The Making of the Atomic Bomb: 25th Anniversary Edition

by Richard Rhodes

When she was thirty-one, in 1909, Meitner had met Albert Einstein for the first time at a scientific conference in Salzburg. He “gave a lecture on the development of our views regarding the nature of radiation.990 At that time I certainly did not yet realize the full implications of his theory of relativity.” She listened eagerly. In the course of the lecture Einstein used the theory of relativity to derive his equation E = mc2, with which Meitner was then unfamiliar. Einstein showed thereby how to calculate the conversion of mass into energy. “These two facts,” she reminisced in 1964, “were so overwhelmingly new and surprising that, to this day, I remember the lecture very well.” She remembered it in 1938, on the day before Christmas. She also “had the packing fractions in her head,” says Frisch—she had memorized Francis Aston’s numbers for the mass defects of nuclei.991 If the large uranium nucleus split into two smaller nuclei, the smaller nuclei would weigh less in total than their common parent. How much less? That was a calculation she could easily work: about one-fifth the mass of a proton less. Process one-fifth of the mass of a proton through E = mc2. “One fifth of a proton mass,” Frisch exclaims, “was just equivalent to 200 MeV. So here was the source for that energy; it all fitted!”992