Patent Grant
10032597
Field of the Invention
The present invention relates to a transmission X-ray generating tube, an X-ray generating apparatus, and an X-ray imaging system with an anode, and an anode used therefor, the anode including a target for generating an X-ray through irradiation of an electron beam and a tubular anode member with an opening for holding the target.
Description of the Related Art
A transmission X-ray generating tube including a transmission target is known. The transmission target uses an X-ray emitted from a side thereof, which is opposite to a side, on which an electron beam enters the target. The transmission X-ray generating tube may include a target made of diamond as an end window of the X-ray generating tube. Such a transmission X-ray generating tube has advantageous features in that a radiation angle can become wider, heat dissipation performance can become higher, and an X-ray generating apparatus can be downsized. The target in such a transmission X-ray generating tube is hermetically bonded to an anode member via a bonding material such as a silver brazing material, an Ag—Sn based brazing material, or an Au—Sn based brazing material formed on a periphery of the target. Such a brazing material is adopted that has a melting point of from 200° C. to a temperature of the anode member when operated or higher. When the Ag—Sn based brazing material is used, by controlling composition ratios therein or using a ternary or higher brazing material, material design of a wide range of melting points is possible (100° C. to 900° C.)
In Japanese Patent Application Laid-Open No. 2013-51153, there is disclosed a transmission X-ray generating tube including a tubular anode member having opening diameter with a distribution and a transmission target held by the anode member. Further, in Japanese Patent Application Laid-Open No. 2013-55041, there is disclosed an X-ray generating tube including a tubular anode member formed of a member having a high X-ray blocking property and a thermally conductive member, and a transmission target held by the anode member. In such an X-ray generating tube including the transmission target as an end window, when X-ray generating operation is repeated, a desired tube current sometimes cannot be obtained and hence it is difficult to secure a necessary X-ray output. A transmission X-ray generating tube that can obtain a stable X-ray output has been required.
However, both of the structures disclosed in Japanese Patent Application Laid-Open No. 2013-51153 and in Japanese Patent Application Laid-Open No. 2013-55041 have the following problem. That is, as X-ray generating operation and X-ray generation stop operation are repeated, vacuum leakage is sometimes caused. When such vacuum leakage is caused, a problem arises that a mean free path of electrons in the atmosphere in the X-ray generating tube is reduced, the tube current is reduced, and the X-ray output is reduced. Thus, the structures are required to be improved.
Review by inventors of the present invention revealed that a cause of reduction in X-ray output described above was a stress amplitude of the anode accompanying the repeated operation of the X-ray generating tube. Specifically, the cause of the reduction in X-ray output was identified as a circumferential tensile stress produced in a bonding material for bonding together the transmission target and the anode member.
It is an object of the present invention to inhibit vacuum leakage from a bonding material for hermetically bonding a target to a surrounding member due to a crack that develops because of a difference in coefficient of thermal expansion between the target and the bonding material, and to increase durability of an X-ray generating tube, and by extension, an X-ray generating apparatus and an X-ray imaging system, and an anode therein.
In order to achieve the above-mentioned object, according to a first aspect of the present invention, there is provided a transmission X-ray generating tube, including an anode including: a target for generating an X-ray through irradiation of an electron beam from an electron emitting source; and a tubular anode member having an opening for holding the target,
the tubular anode member including a first metal tube, and a second metal tube fixed to the first metal tube and having a coefficient of thermal expansion that is larger than a coefficient of thermal expansion of the first metal tube,
in which a peripheral portion of the target is bonded to the tubular anode member via a bonding material arranged so as to extend over the first metal tube and the second metal tube.
According to a second aspect of the present invention, there is provided an X-ray generating apparatus, including:
a transmission X-ray generating tube; and
a tube voltage circuit,
in which the transmission X-ray generating tube having an anode including: a target for generating an X-ray through irradiation of an electron beam from an electron emitting source; and a tubular anode member having an opening for holding the target,
in which the tube voltage circuit is electrically connected to each of the target and the electron emitting source, for applying a tube voltage between the target and the electron emitting source.
According to a third aspect of the present invention, there is provided an X-ray imaging system, including:
an X-ray generating apparatus;
an X-ray detector for detecting an X-ray that is emitted from the X-ray generating apparatus and passes through a subject; and
a system control device for integrally controlling the X-ray generating apparatus and the X-ray detector,
in which the X-ray generating apparatus, including:
a transmission X-ray generating tube; and
a tube voltage circuit;
in which the transmission X-ray generating tube having an anode including: a target for generating an X-ray through irradiation of an electron beam from an electron emitting source; and a tubular anode member having an opening for holding the target,
in which the tube voltage circuit is electrically connected to each of the target and the electron emitting source, for applying a tube voltage between the target and the electron emitting source.
Further, according to a fourth aspect of the present invention, there is provided an anode for an X-ray generating tube to be used in a transmission X-ray generating tube, the anode including: a target for generating an X-ray through irradiation of an electron beam from an electron emitting source; and a tubular anode member having an opening for holding the target,
the tubular anode member including a first metal tube, and a second metal tube fixed to the first metal tube and having a coefficient of thermal expansion that is larger than a coefficient of thermal expansion of the first metal tube,
in which a peripheral portion of the target is bonded to the tubular anode member via a bonding material arranged so as to extend over the first metal tube and the second metal tube.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present invention are described in the following with reference to the attached drawings, but the present invention is not limited to these embodiments. Note that, well-known or publicly known technologies in the art are to be applied to parts that are not specifically illustrated or described herein.
<Anode and X-Ray Generating Tube>
The X-ray generating tube 102 according to this embodiment includes a cathode 4, an electron emitting source 5 connected to the cathode 4, the anode 2, and an insulating tube 3 sandwiched between the anode 2 and the cathode 4. The anode 2 includes the target 9 for generating an X-ray through irradiation of electrons, a tubular anode member 6 having an opening 18 that is closed by the target 9, and an anode plate 19. In the X-ray generating tube 102 of this embodiment, an X-ray flux 14 is generated by irradiating the target 9 with an electron beam 17 emitted from the electron emitting source 5 included in the electron emission source 15 so that the electron beam 17 collides with the target 9.
As illustrated in
The target layer 21 is an X-ray generation source for emitting a necessary kind of ray by appropriately selecting a material contained in the target layer and a thickness thereof together with a tube voltage Va. As a material of the target layer, for example, a metal material having an atomic number of 40 or more such as Mo (molybdenum), Ta (tantalum), W (tungsten), or the like can be contained. The target layer 21 can be formed on the target base member 22 by an arbitrary film forming method such as vapor deposition or sputtering.
The target base member 22 is formed of a material that transmits an X-ray to a high degree and is highly refractory such as beryllium, natural diamond, or artificial diamond. Of those, a diamond substrate formed of artificial diamond by a high pressure and high temperature method or chemical vapor deposition is preferred from the viewpoint of heat dissipation, reproducibility, uniformity, costs, and the like. It is preferred that the target base member 22 have an outer shape of a rectangular parallelepiped or a disk. The target base member 22 in the shape of a disk can have a diameter of 2 mm or more and 10 mm or less. Further, a lower limit and an upper limit of a thickness of the target base member 22 depend on strength, thermal conductivity in a direction in parallel with the target layer 21, and radiation transmittance, and the thickness is 0.3 mm or more and 4.0 mm or less. In the case where the target base member 22 is in the shape of a rectangular parallelepiped, the range of the diameter described above is replaced with a length of a shorter side and a length of a longer side of a surface of the rectangular parallelepiped. The target base member 22 not only acts as a transmission window for taking an X-ray generated at the target layer 21 out of the X-ray generating tube 102, but also acts as a member forming a vacuum container together with other members.
The anode member 6 not only has the function of defining an anode potential of the target layer 21 but also has the function of holding the target 9. The anode member 6 and the target 9 are bonded together via a bonding material 8. Further, the anode member 6 is electrically connected to the target layer 21 via an electrode (not shown).
The anode member 6 can have the function of blocking an X-ray by being formed of a material having a high specific gravity. From the viewpoint of downsizing the anode member 6, it is preferred that a material forming the anode member 6 have a mass attenuation coefficient μ/ρ [m2/kg] and a density ρ [kg/m3] so that a product thereof is large. Further, from the viewpoint of further downsizing, it is preferred that a metallic element having specific absorption edge energy be appropriately selected as a material forming the anode member 6, based on the kind of the X-ray generated from the target layer 21. The anode member 6 can contain Cu, Ag, Mo, Ta, W, or the like, and can contain the same metallic element as a target metal contained in the target layer 21. The mass attenuation coefficient depends on the voltage, and for example, when the voltage is 100 kV, W: 0.4438, Ta: 0.4302, Mo: 0.1096, Ag: 0.1470, and Cu: 0.04584 [m2/kg]. With regard to a linear attenuation coefficient μ, which is a product of the mass attenuation coefficient and the density, W: 8565.3, Ta: 7162.8, Mo: 1120.1, Ag: 1543.5, and Cu: 410.7 [m−1]. The anode member 6 is in a tubular shape so as to surround the target 9, and thus functions as a forward shielding member that defines a range of an emission angle of an X-ray emitted from the target layer 21 to shape the X-ray into the X-ray flux 14. Further, the anode member 6 functions as a rear block that limits a range in which reflected and backscattered electrons (not shown) or a backscattered X-ray (not shown) reach from the target layer 21 toward the electron emission source 15.
The bonding material 8 is, for example, a brazing material of various kinds such as a silver brazing material, gold brazing material, or a copper brazing material, solder, or the like. Members to be bonded can be bonded together by sandwiching the bonding material 8 in a heat-softened state between the members to be bonded and then cooling the sandwiched bonding material 8. It is preferred that the bonding material 8 be a brazing material from the viewpoint of handleability and bonding power. Among brazing materials, a silver brazing material is preferred, because brazing can be carried out at a relatively low brazing temperature that is high enough to prevent remelting even if the vacuum container is fired at high temperature in a manufacturing step after the brazing.
Electrons contained in the electron beam 17 are accelerated to have incident energy necessary for generating an X-ray by an electric field between the electron emission source 15 and the target 9. The accelerating electric field is incorporated when an X-ray generating apparatus 101 illustrated in
A trunk of the X-ray generating tube 102 is formed by the insulating tube 3 that is formed for electrical insulation purposes between the electron emission source 15 defined at a cathode potential and the target layer 21 defined at the anode potential. The insulating tube 3 is formed of an insulating material such as a glass material or a ceramic material. The insulating tube 3 can also have the function of defining a distance between the electron emission source 15 and the target layer 21.
The fully enclosed space 16 in the X-ray generating tube 102 id depressurized so that the electron emission source 15 functions. It is preferred that the inside of the X-ray generating tube 102 have a vacuum of 10−8 Pa or more and 10−4 Pa or less, and, from the viewpoint of the life of the electron emission source 15, it is further preferred that the vacuum be 10−8 Pa or more and 10−6 Pa or less. It is preferred that, as a vacuum container, the X-ray generating tube 102 have hermeticity for maintaining such a vacuum and a durability against atmospheric pressure. After a vacuum is produced using a vacuum pump (not shown) via a discharge pipe (not shown), the inside of the X-ray generating tube 102 can be depressurized by sealing the discharge pipe. Further, for the purpose of maintaining the vacuum degree, a getter (not shown) may be arranged in the X-ray generating tube 102.
The electron emission source 15 is arranged so as to be opposed to the target layer 21 of the target 9. As the electron emission source 15, for example, a tungsten filament, a hot cathode such as an impregnated cathode, or a cold cathode such as a carbon nanotube can be used. For the purpose of controlling a beam diameter, an electron current density, and on/off of the electron beam 17, the electron emission source 15 can include a grid electrode and an electrostatic lens electrode (not shown).
Basic structures of the anode 2 and the X-ray generating tube 102 are as described above. According to the present invention, in order to prevent a crack from developing due to a circumferential tensile stress of the target 9 that is applied to the bonding material 8 as the state thereof transitions from a heated state when bonded to a cooled and contracted state, the anode 2 has a structure as described below.
A basic form of the anode for the X-ray generating tube according to a first embodiment of the present invention is described with reference to
In the anode 2 according to the first embodiment, the anode member 6 includes a first metal tube 10 and a second metal tube 11. A peripheral portion of the target 9 is bonded to the anode member 6 via the bonding material 8 arranged so as to extend over the first metal tube 10 and the second metal tube 11. The second metal tube 11 has a coefficient of thermal expansion that is larger than that of the first metal tube 10. Further, the target 9 is bonded to an inside of the opening 18 in the anode member 6.
Further, the first metal tube 10 is arranged inside the second metal tube 11, and an inner surface of the second metal tube 11 and an outer surface of the first metal tube 10 are connected to each other at a portion in a tube axial direction of the second metal tube 11 so that the first metal tube 10 and the second metal tube 11 do not move relative to each other at a melting point of the bonding material 8. The first metal tube 10 and the second metal tube 11 are connected to each other by fitting using their difference in coefficient of thermal expansion, heat seal, bonding via a bonding material having a melting point that is higher than that of the bonding material 8, casting, or the like. The first metal tube 10 and the second metal tube 11 are formed on an outer surface side of the anode plate 19 so as to surround a through hole 20 formed in the anode plate 19. The first metal tube 10 is shorter than the second metal tube 11 in the tube axial direction of the second metal tube 11, and a front end (X-ray emission side) of the first metal tube 10 is recessed from a front end of the second metal tube 11. Therefore, the second metal tube 11 has a region in which the inner surface thereof on the front end side is not covered with the first metal tube 10. Any one or both of a rear end of the first metal tube 10 and a rear end of the second metal tube 11 (electron beam incident side and opposite to the X-ray emission side) are in contact with the outer surface of the anode plate 19. A front end side of the anode member 6 is formed only of the second metal tube 11, and the remaining portion has a dual structure formed of the first metal tube 10 and the second metal tube 11, and an inner step is formed using a level difference therebetween by an end face of the first metal tube 10 on the front end side.
The target 9 is formed inside the second metal tube 11 under a state in which the target layer 21 is on the fully enclosed space 16 side of the X-ray generating tube 102. The target 9 is bonded to the anode member 6 via the bonding material 8 intervening in a region between a circumferential side surface of the target base member 22 and a region inside the second metal tube 11 that is not covered with the first metal tube 10, and a region between an outer peripheral portion of a surface of the target 9 on the electron beam irradiation side and the end face of the first metal tube 10 on the front end side. Specifically, the target 9 is bonded to the anode member 6 via the bonding material 8 that is arranged so as to extend over the first metal tube 10 and the second metal tube 11.
As illustrated in
The end face of the first metal tube 10 on the front end side in this embodiment has a step 100 that is opposed to the target 9 in the tube axial direction and overlaps the target 9 in a tube radial direction. Further, the inner surface of the second metal tube 11 includes an opposed portion 111 that is opposed to a circumferential side surface of the target 9. The bonding material 8 in this embodiment is in contact with and extends over the opposed portion 111 of the second metal tube 11 and the step 100 of the first metal tube 10. The step 100 is a surface opposed to the electron irradiation surface 90 as a surface of the target 9 on the side to be irradiated with electrons.
The first metal tube 10 has a coefficient of thermal expansion that is smaller than that of the second metal tube 11, and thus, has a smaller amount of contraction as heat is dissipated therefrom after the bonding. Therefore, in the structure described above, by the contraction of the second metal tube 11 having a larger amount of contraction, the bonding material 8 is pushed by the end face of the first metal tube 10 on the front end side, and compressive stress acts on the bonding material 8 in a direction of a central axis of the target 9. This compressive stress acts in a circumferential direction of the target 9 in accordance with a Poisson's ratio to partly alleviate the tensile stress that acts on the bonding material 8 in the circumferential direction of the target 9. Therefore, a region with a smaller tensile stress is partly formed, and a probability of vacuum leakage due to crack development can be reduced.
Note that, when the first metal tube 10 has a Young's modulus that is larger than that of the second metal tube 11, such compressive stress is not absorbed by deformation of the first metal tube 10 and efficiently acts on the bonding material 8. Therefore, a mode in which the first metal tube 10 has a Young's modulus that is larger than that of the second metal tube 11 is more preferred because compression of the bonding material 8 in the tube axial direction is more likely to occur. For example, by forming the second metal tube 11 of copper and forming the first metal tube 10 of tungsten, both a difference in coefficient of thermal expansion and a difference in Young's modulus can be utilized.
In Modified Example 1 and Modified Example 2 illustrated in
When, as illustrated in
In Modified Example 3 illustrated in
Note that, the second metal tube 11 in this Modified Example 3 includes an opposed portion 111 opposed to a circumferential side surface of the target 9. The opposed portion 111 is bonded to the circumferential side surface of the target 9 via the bonding material 8.
In Modified Example 4 illustrated in
In Modified Example 5 illustrated in
In Modified Examples 6 and 7 illustrated in
Among the examples described above, in the examples illustrated in
As illustrated in
Note that, similarly to the first metal tube 10, the third metal tube 12 can have a Young's modulus that is larger than that of the second metal tube 11. In such a structure, the second metal tube 11 has a Young's modulus that is smaller than those of the first metal tube 10 and of the third metal tube 12, and thus, the compressive stress is not absorbed by deformation of the first metal tube 10 and of the third metal tube 12 and efficiently acts on the bonding material 8. Therefore, a mode in which the third metal tube 12 has, similarly to the first metal tube 10, a Young's modulus that is larger than that of the second metal tube 11 is more preferred because compression of the bonding material 8 in the tube axial direction is more likely to occur. For example, by forming the second metal tube 11 of copper and forming the first metal tube 10 and the third metal tube 12 of tungsten, both a difference in coefficient of thermal expansion and a difference in Young's modulus can be utilized.
Note that, the broken line in
In the anode according to each of the first embodiment and the second embodiment described above, from the viewpoint of causing the compressive stress to be more likely to act on the bonding material 8, it is preferred that the third metal tube 12 have a coefficient of thermal expansion that is smaller than that of the bonding material 8. Further, it is preferred that the first metal tube 10 have a coefficient of thermal expansion that is smaller than that of the bonding material 8. Still further, it is preferred that the second metal tube 11 have a coefficient of thermal expansion that is smaller than that of the bonding material 8.
<X-Ray Generating Apparatus>
It is preferred that the container 120 for containing the X-ray generating tube 102 and the tube voltage circuit 103 have a strength sufficient for a container and have excellent heat dissipation performance, and, as a material thereof, a metal material such as brass, iron, or a stainless steel is suitably used.
In this embodiment, space in the container 120 except space necessary for placing the X-ray generating tube 102 and the tube voltage circuit 103 is filled with an insulating liquid 109. The insulating liquid 109 is an electrically insulating liquid, and plays a role in maintaining electrical insulation in the container 120 and a role as a cooling medium of the X-ray generating tube 102. It is preferred that, electrically insulating oil such as a mineral oil, a silicone oil, or a perfluoro oil be used as the insulating liquid 109.
<X-Ray Imaging System>
A system control device 202 integrally controls the X-ray generating apparatus 101 and an X-ray detector 206, and controls the X-ray generating apparatus 101 and other related apparatus in a coordinated manner. The system control device 202 is connected to the X-ray generating tube 102 via the tube voltage circuit 103, and controls X-ray generating operation of the X-ray generating apparatus 101. The X-ray flux 14 emitted from the X-ray generating apparatus 101 passes through a subject 204, to thereby be detected by the X-ray detector 206. The X-ray detector 206 converts the detected X-ray flux 14 into image signals and outputs the image signals to a signal processing portion 205. Under the control of the system control device 202, the signal processing portion 205 applies predetermined signal processing to the image signals, and outputs the processed image signals to the system control device 202. Based on the processed image signals, the system control device 202 outputs display signals to a display device 203 for displaying an image on the display device 203. The display device 203 displays on a screen an image of the subject 204 based on the display signals.
The peripheral portion of the target according to the present invention blocks the opening in the anode member and is bonded to the anode member. Further, the anode member includes the first metal tube and the second metal tube having a coefficient of thermal expansion that is larger than that of the first metal tube. The target is bonded to the anode member via the bonding material that is arranged so as to extend over the two. As the bonding material is cooled and contracted, a tensile stress acts on the bonding material along the circumferential direction of the target. At the same time, a difference in coefficient of thermal expansion between the first metal tube and the second metal tube can cause the compressive stress in, for example, the tube axial direction, to act on the bonding material. Further, the second metal tube has a Young's modulus that is smaller than that of the first metal tube. Therefore, the compressive stress is not absorbed by deformation of the first metal tube and efficiently acts on the bonding material. The compressive stress acts on the bonding material and the compressive stress in accordance with the Poisson's ratio of the bonding material acts in the circumferential direction of the target to alleviate the tensile stress. As a result, an X-ray generating tube can be provided in which a crack in the bonding material is less liable to develop and vacuum leakage is inhibited.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-147339, filed Jul. 18, 2014, and Japanese Patent Application No. 2015-119318, filed Jun. 12, 2015, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-147339 | Jul 2014 | JP | national |
| 2015-119318 | Jun 2015 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6064718 | Holland | May 2000 | A |
| 7526069 | Matsumura | Apr 2009 | B2 |
| 20130328184 | Iwayama | Dec 2013 | A1 |
| 20140140480 | Ogura et al. | May 2014 | A1 |
| 20140140486 | Yanagisawa et al. | May 2014 | A1 |
| Number | Date | Country |
|---|---|---|
| 2013-51153 | Mar 2013 | JP |
| 2013-55041 | Mar 2013 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20160020060 A1 | Jan 2016 | US |
