Imaging and spectroscopic performance studies of pixellated CdTe Timepix detector

In this work the results on imaging and spectroscopic performances of 14 x 14 x 1 mm CdTe detectors with 55 x 55 mu m and 110 x 110 mu m pixel pitch bump-bonded to a Timepix chip are presented. The performance of the 110 x 110 mu m pixel detector was evaluated at the extreme conditions beam line I15 of the Diamond Light Source. The energy of X-rays was set between 25 and 77 keV. The beam was collimated through the edge slits to 20 mu m FWHM incident in the middle of the pixel. The detector was operated in the time-over-threshold mode, allowing direct energy measurement. Energy in the neighbouring pixels was summed for spectra reconstruction. Energy resolution at 77 keV was found to be Delta E/E = 3.9%. Comparative imaging and energy resolution studies were carried out between two pixel size detectors with a fluorescence target X-ray tube and radioactive sources. The 110 x 110 mu m pixel detector exhibited systematically better energy resolution in comparison to 55 x 55 mu m. An imaging performance of 55 x 55 mu m pixellated CdTe detector was assessed using the Modulation Transfer Function (MTF) technique and compared to the larger pixel. A considerable degradation in MTF was observed for bias voltages below -300V. Significant room for improvement of the detector performance was identified both for imaging and spectroscopy and is discussed.