Nuclear Instruments and Methods in Physics Research A 518 (2004) 82–85 An extensive aging study of bakelite Resistive Plate Chambers G. Carboni a , S. De Capua a , D. Domenici a, *, G. Ganis a,1 , R. Messi a , G. Passaleva b , E. Santovetti a , M. Veltri c,2 a Universit " a degli studi di Roma ‘‘Tor Vergata’’ and Sezione INFN Roma 2, Roma, Italy b Universit " a degli studi di Firenze and Sezione INFN, Firenze, Italy c Universit " a degli studi di Urbino, Urbino, Italy Abstract We present recent results of an extensive aging test, performed at the CERN Gamma Irradiation Facility, on two bakelite Resistive Plate Chambers (RPC) detectors. With a method based on a model describing the behavior of an RPC exposed to a large particle flux, we have periodically measured the electrode resistivity r of the two detectors over 3 years. We observed a large increase of r with time, from initial values of about 10 10 O cm to more than 200  10 10 O cm: A corresponding degradation of the RPC rate capability, from about 3 kHz=cm 2 to less than 200 Hz=cm 2 ; was observed. The reversibility of the process, using a humid gas mixture, has also been studied. r 2003 Elsevier B.V. All rights reserved. PACS: 29.40.Cs Keywords: RPC; Detector; Current; Resistivity; Bakelite; Humid gas 1. Introduction The main challenge for Resistive Plate Cham- bers (RPC) in the last decade has been the improvement of the rate capability, to make suitable these detectors for the newcoming LHC experiments (see [1–3]). Standing particle flux densities up to few kHz=cm 2 [4–6] has been achieved by operating in avalanche mode, rather than streamer mode, and by using bakelite electrodes with resistivities as low as 10 9 O cm: We present the latest results of a three years aging test on two bakelite RPCs performed at the Gamma Irradiation Facility [7] at CERN. The test has been made in the framework of the R&D for the LHCb experiment to verify the stability of the detector performances with time, in particular their rate capability. Since this is directly related to the RPC resistivity, a simple method [8] has been developed to measure the electrode resistivity on line. 2. Experimental setup Two identical detectors (50  50 cm 2 with a 2 mm gas gap) were built using bakelite plates (2 mm thick) of nominal resistivity B10 10 O cm; ARTICLE IN PRESS *Correponding author. E-mail address: domenici@roma2.infn.it (D. Domenici). 1 Now at Forschungszentrum Karlsruhe GmbH, Postfach 3640, 76021 Karlsruhe, Germany. 2 Also sezione INFN, Firenze, Italy. 0168-9002/$-see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2003.10.030