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Acquisition and Detection Geometry of the CT X-ray Imaging Process
Rusz, Jakub ; Harabiš, Vratislav (referee) ; Drastich, Aleš (advisor)
The basic components of acquisition and detection geometry of a 3rd generation single slice CT scanner are described here. Then the high contrast spatial resolution of the imaging process is explained and what effects does the setting of acquisition and detection geometry changes in the limiting high contrast spatial resolution. At the end a laboratory exercise and a simulator is presented, which will show and explain these effects.
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Simulation of the CT X-ray Detectors
Koutek, Petr ; Walek, Petr (referee) ; Drastich, Aleš (advisor)
The bachelor thesis deals with the basic properties of the detectors used in X-ray CT, and their influence on the choice of acquisition parameters. The theoretical part summarizes the general issues of projection reconstruction view and basic characteristics of the detectors. In the practical part is created simulator which simulate the effect of deacy time, afterglow and the light output.
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Study of chemical cleaning of surfaces by LEIS method
Staněk, Jan ; Polčák, Josef (referee) ; Bábor, Petr (advisor)
This thesis deal with studying chemical etched surfaces of cadmium telluride crystals (CdTe crystals) by low-energy ion scattering spectroscopy (LEIS method). In the theoretical part, there is description of physical essence of LEIS method, including experimental arrangement of Qtac100 instrument, on which the experiment is measured. The LEIS method is also compared with X-ray photoelectron spectroscopy (XPS). There is summary of properties and structure of CdTe crystals including principle of X-ray detectors, which are the primary use of the crystals. In experimental part there is a description of measuring process, starting with a calibration measurement, ongoing with a chemical etching and ending with a surface analysis. There are examples of LEIS spectra with comments and interpretation including comparison with XPS data.
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Influence of external fields on electric field and photocurrent in CdTe detectors
Rejhon, Martin ; Franc, Jan (advisor)
This thesis is focused on a study of CdTe and CdZnTe semiconductor detectors working under high flux of radiation. We studied experimentally an influence of high flux of X-rays and optical radiation on polarization of the detector. The polarization phenomenon decreases the efficiency of the detector due to a screening of an applied electric field by a space charge accumulated at deep levels due to a trapping of photogenerated carriers. In order to measure the electric field profiles in the detectors we employed a method based on cross polarizers technique and Pockels effect. The main objective of this work was to study the possibilities of an optical de-polarization of CdTe and CdZnTe detectors for different photon energies of additional light, its dynamics and physical origin. We have found that detectors can be de-polarized by above bandgap light. Moreover, CdZnTe detector can be depolarized by near infrared light and in a pulse mode. The de- polarization is associated with a compensation of the space charge at deep traps.
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Influence of external fields on electric field and photocurrent in CdTe detectors
Rejhon, Martin ; Franc, Jan (advisor) ; Oswald, Jiří (referee)
This thesis is focused on a study of CdTe and CdZnTe semiconductor detectors working under high flux of radiation. We studied experimentally an influence of high flux of X-rays and optical radiation on polarization of the detector. The polarization phenomenon decreases the efficiency of the detector due to a screening of an applied electric field by a space charge accumulated at deep levels due to a trapping of photogenerated carriers. In order to measure the electric field profiles in the detectors we employed a method based on cross polarizers technique and Pockels effect. The main objective of this work was to study the possibilities of an optical de-polarization of CdTe and CdZnTe detectors for different photon energies of additional light, its dynamics and physical origin. We have found that detectors can be de-polarized by above bandgap light. Moreover, CdZnTe detector can be depolarized by near infrared light and in a pulse mode. The de- polarization is associated with a compensation of the space charge at deep traps.
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Study of chemical cleaning of surfaces by LEIS method
Staněk, Jan ; Polčák, Josef (referee) ; Bábor, Petr (advisor)
This thesis deal with studying chemical etched surfaces of cadmium telluride crystals (CdTe crystals) by low-energy ion scattering spectroscopy (LEIS method). In the theoretical part, there is description of physical essence of LEIS method, including experimental arrangement of Qtac100 instrument, on which the experiment is measured. The LEIS method is also compared with X-ray photoelectron spectroscopy (XPS). There is summary of properties and structure of CdTe crystals including principle of X-ray detectors, which are the primary use of the crystals. In experimental part there is a description of measuring process, starting with a calibration measurement, ongoing with a chemical etching and ending with a surface analysis. There are examples of LEIS spectra with comments and interpretation including comparison with XPS data.
|
|
|
Influence of external fields on electric field and photocurrent in CdTe detectors
Rejhon, Martin ; Franc, Jan (advisor)
This thesis is focused on a study of CdTe and CdZnTe semiconductor detectors working under high flux of radiation. We studied experimentally an influence of high flux of X-rays and optical radiation on polarization of the detector. The polarization phenomenon decreases the efficiency of the detector due to a screening of an applied electric field by a space charge accumulated at deep levels due to a trapping of photogenerated carriers. In order to measure the electric field profiles in the detectors we employed a method based on cross polarizers technique and Pockels effect. The main objective of this work was to study the possibilities of an optical de-polarization of CdTe and CdZnTe detectors for different photon energies of additional light, its dynamics and physical origin. We have found that detectors can be de-polarized by above bandgap light. Moreover, CdZnTe detector can be depolarized by near infrared light and in a pulse mode. The de- polarization is associated with a compensation of the space charge at deep traps.
|
|
|
Simulation of the CT X-ray Detectors
Koutek, Petr ; Walek, Petr (referee) ; Drastich, Aleš (advisor)
The bachelor thesis deals with the basic properties of the detectors used in X-ray CT, and their influence on the choice of acquisition parameters. The theoretical part summarizes the general issues of projection reconstruction view and basic characteristics of the detectors. In the practical part is created simulator which simulate the effect of deacy time, afterglow and the light output.
|
|
|
Acquisition and Detection Geometry of the CT X-ray Imaging Process
Rusz, Jakub ; Harabiš, Vratislav (referee) ; Drastich, Aleš (advisor)
The basic components of acquisition and detection geometry of a 3rd generation single slice CT scanner are described here. Then the high contrast spatial resolution of the imaging process is explained and what effects does the setting of acquisition and detection geometry changes in the limiting high contrast spatial resolution. At the end a laboratory exercise and a simulator is presented, which will show and explain these effects.
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