Three-dimensional induced-charge modeling and waveform-based high-resolution spectroscopy of quasi-hemispherical CdZnTe detectors

摘要: Quasi-hemispherical cadmium zinc telluride (CdZnTe) detectors combine low-capacitance single-channel readout with room-temperature gamma-ray spectroscopy, but spatially nonuniform electric field, weighting potential, carrier transport, and trapping produce position-dependent spectral broadening. A three-dimensional induced-charge model was developed by coupling step-level Geant4 energy deposition, COMSOL electric and weighting fields, carrier drift and trapping, and the Shockley-Ramo theorem. The calculations show that the electric field and weighting-potential gradient are localized near the collecting anode, so most of the induced signal is generated during the final stage of electron transport. Different interaction positions consequently produce different signal-growth durations and rates, and electron lifetime has the strongest influence on simulated spectral broadening within the investigated parameter range. Motivated by this position-dependent signal formation, a waveform-based event-selection method was developed using measured pulse rise time and maximum rise-time slope. The two-dimensional parameter space was discretized, a local spectrum was fitted for each valid cell, and cells with superior energy resolution were retained. The measured energy resolution improved from 6.816% to 3.585% at 121 keV, from 1.686% to 0.963% at 662 keV, and from 1.274% to 0.853% at 1173 keV. Mixed-radionuclide measurements also showed improved peak separation while retaining an explicitly measurable energy-dependent fraction of full-energy-peak events. The method was implemented in a compact spectroscopy module. Because the simulation does not include the complete electronics transfer function, its connection to the measured waveforms is physical rather than a direct waveform prediction. The retained peak counts remain traceable, providing a basis for subsequent quantitative radionuclide analysis after detector-efficiency calibration and uncertainty evaluation.