David M. Dennison

David Mathias Dennison (April 26, 1900 in Oberlin, Ohio – April 3, 1976)[1] was an American physicist who made contributions to quantum mechanics, spectroscopy, and the physics of molecular structure.[2]

Dennison, David M., 1969 Ann Arbor
David M. Dennison at his home in Ann Arbor, Michigan. 1969

Education

In 1917, Dennison entered Swarthmore College, where he graduated in 1921. He then went to the University of Michigan, in Ann Arbor, for graduate studies in physics with Walter F. Colby and Oskar Klein. Klein, already associated with the Kaluza–Klein theory (1921), joined the faculty at Michigan in 1922, after a six-year stay at the Institute for Theoretical Physics, under Niels Bohr, at the University of Copenhagen.[3] It was through Klein that Dennison heard and leaned much about the current theoretical physics being developed in Europe, which created a yearning in him to go to Copenhagen for further study. Dennison's thesis was on the molecular structure and infrared spectrum of the methane molecule,[4] and he was awarded his doctorate in 1924.[5][6][7]

From 1924 to 1926, Dennison had an International Education Board (IEB) Fellowship to do postgraduate study and research in Europe. By the end of that time, Harrison McAllister Randall, chairman of physics department at the University of Michigan, had arranged for Dennison to stay in Europe another year on a University of Michigan fellowship. Dennison arrived at the Institute of Theoretical Physics at the University of Copenhagen, in October 1924.[8] During his three years in Europe, he mostly did postdoctoral research in Copenhagen, where he had associations with other visiting physicists working there, such as Paul Dirac, Samuel Abraham Goudsmit, Werner Heisenberg, Walter Heitler, Ralph H. Fowler, Friedrich Hund, Hendrik Anthony Kramers, Yoshio Nishina, Wolfgang Pauli, and George Eugene Uhlenbeck. In the last half of 1925, Heisenberg and Max Born published their matrix mechanics formulation of quantum mechanics. In the fall of 1926 he went to the University of Zurich to study and work with Erwin Schrödinger, who had early in the year published his papers on his wave mechanics formulation of quantum mechanics. In early spring of 1927, Dennison went back to Copenhagen, and in late spring he went to the University of Cambridge to work with Ralph Fowler for six weeks – there at the time were Ernest Rutherford, Nevill Francis Mott, Pyotr Kapitsa, Patrick Blackett, and John Cockcroft. The last few weeks of his fellowship were spent at the University of Leiden with Paul Ehrenfest.[6][7]

In 1925, George Eugene Uhlenbeck and Samuel Abraham Goudsmit had proposed spin, and Wolfgang Pauli had proposed the Pauli exclusion principle. In 1926, Enrico Fermi and Paul Dirac introduced Fermi–Dirac statistics. While at Cambridge, Dennison used quantum mechanicals calculations on molecular hydrogen to show that protons, like electrons, were subject to Fermi–Dirac statistics, or had spin-½, and therefore obeyed the Pauli exclusion principle.[9][10]

Career

In 1927, upon Dennison's return from Europe, he started his lifelong career at the University of Michigan until 1976.[11] Otto Laporte had arrived at Michigan in 1926, and George Uhlenbeck and Samuel Goudsmit arrived in 1927. These four men were a team in developing theoretical physics, including quantum mechanics, for many years. They had been brought there by the chairman of the physics department, Harrison McAllister Randall, to build the theoretical capabilities of the department.[7][12]

Dennison was a student of Niels Bohr, and knew Hans Bethe, Wolfgang Pauli, and Enrico Fermi before they became world-famous.[13] Most of Dennison's work was on molecular structure. Following the discovery of the spin of the electron in 1925 by George Uhlenbeck and Samuel Goudsmit, the specific heat of hydrogen was a major unsolved problems. Dennison solved this problem in 1927 by postulating that the spin of protons does not transition frequently during measurements. This new theory agreed precisely with experiments given that the proton's spin was 1/2.[14] In 1932 Dennison and Uhlenbeck solved the two-minima "reversing umbrella" problem for the position of nitrogen in ammonia. This result predicted absorption at microwave wavelengths, which inspired Neal Williams to build a molecular microwave spectrograph, one of the first ever built. During World War 2 Dennison received a citation from the US Navy for his work with the VT radio proximity fuse.[13] After the war, Dennison returned to work on molecular structure, as well as working on the design of the new synchrotron at Michigan. With Theodore H. Berlin, he developed the theory of stable orbits in a synchrotron with straight sections, a feature that soon became standard in most large synchrotrons.[14]

The David M. Dennison Building on the campus of the University of Michigan was originally named in his honor, but was remodeled and renamed as the Weiser building (in 2017) due to a large cash donation from Ron Weiser.[15] The Colloquium Hall of the Department of Physics now bears Dennison's name. Dennison Reef, in Crystal Sound, Antarctica is also named in his honor.

Selected Literature

  • David M. Dennison The Molecular Structure and Infra-Red Spectrum of Methane, The Astrophysical Journal 62 84 (1925)
  • David M. Dennison The Rotation of Molecules, Phys. Rev. 28 (2) 318–333 (1926). Institute for Theoretical Physics, Copenhagen, Denmark, Received 27 April 1926.
  • David M. Dennison A Note on the Specific Heat of the Hydrogen Molecule Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character Vol. 115, No. 771 pp. 483–486 (1927). Communicated by R. H. Fowler; received 3 June 1927.
  • David M. Dennison The Infrared Spectra of Polyatomic Molecules Part I, Rev. Mod. Phys. 3 (2) 280–345 (1931). University of Michigan.
  • David M. Dennison The Infra-Red Spectra of Polyatomic Molecules. Part II, Rev. Mod. Phys. 12 (3) 175–214 (1940). University of Michigan, Ann Arbor, Michigan.
  • David M. Dennison, Recollections of Physics and of Physicists During the 1920s, Am. J. Phys. 42 1051–1056 (1974)

References

  • Kragh, Helge Quantum Generations: A History of Physics in the Twentieth Century (Princeton University Press, fifth printing and first paperback printing, 2002) ISBN 0-691-01206-7
  • Max Jammer The Conceptual Development of Quantum Mechanics (McGraw-Hill, 1966)

Notes

  1. ^ American Institute of Physics
  2. ^ Crane, H. Richard; Hecht, Karl T. (July 1976). "David M. Dennison". Physics Today. 29 (7): 71. Bibcode:1976PhT....29g..71C. doi:10.1063/1.3023597.
  3. ^ In 1926, while at the University of Michigan, Kline would publish on the Klein–Gordon equation. In that year, he returned to the University of Copenhagen for five years. Working with Yoshio Nishina there, he would publish on the Klein–Nishina formula in 1929.
  4. ^ Doctoral thesis, 1924, University of Michigan: David M. Dennison The Molecular Structure and Infra-Red Spectrum of Methane, The Astrophysical Journal 62 84 (1925).
  5. ^ Kragh, 2002, p. 160
  6. ^ a b David M. Dennison, Recollections of Physics and of Physicists During the 1920s, Am. J. Phys. 42 1051–1056 (1974)
  7. ^ a b c Author Catalog: Dennison Archived February 5, 2007, at the Wayback Machine – American Philosophical Society
  8. ^ Duncan and Janssen Archived 2009-05-20 at the Wayback Machine – Anthony Duncan and Michel Janssen On the verge of Umdeutung in Minnesota: Van Vleck and the Correspondence principle. Part One. p. 14.
  9. ^ Jammer, 1966, p. 343.
  10. ^ David M. Dennison A Note on the Specific Heat of the Hydrogen Molecule Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character Vol. 115, No. 771 pp. 483-486 (1927). Communicated by R. H. Fowler; received 3 June 1927.
  11. ^ Instructor 1927-1928, Assistant Professor 1928-1930, and Associate Professor starting in 1930.
  12. ^ Otto Laporte – National Academy of Sciences Press
  13. ^ a b University of Michigan (2013). "Bentley Historical Library: Tappan's Vision." http://bentley.umich.edu/exhibits/tappan/panel8.php
  14. ^ a b University of Michigan (2013). "Faculty History Project: Memorial: David M. Dennison." http://um2017.org/faculty-history/faculty/david-m-dennison/memorial
  15. ^ [1] - McKinley founder Ron Weiser donates $50 million to University of Michigan

External links

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Atomic bombings of Hiroshima and Nagasaki

During the final stage of World War II, the United States detonated two nuclear weapons over the Japanese cities of Hiroshima and Nagasaki on August 6 and 9, 1945, respectively. The United States dropped the bombs after obtaining the consent of the United Kingdom, as required by the Quebec Agreement. The two bombings killed 129,000–226,000 people, most of whom were civilians. They remain the only use of nuclear weapons in the history of armed conflict.

In the final year of the war, the Allies prepared for what was anticipated to be a very costly invasion of the Japanese mainland. This undertaking was preceded by a conventional and firebombing campaign that destroyed 67 Japanese cities. The war in Europe had concluded when Germany signed its instrument of surrender on May 8, 1945. As the Allies turned their full attention to the Pacific War, the Japanese faced the same fate. The Allies called for the unconditional surrender of the Imperial Japanese armed forces in the Potsdam Declaration on July 26, 1945—the alternative being "prompt and utter destruction". The Japanese rejected the ultimatum and the war continued.

By August 1945, the Allies' Manhattan Project had produced two types of atomic bombs, and the 509th Composite Group of the United States Army Air Forces (USAAF) was equipped with the specialized Silverplate version of the Boeing B-29 Superfortress that could deliver them from Tinian in the Mariana Islands. Orders for atomic bombs to be used on four Japanese cities were issued on July 25. On August 6, one of the modified B-29s dropped a uranium gun-type bomb codenamed "Little Boy" on Hiroshima. Three days later, on August 9, a plutonium implosion-type bomb codenamed "Fat Man" was dropped by another B-29 on Nagasaki. The bombs immediately devastated their targets. Over the next two to four months, the acute effects of the atomic bombings killed 90,000–146,000 people in Hiroshima and 39,000–80,000 people in Nagasaki; roughly half of the deaths in each city occurred on the first day. Large numbers of people continued to die from the effects of burns, radiation sickness, and other injuries, compounded by illness and malnutrition, for many months afterward. In both cities, most of the dead were civilians, although Hiroshima had a sizable military garrison.

Japan announced its surrender to the Allies on August 15, six days after the bombing of Nagasaki and the Soviet Union's declaration of war. On September 2, the Japanese government signed the instrument of surrender, effectively ending World War II. The effects of the bombings on the social and political character of subsequent world history and popular culture has been studied extensively, and the ethical and legal justification for the bombings is still debated to this day.

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David Dennison

David Dennison may refer to:

David Dennison (cricketer) (born 1961), Irish cricketer

David Dennison, one of three notable pseudonyms of Donald Trump

David M. Dennison (1900–1976), American physicist

David S. Dennison Jr. (1918–2001), American politician in the US House of Representatives

Dennison Reef

Dennison Reef (66°29′S 66°50′W) is a reef between the Shull Rocks and the Pauling Islands, lying east of the south end of the Biscoe Islands in Crystal Sound. It was mapped from air photos obtained by the Ronne Antarctic Research Expedition (1947–48) and from surveys by the Falkland Islands Dependencies Survey (1958–59). It was named by the UK Antarctic Place-Names Committee for David M. Dennison, a physicist who took x-ray diffraction pictures which were used to interpret the crystal structure of ice.

Edwin C. Kemble

Edwin Crawford Kemble (January 28, 1889 in Delaware, Ohio – March 12, 1984) was an American physicist who made contributions to the theory of quantum mechanics and molecular structure and spectroscopy. During World War II, he was a consultant to the Navy on acoustic detection of submarines and to the Army on Operation Alsos.

Harrison M. Randall

Harrison McAllister Randall (December 17, 1870 – November 10, 1969) was an American physicist whose leadership from 1915 to 1941 brought the University of Michigan to international prominence in experimental and theoretical physics.

Index of physics articles (D)

The index of physics articles is split into multiple pages due to its size.

To navigate by individual letter use the table of contents below.

List of physicists

Following is a list of physicists who are notable for their achievements.

Otto Laporte

Otto Laporte (July 23, 1902 – March 28, 1971) was a German-born American physicist who made contributions to quantum mechanics, electromagnetic wave propagation theory, spectroscopy, and fluid dynamics. His name is lent to the Laporte rule in spectroscopy and to the Otto Laporte Award of the American Physical Society.

Robert Bacher

Robert Fox Bacher (August 31, 1905 – November 18, 2004) 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 (Caltech) and the Massachusetts Institute of Technology (MIT), 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 (1936), 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 (Physics) Division, and later its G (Gadget) 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 (PSAC) 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.

Weiser Hall

Weiser Hall, formerly the David M. Dennison Building, is a building located on the University of Michigan campus in Ann Arbor, Michigan.

The building is located at 500 Church Street. It was built in 1963 by Albert Kahn Associates, and stands twelve stories in height. It is a brick building with a modern style. Twelve floors are above-ground, and there is one basement floor. The high-rise is used mainly for undergraduate education, particularly physics and mathematics. The low-rise section contains a number of large lecture halls; the two sections are connected by a breezeway on the second floor. The building is also home to the astronomy and astrophysics department.

In 2015, Dennison was renamed to Weiser Hall.

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