Interaction depth in CdTe/CdZnTe spectrometers by electron drift time

This paper introduces a method to determine the interaction depth in 3-D position sensitive gamma-ray spectrometers through the measurement of the electron drift time. In this method, the electron drift time is measured as the time interval between the leading edges of the signals from the cathode and the anode pixel. As an implementation, a self-triggered VA-TA DAQ system with 128 independent timing channels has been developed to read out the timing when the signal leading edges cross a pre-selected threshold. Each timing channel has a dynamic range of 14 us and a timing resolution of ~60 ns. This VA-TA DAQ system is applied to a 2×2×1.5 cm^-3 CdTe detector with an pixellated anode array. For signals from a particular pixel, the distribution of the measured electron drift time matched the expected distribution. The energy spectra from different interaction depths are separated by the measured electron drift time. For multiple interaction events involving multiple pixels, the reconstruction of the interaction depths based upon the electron drift times is being investigated. The results will be presented