Made available in DSpace on 2014-06-12T23:16:21Z (GMT). No. of bitstreams: 2 arquivo8663_1.pdf: 849697 bytes, checksum: e6471c5d7a6bcfb231ee39df5b803ace (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Um conhecimento detalhado do espectro de raios-X é essencial para a análise de equipamentos que emitem este tipo de radiação em unidades de radiodiagnóstico. As informações sobre vários parâmetros contidas neste espectro são importantes para o controle de qualidade dos aparelhos de raios-X. A espectrometria dos feixes de raios-X tem utilizado detectores de GeHP que apresentam boa eficiência de detecção e alta resolução. Contudo, eles necessitam de resfriamento com Nitrogênio líquido, o que dificulta a sua mobilidade e os torna dispendiosos em várias aplicações. Neste estudo foram utilizados detectores de Cd0,9Zn0,1Te (CZT) e Si-PIN refrigerados termoeletricamente para a construção de um sistema de espectrometria. A resposta dos detectores para fótons monoenergéticos foi investigada com raios-X e g emitidos por fontes calibradas de Am241, Ba133, Cd109 e Co57. Também foram obtidos espectros de raios-X contínuos a partir de irradiações com um gerador de raios-X industrial para tensões de aceleração na faixa de 40 kV a 120 kV, com e sem uso de filtros. A distorção nos espectros devida à transmissão de raios-X primários e ao escape de raios-X secundários vindos do cristal foi corrigida pela eficiência de detecção por meio do código Monte Carlo GEANT4. Os espectros de raios-X corrigidos apresentaram uma boa concordância com os espectros do catálogo de referência. Os resultados indicaram que os detectores de CZT e Si-PIN possuem desempenho compatível com os detectores de GeHP e portanto, são adequados para espectrometria de raios-X diagnóstico e fluorescência de raios- X, respectivamente, considerando-se que a correção apropriada seja aplicada

Abstract To realize faster and more precise treatment of patients, CT technology has an urgent demand to make the CT detector arrays larger, and to cover a larger section of the body during one scan of X-ray imaging. A novel detector micro-module is developed in this thesis to meet this demand. In the novel detector micro-module, photocurrent signals are read out from the bottom side of the photodiode array chip. By avoiding the use of the top surface of the chip for routeing, as is the case in conventional CT modules, rectangular detector building blocks containing a certain number of detector elements can be produced. By tiling such building blocks in both x- and y-directions in a plane, detector arrays with any number of detector elements (in multiples of the number in a single building block) can be built. This cannot be achievable by the conventional method. The novel detector micro-module developed in this thesis consists of an array of 16×16 active elements, and the size of the array is 21×21mm2. The array of detector elements is soldered to a multilayer LTCC (low temperature co-fired ceramics) substrate via a BGA (ball grid array) with each element soldered onto one solder sphere, from which photocurrent signals are read out. In this thesis, the working principle and the evolution of CT detector modules are reviewed and the necessity of developing the novel detector modules is justified. The concept and the structure of the novel detector micro-module are presented. The thermo-mechanical stress modeling and simulation of the structure is performed. The design and the process technology of the photodiode array for the novel detector micro-modules are discussed. The electronic characteristics of the novel detector micro-modules and the related front-end electronics are theoretically analyzed. The LTCC multi-layer substrate is developed. The assembly process of the novel detector micro-module is developed. The basic detector characteristics and light response measurement results of the novel micro-module are presented and discussed. By improving the photodiode silicon process technology, a dark current density as low as 33pA/cm2 is achieved. Excellent mechanical accuracy is achieved with the LTCC substrate. The dimensional tolerance is +/-10μm and the flatness value is less than 50μm over a distance of a 30.5mm distance. A 64-slice detector module is produced successfully by tiling several novel micro-modules. The novel detector micro-modules are superior to conventional CT modules on many respects while being tileable. Their light sensitivity curve is smoother. They exhibit extremely low signal cross-talk; They have nearly zero wiring capacitance compared to up to 20pF in commercial CT detector modules. They also have almost zero wiring resistance compared to tens of ohm or more than one hundred ohms in the present products. This result will have a significant impact on CT technology and the CT industry because the detector will be no longer the limiting factor in CT system performance.

As of writing this thesis there are two detectors at TRIUMF’s DRAGON facility which directly measure the kinetic energy (E) of heavy ions at the focal plane of its recoil separator. These are an ionization chamber and a double-sided-silicon-strip detector (DSSSD). The ionization chamber has in- ferior resolution to the DSSSD but can discriminate isobaric contaminants in a E-∆E spectrum. A DSSSD has superior energy resolution and timing but cannot discriminate isobaric contaminants in many cases. A hybrid ioniza- tion chamber / double-sided-silicon-strip detector has been designed using the GEANT4 simulation package that combines the strengths of both these detec- tor types. This hybrid detector design consists of an ionization chamber set in front of a DSSSD positioned at the end of the beamline of the recoil separator. The design presented here is specific to DRAGON’s needs but can conceiv- ably be re-purposed in other environments requiring heavy ion detection and identification and may be useful in fields such as health physics. / Thesis / Master of Science (MSc)

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No description available.

Recently, plenty of large/public buildings have been completed in Taiwan. For bright indoor environment and comfortable feelings, these buildings often utilized lots of large spaces such as atria. However, it is difficult to maintain tenable conditions within atria and large spaces in case of fire. Therefore, the alert of smoke detectors and the efficiency of smoke control systems are both very important when a fire occurred and people needed to evacuate. In large space buildings, the smoke exhaust fan and smoke storage are major design concepts of the passive smoke management systems in order to maintain tenable conditions in means of egress. In this research, the operation strategies of passive smoke management and fire detection systems in large space buildings will be systematically analyzed. The full-scale hot smoke test can be performed to evaluate the temperature distribution of smoke layer and the smoke descending rate at ABRI large space fire lab in Tainan. In the other hand, the beam detectors can not only detect smoke layer by fire more earlier but show excellent smoke rejection if they can be effectually connected with passive smoke control systems. It is anticipated that through the execution of this research project, the concept developed in this study can be applied to improve the passive smoke management performance of large space buildings in Taiwan.

A miniature, ultra-low power, sensitive, microbridge gas sensor has been developed.The heat loss from the bridge is a function of the thermal conductivity of thegas ambient. Miniature thermal conductivity sensors have been developed for gaschromatography systems [1] and microhotplates have been built with MEMS technologywhich operates within the mW range of power [2]. In this work a lower power microbridgewas built which allowed for the amplification of the effect of gas thermalconductivity on heat loss from the heated microbridge due to the increase inthe surface-to-volume ratio of the sensing element. For the bridge fabrication,CMOS compatible technology, nanolithography, and polysilicon surfacemicromachining were employed. Eight microbridges were fabricated on each die,of varying lengths and widths, and with a thickness of 1 μm. A voltagewas applied to the sensor and the resistance was calculated based upon thecurrent flow. The response has been tested with air, carbon dioxide, helium,and nitrogen. The resistance and temperature change for carbon dioxide was thegreatest, while the corresponding change for helium was the least. Thus the selectivity of the sensor todifferent gases was shown, as well as the robustness of the sensor. Another aspect of the sensor is that it hasvery low power consumption. The measuredpower consumption at 4 Volts is that of 11.5 mJ for Nitrogen, and 16.1 mJ forHelium. Thesensor responds to ambient gas very rapidly. The time constant not only showsthe fast response of the sensor, but it also allows for more accuratedetection, given that each different gas produces a different correspondingtime constant from the sensor. The sensor is able to detect differentconcentrations of the same gas as well. Fromthe slopes that were calculated, the resistance change at 5 Volts operation wasfound to be 2.05mΩ/ppm, 1.14 mΩ/ppm at 4.5 Volts, and 0.7 mΩ/ppm at 4 Volts. Thehigher voltages yielded higher resistance changes for all of the gases thatwere tested. Theversatility of the microbridge has been studied as well. Experiments were donein order to research the ability of a deposited film on the microbridge, inthis case tin oxide, to act as a sensing element for specific gases. In thissetup, the microbridge no longer is the sensing element, but instead acts as aheating element, whose sole purpose is to keep a constant temperature at whichit can then activate the SnO film, making it able to sense methane. In conclusion,the microbridge was designed, fabricated, and tested for use as an electrothermalgas sensor. The sensor responds to ambient gas very rapidly with differentlevels of resistance change for different gases, purely due to the differencein thermal conductivity of each of the gases. Not only does it have a fastresponse, but it also operates at low power levels. Further research has beendone in the microbridge's ability to act as a heating element, in which the useof a SnO film as the sensing element, activated by the microbridge, was studied. REFERENCES: 1. D. Cruz,J.P. Chang, S.K. Showalter, F. Gelbard, R.P. Manginell, M.G. Blain," Microfabricated thermal conductivity detector for themicro-ChemLabTM," Sensors andActuators B, Vol. 121 pp. 414-422, (2007). 2. A. G. Shirke, R. E. Cavicchi, S. Semancik, R. H. Jackson, B.G. Frederick, M. C. Wheeler. "Femtomolar isothermal desorption usingmicrohotplate sensors," J Vac Sci TechnolA, Vol. 25, pp. 514-526 (2007).

This thesis describes the development of a novel comprehensive Monte Carlo simulation code, ARTEMIS, for the investigation of electron-hole pair transport mechanisms in a-Se x-ray imaging detectors. ARTEMIS allows for modeling of spatiotemporal carrier transport in a-Se, combining an existing Monte Carlo simulation package, PENELOPE, for simulation of x-ray and secondary electron interactions and new routines for electron-hole pair transport with three-dimensional spatiotemporal signal output considering the effects of applied electric field. The detector Swank factor, an important imaging performance metric is calculated from simulated pulse-height spectra and shown to depend on incident x-ray energy and applied electric field. Simulation results are compared to experimental measurements and are found to agree within 2%. Clinical x-ray spectra are also used to study detector performance in terms of energy weighting and electronic noise. Simulation results show energy-weighting effects are taken into account in the ARTEMIS model, where the Swank factor and DQE have a higher dependence on the high-energy incident x rays due to increased carrier yield. Electronic noise is found to widen the pulse-height spectra and degrade the Swank factor. The effect of recombination algorithms and burst models are studied. A comparison of a first-hit algorithm and a nearest-neighbor approach shows no significant difference in the simulation output while achieving reduced simulation time. The examination of the initial generation of carriers in the burst shows that the recombination efficiency of carriers is dependent on the carrier density and electric field. Finally, the spatial resolution characteristics of a flat-panel a-Se detector are studied by using the ARTEMIS model for spatial output and image generation. The modulation transfer functions are calculated from simulated detector point response functions for monoenergetic and clinical radiation qualities.

Graduate

With the deep exploration of particle physics, particle accelerators, detection methods, data recording and processing, and application of computing technology are continuously developing. It has not only brought progress in particle physics, but also promoted the development of the Science and Technology. The main focus of this thesis is data recording and processing. It provides a calibration method for pulses processed by ADCs. It uses some existing filters to achieve the accurate parameters of pulses and existing concept to do the comparison among filters. The  FPGA implementation scheme is also discussed in the paper.