Performance of a new accelerating-electrode-equipped fast-time-response PMT coupled with fast LGSO.

In this study, we measured the performance of a newly developed Hamamatsu Photonics R13478 photomultiplier tube (PMT) and compared the results with those of an existing R9800 PMT. In R13478, an accelerating electrode is placed between the focusing electrode and first dynode for time resolution improvement through reduced transit time jitter. We investigated the time resolution dependence on the supply voltage and time pickoff method for R13478 and R9800 PMTs, each coupled with a 2.9  ×  2.9  ×  20 mm3 fast LGSO:Ce (0.025 mol%) crystal. In addition, we measured the PMT time resolutions coupled with the crystals in edge and laid positions to determine the effects of the reduced position dependence of transit time in R13478. R13478 exhibited a better time performance than R9800 in various ways. The rise time of R13478 for our experimental setup was 1.54 ns, 100 ps shorter than that of R9800 because of the reduced transit time. Further, R13478 achieved a 169 ps single time resolution at the recommended supply voltage, while this value was 187 ps for R9800. The time resolution of R13478 was also significantly better for a low time pickoff threshold level and a high supplied voltage, which are conditions vulnerable to transit time jitter and noise, respectively. A considerable difference in time resolution was observed for the laid position (R13478: 144 ps; R9800: 167 ps), indicating that the accelerating electrode reduced spatial transit time difference. Overall, we showed the effects of the differentiated characteristics of R13478 PMT compared with R9800 and confirmed its excellent time performance. We suggest use of this device as a photodetector effective for fast timing applications such as time-of-flight positron emission tomography.