Radioactivity

 Radioactivity is discovered by Henri Becquerel, Pierre and Marie Currie. Radioactivity is phenomenon of spontaneous disintegration of unstable atomic nuclei to atomic nuclei. Nuclei of heavy elements are generally unstable because n/p ≠1. In order to get stable nuclei they emit active radiations like α, β, and γ-rays spontaneously. Such substances or elements are called radio active substance or elements. The phenomenon of spontaneous emission of α, β, and γ-rays is called the radioactivity. It is a nuclear phenomenon elements having atomic no. greater than 83 are all radioactive. Some lighter elements are also radioactive .

The unit of radioactivity is Curie (C).
Eg-    88Ra226, 82Pb214 and 92U235