Which experiment led Ernest Rutherford to propose the atomic nucleus in 1911?

The gold foil experiment led Ernest Rutherford to propose the atomic nucleus in 1911.

The work is more precisely called the Geiger–Marsden or Rutherford scattering experiment. In experiments conducted at the University of Manchester, alpha particles were directed at an extremely thin sheet of gold foil and detected on a surrounding fluorescent screen. Most particles passed through with little deflection, but a very small number were scattered through large angles, with some apparently bouncing backward.

That result was startling because the prevailing Thomson model pictured positive charge spread throughout the atom, which could not easily produce such strong reversals. Rutherford’s 1911 interpretation proposed that nearly all the atom’s positive charge and mass are concentrated in a tiny, dense central nucleus, while most of the atom is empty space. The nuclear model replaced the “plum pudding” picture.

The experiment was not a single instant performed by Rutherford alone. Hans Geiger and Ernest Marsden carried out the scattering measurements under Rutherford’s direction, including a notable 1909 report on diffuse reflection of alpha particles. Rutherford published the nuclear interpretation in 1911. Later work refined the model: Bohr introduced quantized electron orbits, and the neutron was identified decades afterward. “Gold foil experiment” is therefore the standard quiz answer, while “Rutherford scattering experiments” is the more historically precise name.