The Alpha Particle Scattering experiment

The Alpha Particle Scattering experiment (He2+) involved observing the trajectory of these particles as they collided with a thin metal foil. It was observed that the majority of alpha particles passed straight through or experienced a slight deflection. However, approximately 1 in every 20,000 particles underwent a deflection greater than 90º, with some even reversing their direction back toward the initial path. Considering the high kinetic energy of alpha particles and their positive charge, these significant deviations could only be explained if the majority of atomic mass were concentrated in a small, positive nucleus. In addition to qualitatively indicating the existence of the nucleus, this experiment also provided measurements of its charge and size.