【摘要】 正电子湮没寿命测量作为一种典型的核物理时间测量方法,其最为关键的两个性能参数是时间分辨率和符合计数率。决定时间分辨率的主要因素是探测器中闪烁晶体及光电转换器件的时间响应,而符合计数率不仅取决于探测器的探测效率,还取决于电子学系统对时间信号的判选方法。本文提出并设计了一种能够有效提高正电子湮没寿命符合测量计数率的方法。该方法通过对两探测器信号中的起始信号成分进行逻辑"或"运算产生外触发信号,利用高速数字化采集设备在此触发信号的触发下实现对有效事例的高效判选。其中任意一个探测器既可作为起始探测器也可作为终止探测器,有效提高了谱仪对探测器信号的利用率。实验表明:该方法在不影响时间分辨率和正电子湮没寿命谱与其峰谷比前提下,可获得更高效的符合计数率。更多还原

【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.更多还原