| 摘要 |
PROBLEM TO BE SOLVED: To uniformize the width of a focus of an electron beam formed on a positive electrode target by shifting the lengthwise central position of a convergence slot located in a negative electrode structure to the radiation port side, to which an X ray advances from the lengthwise central position of a filament. SOLUTION: A convergence slot 17 is formed in a part of a negative electrode structure arranged by facing to a positive electrode target, and a filament 22 is so disposed in the convergence slot 17 that its lengthwise direction coincides with that of the convergence slot 17. The lengthwise central position (p) of the convergence slot 17 is disposed by shifting it to the side, to which an X-ray advances from the lengthwise central position (p) of the filament 22. Width W in a direction perpendicular to the lengthwise direction of the convergence slot 17 is so formed as to be increased on the side, to which the X-ray advances, and gradually linearly reduced toward the radiation port on its opposite side. Thereby, the width and density of an electron beam focus can be further uniformized, the extent of blur in photographing an object is stabilized, and image quality is improved.
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