The influence of exposure to air on the quantum efficiency of thin CsI photocathodes

The ageing of CsI film by exposure to air is discussed. Such exposures may take place during the transfer of a CsI photocathode from the evaporation vessel to the detector. The direct current (DC) was measured using a deuterium lamp for UV irradiation. It has been recorded as a function of the length of exposure to air for the case of small photocathodes. A 1 h exposure was found to have no remarkable effect in comparison to 8 or 15 min, but the current was decreased by 90% after 24 h exposure. A simple technique for CsI evaporation has been developed.