Recent developments for the readout of a matrix of scintillators by means of a multi-pixel HPD

We have been investigating the possibility to readout a large number of crystals (more than 400) by means of WaveLength Shifting (WLS) square section fibers and multi-pixel Hybrid PhotoDiodes (HPDs) for PET applications. However, due to the small light yield, the detection efficiency for 511 keV photons could be too low. To overcome this limitation, we have recently proposed to shape the surface of each finger crystal like an "half-pipe" to achieve a better scintillator-WLS fiber coupling. In this paper, we present the results of the light yield experimental measurements on a test 5 x 5 "half-pipe" YAP:Ce crystal matrix and a comparison with square fibers-standard matrix configuration. In view of future availability of large-area HPD, we have also assembled a small detector head using a test 4 x 4 YAP:Ce crystal matrix directly coupled to a 61-pixel HPD. Experimental measurements on the imaging capabilities are also presented. (C) 2003 Elsevier Science B.V. All rights reserved.