the cataclysmic explosion of uranium ... I'm sure old Nobel would approve." In March 1940, Arthur Compton, Vannevar Bush, James B. Conant, Karl T. Compton, and Alfred Lee Loomis traveled to Berkeley to discuss Lawrence's proposal for a 184-inch cyclotron with a 4,500-ton magnet that was estimated to cost $2.65 million. The Rockefeller Foundation put up $1.15 million to get the project started. World War II and the Manhattan Project Radiation Laboratory After the outbreak of World War II in Europe, Lawrence became drawn into military projects. He helped recruit staff for the MIT Radiation Laboratory, where American physicists developed the cavity magnetron invented by Oliphant's team in Britain. The name of the new laboratory was deliberately copied from Lawrence's laboratory in Berkeley for security reasons. He also became involved in recruiting staff for underwater sound laboratories to develop techniques for detecting German submarines. Meanwhile, work continued at Berkeley with cyclotrons. In December 1940, Glenn T. Seaborg and Emilio Segrè used the cyclotron to bombard uranium-238 with deuterons producing a new element, neptunium-238, which decayed by beta emission to form plutonium-238. One of its isotopes, plutonium-239, could undergo nuclear fission which provided another way to make an atomic bomb. Lawrence offered Segrè a job as a research assistant—a relatively lowly position for someone who had discovered an element—for US$300 a month for six months. However, when Lawrence learned that Segrè was legally trapped in California, he reduced Segrè's salary further to US$116 a month. When the regents of the University of California wanted to terminate Segrè's employment owing to his foreign nationality, Lawrence managed to retain Segrè by hiring him as a part-time lecturer paid by the Rockefeller Foundation. Similar arrangements were made to retain his doctoral students Chien-Shiung Wu (a Chinese national) and Kenneth Ross MacKenzie (a Canadian national) when they graduated. In September 1941, Oliphant met with Lawrence and Oppenheimer at Berkeley, where they showed him the site for the new cyclotron. Oliphant, in turn, took the Americans to task for not following up the recommendations of the British MAUD Committee, which advocated a program to develop an atomic bomb. Lawrence had already thought about the problem of separating the fissile isotope uranium-235 from uranium-238, a process known today as uranium enrichment. Separating uranium isotopes was difficult because the two isotopes have very nearly identical chemical properties, and could only be separated gradually using their small mass differences.