Research On The Key Techniques Of CdZnTe Detector

CdZnTe detector is a very promising room temperature semiconductor detector and has attracted much interest.In the past two decades,the performances of CdZnTe detectors have been significant improved.Nowadays CdZnTe detectors are applied in portable spectrometers,imaging module and Compton camera.Among the world,the detectors of typical electrode structures using single polarity charge sensing technique achieve resolution below 2.0%@662keV.After the depth correction the energy resolution is close to 1.0%.While the energy resolution of domestic CdZnTe detectors are worse than 2.5%.Most of the single polarity charge sensing electrodes(such as coplanar,hemispherical)are protected by patents,which limit the commercial application in China.To date,there are rare publication about the new design of unipolar electrodes and the research of depth sensing and correction in China.This research has two goals.The first goal is to design a new electrode structure with simple electronic readout and able to achieve relatively high resolution.The second goal is to develop a Three-Dimensional position sensitive CdZnTe(3D CZT)detector and study the depth sensing and correction experimentally.In this dissertation,theory and experiment are combined to investigate the single polarity charge sensing,depth sensing and correction techniques deeply.A CdZnTe detector physics model was established.Induced Current Calculator(ICC)package was develop to simulate the induced signal of the detector and the output signal of the electronic systems.Based on Geant4,Ansoft Maxwell and ICC,a CdZnTe detector simulation platform was developed.Electrode structure designs and electronic readout methods were studied using this platform.In the research of new electrode structure,Strengthened Electric Field(SEF)technique was proposed to modulate the electric field inside the line anode detector.By implementing this technique,the electric field is more uniform and is strengthened in most of the volume,thus improving the charge collection efficiency.Based on SEF technique,two simple electrode structures which only require single-channel readout were design and optimized.A SEF line anode(SEFLA)prototype and an SEF point anode(SEFPA)prototype were fabricated and achieved energy resolution of 1.5% and 1.6% @662 keV,respectively.The depth correction study of SEFLA detector demonstrated the detector has the ability to achieve energy resolution of 1.2%.A 3D CZT detector was developed to investigate the influence of pixel structure and readout methods.The Investigation of the spectral distortion in pixel CdZnTe detector indicated that the reason for high counts in low energy region is charge sharing.Another remarkable conclusion was that charge sharing has a significant contribution to the low energy tail of full energy peak,which changes the view that low energy tail was mainly caused by carriers trapping.Two depth sensing techniques were investigated experimentally,and 3D interaction position and the energy spectrum were reconstructed.Experiment demonstrated that the pixel electrode structure with guard ring and small gap can overcome charge sharing and edge effect effectively.We explored the feasibility of our system in Compton imaging.The performance of the imaging was studied by theoretical simulation and experimentally.The angle resolution reconstructed with Simple Back Projection algorithm is 36 degree.This study lays the foundation for the development of Compton imaging system in the future.