Discovery of Radioactivity:             In 1895 Henri Becquerel discovered this phenomenon of radioactivity. He found that certain elements like uranium, radium, thorium etc emit radiations that cause fogging of photographic plates. What is radioactivity ? “Emission of nuclear radiations from a substance as a result of nuclear fission is called radioactivity.” Types of Radioactivity: RadioactivityRadioactivity – Definition , Discovery, Types and Facts