Development of microstrip gas chambers on substrates with electronic conductivity

This paper describes several recent developments on microstrip gas chambers (MSGCs). We have studied the operating behaviour of the detectors in different gas mixtures; maximum stable gains have been achieved in mixtures of argon and dimethyl-ether (DME) in almost equal proportions. Using detectors manufactured on semiconducting glass substrates, capable of withstanding very high rates (above 10⁶ mm^-2 s^-1), we have demonstrated extended lifetime without gain modifications up to a collected charge of 130 mC cm^-1 in clean laboratory operating conditions. We have also verified that relaxing the requirements on cleanness conditions, either in the gas mixing system or in the detector construction, may result in fast ageing of the devices under irradiation. As an alternative to semiconducting glass, we have developed a novel technique to coat regular glass with a thin lead silicate layer having an electron conductivity; a new development consisting in coating already manufactured MSGCs with the thin semiconducting layer is also described. The preliminary results show an excellent rate capability for this kind of device, intrinsically simpler to manufacture