Becquerel , Antoine Henri

(1852–1908) French physicist

Becquerel was born in Paris; his early scientific and engineering training was at the Ecole Polytechnique and the School of Bridges and Highways, and in 1876 he started teaching at the Polytechnique. From 1875 he researched into various aspects of optics and obtained his doctorate in 1888. In 1899 he was elected to the French Academy of Sciences, continuing the family tradition as his father and grandfather, both renowned physicists, had also been members. He held chairs at the Ecole Polytechnique, the Museum of Natural History, and the National Conservatory of Arts and Crafts, and became chief engineer in the department of bridges and highways.

Becquerel is remembered as the discoverer of radioactivity in 1896. Following Wilhelm Röntgen's discovery of x-rays the previous year, Becquerel began to look for x-rays in the fluorescence observed when certain salts absorb ultraviolet radiation. His method was to take crystals of potassium uranyl sulfate and place them in sunlight next to a piece of photographic film wrapped in black paper. The reasoning was that the sunlight induced fluorescence in the crystals and any x-rays present would penetrate the black paper and darken the film.

The experiments appeared to work and his first conclusion was that x-rays were present in the fluorescence. The true explanation of the darkened plate was discovered by chance. He left a plate in black paper next to some crystals in a drawer and some time later developed the plate. He found that this too was fogged, even though the crystals were not fluorescing. Becquerel investigated further and discovered that the salt gave off a penetrating radiation independently, without ultraviolet radiation. He deduced that the radiation came from the uranium in the salt.

Becquerel went on to study the properties of this radiation; in 1899 he showed that part of it could be deflected by a magnetic field and thus consisted of charged particles. In 1903 he shared the Nobel Prize for physics with Pierre and Marie Curie.