NEW-GENERATION POSITION-SENSITIVE PMT FOR NUCLEAR-MEDICINE IMAGING

Recently, Hamamatsu has developed a new dynode structure in a position -sensitive photomultiplier tube (PSPMT) based on metal channel technol ogy, producing a very focused charge distribution. Hamamatsu R5900-C8 is the first metal channel dynode PSPMT with a crossed wire anode. The outline dimension is 28 x 28 x 20 mm(3) with an active area of 21 x 2 2 mm(2) and four wire anodes (4X + 4Y). A weighted summing device was realised to calculate the charge distribution centroid where each anod e was directly connected to a preamplifier and amplifier. Tests of pos ition linearity, energy response and spatial resolution were carried o ut coupling the PSPMT to an NaI(Tl) planar crystal and to a YAP:Ce sci ntillation array. To test the influence of charge spread on position l inearity, the photocathode was irradiated by a light spot with 1 mm of aperture size. Position non-linearity resulted when a scintillating a rray with 1 x 1 mm(2) pixel size was coupled to PSPMT. On the contrary , increasing the spread of charge distribution by a planar scintillati on crystal, a good linearity response was obtained. Impressive spatial resolution values were obtained from the YAP:Ce scintillating array. They ranged between 0.5 and 0.2 mm irradiating the crystals by Co-57 a nd Cs-137 source, respectively.