A Modeling Method to Calibrate the Interaction Depth in 3-D Position Sensitive CdZnTe Gamma-Ray Spectrometers

The gamma ray interaction depth in 3-D position scnsitive CdZnTe dctectors is currently determined by the pulse height ratio ofthe cathode signal to the anode pixel signal (CIA ratio). In expcriments with our 3-D CdZnTe dctectors, thc photopeak area as a fuuction of the CIA ratio deviates from the expected exponential attcnuation with depth. This indicatcs that the CIA ratio is not proportional to thc true interaction depth. This paper proposes a method to calibrate the measured CIA ratio to thc intcraction depth by modeling the,signals from thc cathode and anode pixels. Knowing the detector’s mobility-lifctime products of thc electrons and holes from measurements, the expccted pulsc heights of the signals from thc cathode and anode pixels can bc calculated for differcnt intcraction depths. The rclationship belwcen thc CIA ralios and the interaction depths can then bc determined and used as thc calibration. Thc calculation for our 3-D CdZnTe detectors shows that an 8% crror in depth detcrmination is incurred without the calibration.