Patent Application
20140153695
The present invention relates to a radiation generating apparatus used for non-destructive X-ray imaging in the fields of medical devices and industrial devices, and a radiation imaging apparatus using the radiation generating apparatus.
Generally, a radiation tube accelerates an electron emitted from an electron emitting source at high voltage to irradiate a target with the electron to generate a radiation such as an X-ray. The radiation generated at this time is emitted in all directions. PTL 1 discloses a transmission X-ray generation apparatus in which X-ray shielding members are placed on an electron incident side and an X-ray emission side of a target to shield an unnecessary X-ray.
In order to generate a radiation suitable for radiation imaging, a high voltage needs to be applied between an electron emitting source and a target to irradiate the target with an electron beam with high energy. However, generally, generation efficiency of a radiation is extremely low, and about 99% of consumed power generates heat at the target. Since the generated heat increases a temperature of the target, a unit for preventing heat damage of the target is required. PTL 2 discloses an X-ray generation tube in which a cooling mechanism is provided around an X-ray transmission window to increase heat radiation efficiency of a target portion.
PTL 1: Japanese Patent Application Laid-Open No. 2007-265981
PTL 2: Japanese Patent Application Laid-Open No. 2004-235113
In imaging with a short time pulse and a large tube current in the medical field or imaging with a small focal point of an electron beam in the industrial field, a temperature of a target may instantaneously increase. In such a case, only heat radiation via a conventional radiation shielding member is insufficient.
If the radiation shielding member is increased in thickness to increase heat radiation properties, an entire radiation generating apparatus is increased in weight because the radiation shielding member is generally made of heavy metal. Also, providing a cooling mechanism separately from the radiation shielding member makes it difficult to reduce a size of the entire radiation generating apparatus.
Thus, the present invention has an object to provide a radiation generating apparatus that can shield an unnecessary radiation and cool a target with a simple structure and is reduced in weight, and a radiation imaging apparatus using the radiation generating apparatus.
In order to solve the above problem, according to an aspect of the present invention, a radiation generating apparatus comprises: an envelope having a first window through which a radiation is transmitted; and a radiation tube being held within the envelope, and having a second window which is arranged in opposition to the first window, and through which the radiation is transmitted, wherein the radiation tube has a radiation shielding member having a protruding portion protruding from the second window toward the first window, and a thermal conducting member having a higher thermal conductivity rather than that of the radiation shielding member is connected to the protruding portion of the radiation shielding member.
According to the present invention, shielding performance of an unnecessary radiation can be ensured, and heat of the target can be effectively radiated. Further, a thermal conducting member having a lower density than a radiation shielding member is used, thereby allowing an entire radiation generating apparatus to be reduced in weight. This allows radiation imaging with a large tube current and a small focal point, thereby obtaining a captured image with high resolution. Also, with a reduced weight, the apparatus can be easily applied to home medical tests and on-site medical tests for emergency.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Now, embodiments of the present invention will be described with reference to the drawings.
A voltage control portion 3 includes a circuit board and an insulation transformer, and outputs a signal to control generation of a radiation via a terminal 4 to an electron emitting source 5 in the radiation tube 10. A potential of an anode portion 12 is determined via a terminal 7.
The envelope 1 may have sufficient strength as a container, and is made of metal or a plastic material.
The insulating fluid 8 is a liquid or a gas having electrically insulating properties placed as a cooling medium. The liquid preferably includes electrically insulating oil. The electrically insulating oil favorably includes mineral oil, silicone oil, or the like. A different usable insulating fluid 8 includes a fluorinated electrically insulating liquid. The gas includes an atmosphere, and using the gas can reduce weight of the apparatus as compared to when using an insulating liquid.
The envelope 1 includes a first window 2 through which a radiation is transmitted and taken out of the envelope. A radiation emitted from the radiation tube 10 is emitted to an outside through the first window 2. The first window 2 is made of glass, aluminum, beryllium, or the like.
The radiation tube 10 includes a cylindrical evacuated container 9 as an outer frame, an electron emitting source 5 placed therein, a target portion 6, and a window member 8.
The evacuated container 9 maintains an inside of the radiation tube 10 in a vacuum state, and a body portion thereof is made of an insulating material such as glass or ceramic. A cathode portion 11 and an anode portion 12 are made of a conductive alloy (Kovar). A degree of vacuum inside the evacuated container 9 may be about 10−4 to 10−8 Pa. An unshown getter may be placed in the evacuated container 9 to maintain the degree of vacuum. The evacuated container 9 includes a cylindrical opening in the anode portion 12, and a cylindrical window member 13 is joined to the opening. The window member 13 has a cylindrical radiation transmitting hole (hereinafter simply referred to as a transmitting hole) 21 through which a part of a radiation (an X-ray in this embodiment) generated in the target portion 6 is transmitted. The cylindrical target portion 6 is joined to an inner wall of the transmitting hole 21 to seal the evacuated container 9.
The electron emitting source 5 is placed to face the target portion 6 in the evacuated container 9. The electron emitting source 5 may be formed of a tungsten filament, a hot cathode such as an impregnated cathode, or a cold cathode such as a carbon nanotube. An extraction electrode is placed in the electron emitting source 5, an electron emitted by an electric field formed by the extraction electrode is converged by a lens electrode to enter the target 6 and generate a radiation. At this time, an accelerating voltage of about 40 to 120 kV is applied between the cathode portion 11 electrically connected to the electron emitting source 5 and the anode portion 12 electrically connected to a target 14 depending on intended use of a radiation.
The target portion 6 includes the target 14 and a substrate 15 as a second window. The target 14 is placed on a surface of the second window 15 on a side of an electron emitting source. The target 14 is preferably made of a material having a high melting point and high radiation generation efficiency. For example, tungsten, tantalum, molybdenum, or the like can be used. In order to reduce absorption of a generated radiation when transmitting through the target 14, an appropriate thickness of the target 14 is about several μm to several ten μm.
The second window 15 supports the target 14, and transmits at least a part of the radiation generated in the target 14, and is placed in a position facing the first window 2 in the radiation transmitting hole 21 in the window member 13. The second window 15 is preferably made of a material having strength to support the target 14 and scarcely absorb the radiation generated in the target 14, and having high thermal conductivity so as to quickly radiate heat generated in the target 14. For example, diamond, silicon nitride, aluminum nitride may be used. To satisfy the above requirement for the second window 15, an appropriate thickness of the second window 15 is about 0.1 mm to several mm.
As illustrated in
The first shielding member 20 is placed to protrude from the second window 15 toward the electron emitting source 5, and has an electron transmitting hole 22 arranged in communication with the second window 15. An electron emitted from the electron emitting source 5 passes through the electron transmitting hole 22 and collides with the target 14. Among the radiations generated in the target 14, a radiation scattered on the side of the electron emitting source of the target 14 is shielded by the first radiation shielding member 20.
The second shielding member 19 is placed to protrude from the second window 15 toward the first window 2, and has the transmitting hole 21 arranged in communication with the second window 15. A radiation having transmitted through the second window 15 passes through the transmitting hole 21, and an unnecessary radiation is shielded by the second shielding member 19.
In terms of taking out a larger dose of radiation to an outside of the envelope 1, an opening area of the transmitting hole 21 preferably gradually increases from the second window 15 toward the first window 2. This is because the radiation having transmitted through the second window 15 is radiating out.
A center of the electron transmitting hole 22 in the first shielding member 20, a center of the transmitting hole 21 in the second shielding member 19, and a center of the target 14 are preferably on the same line. This is because such arrangement allows a radiation generated by irradiation of the transmission target 14 with an electron to be reliably taken out in a larger dose.
The shielding member 16 is preferably made of a material having high radiation absorption and high thermal conductivity. For example, metal material such as tungsten, tantalum, or an alloy thereof may be used. To sufficiently shield an unnecessary radiation, appropriate thicknesses of the first shielding member 20 and the second shielding member 19 are about 0.5 to 5 mm depending on a set accelerating voltage of an electron.
As illustrated in
As illustrated in
The thermal conducting member 17 is preferably made of a material having higher thermal conductivity than the shielding member 16 and high heat resistance, and may be selected from metal materials, carbon materials, ceramic or the like. The metal materials may include silver, copper, aluminum, cobalt, nickel, iron, or the like, or alloys or oxides thereof. The carbon materials may include diamond, graphite, or the like. The ceramic may include aluminum nitride, silicon carbide, alumina, silicon nitride, or the like. Further, the thermal conducting member 17 is desirably made of a material having a lower density than the radiation shielding member 16.
As the thermal conducting member 17, a material having a lower density than the shielding member 16 is used, thereby reducing weight as compared to the case where the window member 13 includes only the shielding member 16.
Heat generated in the target 14 is directly transferred to the thermal conducting member 17 directly or through the second window 15, or transferred to the thermal conducting member 17 via the shielding member 16. Further, the heat is transferred to an insulating fluid in contact with the thermal conducting member 17 and quickly radiated, thereby preventing a temperature increase of the target 14. Since the thermal conductivity of the thermal conducting member 17 is higher than the thermal conductivity of the shielding member 16, a speed of heat radiation is increased as compared to the case where the window member 13 includes only the shielding member 16.
Further, as illustrated in
The thermal conducting member 17 may be partially placed on an outer periphery or an inner periphery of the second shielding member 19 rather than surrounding the entire outer periphery or inner periphery.
Also, to further increase heat radiation properties, the shielding member 16 and the thermal conducting member 17 are preferably placed so that the target member 6 protrudes toward the first window 2 beyond an end surface position of the evacuated container 9.
As a method for applying an accelerating voltage, either an anode grounding system or a neutral grounding system may be used. The anode grounding system is a system in which when a voltage applied between the target 14 and the electron emitting source 5 is Va [V], a potential of the target 14 as an anode is set to ground (0 [V]), and a potential of the electron emitting source 5 with respect to the ground is set to −Va [V]. Meanwhile, the neutral grounding system is a system in which a potential of the target 14 with respect to the ground is set to +(Va−α) [V], and a potential of the electron emitting source 5 with respect to the ground is set to −α [V] (where Va>α>0). The value of α is within a range of Va>α>0, and generally close to Va/2. The neutral grounding system is used to reduce an absolute value of the potential with respect to the ground, thereby reducing creepage distance. The creepage distance is herein a distance between the voltage control portion 3 and the envelope 1 and a distance between the radiation tube 10 and the envelope 1. If the creepage distance can be reduced, a size of the envelope 1 can be reduced, and thus a weight of the insulating fluid 8 can be reduced, thereby further reducing size and weight of the radiation generating apparatus.
As illustrated in
As illustrated in
This example is similar to Example 1 except that molybdenum is selected as the shielding member 16, and aluminum is selected as the thermal conducting member 17, and sheet molybdenum is used as the target 14. This example is different from Example 1 in using an anode grounding system as a voltage control system. To set 50[V] to an extraction electrode, 3000 [V] to a lens electrode, and Va in the anode grounding system to 50 [kV], the voltage of the target 14 was set to +50 [kV] and the voltage of the electron emitting source 5 was set to 0 [kV].
This example is similar to Example 1 except that tungsten is selected as the shielding member 16, and SiC or graphite sheet is selected as the thermal conducting member 17.
This example is similar to Example 1 except that an alloy of tungsten and molybdenum (ratio of components: 90% tungsten and 10% molybdenum) is selected as the shielding member 16, and an alloy of copper and aluminum (ratio of components: 90% copper and 10% aluminum) is selected as the thermal conducting member 17.
This example is similar to Example 1 except that tungsten is selected as the shielding member 16, and fin-shaped copper illustrated in
In this example, as illustrated in
This example is similar to Example 7 except that copper having a fin structure in
In any of the above examples, the radiation generating apparatus was able to be satisfactorily handled. A radiation was emitted under the above conditions, and a dose of the generated radiation was measured. Thus, it was confirmed that a stable dose of radiation could be obtained. At this time, an unnecessary radiation does not leak, and there was no damage to a target.
Next, with reference to
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 Applications No. 2011-171610, filed Aug. 5, 2011 and No. 2011-243055, filed Nov. 7, 2011, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-171610 | Aug 2011 | JP | national |
| 2011-243055 | Nov 2011 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2012/069519 | 7/24/2012 | WO | 00 | 1/9/2014 |
