4. Resolving to build and use the bomb

And so, shown the way to fission by Germans, a Dane, a Frenchman, and an Italian, nudged forward by Hungarian and German expatriates, and all but cuffed about the ears by Britons (and an Australian living in England), the Americans finally embraced a project to build an atomic bomb. Or, more precisely, at the 9 October meeting with Roosevelt and Wallace, Bush was authorized to explore the feasibility of the bomb, to determine what research and which resources, natural and financial, would be needed. It was not quite yet a decision to build the bomb, though implicit throughout the detailed conversation the three men had was an understanding that, if the bomb could be built, it should be. The logical extension of this understanding was an assumption even more significant: that if the bomb could be built, it should then be used, against anyone with whom the United States was at war. From the first—that is, from the moment he heard the news about Pearl Harbor—Franklin Roosevelt resolved that the United States must unequivocally (if not yet unconditionally) defeat Japan (and Germany), and must do so at the smallest possible price in American lives. When Alexander Sachs, Vannevar Bush, or anyone talked to the President about the bomb, they emphasized its unprecedented power, but they did so by comparing it to current weapons. It was, after all, a bomb they were seeking, even if it was an ‘extremely powerful’ one, as Szilard and Einstein had written in 1939. Already in July 1941 Bush had written to Roosevelt of a bomb ‘a thousand times more powerful than existing explosives’, unparalleled in its magnitude but not its nature, for it was still a bomb. ‘Certainly, there was no question in my mind,’ wrote Leslie Groves, ‘or, as far as I was ever aware, in the mind of either President Roosevelt or President Truman or any other responsible person, but that we were developing a weapon to be employed against the enemies of the United States.’ Groves dated this assumption to September 1942, when he assumed control of what had become the Manhattan Project, established a month earlier to build an atomic bomb. Yet there is no reason to think that Roosevelt waited eleven months from the pivotal meeting with Bush to decide that an atomic bomb, if developed and needed to win the war, should be used. Indeed, Winston Churchill wrote later, ‘there never was a moment’s discussion as to whether the atomic bomb should be used or not’.14

Authorized by Roosevelt, who promised Bush money for nuclear research from a secret fund available only to the President, the American bomb quest began, like those in Japan and Germany, on several fronts at once. Fermi, Szilard, John Dunning, and Harold Urey were at Columbia, the first two working chiefly on building a nuclear reactor (or ‘pile’) to create a chain reaction, the second two experimenting with the gaseous diffusion method of procuring U-235. At Princeton, Eugene Wigner was also working on a pile. Other methods of uranium separation—by centrifuge, and by thermal diffusion—were also under way. On 6 December, Bush, with Conant, summoned Compton and Lawrence to Washington. There it was decided that Compton, at Chicago, would work to design the bomb. Lawrence was to try to make fissionable uranium using his magnetized racetracks; he departed from lunch to get back to Berkeley. Neither Bush nor Conant had much faith in plutonium production at this stage. The following day, Pearl Harbor was attacked. The bomb was now more urgent.

The multiple centers of research and labor frustrated Compton and, in his opinion, prevented the coordination of effort essential to move the project along. In January, though ill with the flu, Compton gathered Szilard, Lawrence, and several others at his home. The time had come, said Compton, to pull together. Work at various locations caused duplication of effort and was unsustainable. The scientists made the case for consolidation in their own laboratories. Compton argued for Chicago. The city was centrally located and unlikely to be bombed, the facilities were good, housing existed despite wartime shortages, and there remained competent scientists available locally. In the end, Compton simply overrode objections. He hoped, he said, that the others would join him. Ernest Lawrence remained a doubter. ‘You’ll never get the chain reaction going here,’ he insisted. ‘The whole tempo of the University of Chicago is too slow.’ Compton disagreed, and two men ended up betting a cheap cigar on whether it would happen. Feverish, Compton rose with difficulty and went to his study to call Fermi in New York and Wigner in Princeton. Both men agreed to relocate, bringing to Chicago their plans for a reactor. His sights set at this stage mainly on plutonium, despite Bush’s and Conant’s doubts, Compton engineered the (voluntary) eviction of the university’s math department from Eckhart Hall and christened the Chicago project as a whole the Metallurgical Laboratory, or Met Lab.16

‘Now is the time for faith,’ Compton wrote to Conant. ‘It isn’t faith we need now, Arthur,’ Conant replied. ‘It’s works.’ Compton kept reading his Bible, sometimes to his fellow scientists, but he worked, too. To raise morale among the scientists displaced to Chicago, Compton and his staff found housing (Fermi’s assistants Herbert Anderson and John Marshall were placed in Compton’s son’s room), schools for children, and family doctors and dentists. The Fermis found a house near campus. It came furnished with a short-wave radio and included two youngJapanese women as tenants upstairs. Fermi was still classified as an ‘alien’, so both radio and women were removed. Compton set the Met Lab three sequential tasks: first, create a chain reaction, using uranium 238; second, extract from the fissioned uranium the plutonium that would presumably be produced; and, third, extrapolate from this pilot experience the conviction and expertise needed to build a production plant big enough to yield the nuclear fuel for a bomb. He needed a nuclear reactor, and he gave Fermi the task of building it.17

In a squash court under the university’s Amos Alonzo Stagg Field, the turf largely abandoned since the school had given up varsity football some years earlier, Fermi created his pile. His goal was to induce fission in uranium 235, embedded in U-238 in the ratio of 1:140. To prevent capture of his projectile neutrons by U-238, Fermi needed to slow his bullets down, thereby increasing his chances of hitting U-235, and for that a moderator would be essential. Lacking heavy water—recall that the Germans relied on this substance, which had its absorptive hydrogen replaced by more cooperative deuterium—and at the urging especially of Szilard, Fermi settled on graphite. The German reactor would founder in part because the graphite its builders obtained was impacted with boron and thus insufficiently ‘clean’. In the United States, the National Carbon Company provided graphite made pure by its well-chosen coke base and extra time in the furnace. Supplies of the moderator—enough, figured Laura Fermi, to provide everyone on earth with a standard pencil—began arriving in Chicago in September 1942. Physicists, technicians, and a crop of local high-school dropouts unloaded the graphite, planed and shaped and smoothed it with saws and a lathe into bricks 16.5 inches long and weighing 19 pounds, then drilled into some of the bricks channels that would hold slugs of uranium oxide, the fission source. They worked at close quarters in the squash court, the surfaces of which became black and slippery with graphite powder: ‘Hell’s Kitchen,’ thought Laura Fermi. Her husband had planned a roughly spherical pile 26 feet in diameter, but he ran out of room at the ceiling, so the finished reactor was flat on top.

On 2 December 1942, the first day of Chanukah and also a day of mourning for Jews, an estimated two million of whom had already been murdered by the Nazis, Fermi was ready to test his strange machine. Over forty people squeezed onto the balcony of the squash court, among them the head of research for the Du Pont Company, whom Leslie Groves was hoping to attract to the bomb-building project. The pile was punctured at various points by control rods made with cadmium, an absorber of neutrons. A young physicist named George Weil, the only person on the floor next to the pile, was responsible for manipulating these. Three young men stood atop the pile wielding buckets of cadmium salts; the physicist Norman Hilberg held an axe that could cut a rope holding a master safety rod should it be necessary to halt a runaway reaction. Just after 10.30 a.m., on Fermi’s order, Weil pulled the last safety rod, 13 feet in height, out 1 foot. Radiation-measuring instruments clicked audibly. A graph confirmed the presence of radiation. Fermi checked his calculations against the readings and told Weil to withdraw the rod another 6 inches. As if alarmed by the subsequent rise in neutron activity, the safety rod, on its own volition, slammed down into place. ‘I’m hungry,’ Fermi said. ‘Let’s go to lunch.’

The experiment resumed at 2.00 p.m. The last control rod was withdrawn another 6 inches and the meters showed another jump in activity. ‘The clicks came more and more rapidly,’ wrote Fermi’s colleague Herbert Anderson, ‘and after a while they began to merge into a roar; the counter couldn’t follow anymore.’ Technicians changed the scale of the recording devices, trying to keep up with the pile’s intensity. Fermi proclaimed that the pile had gone critical. He let it run for twenty-eight minutes altogether as the neutron counter continued to click and the stylus on the chart recorder swung upward. ‘When do we become scared?’ the physicist Leona Woods asked Fermi. Finally, as the instruments showed that radiation levels in the balcony were becoming worrisome, Fermi ordered that the safety rods be dropped into place. The reactor had performed as expected and produced atomic power. Eugene Wigner passed around a bottle of Chianti, and everyone drank a bit from paper cups. Compton, who had won a cigar from Lawrence, phoned Conant in Washington, and neither man concealed his excitement. But, as people left the cold squash court, Leo Szilard approached Fermi, shook his hand, and told him gloomily that this was ‘a black day in the history of mankind’.18

Not every top American physicist moved to Chicago in 1942. Coming out of the September 1941 meeting with Compton and Conant and especially the 6 December meeting in Washington, wherein Bush charged him with producing U-235 for the bomb, Ernest Lawrence, while staying in close touch with the Met Lab, was more determined than ever to maintain Berkeley as a center for nuclear research. Since the late 1920s, Lawrence had been interested in smashing atoms, exploring their intricacies and unleashing their energy, and he had built larger and larger machines to help him do this. These were his cyclotrons, circular structures that allowed him to fire atomic particles around magnetized racetracks at tremendous speed; his latest, the frame of which he had showed Marcus Oliphant the previous summer, might (he hoped) accelerate particles to an energy of 100 million volts, if it did not first spring a leak, blow a tube, or cause a blackout on campus and in nearby neighborhoods of Berkeley. The atom-smashing all but accidentally produced radiation, unknown to Lawrence and unmeasured because of his impatience to increase 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

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