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Centenary of a theory

Rutherford and Soddy explained, in 1902, how radioactive transformations take place

The scientific world has gotten used to seeing French physicist Henri Becquerel and the Franco-Polish couple, Pierre and Marie Curie, as the first pioneers in the world of radioactive particles. This is partly true. Without their experiments and observations, and those of other physicists, presented from 1896 onwards in the Academy of Sciences in Paris, there would not have been the opportunity for new discoveries and hypotheses. But it was the theoretical work of two physicists, Ernest Rutherford, from New Zealand, and Frederick Soddy, from England, that effectively explained how radioactive activities take place.

Between November 1902 and May 1903, they published a series of five articles in which they put forward the hypothesis that radioactivity is associated with atomic phenomena of disintegration, that lead to the transformation of one chemical element into another. In 1904, the hypothesis of two scientists was consolidated and accepted by other researchers, and in 1908 they won the Nobel Prize for Chemistry. In other words, modern comprehension of these phenomena started to exist 100 years ago. Up until then, all that was known about radioactivity were descriptions of laboratory experiments with “substances that shine”, such as hosphorescent zinc sulfide, calcium sulfide, strontium, barium and uranium, among others.

Although he was among the pioneers in this kind of research, Becquerel discovered “things” that he did not understand well what they were, and ended up losing interest in them after a few years. “The Curies also played an important role, realizing that radioactivity was something new, capable of being influenced by light or heat, and discovering new radioactive elements besides uranium”, explains Roberto de Andrade Martins, a professor at the Institute of Physics of the State University of Campinas (Unicamp) and a specialist in the subject. “Rutherford and Soddy, then, took a fundamental step, clarifying what happened inside radioactive materials.”