Ernest Rutherford made several discoveries, the most notable ones were the discovery of the nucleus in atoms, radiation half-life and the differentiation between alpha and beta radiation. Out of all of his discoveries, the discovery of the nucleus is possible his most well known one. The majority of Rutherford's work was accomplished after he was already a Nobel Prize laureate.
Rutherford made the discovery of the nucleus in 1911. The scientists experiment was originally to test the plum pudding model that was put forward by physicist Sir Joseph John Thompson in 1897. This model showed that atoms were spheres of positive charges that had electrons spiked through them.
Rutherford's experiment consisted of firing He2+ particles at foil. He thought that he could measure the deflection and learn more about the molecular structure of the foil. He expected the particles to exit the foil with some loss of momentum and slight deflection. Most of the particles sent through the foil went through with almost no deflection at all, but a few particles were deflected at 90 degrees or sometimes sent straight back towards the originating point. This led Rutherford to the discovery that most of the foil that he was firing at was made up of mostly empty space with a few small, very dense lumps inside of it. These lumps would be come to know as the nucleus of an atom.