Resistive Plate Chambers in ATLAS

The ATLAS first level muon trigger is based, in the rapidity region |η| ≤ 1.05, on fast and finely segmented gaseous detectors, Resistive Plate Chambers (RPCs). A prototype of a small scale RPC trigger tower has been assembled and tested. We present results on efficiency, time resolution, cluster size and collected charge. The detectors, filled with a non-flammable and environment-safe gas mixture, have been operated in avalanche mode. The measurements have been made at the CERN SPS accelerator in the H8 test-beam area with muon fluxes up to 900 Hz/cm2. A 14 mCi 60Co radiactive source has been used to illuminate the chambers with a flux of low energy photons, simulating LHC background conditions.