"These six papers document Becquerel's discovery of radioactivity. On 24 February 1896, Becquerel announced to the Academy that fluorescent crystals of potassium uranyl sulfate had exposed a photographic plate wrapped in black paper while they both lay for several hours in direct sunlight; on 3 March, he reported similar exposures when both crystals and plate lay in total darkness ... On 18 May, he reported that a disk of pure uranium produced penetrating radiation three or four times as strong as that produced by the potassium uranyl sulfate crystals. In 1903 Becquerel shared with Marie and Pierre Curie the Nobel Prize for Physics, as his investigations had opened the way for the Curies' discovery of radium" (Norman).