Getting fuel for the bomb is a harder task than it
sounds. Uranium-235, or U-235, exists in less than one percent of natural occurring
uranium, U-238. The U-235 must be extracted from the U-238 since U-238 is not
fissionable. The two materials are naturally bonded and since their chemical makeup
is almost identical, it is almost impossible to tell apart the two metals.
Two major sites were created for the production of fuel for the bomb.
One in Tennessee and one in Washington. In the spring of 1942-1943, workers
transformed a small chunk of Tennessee into a facility and a new city, Oak Ridge.
Soon Oak Ridge had giant buildings to house machines and 20,000 workers working
daily to produce little chunks of U-235. Separating the U-235 from the U-238 took
the most time. Towards the early stages of production, two processes were used.
The first was electromagnetic separation, successfully demonstrated by physicist,
Ernest O. Lawrence. The principle was that electrically charged atoms moving through
a magnetic field would move in the shape of an arc of a circle. The lighter the
atom, the tighter the circle. This helped separated the lighter U-235 from the
heavier U-238. The problem was that this was very slow since it worked atom by atom.
Soon the development of the "Cauldron" made this process a little faster
being able to collect U-235 in the form of tiny flakes. This still was too slow.
The government decided to develop another separation method and set one up in Oak
Ridge. This second process was know as the gaseous barrier diffusion separation.
It involved converting uranium into a gas and then using a special superfine screen
to separate the U-235 from the U-238. The lighter and a little smaller U-235 would
go through the screen while the U-238 would not. This process was also very slow and
it could not make a pure enough sample with just one screening process. This
convinced Groves and Oppenheimer to create a third installation where thermal diffusion is
used. The thermal diffusion method also used the different weights to distinguish
the two types of atoms. This process used a tank with hot and cold zones. The
heavier U-238 moved to the colder zone and the lighter U-235 moved to the hotter zone.
The enriched material would then be shipped into another tank to purify the sample
even more. Eventually, scientists linked all three processes together to produce
fuel for the bomb in a much faster way.
The second facility located in Hanford, Washington, engineers worked to
produce another type of atomic fuel known as plutonium. Plutonium was created in
nuclear reactors by bombarding uranium with neutrons for 100 days. One uranium atom
out of 4000 is transformed into plutonium. Soon much plutonium and U-235 was made
and shipped to Los Alamos, New Mexico where scientists made preparations for creating the
bombs Little Boy and Fat Man.
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