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The Muon Detector

The muon detector consists of one square metre of plastic scintillator viewed by a photomultiplier tube. The muon produces a flash of light in the scintillator and the photomultiplier tube (a sophisticated photo-electric cell) produces an electronic signal which is proportional in amplitude to the amount of light. The output signal from the tube goes to a piece of electronic circuitry (a discriminator) which senses whether the signal is the right size to be due to a muon passing through the detector. If this is so, the muon is counted. The total count for each 15 minute interval (about 100,000) is recorded in a data file and also displayed using LabView as an hourly average.

Also recorded is the atmospheric pressure (displayed) and the laboratory (inside) temperature.

The level at which the discriminator is set is determined by finding the "single particle peak" (see Cosmic Ray Related Undergraduate Experiments [131KB, PostScript]) using a multichannel analyser and setting the level of the discriminator in the trough below that signal level. Since almost all muons produce a signal close to the single particle peak, this ensures efficient data collection.

The muon detector located at Adelaide University, with the light-tight box on the right, the computer on the left and the high-voltage power supply in the middle. Click on the image to see a larger version [1152x864, 349KB, JPEG].