Energy resolution limiting factors of multi-pixel events in 3D position sensitive CZT gamma-ray spectrometer

The energy resolution limiting factors of a prototype 3D position-sensitive CZT gamma-ray spectrometer are investigated with both single and multi-pixel events from 662 keV gamma rays. The spectrometer was developed using a 10x10x10 mm³ CZT detector with 8×8 pixellated anode and a RENA-3 readout system from NOVA R&D. The RENA-3 system has energy and timing readout channels for the cathode and each individual pixel that enable the reconstruction of the energy depositions and interaction locations for both single and multi-interaction events in the detector by either C/A ratio or electron drift time. So 3D correction of detector response non-uniformity can be applied to all interaction events to optimize the overall energy resolution of the detector. For single interaction events in the detector, the energy resolution at 662 keV after 3D correction is ∼1% FWHM, which is mainly limited by the electronic noise of the readout system. For multi-pixel events from either multi-interaction or charge sharing in the detector, weighting potential crosstalk among multiple collecting pixels and electronic crosstalk between different ASIC channels turn out to have a big impact on energy resolution. Investigation shows that the weighting potential and electronic crosstalk could account for ≫2% FWHM energy resolution degradation at 662 keV for adjacent-pixel events. These effects are verified with 3D weighting potential modeling and electronic crosstalk measurement using test pulses. It is also demonstrated that the energy resolution of adjacent-pixel events can be improved to 1.8∼1.9% FWHM at 662 keV with proper calibration and correction.