In the Rutherford gold foil experiment, what subatomic structure did the results reveal inside atoms?

The Rutherford gold foil experiment revealed that atoms contain a tiny atomic nucleus.

In the 1909 Geiger–Marsden experiment, alpha particles were fired at an extremely thin sheet of gold foil. Most passed straight through, but a small number were deflected through large angles, with a few apparently bouncing backward.

Ernest Rutherford interpreted the result in 1911. He proposed that nearly all an atom's positive charge and mass are concentrated in a very small, dense nucleus, while the rest of the atom is mostly empty space. This replaced the earlier “plum pudding” model associated with J. J. Thomson.

The experiment did not itself identify neutrons, which James Chadwick discovered in 1932. It established the nuclear model of the atom, a foundation for later atomic and nuclear physics.