Rutherford's alpha particle scat- tering experiment on thin gold foil was responsible for the discovery of-

Ernest Rutherford's 1911 alpha particle scattering experiment, conducted by firing alpha particles at a thin gold foil, led to the discovery of the atomic nucleus [1]. While most particles passed through the foil, a small fraction was deflected at large angles or bounced back, indicating the presence of a dense, positively charged central core [1]. This observation disproved J.J. Thomson's 'plum pudding' model, which suggested charge was uniformly distributed. Rutherford concluded that nearly all the atom's mass and its positive charge are concentrated in this tiny interior space, which he termed the nucleus. Although the nucleus contains protons and neutrons, the experiment specifically identified the existence of the nuclear structure itself. Electrons had been discovered earlier by Thomson in 1897, and the neutron was later discovered by James Chadwick in 1932 [1].

Sources

1. [1] https://www.fnal.gov/pub/inquiring/timeline/03.html