PERFORMANCE OF RESISTIVE PLATE COUNTERS WITH FREONLESS GAS-MIXTURES FOR MEASUREMENTS OF COSMIC-RAY MUONS

Various operational features of bakelite Resistive Plate Counters with a bulk resistivity of 10(12) Omega cm are studied with different argo n, methane and isobutane mixtures, but avoiding freon as counter gas c ontribution. The efficiency and the time resolution of the detector as well as the cross-talk behavior of neighbored read-out pads are inves tigated for different voltages by use of cosmic ray muons. The signals of the detector are classified by number and shape of the afterpulses . Relative abundances of these classes are measured and the timely app earance of the afterpulses is investigated. An efficiency of more than 90% is found For argon-isobutane mixtures and less than 27% for argon -methane mixtures. The time resolution differs between 1.27 and 4.19 n s, depending on the kind of quenching gas. A strong asymmetry of the t ime resolution spectra of the various gas mixtures has been observed. The shape of the signals depends on the used quenching gas. (C) 1998 E lsevier Science B.V. All rights reserved.