Becquerel, Antoine Henri (1852-1908) was a French physicist who discovered radioactivity in 1896, an achievement for which he shared the 1903 Nobel Prize in Physics with Pierre Curie (1859-1906) and Marie Curie (1867-1934). The Curies did not participate in Becquerel's discovery but investigated radioactivity and gave the phenomenon its name. Becquerel was born in Paris on 15 December 1852 and educated at the École Polytechnique and École des Ponts et Chaussées, where he received a training in engineering. In 1875, he began private scientific research, investigating the behaviour of polarized light in magnetic fields and in crystals, linking the degree of rotation to refractive index. Both Becquerel's grandfather and father were respected physicists with positions at the Museum of Natural History and other institutions. On their deaths, in 1878 and 1891 respectively, Becquerel succeeded to their posts. He became a member of the Academy of Sciences in 1889, a professor at the Museum in 1892 and at the École Polytechnique in 1895. Becquerel then began the work for which he is remembered, not necessarily because of his position but because of the discovery of X-rays made by Wilhelm Röntgen (1845-1923) early in 1896. This prompted Becquerel to investigate fluorescent crystals for the emission of X-rays, and in so doing he accidentally discovered radioactivity in uranium salts in the same year. Pierre and Marie Curie then searched for other radioactive materials, which led them to the discovery of polonium and radium in 1898. Becquerel subsequently investigated the radioactivity of radium, and showed in 1900 that it consists of a stream of electrons. In the same year, Becquerel also obtained evidence that radioactivity causes the transformation of one element into another. Following his award of the 1903 Nobel Prize in Physics jointly with the Curies, Becquerel became vice-president (1906) and president (1908) of the Academy of Sciences. He died soon after on 25 August 1908 in Brittany. Becquerel's discovery of radioactivity was prompted by the mathematician Henri Poincaré (1854-1912), who told Becquerel that X-rays were emitted from a fluorescent spot on the glass cathode-ray tube used by Röntgen. This immediately suggested to Becquerel that X-rays might be produced naturally by fluorescent crystals, with which he was familiar through his father's interest in fluorescence. He therefore placed some crystals of potassium uranyl sulphate on a photographic plate wrapped in paper, and put it in sunlight to make the crystals fluoresce. When he developed the plate, Becquerel found it to be fogged, showing that a radiation resembling X-rays had penetrated the paper and exposed the plate. Becquerel then tried to repeat the experiment to make further investigations, but the weather was cloudy and the uranium crystals would not fluoresce as there was no sunlight. He put a wrapped plate and the crystals into a drawer and waited. The weather did not improve and Becquerel impatiently decided to develop the plate. To his astonishment, the plate had been strongly exposed to radiation. Clearly it was not connected with fluorescence, but was emitted naturally by the crystals all the time. Becquerel studied the radiation and found that it behaved like X-rays in penetrating matter and ionizing air. He showed that it was due to the presence of uranium in the crystals, and subsequently found that a disc of pure uranium metal is highly radioactive. This led Pierre and Marie Curie to isolate polonium and radium, which is even more radioactive. Becquerel later subjected the radiation from radium to magnetic fields and was able to prove by the amount of deflection that it must consist of the electrons that had been discovered by J.J. Thomson (1856-1940) in 1897. Becquerel also discovered that radioactivity could be removed from a radioactive material by chemical action, but that the material subsequently regained its radioactivity. Becquerel's discovery of radioactivity and its investigation by himself and the Curies caused a revolution in physics. It marked the beginning of nuclear physics by showing that atoms, and then nuclei within atoms, are made up of smaller particles. Furthermore, the spontaneous regeneration of radioactivity observed by Becquerel was evidence that one element can be transformed into another with the production of energy. A full explanation of radioactivity was achieved by Ernest Rutherford (1871- 1937), leading eventually to nuclear fission and the production of nuclear energy. Author not available, Becquerel, Antoine Henri (1852-1908). , The Hutchinson Dictionary of Scientific Biography, 01-01-1998. |