1. The Setup: Rutherford shot alpha particles (positively charged helium nuclei) at a thin sheet of gold foil. He placed a fluorescent screen around the foil.
2. The Observation: He noticed that most of the alpha particles passed straight through the foil, causing flashes of light on the screen directly behind the foil. This suggested that atoms were mostly empty space.
3. The Unexpected: However, he also observed some alpha particles scattering at large angles, even bouncing back towards the source. This was completely unexpected based on the "plum pudding" model of the atom, which suggested a diffuse positive charge throughout the atom.
4. The Interpretation: Rutherford concluded that the large-angle scattering was caused by a concentrated positive charge within the atom, which he called the nucleus. He reasoned that the alpha particles were deflected by the strong electric repulsion between their positive charge and the positive charge of the nucleus.
So, Rutherford didn't directly see the particles' paths, but he was able to infer the paths based on where they hit the fluorescent screen. The deflection of some particles at large angles provided strong evidence for the existence of the nucleus, a tiny, dense, and positively charged core within the atom.
