Achieving direct imaging of the annihilation position of a positron on an event-by-event basis using an ultrafast detector would have a great impact on the field of nuclear medicine. Cherenkov emission is the most attractive physical phenomenon for realizing such an ultrafast timing performance. Moreover, a microchannel-plate photomultiplier tube (MCP-PMT) is one of the most promising photodetectors for fully exploiting the fast timing properties of Cherenkov emission owing to its excellent single photon time resolution of 25 ps full width at half maximum (FWHM). However, as the MCP structure generally contains a lead compound, the gamma rays frequently and directly interact with the MCP, resulting in the degradation of its timing performance and generation of undesirable side peaks in its coincidence timing histogram. To overcome this problem, we have developed a new MCP-PMT based on an MCP consisting of borosilicate glass, thus drastically reducing the probability of the photoelectric effect occurring in the MCP. To evaluate its insensitivity to gamma rays and its timing performance, a coincidence experiment was performed and showed that the probability of direct interactions was reduced by a factor of 3.4. Moreover, a coincidence time resolution of 35.40.4 ps FWHM, which is equivalent to a position resolution of 5.31 mm, was obtained without any pulse height/area cut, improving to 28.73.0 ps when selecting on the highest amplitude events by careful optimization of the voltage divider circuit of the new MCP-PMT. The timing performance of this new MCP-PMT presents an important step toward making direct imaging possible.

使用超快探测器逐个事件地实现正电子湮没位置的直接成像将对核医学领域产生重大影响。切伦科夫发射是实现这种超快时序性能的最有吸引力的物理现象。此外，微通道板光电倍增管 (MCP-PMT) 是最有前途的光电探测器之一，可充分利用切伦科夫发射的快速定时特性，因为它具有 25 ps 的半峰全宽 (FWHM) 的出色单光子时间分辨率。然而，由于MCP结构一般含有铅化合物，伽马射线频繁且直接地与MCP相互作用，导致其计时性能下降，并在其重合计时直方图中产生不希望的侧峰。为了克服这个问题，我们基于由硼硅玻璃组成的 MCP 开发了一种新的 MCP-PMT，从而大大降低了 MCP 中发生光电效应的概率。为了评估其对伽马射线的不敏感性及其计时性能，进行了巧合实验，结果表明直接相互作用的概率降低了 3.4 倍。此外，在没有任何脉冲高度/面积切割的情况下，获得了 35.40.4 ps FWHM 的重合时间分辨率，相当于 5.31 mm 的位置分辨率，通过仔细优化选择最高幅度事件时提高到 28.73.0 ps新型 MCP-PMT 的分压器电路。这种新型 MCP-PMT 的定时性能向实现直接成像迈出了重要一步。