Henry Becquerel discovered radioactivity accidentally in 1896.
Some elements contain atoms with unstable nuclei. With time, the unstable nucleus disintegrates. While doing so, it shoots out a tiny particle and sometimes wave energy as well. Since the particles and the waves radiate from the nucleus, it is called nuclear radiation.
These are particular isotopes of an element whose atoms have different number of neutrons in the nucleus.
List of radioactive isotopes:
Three main types of nuclear radiation:
Alpha particles (α) , Beta particles (β) and Gamma rays (γ)
Properties of alpha, beta and gamma radiation: