Full Record

New Search | Similar Records

Author
Title Coded Aperture Imaging Applied to Pixelated CdZnTe Detectors.
URL
Publication Date
Date Accessioned
Degree PhD
Discipline/Department Nuclear Engineering and Radiological Sciences
Degree Level doctoral
University/Publisher University of Michigan
Abstract In the past decade, there has been a significant increase in demand for radiation detectors to detect, identify, and locate potentially threatening nuclear materials. The Polaris system was developed to be used for such applications. This portable, room-temperature operated detector system is composed of 18 thick CdZnTe detectors, and has the ability to detect gamma rays of energies between 30 keV and 3 MeV with an energy resolution <1% FWHM at 662 keV. Detection is extended to source directionality using Compton imaging to map out gamma-ray distributions in 4-pi space. This modality is most effective at imaging gamma-ray energies greater than 300 keV. Due to the low Compton-interaction probability in CdZnTe at lower energies, an alternate imaging technique, coded aperture imaging (CAI), was implemented to extend gamma-ray imaging to the energy range where photoelectric absorption is most probable. The purpose of this work is to describe the evolution of the CAI modality as applied to the Polaris system. During the course of this study, for the first time, CAI is applied to thick 3D position sensitive CdZnTe detectors to image lower-energy gamma rays. With the knowledge of 3D positions of gamma interactions, masks are applied to five of the six sides of a single CdZnTe crystal, extending the field-of-view (FOV) to near 4-pi through simulation and measurement. Material properties such as “pixel jumping” that are caused by non-uniform electric fields within the detector that result in degradation of image quality are also studied. Next, a single mask is applied to a 3 x 3 array of detectors showing improved image quality when combining images from multiple detectors. Finally, CAI is combined with Compton imaging and applied to the 18-detector Polaris system allowing for the extension of gamma-ray imaging capabilities across the entire dynamic range of the electronic readout system. This work was funded by the US Department of Homeland Security Domestic Nuclear Detection Office and National Science Foundation Academic Research Initiative.
Subjects/Keywords Radiation Detectors; CdZnTe; Polaris Array; Gamma Ray Imaging; Coded Aperture Imaging; Nuclear Engineering and Radiological Sciences; Engineering
Contributors He, Zhong (committee member); Fessler, Jeffrey A. (committee member); Kearfott, Kimberlee J. (committee member); Pozzi, Sara A. (committee member)
Language en
Rights Unrestricted
Country of Publication us
Record ID handle:2027.42/108755
Repository umich
Date Retrieved
Date Indexed 2020-09-09
Grantor University of Michigan, Horace H. Rackham School of Graduate Studies
Issued Date 2014-01-01 00:00:00
Note [thesisdegreename] PHD; [thesisdegreediscipline] Nuclear Engineering and Radiological Sciences; [thesisdegreegrantor] University of Michigan, Horace H. Rackham School of Graduate Studies; [bitstreamurl] http://deepblue.lib.umich.edu/bitstream/2027.42/108755/1/sonalj_1.pdf;

Sample Search Hits | Sample Images | Cited Works

…Images Improvement Due to Moving Sources Conclusions References 79 79 88 93 94 Chapter 8 – Current Polaris Array System Geometry Imaging Algorithm Image Characteristics Combined Coded Aperture – Compton Imaging Future Work References 95 95 96 96 98 100…

…resolution of a radiation detection system. 3 Figure 1.2: A comparison of the energy spectra for NaI(Tl), CdZnTe, and HPGe detector types. 4 Figure 2.1: Current 18-detector Polaris detector system with aluminum enclosure removed, consisting of…

…pixels are most likely due to background. 76 Figure 6.22: Counts versus beam position across all depths of the detector. Each color represents a different detector pixel. 77 Figure 7.1: The first Polaris system assembled in Fall 2010. Two planes of 3…

…3 arrays of CdZnTe detectors located between two random masks, cathode sides facing outwards. 80 Figure 7.2: Images tracking a Co-57 (122 keV) source at various positions in the field of view using all nine detectors of a Polaris plane…

…irradiation. 82 Figure 7.5: The combination of three Bad images (top) resulting in a Good image (bottom). 83 Figure 7.6: Improved CAI formed by combing images from all nine detectors from a single Polaris plane. 84 Figure 7.7: Co-57…

…source directions increases. All measurements were taken at a constant y coordinate. 93 Figure 8.1: Polaris II system with two 32 32 random masks applied to each 3 3 array of detectors. 95 Figure 8.2: Comparison of CAI of Co-57 (122 keV)…

…point source using Polaris I (top) vs. Polaris II (bottom). The decreased masked distance improved the CAI FOV, while worsening angular resolution. 97 Figure 8.3: Image of low-energy (Co-57) source over high-energy source…

…potentially threatening nuclear materials. The Polaris system was developed to be used for such applications. This portable, roomtemperature operated detector system is composed of 18 thick CdZnTe detectors, and has the ability to detect gamma rays of energies…

.