The use and development of ring-imaging Cherenkov counters

The present status of four major fixed-target experiments E789 and E665 at FNAL and WA89 and NA45 at CERN that use RICH (ring-imaging Cherenkov) counters is reviewed. The flexibility in adapting the basic RICH counter design to different outer geometrical constraints is discussed. It is noted that the design rules for the layout of a RICH counter allow for considerable flexibility and that it is possible to adapt the geometry of a RICH counter to a number of experimental constraints. This is of specific importance in colliding-beam experiments, where such constraints tend to be severe. As an example of the ongoing generic development of the RICH method, the recent discovery of a high-quantum-efficiency, air-resistant CsI-TMAE photocathode is reported