Photomultiplier Tubes: Configurations and Dark Current Analysis

This lecture focuses on photomultiplier tubes (PMTs), detailing their configurations and the dynamics of dark current. The instructor begins by explaining the concept of dynamic range in PMTs, emphasizing the limitations imposed by dark current at low input power and saturation effects at high levels of radiation. The discussion includes the mechanisms of thermionic emission and the Richardson equation, which describes the primary dark current on the photocathode. The instructor elaborates on how this dark current is amplified to produce output dark current on the anode, highlighting the significance of gain and leaky current. The lecture also covers noise equivalent power (NEP) and the impact of spatial charge on the photocathode's dynamic range. Various PMT configurations are presented, including side-on and head-on types, as well as reflection and transmission modes. The lecture concludes with a summary of PMT characteristics, including quantum efficiency, gain, and noise factors, while addressing the potential for developing position-sensitive PMTs for advanced applications.