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.
[Illustration: Franklin D. Roosevelt]
Albert Einstein
Old Grove Rd.
Nassau Point
Peconic, Long Island