Alpha (α)-

Consists of 2 protons and 2 neutrons identical to helium particles. Alpha particles travel slowly and can be stopped by a sheet of paper or skin. 

Beta (β)-

Is a negatively charged particle like an electron. Beta particles travel at about the speed of light and can penetrate further than alpha particles, but can be stopped by thick aluminum foil.

Gamma (γ)-

a wave with no mass or charge. Travels the fastest and penetrates the furthest of ionizing radiation particles. Can only be stopped by dense material like lead.