In January of 1900, the New-Zealand born English physicist Ernest Rutherford (1871-1937) submitted an important paper in which he described the properties of “thorium emanation,” a mysterious radioactive substance that he concluded must be composed of “some sort of particles.” Rutherford later showed that emanation had all the properties of a gas, which we know today as radon. For this and related discoveries, Rutherford was awarded the Nobel Prize in chemistry in 1908. But Rutherford did not discover thorium emanation. In September 1898, Rutherford had been appointed as professor of physics at McGill University in Montreal, where he met the recently appointed professor of electrical engineering, the American Robert Bowie Owens. Owens was interested in the new phenomenon of radioactivity, and the two men decided to collaborate. Rutherford continued the studies of uranium salts he had started in Cambridge, while Owens tackled the newly discovered radioactivity of thorium salts. Owens’s results were the more interesting and the more puzzling: he found that the level of radioactivity of the thorium salts increased noticeably with time, eventually reaching a maximum value. Furthermore, there were sudden shifts in the ionization of the air produced by his samples. Even opening the door to the laboratory changed the results. Eventually, Owens found that passing air through the sample container caused the level of radioactivity to diminish. If instead the sample was left undisturbed, it regained its previous activity in a few minutes. Rutherford’s uranium salts showed no such variability. Owens concluded that his experiments “indicate that the cause, whatever it is, lies close to the surface of the active material. It is possible that some intense type of radiation coming from the body of a thick layer of certain salts changes the nature of their surfaces, forming in the neighbourhood a more active material which if removed from the containing vessel diminishes the amount of ionization produced.” Owens published his explanation of the unusual effect in two papers in 1899: including a single-author full paper in the Philosophical Magazine on his the thorium studies, probably submitted in July of 1899. Sadly, today Owens has been almost completely forgotten. The current talk will give some details of his life and argue that he is entitled to a share (at least!) of credit for the discovery of radon.

Who discovered radon? The case in support of Robert Bowie Owens (1870-1940)

ACS Spring 2022

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