X-ray absorption and charge transport in a pixellated CdTe detector with single photon processing readout

Abstract

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 [2–4]. The response to individual photons has been investigated using a CdTe detector with a pixel size of 110μm, bonded to a TIMEPIX [5] readout chip operating in time over threshold mode. The device has been illuminated with mono-energetic photons generated by fluorescence in different metals and by gamma emission from 241Am and 137Cs. Each interaction will result in charge distributed in a cluster of pixels where the total charge in the cluster should sum up to the initial photon energy. By looking at the individual clusters the response from shared photons as well as fluorescence photons can be identified and separated. By using energies below and above the K-edges of Cd and Te the contribution from fluorescence can be further isolated. The response is analyzed to investigate the effects of both charge diffusion and fluorescence on the spectral response in the detector.