Measurement of Cherenkov angles with a CsI photocathode in a multiwire chamber

Cherenkov rings caused by cosmic rays in 1 cm thick NaF and LiF radiators have been measured with a 10 x 10 cm2 multiwire chamber. One cathode plane of the multiwire chamber is divided into 1 x 1 cm2 pixels, which are covered with a 500 nm thick layer of CsI. The distance between the CsI cathode plane and the anode wire plane is only 0.5 mm enabling high, fast and narrow signals. The main features of the measured angular distribution are predicted by Monte Carlo simulation for β = 1 particles. The measured rms resolution of the Cherenkov angle determined from a single photon is 51 mrad for NaF and 40 mrad for LiF with contributions from dispersion and photon detector position resolution being of the same order of magnitude. (orig.)