TESTS OF SOLID CSI PHOTOCATHODES IN A MULTIWIRE CHAMBER

A methane filled, 3.1 mm thick multiwire chamber with CsI photocathode and NaF window as Cerenkov radiator has been tested with electrons from Sr-90 and with photons from Na-22. The measured quantum efficiency of solid CsI in a MWPC environment is close to that measured by Seguinot et al. giving about 30 detected Cerenkov photons per cosmic particle traversing 1 cm of NaF. A measurement of the time distribution of signals due to single electrons created at the CsI photocathode yielded a full width at half maximum (FWHM) of 8.3 ns. Stability tests of detector performance were carried out over a period of more than a year.