Henri Becquerel received the 1903 Nobel Prize in Physics for his discovery of spontaneous radioactivity. He shared the prize with Marie Curie and Pierre Curie, whose investigations expanded the study of radioactive substances.
Becquerel made his breakthrough in 1896 while investigating whether uranium salts emitted radiation related to X-rays. He discovered that uranium produced penetrating rays even when the material was not exposed to sunlight, showing that the phenomenon came from the substance itself. This overturned the idea that the radiation required external illumination.
Marie Curie later introduced the term radioactivity and, with Pierre Curie, identified the elements polonium and radium. Ernest Rutherford subsequently helped clarify the nature of radioactive decay. Becquerel’s name is preserved in the becquerel, the International System of Units unit for radioactive activity, equal to one nuclear decay per second.