A spark-protected high-rate detector

We developed a very low resistivity RPC-type detector, the anode of which w as a plate made from materials with resistivity up to 5 x 10(7) Ohm cm, the cathode being a metallic mesh preceded by a drift region. In such a detector it was actually possible to combine the versatility and high counting-rate capability of metallic PPACs with the extreme robustness and "protectiveness" of Resistive Plate Chambers. Occasional discharges triggered by large deposits of primary ionisation or by extreme counting rates are quenched by the resistive anode and are const rained to the streamer phase of the sparking process. The study shows that this discharge affects the detector only locally and that the charge releas ed if limited to a few tens of nC. Proportional counting rates up to 10(5) Hz/mm(2) were achieved at gains abo ve 10(4). The energy resolution at 6 keV was 20% FWHM. The observed gain-ra te trade-off is well described by an analytic model and further improvement s may be expected by lowering the resistivity of the anode material. The properties of several custom-made, controllable resistivity, anode mate rials are described and prospects of improvement in the performance of the detector are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.