Alpha Scattering Apparatus

The Alpha Scattering apparatus models one of the foundational experiments in atomic physics, using gravity as a mechanical analogue for the inverse-square repulsion an alpha particle feels near a nucleus. By rolling steel balls down a ramp and across a specially shaped hill, students can reproduce the deflection patterns Rutherford observed and see how a small, dense center of force scatters incoming particles through a range of angles.

At the center of the demonstration is a spun aluminum hill, 280 mm in diameter and 60 mm high, whose profile is the key to the analogy. The hill's height above the base line is varied according to the reciprocal of the radius, so that a ball rolling across it experiences a gravitational potential that mirrors the inverse-square electrostatic repulsion between an alpha particle and a nucleus. A ball launched toward the hill curves away from the central peak just as an alpha particle is deflected by the nucleus, with the closest approaches producing the sharpest scattering.

Balls are introduced using a wooden launching ramp measuring 300 by 48 mm and 105 mm high, with a guide groove down its curved front face to direct each ball along a consistent path. Index marks at 40, 60, 80, and 100 mm above the base provide a set of known launching heights, allowing the launch speed to be varied in a repeatable way and letting students investigate how the impact parameter and energy of the incoming ball affect its scattering angle. The set includes three steel balls, one 12.5 mm and two 19 mm, so that different projectile sizes can be compared. Together the components turn an abstract nuclear-physics result into a hands-on mechanical investigation suitable for demonstration or student-led experiment.