Performance of a Resistive Plate Chamber operated in avalanche mode under 137Cs irradiation

A 2 mm gas gap Resistive Plate Chamber with bakelite plates has been operated in avalanche mode with a 137 Cs source. We report measurements of the efficiency for a cosmic ray detection and the charge developed in the gap, performed for two different gas mixtures: the first containing a high percentage of environmental friendly “freon” C 2 H 2 F 4 ; the second one having a high percentage of argon. We show that the freon-based mixture exhibits a wide full-efficiency plateau with low streamer probability, while the argon-based mixture allows a reduction in the detector power consumption.