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.