What Henri Becquerel used for his X-Rays

He chose to work with was a double sulfate of uranium and potassium which he exposed to sunlight and placed on photographic plates wrapped in black paper. When he developed, the plates revealed an image of the uranium crystals. Becquerel concluded "that the phosphorescent substance in question emits radiation which penetrates paper opaque to light." He believed that the sun's energy was being absorbed by the uranium which then emitted X rays. When he investigated, on the 26th and 27 of February, was delayed because the skies over Paris were overcast and the uranium-covered plates Henri intended to expose to the sun were returned to a drawer. He developed the photographic plates expecting only faint images to appear. He was shocked, when the images were clear and strong. He came to the conculsion that the uranium emitted radiation without an external source of energy such as the sun. He had did it, he had discovered radioactivity, the spontaneous emission of radiation by a material. Becquerel demonstrated, later, that the radiation emitted by uranium shared certain characteristics with X rays but, unlike X rays, could be deflected by a magnetic field and therefore must consist of charged particles.