Patent Application
20150373821
The present invention relates to a radiation generating apparatus that is applicable to radiation imaging in the fields of medical apparatuses and industrial apparatuses, and also relates to a radiation imaging system including the same.
In a typical radiation generating apparatus, a high voltage is applied between a cathode and an anode that are provided in a radiation tube, and electrons emitted from the cathode are applied to the anode, whereby radiation is generated. To provide a satisfactory resistance to the high voltage and to cool the radiation tube, the radiation tube included in such a radiation generating apparatus is provided in a container that is filled with an insulating liquid.
Most of energy generated by the electrons applied to the anode is converted into heat. The heat generated by the anode is sequentially transmitted to the wall of the radiation tube, to the insulating liquid, and to the container, and is released into the atmosphere on the outside of the container. To fully cool an area around the anode and to release the heat generated by the anode to the outside via the container, it is important that the heat in a high-temperature area is effectively transported to a low-temperature area by causing the insulating liquid, which functions as a coolant, to flow through a wide area.
A high voltage is applied to the two electrodes of the radiation tube. Therefore, even if the container is filled with the insulating liquid, a member that insulates peripheral members from the high voltage may be additionally provided. PTL 1 discloses an X-ray generating apparatus including an insulating sleeve (outer tube) made of a dielectric material and provided on the outer side of an X-ray tube, with a gap between the insulating sleeve and the X-ray tube being filled with an insulating oil.
PTL 1: Japanese Patent Laid-Open No. 2007-80568
Although the presence of the outer tube 5 prevents the increase in the damage to peripheral members caused by such discharge, it is difficult to reduce the rate of incidence of creeping microdischarge that may occur between the cathode 31 and the anode 33 to which a high voltage is applied. Hence, if such creeping microdischarge occurs repeatedly, electric discharge decomposition of the insulating liquid 4 may advance, accelerating the deterioration of the insulating liquid 4. Moreover, such creeping microdischarge may form a tracking path leading to the tubular member 32 of the radiation tube 2, accelerating the long-term deterioration of the voltage resistance of the radiation generating apparatus as a whole.
That is, there is a contradiction between an effect of cooling the radiation tube with the flow of the insulating liquid and an effect of suppressing the creeping discharge on the radiation tube.
In light of the above, the present invention provides a radiation generating apparatus including a radiation tube provided in a container filled with an insulating liquid and an outer tube provided for improving the voltage resistance of the radiation generating apparatus, in which effective cooling of a high-temperature area including an anode and peripheral members and suppression of creeping discharge are both realized.
A radiation generating apparatus includes a radiation tube including an electrically insulating tubular member, a cathode provided at one of two openings of the tubular member, and an anode provided at the other opening of the tubular member; an electrically insulating outer tube surrounding at least a peripheral side of the radiation tube with a separation interposed therebetween; and a container that contains the radiation tube and the outer tube. A space in the container is filled with an insulating liquid. At least a portion of a gap between the tubular member and the outer tube is wider than at least one of a gap between the cathode and the outer tube and a gap between the anode and the outer tube.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Referring to
The insulating liquid 4 functions as an insulator that provides the radiation tube 2 with a satisfactory creepage-surface voltage resistance and also functions as a coolant that cools the radiation tube 2 that generates heat when radiation is generated. The insulating liquid 4 may be an electrically insulating oil such as mineral oil, silicone oil, or the like. Other available examples of the insulating liquid 4 include fluorine-based electrically insulating liquid.
To effectively release the heat generated by the anode 33 to the outside via the container 7, it is important to cause the insulating liquid 4 to flow through a wide area and to quickly transport the heat from a high-temperature area to a low temperature area. When a high voltage is applied to the radiation tube 2, the insulating liquid 4 undergoes convection by an electrohydrodynamic (EHD) effect. That is, the insulating liquid 4 can be made to flow by utilizing such an EHD effect.
The container 7 may have a ground potential by being grounded via a grounding terminal, considering the stability and safety in the operation of the radiation generating apparatus 1. The container 7 may be made of metal such as iron, stainless steel, lead, brass, copper, or the like, considering the radiation-blocking characteristic, strength, and the surface-potential-defining characteristic. If the container 7 has a ground potential, a voltage of +Va may be applied between the cathode 31 and the anode 33 with the potential of the cathode 31 defined as −Va/2 and the potential of the anode 33 defined as +Va/2, considering the stability of voltage resistance on the inside of the radiation generating apparatus 1. The container 7 has a radiation emitting window 8 provided at a position corresponding to the focal point of radiation 27 (see
The peripheral side of the radiation tube 2 is enclosed by an outer tube 5. The outer tube 5 prevents the driving circuit 3 from being damaged by an increase in microdischarge that may occur on the creepage surface of the radiation tube 2. A gap 6 is provided between the outer tube 5 and the radiation tube 2. The insulating liquid 4 flows through the gap 6, functioning as a passage, as illustrated by the arrows in
In general, the degree of static electricity on an insulating surface with the flow of the insulating liquid 4 depends on the flow speed of the insulating liquid 4. As illustrated in
Therefore, among different portions of the gap between the radiation tube 2 and the outer tube 5, a central portion (gap A) between the tubular member 32 and the outer tube 5 is wider than a portion (gap C) between the cathode 31 and the outer tube 5 and/or a portion (gap B) between the anode 33 and the outer tube 5. Thus, the flow speed of the insulating liquid 4 in the gap A is made lower than the flow speed of the insulating liquid 4 in the gap B and/or the gap C. The gap 6 may be widened at least in a portion thereof between the tubular member 32 and the outer tube 5. For example, as illustrated in
The gap A may be constant as illustrated in
The insulating liquid 4 may be made to flow by a liquid delivering device (not illustrated). On a condition where a high voltage of about 40 kV to 150 kV is applied between the cathode 31 and the anode 33, the insulating liquid 4 may alternatively be made to flow spontaneously by utilizing an EHD effect.
Since the insulating liquid 4 is made to flow through the gap 6 between the outer tube 5 and the radiation tube 2 as described above, the heat generated from the radiation tube 2 is efficiently released to the outside, allowing the radiation generating apparatus 1 to continuously operate with a high power. Moreover, with the gap 6 that is widened partially, the amount of charging on the surface of the tubular member 32 is reduced, and the rate of incidence of creeping microdischarge is thus reduced.
In
Referring now to
The radiation tube 2 is of a transmission type and includes an electron source 21, a transmissive target 24, a shielding member 25, and the vacuum container 34.
The vacuum container 34 includes the tubular member 32 that is electrically insulating, the cathode 31 provided over the opening at one of the two ends of the tubular member 32, and the anode 33 provided over the opening at the other end of the tubular member 32. The vacuum container 34 maintains the vacuum produced in the radiation tube 2. The degree of vacuum in the vacuum container 34 may be about 10−4 Pa to about 10−8 Pa.
The shielding member 25 defines the angle of radiation emitted to the outside and blocks the radiation from scattering into the vacuum container 34. The shielding member 25 is joined to the anode 33 of the vacuum container 34. The shielding member 25 has a passage that communicates with the outside of the vacuum container 34. The target 24 is fitted in the passage, whereby the vacuum container 34 is sealed.
The electron source 21 is provided opposite the target 24. An electron beam 26 emitted from the electron source 21 passes through the opening of the shielding member 25 and enters the target 24, whereby radiation 27 is generated. The shielding member 25 may be made of lead or tungsten. The electron source 21 is connected to the cathode 31 via a current introducing terminal 37.
A positive potential of 10 kV to 200 kV with respect to the electron source 21 (cathode 31) is applied to the target 24 (anode 33). The target 24 includes a supporting substrate made of diamond and a target film made of tungsten and provided on the supporting substrate.
The potentials of the cathode 31 and the anode 33 are defined by the driving circuit 3. The cathode 31 and the anode 33 define the electrostatic field produced in the radiation tube 2. Hence, the cathode 31 and the anode 33 may be arranged such that lines of electric force of the electrostatic field are as parallel as possible near each of the electron source 21 and the target 24. Therefore, the cathode 31 and the anode 33 may each define the potential in a space having a predetermined area. Furthermore, the cathode 31 and the anode 33 may each have a shape conforming to the cross section of a corresponding one of the openings of the insulating tubular member 32. In the configuration illustrated in
The materials of the cathode 31 and the anode 33 may be determined in accordance with conductivity, airtightness, strength, and the matching with the coefficient of linear expansion of the tubular member 32. For example, the cathode 31 and the anode 33 may be made of Kovar (a registered trademark), tungsten, or the like.
The tubular member 32 is electrically insulating and has at least two openings at which the cathode 31 and the anode 33 are provided respectively. The cross-sectional shape of the outer periphery or the inner periphery of the tubular member 32 is not limited to a circular shape and may be any polygonal shape. The tubular member 32 may be made of insulating ceramic such as boron nitride or alumina, or insulating inorganic glass such as borosilicate glass, considering the electrically insulating characteristic, airtightness, the low gas-emission characteristic, heat resistance, and the matching with the coefficients of linear expansion of the cathode 31 and the anode 33.
The cathode 31 and the anode 33 are each joined to the tubular member 32 with a joining member (not illustrated). The joining member may be hard solder (metal intended for soldering), such as silver solder or copper solder, having conductivity and heat resistance and providing a good characteristic of joining different materials of metal and an insulating material.
The radiation tube 2 may also be provided with an extraction electrode 28 and a lens electrode 29.
The outer tube 5 may be made of oil-resistant resin such as polyetherimide or acrylic resin.
In the first embodiment, the outer tube 5 is provided on the outer side of the radiation tube 2. Hence, to position the outer tube 5, the outer tube 5 may be secured to the radiation tube 2 with insulating screws or the like and may further be secured to the container 7 with insulating supporting members (not illustrated).
Referring now to
The radiation generating apparatus 1 is provided with a movable diaphragm unit 41 at the radiation emitting window 8, according to need. The movable diaphragm unit 41 adjusts the size of a radiation field formed by the radiation 27 emitted from the radiation generating apparatus 1. The movable diaphragm unit 41 may have an additional function of simulating the radiation field by using a visible-light field.
A system control device 202 controls the radiation generating apparatus 1 in conjunction with a radiation detecting device 201. The driving circuit 3, which is also controlled by the system control device 202, outputs control signals to the radiation tube 2. In accordance with the control signals, the radiation 27 emitted from the radiation generating apparatus 1 is transmitted through an examination object 204 and is detected by a detector 206. The detector 206 converts the detected radiation 27 into an image signal and outputs the image signal to a signal processing unit 205. The signal processing unit 205, which is controlled by the system control device 202, processes the image signal as predetermined and outputs the processed image signal to the system control device 202. In accordance with the processed image signal, the system control device 202 outputs a display signal for displaying a corresponding image to a display device 203. The display device 203 displays an image that is based on the image signal as an image of the examination object 204 on a display.
A typical example of the radiation 27 is X-rays. An X-ray imaging system is applicable to nondestructive inspections of industrial products and pathological diagnoses of human bodies and animals.
Referring to
Major dimensions of the radiation tube 2 according to Example 1 were as follows: the outside diameter of the tubular member 32 was 50 mm, and a length (L3) of the radiation tube 2 inclusive of the cathode 31 and the anode 33 was 80 mm. The tubular member 32 was chiefly made of alumina ceramic. The cathode 31 was chiefly made of stainless steel. The anode 33 was chiefly made of stainless steel and copper.
Major dimensions of the outer tube 5 were as follows: a length (L4) was 100 mm, an inside diameter (L1) at each of portions thereof facing the cathode 31 and the anode 33, which were conductive members, was 60 mm, and an inside diameter (L2) at a portion thereof facing the tubular member 32 was 70 mm. The outer tube 5 was made of acrylic resin with a thickness of 5 mm.
In the above configuration, the gap 6 was provided between the outer tube 5 and the radiation tube 2 such that the gaps B and C were each 5 mm and the gap A was 10 mm, whereby the cross-sectional area of the passage for the insulating liquid 4 was expanded in an area along the surface of the tubular member 32. By employing such a configuration, the flow speed of the insulating liquid 4 flowing along the tubular member 32 was made lower than the flow speed of the insulating liquid 4 flowing along the cathode 31 and the anode 33. Consequently, the amount of charging on the surface of the tubular member 32 was reduced.
The radiation tube 2 and the outer tube 5 configured as described above were incorporated into the radiation generating apparatus 1 illustrated in
Meanwhile, the amount of the insulating liquid 4 flowing along the surface of the radiation tube 2 was not reduced. Therefore, cooling efficiency was not reduced.
Another radiation generating apparatus 1 was prepared. The radiation generating apparatus 1 was the same as that of Example 1, except that the outer tube 5 illustrated in
In the above configuration, the gap 6 was provided between the outer tube 5 and the radiation tube 2 such that the gaps B and C were each 5 mm and the gap at the central part of the tubular member 32 was 10 mm, whereby the cross-sectional area of the passage for the insulating liquid 4 was expanded in an area along the central part of the tubular member 32.
In Example 2 also, a high voltage of 100 kV was applied between the cathode 31 and the anode 33, and the rate of incidence of creeping microdischarge was compared with that of Comparative Example illustrated in
According to the above embodiments of the present invention, since the peripheral side of the radiation tube is enclosed by the insulating outer tube, peripheral members including the driving circuit and so forth are prevented from being damaged with an increase in creeping discharge that may occur near the radiation tube. Particularly, in the embodiments of the present invention, the cross-sectional area of the passage for the insulating liquid provided between the radiation tube and the outer tube is expanded in an area surrounding the insulating tubular member. Hence, the flow speed of the insulating liquid flowing along the surface of the tubular member is reduced, whereby charging on the surface of the tubular member is reduced. Therefore, the rate of incidence of creeping discharge is reduced without lowering the effect of cooling the radiation tube. Consequently, voltage resistance is improved while the radiation tube is cooled efficiently. Thus, a radiation generating apparatus having a higher power and being capable of long, continuous emission of radiation is provided. Furthermore, since the creeping discharge from the radiation tube is suppressed and the rate of incidence of microdischarge is reduced, a radiation imaging system with a low rate of incidence of electromagnetic noise is provided.
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. 2013-016599, filed Jan. 31, 2013, which is hereby incorporated by reference herein in its entirety.
1 radiation generating apparatus
2 radiation tube
4 insulating liquid
5 outer tube
6 gap
7 container
21 electron source
24 target
31 cathode
32 tubular member
33 anode
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-016599 | Jan 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/000045 | 1/8/2014 | WO | 00 |
