Henri Becquerel was a French physicist noted for discovering the phenomenon of natural radioactivity. Following Röntgen’s discovery of the X-ray in 1895, Becquerel decided to investigate whether there was any connection between X-rays and naturally occurring phosphorescence. In 1896, Becquerel exposed uranium salts to sunlight and placed them on photographic plates wrapped in black paper. When developed, the plates revealed an image of the uranium crystals. This meant that the uranium emitted radiation without an external source of energy such as the sun. Later, Becquerel showed that the rays emitted by uranium caused gases to ionize and that they differed from X-rays in that they could be deflected by electric or magnetic fields. For his discovery of spontaneous radioactivity, Becquerel was awarded half of the Nobel Prize for Physics in 1903, the other half being given to Pierre and Marie Curie for their study of the Becquerel radiation.