the Gold Foil Experiment
He put a zinc sulfide screen behind the foil in order to reflect light (show the particles) and he placed them on the microscope. The experiment was done in total darkness so the particles would be seen. They observed that particles bounced back as well as passed through the foil. The experiment proved that atoms are made up of more than just empty space and electrons. He discovered the nucleus.
why this experiment?
Rutherford was testing "The Plum Pudding Theory", he assumed the atoms would bounce back instead of going straight through the foil. Meaning, atoms are more than simply empty space and electrons.