Rutherford used an apparatus similar to that depicted in Fig. When the air from the chamber was removed, the alpha source made a spot on the photographic plate. When air was added, the spot disappeared. Thus, only a few centimeters of air were enough to stop the alpha radiation. Because alpha particles carry more electric charge, are more massive, and move slowly compared to beta and gamma particles, they interact much more easily with matter.
Beta particles are much less massive and move faster, but are still electrically charged.
A sheet of aluminum one millimeter thick or several meters of air will stop these electrons and positrons.