What Is Real?: The Unfinished Quest for the Meaning of Quantum Physics

by Adam Becker

U-238 is a different story. Those three extra neutrons give it a little more stability, so hitting it with a neutron won’t split it as easily. This makes it impossible to build a bomb out of U-238. And fortunately, about 99.3 percent of uranium in nature is U-238. To build an atomic bomb, you would need to separate the tiny quantity of U-235 from the enormous bulk of U-238—and since they’re chemically identical, the only way to separate them is to take advantage of the fact that U-238 is 1.3 percent heavier than U-235. This guaranteed that nuclear power would be phenomenally difficult to achieve, requiring enormous quantities of uranium and city-sized industrial diffusion and centrifuge facilities. “It can never be done unless you turn the United States into one huge factory,” concluded Bohr. Yet the risk of not pursuing nuclear power was too high. If Nazi Germany were to build an atomic bomb, the war would be over. The Einsteins and Fermis and Borns of the world would never be able to escape Hitler’s Reich. “A little bomb like that,” said Fermi, cupping his hands as he looked out over Manhattan, “and it would all disappear.”