Henri Becquerel, in full Antoine-Henri Becquerel (born December 15, 1852, Paris, France—died August 25, 1908, Le Croisic), was a French physicist who discovered radioactivity through his investigations of uranium and other substances.

In 1896, Becquerel investigated the newly discovered x-rays, which had been discovered in 1895 by Wilhelm Roentgen leading to studies of how uranium salts are affected by light. By accident, he discovered that uranium salts spontaneously emit a penetrating radiation that can be registered on a photographic plate. Further studies made it clear that this radiation was something new and not X-ray radiation: he had discovered a new phenomenon, radioactivity.

The term 'radioactivity' was actually coined by Marie Curie, who together with her husband Pierre, began investigating the phenomenon recently discovered by Becquerel. The Curies extracted uranium from ore and to their surprise, found that the leftover ore showed more activity than the pure uranium. They concluded that the ore contained other radioactive elements. This led to the discoveries of the elements polonium and radium. It took four more years of processing tons of ore to isolate enough of each element to determine their chemical properties.

In 1903, Beecquerel shared the Nobel Prize for Physics with Pierre and Marie Curie.

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