Who first discovered radioactivity?

The discovery of radioactivity is credited to French physicist Henri Becquerel in 1896. While studying phosphorescent materials, Becquerel investigated whether certain substances emitted radiation similar to X-rays, which had been recently discovered by Wilhelm Roentgen. He experimented with uranium salts and observed that they emitted penetrating rays capable of fogging photographic plates, even in the absence of sunlight.

This unexpected phenomenon revealed a new type of radiation, independent of external energy sources. Becquerel’s discovery marked the beginning of the study of radioactivity, a field further advanced by the groundbreaking work of Marie and Pierre Curie. For his contribution, Becquerel shared the 1903 Nobel Prize in Physics with the Curies.