The Design and Performance of a Gas Čerenkov Counter with Large Phase-Space Acceptance

We describe the design and performance of a threshold gas Čerenkov counter used to detect electrons from lambda beta decay. To achieve the very large phase-space acceptance required, the counter incorporates a novel technique of light collection, the light funnel which we developed for this purpose. By means of the light funnel one can, in principle, make the entire phase-space acceptance of a photomultiplier tube useful for particle detection.