Performance of Bulk Semi-Insulating GaAs-Based Sensors with Different Pixel Sizes for Timepix Radiation Camera

Prototype bulk semi-insulating GaAs sensors were connected to the Timepix readout chip and their performance was examined. Overall, three sensors with pixel pitch of 55 μm, 165 $\mu m$ and 220 μm were tested. Firstly, open beam illumination responses were obtained on which typical patterns of detection efficiency inhomogeneities appear, however, the patterns are, to large extend, removable by post processing corrections. Secondly, sensors were able to retrieve images of biological and technical samples of high quality with spatial resolution of 8.7 lp/mm (55 μm pitch), 2.7 lp/mm (165 μm pitch) and 2.0 lp/mm (220 μm pitch). Also, 55 μm, 165 μm pitch sensors were able to perform spectrometric measurement. Energy resolution of 55 μm pitch sensor is 5 % at 59.5 keV and 10% at 160.6 keV in case of 165 μm pitch sensor.