What Does Radioactivity Mean?

The word radioactivity refers to a spontaneous kind of emission of radiation. The radiation is a result of a nuclear reaction or they may be emitted by unstable atomic nuclei. The radiation includes gamma rays, nucleons, alpha particles and electrons. Radioactivity is defined as the energy that is given out when the nuclei of atoms breaks down.  

The term radioactivity dates back to the nineteenth century and was discovered by Henry Becquerel in the year 1896. The substance he discovered to be radioactive was Uranium salt. The discovery of radioactivity marked the start of nuclear physics. A few years later in 1898 Marie Curie discovered radium and polonium another two highly radioactive elements. All chemical elements are capable of being rendered radioactive by the subtraction or addition of some neutrons. This was discovered only by around 1934.