Becquerel’s earliest work was concerned with the plane polarization of light, with the phenomenon of phosphorescence and with the absorption of light by crystals (his doctorate thesis). He also worked on the subject of terrestrial magnetism. In 1896, his previous work was overshadowed by his discovery of the phenomenon of natural radioactivity. Following a discussion with Henri Poincaré on the radiation which had recently been discovered by Röntgen (X-rays) and which was accompanied by a type of phosphorescence in the vacuum tube, Becquerel decided to investigate whether there was any connection between X-rays and naturally occurring phosphorescence. He had inherited from his father a supply of uranium salts, which phosphoresce on exposure to light. When the salts were placed near to a photographic plate covered with opaque paper, the plate was discovered to be fogged. The phenomenon was found to be common to all the uranium salts studied and was concluded to be a property of the uranium atom. Later, Becquerel showed that the rays emitted by uranium, which for a long time were named after their discoverer, caused gases to ionize and that they differed from X-rays in that they could be deflected by electric or magnetic fields.Before his crowning of Nobel Prize, he worked as an engineer in the Department of Bridges and Highways in France, and later served as the physics chair at the Muséum National d’Histoire Naturelle. It was while studying uranium salts that he accidentally discovered radioactivity. 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.The full impact of Becquerel discovery wasn’t appreciated till Marie and Pierre Curie discovery. They shared the Nobel Prize.He also discovered that all uranium compounds (not just specific salts) fogged the plates, unlike luminescence which was confined to particular salts.
Becquerel published his findings in many papers, principally in the Annales de Physique et de Chimie and the Comptes Rendus de l’Academie des Sciences.He was elected a member of the Academie des Sciences de France in 1889 and succeeded Berthelot as Life Secretary of that body. He was a member also of the Accademia dei Lincei and of the Royal Academy of Berlin, amongst others. He was made an Officer of the Legion of Honour in 1900.He was married to Mlle. Janin, the daughter of a civil engineer. They had a son Jean, b. 1878, who was also a physicist: the fourth generation of scientists in the Becquerel family.Henri’s son Jean Becquerel also became a physicist, and four generations of Becquerels were educated at the École Polytechnique and became professors of physics at the French Museum of Natural History.Antoine Henri Becquerel died at Le Croisic on August 25, 1908.