Radioactivity was discovered in 1896 by Henri Becquerel who found out that uranium spontaneously produced radiation. It could be bent in a magnetic field, suggesting three different types of radiation: positive, negative, and electrically neutral. Marie and Pierre Curie studied uranium ore and found higher levels of radioactivity than in pure uranium, hence discovering more radioactive elements, namely polonium and radium. Ernest Rutherford classified the types of radiation based on their penetrative properties, and identified α particles as being helium nuclei and β particles as being electrons. Paul Villard identified γ rays from radium as being high energy photons similar to x-rays.
Alpha particle is a helium nuclei, β particle is an electron and γ is electromagnetic waves.
α, β, and γ particles are deflected in electric and magnetic fields, and are stopped by different thicknesses of various materials.