JP2006086000A - X-ray tube device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotary anode type X-ray tube device which is improved so as to be manufactured at a low cost while realizing a long life using a dynamic pressure groove bearing. <P>SOLUTION: An anode 11 is installed on a rotor 12 and held rotatably by a dynamic pressure groove bearing 13, and a carbon nanotube film 16 is formed on the surface of an electrode plate 15 of a cathode 14, and by arranging a gate 17 in the front, these anode 11 and cathode 14 or the like are sealed in vacuum in a glass housing 18, and by the field electron emission from the carbon nanotube film 16, electron flow is generated and by colliding against the anode 11, X-rays are generated. Thereby, without using a filament and eliminating the possibility of evaporation and adhesion of the filament material, voltage withstanding characteristics can be made long-lived even if the housing 18 is made of glass. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an X-ray tube apparatus used for medical diagnosis, industrial inspection, and the like, and more particularly to a rotary anode type X-ray tube apparatus.

  Conventionally, a rotary anode type X-ray tube apparatus is made of a glass vacuum envelope in which a cathode (cathode) using a filament as an electron emission source is opposed to a rotating anode (anode) target. Enclosed in a vessel. The rotating anode is usually held rotatably by a ball bearing. However, since the ball bearing is lubricated by the solid lubricant, the lubricant is worn out for a long period of use, and the lubrication is lost. Therefore, in recent years, dynamic pressure groove bearings have been introduced to extend the life of rotating parts.

  On the other hand, when the filament is used for a long time, it gradually evaporates, and tungsten, which is the evaporated filament material, adheres to the inner surface of the glass envelope, which deteriorates the creeping withstand voltage of the glass envelope, and withstand voltage characteristics Cause deterioration.

  For this reason, filament deposition occurs using a metal envelope with a metal central portion of the envelope in order to obtain a withstand voltage life that is commensurate with the rotating part whose life has been extended by introducing a dynamic pressure groove bearing. However, the breakdown voltage characteristics are not deteriorated. This is because if the envelope is made of metal and the metal is grounded, the withstand voltage characteristic will not be deteriorated even if the filament material adheres to the inner surface of the envelope. This is because it can be maintained for a long time.

  However, the metal envelope has a drawback that it has a complicated structure, requires many steps for manufacturing, and is expensive as compared with a glass envelope. That is, the metal envelope has many joints, has a large number of parts, is not easy to assemble, and has high component costs and assembly costs.

Recently, for example, as shown in Non-Patent Document 1 below, research has been conducted for realizing an X-ray tube using a carbon nanotube as an electron source. In this X-ray tube, instead of thermionic emission from the conventional filament, an electron source is formed by using field electron emission from the tip of the carbon nanotube, and the target is irradiated with an electron beam from the electron source. It is to take out the line.
Fumio Okuyama "X-ray tube using carbon nanotubes as an electron source" Journal of Japanese Society of Radiological Technology, Vol. 58, No. 3, 309 (March 2002).

Patent Document 1 below also describes an X-ray tube using carbon nanotubes. However, by adopting a structure that efficiently generates a flat and uniform electron beam by field emission from the planar carbon nanostructure provided on the planar cathode surface, the X-ray tube device can be reduced in size and consumption. Only the pursuit of electric power and the possibility of high-speed pulse operation is pursued, and no mention is made of the problems in the above-described rotary anode X-ray tube apparatus.
JP 2003-288853 A

  The object of the present invention is to incorporate research results on an X-ray tube using carbon nanotubes as an electron source, and to focus on the characteristics of the carbon nanotube electron source and to solve the problems in the above-described rotary anode X-ray tube device An object of the present invention is to provide an X-ray tube apparatus capable of achieving both ease of manufacture, low manufacturing cost and long life as a whole.

  In order to achieve the above object, in an X-ray tube apparatus according to the present invention, a rotating anode rotatably supported by a dynamic pressure groove bearing, and a cathode using carbon nanotubes as an electron source disposed opposite to the rotating anode. And an envelope made of glass in which the rotating anode and the cathode are vacuum-sealed.

  Carbon nanotubes are used as the electron source of the cathode, and electrons are emitted by field emission. Therefore, heating is not performed unlike the case of using a filament. Therefore, it does not occur that the filament material evaporates and adheres to the inner surface of the envelope to deteriorate the withstand voltage characteristics. This means that the withstand voltage characteristics do not deteriorate over a long period of time even if the envelope is made of glass. Therefore, the use of a cathode having a carbon nanotube electron source opens the way to obtain an X-ray tube apparatus having a long life corresponding to the life of a dynamic pressure groove bearing even in a glass envelope. If the envelope can be made of glass, the manufacturing is easy and the manufacturing cost is low. Therefore, the life of the entire X-ray tube apparatus can be extended while being easy to manufacture and at low manufacturing costs.

  Next, an X-ray tube apparatus embodying the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic sectional view of one embodiment of the present invention. In FIG. 1, a rotary anode X-ray tube apparatus 10 according to an embodiment has a disk-like anode 11, which is attached to a rotor 12 and is driven by a dynamic pressure groove bearing 13. It is held rotatably. A cathode 14 is disposed so as to face the anode 11, a carbon nanotube film 16 is formed on the surface of an electrode plate 15 provided on the cathode 14, and a mesh-like conductive metal is formed on the front surface of the carbon nanotube film 16. The gate 17 is arranged. The rotary anode 11 and the cathode 14 are vacuum-sealed in an envelope 18 made of glass.

  A stator (not shown) is provided outside the glass envelope 18, and a rotating magnetic field formed by the stator causes an induced current to flow through the rotor 12 to generate torque, which causes the rotor 12 to move at high speed. The anode 11 also rotates at a high speed integrally with the anode 11. In the cathode 14, a positive potential is applied to the gate 17 with respect to the electrode plate 15 on which the carbon nanotube film 16 is formed, whereby electrons are drawn out from the carbon nanotube film 16, and the electron flow is further increased to a positive high potential. Then, the X-rays are generated by colliding with the target on the surface of the anode 11.

  In a conventional rotary anode type X-ray tube apparatus that rotatably supports an anode using a bearing, the rotational speed is increased to a predetermined number only when X-rays are generated (a load is applied) in consideration of the life of the bearing. In the rotary anode type X-ray tube apparatus of this embodiment, since wear is not generated as described above and the long-life dynamic pressure groove bearing 13 is employed, a load can be constantly applied during use. It can be continuously rotated at a high speed. This eliminates the need for time to start up rotation as a preparation for applying a load.

  In addition, since the electron source is formed by field electron emission from the carbon nanotube film 16, if a positive potential is applied to the gate 17, electrons can be generated instantaneously to generate X-rays. This is in contrast to the case of a cathode using a conventional filament. When the thermoelectrons from the filament are used, it is necessary to heat the filament. Therefore, the heating requires about 0.5 to 1.5 seconds, but this time is unnecessary.

  Further, when a filament is used, a filament material such as tungsten evaporates from the heated filament and adheres to the inner surface of the envelope. By using field electron emission from the carbon nanotube film 16, such evaporation and adhesion can be prevented. Is unrelated. Therefore, even if the envelope 18 is made of glass, the filament material does not evaporate and adhere to the inner surface of the envelope 18, so that the withstand voltage characteristics are not deteriorated and the life is not shortened. Therefore, even if the envelope 18 is made of glass, it is possible to extend the withstand voltage characteristics so as to meet the long life of the dynamic pressure groove bearing 13.

  If the envelope 18 is made of glass, the number of parts and the number of manufacturing processes are not large as in the case of a metal envelope, and the envelope 18 is manufactured by a simple manufacturing process using a small number of parts. Therefore, it is possible to avoid an increase in parts cost and assembly cost. That is, by using the glass envelope 18, the parts cost and assembly cost can be reduced as compared with the case of the metal envelope, and the entire rotary anode X-ray tube apparatus can be manufactured at a low cost.

  Of course, the present invention is not limited to this embodiment, and the specific structure can be variously configured.

  According to the rotating anode type X-ray tube apparatus of the present invention, since the carbon nanotube is used as an electron source by paying attention to the property of the field electron emission from the carbon nanotube, the withstand voltage characteristic even when the glass envelope is used. Therefore, it is possible to form an envelope having a withstand voltage characteristic that is long enough to meet the long life of the dynamic pressure glove bearing, and can be manufactured at low cost. Further, since the anode can be always rotated, the time required for starting up the rotation is not required, and the time required for heating the filament is not required, so that X-rays can be generated immediately.

1 is a schematic cross-sectional view showing a rotary anode type X-ray tube device according to one embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Rotary anode type X-ray tube apparatus 11 ... Rotary anode 12 ... Rotor 13 ... Dynamic pressure glove bearing 14 ... Cathode 15 ... Electrode plate 16 ... Carbon nanotube film 17 ... Gate 18 ... Product made from glass Envelope

Claims (1)

  A rotating anode that is rotatably supported by a dynamic pressure groove bearing, a cathode that is disposed opposite to the rotating anode and that uses carbon nanotubes as an electron source, and the rotating anode and the cathode are vacuum sealed. An X-ray tube apparatus characterized by comprising an envelope.

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