Comparison of energy resolution spectra of CdTe TIMEPIX detector working in photon counting and time-over-threshold mode

Hybrid pixel detectors like the Medipix and TIMEPIX developed by the Medipix collaboration combined with high-z materials are of growing interest. In particular the TIMEPIX detector can be operated in photon counting mode and time-over-threshold mode (ToT) to obtain spectral information. Previous studies showed that 110 μm pixel sizes obtain a better energy resolution than 55 μm pixel sizes. Furthermore, threshold scans obtained a better spectral resolution than operation in ToT mode. In this work the influence of noise sources in different measurement approaches on the spectral response of a TIMEPIX chip bump-bonded to CdTe sensor are presented. Two 1mm thick CdTe sensors with pixel sizes of 55 μm and 110 μm, bump-bonded to a TIMEPIX readout chip, were evaluated at the Diamond Light Source synchrotron. A finely collimated, perpendicular pencil beam with x-ray energies of 25 keV and 79 keV was used to investigate single pixels. A small area of 10×10 pixels was investigated in ToT-mode and compared to a threshold scan of the same pixels on both detectors. The measurements are compared to an analytical SPICE/Python simulation that emulates photon counting and time-over-threshold mode.