Evaluation of LAAPD arrays for high-resolution scintillator matrices readout.

In this paper, we evaluate the performance of recently released avalanche photodiode arrays from Advanced Photonix, Inc. (API) for scintillator matrices readout. The Large Area Avalanche Photodiode (LAAPD) quadrant device is a monolithic 2x2 pixels structure with an active area of 5.3 mm² per pixel. The device allows stable operation with high gains up to 200, and detection efficiency of 73+-10 % for 420 nm photons. It is furthermore characterized by a high linear fill factor of 90 % and low noise equal to16 electrons ENC measured at room temperature. We have measured pixel-to-pixel gain non-uniformity smaller than 1.5 % and inter-pixel crosstalk of 1.7 % in the pulse mode operation with the device gain of 50. The energy resolution of 12.3+-0.5 % was achieved for the 511 keV photopeak from a ²²Na source placed on top of a 2x2x10 mm³ LSO crystal coupled to one pixel of quadrant LAAPD. An array of LSO crystals was later coupled to the device allowing individual crystal identification. Coincidence timing resolution of 1.9+-0.1 ns FWHM has been obtained for quadrant pixel with LSO scintillator for the 511 keV peak from ²²Na source. Finally, we compared the characteristics and readout performance of LAAPD array with published results of some commerciallly available APD arrays.