The experiment involved firing alpha particles at thin gold foil, where the number of alpha particles scattered at various angles were counted using a detector. This provided evidence for the existence, charge and small size of the nucleus.The fact that most alpha particles passed straight through unscattered suggested that the atom is mostly empty space. The fact that some were scattered through large angles > 90 degrees suggested that the nucleus has positive charge concentrated in a tiny central nucleus. This is because alpha particles have a +2 (positive) charge, and like charges repel.