TESTS OF A SOLID CSI PHOTOCATHODE IN A THIN MULTIWIRE PROPORTIONAL CHAMBER

A methane filled, 3 mm thick multiwire chamber with CsI photocathode and NaF window as Cherenkov radiator has been tested with electrons from Sr-90 and with cosmic rays. Simulation calculations of the measured pulse height distributions show that the quantum efficiency of solid CsI in a MWPC environment could be close to that measured by Seguinot et al. About 30 Cherenkov photons are detected per cosmic particle traversing 1 cm of NaF. The time spread of Cherenkov signals with respect to a scintillation counter trigger has been measured to be 4.5 ns FWHM. Results are also presented for detector performance over a three months period.