The Manhattan Project
The Manhattan Project was the code name for the US effort during World War II
to produce the atomic bomb. It was named for the Manhattan Engineer District
of the US Army Corps of Engineers, since much of the early research was done
in New York City. It was top-secret engineering and industrial project in
the United States during World War II, started by refugee physicists in the
United States, the program was slowly organized after nuclear fission was
discovered by German scientists in 1938, and many US scientists were scared
that Hitler would attempt to build a fission bomb.
Szilard, a nuclear scientist then living in England, was the first idealize a
realistic modern atomic bomb and came up with the basis to the project.He
was obsessed with the fear that the Nazis would build the atom bomb first.
He got together with some of his friends including Einstein who talked to
Roosevelt. Roosevelt approved the project in 1939
Physicists from 1939 onward conducted much research to find answers to such
questions as how many neutrons were emitted in each fission, which elements
would not capture the neutrons, would they moderate or reduce their velocity,
and whether only the lighter and more rare isotope of uranium (U-235) or the
common isotope (U-238) could be used. They learned that each fission releases
a few neutrons. A chain reaction, therefore, was theoretically possible, if
not too many neutrons escaped from the mass or were captured by impurities.
In 1942 General Leslie Groves was chosen to lead the project, and he
immediately purchased a site at Oak Ridge, Tennessee for facilities to
separate the necessary uranium-235 from the much more common uranium-238. He
also appointed theoretical physicist J. Robert Oppenheimer as director of the
weapons laboratory, who ordered the construction of the headquarters on an
isolated mesa at Los Alamos, New Mexico.
After much difficulty an absorbent barrier suitable for separating isotopes
of uranium was developed and installed in the Oak Ridge gaseous diffusion
plant. Finally, in 1945, a uranium-235 of bomb purity was shipped to Los
Alamos, where it was fashioned into a gun-type weapon. In a barrel, one piece
of uranium was fired at another, together forming a supercritical, explosive
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 uncommon in 1942. The
measurements of the interactions of fast neutrons with the materials in a
bomb are important 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
theenergy produced. The neutron scattering properties of materials had to be
measured to find the best reflectors.
From its beginning with Enrico Fermi’s graphite-pile reactor under the
bleachers of Stagg Field at the University of Chicago to the explosion of the
first atomic bomb near Alamogordo, New Mexico, the Manhattan Project took a
little less than 3 years to make a working atomic bomb. During that time, the
U.S. Army Corps of Engineers managed the construction of very large
state-of-the art plants to enrich uranium, three production reactors to make
plutonium, and two reprocessing plants to extract
plutonium from the reactor fuel.
Another type of atomic bomb was also constructed using the synthetic element
plutonium. Enrico Fermi built a reactor at Chicago in late 1942, the
prototype of five production reactors erected at Hanford, Wash. These
reactors manufactured plutonium by bombarding uranium-238 with neutrons. At
Los Alamos the plutonium was surrounded with high explosives to compress it
into a super dense, super critical mass far faster than could be done in a
On July 16, 1945 at 5:29 AM the first atomic bomb was detonated in
Alamogordo, New Mexico.President Harry Truman was informed of the
successful detonation and after much thought he made orders to modify B-29s
for the atomic bombs. The 504th Composite Wing was formed and in late July
of 1945 moved to the Tinian island in the Marian Islands for last minute
tests.The first atomic strike ever was at 5:45 AM on August 6, 1945. The
atom bomb “Little Boy” was dropped on Hiroshima, Japan. 70,000-100,00 were
killed instantly, and 51,000 were injured. An even more powerful bomb, “Fat
Man” was dropped on Nagasaki, Japan on August 9th killing an additional
50,000-80,000 instantly.The war was soon over, Japan surrendered
unconditionally to the United States.
Brodie, Bernard, and Brodie, Fawn. From Crossbow to H-Bomb (Dell, 1962).
Friedman, Col. Richard S., and others. Advanced Technology Warfare (Harmony
Hogg, Ian, ed. Jane’s Military Review (Janes Publishing, 1986).
Hogg, Ian. The Weapons That Changed the World (Arbor House, 1986).