Radioactivity and Radioactive Elements

Henri Becqueral observed that certain elements emit radiation on their own. This phenomenon is known as radioactivity. And such elements are called radioactive elements.
Other scientists in this field include Marie Curie, Piere Curie, Rutherford and Fredrick Soddy.

α-rays = 2 protons +2 neutrons
β-rays = -ve particles (electron or positron)
γ-rays are electromagnetic radiatons of very high energy (do not contain particles)
α-rays have the least penetrating power. β-rays have a penetrating power 100 times that of α-rays.
And γ-rays have 1000 times that of α-rays