The
Manhattan Project was the codename for a project
conducted during World War II.The
project was led by the United States
, and included participation from the United Kingdom
and Canada
.
Formally designated as the
Manhattan Engineer District
(MED), it refers specifically to the period of the project
from 1942–1946 under the control of the
U.S. Army Corps of
Engineers, under the administration of
General Leslie R.
Groves. The scientific research was
directed by American
physicist J. Robert
Oppenheimer.
The project's roots lay in scientists' fears since the 1930s that
Nazi Germany was also
investigating nuclear weapons of
its own. Born out of a small research program in 1939, the
Manhattan Project eventually employed more than 130,000 people and
cost nearly
US$2
billion ($ billion in current value).
It resulted in the creation of multiple production and research
sites that operated in secret.
Project research took place at over thirty sites across the United
States, Canada, and the United Kingdom.
The three primary
research and production sites of the project were the
plutonium-production facility at what is now the Hanford Site
, the uranium-enrichment
facilities at Oak Ridge, Tennessee
, and the weapons research and design laboratory now
known as Los Alamos National Laboratory
. The MED maintained control over U.S.
weapons production until the formation of the
Atomic Energy
Commission in January 1947.
Discovery of nuclear fission
The first decades of the 20th century led to radical changes in the
understanding of the
physics of the atom,
including the discovery of the
nucleus, the idea of
radiation, and the fact that the splitting of
atomic nuclei in a chain reaction could lead to massive release of
energy (
nuclear fission).
By 1933 the atom was thought to consist of a small, dense nucleus
containing most of the atom's
mass in
the form of
protons and
neutrons and surrounded by a shell of
electrons. Study on the phenomenon of
radioactivity began in 1896 with the discovery
of uranium ores by
Henri Becquerel
and was followed by the work of
Pierre
and
Marie Curie on
radium. Their research seemed to promise that atoms,
previously thought to be ultimately stable and indivisible,
actually had the potential of containing and releasing immense
amounts of energy. In 1919
Ernest
Rutherford achieved the first artificial nuclear
disintegrations by bombarding
nitrogen with
alpha particles emitted from a
radioactive source, thus becoming the first person in history to
intentionally "split the atom". It became clear from the Curies'
work that there was a tremendous amount of energy locked up in
radioactive decay—far more than
chemistry could account for. The source of this energy, as given by
Albert Einstein's famous
E = mc2
formula, was that some of the mass in the nucleus was being
converted to energy, and that a very small amount of mass could
produce an enormous amount of energy. But even in the early 1930s
such illustrious physicists as Einstein and
Ernest Rutherford could see no way of
artificially releasing that energy any faster than nature naturally
allowed it to leave. "Radium engines" in the 1930s were the stuff
of science fiction, such as was being written at the time by
Edgar Rice Burroughs.
H.G. Wells included
air-dropped "atomic bombs" in his 1914
novel
The World Set Free.
Though Wells' "atomic bombs" bore little resemblance to actual
nuclear weapons—they were simply regular bombs that never stopped
exploding—
Leó Szilárd later
commented that this story influenced his later research into this
subject.
Progress in controlling and understanding nuclear fission
accelerated in the 1930s when further manipulation of the nuclei of
atoms became possible. In 1932 Sir
John
Cockcroft and
Ernest Walton were
first to "split the atom" (cause a nuclear reaction) by using
artificially accelerated particles. In 1934
Irène and
Frédéric Joliot-Curie
discovered that artificial
radioactivity could be induced in stable
elements by bombarding them with alpha particles. The same year
Enrico Fermi reported similar results
when bombarding uranium with
neutrons
(discovered in 1932), but he did not immediately appreciate the
consequences of his results.
In
December 1938 Germans
Otto Hahn and Fritz
Strassmann published experimental results about bombarding
uranium with neutrons. They showed that it produced an
isotope of
barium.
Shortly after, their Austrian co-worker
Lise Meitner (a political refugee in Sweden at
the time) and her nephew
Otto Robert
Frisch correctly interpreted the results as the splitting of
the uranium nucleus after the absorption of a neutron—nuclear
fission, which released a large amount of
energy and additional neutrons. A direct
experimental evidence of the nuclear fission was performed by
Frisch, following a fundamental idea suggested to him by
George Placzek.
That such mechanisms might have implications for civilian power or
military weapons was perceived by numerous scientists in many
countries, around the same time. While these developments in
science were occurring, many political changes were happening in
Europe.
Adolf Hitler was appointed
chancellor of Germany in January 1933. Within three months of
taking power, the Nazis passed the
Law
for the Restoration of the Professional Civil Service, which
caused all
Jewish civil servants, including
many physicists, to be fired from their posts. Consequently many
European physicists who later made key discoveries went into exile
in the United Kingdom and the United States. After
Nazi Germany invaded Poland in 1939 and
World War II began, many scientists in
the United States and the United Kingdom became anxious about what
Germany might do with
nuclear
technology.
Albert Einstein in
particular wrote several letters to
Franklin Roosevelt urging him to
establish nuclear capability before the Germans. These letters,
especially one called the
Einstein–Szilárd letter
(dated August 2, 1939, but not personally received by Roosevelt
until October 1939), brought American government attention and
support to nuclear research.
Etymology
It is widely believed that the Manhattan Project's name is simply a
code name. In fact, the project was named after the location where
many of its early operations were conducted - Manhattan. According
to historian
Robert Norris, Manhattan
contained at least ten sites where the project's work was being
conducted—the island was ideal because of its port facilities, the
military presence, a large available work force, a population of
expatriate European physicists, and
Columbia University, a center of early
nuclear research.
Uranium Committee (1939–1941)
In 1939, President
Franklin
Roosevelt called on
Lyman Briggs of
the
National Bureau of
Standards to head "
The Uranium
Committee" as a result of the
Einstein–Szilárd
letter. Even though Roosevelt had sanctioned the project,
progress was slow and was not directed exclusively towards military
applications.
Meanwhile,
in the United
Kingdom
, Otto Frisch and
Rudolf Peierls made a breakthrough by
discovering the fissile properties of uranium-235. A British
committee, the
MAUD Committee,
concluded that:
(i) The committee considers that the scheme for a
uranium bomb is practicable and likely to lead to decisive results
in the war
(ii) It recommends that this work continue on the highest priority
and on the increasing scale necessary to obtain the weapon in the
shortest possible time
(iii) That the present collaboration with America should be
continued and extended especially in the region of experimental
work
Their reports were sent to Briggs, but were ignored. One of the
members of the MAUD Committee, Mark
Oliphant, flew to the United States in late August 1941 to find
out why the U.S. was ignoring the MAUD Committee's findings. He
reported that "this inarticulate and unimpressive man (Briggs) had
put the reports in his safe and had not shown them to members of
his committee."
Oliphant then met with the whole Uranium Committee and other
physicists to galvanize the USA into action. As a result, in
December 1941 Vannevar Bush created
the larger and more powerful Office of
Scientific Research and Development—which was empowered to
engage in large engineering projects in addition to research—and
became its director.
Acceleration of the Project
Now that the bomb project was under the OSRD, the
project leaders began to accelerate the work. Arthur Compton organized the University of
Chicago Metallurgical Laboratory in early 1942 to study
plutonium and fission piles (primitive nuclear reactors), and asked theoretical
physicist J. Robert Oppenheimer of the University of
California, Berkeley
to take over research on fast neutron calculations—key to
calculations about critical mass and weapon detonation—from
Gregory Breit, who had quit because of
concerns over lax operational
security. John Manley, a
physicist at the Metallurgical Laboratory, was assigned to help
Oppenheimer find answers by coordinating and contacting several
experimental physics groups scattered across the country.
During 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) quickly confirmed that a fission bomb was
feasible.
There were still many unknown factors in the development of a
nuclear bomb, however, even though it was considered to be
theoretically possible. The properties of pure uranium-235 were
still relatively unknown, as were the properties of plutonium, a
new element which had only been discovered in February 1941 by
Glenn Seaborg and his team. Plutonium
was the product of uranium-238 absorbing a neutron which had been
emitted from a fissioning uranium-235 atom, and was thus able to be
created in a nuclear reactor. But at this point no reactor had yet
been built, so while plutonium was being pursued as an additional
fissile substance, it was not yet to be relied upon. Only microgram
quantities of plutonium existed at the time (produced from neutrons
derived from reaction started in a cyclotron).
The scientists at the Berkeley conference determined that there
were many possible ways of arranging the fissile material into a
critical mass, the simplest being the
shooting of a "cylindrical plug" into a sphere of "active material"
with a "tamper"—dense material which would focus neutrons inward
and keep the reacting mass together to increase its efficiency
(this model "avoids fancy shapes", Serber would later write). They
also explored designs involving spheroids,
a primitive form of "implosion" (suggested by Richard C. Tolman), and explored the speculative
possibility of "autocatalytic methods"
which would increase the efficiency of the bomb as it
exploded.
Considering the idea of the fission bomb theoretically settled—at
least until more experimental data was available—the conference
then turned in a different direction. Hungarian physicist Edward
"Ede" Teller pushed for discussion on an even more powerful bomb:
the "Super", which would use the explosive force of a detonating
fission bomb to ignite a fusion
reaction in deuterium and tritium. Such a bomb, they calculcated, would have
an explosive yield of 10 megatons, hundreds of times more powerful
than the atomic bomb. The concept was based on studies of energy
production in stars made by Hans Bethe before the war, and
suggested as a possibility to Teller by Enrico Fermi not long before the conference.
When the detonation wave from the fission bomb moved through the
mixture of deuterium and tritium nuclei, these would fuse together to produce
much more energy than fission could. But Bethe was skeptical. As
Teller pushed hard for his "superbomb"—now usually referred to as a
"hydrogen bomb"—proposing scheme after scheme, Bethe refused each
one. The fusion idea had to be put aside in order to concentrate on
actually producing fission bombs.
Teller also raised the speculative possibility that an atomic bomb
might "ignite" the atmosphere because of a hypothetical fusion
reaction of nitrogen nuclei. Bethe calculated, according to Serber,
that it could not happen. However, a report co-authored by Teller
showed that ignition of the atmosphere was not impossible, just
unlikely. In Serber's account, Oppenheimer mentioned it to Arthur
Compton, who "didn't have enough sense to shut up about it. It
somehow got into a document that went to Washington" which led to
the question being "never laid to rest".
The conferences in June 1942 provided the detailed theoretical
basis for the design of the atomic bomb, and convinced Oppenheimer
of the benefits of having a single centralized laboratory to manage
the research for the bomb project rather than having specialists
spread out at different sites across the United States.
Project sites
Though it
involved over thirty different research and production sites, the
Manhattan Project was largely carried out at four secret
laboratories that were established by power of eminent domain in four cities: Los Alamos,
New Mexico
; Oak Ridge, Tennessee
; Richland, Washington
; Chalk River, Ontario, Canada
. The Tennessee site was chosen because of
the vast quantities of cheap hydroelectric power already available
there (from the Tennessee
Valley Authority) to power uranium enrichment processes.
The
Hanford
Site
near Richland, Washington, was chosen for its
location near the Columbia River, a
river that could supply water to cool the reactors which would
produce the plutonium. The Canadian site, Chalk River,
Ontario, was chosen for its proximity to the industrial
manufacturing of Ontario and Quebec, located on a rail head,
adjacent to a large military base, Camp Petawawa, located on the
Ottawa River it had access to abundant water. All the sites were
suitably far from coastlines and therefore less vulnerable to
possible enemy attack from Germany or Japan.
The
Los Alamos
National Laboratory
was built on a mesa that previously hosted the
Los Alamos Ranch School, a
private school for teenage boys. The site was chosen
primarily for its remoteness. Oppenheimer had known of it from his
horse-riding near his ranch in New Mexico, and he showed it as a
possible site to the government representatives, who promptly
bought it for $440,000. In addition to being the main "think-tank",
Los Alamos was responsible for final assembly of the bombs, mainly from materials and components produced by
other sites. Manufacturing at Los Alamos included casings,
explosive lenses, and fabrication of fissile materials into
bomb cores.
Oak Ridge facilities covered more than 60,000 acres (243 km²)
of several former farm communities in the Tennessee Valley area. Some Tennessee
families were given two weeks' notice to vacate family farms that
had been their homes for generations. So secret was the site during
World War II that the state governor was unaware that Oak Ridge
(which was to become the fifth largest city in the state) was being
built. At one point Oak Ridge plants were consuming 1/6th of the
electrical power produced in the U.S., more than New York City. Oak
Ridge mainly produced uranium-235.
Chalk River, was established to house the allied effort that was
going on at McGill University, in Montreal. Since the site was 120
miles west of Ottawa, a new community was also built at Deep River,
Ontario to be the home of the project team members. Both were
established in 1944, with scientists, engineers, trades from
Canada, the United Kingdom, New Zealand, Australia, France, Norway,
etc. providing their contribution to the war effort.
The
Hanford Site, which grew to almost 1,000 square miles
(2,600 km²), took over irrigated farm land, fruit orchards, a railroad, and two farming communities, Hanford
and White Bluffs
, in a highly populated area where three cities
converge called the Tri Cities, (Kennewick, Pasco, and
Richland. WA),adjacent to the Columbia River. Hanford hosted nuclear
reactors cooled by the river and was the
plutonium production center.
The existence of these sites and the secret cities of Los Alamos,
Oak Ridge, Richland, and Chalk River were not made public until the
announcement of the Hiroshima explosion, and the sites remained
secret until after the end of WWII.
The
project originally was headquartered at 270 Broadway
in Manhattan
. Other offices were scattered throughout the
city, including the New York Friars' Club
building. The Broadway headquarters lasted
little more than a year before it was moved in 1943, although many
of the other offices in Manhattan remained.

A selection of U.S. sites important to
the Manhattan Project.
Major Manhattan Project sites and subdivisions included:
- Site
W
(Hanford, Washington
): a plutonium production facility (now Hanford Site
)
- Site
X
(Oak Ridge, Tennessee
): enriched uranium production and plutonium
production research (now Oak Ridge National Laboratory
) Site X also included:
- X-10 Graphite Reactor
: graphite reactor research pilot plant (on the site
of what is now Oak Ridge National Laboratory)
- Y-12
: electromagnetic separation uranium enrichment
plant
- K-25
: gaseous
diffusion uranium enrichment plant
- S-50: thermal diffusion
uranium enrichment plant
- Site
Y
(Los Alamos, New Mexico
): a bomb research laboratory (now Los Alamos
National Laboratory
)
- Metallurgical Laboratory (Chicago,
Illinois
): reactor development (now Argonne
National Laboratory
)
- Project
Alberta (Wendover,
Utah
and Tinian
):
preparations for the combat delivery of the bombs
- Project Ames
(Ames,
Iowa
): production of raw uranium metal (now Ames
Laboratory
)
- Dayton Project
(Dayton,
Ohio
): research and development of polonium refinement
and industrial production of polonium for atomic bomb
triggers
- Project Camel
(Inyokern,
California
): high explosives research and non-nuclear
engineering for the Fat
Man
bomb
- Project Trinity
(Alamogordo, New Mexico
): preparations for the testing of the first atomic
bomb
- Radiation
Laboratory
(Berkeley, California
): electromagnetic separation enrichment research
(now Lawrence Berkeley National
Laboratory
)
- Project '9' (Trail,
British Columbia
): heavy water (deuterium) production.
Need for coordination
The measurements of the interactions of fast neutrons with the materials in a bomb were
essential; because the scientists needed to know the number of
neutrons produced in the fission of uranium and plutonium, and
because the substance surrounding the nuclear material needed the
ability to reflect, or scatter,
neutrons back into the chain reaction before it was blown
apart—this 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 1942.
The need for better coordination was clear. By September 1942, the
difficulties in conducting studies on nuclear weapons at
universities scattered throughout the country indicated the need
for a laboratory dedicated solely to that purpose. A greater need
was the construction of industrial plants to produce uranium-235
and plutonium—the fissionable materials to be used in the
weapons.
Vannevar Bush, the head of the
civilian Office of
Scientific Research and Development (OSRD), asked President
Roosevelt to assign the operations connected with the 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.
Marshall and his deputy, Col. Kenneth
Nichols, struggled to understand the proposed processes and the
scientists with whom they had to work. Thrust 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,
Tennessee
, would be suitable for the first production plant,
they did not know how large the site needed to be, and thus delayed
its acquisition.
Because of its experimental nature, the nuclear weapons work could
not compete for priority with the Army's more urgent tasks. The
scientists' construction of the work and production plants were
often delayed by Marshall's inability to obtain critical
materials—such as steel—needed in other
military projects.
Even selecting a name for the project was difficult. The title
chosen by Gen. Brehon B.
Somervell, "Development of
Substitute Materials," was objectionable because it seemed to
reveal too much.
Manhattan Engineer District
Vannevar Bush became dissatisfied with Col. James Marshall's
failure to get the project moving forward expeditiously and made
this known to Secretary of War Stimson and Army Chief of Staff
George Marshall. Marshall then directed General Somervell to
replace Col. Marshall with a more energetic officer as director.
In the
summer of 1942 , Col. Leslie Groves
was deputy to the chief of construction for the Army Corps of
Engineers and had overseen the very rapid construction of the Pentagon
, the world's largest office building. He was
widely respected as an intelligent, hard driving, though brusque
officer who got things done in a hurry. Hoping for an overseas
command, Groves vigorously objected when Somervell appointed him to
the weapons project. His objections were overruled, and Groves
resigned himself to leading a project he thought had little chance
of success. Groves appointed Oppenheimer as the project's
scientific director, to the surprise of many. (Oppenheimer's
radical political views were thought to pose security problems).
However, Groves was convinced Oppenheimer was a genius who could
talk about and understand nearly anything, and he was convinced
such a man was needed for a project such as the one being
proposed.
Groves renamed the project The Manhattan Engineer
District. The name evolved from the Corps of Engineers
practice of naming districts after its headquarters' city
(Marshall's headquarters were at 270 Broadway
in New York City). At that time, Groves was
promoted to brigadier
general, giving him the rank necessary to deal with senior
people whose cooperation was required, or whose own projects were
hampered by Groves' top-priority project.
Within a week of his appointment, Groves had solved the Manhattan
Project's most urgent problems. His 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, beneath the bleachers of Stagg Field
at the University of Chicago, where a team led by
Enrico Fermi, for whom Fermilab
is named, initiated the first artificial self
sustaining nuclear chain reaction in an experimental nuclear reactor named Chicago
Pile-1
. A coded phone call from Compton saying, "The
Italian navigator [referring to Fermi] has
landed in the new world, the natives are friendly" to Conant in
Washington,
D.C.
, brought news of the experiment's
success.
Uranium bomb

A gun-type nuclear bomb.
The
Hiroshima bomb, Little Boy
, was made from uranium-235, a rare isotope of uranium that has to be physically separated from the more
plentiful uranium-238 isotope, which is not suitable for use in an
explosive device. Since U-235 makes up only 0.7% of raw
uranium and is chemically identical to the 99.3% of U-238, various
physical methods were considered for separation. Most of the
uranium enrichment work was
performed at Oak Ridge.
One
method of separating uranium 235 from raw uranium ore was devised
by Franz Simon and Nicholas Kurti, at Oxford
University
. Their method using gaseous diffusion was scaled up in a
large separation plant
at Oak Ridge, using uranium hexafluoride (UF6) gas as the
process fluid. During the war this method was important
primarily for producing partly enriched material to feed the
electromagnetic separation process undertaken in calutrons (see
below).
Another
method—electromagnetic isotope
separation—was developed by Ernest
Lawrence at the University of
California Radiation Laboratory at the University of
California, Berkeley
. This method was implemented in Oak Ridge at
the Y-12
Plant
, employing devices known as calutrons, which were effectively mass spectrometers. Copper was originally intended for electromagnet
coils, but there was an insufficient amount available due to war
shortages. The project engineers were forced to borrow
silver from the U.S.
Treasury
. A total of 70,000,000 pounds of silver from
the U.S. Treasury reserves was used for coils, and was returned
after the project ended. Initially the method seemed promising for
large scale production but was expensive and produced insufficient
material and was later abandoned after the war.
Other techniques were also tried, such as thermal diffusion and the
use of high-speed centrifuges. Thermal diffusion was not used to
produce highly-enriched uranium, but was used during the war in the
S-50 facility to begin
enrichment of the uranium, and its product was passed as the feed
into the other facilities.
The uranium bomb was a gun-type
fission weapon. One mass of U-235, the "bullet," is fired down
a more or less conventional gun barrel
into another mass of U-235, rapidly creating the critical mass of
U-235, resulting in an explosion. The method was so certain to work
that no test was carried out before the bomb was dropped over
Hiroshima, though extensive laboratory
testing was undertaken to make sure the fundamental assumptions
were correct. Also, the bomb that was dropped used all the existing
extremely highly purified U-235 (and even most of the less highly
purified material) so there was no U-235 available for such a test
anyway. The bomb's design was known to be inefficient and prone to
accidental discharge.
Plutonium bomb
The basic concept of an implosion-style nuclear weapon.
Actual pictures and details of the bomb's inner workings
remain classified.
The bombs
used in the first test at Trinity Site
on July 16, 1945, in New Mexico (the gadget of the Trinity test
), and in the Nagasaki bomb, Fat Man
, were made primarily of plutonium-239, a synthetic
element.
Although uranium-238 is useless as a
fissile isotope for an atomic bomb, it is key in producing
plutonium . The fission of U-235 releases neutrons, which are
absorbed by U-238, which creates uranium-239. U-239 rapidly decays to neptunium-239 (U-239 has a half-life of 23.45
minutes). Neptunium-239 (with a half-life of 2.35 days) then decays
into plutonium-239. The production and
purification of plutonium used techniques developed in part by
Glenn Seaborg while working at
Berkeley and Chicago. Beginning in 1943, huge plants were built to
produce plutonium at the Hanford Site
.

A mock-up of the plutonium bomb, Fat
Man
In 1943–1944, development efforts were directed to a gun-type fission weapon with
plutonium, called "Thin Man". Once
this was achieved, the scientists thought the uranium version,
"Little Boy," would require a relatively simple adaptation.
Initial research on the properties of plutonium was done using
cyclotron-generated plutonium-239, which was extremely pure, but
could only be created in very small amounts. On April 5, 1944,
Emilio Segrè at Los Alamos
received the first sample of Hanford-produced plutonium. Within ten
days, he discovered a problem: reactor-bred plutonium was far less
isotopically pure than cyclotron-produced plutonium. A higher
concentration of Pu-240, formed from Pu-239 by capture of an
additional neutron, gave it a much higher spontaneous fission rate
than U-235. Pu-240 was even harder to separate from Pu-239 than
U-235 was to separate from U-238, so no purification was attempted.
This made the Hanford plutonium unsuitable for use in a gun-type
weapon .
The gun-type bomb worked by mechanically assembling the critical
mass from two subcritical masses: a "bullet" and a target. The
chain reaction resulting from collision of the "bullet" with the
target released tremendous energy, producing an explosion, but also
blew apart the critical mass and ended the chain reaction. The
configuration of the critical mass determined how much of the
fissile material reacted in the interval between assembly and
dispersal, and therefore the explosive yield of the bomb. Even a 1%
fission of the material would result in a workable bomb, equal to
thousands of tons of high explosive. A poor configuration, or slow
assembly, would release enough energy to disperse the critical mass
quickly, and the yield would be greatly reduced, equivalent to only
a few tons of high explosive.
The chain reaction of U-235 was slow enough that gun-type assembly
would work, but in a gun-type bomb made with the Hanford plutonium,
"early" neutrons from spontaneously fissioning Pu-240 would start
the chain reaction more quickly during detonation. This would
release enough energy to disperse the critical mass with only a
minimal amount of plutonium reacted, reducing the resulting yield
of the weapon.
In July 1944, based on the measurements of spontaneous fission for
Hanford plutonium, the decision was made to cease work on a
gun-type assembly for plutonium. There would be no "Thin
Man."
Ideas for alternative detonation schemes had existed for some time
at Los Alamos. One of the more innovative was the idea of
"implosion". Using chemical explosives, a sub-critical sphere of
fissile material could be squeezed into a smaller and denser form.
When the fissile atoms were packed closer together, the rate of
neutron capture would increase, and the mass would become a
critical mass. The metal needed to travel only very short
distances, so the critical mass would be assembled in much less
time than it would take to assemble a mass by a bullet impacting a
target.Initially, implosion had been entertained as a possible,
though unlikely, method.
The gun method was further developed for uranium only, while most
efforts were then directed towards rapidly developing an implosion
system. Oppenheimer chose to pursue a design based on the April
1944 suggestion by James L. Tuck to use explosive lenses to create spherical,
converging implosion waves.
By the end of July 1944, the entire Manhattan Project had been
reorganized around building the implosion-type bomb.
The required implosion was achieved by using shaped charges with many explosive lenses to
produce the perfectly spherical explosive wave which compressed the
plutonium sphere.
Because of the complexity of an implosion-style weapon, it was
decided that, despite the waste of fissile material, an initial
test would be required. The first nuclear
test took place on July 16, 1945, near Alamogordo
, New
Mexico
, under the supervision of Groves's deputy
Brig. Gen. Thomas
Farrell. Oppenheimer gave the test the code name
"Trinity
".
Similar efforts
A similar
effort was undertaken in the USSR
in
September 1941 headed by Igor
Kurchatov (with some of Kurchatov's World War II knowledge
coming secondhand from Manhattan Project countries, thanks to
spies, including at least two on the scientific team at Los Alamos,
Klaus Fuchs and Theodore Hall, unknown to each
other).
After the MAUD Committee's report, the British and Americans
exchanged nuclear information but initially did not pool their
efforts. A British project, code-named Tube
Alloys, was started but did not have United States resources.
Consequently the British bargaining position worsened, and their
motives were mistrusted by the Americans. Collaboration
therefore lessened markedly until the Quebec Agreement of August 1943, when a
large team of British, Canadian and Australian scientists joined
the Manhattan Project at McGill University in Montreal and at a new
project site located at Chalk River, Ontario
, with living facilities for those working in
the newly created community of Deep River, Ontario.
The question of Axis efforts on the bomb
has been a contentious issue for historians. It is believed that
efforts undertaken in Germany, headed by Werner Heisenberg, and in Japan, were also undertaken during
the war with little progress. It was initially feared that Hitler was very close to developing his own bomb.
Many German scientists in fact expressed surprise to their Allied
captors when the bombs were detonated in Japan. They were convinced
that talk of atomic weapons was merely propaganda. However, Werner
Heisenberg (by then imprisoned in Britain at Farm Hall with several other nuclear project
physicists) almost immediately figured out what the Allies had
done, explaining it to his fellow scientists (and hidden
microphones) within days. The Nazi reactor effort had been severely
handicapped by Heisenberg's belief that heavy water was necessary as a neutron moderator (slowing preparation
material) for such a device. The Germans were short of heavy water
throughout the war because of Allied efforts to prevent Germany
from obtaining it, and the Germans never did stumble on the secret
of purified graphite for making nuclear reactors from natural
uranium.
Niels Bohr, Werner Heisenberg and Enrico Fermi were all colleagues who were key
figures in developing the quantum
theory together with Wolfgang
Pauli, prior to the war. They had known each other well in
Europe and were friends. Niels Bohr and
Heisenberg even discussed the possibility of the atomic bomb prior
to and during the war, before the United States became involved.
Bohr recalled that Heisenberg was unaware that the supercritical
mass could be achieved with U-235, and both men gave differing
accounts of their conversations at this sensitive time. Bohr at the
time did not trust Heisenberg, and never quite forgave him for his
decision not to flee Germany before the war when given the chance.
Heisenberg, for his part, seems to have thought he was proposing to
Bohr a mutual agreement between the two sides not to pursue nuclear
technology for destructive purposes. If so, Heisenberg's message
did not get through. Heisenberg, to the end of his life, maintained
that the partly-built German heavy-water nuclear reactor found
after the war's end in his lab was for research purposes only, and
a full bomb project had not been contemplated (there is no evidence
to contradict this, but by this time late in the war, Germany was
far from having the resources for a Hanford-style plutonium bomb,
even if its scientists had decided to pursue one and had
known how to do it).
See also
Notes
- The most comprehensive history of the Manhattan Project is
Richard
Rhodes, The Making of the Atomic Bomb (Simon &
Schuster, 1986).
- Stephen I. Schwartz Atomic Audit: The Costs and
Consequences of U.S. Nuclear Weapons. Washington, D.C.:
Brookings Institution Press, 1998. Manhattan Project expenditures
- Rhodes, 137
- Rhodes, 24
- Rhodes, 201-203
- Rhodes, 251-253
- Rhodes, 256-260
- Rhodes, 262-263
- Frisch O. R.: "The Discovery of Fission—How It All Began".
Physics Today 20 (1967), 11, pp. 43–48. Wheeler J. A.: "MIn 1933
Hungarian physicist Leó Szilárd had proposed that if
any neutron-driven process released more neutrons than
those required to start it, an expanding nuclear
chain reaction might result. Chain reactions were familiar as a
phenomenon from chemistry (where they typically caused explosions
and other runaway reactions), but Szilárd was proposing them for a
nuclear reaction for the first time. However, Szilárd had
proposed to look for such reactions in the lighter atoms, and
nothing of the sort was found. Upon experimentation shortly after the
uranium fission discovery, Szilárd found that the fission of
uranium released two or more neutrons on average, and immediately
realized that a nuclear chain reaction by this mechanism was
possible in theory. Szilárd kept this secret at first because he
feared its use as a weapon by fascist governments. He convinced others to do so,
but identical results were soon published by the Joliot-Curie
group, to his great dismay. echanism of Fission". Physics Today 20
(1967), 11, pp. 49–52
- Rhodes, 185
- Rhodes, 306-309; 312-315>
- Broad, William J., "Why They Called It the Manhattan Project", New York
Times, October 30, 2007.
- Rhodes, 322-325
- Rhodes, 369
- Rhodes, 372
- Rhodes, 416
- Rhodes, 415
- Rhodes, 381; 388-389
- Serber, Robert. The Los Alamos Primer (Los Alamos
Report LA-1, compiled April 1943, declassified 1965): p. 21.
- Rhodes, 417
- Rhodes, 421
- Rhodes, 419
- In Bethe's account, the possibility of this ultimate
catastrophe came up again in 1975 when it appeared in a magazine
article by H.C. Dudley, who got the idea from a report by
Pearl Buck of an
interview she had with Arthur Compton in 1959. The worry was not
entirely extinguished in some people's minds until the
Trinity
test.
- Why They Called It the Manhattan Project,
nytimes.com, accessed Nov 2, 2007.
- Natural self-sustaining nuclear reactions have occurred in the
distant past (circa two billion years ago); see Natural nuclear fission
reactor
- The Atomic Heritage Foundation—Atomic History
Timeline 1942–1944
References
- Overall, administrative, and diplomatic histories of the
Manhattan Project
- DeGroot, Gerard, The Bomb: A History of Hell on Earth,
London: Pimlico, 2005. ISBN 0-7126-7748-8
- Feynman, Richard P. "Surely You're Joking,
Mr. Feynman!". W. W. Norton & Company, 1997. ISBN
978-0393316049.
- Groves, Leslie. Now it Can be
Told: The Story of the Manhattan Project. New York: Harper,
1962. ISBN 0-306-70738-1.
- Herken, Gregg. Brotherhood of the Bomb : The Tangled Lives
and Loyalties of Robert Oppenheimer, Ernest Lawrence, and Edward
Teller. New York: Henry Holt and Co., 2002. ISBN
0-8050-6588-1.
- Hewlett, Richard G., and
Oscar E. Anderson. The New World, 1939–1946. University
Park: Pennsylvania State University Press, 1962.
- Howes, Ruth H. and Herzenberg, Caroline L. Their Day in the
Sun: Women of the Manhattan Project. Philadelphia: Temple
University Press, 1999. ISBN 1-56639-719-7.
- Jungk, Robert. Brighter Than a
Thousand Suns: A Personal History of the Atomic Scientists.
New York: Harcourt, Brace, 1956, 1958.
- Norris, Robert S., Racing for the Bomb: General Leslie
R. Groves, The Manhattan Project's Indispensable Man.
Vermont: Steerforth Press, First Paperback edition, 2002. ISBN
1-58642-067-4.
- Rhodes, Richard. The Making
of the Atomic Bomb. New York: Simon & Schuster, 1986. ISBN
0-671-44133-7.
- Rhodes, Richard. Dark Sun: The Making of the Hydrogen
Bomb. New York: Simon & Schuster, 1995. ISBN
0-684-80400-X.
- Kelly, Cynthia. Remembering the Manhattan Project:
Perspectives on the Making of the Atomic Bomb and Its Legacy
New Jersey: World Scientific, 2005.
ISBN 978-981-256-040-7.
- Kelly, Cynthia. Oppenheimer and the Manhattan Project:
Insights into J Robert Oppenheimer, “Father of the Atomic
Bomb” New Jersey: World
Scientific, 2005. ISBN 978-981-256-418-4.
- Technical histories
- Groueff, Stephane. Manhattan Project: The Untold Story of
the Making of the Atomic Bomb. Boston: Little, Brown & Co,
1967.
- Hoddeson, Lillian, Paul W. Henriksen, Roger A. Meade, and
Catherine L. Westfall. Critical Assembly: A Technical History
of Los Alamos During the Oppenheimer Years, 1943–1945. New
York: Cambridge University Press, 1993. ISBN 0-521-44132-3.
- Serber, Robert. The Los Alamos
Primer: The First Lectures on How to Build an Atomic Bomb.
Berkeley: University of California Press, 1992. ISBN
0-520-07576-5—Original 1943, Los Alamos Report "LA-1", declassified
in 1965. (Available on Wikimedia Commons).
- Sherwin, Martin J. A World Destroyed: The Atomic Bomb and
the Grand Alliance. New York: Alfred A. Knopf, 1975. ISBN
0-394-49794-5.
- Smyth, Henry DeWolf.
Atomic Energy for Military Purposes; the Official Report on the
Development of the Atomic Bomb under the Auspices of the United
States Government, 1940–1945. Princeton: Princeton University
Press, 1945. See Smyth Report.
- Yenne, William. "The Manhattan Project", Secret Weapons of
World War II: The Techno-Military Breakthroughs That Changed
History. New York: Berkley Books, 2003, p. 2–7.
- Participant accounts
- Badash, Lawrence, Joseph O. Hirschfelder, Herbert P. Broida,
eds. Reminiscences of Los Alamos, 1943–1945. Dordrecht,
Boston: D. Reidel, 1980. ISBN 90-277-1097-X.
- Bethe, Hans A. The Road from Los
Alamos. New York: Simon and Schuster, 1991. ISBN
0-671-74012-1.
- Nichols, Kenneth David. The
Road to Trinity: A Personal Account of How America's Nuclear
Policies Were Made. New York: William Morrow and Company Inc,
1987. ISBN 0-688-06910-X.
- Serber, Robert. Peace and War:
Reminiscences of a Life on the Frontiers of Science. New York:
Columbia University Press, 1998. ISBN 0-231-10546-0.
- Ulam, Stanisław.
Adventures of a Mathematician. New York: Charles
Scribner's Sons, 1983. ISBN 0-520-07154-9.
External links