Another group of scientists in Berlin, Germany, decided to repeat Fermi’s experiments in 1938. Otto Hahn and Fritz Strassmann bombarded uranium with neutrons. When they analyzed the results of the subsequent reaction, they found they had produced barium atoms. Hahn and Strassmann were two of the very best chemists in Europe. Their chemical analysis of the uranium reaction was much more exhaustive than Fermi’s, and yet they could hardly believe what they were finding. It was almost unthinkable that barium, an element almost half as heavy as uranium, would be produced by a neutron absorbed into the uranium nucleus. This result was puzzling because it was not known at the time that atoms could split and transform into other types of elements. Hahn and Strassmann also discovered that their original sample of uranium had lost a small amount of...