The purpose of the Geiger and Marsden experiment was to investigate the structure of the atom and specifically, the distribution of positive charge within an atom.
The results of the experiment showed that most of the alpha particles passed through the gold foil with little to no deflection, but a small percentage were deflected at large angles, indicating the presence of a concentrated positive charge in the atom.
The vacuum in the experiment was created by using a vacuum pump, which removes air and other gases from a sealed chamber, creating a low-pressure environment.
Gold foil was used because it is a very thin and malleable material, allowing alpha particles to pass through it easily. Additionally, gold was chosen for its high density and therefore, a higher chance of interaction with the alpha particles.
The Geiger and Marsden experiment provided evidence for the existence of a small, concentrated positive charge within the atom, which led to the development of the nuclear model of the atom. This experiment also disproved the previously accepted plum pudding model of the atom.