Alpha particles come from the decay of an unstable atomic nucleus such as uranium. They are the least penetrating of all types of radiation. They can be stopped by clothing, a sheet of paper, or skin. Alpha particles can have a potential biological effect if taken into the body through cuts or by breathing in the air. Uranium, plutonium, thorium, and radon are typical materials that have alpha radiation.
Beta particles are electrons that come from the nucleus.
They are effectively stopped by plastic, glass, or metal like aluminum. Higher energy beta particles can penetrate the skin. Beta particles may have a potential biological effect if ingested, inhaled, or taken through the skin. Tritium is a typical material that has beta particles. Gamma rays and x-rays are very penetrating electromagnetic waves.