PILES AND PLUTONIUM
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
obtain four tons of graphite and fifty tons of uranium
recommendation led to the first outlay of government funds -- $6,000 in
1940 -- and reflected the importance attached to the Fermi-Szilard pile
(reactor) experiments already underway at Columbia
University. Building upon the
work performed in 1934 demonstrating the value of moderators in
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
reaction. A pile containing a large amount of natural uranium
produce enough secondary neutrons to keep a reaction going.
was, however, a large theoretical gap between building a
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
uranium-235 or substantial enrichment of natural uranium with
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
proof that we were not pursuing a chimera."
conducted in early 1941 at the Radiation Laboratory at the University of California, Berkeley,
the link between pile research and bomb construction. Edwin M.
and Philip H. Abelson had been studying uranium fission fragments
produced in a cyclotron there
(above). Their research led to the chemical identification of
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
which he later named plutonium. By May, he had proven that
was 1.7 times more likely than uranium-235 to fission. This
the Fermi-Szilard experiment more important than ever, as it suggested
possibility of producing large amounts of the fissionable plutonium in
pile using plentiful uranium-238, and then separating it
Surely this would be less expensive and simpler than building
plants. A second, perhaps easier, path to the atomic bomb now
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.
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