By: Michael Smalley
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During WWII, German dictator Adolf Hitler started to show interest in creating a massive amount of energy by splitting uranium nuclei. At this time he was preparing to start up research in order to create an atomic bomb. This worried physicist Leo Sziland, who wrote a letter to the U.S. president Roosevelt encouraging him to build the atomic bomb before Hitler could. Nobel peace prize recipient Albert Einstein also endorsed the letter with his name (5).
The United States along with the United Kingdom and Canada would start a project in a race to build the first atomic bomb. The Manhattan Project as it would be called only during this period of the war until the end lasted from 1942-1946 (7).
In this paper, I will talk about the Manhattan Project, the concept of nuclear fission, the development of the first atomic bombs, the dropping of these bombs, the effects the bombs had on both humans and the environment, and finally, there will be a quick check up of atomic bombs today.
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Manhattan Project
The name Manhattan Project relates only to the period of atomic research from 1942-1946, the heart of WWII. (7)
Before the program could even evolve and create any atomic bombs there was a great amount of physics background about nuclear energy between 1932 and 1939 (3). James Chadwick was a huge part of the advancement towards nuclear experience when in 1932 he discovered the neutron. This discovery would go on to explain the reason for the different atomic weights of the same elements. A different amount of neutrons within an element’s nucleus was accounting for the different weights. Advancement also happened this year when two men split a lithium atom by bombarding it with protons, allowing them to get from this lithium, two helium nuclei (3).
In 1934 atom bombardment took another huge stride when scientists learned that using a neutron to bombard atoms worked better than the usually used protons and alpha particles. Little did the scientists know, but the process that was just performed would become known as fission. Later two radio chemists Hahn and Strassmann would discover that the result of splitting an atom were actual lighter elements. They realized that the loss in mass must have then produced kinetic energy, which in turn could be used to produce heat. Another colleague than realized that so much energy had been released that some new process had to be at work (3).
With this discovery also came the discovery that there was not just a huge amount of energy created by fission, but that there were also the emission of neutrons. These neutrons would in essence boil off the two resulting fragments that flew off the separation. The neutrons would then continue to on come in contact with other atoms resulting in the same way. All of this would cause a chain-reaction. It was now possible to create an explosion of huge force if the splitting went unchecked (3).
In 1939 the Americans would start a small research program. With the scare of Nazi Germany possibly building its own bomb the Manhattan Project was born. The program would grow to employ 130,000 people and would have a total cost of around $2 billion (That would be the equivalent to $24 billion in 2004).(7)
1945 was marked by success of the Manhattan project, as they then detonated three nuclear bombs. There was the test detonation on July 16, at the Trinity test site. Then there were two actual bomb drops on the WWII enemy Japan. August 6 was the drop on Hiroshima with the uranium bomb known as “Little Boy.” Then on August 9 they dropped the last bomb on Nagasaki, this bomb went by the code name, “Fat Man.” After the two bombs dropped the Japanese empire surrendered to the United States. The program would continue one more year before the Atomic Energy Commission was formed in January of 1947. (7)
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Nuclear Fission
Nuclear energy that is being produced within an atomic bomb comes from the process known as fission or splitting of either Uranium or Plutonium nuclei (8). In simpler terms this is when some of the mass of the nucleus within an atom converts into energy. This energy can be understood better when looking at Albert Einstein’s famous equation E = mc2. The E of course stands for energy, the m is for mass, and the c is the speed of light. Now since the speed of light is an exceptionally large number, the amount of mass needed to create an enormous amount of energy is very small. So, a one-kilogram sample of matter within this equation would create 9 * 1016 joules of energy. That amount of energy is equivalent to that of energy 300 metric tons of coal would create (2). This same one-kilogram sample would create the same energy as the energy created by exploding 22 megatons of TNT (8). This is no small amount of energy being created.
Fission occurs during an atomic explosion when the Uranium or Plutonium nuclei are split by bombarding them with neutrons. The results are two fragments, called fission products. The two fragments have a sum mass that is slightly less than the value of the original mass before splitting (2). The difference in masses is somewhere around 0.1% of the original mass (3). This lost mass is then converted into an exceptional amount of energy as was showed up above with Einstein’s equation.
The mass difference can be explained within the concept of binding energy. Binding energy is the amount of energy that would have to be added to the nucleus to break it up. When there is a release of nuclear energy from the fission of a heavy atom, the elements in the middle of the periodic table, which have an intermediate weight, also have a higher binding energy per nucleon. So when a heavy atom goes through fission, the resultant fission products have that previously explained smaller nuclear mass. Again that loss in mass in converted into energy within the fission process (2).
The math and energy parts of nuclear physics can be found through equations using the binding energy of the original atom and then the binding energy of the two fission products. B(o) will represent the binding energy; the two products will be represented by B1 and B2. The equation for the amount of energy released during each fission is:
E = (B1 + B2) – Bo (2)
Then the amount of the talked about lost mass and the amount of energy that it creates is given by the equation:
E / c2 = ((B1 + B2) – Bo) / c2 (2)
A fission reaction will release between two to four neutrons, which all depends on the speed of the neutron that causes the fission. In order for the ensuring chain reaction to continue the resulting neutrons must come in contact and perform another fission (2). To allow for this to happen there must be a critical mass available. A critical mass is known as the amount of fissile material to allow for a chain reaction to continue. As the size of the sphere or nuclear material starts to become a supercritical mass, this allows for successive generations within the chain reaction to happen very quickly. This very quick succession creates a large amount of energy to be released very quickly also, allowing then for a possible explosion to take place. To stop this from happening, a material called a tamper will be placed around the nuclear material. It will eliminate a premature disruption and plus it will reduce the number of neutrons that escape during the fission process (8).
The Uranium Bomb
During the time of the Manhattan Project there would be two atomic bombs that would be dropped on the enemy, the Japanese empire. One bomb would be a uranium bomb with the code name, “Little boy.” The other would be a plutonium bomb with the code name, “Fat man.” (7)
The uranium bomb that
was dropped on Hiroshima, was made out of Uranium 235. This is a rare isotope
that has to be physically separated from the isotope Uranium 238, which is in
turn not suitable for an atomic bomb to be made with. The main source of
separation for Uranium 235 was the use of gaseous diffusion. It used uranium
hexafluoride gas as the process fluid (7). The uranium atomic bomb was to be
built as a gun-type atomic bomb. A gun-type atomic bomb works by bombarding two
fissionable materials together that would be too small to start an explosion by
themselves, at a very high speed (1).
The bomb has an apparatus within it that
is very similar to a gun barrel. The two materials are fired at each other and
they will collide within the barrel. When they collide, they produce a
supercritical mass that will be formed allowing for a nuclear reaction and
explosion to be sustained (1).
The Plutonium Bomb
There was also a plutonium bomb that was dropped on Nagasaki, which was made out of Plutonium 239, a synthetically prepared element. They make Plutonium 239 by using the previous idea of the useless fissile element Uranium 238. This is done by the fission of Uranium 235, which produces very slow neutrons that are then absorbed by Uranium 238. After a couple of days the decay of this develops Plutonium 239 (7).
When the first samples of the synthetically produced Plutonium 239 came in, there was a flaw that was found. The plutonium was having a much higher spontaneous fission rate that the previously used Uranium 235. It was figured out that there was an isotope, Plutonium 240 that was the cause of the problem. The plutonium being made by reactors and not by the cyclotron breeding had a much higher neutron flux. This would make it to where a gun style bomb would be impossible to use. Using the slow speed gun style would cause the bomb to fissile, or to explode before it was able to sustain a chain reaction (7).
The idea of a
gun style weapon was scrapped and a new innovative style was born. This style
is known as implosion. The thought was that they could have a sub-critical
sphere of fissile material that with the help of explosives would be forced to
collapse on itself, thus creating a very dense sub-critical mass. At first this
seemed very unlikely and an impossible idea, but once it was found that this was
the only way the plutonium bomb would work all around the project was refocused
on fixing the implosion problem (7).
The implosion bomb would be figured out and this is what the physicists came up with. They would have fissile material surrounded by conventional high explosives. This would be placed within a very strong container, with the simplest form of container being a sphere. The conventional explosives then could be positioned around the container as either a shell or even just as a large number of individual charges. Then the explosives would be detonated causing the container to compress. If the container compressed enough the fissile material inside becomes so dense that it causes an explosion with the release of a great amount of energy (1).
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Tests
The very first atomic bomb test would take place on July 16, 1945 at 5:29 a.m. Mountain Time. It would be exploded at one hundred feet above the desert floor in a part of New Mexico known as “Jornada del Muerto,” or, “the Journey of the Dead Man (6).” When J. Robert Oppenheimer saw the fireball and then the mushroom cloud he stated a passage from Bhagavad-Gita, “I am become death the destroyer of worlds (6).”
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Dropping the Bombs
On July 26, President Truman issued the Potsdam Declaration. This declaration called for the complete surrender of the Japanese forces with a list of peace terms. Truman had been informed of the successful dropping of the bomb in New Mexico ten day earlier. Along with the declaration were the warnings of consequences that would happen if there were continued resistance (4).
When Japan rejected the declaration, Truman authorized the use of the bombs. This choice was weighed against that of the lost lives that would be caused by an invasion of Japan. The need was there to supply an effective blow to the Japanese and the bomb was just the weapon to supply this blow. The cities of Nagasaki and Hiroshima were strategically chosen for they had been touched very little by American bombing runs (4).
On August 6, 1945 at
9:15 a.m. Japanese time, a B-29 plane, dropped the uranium bomb, code-named,
“Little Boy,” on Hiroshima. 
Within minutes most of the city had vanished.
Estimates would later state that around 60,000 to 70,000 people were killed or
missing. The death from radiation would reach over 100,000. Of the 90,000
buildings in the city, 60,000 of them were destroyed. The city was absolutely
destroyed (4).
Then on August 8 there was an order to the base in Guam that called for the use of the other bomb on either the primary target Kokura, or the secondary target Nagasaki. On the next day during the strike there was too much smoke cover over the city of Kokura so the plane set course for Nagasaki. At 11:02 a.m. Japanese Time, the bomb code-named, “Fat Man,” exploded over the factory district of Nagasaki at a height of 1,800 feet for this would achieve the greatest effect from the blast of the bomb. This blast would destroy around 40 percent of the city and claim the lives of around 42,000 people. The amount of energy that would be produced by this type of bomb would be 20,000 tons of TNT, or 40 million pounds. This would be enough TNT to fill two cargo ships (4).
On September 2, 1945, the Japanese Government, which had seemed ready to fight to the end in July, suddenly surrendered (4).
While the power, display, and wonder of atomic bombs are great, we as humans have seen them to be enormous threat to life. Though it won a very key war in the history of mankind, I can say that I would have no problem ever seeing an atom bomb drop again during war. The Manhattan project was successful in its goal to create an atomic bomb before the axis could complete theirs. Maybe before we celebrate the dropping of the bombs and the winning of the war, maybe we should think about what might have happened if the Germans had beat us to the punch.