Manhattan Project





The Manhattan Project was an effort during World War II in the United States
to develop the first nuclear weapon. It was directed by American physicist
Dr. Julius Robert Oppenheimer.

The industrial problem was centered around the production of sufficient
fissile material, of sufficient purity. This effort was two-fold, and is
represented in the two bombs that were dropped.

The Hiroshima bomb, Little Boy, was 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. The bulk of this separation work was done at Oak Ridge.

The Nagasaki bomb, Fat Man, in contrast, consisted primarily of
plutonium-239, a synthetic element which could be induced to
supercriticality only by implosion. 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. These 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 completely destroyed 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.

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.

US President Franklin D. Roosevelt was presented with a letter signed by
Albert Einstein (transcribed by Leo Szilard) on October 11, 1939, which
urged the United States to rapidly develop an atomic bomb program. The
president agreed. The Navy awarded Columbia University the first Atomic
Energy funding of $6,000, which grew into the Manhattan Project under
Oppenheimer and Enrico Fermi's work.

Scientists in Germany discovered nuclear fission in late 1938. Refugee
scientists Leo Szilard, Edward Teller and Eugene Wigner 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. In
response to the warning, Roosevelt ordered increased research in nuclear physics.

Under the auspices of National Bureau of Standards chief Lyman Briggs, small
research programs had begun 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 summer of 1941, when
word came from Britain of calculations by Otto Frisch and Fritz Peierls that
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. No sooner was this decision made than the Japanese bombed Pearl
Harbor on December 7th, 1941. The war had begun 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 study the feasibility of a
nuclear weapon.

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,
Richard Tolman and Emil Konopinski 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" might be constructed. This
concept was based on studies made by Bethe before the war of energy
production in stars. 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 summer conferences, the results of which were later summarized by Serber
in "The Los Alamos Primer" (LA-1), provided the 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.

With the prospect of a long war, a group of theorists under the direction of
J. Robert Oppenheimer met at Berkeley during the summer of 1942 to develop
preliminary plans for designing and building a nuclear weapon. Crucial
questions remained, however, about the properties of fast neutrons. John
Manley, a physicist at the University of Chicago Metallurgical Laboratory,
was assigned to help Oppenheimer find answers to these questions by
coordinating several experimental physics groups scattered across the country.

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.

...

A similar effort was undertaken in the USSR headed by Igor Kurchatov. Token
efforts in Germany, headed by Werner Heisenberg, and in Japan, were also
undertaken.

With the cryptology and cryptographic efforts centered at Bletchley Park and
Arlington Hall 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.