U . K . Imaging and spectroscopic performance studies of pixellated CdTe Timepix detector

In this work the results on imaging and spectroscopic performances of 14×14×1 mm CdTe detectors with 55×55 μm and 110×110 μm pixel pitch bump-bonded to a Timepix chip are presented. The performance of the 110× 110 μm 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 μm 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 ∆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 110×110 μm pixel detector exhibited systematically better energy resolution in comparison to 55×55 μm. An imaging performance of 55× 55 μm 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 −300 V. Significant room for improvement of the detector performance was identified both for imaging and spectroscopy and is discussed.