Development of a new photomultiplier tube with high sensitivity for a wavelength-shifter fiber readout

We have developed a new photomultiplier tube (PMT) with high sensitivity for a wavelength-shifter fiber readout of plastic scintillators. Improvements of the photoelectron yield were made on a 2-in. PMT (Hamamatsu R329) by adopting (1) a prism-shaped photocathode, (2) an extended-green photocathode material, and (3) an optical mirror surface of the electrodes. As a result, the number of photoelectrons obtained by the new PMT has increased to be 1.8-times that by R329. Other PMT characteristics, such as uniformity of sensitivity, time response and darkcurrent are not so much different from those of R329 for practical applications.