| High-purity, quartz Cerenkov detectors can be used to count extreme flux rates of rela-tivistic electrons with very high precision. This allows for many indirect measurements ofthe universe including the cross-sections of weakly-interacting electrons with lead, calciumor liquid hydrogen targets. With this goal, several Cerenkov detectors were designed andconstructed. Data was collected at Stanford Linear Accelerator Center (SLAC) to test thesedetectors. The data collected at SLAC shows the light yield and resolution of several config-urations of the detectors. A calibration of six photo-multiplier tubes (PMTs) was completedto analyze the electron testbeam data. The PMT calibration included a precise measure-ment of the gain using a low-light method only applicable at high voltage, a light sourcecalibration, and a measurement of the gains at low voltages using the calibrated light source.A description of the gain measurement apparatus is presented along with the measurementtechnique and results.Keywords:Particle Physics, PMT calibration, Photo-multiplier characterization, gain measurement,Poisson statistics, Quartz Cerenkov detectors |