The guiding hypothesis of the Curies’ radioactivity research: secondary X-rays and the Sagnac connection. MARTINS, Roberto de Andrade (original) (raw)
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Historical Essays on Radioactivity, 2021
Pierre and Marie Curie's main discoveries on radioactivity are usually regarded as empirical investigations that were developed without any theoretical guidance. Their papers avoid indeed theoretical discussion, but it is possible to identify the main hypothesis that directed their work. They thought that the radiation emitted by uranium compounds (and, later, by other similar substances) was similar to the secondary radiation emitted by heavy metals when they are hit by X-rays. This hypothesis, together with other relevant assumptions, was suggested by Georges Sagnac's investigation on X-rays. This paper describes Sagnac's studies and how the acceptance of the secondary radiation hypothesis guided the study of radioactivity by the Curies. For the Curies, this hypothesis explained one of the anomalous characteristics of radioactivity-the continuous emission of energy without any noticeable change of the emitting bodies. When the magnetic deviation of the beta-rays of radioactive bodies was discovered, in 1899, this presented a challenge to their hypothesis. They carefully checked that discovery, and attempted to produce a magnetic deflection of X-rays, with negative results. However, in 1900 Pierre Curie and Georges Sagnac investigated secondary X-rays and concluded that they contained both "soft" X-rays and a negatively charged radiation (similar to betarays). Because of those results, they still kept their faith in the secondary radiation hypothesis at the time when Rutherford and Soddy began to develop the disintegration theory of radioactivity.
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