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Ever since the first nuclear weapon was built in 1945, nuclear war has been a threat. The two major nuclear powers in the world today are the Soviet Union and the United States. If a war ever broke out between the two, which involved the use of nuclear weapons, ....

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.... which go on to split other nuclei. If this continues a process called a chain reaction will occur. When this happens a fission explosion is the result. To form a chain reaction, a certain amount of material is needed. This amount is known as the critical mass. If the amount is too small it is known as a subcritical mass. The critical mass of a material depends on its purity. The materials used in making fission weapons are uranium and plutonium. They are the only elements able to be used in making a fission weapon. There are two different ways to make a fission weapon: the gun-type method and the implosion method. In the gun-type method, two ....