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BASIC RESEARCH AT LOS ALAMOS (Los Alamos: Laboratory, 1943-1944)
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Bringing It All Together, 1942-1945
The first few months at Los Alamos were
occupied with briefings on nuclear physics for the
technical staff and with planning research priorities and
organizing the laboratory.
Leslie Groves called once again on Warren
Lewis to head a committee, this time to evaluate the Los
Alamos program. The committee's recommendations
resulted in the coordinated effort envisioned by those who
advocated a unified laboratory for bomb research.
Enrico Fermi (left) took control of
critical mass experiments and
standardization of measurement
techniques. Plutonium purification work, begun at
the Met Lab, became high priority at Los
Alamos, and increased attention was paid to
metallurgy. The committee also recommended that an
engineering division be organized to collaborate with
physicists on bomb design and
fabrication. The laboratory was thus organized into
four divisions: theoretical (Hans A. Bethe, right); experimental physics (Robert F. Bacher);
chemistry and metallurgy (Joseph W. Kennedy); and ordnance
(Navy Captain William S. "Deke" Parsons). Like other
Manhattan Project installations, Los Alamos soon began to
expand beyond initial expectations.
As director,
J. Robert Oppenheimer (left) shouldered
burdens both large and small, managing the
numerous mundane matters such as living quarters,
mail censorship, salaries, promotions, and other "quality
of life" issues that were inevitable in an intellectual
pressure-cooker with few social amenities. Oppenheimer
relied on a group of advisers to help him keep the "big
picture" in focus, while a committee made up of Los Alamos
group leaders provided day-to-day communications between
divisions.
Early experiments on both uranium and plutonium provided
welcome results. Uranium emitted
neutrons in less than a billionth of a
second -- just enough time, in the world of nuclear
physics, for an efficient explosion. Emilio
Segrè (right) later provided an additional cushion
with his discovery in December 1943 that, if cosmic rays
were eliminated, the subcritical uranium masses would not
have to be brought together as quickly as previously
thought; nor would the uranium have to be as pure.
Muzzle velocity for the scaled-down artillery piece could
be lower, and the gun could be shorter and lighter.
Segrè's tests on the first samples of plutonium
demonstrated that plutonium emitted even more neutrons
than uranium due to the spontaneous fission of
plutonium-240. Both theory and experimental data now
agreed that a bomb using either element would detonate if
it could be designed and fabricated into the correct size
and shape. But many details remained to be worked
out, including calculations to determine how much
uranium-235 or plutonium would be needed for an explosive
device.
Bacher's experimental physics division patiently
generated the essential
cross section measurements needed to
calculate critical and efficient mass. The same
group utilized particle accelerators to
produce the large numbers of neutrons needed for its cross
section experiments. Bacher's group also compiled
data that helped identify
tamper materials that would most
effectively push neutrons back to the core and enhance the
efficiency of the explosion. Despite Los Alamos's
postwar reputation as a mysterious retreat where brilliant
scientists performed miracles of nuclear physics, much of
the work that led to the atomic bombs was extremely
tedious.
The chemists' job was to purify the uranium-235 and
plutonium, reduce them to metals, and process the
tamper material. Only highly
purified uranium and plutonium would be safe from
predetonation. Fortunately, purification standards
for uranium were relatively modest, and the chemical
division was able to focus its effort on the lesser known
plutonium and make substantial progress on a multi-step
precipitation process by summer 1944. The metallurgy
division had to turn the purified uranium-235 and
plutonium into metal. Here, too, significant
progress was made by summer as the metallurgists adapted a
stationary-bomb technique initially developed at Iowa
State College.
Parsons (right), in charge of ordnance engineering,
directed his staff to design two artillery pieces of
relatively standard specifications except for their
extremely light barrels -- one for a uranium bomb and one
for a plutonium bomb. The guns needed to achieve
high velocities, but they would not have to be durable
since they would only be fired once. Here again
early efforts centered on the more problematic plutonium
weapon, which required a higher velocity due to its higher
risk of predetonation. Two plutonium guns arrived in
March 1944 and were field-tested successfully. In
the same month, two uranium guns were ordered.
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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), 39-40. Click
here for more information on the group photograph
of scientists at Los Alamos. The photograph of
Enrico Fermi is courtesy the
Argonne National Laboratory. The photograph of
Hans Bethe is courtesy the
Los Alamos National Laboratory (LANL). The photograph of
Robert Oppenheimer in front of a
blackboard is reproduced by permission of the J. Robert
Oppenheimer Memorial Committee. The photograph of
Emilio Segrè is courtesy the
Lawrence Berkeley National Laboratory. The photographs of the
neutron cross section experiment and of
the blocks of uranium are courtesy
LANL; they are reprinted in Rachel Fermi and Esther
Samra,
Picturing the Bomb: Photographs from the Secret World
of the Manhattan Project (New York: Harry N. Abrams, Inc., Publishers, 1995), 99
and 109. The photograph of Deke Parsons is
reproduced from
Los Alamos Scientific Laboratory,
Los Alamos: Beginning of an Era, 1943-1945
(Los Alamos: Public Relations Office, Los Alamos
Scientific Laboratory, ca. 1967-1971), 59.
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