Beginning of Essay
I think that right now, fission is the only way that we can get more energy out of a nuclear reaction than we put in. First, the energy per fission is very large. In practical units, the fission of 1 kg (2.2 lb) of uranium-235 releases 18.7 million kilowatt-hours ....

Middle of Essay
.... will induce fission is rather low, but can be increased by a factor of hundreds when the neutron is slowed down through a series of elastic collisions with light nuclei such as hydrogen, deuterium, or carbon. This fact is the basis for the design of practical energy-producing fission reactors. In December 1942 at the University of Chicago, the Italian physicist Enrico Fermi succeeded in producing the first nuclear chain reaction. This was done with an arrangement of natural uranium lumps distributed within a large stack of pure graphite, a form of carbon. In Fermi's "pile," or nuclear reactor, the graphite moderator served to slow the neutrons. N ....