Detectors, based on liquefied noble gases, are becoming more and more important in the field of neutrino and rare events physics. The measurement of scintillation light produced at the passage of an ionizing particle in the liquid medium plays a crucial role in these detectors and Photo-Multiplier Tubes (PMTs), directly immersed in liquid argon or xenon at cryogenic temperature, represent the most adopted devices, when working in absence of magnetic field. In view of future application, the behavior of a number of large cathode area (8 inches diameter) PMT models has been studied both at room and at cryogenic temperature. A complete characterization at cryogenic temperature has been performed in terms of gain, timing, signal shape, linearity, photo-cathode uniformity, dark counts and after-pulses rates and spectra. Moreover, an evaluation of the Quantum Efficiency of these devices, coated with wave-length shifter materials, has been carried out in the VUV region (from $\lambda$=120 nm to $\lambda$ = 220 nm incident light).

Universita` di Pavia , INFN Pavia