How were alpha particles detected in the gold-foil experiment?

In the gold-foil experiment, alpha particles were detected using a screen coated with zinc sulfide. This screen served as a counter by becoming fluorescent upon impact.1

When an alpha particle struck the screen, it produced a small burst of light known as a scintillation. These flashes were observed through a viewing microscope attached to the back of the screen. Because the screen was movable, researchers were able to track the trajectory of the particles and determine whether they had been deflected by the gold foil. This method allowed Ernest Rutherford and his associates, Hans Geiger and Ernest Marsden, to observe that while most particles passed straight through the foil, some were scattered at large angles, leading to the discovery of the atomic nucleus.1