The Manhattan Project: Making the Atomic Bomb

Limited Government Funding: 1940

The Uranium Committee's first report, issued on November 1, 1939, recommended that, despite the uncertainty of success, the government should immediately obtain four tons of graphite and fifty tons of uranium oxide. This recommendation led to the first outlay of government funds-$6,000 in February 1940-and reflected the importance attached to the Fermi-Szilard pile experiments already underway at Columbia University. Building upon the work performed in 1934 demonstrating the value of moderators in producing slow neutrons, Fermi thought that a mixture of the right moderator and natural uranium could produce a self-sustaining chain reaction. Fermi and Szilard increasingly focused their attention on carbon in the form of graphite. Perhaps graphite could slow down, or moderate, the neutrons coming from the fission reaction, increasing the probability of their causing additional fissions in sustaining the chain reaction. A pile containing a large amount of natural uranium could then produce enough secondary neutrons to keep a reaction going.

There was, however, a large theoretical gap between building a self-generating pile and building a bomb. Although the pile envisioned by Fermi and Szilard could produce large amounts of power and might have military applications (powering naval vessels, for instance), it would be too big for a bomb. It would take separation of uranium-235 or substantial enrichment of natural uranium with uranium-235 to create a fast-neutron reaction on a small enough scale to build a usable bomb. While certain of the chances of success in his graphite power pile, Fermi, in 1939, thought that there was "little likelihood of an atomic bomb, little proof that we were not pursuing a chimera."¹²

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