Cathode Uniformity of New Square Photomultiplier Tubes

Square photomultiplier tubes (PMTs) should have better light collection than round PMTs when used in square or rectangular Anger-type ¿-ray or neutron position detectors. Photocathode response uniformity of new RCA square PMTs type S83003E (51.5×51.5 mm2) was measured and compared with conventional round PMTs. The PMTs were scanned with a small scintillation source while the anode signal amplitudes were processed in a computer-based multichannel analyzer. The analyzer was programmed in a mode which virtually eliminates effects due to statistical fluctuations in source rate and output amplitude. Pulse heights as a function of source position on the PMT face are shown for typical tubes. The response uniformity of 64 square PMTs and 21 round ones was evaluated. It is shown that the center region of the square PMTs is as uniform as that of the round ones and that the response in the corners is comparable to that in the center. Thus square PMTs appear to have an advantage for use in square or rectangular position detectors.