Abstract: [Background] Positron annihilation lifetime measurement as a typical time measuring method of nuclear physics, its time resolution and coincidence count rate are the most important performance parameters. The main factors that determine the time resolution of the spectrometer are the time response of the scintillation crystal and the photoelectric conversion device of the detector, and the coincidence count rate depends not only on the detection efficiency of the detector but also on the judgment method of the time signals by the electronic system.[Purpose] This paper aims to find a novel method for improving the utilization rate of detector signals and the coincidence count rate of positron annihilation lifetime measurement effectively.[Methods] The detector signals were divided into two same parts by splitters. One part of the signals was applied to generate an external triggering signal by performing a logic disjunction (OR) operation on the start-signal components to trigger the digitizer for acquiring the other part of signals. Two time interval measurement units which are used for timing, time interval calculation and data statistics were set. To verify the feasibility of this method, the digital storage oscilloscope was used.[Results] Measurement results showed that, the timing resolution of this testing system is 222 ps. Positron annihilation short lifetime τ₁ for sample pure Fe is about 108 ps and the long lifetime τ₃ for HDPE is about 2.4 ns. And compared with the conventional measurement, this method gave double the coincidence count rate approximately.[Conclusions] In the conventional measurement, regardless of which detector is used as start-detector or stop-detector, it doesn't influence the measured positron annihilation lifetime spectrum. By using the logic OR operation on the start-signal components of two detectors for triggering, the coincidence count rate will be improved effectively, however, the time resolution and positron annihilation lifetime spectrum or its peak-to-valley are uninfluenced. And each detector can be regarded as a start-detector and the stop-detector.

Key words: Positron annihilation lifetime spectrum, Start-signal, Trigger and judgment method, Coincidence count rate