The RED100 double-phase emission detector is currently being prepared for the experiment aimed on the registration of the phenomenon of coherent neutrino scattering off xenon nuclei, having several dozens of Hamamatsu R11410-20 PMTs in its structure. Since the detector must be capable to detect rare events with small amount of the released energy, it is mandatory to evaluate the sensitivity and noise characteristics of the PMTs involved. For this purpose, a characterization procedure has been carried out for each PMT unit, including the study of its single photon response and noise characteristics. Among the systematic characteristics of 34 PMT samples, results of a special study of a number of non-standard features are presented. For example, observation of single photon emission of the PMT’s internal structure is described, including the results of the photon emission intensity study as a function of the PMT bias voltage and temperature. Another important feature of the device concludes in an unusually big Cherenkov light yield of charged particles in the volume of the PMT quartz window. Properties of the window material together with high quantum efficiency for VUV light ($>$30%) lead to appearance of signals with amplitudes about 100 photoelectrons from atmospheric muons passing the horizontally placed PMT window. Such effect makes feasible the usage of a R11410-20 as a standalone particle detector. Special investigations were held concerning the value of 511 keV photons (among the atmospheric muons) Cherenkov light yield during their registration with the R11410-20 PMT window.

National Research Nuclear University MEPhI (Moscow Engineering Physics Institute)