Operation of low-noise single-gap RPC modules exposed to ionisation rates up to

Two single gap medium-size RPC modules, made of bakelite plates of very good mechanical quality of the surface and having initial volume resistivity of 1 × 10 10 Ω cm , were tested in the Gamma Irradiation Facility at CERN at ionisation rates up to 1 kHz / cm 2 . The internal surfaces facing the gas volume of one RPC module were cladded with a thin layer of linseed oil varnish for comparison of oiled and non-oiled RPC operation. The results refer to the gas mixture of C 2 H 2 F 4 /isobutane (97:3) with SF 6 addition below 1%. The single gap modules exhibited full detection efficiency plateau for the high voltage range of about 1 kV at full intensity of gamma rays. Good timing characteristics allowed to reach 95% efficiency at fully opened irradiation source with time window of 20 ns. The intrinsic noise rate for a non-oiled and an oiled RPC gap was, respectively, below 5 and 1 Hz / cm 2 at full efficiency over 1 kV voltage range.