Discovery of radioactivity. This photograph led to the discovery of radioactivity by Antoine Henri Becquerel in 1896. Dark patches show where he put crystals of uranium salt on a photographic plate. His comments are above. Becquerel (1852-1908) was professor of physics at the Ecole Polytechnique in Paris. He put uranium salt on the plate expecting that when exposed to sunlight it would produce X- rays and fog the plate. But since it was cloudy he put the experiment in a drawer; three days later, on 1 March 1896, he developed the plate anyway. It had been fogged by uranium salt alone. Becquerel realised he had found a new form of radiation. He won the Nobel Prize for physics in 1903.