A Method for Calculating the Efficiency of Large Aperture Gas Cherenkov Counters

A method for calculating the efficiency of large aperture gas Cherenkov counters is presented. It is based on a careful Monte Carlo simulation of the geometrical response of the apparatus and on the measurement of the number of photoelectrons detected by the photomultipliers for some selected directions of the particles traversing the radiating volume. An application to a counter whose efficiency was systematically measured with great care is presented. The results are very satisfactory.