Robert Bacher
Robert Fox Bacher was an American nuclear physicist and one of the leaders of the Manhattan Project. Born in Loudonville, Ohio, Bacher obtained his undergraduate degree and doctorate from the University of Michigan, writing his 1930 doctoral thesis under the supervision of Samuel Goudsmit on the Zeeman effect of the hyperfine structure of atomic levels. After graduate work at the California Institute of Technology and the Massachusetts Institute of Technology, he accepted a job at Columbia University. In 1935 he accepted an offer from Hans Bethe to work with him at Cornell University in Ithaca, New York. It was there that Bacher collaborated with Bethe on his book Nuclear Physics. A: Stationary States of Nuclei, the first of three books that would become known as the "Bethe Bible".
In December 1940, Bacher joined the Radiation Laboratory at MIT, although he did not immediately cease his research at Cornell into the neutron cross section of cadmium. The Radiation Laboratory was organized into two sections, one for incoming radar signals, and one for outgoing radar signals. Bacher was appointed to handle the incoming signals section. Here he gained valuable experience in administration, coordinating not just the efforts of his scientists, but also those of General Electric and RCA. In 1942, Bacher was approached by Robert Oppenheimer to join the Manhattan Project at its new laboratory in Los Alamos, New Mexico. It was at Bacher's insistence that Los Alamos became a civilian rather than a military laboratory. At Los Alamos, Bacher headed the project's P Division, and later its G Division. Bacher worked closely with Oppenheimer, and the two men discussed the project's progress on a daily basis.
After the war, Bacher became director of the Laboratory of Nuclear Studies at Cornell. He also served on the U.S. Atomic Energy Commission, the civilian agency that replaced the wartime Manhattan Project, and in 1947 he became one of its inaugural commissioners. He left in 1949 to become head Division of Physics, Mathematics, and Astronomy at Caltech. He was appointed a member of the President's Science Advisory Committee in 1958. In 1962, he became Caltech's vice president and provost. He stepped down from the post of provost in 1970, and became a professor emeritus in 1976. He died in 2004 at the age of 99.
Early life and career
Bacher was born in Loudonville, Ohio, on August 31, 1905, the only child of Harry and Byrl Fox Bacher. In 1908, the family moved to Ann Arbor, Michigan, where Harry worked as a banker and Byrl as a voice teacher on the University of Michigan faculty. Bacher attended the W. S. Perry School, and later Ann Arbor High School. While there he met Professor Harrison M. Randall, the head of the physics department at the University of Michigan, who encouraged him to study physics.Bacher entered the University of Michigan, where he joined the Kappa Sigma fraternity and lived in the frat house. He became the house manager in his sophomore year, but moved back home in his junior year to concentrate on physics. At Randall's suggestion he applied to the Harvard Graduate School of Arts and Sciences, which he entered in 1926 to study for his doctorate. His fees were paid by his family, but his father had a heart attack and could no longer afford them, so in 1927 Bacher moved back to Ann Arbor, where he lived at home, and attended the University of Michigan. He received a Charles A. Coffin Foundation Fellowship from General Electric.
To build up the theoretical physics department at the University of Michigan, Randall recruited four distinguished young physicists to work at Ann Arbor in 1927: Otto Laporte, George Uhlenbeck, Samuel Goudsmit, and David M. Dennison. The University of Michigan was no longer a backwater in theoretical physics. Bacher immediately signed up for Goudsmit's course on atomic structure. With Goudsmit he investigated the Zeeman effect of hyperfine structure of atomic levels, which became the subject of his 1930 PhD thesis.
On May 30, 1930, Bacher married Jean Dow. His mother gave them a Ford Model A and the use of the family's lakeside holiday house, where they entertained guests including Paul Ehrenfest and Enrico Fermi. In 1931, with a National Research Council Fellowship, he spent a year at the California Institute of Technology because Ira Bowen taught there. At Caltech Bacher attended lectures by Robert Oppenheimer, but spent most of his time at the Mt. Wilson Observatory, which had a better library. Bacher decided to create a work listing the energy, coupling constant, parity and electron configurations of all the known atoms and ions, working with Goudsmit back in Ann Arbor. The result was a book, Atomic Energy States as Derived from the Analysis of Optical Spectra, which they dedicated to Randall.
In the second year of his National Research Council Fellowship, Bacher moved across the country to the Massachusetts Institute of Technology to work with John C. Slater, who had taught Bacher at Harvard. While there, Slater asked him to conduct a seminar on James Chadwick's recent discovery of the neutron. Reading Chadwick's paper, he realized that anomalies in then-current theory would be resolved if the spin of the neutron was. This became the subject of a letter he submitted to the Physical Review with visiting scholar Edward Condon. A year later, Bacher became the first to suggest the neutron had a magnetic moment equal to about minus one nuclear magneton, based on the unusually small magnetic moment of nitrogen determined from its hyperfine structure.
Afterwards Bacher returned to the University of Michigan on an Alfred H. Lloyd Fellowship. Jobs were hard to find at this time due to the Great Depression, and in 1934 he accepted a job at Columbia University, where he worked with Isidor Isaac Rabi, Jerrold Zacharias, Jerome Kellogg and Sid Millman. However it was difficult living in New York on his salary, and Jean gave birth to their first child, Martha, in December 1935. A second child, Andrew, was born in 1938. Bacher therefore accepted an offer from Hans Bethe to work with him at Cornell University in Ithaca, New York. Ithaca was a university town similar to Ann Arbor, where Bacher and Jean had been raised. At Cornell Bacher worked with Bethe on his book Nuclear Physics. A: Stationary States of Nuclei, the first of three books that would become known as the "Bethe Bible".
World War II
Radiation Laboratory
In December 1940 Bacher joined the Radiation Laboratory at MIT, but did not immediately cease his research. He reached an arrangement with its director, Lee Alvin DuBridge, to return to Cornell for four days every three weeks until it was completed. He was researching the neutron cross section of cadmium, a topic of interest to Enrico Fermi, who was attempting to build a nuclear reactor, but whose figures did not agree with Bacher's. Bacher carefully checked his results, and Fermi, convinced of their correctness, urged Bacher to publish them. Bacher submitted a paper to the Physical Review with instructions to withhold publication until after the war, and the paper was not published until 1946.DuBridge organized the Radiation Laboratory into two sections, one for incoming radar signals, and one for outgoing radar signals. Bacher was appointed to handle the incoming signals section. Here he gained valuable experience in administration, coordinating not just the efforts of his scientists, but also those of General Electric and RCA. He later recalled:
Manhattan Project
In 1942, Bacher and Rabi, the Radiation Laboratory's assistant director, were approached by Oppenheimer to join the Manhattan Project at its new laboratory in Los Alamos, New Mexico. They convinced Oppenheimer that the plan for a military laboratory would not work, since a scientific effort would need to be a civilian affair. The plan was modified, and the new laboratory would be a civilian one, run by the University of California under contract from the War Department. Bacher felt that this was his first contribution to the success of the project. He met with Oppenheimer at Los Alamos in April 1943, but was not convinced that he was needed. Oppenheimer wrote to him that:File:Leslie Groves, Richard Tolman and Robert Bacher.jpg|thumb|left|Bacher is awarded the Medal for Merit by Major General Leslie R. Groves, Jr. |alt= Two men in suits, with medals pinned on the left breast. One shakes hands with a fat man in an Army uniform.
Bacher then accepted the job at Los Alamos, moving there in May 1943 with his family to become the head of the Experimental Physics Division. His wife Jean Dow Bacher was also hired to work as a human computer in the Theoretical Division. For his seven group leaders he had John H. Williams, Robert R. Wilson, John H. Manley, Darol K. Froman, Emilio G. Segrè, Bruno B. Rossi and Donald W. Kerst. Bacher worked closely with Oppenheimer, and the two men discussed the project's progress on a daily basis.
In July 1944, Oppenheimer reorganized the laboratory to focus on the problem of building an implosion-type nuclear weapon, which was necessary because the gun-type design would not work with plutonium. P Division was broken up, and Bacher became the head of the G Division. This much larger division contained eleven groups headed by leaders who included William Higinbotham, Seth Neddermeyer, Edwin McMillan, Luis Alvarez and Otto Frisch.
While George Kistiakowsky's Explosives Division developed the explosive lenses, G Division designed the rest of the weapon. There were numerous difficulties to overcome, not the least of which was devising a means of detonating the lenses with the required speed. Robert F. Christy's solid core design was chosen as the most likely design to succeed.
To coordinate the efforts of the laboratory, Oppenheimer created the "Cowpuncher Committee", so-called because they were to "ride herd" on the implosion effort and coordinate all the efforts of the laboratory. It included Bacher, along with Samuel Allison, George Kistiakowsky, Deak Parsons, Charles Lauritsen and Hartley Rowe.
Three days before the day the bomb was to be test detonated in the New Mexico desert, Bacher was part of the pit assembly team, which assembled the nuclear capsule in an old farmhouse near the Alamogordo testing site. When the capsule was driven to the shot tower and inserted into the spherical tamper, inside the explosive assembly, it stuck. Bacher recognized that expansion of the capsule due to the heat given off by the plutonium core was causing the jam, and that leaving the two parts in contact would equalize temperatures and allow the capsule to be inserted fully. After watching the test, his reaction was merely "Well, it works."
Bacher was packaging the third core for shipment to Tinian on August 12 at the Ice House at Los Alamos when he received word that the Japanese had initiated surrender negotiations. He had already set G Division the task of designing and building new types of cores and assemblies, and he co-authored a report with Robert Wilson urging the development of Edward Teller's Super bomb. He served on a committee chaired by Richard Tolman that looked into declassifying documents produced by the Manhattan Project, and one chaired by Manson Benedict that investigated the technical feasibility of international control of nuclear energy. For his services to the Manhattan Project Bacher was awarded the Medal for Merit on January 12, 1946.