Level: introductory
References: Otto Hahn and Fritz Strassmann, "The Detection and behavior of the alkaline earth metals which result from the irradiation of uranium by neutrons," Die Naturwissenschaften 27, 11-15 (1939). Lise Meitner and Otto Frisch, "Disintegration of uranium by neutrons. A new type of nuclear reaction," Nature 143, 239-40 (1939).
Notes: Otto Hahn (1879-1968) and Fritz Strassmann (1902-1980) were not the first to irradiate uranium with neutrons. They were the first to realize, however, that there were nuclei considerably smaller than uranium among the products. They expected that the uranium nuclei would absorb one or more neutrons and undergo beta decay to produce elements with atomic numbers greater than 92. The putative transuranium elements might then undergo one or a few alpha decays. Under this hypothesis, radium (element 88) was a plausible reaction product. This is what Hahn and Strassmann believed that they had detected, at first. What they found, however, was not just similar to barium (as radium would be, since it is in the same column of the periodic table): it was barium.
Lise Mietner (1878-1968) and Otto Frisch (1904-1979) explained the observation of Hahn and Strassmann by hypothesizing (correctly) that the uranium nucleus was split into two smaller nuclei. Meitner had been a senior researcher (Head of the Radiophysics Department) and collaborator of Hahn's at the Kaiser Wilhelm Institute in Berlin before she fled the Nazi government's anti-Jewish laws.
Hahn was awarded the Nobel Prize in chemistry in 1944 for the discovery of nuclear fission. Meitner, who recognized that the process was the splitting of a nucleus (and who called it fission) did not share this award.
Solutions: To download solutions, go to:
http://web.lemoyne.edu/giunta/classicalcs/fission.doc
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