A CMOS application specific integrated circuit (ASIC) was developed for 3D Position Sensitive
Detectors (PSD). The preamplifiers were optimized for pixellated Cadmium-Zinc-Telluride (CZT)
Mercuric-Iodide (HgI2) and Thallium Bromide (TlBr) sensors. The ASIC responds to an ionizing
event in the sensor by measuring both amplitude and timing in the pertinent anode and cathode
channels. Each channel is sensitive to events and transients of positive or negative polarity and performs
low-noise charge amplification, high-order shaping, peak and timing detection along with analog
storage and multiplexing. Three methodologies are implemented to perform timing measurement
in the cathode channel. Multiple sparse modes are available for the readout of channel data. The ASIC
integrates 130 channels in an area of 12 x 9 mm2 and dissipates ~330 mW. With a CZT detector
connected and biased, an electronic resolution of ~200 e- rms for charges up to 100 fC was measured.
Spectral data from the University of Michigan revealed a cumulative single-pixel resolution of ~0.55
% FWHM at 662 KeV.
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 cm x 1.5 cm x 1 cm3 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 x 1.27 mm x 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.
A 3D CdZnTe detector can provide 3D position information as well as energy information of each individual interaction when a gamma ray is scattered or absorbed in the detector. This unique feature provides the 3D CdZnTe detector the capability to do Compton imaging with a single detector. After detector calibration, real-time data acquisition and imaging are implemented with a single detector system. Because the detector has a finite size and any point in the detector can be the first scattering position, 3D gamma-ray imaging in near field is possible. In this work we will show the result of the 4π Compton imaging with a single 15mm × 15mm × 10mm CdZnTe detector. Different algorithms for sequence and imaging reconstruction will be addressed and compared. The angular uncertainty is estimated and the most recent results from measurements are presented.