Gamma-ray spectroscopy using depth-sensing coplanar grid cadmium zinc tellurium semiconductor detectors.

Abstract

This dissertation details the analysis and characterization of coplanar grid CdZnTe detectors used for gamma-ray detection and spectroscopy. These detectors employ two anode signals to achieve spectra with good energy resolution at room temperature. Factors such as the coplanar grid design, electron trapping compensation, electronic noise, and the material properties have been found to affect the performance of these detectors. These effects have been studied in this work with simulations and experiments to result in detectors with improved spectroscopic performance. Using depth sensing and the relative gain method, a new coplanar grid design was experimentally shown to perform better than previous designs. 2.25 cm<super>3</super> CdZnTe crystals utilizing the new grid design achieved energy resolution as good as 1.65% FWHM at 662 keV. A detector with a volume of 10.8cm<super>3</super> was tested, employing the novel multi-pair coplanar grid design. Preliminary results from this new detector have been recorded and a design proof-of-concept was shown. A temperature-effects study conducted on two coplanar grid detectors indicate that CdZnTe is best operated at temperatures above 0&deg;C. Modeling of the coplanar grid detector was conducted using simulation tools such as Maxwell and Geant4. Using such modeling tools, important factors that can affect the performance of coplanar grid detectors were studied, such as the surface characteristics of CdZnTe. In addition, the major sources of peak broadening were quantified, and the excellence of the coplanar grid design was verified from its negligible contribution to the overall photopeak broadening.