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What is meant by the Geiger-Muller region in the operation of a Geiger counter?
The Geiger-Müller region is the area on the performance curve of a Geiger-Müller (GM) tube where the voltage (or difference of potential, if you prefer) between the inner wi…re (the anode) and the outer case (the cathode) is sufficiently high to cause a current avalanche when any "substantial" unit of ionizing radiation (either particulate or electromagnetic) enters the detector. So much of the gas in the tube is ionized, and so many of the ions have moved in a given ionizing event that increasing the voltage won't affect any increase in this so-called avalanche current. Even increases of differential voltage in the range of hundreds of volts won't substantially alter the performance of the tube. This region, the one where current avalanches and no increase in current can be had by further increasing the voltage, is the Geiger-Müller region. This unit of ionizing radiation will ionize enough of the gas inside the tube that when the ions of gas move toward the electrodes (positive toward the negative and negative toward the positive), they will ionize more gas in the tube until much or most of the gas is ionized and moving. This will create a big "pulse" or a "current shot" or an avalanche of current that can be detected by support circuits in the electronics package that supports the GM tube. Additionally, the large-scale involvement of much of the gas in its ionized form to support this current flow will eventually insulate the anode with a big positive charge. The effect will be to "cut off" the tube and force it to "reset" or "un-ionize" throughout. This will restore conditions so that another pulse will again cause the same chain of events resulting in a "click" on counter. The electronics package records a "pulse" or a "count" of ionizing radiation, as it was designed to do. Links can be found below. (MORE)
