3D position sensitive CdZnTe gamma-ray spectrometers – improved performance with new ASICs

A 3-dimensional position sensitive CdZnTe gamma-ray spectrometer based on VAS3.1/TAT3 ASICs was developed and tested. The 3-D CZT spectrometer employs a 1.5 × 1.5 × 1 cm CdZnTe crystal with 11 by 11 pixelated anodes wire-bonded to the readout electronics. The signals from the anode pixels and the cathode were both read out through the ASICs. The pixel position provides the lateral 2-D coordinates, while the third coordinate can be determined by using depth-sensing techniques. With the help of 3-D position sensitivity, the variation in weighting potential, electron trapping and material non-uniformity can be mitigated to the scale of the position resolution, estimated to be 1.27 mm × 1.27 mm × 0.2 mm. The energies and 3-D coordinates can be reconstructed for multiple interaction events from a single incident gamma ray. The third-generation ASICs – VAS3.1/TAT3 has been developed to improve the electronic noise, uniformity, linearity and stability. Energy resolution of 0.93% FWHM and 1.52% FWHM have been achieved for single-pixel events and two-pixel events, respectively, including ~4.5 keV FWHM electronic noise.