Light-guide design for timing measurements in large counters

The geometrical factors influencing the time resolution in large counters are examined. Calculations of the number of photons collected in the leading edge of the light pulse are used to compare various geometries for adapting a rectangular counter to a photomultiplier. Restrictions on the sharpness of bending in twisted light guides are examined. A simple conical adaptor between the end of a twisted guide and the photomultiplier is found to be the best solution. (2 refs).