Pulse measurement for 17-inches KamLAND photomultiplier tube

In order to provide input for the Monte Carlo simulation in KamLAND experiment, we studied the several types of abnormal pulses with a Hamamatsu R7250 17" photomultiplier tube (PMT), which is being used in KamLAND detector. In prepulse measurement, by using different incident light intensities, we measured the secondary emission ratio for first dynode and the dynode efficiency to photons, which can also be used in studying of Single Photoelectron (SPE) spectrum width. In afterpulse measurement we separated two types of afterpulses by using the coincidence of delayed afterpulse signal and normal PMT signal. Both of them will produce single photoelectron signal and the probability of occurrence is 3.5% and 4.5%. In latepulse studies we introduced a multi-hit Time Digital Converter (TDC) to perform the time spectrum measurement. Comparing with Hamamatsu latepulse measurements, we obtained a much more detailed time spectrum and have more accurate background subtraction. The total probability of occurrence for latepulse is measured to be 9%. Our results in amplitude study for latepulses indicate that all the peaks seen in the time spectrum are single photoelectron spectrums.