Meit·ner \ˈmīt-nər\ Lise (1878–1968), German physicist. One of the first women to pursue a career in physics, Meitner received a PhD in the subject from the University of Vienna before being hired by Max Planck as an assistant at the Institute for Theoretical Physics at the University of Berlin. Beginning in 1918, she was head of the physics department at Berlin's Kaiser-Wilhelm Institut. With German physical chemist Otto Hahn, Meitner discovered an isotope of protactinium, the parent element of actinium, in 1918. With Hahn and Otto von Baeyer, she studied beta emissions from thorium, radium, and uranium, while conducting her own studies on the range of radioactive particles. Forced in 1938 to flee Berlin for Stockholm, she assumed a post at the Nobel Institute. With physicist O. R. Frisch, she became the first to realize that recent experiments by Hahn and others in which uranium had been bombarded with neutrons had resulted in the splitting of the uranium nucleus into two nuclei of smaller masses accompanied by the release of a massive amount of energy. In a 1939 paper they introduced the term fission for this nuclear process. After 1947 Meitner did her research at Sweden's Royal Institute for Technology and a laboratory at the Royal Academy for Engineering Sciences. In 1997 the International Union of Pure and Applied Chemistry formally approved meitnerium as the name for element 109.