What it shows:

A qualitative demonstration of Rutherford's α-particle scattering experiment using magnetic pucks on an air table.

How it works:

In its simplest form, we use an Ealing air table, ¹ 1m square, with a fixed magnetic puck at the center. A second puck with the same polarity is repelled and scattered by the first; the scattering angle being dependant upon the impact parameter b (see figure 1). A more complex setup is described in the Comments.

Setting it up:

Although designed to sit on a lecture bench, we have constructed a tripod table 70cm high so that it can be placed on the floor and be a good height for the lecturer to use. The air supply comes from two Air Source® blowers. The table should be leveled; do this by turning on the blowers and adjusting the legs until a puck sits stationary at the center.

Comments:

The pucks only need a slight push—the magnets inside them are not strong and too much speed results in physical contact, which ruins the effect.

A more sophisticated setup is possible with all the technology at our disposal. A TV camera is mounted high above the air table on a fully extended tripod with its head reversed and looking down. The camera is linked to a storage oscilloscope that is adapted to behave as a television monitor (see description of the electronics in Single Photon Interference). The pucks themselves have fluorescent markings, so the setup, when illuminated purely by UV light (4ft UV lamp fixtures duct-taped to the legs of the tripod), shows simply the pucks in space. Using the storage facility of the CRO, the track of the α-puck is recorded with text-book quality results!

1 Ealing-Daw Air Table 34-0000, Ealing Corp., Cambridge, MA