Rutherford's α-particle scattering experiment on gold foil is responsible for the discovery of:

Rutherford's alpha particle scattering experiment on a thin gold foil (1909-1911) led to the discovery of the atomic nucleus. In this experiment, most alpha particles passed straight through the gold foil, but a few were deflected at large angles and a very small number bounced back. This led Rutherford to conclude that an atom has a tiny, dense, positively charged center (nucleus) containing most of its mass, with electrons revolving around it in mostly empty space. The electron was discovered by J.J. Thomson (1897), the proton by Rutherford (later, in 1917 through a different experiment), and the neutron by James Chadwick (1932).