A long-run study of aging in glass timing RPCs with analysis of the deposited material

Aging of glass RPCs has been extensively studied along the last years. Most authors refer effects such as an increase of dark counting rate, reduction of the counter efficiency and the appearance of deposits over the electrodes surfaces. Understanding the origin of these deposits and their effect on the counter performance is of considerable practical importance. In this study, aimed at timing RPCs operating in avalanche mode, we irradiated 0.3mm gas gaps for 790 days of continuous operation at 300Hz/cm, corresponding to an accumulated charge of more than 20mC/cm. No evidence of any systematic long-term increase of dark current was found, but a visual inspection confirmed the existence of a bluish deposit over the glass electrodes. The identification of the deposit components was made by liquid extraction with organic solvents and subsequent analysis by gas chromatography with mass spectroscopy detection. The identified species are oligomers of tetrafluoroethylene. & 2009 Elsevier B.V. All rights reserved.