Barring discovery of any new and unforeseen technological impedimenta, Lawrence was beginning to be optimistic that Dogpatch could provide the uranium to meet Compton’s revised schedule—a bomb by mid-1945. The chief uncertainty remaining was the design of the weapon.
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Many of Lawrence’s boys who had not been sent to Oak Ridge began to show up at Los Alamos early in the year. By February 1944, Emilio Segrè was a group leader in the Physics Division.94 Luis Alvarez finally got to the desert lab from MIT in late spring, following a detour to the Met Lab at Oppenheimer’s request. Alvarez was assigned to work with George Kistiakowsky, another recent arrival, on electrical detonators for the implosion bomb.95 After helping to find equipment and recruit other scientists for Los Alamos, Ed McMillan worked on early implosion experiments and, later, on design of the gun.96
The main effort at the lab was now focused upon the gun and the implosion gadget, although work was stalemated on the latter, Tolman reported to Groves in March. The “prime objective” for the remainder of the year, Oppenheimer wrote Groves, was “to bring to a successful conclusion the development of the implosion unit with (U-235).”97
Alternative concepts for the atomic bomb had been gradually discarded, one by one. An imaginative proposal put forward by Bohr was studied by Bethe and Teller and found to be “a quite useless military weapon,” Oppenheimer informed Groves.98 Work on the hydride bomb, the weapon that Teller had championed early on at the lab, was finally, and reluctantly, abandoned by him in the winter of 1943–44. Studies showed that uranium hydride could not be easily compressed in a gun, and that any explosion that resulted would be far less efficient than a weapon using metallic uranium or plutonium.99 The yield of Teller’s hydride would be “negligible or less,” concluded Princeton’s Richard Feynman.100
But a far more serious problem would soon come to light, in an experiment by Segrè. When the first significant sample of reactor-produced plutonium arrived in early summer, Segrè’s group was surprised to find it had a rate of spontaneous fission five times that of the plutonium produced on the 60-inch at Berkeley. Further studies confirmed that reactor-bred plutonium contained too much Pu-240, an isotope with a high rate of spontaneous fission, to be usable in a gun-type bomb. Upon firing, a plutonium gun would “preinitiate” and fizzle—spewing molten radioactive metal in all directions.101 Oppenheimer ordered work on Thin Man, the plutonium gun, abandoned.
The so-called implosion crisis forced a reorganization of the laboratory that August. Oppenheimer gave Bacher and Kistiakowsky the job of making the spherical implosion design—Fat Man—a success, creating two new divisions at the lab for the purpose.102 Calculations carried out earlier by Teller and John von Neumann, a Princeton mathematician brought to the lab as a consultant, had shown how the compression attainable in the implosion design made it potentially far more efficient than the gun. Henceforth, the emphasis at the lab would be upon “fast” implosion and Fat Man.103
Despite his previous work on the subject, Teller lost interest in the implosion problem as Oppenheimer brought in more of his colleagues to solve it. (Teller’s heart remained with the purely theoretical. A visit to Y-12 earlier in the year had confirmed his belief that the atomic bomb was an engineering, not a physics, challenge. Although he pronounced Y-12 “Super-colossal,” he wrote, “[it is] wonderful that I do not have to live there.”)104 With the hydride having hit a dead end, Teller returned to his first pet project: the Super.
Since the fall, Teller had been urging that the level of effort on the superbomb be increased at the lab—citing recent reports that the Germans were experimenting with heavy water, and calculations which indicated that less deuterium might be required than originally anticipated.105 Preoccupied with the gadget, Oppenheimer and the lab’s governing board had denied Teller’s request. But Oppie encouraged Edward to continue exploring the possibility of a superbomb with a small group in the Theoretical Division.
One of the key unanswered question from the 1942 Berkeley seminar that was of relevance to the Super concerned what happened to the radiation created in an atomic bomb. Resolving the issue of the superbomb’s feasibility awaited discovery of whether its internal components permitted or impeded the transfer of energy in the form of radiation. Teller and Konopinski had yet to do the calculations on the phenomenon known as opacity that they had promised to do at Berkeley.106 On a visit to New York, Teller persuaded a friend and confidante, Columbia University physicist Maria Göppert Mayer, to carry out the laborious work that might answer the question. Teller had known Mayer since the mid-1930s, describing her as his “Dutch aunt,” to whom he confessed both professional and personal problems. (“Slender and blond, she had a natural delicacy and grace as well as considerable strength of mind,” Teller later wrote of Mayer. Maria was married to a chemist, and the couple had two small children.)107
Oppenheimer gave Teller permission to hire Mayer for the opacity calculations, but forbade him from disclosing the intended application. (Teller later recalled their conversation: “I had to tell her it is uranium, and I had to tell her at what temperature.… There was a clear intake of breath. And no more questions.”)108
But even Teller acknowledged that his own most recent calculations on the Super showed the need for more tritium. The loss of energy due to radiation seemed greater than he had predicted two years earlier. Accordingly, Edward conceded that development of the superbomb “may require longer than was originally anticipated.”109 Oppenheimer agreed to let Teller continue his work, so long as it did not jeopardize the timetable for the fission gadget.*110
During the early summer of 1944, amid the crisis over Thin Man, Teller had twice refused a request from T Division’s
