Fast timing with photomultiplier dynode pulses

Timing results are presented that were obtained with a time-definition system using photomultiplier dynode pulses without any further shaping. The dynode pulses are fed into a zero-crossover time discriminator with upper- and lower-level energy selectors. Timing measurements were performed with the XP2020(Q) photomultiplier and several scintillators: small NE111 cylinders, two different sizes of Pilot U conicals, and BaF/sub 2/ cylinders. The best time resolution of 100(2) ps FWHM per detector pair and /sup 60/Co was obtained with the NE111 scintillators. Several positron-lifetime spectrometers have been built with this timing system. The setup using the BaF/sub 2/ scintillators had a resolution of 150(1) ps FWHM. A detailed description of the adjustment procedure, which ensures reproducibility of the resolutions with a few picoseconds, is given.<>