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dc.contributor.advisorShupe, Michael A.en_US
dc.contributor.authorHilton, Nathan Rhead
dc.creatorHilton, Nathan Rheaden_US
dc.date.accessioned2013-04-11T08:52:04Z
dc.date.available2013-04-11T08:52:04Z
dc.date.issued2002en_US
dc.identifier.urihttp://hdl.handle.net/10150/280187
dc.description.abstractThe material uniformity of cadmium zinc telluride (CZT) crystals in gamma-ray imaging detectors is examined using several existing techniques and a new technique called thermally stimulated current (TSC) imaging that has been developed for this dissertation. The TSC imaging model, simulations, and experimental demonstrations are presented here for the first time. CZT radiation detectors are used in nuclear medicine as well as other medical, industrial, national security, and scientific applications; however, the scarcity and cost of high-quality CZT materials have hindered the use of CZT in these applications. Understanding CZT's material properties and their effects on detector performance should be helpful in developing crystal growth methods that have improved yield of useful detector material. Data obtained from CZT samples using infrared transmission, electron microprobe, X-ray diffraction, and electron backscatter diffraction (EBSD) mapping methods are used to understand their crystal structure. Data obtained from these samples using both TSC imaging and conventional leakage current measurements while these samples were operated as pixelated detector arrays are used to understand their charge transport properties. Collimated gamma-ray mapping was used to understand the detector performance properties of these samples. Correlations among these spatially mapped data are investigated. Contrary to the suggestions of other researchers, it is found that leakage current is not inversely correlated with detector performance. Detector performance in these samples is well correlated with their crystal structure. High-angle grain boundaries are shown to trap charge carriers, and estimates of the locations of these boundaries are derived from the gamma-ray mapping data. EBSD distinguishes itself from X-ray diffraction methods in identifying the locations and types of grain boundaries intersecting the sample surface. Using the new TSC imaging method, evidence is obtained showing a higher density of a particular trap near incommensurate boundaries in a CZT sample. Other researchers have indicated that an electron trap associated with dislocations is present in CZT. Their observation is consistent with a conclusion drawn from these TSC imaging data that due to higher densities of dislocations near incommensurate grain boundaries these boundaries host electron traps while {111} twin boundaries do not.
dc.language.isoen_USen_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.subjectEngineering, Materials Science.en_US
dc.subjectPhysics, Radiation.en_US
dc.subjectEngineering, Materials Science.en_US
dc.titleMaterial uniformity of cadmium zinc telluride in gamma-ray imaging detectorsen_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
thesis.degree.grantorUniversity of Arizonaen_US
thesis.degree.leveldoctoralen_US
dc.identifier.proquest3073233en_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplinePhysicsen_US
thesis.degree.namePh.D.en_US
dc.identifier.bibrecord.b43471973en_US
refterms.dateFOA2018-05-28T16:48:50Z
html.description.abstractThe material uniformity of cadmium zinc telluride (CZT) crystals in gamma-ray imaging detectors is examined using several existing techniques and a new technique called thermally stimulated current (TSC) imaging that has been developed for this dissertation. The TSC imaging model, simulations, and experimental demonstrations are presented here for the first time. CZT radiation detectors are used in nuclear medicine as well as other medical, industrial, national security, and scientific applications; however, the scarcity and cost of high-quality CZT materials have hindered the use of CZT in these applications. Understanding CZT's material properties and their effects on detector performance should be helpful in developing crystal growth methods that have improved yield of useful detector material. Data obtained from CZT samples using infrared transmission, electron microprobe, X-ray diffraction, and electron backscatter diffraction (EBSD) mapping methods are used to understand their crystal structure. Data obtained from these samples using both TSC imaging and conventional leakage current measurements while these samples were operated as pixelated detector arrays are used to understand their charge transport properties. Collimated gamma-ray mapping was used to understand the detector performance properties of these samples. Correlations among these spatially mapped data are investigated. Contrary to the suggestions of other researchers, it is found that leakage current is not inversely correlated with detector performance. Detector performance in these samples is well correlated with their crystal structure. High-angle grain boundaries are shown to trap charge carriers, and estimates of the locations of these boundaries are derived from the gamma-ray mapping data. EBSD distinguishes itself from X-ray diffraction methods in identifying the locations and types of grain boundaries intersecting the sample surface. Using the new TSC imaging method, evidence is obtained showing a higher density of a particular trap near incommensurate boundaries in a CZT sample. Other researchers have indicated that an electron trap associated with dislocations is present in CZT. Their observation is consistent with a conclusion drawn from these TSC imaging data that due to higher densities of dislocations near incommensurate grain boundaries these boundaries host electron traps while {111} twin boundaries do not.


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