Nuclear Fission
Noddack correctly criticized Enrico Fermi's chemical proofs in his 1934 neutron bombardment experiments, from which he postulated that transuranic elements might have been produced, and which was widely accepted for a few years. Her paper, "On Element 93" suggested a number of possibilities, centering around Fermi's failure to chemically eliminate all lighter than uranium elements in his proofs, rather than only down to lead. The paper is considered historically significant today not simply because she correctly pointed out the flaw in Fermi's chemical proof but because she suggested the possibility that "it is conceivable that the nucleus breaks up into several large fragments, which would of course be isotopes of known elements but would not be neighbors of the irradiated element." In so doing she presaged what would become known a few years later as nuclear fission. However Noddack offered no theoretical basis for this possibility, which defied the understanding at the time. The paper was generally ignored.
Later experiments along a similar line to Fermi's, by Irène Joliot-Curie, and Pavle Savić in 1938 raised what they called "interpretational difficulties" when the supposed transuranics exhibited the properties of rare earths rather than those of adjacent elements. Ultimately in 1939 Otto Hahn and Fritz Strassmann, working in consultation with long term colleague Lise Meitner (who had been forced to flee Germany) provided chemical proof that the previously presumed transuranic elements were isotopes of barium. It remained for Meitner and her nephew Otto Frisch utilizing Fritz Kalckar and Niels Bohr's liquid drop hypothesis (first proposed by George Gamow in 1935) to provide a theoretical model and mathematical proof of what they dubbed nuclear fission (Frisch also experimentally verified the fission reaction by means of a cloud chamber, confirming the energy release).
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