The timing properties of scintillation counters consisting of small NE111 plastic scintillators coupled to the XP2020UR photomultipliers have been studied in comparison to that based on the XP2020. The time jitter of both the photomultipliers, their photoelectron yield for the NE111 plastics and the time resolution with60Co and22Na sources were measured. A high time resolution was achieved with the XP2020UR equal to 90 ps for60Co (at 1 MeV) and 140 ps for22Na (at 290 keV) energy settings, about 30% and 20% better respectively than those observed with the XP2020. The large improvement of the time resolution is due to: 30% lower time jitter, about 25% higher photoelectron yield and for the60Co energy settings also to a reduced influence of the space charge effect in the XP2020UR. The normalised time resolution to the photoelectron number, measured with22Na source, is better by a factor of 1.14 which corresponds well to the improvement of the time jitter in the new XP2020UR photomultiplier. © 1993.
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