STUDY OF CSI PHOTOCATHODES IN A MULTIWIRE CHAMBER

A 3 mm thick multiwire chamber with a CsI photocathode and methane gas filling has been used as a detector for UV photons. The chamber was tested with Cherenkov radiation emitted in NaF radiator by electrons from Sr-90 and by cosmic rays [1,2]. About 30 Cherenkov photons were detected per cosmic particle traversing 1 cm of NaF. The measured quantum efficiency of the best photocathode is 80% of the efficiency measured in ref. [3]. The timing resolution for single photons was measured to be 8.3 ns (FWHM) [4]. The detector performance over a three months period was also studied [2]. The photocathode quantum efficiency improved by about 50% after treating the surface with TMAE.