MULTICRYSTAL YAP-CE DETECTOR SYSTEM FOR POSITION-SENSITIVE MEASUREMENTS

Yttrium aluminum perovskite (YAP:Ce) scintillation crystal has a light efficiency of about 40% relative to NaI. Because of the yttrium atomic number (Z = 39) and the relatively high density (5.37 g/cm3) it has a good gamma-ray absorption. Furthermore it is not hygroscopic and is inert. Its peculiarity consists of material processing that provides us with crystal pillars down to 0.3 x 0.3 mm2 aperture size and up to some centimeters in length. An array consisting of 11 x 22 YAP:Ce elements was made where each crystal has an aperture of 0.6 x 0.6 mm2 and a length of 7 mm. Each scintillation crystal is optically separated by a reflective material resulting in a separation layer between elements of about 5 mum. The multicrystal detector was optically coupled to a Hamamatsu Position Sensitive Photomultiplier Tube (R2486). The intrinsic spatial resolution of the PSPMT is better than 0.3 mm but it is strongly dependent on the Point Spread Function (PSF) generated on the photocathode. The multicrystal detector very well matched the PSPMT characteristics resulting in a spatial resolution of about 0.7 mm at 140 keV (Tc-99m) gamma irradiation