Henri Becquerel was the French physicist who discovered radioactivity in 1896. Becquerel was born in Paris and lectured at the Ecole Polytechnique (1875) until he replaced his father as Professor of Physics at the Natural History Museum in Paris. He was an expert in the field of fluorescence and phosphorescence, continuing the work that his father and grandfather had initiated. In 1896 Becquerel began a series of experiments exposing crystals of potassium uranyl sulphate to light. He then placed the crystals on a photographic plate wrapped in paper. When the plate was developed, a faint image could be seen. Becquerel believed that the light absorbed by the crystals had been re-emitted as a radiation similar to X-rays (discovered only a few months before), and that this had penetrated the paper and affected the photographic plate. By chance, Becquerel had also placed an unexposed crystal on another wrapped photographic plate. When this plate was subsequently developed it was found that another faint image had been formed. This showed that the radiation emitted by the crystals was not connected to fluorescence, but that it was an intrinsic property of the crystals. It was Becquerel's work that inspired Marie and Pierre Curie to search for and discover radium, and in 1903 they shared with him the Nobel Prize for Physics.
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