X-ray tube

Abstract

Provided is an X-ray tube capable of obtaining a clear X-ray image by reducing unnecessary X-rays radiated from a holder shaft. The X-ray tube includes an electron source 12 for generating an electron beam B, an anode 13 for accelerating the electron beam B and having a hole 13a allowing the electron beam B to pass through, a cylindrical holder shaft 14 forming a passage for allowing the electron beam B to pass through a hole 13a of the anode 13, a magnetic lens 17 arranged around the holder shaft 14 and configured to converge the electron beam B, a target holder 15 connected to the holder shaft 14, a target 16 arranged in the target holder 15 so that the electron beam B collides with the target 16, and an irradiation window 15b arranged in the target holder 15 and configured to extract X-rays generated from the target 15 to the outside. The inner wall of the holder shaft 14 is made of a carbon material to reduce X-rays generated when the electron beam B hits the holder shaft 14.

Claims

1. An X-ray tube comprising: an electron source configured to generate an electron beam; an anode configured to accelerate the electron beam and having a hole allowing the electron beam B to pass through; a cylindrical holder shaft configured to form a passage which allows the electron beam B to pass through the hole of the anode; a magnetic lens arranged around the holder shaft and configured to converge the electron beam; a target holder connected to the holder shaft; a target arranged in the target holder so that the electron beam collides with the target; and an irradiation window arranged in the target holder for extracting X-rays generated from the target to an outside, wherein an inner wall of the holder shaft is made of a carbon material.

2. The X-ray device as recited in claim 1, wherein a carbon content rate of the carbon material is 99.9% or more.

3. The X-ray device as recited in claim 1, wherein the carbon material is graphite having thermal anisotropy, and wherein a good thermal conduction direction is directed in an axial direction of the holder shaft.

4. The X-ray device as recited in claim 1, wherein the carbon material of the inner wall of the holder shaft is covered so that at least a part of an anode side portion of the holder shaft is covered by a cover which is nonmagnetic and has strength higher than strength of the carbon material, and is held via the cover.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram showing an overall configuration of an X-ray tube according to an embodiment of the present invention.

(2) FIG. 2 is a view showing characteristic portions of the X-ray tube shown in FIG. 1.

(3) FIG. 3 is a view showing a conventional example of an X-ray tube that irradiates a micro-focus X-ray.

EMBODIMENT FOR CARRYING OUT THE INVENTION

(4) Hereinafter, an embodiment of an X-ray tube according to the present invention will be described with reference to the attached drawings. FIG. 1 is a diagram showing an overall configuration of an X-ray tube used in a micro-focus X-ray inspection device according to one embodiment of the present invention. FIG. 2 is an enlarged view of a characteristic structural portion including the holder shaft portion. Note that the same portion as that described with reference to FIG. 3 will be denoted by the same reference numeral.

(5) In the X-ray tube according to the present invention, a filament (electron source) 12 serving as a negative electrode to which a negative voltage is applied is arranged in a high-vacuum vacuum chamber 11 to which a vacuum gauge G and a turbo molecular pump TMP are attached. From the filament 12, an electron beam B is emitted toward the grounded anode 13. At the center of the anode 13, a hole 13a is provided. The electron beam B is accelerated to pass through the hole 13a of the anode 13 and further pass through a cylindrical holder shaft 14 communicating with the hole 13a, and is irradiated onto the target 16 arranged in the target holder 15. The outside of the target holder 15 is cooled by a water cooling mechanism 15a (which may be an air cooling mechanism).

(6) On the outer side of the holder shaft 14, a magnetic lens 17 for converging the electron beam B and a deflector 18 for adjusting the direction of the electron beam B are provided. The electron beam B passing through the holder shaft 14 is narrowed down to the m level by the magnetic lens 17 and is focused on the X-ray focal point on the target 16.

(7) In the X-ray tube according to this embodiment, the holder shaft 14 is divided into a tip end side holder shaft 14a (inner diameter : 10 mm, length: 160 mm) surrounded by the magnetic lens 17 and a basal end side holder shaft 14b surrounded by the deflector 18. The basal end side holder shaft 14b is made of a tungsten alloy in the same manner as in the holder shaft 14 of the conventional structure shown in FIG. 3, and is fixed to and supported by the vacuum chamber 11 with a flange 19 via an O-ring seal 20.

(8) At the connecting portion of the basal end side holder shaft connecting with the tip end side holder shaft 14a, a stepped portion 14c is formed on the inner wall of the tip end side holder shaft 14a, and the connecting portion is connected to the stepped portion 14c in an airtight manner by interposing an O-ring seal 20.

(9) For the tip end side holder shaft 14a, a cylindrical carbon material, preferably pure carbon, is used. Specifically, an artificial graphite of the grade HT (carbon ratio: 99.999%, density: 2.22 g/cm.sup.3, thermal conductivity: 1,700 W/(m.Math.K)) manufactured by Thermo Graphitics Co., Ltd., is used, and is processed so that the good thermal conduction direction is directed in the axial direction (longitudinal direction) of the tip end side holder shaft 14a.

(10) That is, it is configured such that heat is transmitted along the good thermal conduction direction even in vacuum and heat is radiated efficiently using the water cooling mechanism 15a of the target holder 15.

(11) The connection between the target holder 15 (tungsten alloy) and the tip end side holder shaft 14a (carbon material) is made by brazing. In cases where the carbon material is graphite, it can also be joined by a comporoid technique capable of joining with various metals, including a joint portion with the cover 21 described later.

(12) In the vicinity of the end portion of the tip end side holder shaft 14a near the anode 13, a cover 21 made of a non-magnetic material, such as, e.g., titanium and having strength higher than that of the carbon material, is attached to the outside of the tip end side holder shaft 14a. A cut surface (D-cut surface) 21a is formed on a part of the outer peripheral surface of the cover 21. The shaft fixing portion 22 supported by the cover 21 and the screw 23 for fixing the shaft are brought into contact with the cut surface 21a so that the emission direction is directed in the direction of the X-ray irradiation window 15b provided in a part of the target holder 15 and the rotation does not occur at the position.

(13) Although the cover 21 covers a part of the tip end side holder shaft 14a, the cover 21 may cover the entire tip end side holder shaft 14a including the portion surrounded by the magnetic lens 17.

(14) As described above, at least the inner wall of the tip end side holder shaft 14a which is an area where the electron beam B easily hits is made of graphite which is a carbon material. Therefore, even if an electron beam hits, the X-ray generation efficiency can be suppressed to reduce generation of unnecessary X-rays.

(15) Although one embodiment of the present invention has been described above, various modifications can be made without departing from the spirit of the present invention.

(16) For example, in the above-described embodiment, the holder shaft is divided into the tip end side holder shaft 14a surrounded by the magnetic lens 17 and the basal end side holder shaft 14b surrounded by the deflector 18, and only the tip end side holder shaft 14a is made of a carbon material. However, the entire holder shaft may be formed by one holder shaft 14 which is entirely made of a carbon material. In this case, it may be configured such that a cover 21 made of a non-magnetic material is attached to the outside of the vicinity of the end portion of the holder shaft 14 on the side close to the anode 13, and fixed to the vacuum chamber 11 by a flange 19 in the same manner as in the conventional example shown in FIG. 3.

INDUSTRIAL APPLICABILITY

(17) The present invention can be applied to an X-ray tube used for a micro-focus X-ray inspection device or the like.

DESCRIPTION OF REFERENCE SYMBOLS

(18) 11 vacuum chamber 12 filament (electron source) 13 anode 14 holder shaft 14a tip end side holder shaft 14b basal end side holder shaft 14c stepped portion 15 target holder 15a water cooling mechanism 15b X-ray irradiation window 16 target 17 magnetic lens 18 deflector 19 flange 20 O-ring seal 21 cover 21a cut surface B electron beam