| Digital x-ray imaging diagnosis is currently of great interest compared to traditional screen-film system. A large area, flat-panel, direct digital x-ray imaging detector, which uses amorphous selenium (a-Se) alloy layer for detecting x-rays and thin film transistor (TFT) for reading out signal, stands out among digital x-ray imaging detectors. Its excellent properties such as high resolution can meet almost all cases in diagnosing x-ray imaging. Experimental and theoretical studies are carried out for the goal of developing such a flat-panel digital x-ray imaging detector in this thesis. The stress is first put on the preparation of stabilized a-Se alloy film/layer. Arsenic is selected as alloying element for inhibiting crystallization of a-Se film. After long-playing probe the stabilized a-Se alloy films is successfully prepared by vacuum thermal evaporation, its carriers?transport properties are measured by time of flight technique, and about 1300 jim of carriers?mean ranges are achieved at the electric field of 1 OV/ pm The interaction probability of x-ray with a-Se is discussed in the medical used x-ray energy range, the absorbed energy in the primary interaction and the reabsorption of secondary x-rays in a-Se are studied in detail. According to physical interaction process of x-ray with a-Se, an expression of the optical transfer function (OTF) for a-Se layer is obtained after about ten facts related to the spatial resolution is studied theoretically, and the modulation transfer function (MTF), which is the absolute value of the OTF, is provided numerically for the monoenergetic x-ray photons. Based on the weighted averaging method of energy absorption and x-ray spectra, MTF of a-Se layer is further calculated for the case of x-ray spectra. Some important conclusion, such as decreasing a-Se layer thickness and the angle of oblique to improve the spatial resolution, and some useful parameters are obtained through above studies. After charge collection efficiency of a-Se layer is studied, a sensitivity model of a-Se to x-rays, related to charge carrier mean ranges, x-ray photon energy, layer thickness and electric field, is introduced, and the calculation has lead to some useful results. We also investigate the detective quantum efficiency (DQE) of a-Se layer to x-rays in detail, increasing a-Se layer thickness and decreasing the angle of oblique can improve DQE. Spatial resolution, sensitivity and detective quantum efficiency should be optimized while designing the imaging detectox. Based on the former preparation techniques, Thicker a-Se alloy layer is manufactured afler solving some new problems in techniques, and the photoelectric properties of the so-made a-Se alloy layer to x-rays are measured through experiments. The results show that there is linear relationship between x-ray photocurrent and x-ray exposure rate, and the sensitivity of a-Se strongly depends on the electric field. About 45 eV is needed for x-rays to release an electron-hole pair in a-Se at the electric field of 10 V/pin. The fluorescence escape efficiency of CsI:Na (CsI:Tl) phosphor is discussed, and a converting factor model of the phosphor to x-rays is proposed. The calculation shows that the fluorescence photon mean range should be above 10 times of phosphor layer thickness. A new x-ray imaging detector, which uses a-Se layer in combithation with high atomic number phosphor layer, is put forward on the basis of ti-Se + TFT imaging system. It has the advantage of higher...
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