JP2000082430A - Target for x-ray generation and x-ray tube using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a target for X-ray generation and an X-ray tube using it, capable of generating X-rays of minute focused radius, suppressing lowering of impact resistance, and improving cooling effect at the same time. SOLUTION: This target is provided to a copper target carrier 16, and it receives electron beams radiated from a cathode to emit X-rays. The target is provided with a carbon layer 19 having thermal conductivity larger than that of copper, a rhenium layer 20 on the carbon layer 19, and a tungsten thin film 21 on the rhenium layer 20 for receiving the electron beam to emit X-rays. Here, the electron beam is converted into X-rays in the thin film 21, and the X-rays having a small focused radius are emitted from the target. Moreover, the heat generated by the electron beams absorbed into the carbon layer 19 is rapidly conducted to the supporting body 16. Furthermore, the rhenium layer 20 prevents the formation of tungsten carbide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray generating target and an X-ray tube using the same, and more particularly, to an X-ray generating target that emits X-rays having a small focal diameter and using the same. It relates to an X-ray tube.

[0002]

2. Description of the Related Art Conventionally, a microfocus X-ray source that emits X-rays having a minute focal diameter has been known as an X-ray source used for observing a minute portion that cannot be directly seen by the eyes.

A microfocus X-ray source includes a cathode that emits an electron beam, a target that receives the electron beam emitted from the cathode and emits X-rays, and a target support made of copper or the like that supports the target. ing. The target generally has an X-ray generation layer made of tungsten or the like that converts an electron beam into X-rays.

An example of such a microfocus X-ray source is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-144045. In the microfocus X-ray source described in this publication, a first layer made of tungsten having a thickness of about 1 to 15 μm is formed on a second layer made of diamond having a thickness of about 45 μm. Has a target.

Another example of a microfocus X-ray source is disclosed in, for example, Japanese Patent Application Laid-Open No. H6-188092. The microfocus X-ray source described in this publication includes a target support made of copper, and an electron absorbing layer made of a light element such as beryllium (Be) or carbon (C) on the target support. About 1
It has a target in which extremely thin X-ray generation layers of μm are sequentially laminated.

[0006]

However, since the microfocus X-ray source described in the above-mentioned conventional publication has the above-described configuration, it has the following problems.

That is, in the microfocus X-ray source described in Japanese Patent Application Laid-Open No. 4-144045, it was sometimes difficult to obtain an X-ray having a smaller focal diameter.

On the other hand, in the microfocus X-ray source described in Japanese Patent Application Laid-Open No. 6-188092, the impact resistance is reduced, the target is insufficiently cooled, the target is damaged quickly, and the life of the target is shortened. Will do.

Accordingly, the present invention provides an X-ray generation target and an X-ray tube using the same, which are capable of emitting X-rays having a small focal diameter, preventing a decrease in impact resistance, and improving a cooling effect. The purpose is to provide.

[0010]

Means for Solving the Problems In order to achieve the above object, the present inventors have conducted intensive studies on the microfocus X-ray source described in the above-mentioned conventional publication and found the following.

That is, in the microfocus X-ray source described in Japanese Patent Application Laid-Open No. 4-144045, even if the electron beam is narrowed to a small focal point, the tube voltage supplied between the cathode and the target is reduced to about 100 kV. When it comes
When the electrons are converted into X-rays inside the target, they spread, and the focal diameter of the X-rays becomes about 10 μm.
That is, it has been found that there is a limit even if the electron beam is narrowed in order to obtain a small focal point X-ray, and it is difficult to obtain an X-ray having a smaller focal diameter.

Further, in the microfocus X-ray source described in Japanese Patent Application Laid-Open No. 6-188092, tungsten and carbon are joined, and during operation, tungsten and carbon react with each other to provide mechanical and thermal It has been found that tungsten carbide, which is brittle to impact, is formed, and as a result, impact resistance is reduced. In addition, electrons that have entered the electron absorption layer are converted into soft X-rays that are easily absorbed by light elements such as Be and C, and are absorbed by the X-ray generation layer or become heat. Here, beryllium (200 W / m · K) and graphite (100
３００300 W / m · K) and a low thermal conductivity, so that a copper target support (400 W / m · K ·
It has been found that the heat cannot be diffused to K), the target is insufficiently cooled, and if the cooling is insufficient, the target is damaged quickly and the life of the target is shortened due to the minute heating portion.

The present inventors have sufficiently studied the problems of the microfocus X-ray source described in the above publication and, as a result, have completed the following invention.

That is, the present invention provides an X-ray generation target provided on a target support made of copper, which receives an electron beam emitted from a cathode and emits X-rays.
A carbon layer provided on the target support and having a higher thermal conductivity than copper, a rhenium layer provided on the carbon layer,
A tungsten thin film provided on the rhenium layer and receiving an electron beam to emit X-rays.

According to the X-ray tube target of this configuration,
When the electron beam is received by the tungsten thin film, the electron beam is converted into X-rays in the tungsten thin film, and the X-rays are emitted from the target. At this time, an X-ray having a small focal diameter is emitted from the tungsten thin film. When the electron beam that has passed through the tungsten thin film and the rhenium layer is incident on the carbon layer, the carbon layer absorbs the electron beam and generates heat therein. This heat is quickly transmitted to the target support. Further, during operation of the X-ray tube, the formation of tungsten carbide due to the reaction between tungsten and carbon is prevented because the rhenium layer is provided between the tungsten thin film and the carbon layer.

[0016] The carbon layer preferably contains diamond. In this case, the thermal conductivity of diamond is considerably higher than that of copper, so that thermal diffusion takes place very quickly.

The present invention also provides a cathode for emitting an electron beam, a target support made of copper, and an X-ray generator provided on the target support for receiving an electron beam emitted from the cathode and emitting X-rays. X-ray tube comprising a target for use, a cathode and a container for containing the X-ray generation target, wherein the X-ray generation target is provided on a target support, and a carbon layer having a thermal conductivity larger than copper. And a rhenium layer provided on the carbon layer, and a tungsten thin film provided on the rhenium layer and receiving an electron beam to emit X-rays.

In the X-ray tube having this configuration, heat generated in the carbon layer of the X-ray generation target by the irradiation of the electron beam is quickly transmitted to the target support, so that the X-ray tube has an excellent cooling effect. Therefore, the X-ray generation target is less likely to be damaged by heat, and the life of the target can be extended. Further, the reaction between the tungsten thin film and the carbon layer is prevented by the presence of the rhenium layer, and the formation of tungsten carbide which is thermally and mechanically fragile is prevented, so that a reduction in impact resistance can be prevented. For this reason, even if the X-ray generation target is accommodated in the container, it is not necessary to replace the target early, and the X-ray tube can be used for a long time without maintenance. In particular, the X-ray tube of the present invention is effective when the container is a sealed container. That is, when the target is housed in a sealed container, the replacement of the target becomes considerably troublesome, but since such an early replacement is not necessary,
Eliminates troublesome work for a long time.

In the X-ray tube, the X-ray generation target is preferably embedded in the target support with the surface of the tungsten thin film exposed.
In this case, when the X-ray generation target is embedded in the target support, the tungsten thin film, the rhenium layer, and the carbon layer come into contact with the target support, respectively, as compared with the case where the target is provided on the target support. Thermal diffusion from the target is performed more quickly.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing the structure of a side-window type microfocus X-ray tube as an X-ray tube according to the present embodiment. As shown in FIG. 1, a microfocus X-ray tube (hereinafter referred to as “X-ray tube”) 10 includes a nickel-copper alloy envelope 12 and a glass envelope 13.
And A ceramic stem 11 is airtightly fitted into one opening 12a of the envelope 12, and a beryllium X-ray emission window 14 is hermetically attached to an opening 12b on the side surface of the envelope 12. I have. The glass envelope 1 is connected to the other open end of the envelope 12.
3 is airtightly covered. Thus, the sealed container H
Is configured.

An electron gun 15 is disposed inside the envelope 12, and the electron gun 15 includes a heater electrode 15a, a cathode 15
b, a grid electrode 15c made of molybdenum (Mo) and a focus electrode 15d, and the focus electrode 15d is attached to a column 15e of alumina or sapphire. As the cathode 15b, an impregnated cathode in which porous tungsten is impregnated with BaO or the like is used, and its electron emission surface is coated with Os (osmium) or the like. A target support 16 is disposed inside the envelopes 12 and 13.
A target 17 is provided at the tip of. As the target support 16, copper (heat conductivity: 400 W / m · K) having good thermal conductivity and excellent workability and strength is used.

When the cathode 15b is heated by the heater electrode 15a, electrons are emitted from the surface of the cathode 15b at a constant temperature, and the emitted electrons are accelerated by the grid electrode 15c and focused by the focus electrode 15d. And collide with the target 17 as an electron beam. The electrons are converted into X-rays and heat by the collision, and the generated X-rays are emitted to the outside through the X-ray emission window 14. The target 17 is arranged at an angle of, for example, 25 ° with respect to a plane perpendicular to the trajectory of the electrons toward the target 17. Since the target 17 is thus arranged at an angle, most of the generated X-rays reach the X-ray emission window 14 and are emitted from the X-ray emission window 14 to the outside.

FIG. 2 is a sectional view showing a state in which a target 17 is provided at the tip of a target support 16.
As shown in FIG. 2, a concave portion 18 is formed at the tip of the target support 16, and the target 17 is fitted into the concave portion 18. That is, the target 17
It is embedded in the tip of the target support 16.

The target 17 includes a carbon layer 19 bonded to the bottom of the concave portion 18, a protective layer 20 laminated on the carbon layer 19, and an X-ray generating thin film 21 laminated on the protective layer 20. The surface 21 a of the X-ray generation thin film 21 is exposed from the target support 16.

The carbon layer 19 is made of a carbonaceous material having a higher thermal conductivity than copper constituting the target support 16.
As the carbonaceous material, for example, super graphite (trade name, thermal conductivity: 800 W / m · K) or diamond (thermal conductivity: 900 to 2000 W / m · K) is used. Among them, diamond is preferably used because of its higher thermal conductivity than super graphite. The thickness of the carbon layer 19 is preferably about 100 μm
It is.

The protective layer 20 is for preventing a reaction between the carbon layer 19 and the X-ray generating thin film 21.
Rhenium is used because of its excellent heat resistance. The thickness of the protective layer (hereinafter referred to as “rhenium layer”) 20 is preferably 0.5 μm or less.

As the X-ray generation thin film 21, a material having high X-ray generation efficiency and excellent heat resistance is used, and tungsten is used as the material. X-ray generating thin film
The thickness of the “tungsten thin film” 21 is preferably 5 μm or less.

The thickness of the target 17 is determined by the tube voltage to be used, the desired X-ray focal diameter, and the X-ray dose. For example, when the tube voltage is 100 kV, the target 17
Is preferably in the range of several thousand to several μm. The X-ray dose increases as the thickness increases, but the focal diameter also tends to increase.

Here, a method for manufacturing the target 17 will be described. That is, first, a carbon layer 19 is formed inside the concave portion 18 of the target support 16 by film formation, embedding or brazing, and a rhenium layer 20 is formed thereon by a PVD method, a CVD method, a vapor deposition method, or the like. Furthermore, PV
Tungsten thin film 21 by D method, CVD method, evaporation method, etc.
To form Thus, the target 17 is manufactured in a state where the target 17 is embedded in the concave portion 18 of the target support 16.

According to the target 17 having the above configuration,
When the electron beam is received by the tungsten thin film 21, the electron beam is converted into X-rays in the tungsten thin film 21,
X-rays are emitted from the target 17. At this time, X-rays having a small focal diameter are emitted from the tungsten thin film 21. When the electron beam that has passed through the tungsten thin film 21 and the rhenium layer 20 is incident on the carbon layer 19, the electron beam is absorbed by the carbon layer 19 and generates heat therein. Conveyed to.
For this reason, the cooling effect is improved, and the life of the target 17 can be extended. In particular, when diamond is used as the carbon layer 19, the cooling effect is further improved due to its high thermal conductivity, and the life of the target 17 can be further extended.

Further, during operation of the X-ray tube 10, the rhenium layer 2
Since 0 is provided between the tungsten thin film 21 and the carbon layer 19, generation of tungsten carbide due to the reaction between tungsten and the carbonaceous material is prevented. For this reason,
Thermal and mechanical impact resistance due to the formation of tungsten carbide can be prevented.

Further, since the target 17 is embedded in the target support 16, the tungsten thin film 21, the rhenium layer 20 and the carbon layer 19 are respectively in contact with the target support 17, and the target 17 is placed on the target support 16. Target 17
Is more quickly diffused.

Therefore, the target 17 having the above-described configuration is used.
Does not require early replacement of the target 17 and the X-ray tube 1
0 can be used for a long time without the need for maintenance. In particular, the target 17 is effective in an X-ray tube in which the target 17 is housed in the sealed container H and replacement of the target 17 becomes considerably troublesome as in the present embodiment. That is, when the target 17 is accommodated in the sealed container H, the replacement of the target 17 becomes considerably troublesome. However, since such an early replacement is not required, a troublesome work is not required for a long time.

The present invention is not limited to the embodiment described above. For example, the X-ray generation target of the present invention is also applicable to an end-window type X-ray tube 10 shown in FIG. This end-wind type X-ray tube 1
Numeral 0 has a structure in which the positions of the X-ray output window 14 and the electron gun 15 are interchanged.

Further, the target for X-ray generation of the present invention
As shown in FIG. 4, the present invention is also applicable to an end window type microfocus X-ray tube in which the target support 16 is accommodated in a cylindrical hood electrode 22. An X-ray passage 22a is formed at one end of the hood electrode 22,
An electron beam passage opening 22b is formed on the side surface.

The target 17 is not limited to being embedded at the tip of the target support 16, but may be protruded at the tip of the target support 16. In this case, the target 17 is brazed to the tip of the target support 16 with silver or the like.

[0038]

As described above, according to the present invention, an electron beam is converted into an X-ray in a tungsten thin film, and when the X-ray is emitted from a target, an X-ray having a small focal diameter is emitted from the tungsten thin film. Is done. Further, the heat generated by the electron beam being absorbed by the carbon layer due to the incidence of the electron beam on the carbon layer is quickly transmitted to the target support, and the cooling effect is improved. Furthermore, the rhenium layer prevents the formation of tungsten carbide due to the reaction between the tungsten and the carbon layer, thereby preventing a reduction in impact resistance.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an X-ray tube of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of the target of FIG.

FIG. 3 is a sectional view showing another embodiment of the X-ray tube of the present invention.

FIG. 4 is a sectional view showing still another embodiment of the X-ray tube of the present invention.

[Explanation of symbols]

10 ... Micro focus X-ray tube (X-ray tube), 15b ...
Cathode, 16: target support, 17: target, 19: carbon layer, 20: rhenium layer, 21: tungsten thin film.

Claims (6)

[Claims] An X-ray generation target provided on a target support made of copper and receiving an electron beam emitted from a cathode to emit X-rays, wherein the X-ray generation target is provided on the target support and is larger than copper. A carbon layer made of a carbonaceous material having thermal conductivity, a rhenium layer provided on the carbon layer, and a tungsten thin film provided on the rhenium layer and receiving the electron beam and emitting the X-rays. An X-ray generation target, comprising: 2. The X-ray generation target according to claim 1, wherein the carbonaceous material is diamond. 3. A cathode for emitting an electron beam, a target support made of copper, and an X-ray generator provided on the target support for receiving the electron beam emitted from the cathode and emitting X-rays. An X-ray tube including a target, a container for accommodating the cathode and the X-ray generation target, wherein the X-ray generation target is provided on the target support, and has a thermal conductivity higher than copper. A carbon layer made of a carbonaceous material; a rhenium layer provided on the carbon layer; and a tungsten thin film provided on the rhenium layer and receiving the electron beam and emitting the X-ray. X-ray tube. 4. The X-ray tube according to claim 3, wherein the container is a sealed container. 5. The X-ray tube according to claim 3, wherein the carbonaceous material is diamond. 6. The X-ray generation target according to claim 3, wherein the X-ray generation target is embedded in the target support while exposing the surface of the tungsten thin film. X-ray tube.