Measurement of proportional counter gas gain

A method of evaluation of proportional counter gas gain from arbitrary current measurements has been developed. It provides absolute value of the gain in range from 1 to 10/sup 8/ with moderate current sensitivity and without knowledge of used radioactive source properties. As an example we present dependence of the gain versus voltage for drift tubes of ATLAS Muon Spectrometer filled with mixtures Ar-CO/sub 2/(93-7) and Ar-N/sub 2/-CH/sub 4/(91-4-5) at 3 bar absolute pressure. Results are compared with the gain obtained from ADC measurements.