Study of 8 " PMTs at UCLA For Pierre-Auger Surface Detectors

We have tested three candidate PMT’s for the Surface Array Detectors for the Pierre-Auger Observatory, being constructed in Malargue, Argentina. These are 8-inch PMT’s from Hamamatsu (R5912) and ETL (9353KB), and 9-inch PMT’s from Phtonis (XP1802/FLB). We have developed dedicated systems to measure Quantum Efficiency (QE) and Linearity. In addition, basic quantities such as Gain, Dark current, Single Photo-electron spectrum, Dark Pulse Rate, and Afterpulse ratio etc. have been measured. We found that most of specifications required by the Auger Project can be met with existing PMT’s. However, better linearity at low gain operation (at ~10) may require modifications such as reduction in the number of dynode stages.