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Although Bohr had already raised the question with Groves, Oppenheimer promptly sent Groves a summary of the meeting, along with a memorandum prepared by Bethe and Teller.
Oppenheimer had first met Bohr at a particularly low point in his graduate studies and always credited the Danish laureate’s straightforward manner and simple kindness with helping him to stay the course and resolve “to try to learn the trade of being a theoretical physicist.” Dorothy could see that the sturdy, gray-haired theoreticians fatherly presence, with his slow, soft-spoken English, once again had a rallying effect. “He was the master scientist,” she said. “He was older than Oppie … and he was a person who could get everyone all together.” He was also modest and unassuming, and Oppie, who was amused by his code name, took to calling him Uncle Nick, and before long that was how he was affectionately known to everyone. “He was a genuine guru,” said Priscilla Greene. “He was practically the only person Oppie unreservedly admired.”
On one of Bohr’s first evenings at Los Alamos, the Oppenheimers had a big dinner party for him. Most of the senior scientists and their wives were invited, along with the Agnews, who were rather more junior, but lived about seventy-five yards from Oppie’s house so were often included. It started with Oppie’s dry martinis, which had their usual salutary effect, and everyone had a wonderful time. Bohr entertained everyone with the story of his arrival in the United States: how he and his son were hustled from the boat to the hotel in New York by a squad of FBI men, who hurried them through the lobby and straight up to their room with all their luggage, and how everyone collapsed in exhaustion and relief that the Danish physicist’s identity had not been discovered along the way. It was then that one of them noticed that written on the side of his suitcase in large black letters was NIELS BOHR.
At the end of the evening, Harold Agnew went to get his overcoat, found that it was gone, and went home without it. The next morning, he stopped by the Oppenheimers’ house to see if it had turned up. There was an unclaimed coat, but it was too small to be his. Oppie suggested he wait around and maybe his would turn up. “In a little while, along comes Bohr,” recalled Agnew. “His coat was dragging in the snow, his hands hidden by the long sleeves. ‘I think this isn’t my coat,’ he says, ‘because there are keys in the pocket, and I have no keys.’”
Bohr was not used to being on his own, without his devoted wife, Margrethe, to look after him, and often showed up in comically mismatched clothes. Once he came to work in the Tech Area with a rope tied around his waist to hold up his pants because he could not find a belt. There were many anecdotes about Bohr’s absentmindedness, though perhaps the best-known concerned an idea for a fruitful approach to an atomic bomb that had come to him just after the British scientists had first made him aware of their progress. Bohr had sent a cryptic telegram to England stating, in part, “AND TELL MAUD RAY KENT.” The British scientists, including Peierls and Frisch, were convinced that the urgent message was a code, or even an anagram, warning them of something, and they tried to crack it, coming up with strange misspelt solutions like “Radium taken,” which could have been pointing to the Nazis. When Bohr came to Los Alamos, one of the first things he was asked was the meaning of his mysterious cryptogram. It turned out that Maud Ray had been his children’s governess and she had lived in Kent, but as to the germ of an idea the line was meant to convey, that had slipped his mind.
Everyone on the mesa tried to take care of Bohr and took turns wining and dining him at night. Oppie and Kitty often took him to dinner at Miss Warner’s, where he struck up a friendship with the austere proprietress of the teahouse. “They recognized each other’s qualities immediately,” her goddaughter, Harriet “Peter” Miller, later recalled. “She always felt she had something to learn from him.” After the war, Bohr wrote of their special rapport, noting: “[Edith] had an intuitive understanding which was a bond between us.”
Bohr and his son Aage, a brilliant physicist in his own right who would earn his own Nobel, stayed for several weeks. Oppenheimer spent a lot of time with them and could always be seen walking with them between the Tech Area and Fuller Lodge. Both Bohrs were great hikers, and almost every afternoon they would go off on a long strenuous walk, sometimes accompanied by one or two other young physicists, while they would discuss a particularly thorny physics problem. Dorothy loved the way “Uncle Nick” looked in the silly, broad-brimmed straw hat he wore against the strong New Mexico sun, with his beloved pipe firmly planted in the corner of his mouth, always in need of lighting. Bohr also loved to ski, and she would never forget the sight of the legendary Dane expertly negotiating Sawyer’s Hill, the ski slope created by the Ranch School boys, which was only a short walk from the West Gate. He was not the least bit discouraged by the absence of a chair lift, and long after younger colleagues had called it quits, he could be seen energetically poling toward the top.
The Bohrs, like everyone on the Hill, were greatly heartened by the radio reports that the war was turning in their favor. At times the news was confusing, but Otto Frisch recalled that Bohr always listened closely and joked, “We must hear all the rumors before they are denied.” Bohr had not come to Los Alamos to contribute at a technical level so much as to serve as a sounding board and benefactor. He had come to America as a wise man, a scientist-statesman, to alert Roosevelt and his advisors to the perils of hoarding atomic “secrets.”
At the time, the dangers of the arms race he warned of sounded to the politicians like a distant threat compared with the far more pressing problem of winning the war. But his cautionary tone had a profound effect on Oppenheimer, as well as many other of the Los Alamos scientists, who were too caught up in their work to dwell on the ramifications of it all at the time but would later return to Bohr’s whispered admonishments and advice. He never had a single word of criticism for Oppenheimer or his upstart operation, and his faith and confidence that their work was progressing well left every one of the mesa scientists feeling decidedly more encouraged.
Bohr could not stay long, and on January 17, 1944, left for Washington and then London, where he was scheduled to meet with Churchill to relay his concerns about the postwar implications of the bomb and the frightening possibility of the proliferation of nuclear weapons. He promised to try to return as soon as possible, and Oppenheimer, writing to Groves on the day of the Danish physicist’s departure, made it clear that they would be most grateful for his continued collaboration:
By word and deed Dr. Baker has done everything he could to support this project and indicate that he is sympathetic not only with its purposes and general method of procedure, but with the policies and achievements of the project’s overall direction. I should like to make it quite clear that the effect of his presence on the morale of those with whom he came into contact was always positive and always helpful, and I see every reason to anticipate that this will be true in the future.
For most of that first year at Los Alamos, before any significant amounts of nuclear material could be delivered, the main effort had gone into attempts to get as accurate an estimate as possible, as early as possible, of the critical mass of uranium 235. All of the experimental groups—Bob Wilson and the cyclotron, John Manley and the Cockcroft-Walton, and Johnny Williams on the Van de Graaff—were busy measuring cross-sections and other parameters, and then the Theoretical Division, led by Hans Bethe, would apply mathematical methods to the problem. The challenge was how to make fissionable material—either uranium 235 or plutonium 239—release its energy efficiently, at precisely the right time, and in a metal casing that could be carried by a B-29 bomber. It was apparent that there would also be fairly strict requirements for the size, shape, and weight of the actual gun assembly, and Ed McMillan’s group was preoccupied with firing guns and testing assemblies down in an unoccupied canyon. By late 1943, Bob Wilson’s group had confirmed that an intense uranium fission reaction could take place before the bomb blew itself apart. A uranium bomb, using the gun method, was feasible and designing t
he assembly would be a relatively straightforward job, more engineering than physics.
But the gun method was an unwieldy design and extremely wasteful of the scarce uranium 235. As a backup, the implosion weapon based on plutonium was beginning to look better all the time. Seth Neddermeyer had been off on the sidelines exploring the difficulties inherent in implosion, the approach he had suggested early on. He had been pursuing implosion with Oppenheimer’s tacit, if not exactly enthusiastic, approval, but now it was becoming too important to ignore. Since plutonium was thought to have a very fast fission rate, Neddermeyer was experimenting with all different kinds of explosive materials to see which assembly would be quickest.
At the same time, Groves and the Review Committee decided Los Alamos would be responsible for developing methods to purify and fabricate the plutonium into metal for all of the Pu-239 produced at the nuclear pile at Hanford, in Washington, and this would be done on site at Los Alamos, necessitating still more laboratory buildings, facilities, and staff. “That added a considerable extra effort to the Los Alamos activity,” recalled John Manley “It was a logical decision though, because the material was never very abundant, and if you did one experiment and a following test had to have a different shape, the material would have to be reworked. It made a lot of sense to do it right at Los Alamos.”
The expanding work at the laboratory meant that more specialists were needed, and Oppenheimer rededicated himself to recruiting fresh talent for Los Alamos. Oppenheimer had already brought in David Hawkins, a philosopher from the University of California, to take over much of the responsibilities of post administration and allow him to focus on the work of the laboratory. Nineteen-year-old Frederic de Hoffman was part of a team of four physicists from Harvard selected to join the project. Arriving at Los Alamos just after Christmas, he recalled that a rather burly WAC sergeant was at the station at Lamy when the train arrived and hastily brought them to Dorothy McKibbin, who “quickly made a young Viennese feel at home in New Mexico.”
There was a steady stream of new faces at 109 East Palace, among them the Polish mathematician Stanislaw Ulam, along with his attractive French wife, Françoise, who was two months’ pregnant. The Ulams, like the others before them, had been instructed only that they were headed for an undisclosed Manhattan Project site in the Southwest, near Santa Fe. As recent émigrés to the United States, they were totally unfamiliar with the region and, deciding to do a little advance research before their departure date, checked out a WPA guidebook on New Mexico from the college library. At the time, Stan Ulam was teaching at the University of Wisconsin at Madison, and there on the back leaf of the book, where borrowers signed out the volume, were the names of all the previous members of the physics department who had mysteriously disappeared to do hush-hush war work. The Ulams said nothing about their discovery until they arrived at Los Alamos, where they greeted their former colleagues without surprise, explaining that even the tight security surrounding “Project Y” had its loopholes.
One familiar face returning to Los Alamos was the Harvard chemist George Kistiakowsky, a strikingly handsome and charismatic forty-three-year-old Russian who in his previous visits to the post had been one of the most popular unattached men. When he finally arrived at 109 after the long dusty journey by train, which he had made once too often, he announced dramatically, “I am old, I am tired, and I am disgusted!” Dorothy had to laugh. She had come to know Kisty well from his travels to and fro, and had a weakness for his courtly Old World manners and droll charm. He always stopped by her office for a gossip, knowing her to be well versed in the latest news from the Hill. Unlike most of the scientists, he was also an excellent horseman. Dorothy had heard that he was a former Cossack and thought he cut a smart figure in the saddle. “He was very dashing,” she recalled. “He had a tremendous personality. He was tall, and skinny, and had blond hair and blue eyes. He had been with the White Russian Army and had escaped with his life.”
The leading civilian explosives expert at the time, Kistiakowsky was needed to head the division that would be taking up the experimental challenge of developing the implosion device for the plutonium weapon. He had been commuting back and forth from Harvard as a consultant and had been reluctant to commit to working on the bomb because he did not think it would be ready in time to make a difference in the war; it took considerable persuading by both Oppenheimer and Conant to convince him to move to Los Alamos full-time. When he finally relented, Oppenheimer saw to it that he got plum accommodations; he had the small stone powerhouse, which had housed the Ranch School’s old generator, made over into a snug, one-room apartment. Oppie even sold him, for a nominal sum, one of his favorite saddle horses, Crisis, as the project kept him so busy he rarely found time to ride.
Kistiakowsky immediately began bringing in experienced detonation and explosives specialists, and set about doing experiments to figure out the best way to achieve implosion. Among them was the Harvard physicist Kenneth Bainbridge, who like Luis Alvarez had spent the last two years at the MIT Radiation Laboratory working on radar. Bainbridge would head a new group investigating full-scale high-explosive assemblies. The idea was to take a metallic pit, in the center of which was the plutonium fissionable material, and surround it with high explosives. In theory, the plutonium would then be imploded by the detonation of the explosive shell around it. This approach differed from that of firing the two halves of the bomb at each other in a gun barrel, as was sufficient for uranium. As Kistiakowsky recalled the challenge: “Our job was to induce the pit and plutonium to be compressed in an orderly fashion under the extreme pressure of a detonation wave, many millions of pounds per square inch, into something very much smaller than it normally was, whereupon it would become supercritical. A nuclear reaction would then spread and a big bang follow.”
The experimental work progressed in the early part of 1944, using small samples of plutonium Oppenheimer had gotten from Chicago, and then later with small samples that began arriving from Hanford and Oak Ridge. John von Neumann had done mathematical work to show that the spherical shape of the charges could affect the bomb’s explosive yield. James Tuck, one of the new British physicists, had invented a promising new explosive lens that could shape the shock wave, and the mesa scientists set about manufacturing more for their experiments. Von Neumann also brought the first computers to Los Alamos, and the machines, courtesy of IBM, were promptly put to work on calculations of implosion. At the same time, Parsons was pushing ahead on the ordnance development, including bomb hardware, arming and wiring mechanisms, and fusing devices. With the assistance of the army air forces, Parsons’ group developed two bomb models: “Thin Man,” named after President Roosevelt, was based on the gun design, while “Fat Man,” in honor of Winston Churchill, was based on an implosion prototype. In March 1944 they began testing the models with B-29s.
That same month, Hans Bethe assigned Peierls and a small team of physicists to tackle the daunting calculations of implosion. Bethe had worked with the talented and unassuming German physicist in the past and knew him to be very capable, plus he brought with him the new techniques and perspective of the British mission. After a careful review of the British project’s approach and results, Oppenheimer reported to Groves that the British method of calculating the blast wave, while “more laborious and less perspicuous than the methods used here,” might be useful for studying the problem of the hydrodynamics of implosion. He concluded that they were “planning to attack the implosion problem along these lines with the highest possible urgency.”
Peierls was favorably impressed by Oppenheimer’s leadership and the efficiency and flexibility of the laboratory structure, enhanced by the weekly colloquiums held in the closely guarded theater. He was particularly pleased to see that no favoritism was exhibited to members of the American team over the British and that work was guided “by the necessity to get the best possible answer in the shortest possible time.” Peierls could not help noticing the tension between Oppenheimer an
d Teller, and their obviously complex relationship. Teller was supposed to head the “hydrodynamics group” to look into the problems of detonation waves and shock waves, but as he insisted on devoting his time to his pet project, the hydrogen bomb, Bethe had asked Peierls to lead it instead. Teller complained loudly and to anyone who would listen about the lack of support being expended on developing “the Super.” Finally, Oppenheimer agreed to let him carry on with a small group, even though it was clear that his work would not be contributing to their war work.
While Peierls had great admiration for Teller, “whose thoughts [were] often leaps and bounds ahead of his plodding colleagues,” he later reflected in his memoir that the Hungarian’s particular combination of ego and insecurity made him exceedingly difficult to manage. “Perhaps the reason was that Teller was anxious to earn Oppenheimer’s respect, not only as a physicist—which he undoubtedly had—but as a person.” Oppenheimer openly alluded to the tension after he gave a party in honor of Lord Cherwell at Los Alamos and, by some oversight, failed to invite Peierls, the deputy head of the British group. After discovering the mistake, Oppenheimer went to Peierls to apologize. “This is terrible,” he told him, “but there is an element of comfort in the situation: it might have happened with Edward Teller.”
TWELVE
Baby Boom
EVEN BEFORE the first explosions began echoing in the canyons around Los Alamos as the scientists tested their theory of implosion, ominous rumblings of change were disturbing the peaceful mesa. The pioneers, the small, tight-knit group of scientists who had first come to the site, now found there were many faces at dinner in Fuller Lodge they did not recognize. As more and more people arrived to work on the project in the spring of 1944, the housing crunch once again became acute. Families that were “expecting” signed up on the waiting list for larger apartments. The list was posted on a wall, so everyone knew who was pregnant, and for how long, and therefore had priority. Each week the list seemed to grow longer. Not long after Luis Alvarez and his family came to Los Alamos, his wife, Geraldine, became pregnant, and they signed up for a larger apartment. It caused a brief scandal when at the next Town Council meeting, the wife of a well-known European physicist complained that she did not want a Mexican family moving in next door. She was coolly informed that the Alvarez in question was the eminent Berkeley physicist, and the tall blond son of the famous Mayo Clinic physician Walter Alvarez.