned in a reduced size with a flattened top.
Construction halted with the fifty-seventh layer on December 1, when measurements indicated the pile would become sulf-sustaining should the control rods be withdrawn. On December 2, Fermi and his colleagues gathered on the balcony of the squash court to test the reactor, slowly withdrawing the last control rod until the "critical," or self-sustaining, level was reached, then watching the reactor operate for twenty-eight minutes before reinserting the rod and stopping the reaction. Compton telephoned the news to Harvard president James B. Conant, member of the Manhattan Project Military Policy Committee, with the coded message, "The Italian navigator has just landed in the New World."
The University of Chicago is not only the site of the world's first self-sustaining nuclear reaction, but also one of the earliest and most influential centers of the atomic scientists' movement.
On December 2, 1942, scientists at the University of Chicago produced the world's first self-sustaining nuclear chain reaction in a nuclear pile constructed in a squash court beneath the West Stands of Stagg Field, the University's athletic stadium. This experiment, crucial to the control of nuclear fission, was one of several research projects at sites around the country, each concentrating on some task critical to production of an atomic bomb. All were administered by the U.S. Army under the code name of Manhattan Engineer District, or Manhattan Project.
After the discovery of nuclear fission in 1938 by German chemists Otto Hahn and Fritz Strassman, theorizing and experimentation in this country had proceeded rapidly at Columbia, Princeton, Berkeley, Chicago, and elsewhere. Enrico Fermi, who had defected from Italy while accepting the Nobel Prize in physics, arrived at Columbia in 1939 where he theorized that the neutrons emitted in fission might induce fission reactions. Fermi further concluded that it should be possible to sustain a chain reaction in uranium which, under the right conditions, might multiply fast enough to cause a nuclear explosion. Fermi and Columbia physicist Leo Szilard proposed placing uranium in a matrix of graphite, forming a cubical lattice of uranium with potential for inducing a self-sustaining controlled reaction.
Amid fears that German scientists might already be well on their way to constructing an atomic weapon, President Roosevelt in the fall of 1941 approved a full-scale effort to translate these theories into the construction of the bomb. Arthur Holly Compton, professor of physics at the University of Chicago and a Nobel laureate, was placed in charge of the program with work on a reactor to be concentrated in Chicago under the code name Metallurgical Laboratory. Consequently, early in 1942 groups of scientists from Princeton and Columbia arrived at Chicago to combine their efforts.
In November 1942 construction began on the reactor in the West Stands. Layers of graphite blocks containing slugs of uranium metal and uranium oxide alternated with layers of solid graphite blocks, in a roughly spherical shape supported by a wood framework. A square balloon-cloth bag encased the reactor to reduce absorption of neautrons by nitrogen in the air. Higher grades of uranium became available as work progressed, and the pile was redesigned in a reduced size with a flattened top.
Construction halted with the fifty-seventh layer on December 1, when measurements indicated the pile would become sulf-sustaining should the control rods be withdrawn. On December 2, Fermi and his colleagues gathered on the balcony of the squash court to test the reactor, slowly withdrawing the last control rod until the "critical," or self-sustaining, level was reached, then watching the reactor operate for twenty-eight minutes before reinserting the rod and stopping the reaction. Compton telephoned the news to Harvard president James B. Conant, member of the Manhattan Project Military Policy Committee, with the coded message, "The Italian navigator has just landed in the New World."
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