WO2017073523A1

WO2017073523A1 - Rotating anode x-ray tube

Info

Publication number: WO2017073523A1
Application number: PCT/JP2016/081465
Authority: WO
Inventors: 英隆中林; 阿武　秀郎
Original assignee: 東芝電子管デバイス株式会社
Priority date: 2015-10-28
Filing date: 2016-10-24
Publication date: 2017-05-04
Also published as: WO2017073109A1

Abstract

This rotating anode X-ray tube is provided with a fixed shaft, a rotor, a cathode, an anode target, and a vacuum envelope. The cathode is provided with a first filament, and an electron focusing cup. The electron focusing cup is provided with a first inclined flat surface, a second inclined flat surface, a valley bottom section, a first focusing groove part, and a first accommodation groove part. The expressions α>0˚, β>0˚, and α+β≤21˚ are satisfied.

Description

Rotating anode X-ray tube

Embodiments of the present invention relate to a rotary anode type X-ray tube.

Conventionally, an X-ray tube apparatus is used as an X-ray generation source in medical equipment and industrial equipment that diagnose a subject using X-rays. As an X-ray tube device, a rotary anode type X-ray tube device including a rotary anode type X-ray tube is known.

The rotary anode X-ray tube device includes a rotary anode X-ray tube that emits X-rays, a stator coil, a housing that accommodates the rotary anode X-ray tube and the stator coil, and the like. The rotary anode type X-ray tube includes a fixed shaft, a cathode for generating electrons, an anode target, a rotating body, a vacuum envelope, and the like. The rotating body is connected to the anode target and is rotated by a magnetic field generated from the stator coil. The cathode faces the anode target. The anode target emits X-rays when electrons emitted from the cathode collide. Here, a technique in which the cathode is disposed so that the tip surface of the cathode facing the anode target is perpendicular to the tube axis, and the tip surface of the cathode facing the anode target is directed to the fixed axis side. A technique is disclosed in which the cathode is tilted.

US Pat. No. 5,136,625 US Pat. No. 6,256,375

An object of the present embodiment is to provide a rotary anode type X-ray tube capable of improving input to an anode target.

A rotary anode X-ray tube according to an embodiment is:
A fixed shaft having an X-ray tube axis, a rotating body supported by a bearing around the fixed shaft, a first filament that emits an electron beam, and an electron convergence that converges the electron beam emitted from the first filament A cathode having a cup; and a first focal point facing the cathode, the electron beam emitted from the first filament collides and emits X-rays in a main radiation direction perpendicular to the X-ray tube axis. An electron target that has a target surface that is connected to the rotating body, and a vacuum envelope that has a glass container surrounding the anode target and accommodates the cathode and the anode target. The cup has a first inclined flat surface, a second inclined flat surface, a valley bottom portion located between the first inclined flat surface and the second inclined flat surface, and an opening in the first inclined flat surface. 1st yield A groove, and a first storage groove having an opening on the bottom surface of the first converging groove, and storing the first filament, and a straight line parallel to the X-ray tube axis from the center of the first focus. A reference axis, a plane including the reference axis and the main radiation direction as a first reference plane, a virtual straight line extending from the valley bottom portion as a first extension line, the main radiation direction and the first extension line, When α is an angle formed by α and β is an angle formed by the main radiation direction and the target surface, α> 0 °, β> 0 °, and α + β ≦ 21 °.

A rotary anode X-ray tube according to an embodiment is:
A fixed shaft having an X-ray tube axis, a rotating body supported by a bearing around the fixed shaft, a filament for emitting an electron beam, and an electron focusing cup for converging the electron beam emitted from the filament. A cathode having a target surface facing the cathode and having a focal point for emitting X-rays in a main radiation direction perpendicular to the X-ray tube axis by colliding with an electron beam emitted from the filament; An anode target connected to a rotating body; and a vacuum envelope having a glass container surrounding the anode target, and containing the cathode and the anode target, wherein the electron focusing cup faces the anode target. A first groove, a converging groove having an opening on the first surface, and a storage groove having an opening on the bottom surface of the converging groove and accommodating the filament. A straight line parallel to the X-ray tube axis from the center of the focal point is used as a reference axis, and a plane including the reference axis and the main radiation direction is defined as a first reference surface. If the angle formed by one surface is α and the acute angle formed by the main radiation direction and the target surface on the first reference surface is angle β, α> 0 °, β> 0 °, α + β ≦ 21 ° It is characterized by being.

FIG. 1 is a cross-sectional view showing a rotating anode X-ray tube apparatus according to the first embodiment. FIG. 2 is a cross-sectional view showing the cathode of the rotary anode X-ray tube apparatus according to the first embodiment along the YZ plane. FIG. 3 is a plan view showing a state where the cathode shown in FIG. 2 is viewed from the anode target side. FIG. 4 is a cross-sectional view showing a part of the rotary anode X-ray tube apparatus according to the first embodiment, showing a cathode, an anode target, and the like. FIG. 5 is a plan view of the anode target shown in FIG. 1 as viewed from the cathode side, and shows an electron irradiation region and the like. FIG. 6 is a cross-sectional view showing a part of a rotary anode type X-ray tube apparatus according to a modification of the first embodiment, showing a cathode, an anode target, and the like. FIG. 7 is a cross-sectional view showing a part of the rotary anode X-ray tube apparatus according to the second embodiment along the YZ plane, and shows a cathode, an anode target, and the like. FIG. 8 is a plan view showing a state where the cathode shown in FIG. 7 is viewed from the anode target side. FIG. 9 is a cross-sectional view showing a part of the rotary anode X-ray tube apparatus according to the second embodiment along the XZ plane, and shows a cathode, an anode target, and the like. FIG. 10 is a cross-sectional view showing a part of the rotary anode X-ray tube of Comparative Example 1 along the XZ plane, showing the cathode, the anode target, and the like.

Hereinafter, embodiments of the present invention and modifications thereof will be described with reference to the drawings. It should be noted that the disclosure is merely an example, and those skilled in the art can easily conceive of appropriate changes while maintaining the gist of the invention are naturally included in the scope of the present invention. In addition, for the sake of clarity, the drawings may be schematically represented with respect to the width, thickness, shape, etc. of each part as compared to actual aspects, but are merely examples, and The interpretation is not limited. In addition, in the present specification and each drawing, components that perform the same or similar functions as those described above with reference to the previous drawings are denoted by the same reference numerals, and repeated detailed description may be omitted as appropriate. .

First, the rotating anode X-ray tube apparatus according to the first embodiment will be described. FIG. 1 is a cross-sectional view showing a rotary anode X-ray tube apparatus 100 according to the first embodiment. The description of FIG. 1 can also be applied to the description of a second embodiment described later. The first direction X and the second direction Y are orthogonal to each other. The third direction Z is orthogonal to the first direction X and the second direction Y. The XY plane is a plane defined by the first direction X and the second direction Y. The XZ plane is a plane defined by the first direction X and the third direction Z. The YZ plane is a plane defined by the second direction Y and the third direction Z.

As shown in FIG. 1, a rotary anode X-ray tube device 100 houses a rotary anode X-ray tube 1, a stator coil 2 that is a coil for generating a magnetic field, the rotary anode X-ray tube 1, and a stator coil 2. The housing 3 and the control unit 4 are provided. The rotary anode type X-ray tube 1 includes a fixed shaft 10, a rotating body 20, a cathode support component 30, a cathode 60, an anode target 50, a vacuum envelope 70, and the like.

The fixed shaft 10 is formed in a cylindrical shape and extends along the X-ray tube axis A parallel to the third direction Z. One end of the fixed shaft 10 is exposed to the outside of the vacuum envelope 70. The fixed shaft 10 is formed using a material such as Fe (iron) or Mo (molybdenum), for example.

The rotating body 20 has a cylindrical portion 21 formed in a cylindrical shape with one end opened, and a connecting portion 22 formed on the side opposite to the opened side of the cylindrical portion 21. The cylindrical portion 21 and the connecting portion 22 extend along the X-ray tube axis A. That is, the rotating body 20 is provided coaxially with the fixed shaft 10. The rotating body 20 is rotatably supported around the fixed shaft 10 by a bearing (not shown) disposed between the fixed shaft 10 and the cylindrical portion 21. The cylindrical portion 21 faces the stator coil 2 with the vacuum envelope 70 interposed therebetween. The rotating body 20 is formed using a material such as Fe, Mo, or Cu, for example.

The cylindrical portion 21 of the rotating body 20 and the fixed shaft 10 are provided with a gap (a minute gap) (not shown). Here, the bearing is, for example, a dynamic pressure bearing using a liquid metal as a lubricant. A liquid metal (not shown) is filled in a gap between the cylindrical portion 21 and the fixed shaft 10. As the liquid metal, a material such as a Galn (gallium / indium) alloy or a GaInSn (gallium / indium / tin) alloy can be used. Liquid metal has the property of becoming liquid at room temperature. In addition, liquid metal has a characteristic of low vapor pressure. For this reason, a liquid metal can be used inside the rotary anode X-ray tube in a vacuum state. The bearing is formed using the fixed shaft 10, the rotating body 20, and a liquid metal. The bearing is not limited to the above-described dynamic pressure bearing, and can take various forms.

The cathode support component 30 is formed in a flat plate shape, and has a surface 30A on the anode target 50 side and a surface 30B on the opposite side of the surface 30A. In the illustrated example, the surface 30A and the surface 30B are formed perpendicular to the X-ray tube axis A. The cathode support component 30 supports the cathode 60 on the surface 30A, and is fixed to the cathode assembly 31 on the surface 30B. The cathode structure 31 is fixed to the inner wall of the vacuum envelope 70. The cathode structure 31 faces the anode target 50 in the third direction Z.

The cathode 60 is fixed to the cathode support component 30. The cathode 60 has an electron converging cup 15 and a filament coil as a filament. For example, the filament coil is formed using a material whose main component is tungsten. In the first embodiment, the cathode 60 has a first filament coil 61 as a first filament and a second filament coil 62 as a second filament described later. In a second embodiment to be described later, the cathode 60 has a third filament coil 61 as a filament. Note that the number of filaments included in the cathode 60 is not limited to one or two. The cathode 60 only needs to have at least one filament. Further, the filament is not limited to the filament coil, and can be variously modified. For example, a flat filament may be used.

The anode target 50 is formed in a disk shape and is connected to the connection portion 22 of the rotating body 20. The anode target 50 is provided coaxially with the fixed shaft 10 or the like. The anode target 50 rotates integrally with the rotating body 20. The anode target 50 is formed of, for example, molybdenum or tungsten, or an alloy using these.

The anode target 50 has an annular X-ray radiation layer 51 and a target base 52. The X-ray emission layer 51 is formed on the side of the target substrate 52 facing the cathode 60, and has a target surface 50 A on the side facing the cathode 60. The anode target 50 forms a focal point on the target surface 50A and generates X-rays from the focal point when electrons emitted from the cathode 60 collide with the target surface 50A. The X-ray emission layer 51 is made of a metal having a high melting point. Here, the X-ray radiation layer 51 is formed of a tungsten alloy. The anode target 50 is electrically connected to the terminal 91 through the fixed shaft 10 and the rotating body 20.

In the illustrated example, the connecting portion 22 and the target base 52 are formed separately, but the target base 52 may be integrally formed of the same material as the connecting portion 22. Moreover, the shape of the anode target 50 shown in FIG. 1 is an example, and the anode target 50 can take various shapes.

The vacuum envelope 70 accommodates the fixed shaft 10, the rotating body 20, the cathode 60, the anode target 50, and the like. The vacuum envelope 70 is sealed and the inside is maintained in a vacuum state (depressurized state). The vacuum envelope 70 has a glass container 70a and a connecting portion 70b. The glass container 70a surrounds at least the anode target 50. On the one hand, the connection part 70b is airtightly connected to the glass container 70a by fusion, and on the other hand, it is airtightly connected to the fixed shaft 10. The glass container 70a is made of, for example, borosilicate glass. The connection part 70b is made of, for example, Kovar as a metal. Since the coefficient of thermal expansion of Kovar is substantially equal to the coefficient of thermal expansion of borosilicate glass, it is desirable to use Kovar for the connecting portion 70b. The vacuum envelope 70 has an opening 71. The opening 71 is formed in the connection portion 70b. The opening 71 is airtightly joined to one end of the fixed shaft 10 so as to maintain the sealed state of the vacuum envelope 70. In the illustrated example, the rotary anode X-ray tube 1 employs a one-end support bearing structure. The vacuum envelope 70 fixes one end of the fixed shaft 10. That is, one end portion of the fixed shaft 10 functions as a cantilever support portion of the bearing.

The stator coil 2 faces the side surface of the cylindrical portion 21 of the rotating body 20 and is provided so as to surround the outside of the vacuum envelope 70 in an annular shape. Stator coil 2 is electrically connected to a terminal (not shown) and driven through the terminal.

The housing 3 accommodates the rotating anode type X-ray tube 1 and the stator coil 2. The housing 3 is sealed. The housing 3 has an X-ray transmission window 3a that transmits X-rays in the vicinity of the X-ray emission layer 51 on the cathode 60 side. The cooling liquid L is filled in a space between the rotary anode X-ray tube 1 and the housing 3. In the present embodiment, the coolant L is an insulating oil. The material of the coolant L is not particularly limited, and various materials such as an insulating coolant and an aqueous coolant can be used.

The control unit 4 is electrically connected to the cathode 60 via

terminals

81, 82, 83. The control unit 4 drives or controls any one of the plurality of filament coils, or simultaneously performs two or more drives or controls among the plurality of filament coils. When driving the cathode 60, a circuit (not shown) connected to the

terminals

81, 82, and 83 may be used, and terminals other than the

terminals

81, 82, and 83 may be used.

Next, the operation of the rotary anode X-ray tube apparatus 100 will be described.
In the operation of the rotary anode X-ray tube device 100, the stator coil 2 is driven via a terminal (not shown) to generate a magnetic field to be applied to the rotating body 20. For this reason, the rotating body 20 rotates together with the anode target 50. The control unit 4 supplies a current for driving the filament coil of the cathode 60 via the terminals 81 to 83. When the cathode 60 includes a plurality of filament coils, the control unit 4 drives at least one filament coil. In the first embodiment, the control unit 4 drives one filament coil of the first and second filament coils or drives two filament coils simultaneously. In the second embodiment to be described later, the control unit 4 drives one filament. A relatively negative voltage is applied to the driven filament coil. A relatively positive voltage is applied to the anode target 50. That is, a voltage (tube voltage) is applied between the anode target 50 and the cathode 60. A potential difference is generated between the cathode 60 and the anode target 50. Electrons emitted from the filament coil are converged and accelerated toward the anode target 50 and collide with the X-ray emission layer 51. That is, a current (tube current) flows from the cathode 60 to the focal point on the target surface 50A. The target surface 50A emits X-rays from the focal point when electrons collide. Thereby, the X-rays generated from the target surface 50A pass through the vacuum envelope 70 and are emitted to the outside of the housing 3 through the X-ray transmission window 3a.

FIG. 2 is a sectional view showing the cathode 60 of the rotary anode X-ray tube apparatus according to the first embodiment along the YZ plane. FIG. 2 shows a side view of a part of the anode target 50 in a state viewed from the direction opposite to the first direction X.
As shown in FIG. 2, the cathode 60 includes a first filament coil 61 and a second filament coil 62 that emit electrons, and an electron converging cup 15. The filament coil and the electron converging cup 15 are electrically connected to a plurality of terminals such as the

terminals

81, 82, and 83 shown in FIG. The filament coil emits electrons when supplied with current. The electron converging cup 15 converges electrons emitted from the filament coil. In the illustrated example, a focal point BM is formed on the target surface 50 A of the anode target 50.

The electron converging cup 15 includes a front surface 15A, a first inclined flat surface 160, a second inclined flat surface 170, a first converging groove portion 16, a second converging groove portion 17, a first storage groove portion 26, and a second storage space. And a groove portion 27. Here, the electron focusing cup 15 and the first filament coil 61 form one electron gun. The electron converging cup 15 and the second filament coil 62 form one electron gun.

The front surface 15 A is a flat surface and faces the anode target 50. That is, the front surface 15 A corresponds to the front surface of the cathode 60. Further, the front surface 15 A is closest to the anode target 50 in the cathode 60.

The first inclined flat surface 160 and the second inclined flat surface 170 are inclined with respect to the front surface 15A. That is, the first inclined flat surface 160 and the second inclined flat surface 170 are inclined from the XY plane so that the two electron guns can form the focal point BM at the same position. The electron converging cup 15 has a valley bottom portion M between the first inclined flat surface 160 and the second inclined flat surface 170. In the present embodiment, the valley bottom portion M is located at the boundary between the first inclined flat surface 160 and the second inclined flat surface 170. That is, the first inclined flat surface 160 and the second inclined flat surface 170 are inclined so as to be substantially line symmetric with respect to the line segment along the third direction Z passing through the valley bottom portion M. In the present embodiment, the valley bottom portion M is located on the XZ plane and is parallel to the front surface 15A in the XZ plane. Of the distances from the focal point BM to the first inclined flat surface 160 and the second inclined flat surface 170, the distance to the valley bottom portion M is the longest.

The first converging groove 16 has an opening 16 a on the first inclined flat surface 160. Moreover, the 1st convergence groove part 16 has the bottom face 16b. The bottom surface 16b is parallel to the first inclined flat surface 160. The first storage groove 26 has an opening 26 a on the bottom surface 16 b and stores the first filament coil 61. The second converging groove 17 has an opening 17 a on the first inclined flat surface 170. Moreover, the 2nd convergence groove part 12 has the bottom face 17b. The bottom surface 17b is parallel to the second inclined flat surface 170. The second storage groove 27 has an opening 27 a on the bottom surface 17 b and stores the second filament coil 62.

The first inclined flat surface 160 is parallel to the bottom surface 16b, and the second inclined flat surface 170 is parallel to the bottom surface 17b. For this reason, the opening part 26a is parallel to the opening part 16a, and the opening part 27a is parallel to the opening part 17a. The first filament coil 61 extends along a virtual plane parallel to the opening 26a. The second filament coil 62 extends along a virtual plane parallel to the opening 27a.

Among the focal points BM formed on the target surface 50A, a focal point that emits X-rays in the main radiation direction when electrons emitted from the first filament coil 61 are incident on the target surface 50A is defined as a first focal point F1. On the other hand, of the focal point BM formed on the target surface 50A, the focal point that emits X-rays in the main radiation direction when electrons emitted from the second filament coil 62 are incident on the target surface 50A is defined as the second focal point F2. To do. In the present embodiment, the center position of the first focus F1 and the center position of the second focus F2 are the same position. However, in this embodiment, since the structures of the two electron guns are different, the dimension of the first focal point F1 and the dimension of the second focal point F2 are different. As will be described later, for example, the dimension of the first filament coil 61 and the dimension of the second filament coil 62 are different.

Here, the reference axis RA passes through the focal point BM. The reference axis RA is an axis that passes through the center of the first focal point F1 and is parallel to the third direction Z. As described above, since the center positions of the first focus F1 and the second focus F2 are the same, the reference axis RA also passes through the center of the second focus F2. A plane including the reference axis RA and the main radiation direction d is defined as a first reference plane S1.

FIG. 3 is a plan view showing a state in which the cathode 60 shown in FIG. 2 is viewed from the anode target 50 side.
As shown in FIG. 3, the dimensions of the first filament coil 61 and the second filament coil 62 are different. In the illustrated example, the first filament coil 61 is larger than the second filament coil 62 in the first direction X. The converging first converging groove 16 and the second converging groove 17 have a long axis parallel to the first reference plane S1. Moreover, the 1st storage groove part 26 and the 2nd storage groove part 27 have a long axis, respectively. The first filament coil 61 and the second filament coil 62 are each formed to extend linearly and have a long axis.

FIG. 4 is a cross-sectional view showing a part of the rotary anode X-ray tube apparatus 100 according to the first embodiment, showing the cathode 60, the anode target 50, and the like. FIG. 4 shows a cross section along the XZ plane passing through the reference axis RA of the cathode 60 and the anode target 50. FIG. 5 is a plan view of the anode target 50 shown in FIG. 1 as viewed from the cathode 60 side, and shows an electron irradiation region and the like. The main radiation direction d of X-rays is located on the same plane as the XZ plane passing through the reference axis RA. In the present embodiment, the main radiation direction d is parallel to the first direction X and passes through the center of the focal point. The main radiation direction d is perpendicular to the reference axis RA. In addition, the shape when the focal point formed on the target surface 50A is viewed from the outside of the rotary anode X-ray tube 1 in the direction opposite to the main radiation direction d may be referred to as an effective focal point.

Here, in the XZ plane, a virtual straight line extending along the valley bottom portion M is defined as a first extension line E1, a virtual straight line extending along the target surface 50A is defined as a second extension line E2, and the main radiation direction A virtual straight line extending along d is defined as a third extension line E3.
As shown in FIG. 4, the first extension line E1 and the third extension line E3 form an angle α, and the second extension line E2 and the third extension line E3 form an angle β. The angles α and β are acute angles having positive values (0 ° <α <90 °, 0 ° <β <90 °). In this embodiment, for example, α = 4 ° and β = 10 °. Note that the values of the angle α and the angle β are not limited to these, and either the angle α or the angle β may be set larger or equal.

In FIG. 5, an irradiation area AR1 indicates an area irradiated with electrons in the rotary anode type X-ray tube apparatus of the present embodiment. In the irradiation area AR2, for example, the cathode 60 is arranged such that the first extension line E1 is parallel to the third extension line E3, or the first extension line E1 is parallel to the second extension line E2. A region irradiated with electrons when 60 is arranged is shown. The average radius from the X-ray tube axis A to the irradiation area AR1 is r1, and the average radius from the X-ray tube axis A to the irradiation area AR2 is r2. The average radius r1 of the irradiation area AR1 is larger than the average radius r2 of the irradiation area AR2. For example, the average radius r1 is 20% larger than the average radius r2. Further, the irradiation area AR1 has a focal point (electron incident point) BM at a position facing the cathode 60. The focal point BM is a region where electrons are incident at an arbitrary timing.

According to the rotary anode X-ray tube according to the first embodiment configured as described above, the rotary anode X-ray tube 1 includes the cathode 60 and the anode target 50 having the target surface 50A. Yes. The first extension line E1 along the valley bottom portion M and the third extension line E3 along the main radiation direction d form an angle α. That is, the valley bottom portion M is inclined to the side opposite to the anode target 50 by an angle α with respect to the main radiation direction d. Further, the second extension line E2 and the third extension line E3 along the target surface 50A form an angle β. That is, the target surface 50A is inclined to the opposite side of the cathode 60 by an angle β with respect to the main radiation direction d. For this reason, the valley bottom portion M faces the outside of the anode target 50, and the radiation direction e of electrons emitted from the cathode 60 faces the outside of the anode target 50. The average radius r1 of the irradiation area AR1 of the present embodiment is larger than the average radius r2 of the irradiation area AR2. Therefore, the area of the irradiation area AR1 of the anode target 50 irradiated with electrons emitted from the cathode 60 can be increased, and the input to the anode target 50 can be increased.
Therefore, a rotating anode X-ray tube capable of improving the input to the anode target can be obtained.

Of the cathode support component 30, the cathode assembly 31, and the cathode 60 (electron focusing cup 15), which are components having a cathode potential, the component closest to the vacuum envelope 70 is the cathode 60 (electron focusing cup 15). The point Q shown in FIG. 4 is the closest point. Since the shortest distance between the cathode 60 and the vacuum envelope 70 can be maintained at the same level as the conventional one, there is no fear that discharge is likely to occur between the cathode 60 and the vacuum envelope 70.

Further, without adjusting the angle α, it is possible to change the irradiation area AR2 to the irradiation area AR1 by moving the position of the cathode 60 itself away from the X-ray tube axis A. However, in this case, it is not desirable because the cathode 60 approaches or contacts the vacuum envelope 70 and discharge easily occurs. Increasing the inner diameter of the vacuum envelope 70 eliminates the above-mentioned discharge problem. However, since the size of the rotary anode X-ray tube 1 is increased, it is not desirable to increase the inner diameter of the vacuum envelope 70. .

When electrons emitted from the cathode 60 collide with the target surface 50A, about 50% of the electrons are reflected with almost no energy loss. Some of the reflected electrons (recoil electrons) initially collide with the glass container 70a surrounding the anode target 50, but the glass container 70a has electrical insulation, so the surface of the glass container 70a is Charge to negative potential. Then, further collision of recoil electrons with the glass container 70a is suppressed, and overheating of the glass container 70a is suppressed. From the above viewpoint, it is desirable to use the glass container 70 a as a part of the vacuum envelope 70.

According to the experiments by the present inventors, among the recoil electrons radiated from the focal point BM, the amount of recoil electrons toward the glass container 70a is larger as the angle β is larger. Therefore, it is desirable that the angle β is in the range of β ≦ 21 ° which is conventionally employed. By limiting the angle β to the range of β ≦ 21 °, among the recoil electrons radiated from the focal point BM, the amount of the recoil electrons directed to the glass container 70a can be kept at an acceptable level as before. . When the angle β is in the range of 21 ° <β, the recoil electrons toward the glass container 70a increase compared to the conventional case. As a result, recoil electrons that initially collide with the inner wall of the glass container 70a are increased, the inner wall of the glass container 70a is heated more than before, and the inner wall of the glass container 70a is dissolved and gas from the inner wall of the glass container 70a is heated. Release may be more likely to occur. This may induce a failure of the X-ray tube.

Further, according to the experiments by the present inventors, the shape distortion of the focal point BM in the rotary anode type X-ray tube having the glass container 70a is almost constant if α + β is constant. Therefore, by limiting α + β to the range of α + β ≦ 21 °, which has been conventionally employed, the shape distortion of the focal point BM can be kept within the conventional allowable level.

That is, by limiting α + β to the range of α + β ≦ 21 °, it is possible to prevent the above-described failure of the rotary anode X-ray tube due to gas release, and the shape distortion of the focal point BM is as high as the conventional level. Can fit in.

When X-ray imaging is performed with the rotary anode X-ray tube apparatus 100 equipped with the rotary anode X-ray tube 1 as described above, the anode target 50 is, for example, 150 rps (the number of rotations of the anode target 50 per second). Alternatively, while rotating at a higher speed, electrons emitted from the cathode 60 are applied to the target surface 50A of the X-ray emission layer 51 to emit X-rays. The heat generated in the X-ray radiation layer 51 is conducted to the target base 52 and accumulated in the entire anode target 50, while being gradually dissipated mainly by radiation.

Here, the temperature of the irradiation area AR1 is Tf. Let Ts be the temperature of the focal point BM. Note that the temperature Tf of the irradiation area AR1 represents the average temperature of the irradiation area AR1 excluding the focal point BM, and the temperature Ts of the focal point BM represents the highest temperature reached at the moment at the focal position. Then, the average temperature Tb of the target base 52 rises due to heat accumulation based on the difference between the amount of heat input due to the incidence of electrons on the anode target 50 and the amount of heat dissipated due to heat dissipation or the like, or decreases due to heat dissipation.

The temperature Ts of the focal point BM becomes a peak temperature due to the instantaneous input heat amount due to the electron incidence at the focal point position in addition to the temperature Tf of the irradiation area AR1. Further, the temperature Ts of the focal point BM is relatively greatly influenced by the rotational speed of the anode target 50 because the instantaneous heat storage action at the focal point BM differs depending on the rotational speed of the anode target 50. That is, when compared with the temperature Tf of the same irradiation area AR1, if the rotation speed of the anode target 50 is low, the temperature Ts of the focal point BM is relatively high, and if the rotation speed of the anode target 50 is high, the focal point BM. The temperature Ts is closer to the temperature Tf.

The temperature of each part of the anode target 50 can be expressed by the following approximate expression as shown in a paper published in Toshiba Review Vol. 37, No. 9, pp. 777-780.

Ts = Tf + (2 · P · w ^−1/2 ) / [S · (π · ρ · C · λ · ν) ^−1/2 ]
Here, P is the incident power of electrons, that is, the input power to the anode target 50, w is the width of the incident electrons in the rotation direction of the anode target 50 (that is, the focal width), and S is the area of the electron incident surface (that is, the focal point). ), Ρ is the density of the surface member quality of the anode target 50 (that is, the density of the material of the X-ray radiation layer 51), C is the specific heat of the surface member quality of the anode target 50, and λ is the surface member quality of the anode target 50. The thermal conductivity, ν, represents the peripheral speed of the anode target 50 at the position of the focal point BM.

Further, if the rapid temperature rise value that occurs at the focal position of the anode target 50 is ΔTs and the temperature rise value that occurs on the average in the irradiation region AR1 is ΔTf, the following relationship is established.

Ts = Tb + ΔTf + ΔTs = Tf + ΔTs
ΔTs = (2 · P · w ^−1/2 ) / [S · (π · ρ · C · λ · ν) ^−1/2 ]
As is clear from this, the rapid temperature rise ΔTs that occurs at the focal position of the anode target 50 is approximately proportional to the input power P to the anode target 50 and is also approximately proportional to the square root of the focal spot size w. Is approximately inversely proportional to the area S of the anode target 50 and is also approximately inversely proportional to the square root of the rotational speed of the anode target 50, that is, the square root of the peripheral speed ν of the anode target 50 at the position of the focal point BM.

From the above, when the irradiation region AR1 is formed outside the anode target 50, X-rays can be output continuously over a long period of time, or the amount of heat input to the anode target 50 can be increased. I can do it. That is, it is possible to provide a rotary anode X-ray tube 1 with higher output.

FIG. 6 is a cross-sectional view showing a part of a rotary anode X-ray tube apparatus 100 according to a modification of the first embodiment, and shows a cathode 60, an anode target 50, and the like. FIG. 6 is different from the embodiment shown in FIG. 4 in the shapes of the cathode support component 30 and the cathode 60.

The cathode support component 30 has a surface 30A as a third surface. Here, of the surface 30A, a region that is in contact with the cathode 60 and supports the cathode 60 is referred to as a surface 30C. Here, in FIG. 6, a fourth extension line E4 is set as a virtual straight line perpendicular to the X-ray tube axis A. The fourth extension line E4 is located between the valley bottom portion M and the surface 30C. An end P of the surface 30C on the X-ray tube axis A side is located on the fourth extension line E4. The surface 30C is inclined by the angle α from the fourth extension line E4 to the side opposite to the anode target 50. That is, the cathode support component 30 is bent so that the surface 30C is inclined by the angle α with respect to the fourth extension line E4. The valley bottom portion M is parallel to the surface 30C. That is, the valley bottom portion M is inclined by an angle α on the opposite side to the anode target 50 with respect to the fourth extension line E4. In this manner, by bending the cathode support component 30, the valley bottom portion M and the target surface 50A form a positional relationship equivalent to the positional relationship shown in FIG.
Also in such a modification, the same effect as the first embodiment described above can be obtained.

In the above embodiment and modification, the case where the cathode 60 is supported by the cathode support component 30 has been described. However, the rotary anode X-ray tube 1 does not necessarily include the cathode support component 30. . Even in this case, if the valley portion M of the cathode 60 and the target surface 50A of the anode target 50 have the positional relationship shown in the above embodiment and the modification, the same effects as in the above embodiment and the modification are obtained. It is possible to obtain

Next, the rotary anode X-ray tube 1 of the second embodiment will be described.
FIG. 7 is a cross-sectional view showing a part of the rotary anode X-ray tube apparatus 100 according to the second embodiment along the YZ plane, showing the cathode 60, the anode target 50, and the like. FIG. 7 is different from FIG. 2 in that the cathode 60 includes one third filament coil 63.

As shown in FIG. 7, the cathode 60 includes one third filament coil 63 and an electron focusing cup 15. The electron converging cup 15 includes a front surface 15 A as a first surface, a third converging groove 18, and a third storage groove 28. The front surface 15 A is a flat surface and faces the anode target 50.

The third converging groove 18 has an opening 18a on the front surface 15A. Moreover, the 3rd convergence groove part 18 has the bottom face 18b. The bottom surface 18b is parallel to the front surface 15A. The third storage groove 28 has an opening 28 a on the bottom surface 18 b and stores the third filament coil 63.

FIG. 8 is a plan view showing a state in which the cathode 60 shown in FIG. 7 is viewed from the anode target 50 side.
As shown in FIG. 8, the third filament coil 63 is disposed so as to extend in the first direction X and pass through the center of the electron converging cup 15. The opening 18 a and the opening 28 a have a long axis parallel to the first direction X and are provided so as to pass through the center of the electron converging cup 15.

The third filament coil 63 and the electron converging cup 15 are electrically connected to the

terminals

81, 82, 83 as shown in FIG. The third filament coil 63 emits electrons when supplied with current. The electron converging cup 15 converges the electrons emitted from the third filament coil 63.

FIG. 9 is a cross-sectional view showing a part of the rotary anode X-ray tube apparatus 100 according to the second embodiment along the XZ plane, a view showing the cathode 60, the anode target 50, and the like. FIG. 9 is different from FIG. 4 in that the cathode 60 includes one filament coil and thus does not have the valley bottom portion M.

Here, an imaginary straight line extending along the front surface 15A of the cathode 60 in the XZ plane is defined as a fifth extension line E5. As shown in FIG. 9, the fifth extension line E5 and the third extension line E3 form an angle α, and the second extension line E2 and the third extension line E3 form an angle β. The angles α and β are acute angles having positive values (0 ° <α <90 °, 0 ° <β <90 °). In this embodiment, for example, α = 4 ° and β = 10 °. Note that the values of the angle α and the angle β are not limited to this, and either the angle α or the angle β may be set larger or equal.

In the illustrated example, the front surface 15A is inclined to the side opposite to the anode target 50 by an angle α from the main radiation direction d. The target surface 50A is inclined to the side opposite to the cathode 60 by an angle β from the main radiation direction d. For this reason, the front surface 15 A faces the outside of the anode target 50, and the radiation direction e of electrons emitted from the cathode 60 faces the outside of the anode target 50.

Therefore, in the second embodiment, the same effect as in the first embodiment described above can be obtained.

Next, the rotating anode X-ray tube 1 of Comparative Example 1 will be described.
FIG. 10 is a cross-sectional view showing a part of the rotary anode X-ray tube 1 of Comparative Example 1 along the XZ plane, showing the cathode 60, the anode target 50, and the like. The rotating anode X-ray tube 1 of Comparative Example 1 is different in that α = 0 ° compared to the first embodiment shown in FIG. 4 and the second embodiment shown in FIG. Yes. That is, the first extension line E1 and the third extension line E3 are parallel.

In Comparative Example 1, α + β ≦ 21 °. The electron radiation direction e in the vicinity of the filament coil is parallel to the reference axis RA. That is, the average radius of the electron irradiation area AR2 at this time is smaller than the average radius r1 of the irradiation area AR1 of the above embodiment, and is substantially the same as the average radius r2 of the irradiation area AR2 shown in FIG. For this reason, in Comparative Example 1 in which α = 0 °, it is difficult to obtain the rotary anode X-ray tube 1 that can improve the input to the anode target.

Next, the rotating anode X-ray tube 1 of Comparative Example 2 will be described.
The rotating anode X-ray tube 1 of Comparative Example 2 is different in that α <0 ° compared to the first embodiment shown in FIG. 4 and the second embodiment shown in FIG. Yes. In Comparative Example 2, α + β ≦ 21 °. For example, in Comparative Example 2, it is conceivable to dispose the cathode 60 so that the valley bottom portion M (front surface 15A) is parallel to the target surface 50A. By setting α <0 °, it is possible to easily obtain a focal shape with little distortion. However, in Comparative Example 2, similarly to Comparative Example 1, the average radius of the electron irradiation region is smaller than the average radius r1 of the irradiation region AR1 of the above embodiment, and the average of the irradiation region in Comparative Example 1 is as follows. Even smaller than the radius. For this reason, in Comparative Example 2 in which α <0 °, it is difficult to obtain the rotating anode X-ray tube 1 capable of improving the input to the anode target.

In addition, although several embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

For example, the filament is not limited to a filament coil, and may be a flat filament, for example.

For example, although the case where the valley bottom portion M is linear is shown in the first embodiment, the valley bottom portion M may be a flat surface perpendicular to the first reference plane S1. In this case, the cathode 60 may include three filament coils. Even if the third converging groove and the third storage groove are formed in the valley portion M, and the third filament coil is disposed in the storage groove. good.

In the first embodiment, the opening of the converging groove and the opening of the storage groove are arranged in parallel to the valley bottom portion M, but they are not necessarily arranged in parallel.

Furthermore, although the case where the electron focusing cup 15 has the flat front surface 15A is shown in the first embodiment, the electron focusing cup 15 may not have the flat front surface 15A.

The embodiment of the present invention is not limited to the rotary anode X-ray tube 1 described above, but can be applied to various types of rotary anode X-ray tubes.

Claims

A fixed shaft having an X-ray tube axis;
A rotating body supported by a bearing around the fixed shaft;
A cathode comprising: a first filament that emits an electron beam; and an electron focusing cup that converges the electron beam emitted from the first filament;
Opposite the cathode, and having a target surface on which a first focal point is formed which emits X-rays in a main radiation direction perpendicular to the X-ray tube axis by colliding with an electron beam emitted from the first filament, An anode target connected to the rotating body;
A glass container surrounding the anode target, and a vacuum envelope containing the cathode and the anode target,
The electron converging cup includes a first inclined flat surface, a second inclined flat surface, a valley bottom portion located between the first inclined flat surface and the second inclined flat surface, and the first inclined flat surface. A first converging groove having an opening; and a first storage groove having an opening on a bottom surface of the first converging groove and accommodating the first filament.
A straight line parallel to the X-ray tube axis from the center of the first focus is used as a reference axis,
A plane including the reference axis and the main radiation direction is a first reference plane,
A virtual straight line extending from the valley bottom portion is defined as a first extension line,
An angle formed by the main radiation direction and the first extension line is α,
If the angle formed by the main radiation direction and the target surface is β,
A rotary anode type X-ray tube characterized by α> 0 °, β> 0 °, and α + β ≦ 21 °.
And a cathode support component having a third surface for supporting the cathode,
When a virtual plane located between the valley bottom portion and the third surface and perpendicular to the X-ray tube axis is defined as a third vertical surface,
2. The rotary anode type X-ray according to claim 1, wherein an end of the third surface on the X-ray tube axis side is located on the third vertical surface, and the third surface is inclined from the third vertical surface. tube.
The cathode includes a second filament that emits an electron beam;
The electron converging cup includes a second converging groove having an opening in the second inclined flat surface, and a first receiving groove having an opening in the bottom surface of the second converging groove and accommodating the second filament. The rotary anode X-ray tube according to claim 1, comprising:
A fixed shaft having an X-ray tube axis;
A rotating body supported by a bearing around the fixed shaft;
A cathode comprising: a filament that emits an electron beam; and an electron focusing cup that focuses the electron beam emitted from the filament;
Opposite to the cathode, the electron beam emitted from the filament collides and has a target surface on which a focal point for emitting X-rays in a main radiation direction perpendicular to the X-ray tube axis is formed and connected to the rotating body An anode target,
A glass container surrounding the anode target, and a vacuum envelope containing the cathode and the anode target,
The electron converging cup includes a first surface facing the anode target, a converging groove having an opening in the first surface, a housing groove having an opening in the bottom surface of the converging groove and accommodating the filament, Have
A straight line parallel to the X-ray tube axis from the center of the focal point is a reference axis,
A plane including the reference axis and the main radiation direction is a first reference plane,
An angle formed by the main radiation direction and the first surface in the first reference plane is α,
When an acute angle formed by the main radiation direction and the target surface in the first reference plane is an angle β,
A rotary anode type X-ray tube characterized by α> 0 °, β> 0 °, and α + β ≦ 21 °.
And a cathode support component having a third surface for supporting the cathode,
When a virtual plane located between the first surface and the third surface and perpendicular to the X-ray tube axis is defined as a third vertical surface,
5. The rotary anode X-ray according to claim 4, wherein an end of the third surface on the X-ray tube axis side is located on the third vertical surface, and the third surface is inclined from the third vertical surface. tube.
Furthermore, a cathode support component having a support surface for supporting the cathode,
The rotary anode type X-ray tube according to claim 1, wherein the support surface is perpendicular to the X-ray tube axis.