Michael Pearson, in his article “On the belated discovery of fission” (Physics Today, June 2015, page 40), focuses on physics as being solely responsible for the “belated” discovery of nuclear fission, but that does not tell the whole story. Although physicists at the time did assume that nuclear changes would have to be small, chemists contributed their own false assumption, namely that elements beyond uranium would behave like transition elements. (We now know they are actinides.) For four years, as long as leading radiochemists like Otto Hahn were certain that the activities they found were from transuranic elements, though they were in fact fission fragments,1 physicists saw no pressing reason to set aside their own nuclear concepts and predict nuclear fission.
The article does not make clear, moreover, just how crucial Lise Meitner was to the fission discovery. In the fall of 1938, Meitner and other physicists were highly skeptical of Hahn and Fritz Strassmann’s finding that the slow neutron irradiation of uranium produced radium. Pearson omits Meitner’s further contributions: It was she who urgently requested that Hahn and Strassmann test their radium more thoroughly, which led directly to the barium finding. She also was the one who immediately assured Hahn that a disintegration of the uranium nucleus was possible, after which he added to the proofs of the barium publication the suggestion that uranium might have split in two.2
Had Meitner been in Berlin at the time, the discovery of fission would, without question, have been understood as the superb achievement of an interdisciplinary team. Instead, Meitner was in exile, and she and physics were largely written out of the history of the discovery. The barium finding was published under the names of Hahn and Strassmann only—not, as Pearson’s article implies, because Meitner failed to provide an explanation but because it would have been politically impossible for Hahn and Strassmann to include her, a Jew in exile, as a coauthor. The records also show that Hahn quickly sought political cover and distanced himself from Meitner, claiming that the discovery was due to chemistry alone and that physics had delayed and impeded it, a view that was eventually codified by the Nobel Prize decisions3 and is, unfortunately, apparent in Pearson’s article.
What kept Meitner from being completely obscured was that her theoretical interpretation with Otto Frisch was recognized as a brilliant extension of existing nuclear theory to the fission process.4 But the separate publications created an artificial divide—between chemistry and physics, experiment and theory, discovery and interpretation. It is important to recognize that this divide and Meitner’s exclusion from the fission discovery do not reflect how the science was done but are instead artifacts of her forced emigration and the political conditions in Nazi Germany at the time.
