Evaluation of Hamamatsu R5900 series PMTs for readout of high-resolution scintillator arrays

Two types of Hamamatsu R5900 series photomultiplier tubes (PMTs) have been evaluated as position-sensitive photon detectors for reading out arrays of small scintillator elements. Both PMTs have metal-channel dynode structures and compact dimensions of 26 x 26 x 20 mm(3). Model R5900-C12 is a positio n sensitive PMT (PS-PMT) with photoelectrons shared among 12 plate anodes a rranged in a crossed pattern such that there are six anodes each in the X a nd Y directions. Model R5900-M64 is a multi-channel PMT (MC-PMT) with 64 in dividual channels and low inter-channel crosstalk. Scintillator arrays can be coupled to these PMTs either directly or by using optical fibers. In thi s paper, we present measurements of single photoelectron spectra, pulse lin earity, positioning response, inter-channel gain variation and pixel-to-pix el crosstalk for these PMTs. We have also measured their positioning respon se in reading out high-resolution lutetium oxyorthosilicate (LSO) scintilla tor arrays. Across a sample of 30 R5900-M64 MC-PMTs which were manufactured recently, the maximum gain variation over all channels is less than 3:1, w hile the difference between any two adjacent channels is less than 2:1. Wit h a tapered voltage divider, the output of the anode signal at a gain of 10 (6) remains linear up to 200 photoelectrons for the R5900-M64. For the R590 0-C12, the summed anode signal remains linear up to 400 photoelectrons when irradiated through a 2 mm diameter aperture. Images obtained with a Na-22 source irradiating an array of 1 x 1 x 10 mm(3) LSO crystals coupled by an optical fiber bundle to the R5900-C12 or the R590Q-M64 show excellent cryst al identification. (C) 2000 Elsevier Science B.V. All rights reserved.