Development and optimization of a method for position resolution in CdZnTe detectors
- Author
- Ocampo Giraldo, Luis
- Published
- [University Park, Pennsylvania] : Pennsylvania State University, 2018.
- Physical Description
- 1 electronic document
- Additional Creators
- Ünlü, Kenan
Access Online
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- Graduate Program
- Restrictions on Access
- Open Access.
- Summary
- Cadmium Zinc Telluride (CZT) is one of the most developed wide band gap semiconductor materials being used for making radiation detectors due to its high density and atomic number, excellent spectral resolution, physical stability and room-temperature operation. However, the availability of large-volume CZT detectors for many applications is limited due to the low production yield and high cost of CZT crystals. Crystal defects, which are present even in the highest quality CZT material available today, are the major problem causing response non-uniformity across the detector. To address this challenge, high-resolution position-sensitive (high granularity) detectors have been proposed to correct response non-uniformities by virtually or physically subdividing the detectors area into small voxels and equalizing the responses measured. There are several detector designs that practically implement this approach.This dissertation work focuses on the enhancement of position resolution for two types of CZT detectors, pixelated and virtual Frisch-grid (VFG) using time correlated digital signals. This is done through the development and testing of algorithms for processing digitized charge signals resulting in the creation of the time-correlated samples technique. This technique is evaluated using pixelated detectors and a focused laser beam developed to measure the position interactions of single charge and charge sharing events. This novel approach resulted in a position resolution of 200 m for an estimated equivalent gamma energy of 260 keV and < 50 m at an estimated gamma energy of 2 MeV with a contribution of the electronic noise (FWHM) of 4-5 keV. Further analysis regarding commercially available pixel sizes (0.8 mm to 2.85 mm) was conducted with the pulsed laser system and concluded that a smaller pixel size yields a higher position resolution.The design, fabrication, characterization and testing of the several VFG array prototypes is detailed along with various results that illustrate the optimization of position and energy resolution using time-correlated data. The first arrays were able to achieve an energy resolution of ~0.9% FWHM at 662 keV, using 137Cs, after corrections. These corrections are performed using a correction matrix, which was discovered to be independent of temperature. These results demonstrated the feasibility of position-sensitive VFG CZT detectors and arrays of such detectors for high resolution gamma-ray spectroscopic measurements. At the same time, the 3-D correction technique ensures high spectral resolution of the arrays in a wide dynamic range: <2% (4 keV) at 200 keV and <1% (6.6 keV) at 662 keV at <25C.To further study the optimization of position resolution for VFG detector arrays using time-correlated digital signals, a linear array of six position-sensitive VFG detectors optimized for usage in compact handheld instruments was investigated. This evaluation was carried out using real environment conditions and concluded with a field test to measure uranium hexafluoride cylinders. After applying corrections, the energy resolution was found to be 1.9% (3.5 keV) FWHM at 186 keV. At a higher energy, the resolution can be as good as 0.8% (5.3 keV) at 662 keV. Ultimately, these resolution improvements can significantly enhance the performance of compact handheld instruments compared to the current commercially available standard CZT detector devices.The optimization techniques discussed in this dissertation allow for using standard-grade materials to reduce the device cost without compromising their performance. This improvement of energy resolution significantly enhances the capabilities of the current CZT detectors. Furthermore, the implementation of the time-correlated samples technique coupled with 1-D and 3-D corrections to VFG arrays has the potential to create large detectors which can be deployed on the field under room temperature conditions. This is of particular benefit for safeguards purposes as well as national security among many others. The cost reduction of the devices will allow for the spread of this technology and further product development.
- Other Subject(s)
- Genre(s)
- Dissertation Note
- Ph.D. Pennsylvania State University 2018.
- Technical Details
- The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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