Patent attributes
An X-ray tube includes an electron gun in which a Wehnelt electrode is formed with an opening asymmetric about an electron emitter. The electron emitter is an elongate coil filament which is disposed inside the elongate opening of the Wehnelt electrode. The opening has two longer sides positioned asymmetrically about a center-of-width line of the filament. Each of the two longer sides is curved in the same direction as viewed in a direction normal to the front face of the Wehnelt electrode. The two longer sides have curvature radii R1 and R2 different from each other, so that an electron-beam-irradiation region on a target is not curved but becomes almost straight.