QUANTUM EFFICIENCY AND AGING STUDIES FOR BULK AND POROUS CSI PHOTOCATHODES IN A MWPC

The quantum efficiency of CsI photocathodes operating in a proportiona l gas chamber is measured in the wavelength range 185-220 nm. The test s are carried out with methane gas at atmospheric pressure using a pul sed UV lamp. Two different techniques are used to produce the photocat hodes. The CsI is either evaporated under high vacuum or under low pre ssure of argon. The quantum efficiency of the photocathodes produced b y the first technique is measured to be 9% at 190 nm while it is enhan ced by a factor of 1.3 and 2 at 190 nm and 200 nm respectively for the photocathodes prepared with the second method. No significative drop of the quantum efficiency is observed over a total period of one month .