Rutherford and his colleagues fired alpha particles, helium atoms that had lost their two electrons, at a thin piece of gold foil (only 0.00004 cm in width). They used a screen coated in zinc sulfide to "catch" the alpha particles after they had penetrated the gold foil. The screen would also emit a flash of light where it was hit by an alpha particle, which enabled them to measure to what extent the gold foil affected the particle's path.
Rutherford had predicted the alpha particles would all be able to penetrate the foil, although they would be scattered slightly by collisions with the foil's atoms. The experiment,