Rutherford's alpha (α) particle scattering experiment resulted in the…

A scattering experiment reveals a target's internal structure without directly seeing it: particles are fired at the target and their deflection pattern is observed. If nearly all particles pass through with negligible deflection while only a rare few undergo very large deflections, that pattern shows the target's mass and charge cannot be spread out evenly — they must be concentrated in an extremely small, dense region.

In Rutherford's alpha-particle scattering experiment, a beam of α-particles was fired at a thin gold foil. The vast majority passed straight through undisturbed, but a small fraction were deflected at large angles, and a few bounced almost straight back. Since alpha particles are positively charged and relatively massive, such large deflections could only happen if they encountered a concentrated region of positive charge and mass far denser than the rest of the atom. This led Rutherford to conclude that atoms contain a small, dense, positively charged nucleus at their centre — the alpha-scattering experiment is specifically credited with this discovery.

• Electron — discovered earlier, by J. J. Thomson through cathode-ray tube experiments, not by firing alpha particles at a foil.

• Atomic mass — a numerical quantity of an atom that could already be measured by other methods; it is not something the scattering pattern itself reveals.

• Proton — identified later, through Rutherford's separate experiment of bombarding nitrogen with alpha particles, not the gold-foil scattering setup.

So the discovery specifically attributed to the alpha-particle scattering experiment is the atomic nucleus.