History credits Antoine-Henri Becquerel with the discovery of radioactivity, although Pierre and Marie Curie’s contributions are recognized as equal in importance to the advancement of scientific knowledge. That is why Becquerel and Marie Curie shared the 1903 Nobel Prize in Physics. Becquerel’s discovery of radioactivity was the accidental extension of experiments he was conducting on fluorescent materials in order to better understand X-rays. Experiments with the natural mineral uranium provided him the key to detecting and understanding radiation. It would be Marie Curie, though, whose work on radiation utilized Becquerel’s findings, who would not only build upon the latter’s discovery but would extend and apply it in ways that make her contributions to science the more extraordinary. Specifically, Curie, first with her husband Pierre and, following Pierre’s death, by herself studied the properties of naturally radioactive substances, mainly uranium, and isolated (“discovered”) polonium and radium, which would become vital to the development of nuclear medicine. For her continued contributions to science within the realm of radioactivity she would eventually be awarded a second Nobel Prize in 1911.
The answer to the question of who discovered radioactivity, though, would be Antoine-Henri Becquerel.