GEIGER_MUELLER_TUBE_CIRCUIT

Published:2009/7/14 2:21:00 Author:May | From:SeekIC

A GM tube is useful for detecting radioactivity. The tube is constructed with a cylindrical electrode (cathode) surrounding a center electrode (anode). The tube is evacuated and filled with a neon and halogen gas mixture. A voltage potential of 500 V is applied across the tube, through a 10-MΩ current-limiting resistor (R1). The detection of radiation relies upon its ability to ionize the gas in the GM tube. The tube has an extremely high resistance when it is not in the process of detecting radioactivity. When an atom of the gas is ionized by the passage of radiation, the free electron and positive ionized atom that are created move rapidly toward the two electrodes in the GM tube. In doing so, they collide with and ionize other gas atoms, which creates a small avalanche effect. This ionization drops the resistance of the tube, allowing a sudden surge of electric current that creates a voltage across the resistor R2, which can be seen as a pulse.



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