Properties of reflective and semitransparent CsI photocathodes

Various aspects related to the quantum efficiency of the reflective and semitransparent CsI photocathodes have been investigated experimentally . The investigation explored the dependence of the quantum efficiency on the following: the thickness of the photocathode film, the gas used in the parallel-plate avalanche chamber, exposure to water vapor, and the density of the CsI film . With reflective CsI photocathodes quantum efficiencies of more than 25% at 180 rim have achieved m three different gases : CH4, CH 6, and C4H ii , . Our study reveals that high quantum efficiency is also achievable for the semitransparent CsI photocathodes. For a 95-A semitransparent photocathode the quantum efficiency at 185 rim can be as high as 20%. A simple model to explain the dependence of quantum efficiency on the thickness of CsI photocathodes is suggested, which may be a useful guide for further improvement of the performance of CsI photocathodes Also reported are UV-transmittance measurements for various materials used m our studies, such as methane, ethane, isobutane, CF4, CO, helium, neon, air, TMAE vapor, thin CsI films, and quartz windows, all m the wavelength range 115 rim to 230 rim .