The Manhattan
Project
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What was the Manhattan Project?
The
Manhattan Project, or more fully, the
Manhattan Engineering
District Project, was an effort during World War II to develop the
first nuclear weapons by
the United States with assistance from the United Kingdom and Canada.
Its research was directed by American physicist J. Robert Oppenheimer,
and overall by General Leslie R. Groves after it became clear that
success was possible and that Germany was also investigating that
possibility.
Though it
involved over thirty different research and production sites,
the Manhattan Project was largely carried out in three secret
scientific cities that were established by power of eminent domain:
Hanford, Washington, Los Alamos, New Mexico, and Oak Ridge, Tennessee.
Some families in Tennessee were given two weeks notice to vacate the
family farm lands they had had for generations. The Los Alamos lab was
built on a mesa that previously hosted the Los Alamos Ranch School, a
private residential school that featured the outdoors and horses.
(Famous almuni include William Burroughs.) The existence of these
cities was offically secret until several years after the war.
The industrial
problem centered on the production of sufficient fissile
material, of sufficient purity. This effort was two-fold, and is
represented in the single test and two bombs that were dropped.
The Hiroshima
bomb, Little Boy, was based on uranium-235, a minor
isotope of uranium that has to be physically separated from more
prevalent uranium-238, which is not suitable for use in an explosive
device. The separation was effected mostly by gaseous diffusion of
uranium hexafluoride (UF6), but also by other techniques, such as a
series of centrifuges, and the calutron method, using the cyclotron
principle of magnetic separation. The bulk of this separation work was
done at Oak Ridge.
The device used
in the first and only test and the Nagasaki bomb, Fat
Man, in contrast, consisted primarily of plutonium-239, a synthetic
element which even in pure form too readily undergoes fission to be
used in a gun type device as can Uranium 235. The design of an
implosion device was at the center of the efforts by physicists at
Los
Alamos during the Project. The property of uranium-238 which makes it
less suitable directly for use in an atomic bomb is used in the
production of plutonium -- with sufficiently slow neutrons,
uranium-238
will absorb neutrons and transmute into plutonium-239. The production
and purification of plutonium was at the center of wartime, and
post-war, efforts at the Hanford Site, using techniques developed in
part by Glenn Seaborg.
The choice of
civilian instead of military targets has often been
criticized. However, the U.S. already had a policy of massive
incendiary attacks against civilian targets in Japan. They dropped
20%
explosives, to break up wooden structures and provide fuel, and then
dropped 80% (by weight) small incendiary bombs to set the cities on
fire. The resulting raids devastated many Japanese cities, including
Tokyo, even before atomic weapons were deployed. The allies performed
such attacks because Japanese industry was extremely dispersed among
civilian targets (with many tiny family-owned factories operating in
the midst of civilian housing), and in order to break the will of the
Japanese population to back the war.
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History
In the
years between World War I and World War
II, the United States
had risen to pre-eminence in nuclear physics, driven by the work of
recent immigrants and local physicists. These scientists had developed
the basic tools of nuclear physics -- cyclotrons and other particle
accelerators - and many new substances using these tools, including
radioisotopes like carbon-14.
Early
Ideas on
Nuclear Energy
Enrico Fermi
recalled the beginning of the project in a speech given in
1954 when he retired as President of the APS.
I remember very
vividly the first month, January 1939, that I started
working at the Pupin Laboratories because things began happening very
fast. In that period, Niels Bohr was on a lecture engagement in
Princeton and I remember one afternoon Willis Lamb came back very
excited and said that Bohr had leaked out great news. The great news
that had leaked out was the discovery of fission and at least the
outline of its interpretation. Then, somewhat later that same month,
there was a meeting in Washington where the possible importance of the
newly discovered phenomenon of fission was first discussed in
semi-jocular earnest as a possible source of nuclear power.
Nuclear
scientists Leó Szilárd, Edward Teller and Eugene
Wigner (all Hungarian Jewish refugees from Hitler's Europe) believed
that the energy released in nuclear fission might be used in bombs by
the Germans. They persuaded Albert Einstein, America's most famous
physicist, to warn President Franklin Roosevelt of this danger in an
August 2, 1939 letter which Szilárd drafted [1] . In response to
the warning, Roosevelt encouraged further research into the national
security implications of nuclear fission. The Navy awarded Columbia
University the first Atomic Energy funding of $6,000,000 which grew
into the Manhattan Project under J. Robert Oppenheimer, and Enrico
Fermi's work.
Roosevelt created
an ad hoc Uranium Committee under the chairmanship of
National Bureau of Standards chief Lyman Briggs. It began small
research programs in 1939 at the Naval Research Laboratory in
Washington, where physicist Philip Abelson explored uranium isotope
separation. At Columbia University Italian nuclear physicist Enrico
Fermi built prototype nuclear reactors using various configurations of
graphite and uranium.
Vannevar Bush,
director of the Carnegie Institution of Washington,
organized the National Defense Research Committee in 1940 to mobilize
the United States' scientific resources in support of the war effort.
New laboratories
were created, including the Radiation Laboratory at
the Massachusetts Institute of Technology, which aided the development
of radar, and the Underwater Sound Laboratory at San Diego, which
developed sonar.
The National
Defense Research Council (NDRC) also took over the uranium
project, as Briggs' program in nuclear physics was called. In 1940,
Bush and Roosevelt created the Office of Scientific Research and
Development to expand these efforts.
The uranium
project had not made much progress by the spring of 1941,
when word came from Britain of calculations by Otto Frisch and Fritz
Peierls. The report, prepared by the so-called MAUD Committee, itself a
sub-committee of the Committee for the Scientific Survey of Air Warfare
under G.P. Thomson, professor of physics at Imperial College, London,
showed that a very small amount of the fissionable isotope of uranium,
U-235 - could produce an explosion equivalent to that of several
thousand tons of TNT.
The National
Academy of Sciences proposed an all-out effort to build nuclear weapons.
Bush created a special committee, the S-1 Committee, to guide the
effort. This happened to be on the day before the Japanese attack on
Pearl Harbor, which was on December 7th, 1941, and meant the start of
the war for the United States.
At the University
of Chicago Metallurgical Laboratory, the University
of California Radiation Laboratory and Columbia University's physics
department, efforts to prepare the nuclear materials for a weapon were
accelerated. Uranium 235 had to be separated from uranium ore and
plutonium made by neutron bombardment of natural uranium. Beginning in
1942, huge plants were built at Oak Ridge (Site X) in Tennessee and
Hanford (Site W) outside of Richland, Washington, to produce these
materials.
When the United
States entered World War II in December 1941, several
projects were under way to investigate the separation of fissionable
uranium 235 from uranium 238, the manufacture of plutonium, and the
feasibility of nuclear piles and explosions.
Physicist and
Nobel laureate Arthur Holly Compton organized the
Metallurgical Laboratory at the University of Chicago in early 1942 to
study plutonium and fission piles. Compton asked theoretical physicist
J. Robert Oppenheimer of the University of California to take over
research on fast neutron calculations, essential to the feasibility of
a nuclear weapon.
John Manley, a physicist at the University of Chicago Metallurgical
Laboratory, was assigned to help Oppenheimer find answers by
coordinating and contacting several experimental physics groups
scattered across the country.
In the spring of
1942, Oppenheimer and Robert Serber of the University
of Illinois, worked on the problems of neutron diffusion (how neutrons
moved in the chain reaction) and hydrodynamics (how the explosion
produced by the chain reaction might behave).
To review this
work and the general theory of fission reactions,
Oppenheimer convened a summer study at the University of California,
Berkeley in June 1942. Theorists Hans Bethe, John Van Vleck, Edward
Teller, Felix Bloch, Emil Konopinski, Robert Serber, Stanley S.
Frankel, and Eldred C. Nelson (the latter three all former students of
Oppenheimer) concluded that a fission bomb was feasible. The scientists
suggested that such a reaction could be initiated by assembling a
critical mass - an amount of nuclear explosive adequate to sustain it -
either by firing two subcritical masses of plutonium or uranium 235
together or by imploding (crushing) a hollow sphere made of these
materials with a blanket of high explosives. Until the numbers were
better known, this was all that could be done.
Teller saw
another possibility: By surrounding a fission bomb with
deuterium and tritium, a much more powerful "superbomb" (which he
called simply, the "Super") might be constructed. This concept was
based on studies of energy production in stars made by Bethe before the
war. When the detonation wave from the fission bomb moved through the
mixture of deuterium and tritium nuclei, they would fuse together to
produce much more energy than fission, in the process of nuclear
fusion, just as elements fused in the sun produce light and heat.
Bethe was
skeptical, and as Teller pushed hard for his "superbomb" and
proposed scheme after scheme, Bethe refuted each one. When Teller
raised the possibility that an atomic bomb might ignite the atmosphere,
however, he kindled a worry that was not entirely extinguished until
the Trinity test, even though Bethe showed, theoretically, that it
couldn't happen. (The "super", or thermonuclear device, was produced
several years after the war.)
The summer
conferences, the results of which were later summarized by
Serber in "The Los Alamos Primer" (LA-1), provided the original
theoretical basis for the design of the atomic bomb, which was to
become the principal task at Los Alamos during the war, and the idea of
the H-bomb, which was to haunt the Laboratory in the postwar era.
Seldom has a physics summer school been as portentous for the future of
mankind.
The measurements
of the interactions of fast neutrons with the
materials in a bomb are essential because the number of neutrons
produced in the fission of uranium and plutonium must be known, and
because the substance surrounding the nuclear material must have the
ability to reflect, or scatter, neutrons back into the chain reaction
before it is blown apart in order to increase the energy produced.
Therefore, the neutron scattering properties of materials had to be
measured to find the best reflectors.
Estimating the
explosive power required knowledge of many other nuclear
properties, including the cross section (a measure of the probability
of an encounter between particles that result in a specified effect)
for nuclear processes of neutrons in uranium and other elements. Fast
neutrons could only be produced in particle accelerators, which were
still relatively uncommon instruments in physics departments in 1942.
The need for
better coordination was clear. By September 1942, the
difficulties involved with conducting preliminary studies on nuclear weapons at
universities scattered throughout the country indicated the need for a
laboratory dedicated solely to that purpose. The need for it, however,
was overshadowed by the demand for plants to produce uranium-235 and
plutonium - the fissionable materials that would provide the nuclear explosives.
Vannevar Bush,
the head of the civilian Office of Scientific Research
and Development (OSRD), asked President Franklin Roosevelt to assign
the large-scale operations connected with the quickly growing nuclear
weapons project to the military. Roosevelt chose the Army to work with
the OSRD in building production plants. The Army Corps of Engineers
selected Col. James Marshall to oversee the construction of factories
to separate uranium isotopes and manufacture plutonium for the bomb.
OSRD scientists
had explored several methods to produce plutonium and
separate uranium-235 from uranium, but none of the processes was ready
for production - only microscopic amounts had been prepared.
Only one method -
electromagnetic separation, which had been developed
by Ernest Lawrence at the University of California Radiation Laboratory
at the University of California, Berkeley - seemed promising for
large-scale production. But scientists could not stop studying other
potential methods of producing fissionable materials, because it was so
expensive and because it was unlikely that it alone could produce
enough material before the war was over.
Marshall and his
deputy, Col. Kenneth Nichols, had to struggle to
understand both the processes and the scientists with whom they had to
work. Thrust suddenly into the new field of nuclear physics, they felt
unable to distinguish between technical and personal preferences.
Although they decided that a site near Knoxville, Tenn., would be
suitable for the first production plant, they didn't know how large the
site had to be and so put off its acquisition. There were other
problems, too.
Because of its
experimental nature, the nuclear weapons
work could not compete with the Army's more-urgent tasks for
top-priority ratings. The selection of scientists' work and
production-plant construction often were delayed by Marshall's
inability to get the critical materials, such as steel, that also were
needed in other military productions.
Even selecting a
name for the new Army project was difficult. The title
chosen by Gen. Brehon Somervell, "Development of Substitute Materials,"
was objectionable because it seemed to reveal too much.
The Manhattan
District
In the
summer of 1942, Col. Leslie Groves was
deputy to the chief of
construction for the Army Corps of Engineers and had overseen
construction of the Pentagon, the world's largest office building.
Hoping for an overseas command, Groves objected when Somervell
appointed him to take charge of the weapons project. His objections
were overruled and Groves resigned himself to leading a project he
thought had little chance of succeeding.
The first thing
he did was rechristen the project The Manhattan
District. The name evolved from the Corps of Engineers practice of
naming districts after its headquarters' city (Marshall's headquarters
were in New York City). At the same time, Groves was promoted to
brigadier general, which gave him the rank thought necessary to deal
with the senior scientists in the project.
Within a week of
his appointment, Groves had solved the Manhattan
Project's most urgent problems. This forceful and effective manner was
soon to become all too familiar to the atomic scientists.
The first major
scientific hurdle of the project was solved on December
2, 1942 below the bleachers of Stagg Field at the University of
Chicago. Then and there a team led by Enrico Fermi initiated the first
self-sustaining nuclear chain reaction. A coded message, "The Italian
navigator has landed in the new world" was then sent to President
Roosevelt to tell him that the experiment was a success. For more
details see the history section of the Los Alamos National Laboratory
article.
A similar effort
was undertaken in the USSR headed by Igor Kurchatov
(with a specific difference in that some of Kurchatov's World War II
investigations came secondhand from Manhattan Project countries, thanks
to spies, including one on the scientific team at Los Alamos, Klaus
Fuchs). Token efforts in Germany, (headed by Werner Heisenberg,) and in
Japan, were also undertaken during the war.
Together with the
cryptographic efforts centered at Bletchley Park in
England, Arlington Hall and the Naval Communications Annex (both in
commandeered private girls' schools in Washington DC), and the
development of microwave radar at MIT's Radiation Lab, the Manhattan
Project represents one of few massive, secret, and outstandingly
successful technological efforts spawned by the conflict of World War
II.
http://en.wikipedia.org/wiki/Manhattan_project
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