But things were steadily improving. By February, the “stockpile” of uranium metal at the Rad Lab exceeded 200 micrograms, enriched to an average 35 percent U-235.47 The converted 37-inch had begun producing 2 micrograms an hour.
During a quick visit to Berkeley that month to check on progress, Bush found the upbeat mood at the Rad Lab not only “refreshing” but contagious.48 Bush wrote Roosevelt a few days later that the electromagnetic method could conceivably provide a shortcut to the bomb, delivering enough material for a weapon by the summer of 1943. A finished bomb might then be ready as early as 1944.
In other encouraging news, Oppenheimer’s latest calculations indicated that the amount of U-235 needed for a weapon was at the low end of the original estimates: closer to 2 kilograms than 100.49 Still, even that goal—a mere 4 to 5 pounds of silvery metal, 80 to 90 percent pure—lay far in the future.
Lawrence remained enough of a realist to want to hedge his bets. Unlike Conant, who was now willing to stake everything on the electromagnetic method, Lawrence urged that the government also back the other “horsemen” in the race: the centrifuge, gaseous diffusion, and Fermi’s plutonium-producing atomic pile.50
In letters to Conant that winter, Lawrence’s mood seesawed between jubilation and despair.51 But in the spring, when the output of the 37-inch hit a new peak, Ernest’s confidence returned.
While designing the spectrographs to go between the poles of the big magnet, Brobeck had invented a C-shaped vacuum chamber and increased the power of the beam by another factor of ten. The Rad Lab’s personnel director proposed a name for the new machine that would forever link it to the University of California: the “Calutron.”52
Two weeks after the first new vacuum tank was installed between the poles of the 37-inch magnet, the prototype Calutron was already exceeding expectations. “It, therefore, seems clear that we should proceed immediately with the design and construction of a multiple mass spectrograph using the giant cyclotron magnet,” Lawrence wrote to Conant—requesting an additional $200,000 for the purpose.53 “We are rapidly learning the art, and things look better all the while,” Ernest boasted at the end of March.54
Since the magnet of the 184-inch was due to be finished in another week, Lawrence also judged the time propitious to bring Berkeley’s foremost theoretical physicist closer to the project.
Whereas iron shims had been adequate for focusing the beam of the 37-inch, separating enough uranium for a bomb required a more fundamental understanding of the physics behind the spectrograph. Mindful that he had been scolded before for prematurely revealing secrets, Lawrence this time approached Conant cautiously:
One other matter I should like to bring to your attention is the desirability of asking Oppenheimer to serve as a member of S-1. I think he would be a tremendous asset in every way. He combines a penetrating insight of the theoretical aspects of the whole program with solid common sense, which sometimes in certain directions seems to be lacking, and I am sure that you and Dr. Bush would find him a useful adviser.55
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Oppenheimer, of course, had already been introduced to the bomb project, as Conant had rueful reason to know. What Lawrence proposed to do was make Oppie a full-time consultant to the S-1 Committee, laying bare all of its secrets. Unmentioned by Lawrence in his letter was a concern that had already given Conant pause, and that remained a worry even with Ernest: Oppenheimer’s politics.
Lawrence had continued to show a grudging tolerance, mixed perhaps with some degree of envy, toward Oppenheimer’s bohemian lifestyle. The memory of their earlier blowup over the benefit for Spanish Loyalists had long since faded. When his second son was born that January, Ernest named the boy Robert Donald Lawrence in honor of his two closest friends, Oppenheimer and Cooksey.56 Still, Ernest was no less disapproving of Oppie’s devotion to “left-wing” causes.
It was not only Oppie’s politics but those of the people closest to him that prompted concern. Oppenheimer’s long and tempestuous relationship with Jean Tatlock had finally ended late in 1939.57 A year later, on November 1, 1940, Oppie married Kathryn Puening, the twenty-nine-year-old daughter of a Pittsburgh mining engineer.58
“Kitty” was the widow of Joe Dallet, a Communist organizer from Youngstown, Ohio, and a member of the Abraham Lincoln Brigade who had been killed in battle at Saragossa, Spain, in 1937.59 Kitty herself had joined the Communist Party sometime after marrying Dallet in 1934 but was separated from both the party and her husband by mid-1936. Enrolled shortly after Dallet’s death at the University of Pennsylvania, she had been on a vacation in England, visiting her parents, when she became romantically involved with a former acquaintance, a young British doctor named Richard Stewart Harrison.60 The couple returned to America and were married two months later, in November 1938.61
Oppenheimer met Kitty the following August during a party at the home of a Caltech physicist, Richard Tolman, and his wife, Ruth.62 Kitty and Harrison had meanwhile moved to Pasadena, where he was interning at a nearby hospital. Oppie invited Kitty to Perro Caliente that next summer.63 After spending six weeks at a dude ranch near Reno to establish Nevada residency, Kitty divorced Harrison and wed Oppie on the same day at a civil ceremony in Virginia City. A county clerk and the courthouse janitor served as witnesses. The Lawrences were the first to congratulate the newlyweds upon their return to Berkeley; Molly was mildly shocked to see the bride already wearing a maternity dress.64
In a sudden burst of domesticity, Oppenheimer abandoned his rented bachelor quarters on Shasta Road and sublet a modern, rambling house on Kenilworth Court in nearby Kensington from an art department colleague on sabbatical.65 Oppie also sold his beloved “Garuda” and bought Kitty a pearl-gray Cadillac, dubbed “Bombsight.” Their baby—whom Oppie nicknamed “Pronto”—was expected in May.
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Perhaps
