American Prometheus (49 page)
By contrast, General Groves’ visits were always interruptions—and sometimes comically disruptive. One day, Oppie was showing Groves around a lab when the general put his considerable weight on one of three rubber tubes funneling hot water into a casing. As McAllister Hull recalled for the historian Charles Thorpe, “It [the rubber tube] pops off the wall and a stream of water just below the boiling point shoots across the room. And if you’ve ever seen a picture of Groves, you know what it hit.” Oppenheimer looked over his soaking-wet general and quipped, “Well, just goes to show the incompressibility of water.”
Oppie’s interventions sometimes proved to be absolutely essential to the success of the project. He understood that the single major impediment to building a usable weapon quickly was the meager supply of fissionable material. And so he was constantly looking for ways to accelerate the production of these materials. Early in 1943, Groves and his S-1 Executive Committee had settled on gaseous diffusion and electromagnetic technologies to separate out enriched fissionable uranium for the Los Alamos bomb lab. At the time, another possible technology, based on liquid thermal diffusion, had been rejected as unfeasible. But in the spring of 1944, Oppenheimer read some year-old reports about liquid thermal diffusion and decided that this had been a mistake. He thought this technology represented a relatively cheap path to providing partially enriched uranium for the electromagnetic process. So in April 1944, he wrote Groves that a liquid thermal diffusion plant might serve as a stopgap measure; its production of even slightly enriched uranium could then be fed to the electromagnetic diffusion plant and thereby accelerate production of fissionable material. It was his hope, he wrote, “that the production of the Y-12 [electromagnetic] plant could be increased by some 30 to 40 percent, and its enhancement somewhat improved, many months earlier than the scheduled date for K-25 [gaseous diffusion] production.”
After sitting on Oppie’s recommendation for a month, Groves agreed to explore it. A plant was rushed into production, and by the spring of 1945 it was producing just enough extra partially enriched uranium to guarantee a sufficient amount of fissionable material for one bomb by the end of July 1945.
Oppenheimer had always possessed a high degree of confidence in the uranium gun-design program—whereby a “slug” of fissionable material would be fired into a target of additional fissionable matter, creating “criticality” and a nuclear explosion. But in the spring of 1944, he suddenly faced a crisis that threatened to derail the entire effort to design a plutonium bomb. While Oppenheimer had authorized Seth Neddermeyer to conduct explosive experiments aimed at creating an implosion design bomb—a loosely packed sphere of fissionable material that could be instantly compressed to reach criticality—he had always hoped that a straightforward gun assembly would prove viable for the plutonium bomb. In July 1944, however, it became clear from tests performed on the first small supplies of plutonium that an efficient plutonium bomb could not be triggered within the “gun-barrel” design. Indeed, any such attempt would undoubtedly lead to a catastrophic pre-detonation inside the plutonium “gun.”
One solution might have been to separate further the plutonium materials in an attempt to make a more stable element. “One could have separated out those bad plutonium isotopes from the good ones,” John Manley explained, “but that would have meant duplicating everything that had been done for uranium isotope separation—all those big plants—and there was just no time to do that. The choice was to junk the whole discovery of the chain reaction that produced plutonium, and all of the investment in time and effort of the Hanford [Washington] plant, unless somebody could come up with a way of assembling the plutonium material into a weapon that would explode.”
On July 17, 1944, Oppenheimer convened a meeting in Chicago with Groves, Conant, Fermi and others, to resolve the crisis. Conant urged that they aim merely to build a low-efficiency implosion bomb based on a mixture of uranium and plutonium. Such a weapon would have had an explosive equivalent of only several hundred tons of TNT. Only after successfully testing such a low-efficiency bomb, Conant said, would the lab have the confidence to proceed with a larger weapon.
Oppenheimer rejected this notion on the grounds that it would lead to unacceptable delays. Despite having been skeptical about the implosion idea when it was first broached by Serber, Oppenheimer now marshaled all his persuasive powers to argue that they gamble everything on an implosion-design plutonium bomb. It was an audacious and brilliant gamble. Since the spring of 1943, when Seth Neddermeyer had volunteered to experiment with the concept, little progress had been made. But in the autumn of 1943, Oppenheimer brought the Princeton mathematician John von Neumann to Los Alamos, and von Neumann calculated that implosion was possible, at least theoretically. Oppenheimer was willing to bet on it.
The next day, July 18, Oppenheimer summarized his conclusions for Groves: “We have investigated briefly the possibility of an electromagnetic separation. . . . It is our opinion that this method is in principle a possible one but that the necessary developments involved are in no way compatible with present ideas of schedule. . . . In the light of the above facts, it appears reasonable to discontinue the intensive effort to achieve higher purity for plutonium and to concentrate attention on methods of assembly which do not require a low neutron background for their success. At the present time the method to which an overriding priority must be assigned is the method of implosion.”
Oppenheimer’s assistant, David Hawkins, later explained, “The implosion was the only real hope [for a plutonium bomb], and from current evidence not a very good one.” Neddermeyer and his men in the Ordnance Division were making very little progress on the implosion design. Neddermeyer, shy and retiring, liked to work alone, and methodically. He later admitted that Oppenheimer “became terribly impatient with me in the spring of 1944. . . . I think he felt very badly because I seemed not to push things as for war research but acted as though it were just a normal research situation.” Neddermeyer was also one of the few men on the mesa who seemed immune to Oppie’s charms. In his frustration, Oppie uncharacteristically began to lose his temper. “Oppenheimer lit into me,” Neddermeyer recalled. “A lot of people looked up to him as a source of wisdom and inspiration. I respected him as a scientist, but I just didn’t look up to him that way. . . . He could cut you cold and humiliate you right down to the ground. On the other hand, I could irritate him.” Stoked by this personality conflict, the crisis over the implosion design came to a head late that summer when Oppenheimer announced a major reorganization of the lab.
Early in 1944, Oppenheimer had persuaded an explosives expert from Harvard, George “Kisty” Kistiakowsky, to move to Los Alamos. Kistiakowsky was opinionated and strong-willed. Inevitably, he had numerous run-ins with his ostensible superior, Captain “Deke” Parsons. Neither did Kistiakowsky get along with Neddermeyer, who seemed to him far too lackadaisical in his approach. Early in June 1944, Kistiakowsky wrote Oppenheimer a memo threatening to resign. In response, Oppenheimer swiftly called Neddermeyer in and told him that Kistiakowsky was replacing him. Angry and hurt, Neddermeyer walked out. Although he would feel an “enduring bitterness,” he nevertheless was persuaded to remain in Los Alamos as a senior technical adviser. Acting decisively, Oppenheimer had announced this change without first consulting Captain Parsons. “Parsons was furious,” recalled Kistiakowsky. “He felt that I had bypassed him and that was outrageous. I can understand perfectly how he felt, but I was a civilian, so was Oppie, and I didn’t have to go through him.”
Parsons chafed at what he considered a loss of control over his Ordnance Division, and in September he sent Oppie a memorandum proposing to give himself broad decision-making powers over all aspects of the implosion bomb project. Oppenheimer gently but firmly refused: “The kind of authority which you appear to request from me is something I cannot delegate to you because I do not possess it. I do not, in fact, whatever protocol may suggest, have the authority to make decisions which are not understood and approved by the qualified scientists of the laboratory who must execute them.” As a military man, Navy Captain Parsons wanted the authority in order to short-circuit the debates among his scientists. “You have pointed out,” Oppenheimer wrote him, “that you are afraid your position in the laboratory might make it necessary for you to engage in prolonged argument and discussion in order to obtain agreement upon which the progress of the work would depend. Nothing that I can put in writing can eliminate this necessity.” The scientists had to be free to argue—and Oppenheimer would arbitrate disputes only for the purpose of reaching some kind of collegial consensus. “I am not arguing that the laboratory should be so constituted,” he told Parsons. “It is in fact so constituted.”
In the midst of this ongoing crisis associated with the design of the plutonium bomb, Isidor Rabi paid one of his periodic visits to Los Alamos. He later remembered a gloomy session with a number of top scientists on the project as they talked of the urgency they felt about finding a way to make the plutonium bomb work. The conversation soon turned to the enemy: “Who were the German scientists? We knew them all,” Rabi recalled.
“What were they doing? We went over the whole thing again and looked at the history of our own development and tried to see where they could have been cleverer, where they might have had better judgment and avoided this error or that error. . . . We finally arrived at the conclusion that they could be exactly up to us, or perhaps further. We felt very solemn. One didn’t know what the enemy had. One didn’t want to lose a single day, a single week. And certainly, a month would be a calamity.” As Philip Morrison summed up their attitude in mid-1944, “The only way we could lose the war was if we failed in our jobs.”
Despite the reorganization, by late 1944 Kistiakowsky’s group had still not managed to manufacture shaped explosives (called lenses) that would precisely crush a loosely packed, grapefruit-sized sphere of plutonium symmetrically into a sphere the size of a golf ball. Without such lenses, an implosion bomb seemed impractical. Captain Parsons was so pessimistic that he went to Oppenheimer and proposed that they abandon the lenses and try instead to create a non-lens type of implosion. In January 1945, the issue was hotly debated between Parsons and Kistiakowsky in the presence of both Groves and Oppenheimer. Kistiakowsky insisted that implosion could not be achieved without the lenses, and he promised that his men would soon be able to make them. In a decision critical to the success of the plutonium bomb, Oppenheimer backed him. During the next few months, Kistiakowsky and his team managed to perfect the implosion design. By May 1945, Oppenheimer felt fairly confident that the plutonium gadget would work.
Bomb-building was more engineering than theoretical physics. But Oppenheimer was as singularly adept at marshaling his scientists to overcome technical and engineering obstacles as he had been at stimulating his students to new insights at Berkeley. “Los Alamos might have succeeded without him,” Hans Bethe later said, “but certainly only with much greater strain, less enthusiasm, and less speed. As it was, it was an unforgettable experience for all the members of the laboratory. There were other wartime laboratories of high achievement. . . . But I have never observed in any one of these other groups quite the spirit of belonging together, quite the urge to reminisce about the days of the laboratory, quite the feeling that this was really the great time of their lives. That this was true of Los Alamos was mainly due to Oppenheimer. He was a leader.”
IN FEBRUARY 1944, a team of British scientists led by the German-born Rudolf E. Peierls arrived in Los Alamos. Oppenheimer had first met this brilliant but unassuming theoretical physicist in 1929, when both men were studying under Wolfgang Pauli. Peierls had emigrated from Germany to England in the early 1930s, and in 1940 he and Otto R. Frisch had written the seminal paper “On the Construction of a Superbomb,” which had persuaded both the British and American governments that a nuclear weapon was feasible. During the next several years, Peierls worked on all aspects of Tube Alloys, the British bomb program. In 1942 and again in September 1943, Prime Minister Winston Churchill sent Peierls to America to help expedite work on the bomb. Peierls visited Oppenheimer in Berkeley and was “very impressed with his command of things. . . . He was the first person I met on that trip who had thought about the weapon itself and the implications of the physics of what would be going on.”
Dr. Peierls spent only two and a half days on his first visit to Los Alamos. But Oppenheimer reported to Groves that they had agreed the British team could contribute substantially to studying the hydrodynamics of implosion. A month later, Peierls moved back to Los Alamos for the duration of the war. He admired how articulate and quick Oppenheimer was to understand anyone—but he particularly admired the way “he could stand up to General Groves.”
As Peierls and his team settled into Los Alamos in the spring of 1944, Oppenheimer decided to give Peierls the job ostensibly held by Edward Teller. The mercurial Hungarian physicist was supposed to be working on a complicated set of calculations necessary for the implosion bomb. But Teller wasn’t performing. Obsessed with the theoretical challenges posed by a “Super” thermonuclear bomb, Teller had no interest in a fission bomb. After Oppenheimer decided in June 1943 that wartime exigencies dictated a low priority for the Super, Teller became increasingly uncooperative. He seemed oblivious to any responsibility to contribute to the war effort. Always loquacious, he talked incessantly about a hydrogen bomb. Neither could he contain his resentment at having to work under Bethe. “I was not happy about having him as my boss,” Teller recalled. To be sure, his resentment was fueled by Bethe’s criticisms. Every morning Teller would have a bright new idea about how to make an H-bomb work—and overnight Bethe would prove it cockeyed. After one particularly trying encounter with Teller, Oppie quipped to Charles Critchfield, “God protect us from the enemy without and the Hungarians within.”