The jPET-D4: simple and reliable construction method for 4-layer DOI crystal blocks

The final design of the 4-layer DOI detector module for jPET-D4 system was determined and we produced 120 of the DOI crystal blocks. The jPET-D4 detector module consists of four layers of 16 by 16 Gd₂ SiO₅ (GSO) crystals and a 256 channel flat panel position sensitive photomultiplier tube (256ch FP-PMT). Two kinds of GSO crystals that show different scintillation decay time constants are used in the upper and lower two layers in order to distinguish these layers using pulse shape discrimination. Proper reflector insertion in the crystal block enables to identify crystals of detection in each two layers. For mass production of the DOI crystal block composed of 1024 crystal elements with the proper reflector arrangement, we used appropriate tools which promote simple construction as well as uniform configuration. The construction took only 3 hours per one crystal block. The produced 120 DOI crystal blocks were estimated their characteristics; pulse shape discrimination, energy resolution and full energy peak. The results show that misidentification in each GSO layer is less than 5% on pulse shape discrimination, the average of energy resolutions for the central four crystals of the 1st (farthest from PMT), 2nd, 3rd and 4th-layer are 15.7 plusmn 1.0%, 15.8 plusmn 0.6%, 17.7 plusmn 1.2% and 17.3 plusmn 1.4%, respectively and full energy peak variation among four layers is less than 5% in average