Symposion in Memory of George Placzek (1905-1955)
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George Placzek
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Brno - City of Universities
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Czech Republic, Brno
September 21 - 24, 2005

There will be two life anniversaries of George Placzek in 2005: that of his birth on 26 September 1905, and that of his passing away on 9 October 1955. Placzek was an outstanding scientist who made substantial contributions to the fields of molecular physics, scattering of light from liquids and gases, the theory of atomic nucleus and the interaction of neutrons with condensed matter. His theory of Raman effect is a pioneering work in the field. Lev Landau and George Placzek derived the Landau-Placzek formula for the ratio of intensities of the Brillouin and the Rayleigh scatterings of light. Hans Bethe and George Placzek provided a fundamental theory of neutron absorption resonances, deriving important laws and selection rules. Papers by Niels Bohr, Rudolf Peierls and George Placzek deal with the theory of nuclear reactions and rank among the classics. The well-known optical theorem bears the names of Bohr, Peierls and Placzek. In a series of experiments, Otto Frisch and Placzek discovered that the absorption of neutrons in matter is strongly dependent upon the atomic mass and the velocity of the neutrons, but for slow neutrons and light elements the neutron-capture cross section is inversely proportional to the velocity.

On the eve of the World War II, Placzek was very helpful in formulating the theory of nuclear fission, an example of his many contributions still not properly appreciated. In 1943 1946, he occupied a leading position in the Manhattan Project, forming and later leading its Montreal Theory group in Chalk River. In 1948, he obtained a tenure at the Institute for Advanced Study in Princeton.

George Placzek was born in Brno, Moravia, in what is now the Czech Republic but which in 1905 was part of Austro-Hungary. The oldest son of Alfred and Marianne Placzek, George spent his childhood in Brno and in Alexovice, where the family possessed a textile factory, Skene & Co. He had a brother, Friedrich, one year younger and a sister, Edith, twelve years younger. George studied in the Deutsches Staatsgymnasium in Brno between 1918 and 1924 and then went to study physics in the University of Vienna and in Charles University Prague. He graduated with distinction in Vienna in 1928.

Placzek often served as an insightful critic, identifying weak arguments and forcing his colleagues to formulate their scientific ideas clearly. These features made him a welcome collaborator and team member. Many renowned physicists became his collaborators and friends, e.g. (besides the above mentioned ones), Werner Heisenberg, Enrico Fermi, Edoardo Amaldi, Edward Teller, Felix Bloch, Victor Weisskopf, George Gamow, John Wheeler, Robert Oppenheimer, Leon Van Hove and others.

Placzek belongs to great persons of the physics of the 20th century. He has set an example not only by his discoveries, but also by the stimulating style of his scientific work.