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the energy of his cyclotron while neglecting to activate Geiger counters near the machine. When Joliot and Curie reported, in Nature, inducing radioactivity in their Paris lab, Lawrence and his ‘boys’ quickly mimicked the French team’s findings. As Gregg Herken writes, it was ‘suddenly obvious to the cyclotroneers that they had been creating radioactivity artificially, and unknowingly, for more than a year’. By late 1937 Lawrence’s cyclotron was engaged full time in making radioactive isotopes. Lawrence’s work won him the 1939 Nobel Prize in physics, though, because he felt the war made it too dangerous for him to cross the Atlantic, he got the award on the Berkeley campus, with the Swedish consul general presiding.19

The imperative to produce U-235 moved Lawrence to rethink his cyclotrons. Into his machine he now fitted a mass spectrograph. The cyclotron’s magnet would divide ionized uranium beams into two streams, the U-235 atoms pulled into a tight arc, the heavier U-238 atoms curving further out, by about three-tenths of an inch, than their lighter cousins. The U-235 could be gathered as a kind of metallic smudge where it came to rest. This method of electromagnetic separation of uranium ions differed from gaseous diffusion, favored by Harold Urey and others; separation by centrifuge, undertaken by Jesse Beams at the University of Virginia and plausibly predicated on the principle that heavier atoms, if spun, would fly further out than lighter ones; and thermal diffusion, whereby lighter atoms ran more quickly than heavy ones from a hot to a cold plate. Some skepticism surrounded Lawrence’s electromagnetic separation method: ‘there were many technical difficulties to be overcome,’ was Arthur Compton’s terse assessment. But by mid-1942 Lawrence’s great machine, chauvinistically dubbed the Calutron for its university home, was steadily producing U-235 enriched to a promising 35 percent.20

5. Oppie

Lawrence was a confident man, but he knew himself to be far stronger as an experimentalist than a theoretician. Having suffered, in 1932, the embarrassment of being scoffed at professionally by the likes of James Chadwick and Werner Heisenberg, Lawrence had retrenched intellectually, and had brought into his circle his Berkeley colleague J. Robert Oppenheimer. The initial stood for Julius, his father’s name, but no one called him that. His family called him Robert; fellow graduate students in Europe dubbed him ‘Oppie’. Oppenheimer grew up in privileged circumstances in Manhattan and on Long Island. His father, a German Jewish immigrant, found success in the New York City clothing trade. His mother, the daughter of immigrants, was a painter with a well-tuned aesthetic sense: Robert and his younger brother Frank lived in apartments and houses wherein hung paintings by Van Gogh and Renoir. Emotionally protected by his mother, and physically cosseted—he held up the start of his second-floor classes in school because he refused to climb stairs and would only take a balky elevator—Robert blossomed intellectually, showing an early interest in language, poetry, chemistry, and physics. Young for his class, he took a year off between high school and college, spending the summer of 1922 with friends in New Mexico, where he learned to ride a horse and where he first climbed the Jemez Mountains and saw the Los Alamos Ranch School, which was in the business of teaching and toughening overprivileged boys. Robert started at Harvard the following year. His appetite for work, or at least exposure to a variety of subjects, was prodigious, and he indulged himself by taking five courses and auditing five more each semester. ‘He retreated’, write his two most recent biographers, ‘into the security his powerful intellect assured.’ He chose, eventually, to focus on physics, training with the theoreticians Edwin C. Kemble and Percy Bridgman, the latter the realist who believed that science should be kept separate from politics. Robert had decided on a career path, he said, of the ‘purely useless’.21

He went off to Cambridge, the English one,