Equipment:
Theory: Muons produced by cosmic rays bombard us constantly. These can be detected with two detectors in coincidence.
Description: The muon detector is so old it uses vacuum tubes in the power supply. It needs at least 15 minutes to warm up, and is a beast to move, but it's a nice demonstration. Typically, the coincidence counting rate is 4-5 per second with the two detectors sitting on top of each other. This is obtained with the power supply voltages adjusted to give a singles rate of 25 - 100 per second; the power supply currents should be between 15 and 20 microamps.
To show that the system is only registering a count when a muon passes through both detectors, move one detector away from the other. The coincidence rate should be zero, but will return to several per second when the detectors are stacked again.
Setup time: 24 hours
References: (available in the demo room)