YAP MULTICRYSTAL GAMMA-CAMERA PROTOTYPE

The Anger camera principle has shown a practical limit of a few millim eters spatial resolution. To overcome this limit, a new gamma camera p rototype has been developed, based on a position-sensitive photomultip lier tube (PSPMT) coupled with a new scintillation crystal, The Hamama tsu R2486 PSPMT is a 76-mm diameter photomultiplier tube in which the electrons produced in the conventional bi-alkali photocathode are mult iplied by proximity mesh dynodes and form a charge cloud around the or iginal coordinates of the light photon striking the photocathode. A cr ossed wire anode array collects the charge and detects the original po sition, The intrinsic spatial resolution of PSPMT is better than 0.3 m m. The scintillation crystal consists of yttrium aluminum perovskit (Y AP:Ce or YAlO3:Ce). This crystal has a light efficiency of about 38% r elative to NaI, no hygroscopicity and a good gamma radiation absorptio n, To match the characteristics of the PSPMT, a special crystal assemb ly was produced by the Preciosa Company, consisting of a bundle of YAP :Ce pillars where single crystals have 0.6 X 0.6 mm(2) cross section a nd 3 mm to 18 mm length, Preliminary results from such gamma camera pr ototypes show spatial resolution values ranging between 0.7 mm and 1 m m with an intrinsic detection efficiency of 37 divided by 65% for 140 keV gamma energy.