Test of freonless operation of resistive plate chambers with glass electrodes—1 mm gas gap vs 2 mm gas gap

Non-freon gas mixtures (Ar/iso-C4H10) were tested as the chamber gas for 1 and 2 mm gas gap Resistive Plate Chambers (RPCs) with float glass as the resistive electrodes, operated in the streamer mode. With the narrower (1 mm) gas gap, streamer charge is reduced (∼1/3), which reduces the dead time (and dead area), associated with each streamer, improving the detection efficiency. The best performance was obtained for two cases: Ar/iso-C4H10=50/50 and 60/40. For the 50/50 mixture, a detection efficiency of better than 98% was obtained for the 1 mm gap RPC, while the efficiency was 95% for the 2 mm gap RPC, each operated as a double-gap RPC. The measured time resolution (rms) was 1.45±0.05 (2.52±0.09) ns for the 1 (2) mm gap RPC for the 50/50 mixture.