The year 1939 was a critical turning point not only in the state of the world but also in the development of nuclear power. A worldwide eco­nomic depression had been in effect for 10 years, and the lack of invest­ment resources did not encourage the development of an entirely new energy source. Although it was scientifically possible to achieve a self — sustaining nuclear reactor that would generate thermal power, it was financially impossible. There were innumerable engineering details to be worked out, and there were still scientific unknowns and blank spots in the theories.

The biggest problem was dealing with the very low concentration of a usable isotope of uranium, U-235, mixed in with an unusable isotope, U-238. As it occurs in nature, uranium contains only 0.7 percent of the fissionable isotope that could be used for power generation. Isotope sepa­ration, in which the concentration of U-235 in natural uranium could be improved, had been demonstrated only as laboratory setups involv­ing countable numbers of atoms. To make practical nuclear fuel would require an industrial effort of such enormous scale it was out of the ques­tion for normal commerce.

This chapter focuses on the factors that made 1939 a pivotal year in the development of nuclear power. The components of this historical conver­gence include an ominous but ultimately false fear of atomic bomb con­struction in Germany, the discovery in Italy of neutron interactions at low

energies, a fortuitous transfer of nuclear physics expertise from Europe to the United States, and the development of an infrastructure for high — energy particle physics in California. In the middle of this frenzied race for nuclear fission, a second mode of nuclear energy production, fusion, was theorized into being. Although it seemed out of place, this theory completed the scientific understanding of energy from the nucleus, and its importance is undeniable.