Detector Analog

Modern Physics > Elementary Particles

DCS# 7E10.xx

DETECTOR ANALOG

Select image: setup covered track

APPARATUS

black box	202-13-B-1
magnetic viewing film	202-13-B
spherical magnet	202-13-B
steel balls	202-13-B
Gauss accelerator	202-13-B
tupperware ball catcher	202-16-D
strong magnet "eraser"	206
document camera	201

DESCRIPTION

With a target in the black box and the magnetic viewing film on the lid, use the Gauss accelerator to fire a steel ball or a magnetic marble at the target. This provides an analog for understanding the tracks produced in particle detectors. The magnetic balls (representing charged particles) will leave a track on the film. The non-magnetic balls (representing uncharged particles) will leave no tracks but their presence can be inferred from momentum conservation.

The target that works best is a spherical magnet and steel ball with a spacer between them (the magnet needs to be strong enough to produce a track and weak enough to let go of the steel ball after the collision, so the spacer helps with the latter). The shooter can be either one of the 13 mm ball bearings in the Gauss accelerator, or one of the weak magnetic marbles.

NOTES: The lid of the black box is bowed and should be inserted concave side down.; Place the magnetic viewing film dull side up to reduce glare.

The film can be cleared by sweeping a strong magnet over the sheet a few centimeters above it.

The tracks are more prominent when created with the film on the base, so another possibility is to run the collision first in the black box, then remove the film and examine the tracks. In that case, a magnetic marble can be used as the shooter. In the other configuration the marble's magnet is too weak to leave a track.