Results from the ageing studies of large CsI photocathodes exposed to ionizing radiation in a gaseous RICH detector

We studied the ageing of large CsI photocathodes induced by ionizing particles (90Sr) by correlating the integrated charge dose of the ionic avalanches hitting the photocathode to the local changes of the Quantum Efficiency (QE). The drop of the QE of the irradiated CsI spots is reported as a function of the charge dose. It was found that the ageing process continues even in absence of irradiation.