Geiger plateau

The Geiger plateau is the voltage range in which the Geiger-Müller counter operates. Depending on the characteristics of the specific counter (manufacturer, size, gas type etc.) the exact voltage range may vary. In this region the potential difference in the counter is strong enough to ionize all the gas inside the tube, upon triggering by the incoming ionizing radiation (alpha, beta or gamma radiation). Below the plateau the voltage is not high enough to cause complete discharge; a limited Townsend avalanche is the result, and the tube acts as a proportional counter, where the output pulse size depends on the initial ionization created by the radiation. Higher voltages cause a phenomenon called quenching in which the positively charged ions are drawn to the cathode thus creating a continuous electric pulse in the counter.

The plateau has a slight incline caused by increased sensitivity to low energy radiation, due to the increased voltage on the device. Normally when a particle enters the tube and ionizes one of the gas atoms, complete ionization of the gas occurs. Once a low energy particle enters the counter, it is possible that the kinetic energy in addition to the potential energy of the voltage are insufficient for the additional ionization to occur and thus the ion recombines. At higher voltages, the threshold for the minimum radiation level drops, thus the counter's sensitivity rises.