A modeling method to calibrate the interaction depth in 3-D position sensitive CdZnTe gamma-ray spectrometers

Abstract

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.

Study of a high-resolution, 3D positioning cadmium zinc telluride detector for PET

“…Thirdly, the anode and cathode signal amplitudes and/or charge drift time allow one to estimate the individual (multiple) 3-D interaction coordinates of incoming photons in a CZT detector (Kalemci et al 1999, Li et al 2000, Hong et al 2003). This allows for accurate placement of lines of response required for PET imaging (Pratx and Levin 2009).…”

3D particle track reconstruction in a single layer cadmium-telluride hybrid active pixel detector

“…The ratio of the anode and cathode signal depends on the average depth of interaction [11]. It can be determined after measuring the total induced charge at the anode Q a (Q c = Q) and at the cathode Q c and comparing the Q c /Q a ratio to a simulation-generated lookup- would be almost constant within most of the sensor volume and the determination of z meas would not work properly.…”

Analysis of detector response using 3-D position sensitive CZT gamma-ray spectrometers

“…2, for normal channels, the photopeak centroid decreases smoothly from the anode to the cathode due to uniform electron trapping. There are more counts on the cathode side as discussed in [4]. The FWHM from all depths remain nearly unchanged despite some statistical fluctuation.…”

“…Case D is a pixel with an electron trapping defect smaller than the pixel size at depth d 0 . In case A, because of the bulk electron trapping, the C/A ratio will have a certain systematic error over most of the interaction depth as discussed in [4]. However, the relation between the C/A ratio and the true depth should be linear over most of the interaction depth.…”