Introduction
Atomic Bombs generally work using a trigger to split the nucleus within the bomb's core. The neutrons released in this fission collide with other nuclei causing them to split as well. At each stage more neutrons are released. These then split more and more nuclei all the while releasing an immense amount of energy. This causes the incredible explosions. Through the Manhattan Project, the United States developed two types of Atomic Bombs, called "Little Boy" and "Fat Man." These bombs were developed quite similarly, however, they are made up of different cores and are triggered by different means.
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Fission chain reaction within a Nuclear Bomb.
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General Terms-to-Know
Nucleus
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The central part of an atom that contains the protons and neutrons. (plural: nuclei)
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Fission
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The splitting of a nucleus into many nuclei. This releases a great amount of energy and neutrons.
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Isotope
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Different forms of an element. The various forms each have the same number of protons within the nucleus, but the number of neutrons is different between each isotope. (example: Carbon 14 is an isotope of Carbon. As is Carbon 12.)
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Critical Mass
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The amount of material at which a neutron produced by a fission process will, on average, create another fission event initiating a chain reaction.
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Little Boy
Little Boy was developed with a Uranium core. The Uranium Isotope 235 was used because it could self-sustain the fission causing a chain reaction. However, only about 0.7% of Uranium is Uranium-235, the most common being Uranium-238 which does not have the necessary means to create a fission chain reaction. Thus, the scientists involved in the Manhattan project collected enough Uranium-235 to power the single bomb.
The bomb used a gun-type trigger to initiate the fission. A small explosion combined two masses of Uranium-235 which created the necessary critical mass. This triggered the chain reaction which caused the bomb to explode.
The bomb used a gun-type trigger to initiate the fission. A small explosion combined two masses of Uranium-235 which created the necessary critical mass. This triggered the chain reaction which caused the bomb to explode.
This basic diagram explains a gun-type trigger. A chemical explosion at one end triggers the fission and chain reaction at the other end thus detonating the bomb.
Fat Man
Fat Man utilised a Plutonium core, unlike Little Boy. The Manhattan project intended to use Plutonium-239 in order to achieve the required fission rate in order for the bomb to explode effectively. However, the Plutonium collected for the bomb's development turned out to be Plutonium-240 which had a much higher fission rate. This would cause the bomb to release less energy when detonated because it would undergo fission spontaneously before the gun-type trigger could create the critical mass.
Therefore, instead of detonating through a gun-type trigger, Fat Man used the implosion method. The Plutonium core was surrounded by regular bombs. When triggered, these regular bombs would explode and compress the Plutonium. This increased both its pressure and density and allowed the Plutonium to reach its critical mass thus allowing the fission chain reaction to take place.
Therefore, instead of detonating through a gun-type trigger, Fat Man used the implosion method. The Plutonium core was surrounded by regular bombs. When triggered, these regular bombs would explode and compress the Plutonium. This increased both its pressure and density and allowed the Plutonium to reach its critical mass thus allowing the fission chain reaction to take place.
This diagram explains how Fat Man used an implosion to trigger its explosion. Explosives surrounded the core and, when they explode, they expand, thus squeezing the Plutonium core. This allowed the Plutonium to reach its critical mass and fission commenced, detonating the bomb.