Evaluation of CsI(Tl)-PIN diode array tiling schemes

Methods of tiling scintillator-photodiode detector arrays were investigated. Si PIN photodiodes coupled to CsI(Tl) scintillation crystals are being considered for high-resolution (∼1 mm) gamma-ray imaging. Large area (∼200 cm²) detectors can be assembled by tiling together modular arrays. The goal of the tiling schemes was to maintain uniform pixel pitch and detector performance across the seam where the arrays join. The perimeter of the PIN array has an insensitive area that can be an appreciable fraction of a pixel size when using 1 mm pixels. One tiling scheme used smaller PIN pixels at the edge of the arrays to compensate for this insensitive area ("partial PIN" method). A second approach used a scintillator light-sharing technique to cover the insensitive area ("segmented crystal" method). The partial pixel method resulted in worse energy resolution and sensitivity in the partial pixels compared to the full pixels (20% and 30% FWHM at 140 keV for edge and corner pixels, respectively, versus 12% in full pixels, with relative corner pixel sensitivity of ∼50%), but successfully maintained spatial resolution and pixel pitch. The segmented crystal light-sharing method demonstrated 17%-20% FWHM energy resolution (at 140 keV) in the edge pixels, ∼85% relative sensitivity, and provided good pixel identification (i.e., good spatial resolution). However, the segmented crystal method is considerably more complex to implement, compared with the partial pixel method.