Direct measurement of the avalanche charge in a Resistive Plate Chambers detector

We performed a direct measurement of the avalanche charge with a 10 × 10 cm 2 prototype resistive plate chambers with a 0.2 cm gas gap. We studied its behaviour with respect to the high voltage and its dependence on the presence of the SF6 in the gas mixture (C2H2F4/i-C4H10/SF6 in the ratio 95/4/1 and 96/4/0). The measurements showed a double exponential behaviour of the average avalanche charge with respect to the high voltage. A comparison with other results has been discussed.