IONIZATION COEFFICIENT IN SOME ARGON-BASED MIXTURES IN STRONG ELECTRIC= FIELDS Ines Krajcar Bronic* and Bernd Grosswendt# *Rudjer Bo=9Akovic Institute, Bijenicka 54, P.O.Box 1016, HR-10001 Zagreb, CROATIA #Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, GERMANY Ionization coefficient alpha/P for propane, DME and isobutane and their mixtures with argon in strong non-uniform electric fields was determined from the measurement of gas amplification factor in a proportional counter. Under non-equilibrium conditions the alpha/P depends on the gas pressure. The non-equilibrium effect occurs in weaker electric fields if the mixture contains lower molecular gas concentration.