Frank Friedman Oppenheimer (14 August 1912 – 3 February 1985) was an American particle physicist, cattle rancher, professor of physics at the University of Colorado, and the founder of the Exploratorium in San Francisco.

After the war, Oppenheimer's earlier involvement with the American Communist Party placed him under scrutiny, and he resigned from his physics position at the University of Minnesota.

His parents were Ella (née Friedman), a painter, and Julius Seligmann Oppenheimer, a successful textile importer from Hanau in the Kingdom of Prussia.

He also studied the flute under nationally known teacher George Barrera, becoming competent enough at the instrument to consider a career as a flautist.

[8] During World War II, Oppenheimer'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 Oppenheimer worked at the University of California Radiation Laboratory on the problem of uranium isotope separation under the direction of his brother's friend, Ernest O.

[2] 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,[13] where he participated in the discovery of heavy cosmic ray nuclei.

[14] 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).

[6] 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.

[6]: 99  He and his wife eventually sold one of the Van Gogh paintings that he had inherited from his father, and with the money bought 1,500 acres (610 ha) of ranch land near Pagosa Springs, Colorado, and spent nearly a decade as cattle ranchers.

[19] Under Oppenheimer's tutelage, several students from Pagosa Springs High School took first prize at the Colorado State Science Fair.

[6]: 117  Within two years, supported by endorsements from physicists Hans Bethe, George Gamow, and Victor Weisskopf,[6]: 130  Oppenheimer was offered a position at the University of Colorado teaching physics.

[20] In 1965, Oppenheimer was awarded a Guggenheim Fellowship to study the history of physics and to conduct bubble chamber research at University College London, where he was exposed to European science museums for the first time.

Upon his return from Europe, he was offered a job planning a new branch of the Smithsonian Institution in Washington, D.C., but instead chose to work on setting up a completely independent new type of museum in San Francisco.

[16] Four years later, in 1969, the Exploratorium opened its doors, set within the north wing of the Palace of Fine Arts of San Francisco.

He had visited the Tel Aviv Science Museum in 1965, and later used several of Ivan Moscovich's designs and exhibits in his revolutionary Exploratorium in San Francisco.

[16] The Frank Oppenheimer Fellowship Fund was created at the Exploratorium to provide for the exchange of science museum personnel both nationally and internationally.