The Manhattan Project, An Interactive History Home The Manhattan Project, An Interactive History Home Department of Energy Home Office of History and Heritage Resources Home DOEHome
J.R. Oppenheimer and General Groves
Events People Places Processes Science Resources

Time Periods

1890s-1939:
Atomic Discoveries

1939-1942:
Early
Government Support

1942:
Difficult
Choices

1942-1944:
The Uranium
Path to
the Bomb

1942-1944:
The Plutonium
Path to
the Bomb

1942-1945:
Bringing It All Together

1945:
Dawn of the
Atomic Era

1945-present:
Postscript --
The Nuclear Age


Enrico FermiPILES AND PLUTONIUM
(1939-1942)
Events > Early Government Support, 1939-1942

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 (reactor) experiments already underway at Columbia University.  Building upon theFission chain reaction work performed in 1934 demonstrating the value of moderators in producing slow neutrons, Enrico Fermi thought that a mixture of the right moderator and natural uranium could produce a self-sustaining fission chain reaction.  Fermi and Leo 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.  

60-inch cyclotron at Berkeley's Rad Lab. Ernest Lawrence is second from the left, and Edwin McMillan is on the cyclotron to the right.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."  

Glenn Seaborg adjusts a Geiger-Muller counter.Experiments conducted in early 1941 at the Radiation Laboratory at the University of California, Berkeley, finally completed the link between pile research and bomb construction.  Edwin M. McMillan and Philip H. Abelson had been studying uranium fission fragments produced in a cyclotron there (above).  Their research led to the chemical identification of element 93, neptunium, while research by Glenn T. Seaborg (left) revealed that an isotope of neptunium decayed to yet another transuranium (man-made) element.  In February, Seaborg identified this as element 94, which he later named plutonium.  By May, he had proven that plutonium-239 was 1.7 times more likely than uranium-235 to fission.  This finding made the Fermi-Szilard experiment more important than ever, as it suggested the possibility of producing large amounts of the fissionable plutonium in a uranium pile using plentiful uranium-238, and then separating it chemically.  Surely this would be less expensive and simpler than building isotope-separation plants.  A second, perhaps easier, path to the atomic bomb now seemed possible.

Previous    Next


Sources and notes for this page.

The text for this page was adapted from, and portions were taken directly from the Office of History and Heritage Resources publication: F. G. Gosling, The Manhattan Project: Making the Atomic Bomb (DOE/MA-0001; Washington: History Division, Department of Energy, January 1999), 6-8.  The "chimera" comment is from Laura Fermi, Atoms in the Family: My Life With Enrico Fermi (Chicago: University of Chicago Press, 1954), 164.  The terms "atomic pile" and "nuclear reactor" refer to the same thing.  The term "pile" was more common during early atomic research but gradually was replaced by "reactor" in the later years of the Manhattan Project and afterwards.  In this web site, the phrase "pile (reactor)" is used to refer to early, experimental piles, and "reactor (pile)" is used to refer to later production reactors, which had more elaborate controls and in general more closely resembled post-war reactors.  Much as the term "pile" gradually gave way to "reactor," "atomic" was gradually replaced by "nuclear."  The photograph of Enrico Fermi is courtesy the Department of Energy (via the National Archives).  The fission chain reaction graphic is adapted from a graphic originally produced by the Washington State Department of Health; modifications are original to the Department of Energy's Office of History and Heritage Resources.  The photographs of the cyclotron and of Glenn Seaborg are courtesy the Lawrence Berkeley National Laboratory.

Home | History Office | OpenNet | DOE | Privacy and Security Notices
About this Site | How to Navigate this Site | Note on Sources | Site Map | Contact Us