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Bombs Created

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'Little Boy' - Uranium Bomb: Scientist Richard Feyman was responsible for calculating the Uranium needed in order to achieve critical mass which was the amount of Uranium needed in order to start a chain reaction. R. Feyman calculated that in order for them to have critical mass they have needed 50 Kg of pure Uranium however it was too difficult to obtain just pure Uranium so they just had to use more. The resource was very rare so they just had to use whatever they had and they couldn't make a test bomb.

It was decided that the bomb would be a gun type detonator where a section the Uranium would have the middle section missing, the middle section which was a perfect fit would be away from the big part and for the chain reaction to occur, explosives would blow the centre section to fit into the large section. Both sections would then weld together and start the reaction.

'Fat Man' - Plutonium Bomb: This was a much more difficult element to use because it was not as fissionable as Uranium. Richard Feyman and Hans Bethe calculated that the supercritical mass for plutonium would be  about 16kg however it it could be reduced to just 10kg if the plutonium was surrounded by Uranium-238. This was a big discovery because Plutonium was very limited and Uranium-238 was not.

For the chain reaction to occur, the mass of Plutonium must fuse together while a radioactive source emitted neutrons. The way the bomb was made was that the radioactive source was put into the middle of a sphere which was made of plutonium and when the sphere was detonated the bomb would implode or blow inwards in just a matter of milliseconds which would make all the plutonium fuse together and blow.

Diagrams to understand passage:

Figure1: Diagram of a plutonium bomb

Figure2: Diagram of Uranium-235 bomb.

Little Boy and Fat Man: