| 摘要 |
PURPOSE:To reduce a focal length into an allowable range, by sealing a battery and an X-ray tube in an X-ray tube container so that a bias negative as to a filament is applied to a convergence electrode. CONSTITUTION:In an X-ray tube 2, a glow by-pass diode 7 is connected between a filament 5 and a cathode 4. The X-ray tube 2 and a compensatory bias battery 6 are sealed in a tube container 1. The filament 5 is electrically insulated from the convergence electrode portion 4a of the cathode 4 by an electric insulator 8. A positive bias is applied to the filament 5 by the battery 6. Thermoelectrons emitted from the filament are condensed by the electronic lens action of the convergence electrode portion 4a so that the thermoelectrons proceed to an X-ray focus. Since the bias is applied to the filament, the direction of emission of thermoelectrons from the side portions of the filament is restricted to promote the condensation to reduce the focal length of the X-ray tube 2. |
