Argon-based gas mixtures of various concentration ratios at low pressures w
ere 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 f
or lower admixture concentrations, but at high gas gains R degraded very fa
st. The first Townsend ionization coefficient alpha /P in low-pressure gase
s depended also on the gas pressure. The single-electron spectra had a peak
ed 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 Elsev
ier Science Ltd. All rights reserved.