Spectral response in a pixellated X-ray imaging CdTe detector with single photon processing readout

The image forming process in a CdTe detector is both a function of the X-ray interaction in the material, including scattering and fluorescence, and the charge transport in the material. The response of individual photons has been investigated using two pixellated CdTe image detectors with pixel pitches of 55 μm and 110 μm. The detectors were bonded to TIMEPIX readout chips and operated in time over threshold mode (ToT). We have illuminated the sensors with monoengertic photons generated by X-ray fluorescence in metal sheets and with gamma photons from ²⁴¹Am and ¹³⁷Cs. Results shows a large degradation in energy resolution caused by charge sharing and fluorescence. By summing pixels together we can correct for the charge sharing and some, but not all fluorescence.