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Meitner, Lise (1878-1968), Austrian-Swedish physicist, who first identified nuclear fission. She was born in Vienna, Austria, and educated at the Universities of Vienna and Berlin. In 1918, in association with German physical chemist Otto Hahn, she helped discover the element protactinium. From 1926 to 1933 she was a professor of physics at the University of Berlin in Germany. In 1938 restrictions against Jews imposed by the Nazi regime led Meitner to leave Germany. She ended up in Sweden, joining the atomic research staff at the University of Stockholm. In 1939 Meitner and her nephew, the British physicist Otto Robert Frisch, published the first paper to provide a theoretical explanation for the splitting of the atom and named the process fission (see Nuclear Energy). In 1946 she was a visiting professor at Catholic University in Washington, D.C., and in 1959 she revisited the United States to lecture at Bryn Mawr College. In 1997 the International Union of Pure and Applied Chemistry announced that the chemical element with the atomic number 109 would be given the official name meitnerium (Mt) in her honor.