Rutherford Scattering

Rutherford's classic experiment consisted in bombarding a thin gold foil with

α

particles (helium nuclei). He expected that some particles would be slightly deflected by the positive charge inside the atoms. Most went through without much change, some were deflected, and surprisingly, some came straight back. This led Rutherford to conclude that the positive charge must be concentrated in a very small volume called the nucleus and not across the entire atom, with a typical radius of the order of

-14

10

m.

This Demonstration shows the hyperbolic trajectory of an

α

particle deflected by a gold nucleus. The

α

particle is aimed along the green dashed line. When the impact parameter is small, the particle comes almost straight back along the blue curve. Increasing the impact parameter decreases the deflection angle and the hyperbola opens, approaching a right angle.