of the fission and fusion components of the weapons, and to use the X-rays produced by the fission bomb to first compress the fusion fuel (by process known as "radiation implosion") before igniting it. Ulam's idea seems to have been to use mechanical shock from the primary to encourage fusion in the secondary, while Teller quickly realized that X-rays from the primary would do the job much more symmetrically. Some members of the laboratory (J. Carson Mark in particular) later expressed the opinion that the idea to use the X-rays would have eventually occurred to anyone working on the physical processes involved, and that the obvious reason why Teller thought of it right away was because he was already working on the "Greenhouse" tests for the spring of 1951, in which the effect of X-rays from a fission bomb on a mixture of deuterium and tritium was going to be investigated. Whatever the actual components of the so-called Teller–Ulam design and the respective contributions of those who worked on it, after it was proposed it was immediately seen by the scientists working on the project as the answer which had been so long sought. Those who previously had doubted whether a fission-fusion bomb would be feasible at all were converted into believing that it was only a matter of time before both the US and the USSR had developed multi-megaton weapons. Even Oppenheimer, who was originally opposed to the project, called the idea "technically sweet". Though he had helped to come up with the design and had been a long-time proponent of the concept, Teller was not chosen to head the development project (his reputation of a thorny personality likely played a role in this). In 1952 he left Los Alamos and joined the newly established Livermore branch of the University of California Radiation Laboratory, which had been created largely through his urging. After the detonation of Ivy Mike, the first thermonuclear weapon to utilize the Teller–Ulam configuration, on November 1, 1952, Teller became known in the press as the "father of the hydrogen bomb". Teller himself refrained from attending the test—he claimed not to feel welcome at the Pacific Proving Grounds—and instead saw its results on a seismograph in the basement of a hall in Berkeley. There was an opinion that by analyzing the fallout from this test, the Soviets (led in their H-bomb work by Andrei Sakharov) could