Experimental study of gas mixtures in strong non-uniform electric fields

Argon-based gas mixtures of various concentration ratios at low pressures were studied in a gas proportional counter. Over-exponential increase of gas gain in mixtures with low partial pressure of any admixture was observed. The best energy resolution was measured at a gas gain of several hundreds for lower admixture concentrations, but at high gas gains R degraded very fast. The first Townsend ionization coefficient alpha /P in low-pressure gases depended also on the gas pressure. The single-electron spectra had a peaked shape in mixtures with relatively high content of the molecular gas. In mixtures with lower molecular gas amount they changed the shape toward the over-exponential distribution. A partial pressure of 10 kPa was determined as a requirement for good quenching property of the mixture. (C) 2001 Elsevier Science Ltd. All rights reserved.