| 摘要 |
PURPOSE:To increase the resolution of an image for either the entire area of a photoelectric cathode or its central area by specifying the sectional surface of the photoelectric cathode and making either an imaging surface in the entire area or that only in the central area almost flat. CONSTITUTION:A photoelectric cathode 16 is installed on the window 15 of a vacuum encircling case 1 and an anode 11 and a fluorescent screen 12 are installed on the discharge window 14 of the case 1. And, focusing electrodes 6-9 are installed between the windows 14 and 15, thereby making an X-ray image tube. The median curvature radius of the sectional surface 21 of the cathode 16 increases from the center of the surface 21 up to 1/2-4/5 of its diameter apart from the center in a degree more than that proportional to the distance from the center. It increases from the above point toward the periphery of the surface 21 in a degree less than that proportional to the distance from the center. Therefore, when only the central area of the cathode 16 or the entire area of the cathode 16 is observed, there is only a minimal difference in focusing effect between the electronic orbits 28 and 29 and the central electronic orbit 30, thereby achieving good resolution for both visual fields.
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