Leo Szilard
Eugene P. Wigner
Einstein was the most prestigious scientist then living and it was thought a letter from him to the President of the United States would be most persuasive. Einstein signed such a letter, which explained the possibility of a nuclear bomb and urged that the United States not allow a potential enemy to come into possession of it first.
Largely as a result of this letter, a huge research team was put together in the United States, to which other Western nations also contributed, with but one aim—to develop the nuclear bomb.
The Nuclear Bomb
Although the theory of the nuclear bomb seemed clear and simple, a great many practical difficulties stood in the way. In the first place, if only uranium atoms underwent fission a supply of uranium had at least to be obtained in pure form, for if the neutrons struck nuclei of elements other than uranium, they would simply be absorbed and removed from the system, ending the possibility of a chain reaction. This alone was a heavy task, since there had been so little use for uranium in quantity that there was almost no supply in existence and no experience in how to purify it.
Secondly, the supply of uranium might have to be a large one, for neutrons didn’t necessarily enter the first uranium atom they approached. They moved about here and there, making glancing collisions, and travelling quite a distance, perhaps, before striking head-on and entering a nucleus. If in that time they had passed outside the lump of uranium, they were useless.
