Application of small inexpensive side-on (side-window) photomultiplier tubes for scintillating fiber readout

Small inexpensive side-on photomultiplier tubes (PMTs) with excellent characteristics were tested for scintillating fiber readout. The location of the photocathode and nonuniform response of the photomultiplier poses problems in fiber or light guide readout. To overcome these problems the authors have devised and tested a fiber to PMT coupling technique which partially collimates the cone of light exciting a fiber by using small spherical lenses which are used in fiber-optics communication applications. An improvement was obtained with the focusing technique as opposed to using the fibers alone. The results of the measurements and the properties of the side-on PMT are discussed