Lise Meitner
1878-1968
Austrian-Swedish Physicist and Radiochemist
Lise Meitner is best known for her role in the discovery that heavy unstable nuclei such as uranium-235 could decay by a fission process in which the nucleus could split into two pieces of nearly equal size, releasing additional neutrons and an immense amount of energy. When physicists realized that the neutrons could be used to initiate additional fission events, it became apparent that a chain reaction could realized, leading eventually to the first atomic bombs.
Lisa Meitner entered the University of Vienna in 1901. Although she was encouraged by a number of the physics faculty, including the eminent Ludwig Boltzmann (1844-1906), she received a rather unfriendly reception from the largely male student body. In 1905 she became the second woman to receive a doctorate from the University. Following graduation she moved to Berlin where she planned to study under Max Planck (1858-1947). There she began a lasting collaboration with Otto Hahn (1879-1968), a chemist interested in discovering new elements. As a physicist, Meitner was interested in understanding the alpha, beta, and gamma rays that made the creation of the new elements possible. In 1912 Meitner joined the newly established Kaiser Wilhelm Institute in Berlin, and in 1918 she was made head of its physics department. In 1926 she received a professorial appointment at the University of Berlin, but did not teach any courses.
In 1898 Marie Curie (1867-1934), assisted by her husband Pierre (1859-1906), had announced the discovery of two previously unknown elements, polonium and radium, products of the radioactive decay of uranium. In 1919, the English physicist Ernest Rutherford (1871-1937) discovered that the bombardment of nitrogen atoms by alpha particles resulted in the transmutation of some of them into oxygen atoms. Interest in atomic transmutations increased dramatically following the discovery of the neutron by Sir James Chadwick (1891-1974) in 1932. Since the neutron, unlike the alpha particle, had no charge, it could penetrate the nucleus readily. By 1934 Meitner and Hahn were trying to understand the result of experiments in which Italian physicist Enrico Fermi (1901-1954) had bombarded uranium with neutrons. In particular, they were looking for socalled transuranic element, elements heavier than uranium.
Lise Meitner. (Library of Congress. Reproduced with permission.)It was during the research on uranium that Meitner was forced to leave Germany. Of Jewish ancestry, but initially protected from the Nazi racial policies by her Austrian citizenship, her situation changed abruptly when Germany annexed Austria. Colleagues arranged safe passage for her to the Netherlands, and from there she accepted an invitation to work at the new Nobel Institute in Stockholm. Continuing the research on uranium, Hahn and Fritz Strassman (1902-1980) concluded that the neutron bombardment produced isotopes of radium, because they shared the same chemical properties as barium, as had the radium isolated by the Curies. Meitner doubted this result and asked Hahn and Strassman to prove that they had in fact produced radium. When the chemical tests were run, they found that the radioactive products could not be separated from barium at all. After discussing the new results with her nephew, Otto Frisch (1904-1979), also a physicist, Meitner came to the conclusion that what had occurred was the fission, or splitting, of the uranium nucleus into two nearly equal fragments, one of them a barium isotope, with the release of additional neutrons. Meitner calculated the energy released by the process, which was quite large, and communicated the results to Hahn.
Hahn and Strassman mentioned Meitner's work in their 1939 publication on nuclear fission,but perhaps for political reasons, they understated her contribution. As physicists learned of nuclear fission, many began to think of the possibility of a nuclear explosive, leading in the United States to the Manhattan Project and the explosion of atomic bombs over Japan in 1945. Meitner had been invited to join the project, but unlike the vast majority of refugee scientists, she refused, strongly objecting to the military use of her work. Meitner continued to work in physics and to oppose the military use of atomic energy until nearly the end of her very long and productive life.
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