Henri Becquerel
1852–1908, Paris, France, Le Croisic, Brittany, France
French physicist who discovered spontaneous radioactivity in 1896, founding the science that became nuclear physics.
Becquerel was the third in a celebrated family of physicists: he succeeded his father and grandfather at the Muséum national d'histoire naturelle in Paris and became professor at the École Polytechnique in 1895. In 1896 he discovered that uranium salts spontaneously emit a penetrating radiation — the phenomenon Marie Curie would later name 'radioactivity'. His discovery opened the field that the Curies and Rutherford would develop, and the SI unit of radioactivity, the becquerel, bears his name.
Nobel-winning work
In March 1896, responding to Röntgen's discovery of X-rays, Becquerel investigated whether phosphorescent substances also emitted penetrating radiation. He placed uranium salts on photographic plates wrapped in black paper: some specimens left in a dark drawer during overcast weather still darkened the plates, showing they emitted radiation without any excitation by sunlight — his phosphorescence hypothesis was disproven. He showed that the radiation's intensity was proportional to the amount of uranium, proving it a property of the uranium atom itself, not of the compound. This discovery of 'spontaneous radioactivity' — announced in a series of notes to the Académie des sciences in 1896 — was the foundation of nuclear physics and led directly to the Curies' work.
Workplaces: École Polytechnique, Muséum national d'histoire naturelle
France