Cold cathode X-ray tube and control method thereof
阅读说明:本技术 冷阴极型x射线管及其控制方法 (Cold cathode X-ray tube and control method thereof ) 是由 监物秀宪 于 2019-01-29 设计创作,主要内容包括:提供冷阴极型X射线管,通过防止阳极电流随时间的降低,能够长时间地进行稳定驱动。冷阴极型X射线管(1)具有:电子发射部(10),其包含使用了冷阴极的电子发射元件;阳极部(11),其与电子发射部(10)对置地配置;靶(12),其配置于阳极部(11)的表面的一部分;壳体(15),其在内部配置有电子发射部(10)、阳极部(11)以及靶(12);以及氢产生部(14),其由当与电子碰撞时会产生氢的材料构成,并且配置于存在于壳体(15)的内部的表面中的除靶(12)的表面以外的部分。(Provided is a cold cathode X-ray tube which can be stably driven for a long time by preventing a decrease in anode current with time. A cold cathode X-ray tube (1) is provided with: an electron emission unit (10) including an electron emission element using a cold cathode; an anode section (11) disposed opposite the electron emission section (10); a target (12) disposed on a part of the surface of the anode section (11); a case (15) in which an electron emitting unit (10), an anode unit (11), and a target (12) are disposed; and a hydrogen generation unit (14) which is made of a material that generates hydrogen when it collides with electrons and is disposed in a portion other than the surface of the target (12) in the surface inside the housing (15).)
1. A cold cathode type X-ray tube having:
an electron emission unit including an electron emission element using a cold cathode;
an anode portion disposed to face the electron emission portion;
a target disposed on a part of a surface of the anode portion;
a case in which the electron emitting unit, the anode unit, and the target are arranged; and
a hydrogen generating portion which is made of a material that generates hydrogen when colliding with electrons, and is disposed in a portion other than the surface of the target among surfaces existing inside the housing.
2. The cold cathode X-ray tube of claim 1,
the cold cathode type X-ray tube further has a focusing structure between the electron emitting portion and the target,
the hydrogen generating unit is disposed on a surface of the focusing structure.
3. The cold cathode X-ray tube of claim 1,
the anode part is made of metal,
the hydrogen generating part is disposed on a portion of the surface of the metal where the target is not disposed.
4. The cold cathode X-ray tube of claim 1,
at least a part of the inner wall of the housing is made of any one of glass, ceramic and stainless steel,
the hydrogen generating part is disposed on the at least a part of the inner wall of the housing.
5. The cold cathode X-ray tube of claim 1,
the hydrogen generating section is composed of a silicon nitride film (SiN), a silicon carbide film (SiC), a silicon carbonitride film (SiCN), an amorphous carbon film (a-C), or a diamond-like carbon film (DLC) formed by plasma CVD.
6. A method of controlling a cold cathode X-ray tube according to any one of claims 1 to 5, wherein,
when the cold cathode X-ray tube is not in operation, hydrogen gas or a mixed gas of hydrogen gas and nitrogen gas is injected into the cold cathode X-ray tube, thereby adsorbing hydrogen in the hydrogen generating portion.
Technical Field
The invention relates to a cold cathode type X-ray tube and a control method thereof.
Background
A conventional X-ray tube uses a filament as an electron emitting element, and uses thermal electrons emitted from the filament as an electron source. In contrast, in recent years, several X-ray tubes (cold cathode X-ray tubes) using a cold cathode as an electron emitting element have been proposed (for example, patent documents 1 to 3).
The cold cathode X-ray tube has a property that an electron emission amount is easily affected by a surface state of the cathode, as compared with an X-ray tube using a filament as an electron emitting element. Therefore, the conventional cold cathode X-ray tube has the following problems: for example, the degree of vacuum may be reduced by gas generated during the operation of the X-ray tube, and as a result, the surface state of the cathode may change, which may reduce the anode current over time. As a method for coping with this problem, a method of gradually increasing the extraction voltage is known (for example, non-patent documents 1 and 2).
In addition, non-patent document 3 describes the following, although an example of a field emission display is shown: in the case of using a cold cathode array using a tip (spindt) type Mo material, an oxidizing gas is generated in the vacuum tube during operation, and as a result, a decrease in the anode current with time occurs. Non-patent document 4 describes that hydrogen gas is effective for preventing such a decrease in anode current. In the technique described in non-patent document 4, a metal hydride is arranged in an electron (primary electron) flow from a cathode to an anode, and hydrogen gas generated when electrons collide with the metal hydride is used.
Disclosure of Invention
Problems to be solved by the invention
However, in the above-described conventional technique, it is difficult to sufficiently suppress a decrease with time in the anode current generated in the cold cathode X-ray tube. That is, with the method of first gradually increasing the extraction voltage, if the extraction voltage becomes excessively large, discharge occurs, and therefore the decrease in the anode current with time cannot be sufficiently offset. Further, the method using hydrogen gas has a difficulty in that a metal hydride needs to be coated on a target in order to arrange the metal hydride in an electron (primary electron) flow from a cathode to an anode, and thus cannot be directly applied to a cold cathode X-ray tube. This point will be described in detail below.
In the case of an X-ray tube, a target as a generation source of X-rays is disposed in a portion of an anode surface that directly collides with a flow of electrons (primary electrons) from a cathode to an anode. Therefore, in order to arrange the metal hydride in the electron (primary electron) flow from the cathode to the anode, it is necessary to coat the target with the metal hydride.
However, the target is required to be baked at a high temperature, and if such baking is performed, hydrogen is released from the metal hydride, so that it is difficult to coat the target with the metal hydride for the purpose of generating hydrogen gas. Further, since the target is also at a high temperature during the operation of the X-ray tube, even if it is possible to coat with the metal hydride, film peeling or cracking occurs in the metal hydride due to the high temperature during the operation, and the target cannot function as a hydrogen gas supply source.
Accordingly, an object of the present invention is to provide a cold cathode X-ray tube: stable driving can be performed for a long time by preventing a decrease in the anode current with time.
Means for solving the problems
The cold cathode X-ray tube of the present invention includes: an electron emission unit including an electron emission element using a cold cathode; an anode portion disposed to face the electron emission portion; a target disposed on a part of a surface of the anode portion; a case in which the electron emitting unit, the anode unit, and the target are arranged; and a hydrogen generating portion which is made of a material that generates hydrogen when colliding with electrons, and is disposed in a portion other than the surface of the target among surfaces existing inside the housing.
Effects of the invention
In the cold cathode X-ray tube, since scattered electrons collide with a portion of the anode surface other than a portion directly colliding with an electron flow from the cathode toward the anode (including other surfaces existing inside the case), according to the present invention, hydrogen gas can be generated during operation of the X-ray tube even if the hydrogen generating portion is disposed in a portion other than the surface of the target. Therefore, since the anode current is prevented from decreasing with time, it is possible to provide a cold cathode type X-ray tube capable of stable driving for a long time.
Drawings
Fig. 1 (a) is a schematic cross-sectional view of a cold cathode X-ray tube 1 according to an embodiment of the present invention, and fig. 1 (b) is a schematic cross-sectional view of an
Fig. 2 is a diagram schematically showing temporal changes in anode current of a cold cathode X-ray tube.
Fig. 3 is a schematic cross-sectional view of a cold cathode X-ray tube 1 according to modification 1 of the embodiment of the present invention.
Fig. 4 is a schematic cross-sectional view of a cold cathode X-ray tube 1 according to
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Fig. 1 (a) is a schematic cross-sectional view of a cold cathode X-ray tube 1 according to an embodiment of the present invention. As shown in the drawing, the X-ray tube 1 has a structure in which an
The
Fig. 1 (b) is a schematic cross-sectional view of the
The
The
The focusing
The
The
The
The
When the primary electrons emitted from the
As described above, according to the cold cathode X-ray tube 1 of the present embodiment, since the anode current is prevented from being lowered with time, it is possible to provide a cold cathode X-ray tube capable of being stably driven for a long time. In addition, according to the cold cathode X-ray tube 1 of the present embodiment, since the
Fig. 2 is a diagram schematically showing temporal changes in anode current of a cold cathode X-ray tube. In the figure, the horizontal axis represents time, and the vertical axis represents anode current. A curve C1 shown in the figure represents a change in the anode current of the cold cathode X-ray tube 1 according to the present embodiment, and a curve C2 represents a change in the anode current of the cold cathode X-ray tube in a state where the
As shown in fig. 2, when the
Fig. 3 is a schematic cross-sectional view of a cold cathode X-ray tube 1 according to modification 1 of the embodiment of the present invention. In the present modification, the
According to the present modification, electrons scattered in the lateral direction (backscattered electrons) among the electrons emitted from the
Fig. 4 is a schematic cross-sectional view of a cold cathode X-ray tube 1 according to
According to the present modification, among the electrons emitted from the
While the preferred embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and it is needless to say that the present invention can be implemented in various forms without departing from the scope of the present invention.
Description of the reference symbols
1: a cold cathode type X-ray tube; 2: a control device; 10: an electron emitting portion; 11: an anode section; 11 a: an anode face; 12: a target; 13: a focusing configuration; 13 h: a window; 14: a hydrogen generation unit; 15: a housing; 20: a cathode portion; 21: an electron emitting element; 22: a gate electrode; 22 h: an opening part; p: a power source; t: a transistor.
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