New fast photomultipliers with a screening grid at the anode

Performances of new fast XP20Y0/DA and XP20Y0Q/DA 8 stage photomultipliers (PMTs) equipped with a screening grid at the anode were studied. The time jitter of the new PMTs was measured using a fast light pulser based on an XP22 light emitting diode. The timing properties in coincidence experiments were measured with BaF/sub 2/, LSO, and LaCl/sub 3/:Ce crystals for /sup 60/Co and /sup 22/Na gamma rays and discussed in terms of the measured photoelectron numbers. Particularly, the normalized time resolutions to the number of photoelectrons measured with BaF/sub 2/ crystals were comparable to that measured in the past with the XP2020Q in a superior dynode-timing mode. A significant improvement of timing up to a factor of 1.2 due to the grid at the anode was shown also in the measurements with LSO and LaCl/sub 3/:Ce crystals.