Fast timing with photomultilier dynode pulses

Timing results are presented obtained with a time definition system using photomultiplier dynode pulses without any further shaping. The dynode pulses are fed into a zero cross-over time discriminator with upper and lower level energy selectors. Timing measurements were performed with the XP2020(Q) photomultiplier and several scintillators, being 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 has been obtained with the NE111 scintillators. Several positron lifetime spectrometers have been built with this timing system. The most profitable setup was the one with the BaF/sub 2/ scintillators (30 x 8 mm cylinders) which had a resolution of 150(1) ps FWHM. A detailed description of the adjusting procedure is given which ensures reproducibility of the resolutions within a few ps