Image quality and spectroscopic characteristics of different silicon pixel imaging systems

Imaging capabilities, spatial resolution and spectroscopic analysis have been performed to compare the characteristics of imaging systems based on pixel detectors of different thickness. Each system consists of a single photon counting chip (PCC), developed in the framework of the Medipix Collaboration, bump bonded to a silicon detector. The detector is a matrix of 64times64 square pixels, with 170 mum pitch and thickness ranging from 300 to 800 mum. As expected, the intrinsic detection efficiency increases with detector thickness (for 22 keV photons the detection efficiency doubles in the examined thickness range), nevertheless the spatial resolution can be affected by a charge sharing mechanism between adjacent pixels due to charge diffusion. We have studied this effect and its dependence on the detector bias voltage and the threshold value of PCC with the aim of optimizing both the detection efficiency and the spatial resolution