Change in detector properties caused by electronegative impurities

Detector properties (energy resolution, gas gain, drift-time measurements) depend quite critically on the concentration of impurities. The most frequent impurities in the working gas are water vapour and oxygen. Systematic measurements of the detector properties as a function of both H2O vapour and O2 concentration have been made. Ar/CO2 (80/20) and Ar/CO2/CF4 (70/10/20) have been selected as the working gases. The first mixture is commonly used, the second one is very promising due to its fastness. The concentration of H2O vapour and O2 was varied from 0% to 1.9% and 3%, respectively.