1939 and completed two postdoctoral years at Stanford. Physics career During World War II, Frank's older brother Robert became the director of the Los Alamos Laboratory, part of the Manhattan Project, the Allied effort to produce the first atomic weapons. From 1941 to 1945 Frank worked at the University of California Radiation Laboratory on the problem of uranium isotope separation under the direction of his brother's good friend, Ernest O. Lawrence. In late 1943 he arrived at the Los Alamos Laboratory, working directly under Kenneth T. Bainbridge. His responsibilities included the instrumentation for the Trinity test site, in New Mexico. In 1945 he was sent to the enrichment facility at Oak Ridge, Tennessee, to help monitor the equipment. Oppenheimer was involved in the founding of the Association of Los Alamos Scientists, on August 30, 1945. This organization promoted international peaceful control of nuclear power. He later also joined the Federation of American Scientists, and was a member of the American Physical Society. After the war, Oppenheimer returned to Berkeley, working with Luis Alvarez and Wolfgang Panofsky to develop the proton linear accelerator. In 1947 he took a position as assistant professor of physics at the University of Minnesota, where he participated in the discovery of heavy cosmic ray nuclei. Political scrutiny and blacklisting On July 12, 1947, the Washington Times Herald reported that Oppenheimer had been a member of the Communist Party during the years 1937–1939. At first, he denied these reports, but later admitted they were true. In June 1949, as part of a larger investigation on the possible mishandling of "atomic secrets" during the war, he was called before the United States Congress House Un-American Activities Committee (HUAC). Before the committee, he testified that he and his wife had been members of the Communist Party for about three and a half years. In 1937 they had been involved in local attempts to desegregate the Pasadena public swimming pool, which was open to non-whites only on Wednesday, after which the pool was drained and the water replaced. Oppenheimer said he and his wife had joined at a time when they sought answers to the high unemployment experienced in the United States during the later part of the Great Depression. He refused to name others he knew to be members. This caused a media sensation—that J. Robert Oppenheimer's brother was an admitted former member of the Communist Party—and led to