An Investigation into the Mechanism of Self-quenching Geiger-M ller Counters containing Argon with Small Quantities of Xenon, Oxygen and Nitrogen

Abstract

The time distribution of spurious pulses in counters with treated and untreated cathodes was studied by pulse interval analysis, and plateau characteristics, charge per pulse and Geiger threshold potential are plotted as functions of the xenon concentration. In all the counters investigated, the presence of a minimum threshold indicates an optimum xenon concentration of 3.5%. Measurements of the corona threshold with argon and argon-xenon filling mixtures show a pressure dependent increase in gas multiplication with addition of xenon. This increase in ionization is tentatively explained by the hypothesis of two-body collisions between xenon atoms and argon excited molecules leading to the formation of the molecular ion AXe+. Mobilities obtained from transit time measurements identify the ions involved as A2+ (1 82 cm sec-1 (v cm-1)-1), possibly NO+ (2 45 cm sec-1 (v cm-1)-1) this ion appearing after the counters have been in continuous discharge, and an ion of mobility 1 64 cm sec-1 (v cm-1)-1, which is not inconsistent with the postulated AXe+ molecular ion.