JP2012124099A - Radiation generating apparatus and radiation imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation generating apparatus with high reliability capable of shielding unwanted radiation and cooling a target with a simple structure, and being reduced in size and weight, and a radiation imaging apparatus having the same.SOLUTION: The radiation generating apparatus is characterized: that a transmission type radiation tube is housed in a storage container filled with a cooling medium; the transmission type radiation tube comprises an envelope having an opening part, an electron emission source provided facing the opening part of the envelope inside the envelope, a transmission substrate for transmitting radiation, a target arranged on a surface at the electron emission source side of the transmission substrate and generating the radiation by being irradiated with electrons emitted from the electron emission source, a shielding body for shielding the radiation emitted from the target, and a heat insulation part provided between the transmission substrate and the cooling medium; the shielding body comprises a passage communicating with the opening of the envelope; the transmission substrate is provided in the passage of the shielding; and the cooling medium contacts with at least part of the shielding body.

Description

  The present invention relates to a radiation generator applicable to non-destructive X-ray imaging and the like in the fields of medical equipment and industrial equipment, and a radiation imaging apparatus including the radiation generator.

  In general, a radiation tube (radiation generating tube) accelerates electrons emitted from an electron emission source to high energy and irradiates a target made of a metal such as tungsten to generate radiation such as X-rays. The radiation generated at this time is emitted in all directions. Therefore, in order to shield radiation that is not necessary, the container containing the radiation tube or the surroundings of the radiation tube is covered with a shield (radiation shielding member) such as lead so that unnecessary radiation is not leaked to the outside. Yes. For this reason, it has been difficult to reduce the size and weight of such a radiation tube and a radiation generator that houses the radiation tube.

  As means for solving this problem, in the transmission type radiation tube, by arranging shields on the radiation emission side and the electron incidence side of the target, unnecessary radiation is shielded with a simple structure, and the apparatus is reduced in size and weight. Has been proposed (see Patent Document 1).

  However, in general, such a target (anode) -fixed transmission type radiation tube is relatively inferior in heat dissipation, and it is difficult to generate high-energy radiation. Regarding the heat radiation of the target, the transmission radiation tube of Patent Document 1 has a structure in which the target and the shield are joined, so that heat generated in the target is transmitted to the shield and dissipated, and the temperature rise of the target can be suppressed. It is described.

JP 2007-265981 A

  However, in the transmission type radiation tube of Patent Document 1, the shield is disposed in the vacuum vessel, and the heat transfer area from the shield to the outside of the vacuum vessel is limited. For this reason, the heat dissipation of the target is not always sufficient, and there is a problem in achieving both the cooling capability of the target and the reduction in size and weight of the apparatus.

  Therefore, the present inventors considered a transmissive radiation tube having a structure in which a shield is bonded to a transmissive substrate that supports a target, and at least a part of the transmissive substrate and at least a part of the shield are in contact with a cooling medium. When the target was cooled with, sufficient cooling capacity was obtained.

  However, in the above configuration in which the transmissive substrate and the cooling medium are in contact with each other, the temperature of the cooling medium in the portion in contact with the transmissive substrate is rapidly increased locally by the heat generated by the target. Although this local temperature rise causes convection of the cooling medium and the cooling medium is replaced on the surface of the transmissive substrate, a part of the temperature exceeds the decomposition temperature and the cooling medium may be decomposed (deteriorated). When decomposition of the cooling medium progresses, the pressure resistance of the cooling medium decreases, and problems such as discharge may occur in long-time driving.

  Therefore, the present invention provides a radiation generator capable of shielding unnecessary radiation and cooling a target with a simple structure, enabling a reduction in size and weight, and a more reliable radiation imaging apparatus, and a radiation imaging apparatus including the radiation generator. The purpose is to provide.

In order to solve the above problems, the present invention has a transmission radiation tube housed inside a storage container filled with a cooling medium,
The transmission radiation tube is
An envelope having an opening;
An electron emission source disposed inside the envelope and facing the opening;
A transmissive substrate that transmits radiation;
A target installed on the surface of the transmission substrate on the electron emission source side, which generates radiation by irradiation of electrons emitted from the electron emission source;
A shield that blocks radiation emitted from the target;
A heat insulating member installed between the transmission substrate and the cooling medium;
With
The shield has a passage communicating with an opening of the envelope, and the transmission substrate is provided in the passage.
The cooling medium is in contact with at least a part of the shield.

  According to the present invention, the shield is bonded to the transmission substrate that supports the target, at least a part of the shield is in contact with the cooling medium, and the heat insulating member is provided between the transmission substrate and the cooling medium. Therefore, the heat generated in the target is transmitted to the shielding body, is transmitted to the cooling medium through the shielding body, and is quickly radiated. In addition, since there is a heat insulating member between the transmission substrate and the cooling medium, heat conduction from the transmission substrate to the cooling medium is suppressed, so that deterioration of the cooling medium due to overheating can be suppressed. Thereby, it is possible to realize a radiation generating apparatus that can shield unnecessary radiation and cool a target with a simple structure. In addition, since the number of members that shield unnecessary radiation can be reduced, the radiation generator can be reduced in size and weight. Furthermore, since the deterioration of the cooling medium due to overheating can be suppressed, the pressure resistance of the cooling medium can be ensured for a long time, so that a more reliable radiation generator can be realized.

It is a schematic diagram of the radiation generator of 1st Embodiment and a target peripheral part. It is a schematic diagram of the target periphery part of 2nd Embodiment. It is a schematic diagram of the target periphery part of 3rd Embodiment. It is a schematic diagram of the target periphery part of 4th Embodiment. It is a block diagram of the radiography apparatus using the radiation generator of this invention.

  Hereinafter, although embodiment of this invention is described using drawing, this invention is not limited to these embodiment. In addition, the well-known or well-known technique of the said technical field is applied regarding the part which is not illustrated or described in particular in this specification.

[First Embodiment]
First, a first embodiment of the present invention will be described with reference to FIG. Fig.1 (a) is a schematic diagram of the radiation generator of this embodiment, FIG.1 (b) is the schematic diagram which expanded and represented the target periphery part in Fig.1 (a). The radiation generating apparatus according to the present embodiment includes a transmissive radiation tube 10, and the transmissive radiation tube 10 is accommodated in the storage container 1. The extra space in which the transmissive radiation tube 10 is accommodated inside the storage container 1 is filled with a cooling medium 8. The storage container 1 may be provided with a voltage control unit 3 (voltage control means) including a circuit board (not shown) and an insulating transformer as in the present embodiment. When the voltage control unit 3 is provided, for example, a voltage signal is applied from the voltage control unit 3 to the transmission radiation tube 10 via the terminals 4, 5, 6, and 7, so that the generation of radiation can be controlled.

  The storage container 1 only needs to have sufficient strength as a container, and is made of metal, plastics material, or the like. The storage container 1 may be provided with a radiation transmission window 2 made of glass, aluminum, beryllium or the like as in the present embodiment. When the radiation transmissive window 2 is provided, the radiation emitted from the transmissive radiation tube 10 is emitted to the outside through the radiation transmissive window 2.

  The cooling medium 8 only needs to have electrical insulation, and it is preferable to use, for example, an insulating medium and an electrical insulating oil having a role as a cooling medium for the transmission type radiation tube 10. As the electrical insulating oil, mineral oil, silicone oil or the like is preferably used. Another usable cooling medium 8 is a fluorine-based electrically insulating liquid.

  The transmission radiation tube 10 includes an envelope 19, an electron emission source 11, a target 14, a transmission substrate 15, a shield 16, and a heat insulating member 22. The transmission radiation tube 10 may be provided with an extraction electrode 12 and a lens electrode 13 as in the present embodiment. When these are provided, electrons are emitted from the electron emission source 11 by the electric field formed by the extraction electrode 12, and the emitted electrons are converged by the lens electrode 13 and incident on the target 14 to generate radiation. Moreover, you may provide the exhaust pipe 20 like this embodiment. When the exhaust pipe 20 is provided, for example, after the inside of the envelope 19 is evacuated through the exhaust pipe 20, the inside of the envelope 19 can be evacuated by sealing a part of the exhaust pipe 20. . Further, depending on the material constituting the heat insulating member 22, the lid substrate 21 may be provided as in the present embodiment.

The envelope 19 is for keeping the inside of the transmissive radiation tube 10 in a vacuum, and glass, ceramic material, or the like is used. The degree of vacuum in the envelope 19 may be about 10 ⁻⁴ to 10 ⁻⁸ Pa. A getter (not shown) may be disposed inside the envelope 19 in order to maintain the degree of vacuum. The envelope 19 has an opening, and the shield 16 is joined to the opening. The shield 16 has a passage communicating with the opening of the envelope 19, and the envelope 19 is sealed by joining the transmission substrate 15 to the passage.

  The electron emission source 11 is disposed inside the envelope 19 so as to face the opening of the envelope 19. The electron emission source 11 may be a tungsten filament, a hot cathode such as an impregnated cathode, or a cold cathode such as a carbon nanotube. An extraction electrode 12 is disposed in the vicinity of the electron emission source 11, and electrons emitted by the electric field formed by the extraction electrode 12 are converged by the lens electrode 13 and incident on the target 14 to generate radiation. At this time, the voltage Va applied between the electron emission source 11 and the target 14 is approximately 40 to 120 kV, although it varies depending on the intended use of radiation.

  The transmissive substrate 15 supports the target 14 and transmits at least part of the radiation generated by the target 14, and is provided in a passage of the shield 16 that communicates with the opening of the envelope 19. The material constituting the transmissive substrate 15 is preferably strong enough to support the target 14, has little absorption of radiation generated by the target 14, and has high thermal conductivity so that heat generated by the target 14 can be quickly dissipated. . For example, diamond, silicon nitride, aluminum nitride, or the like can be used. In order to satisfy the above requirements for the transmissive substrate 15, the thickness of the transmissive substrate 15 is suitably about 0.1 mm to several mm.

  The target 14 is installed on the surface of the transmission substrate 15 on the electron emission source side. The material constituting the target 14 is preferably 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 the absorption that occurs when the generated radiation passes through the target 14, the thickness of the target 14 is suitably about several μm to several tens of μm.

  The shield 16 shields radiation emitted from the target 14. The shield 16 is joined to the opening of the envelope 19 and has a passage communicating with the opening. The transmission substrate 15 is joined to the passage. Has been. The target 14 may not be joined to the passage. Further, the shield 16 may be composed of two shields (first shield 17 and second shield 18) having a cylindrical shape such as a cylinder as in the present embodiment (FIG. 1 ( b)).

  The first shield 17 has a function of shielding radiation scattered toward the electron emission source side of the target 14 when electrons enter the target 14 and radiation is generated. There is a communicating passage. The electrons emitted from the electron emission source 11 pass through the passage of the first shield 17 communicating with the opening of the envelope 19, and the radiation scattered to the electron emission source side of the target 14 is the first shield 17. It is shielded with.

  The second shield 18 has a function of shielding unnecessary radiation out of the radiation transmitted through the transmissive substrate 15 and has a passage communicating with the opening of the envelope 19. The radiation that has passed through the transmissive substrate 15 passes through the passage of the second shield 18 that communicates with the opening of the envelope 19, and unnecessary radiation is shielded by the second shield 18.

  In the present embodiment, as shown in FIG. 1B, the opening area of the passage of the second shield 18 is gradually increased (away from the transmissive substrate 15) on the side opposite to the electron emission source from the transmissive substrate 15. Is preferable). This is because the radiation transmitted through the transmission substrate 15 has a radial spread.

  Further, in the present embodiment, the center of gravity of the opening of the passage on each side (the passage of the first shield 17) on the electron emission source side with respect to the transmission substrate 15 and on the opposite side of the transmission substrate 15 with respect to the electron emission source. The center of gravity of the opening of the second shield 18 preferably coincides with the center of gravity of the opening of the passage of the second shield 18. That is, as shown in FIG. 1B, the opening of the passage of the first shield 17 and the opening of the passage of the second shield 18 are in the same vertical direction perpendicular to the target installation surface of the transmission substrate 15 with the transmission substrate 15 in between. It is preferable to arrange on a line. This is because in the present embodiment, the target 14 is irradiated with electrons to generate radiation, and the radiation transmitted through the transmission substrate 15 is emitted.

  The material constituting the shield 16 (the first shield 17 and the second shield 18) is preferably a material having a high radiation absorption rate and a high thermal conductivity. For example, a metal material such as tungsten or tantalum can be used. In order to shield unnecessary radiation, the thickness of the first shield 17 and the second shield 18 is suitably 3 mm or more.

  The heat insulating member 22 is installed between the transmissive substrate 15 and the cooling medium 8 (the surface of the transmissive substrate 15 opposite to the electron emission source). In the present embodiment, since the lid substrate 21 is provided, the lid substrate 21 is provided between the transmission substrate 15 and the lid substrate 21. The lid substrate 21 is joined to the second shield 18. The lid substrate 21 is preferably made of a material having a low radiation absorption rate, such as diamond, glass, beryllium, aluminum, silicon nitride, and aluminum nitride. In order to have strength as a substrate and reduce absorption of radiation, the thickness of the lid substrate 21 is suitably about several tens μm to several mm.

  The material constituting the heat insulating member 22 is preferably a material having lower thermal conductivity, lower radiation absorption rate, and higher heat resistance than the material constituting the second shield 18, and vacuum or gas is suitable. . As gas, inert gas, such as air | atmosphere, nitrogen, argon, neon, and helium, can be used. The gas constituting the heat insulating member 22 may be atmospheric pressure, but since it expands due to heat generated by the target when generating radiation, the inside of the heat insulating member 22 may be preliminarily set as a space having a pressure lower than atmospheric pressure. . Since the pressure of the gas constituting the heat insulating member 22 is proportional to the absolute temperature, the pressure at the time of formation may be set based on the assumed temperature. The transmission radiation tube 10 of the present embodiment can be formed by bonding or welding the lid substrate 21 to the second shield 18 in a vacuum or a gas atmosphere.

  In the present embodiment, by providing the heat insulating member 22 between the transmissive substrate 15 and the cooling medium 8, the transmissive substrate 15 and the cooling medium 8 are not in contact with each other. When the transmissive substrate 15 and the cooling medium 8 are in contact, the temperature of the portion of the cooling medium 8 in contact with the transmissive substrate 15 rapidly increases locally due to the heat generated by the target 14. Although this local temperature rise causes convection of the cooling medium 8 and replacement of the cooling medium 8 occurs on the surface of the transmissive substrate 15, some of the cooling exceeds the decomposition temperature (generally about 200 to 250 ° C. in the case of electrical insulating oil). The medium 8 may be decomposed (deteriorated). When decomposition of the cooling medium 8 progresses, the pressure resistance of the cooling medium 8 decreases, and problems such as discharge may occur in driving for a long time.

  In the radiation generator of this embodiment, the target 14, the first shield 17, and the second shield 18 are in mechanical and thermal contact with each other directly or through the transmission substrate 15. Further, the second shield 18 and the lid substrate 21 constitute a part of the outer wall of the envelope 19 and are in contact with the cooling medium 8 in the storage container 1. Further, a heat insulating member 22 having a lower thermal conductivity than the second shield 18 is formed between the transmissive substrate 15 and the cooling medium 8. For this reason, the heat generated in the target 14 is transmitted to the second shield 18, is transmitted to the cooling medium 8 through the second shield 18, and is quickly dissipated. Therefore, the temperature rise of the target 14 is suppressed. Moreover, since heat conduction from the transmissive substrate 15 to the cooling medium 8 is suppressed, deterioration of the cooling medium 8 due to overheating can be suppressed.

  As described above, according to the radiation generator of the present embodiment, unnecessary radiation can be shielded and the target can be cooled with a simple structure, and the radiation generator can be reduced in size and weight. Furthermore, since the deterioration of the cooling medium due to overheating can be suppressed, the pressure resistance of the cooling medium can be ensured for a long time, so that a more reliable radiation generator can be realized.

  Further, as the voltage control means in the radiation generating apparatus of the present embodiment, either an anode grounding method or a midpoint grounding method can be adopted, but it is preferable to adopt a midpoint grounding method. In the anode grounding method, when the voltage applied between the target 14 and the electron emission source 11 is Va [V], the voltage of the anode target 14 is set to the ground (0 [V]), and the electron emission is performed. In this method, the voltage of the source 11 is set to -Va [V]. On the other hand, in the midpoint grounding method, the voltage of the target 14 is set to + (Va−α) [V], and the voltage of the electron emission source 11 is set to −α [V] (where Va> α> 0). It is a method to do. The value of α is an arbitrary value within the range of Va> α> 0, but is generally a value close to Va / 2. By adopting the midpoint grounding method, the absolute value of the voltage with respect to the ground can be reduced, and the creepage distance can be shortened. Here, the creepage distance is a distance between the voltage control unit 3 and the storage container 1 and a distance between the transmission radiation tube 10 and the storage container 1. If the creepage distance can be shortened, the size of the storage container 1 can be reduced, and the weight of the cooling medium 8 can be reduced accordingly, so that the radiation generator can be further reduced in size and weight. Become.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is an enlarged schematic view showing the peripheral portion of the target of the radiation generating apparatus according to the present embodiment. This embodiment is another example that can be applied when the heat insulating member in the first embodiment is evacuated.

  In FIG. 2, the heat insulation member 22 is a vacuum. In order to make the heat insulating member 22 into a vacuum, a hole (communication hole) 23 is provided in the first shield 17 and the second shield 18 as in the present embodiment, and the inside of the envelope 19 is provided through the hole. It is good also as a structure which makes the inside of the heat insulation member 22 communicate. In the case where the communication hole 23 is provided, the transmission type radiation tube 10 of the present embodiment has the inside of the envelope 19 and the inside of the heat insulating member 22 through the exhaust pipe 20 after the lid substrate 21 is joined to the second shield 18. Are simultaneously exhausted and the exhaust pipe 20 is sealed.

  Also in this embodiment, since the heat conduction from the transmissive substrate 15 to the cooling medium 8 is suppressed by the heat insulating member 22, deterioration of the cooling medium 8 due to overheating can be suppressed, and the pressure resistance of the cooling medium 8 is ensured for a long time. It becomes possible. Therefore, according to the radiation generator of the present embodiment, unnecessary radiation can be shielded and the target can be cooled with a simple structure, and a more reliable and light-weight radiation generator can be realized.

[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 3 is an enlarged schematic view showing a target peripheral portion of the radiation generating apparatus according to the present embodiment. This embodiment is another example of the first embodiment, and a heat insulating member provided between the transmission substrate 15 and the cooling medium 8 is formed of a solid. Other components can be the same as those in the first embodiment.

  In FIG. 3, the heat insulating member 24 is solid. The material constituting the heat insulating member 24 is preferably a material having lower thermal conductivity, lower radiation absorption rate, and higher heat resistance than the material constituting the second shield 18. Examples thereof include silicon oxide, silicon nitride, titanium oxide, titanium nitride, titanium carbide, zinc oxide, and aluminum oxide. Further, the heat insulating member 24 adheres or joins the surface of the transmission substrate 15 to the surface of the transmissive substrate 15 by a film forming method such as sputtering, vapor deposition, CVD, sol-gel, or the like. Can be formed. In order to suppress heat conduction between the transmissive substrate 15 and the cooling medium 8 and reduce the radiation absorption rate, the thickness of the heat insulating member 24 is preferably in the range of several tens of μm to several mm.

  Also in this embodiment, since the heat conduction from the transmissive substrate 15 to the cooling medium 8 is suppressed by the heat insulating member 24, deterioration of the cooling medium 8 due to overheating can be suppressed, and the pressure resistance of the cooling medium 8 is ensured for a long time. It becomes possible. Therefore, according to the radiation generator of the present embodiment, unnecessary radiation can be shielded and the target can be cooled with a simple structure, and a more reliable and light-weight radiation generator can be realized.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 4 is an enlarged schematic view illustrating the target peripheral portion of the radiation generating apparatus according to the present embodiment. This embodiment is another example of the third embodiment. In addition to the space between the transmissive substrate 15 and the cooling medium 8, the space between the inner wall of the passage of the second shield 18 and the cooling medium 8 is also included. The heat insulating member 25 is formed. The material and film forming method of the third embodiment can be used for the material of the heat insulating member 25 and the film forming method.

  In the present embodiment, not only the transmissive substrate 15 but also the heat conduction from the vicinity of the transmissive substrate 15 having a relatively high temperature of the second shield 18 to the cooling medium 8 can be suppressed. For this reason, deterioration of the cooling medium 8 due to overheating can be suppressed, and the pressure resistance of the cooling medium 8 can be ensured for a long time. Therefore, according to the radiation generator of the present embodiment, unnecessary radiation can be shielded and the target can be cooled with a simple structure, and a more reliable and light-weight radiation generator can be realized.

[Fifth Embodiment]
Next, a radiation imaging apparatus using the radiation generator of the present invention will be described with reference to FIG. FIG. 5 is a configuration diagram of the radiation imaging apparatus of the present embodiment. The radiation imaging apparatus according to the present embodiment includes a radiation generation apparatus 30, a radiation detector 31, a signal processing unit 32, an apparatus control unit 33, and a display unit 34. As the radiation generator 30, for example, the radiation generators of the first to fourth embodiments are preferably used. The radiation detector 31 is connected to the device control unit 33 via the signal processing unit 32, and the device control unit 33 is connected to the display unit 34 and the voltage control unit 3.

  The processing in the radiation generating apparatus 30 is comprehensively controlled by the apparatus control unit 33. For example, the device control unit 33 controls radiation imaging by the radiation generator 30 and the radiation detector 31. The radiation emitted from the radiation generator 30 is detected by the radiation detector 31 through the subject 35 and a radiation transmission image of the subject 35 is taken. The captured radiation transmission image is displayed on the display unit 34. Further, for example, the device control unit 33 controls driving of the radiation generating device 30 and controls a voltage signal applied to the transmission radiation tube 10 via the voltage control unit 3.

  1: storage container, 8: cooling medium, 10: transmission type radiation tube, 11: electron emission source, 14: target, 15: transmission substrate, 16: shield, 19: envelope, 22, 24, 25: heat insulation Element

Claims (11)

A transmissive radiation tube is stored inside the storage container filled with the cooling medium,
The transmission radiation tube is
An envelope having an opening;
An electron emission source disposed inside the envelope and facing the opening;
A transmissive substrate that transmits radiation;
A target installed on the surface of the transmission substrate on the electron emission source side, which generates radiation by irradiation of electrons emitted from the electron emission source;
A shield that blocks radiation emitted from the target;
A heat insulating member installed between the transmission substrate and the cooling medium;
With
The shield has a passage communicating with an opening of the envelope, and the transmission substrate is provided in the passage.
The radiation generating apparatus according to claim 1, wherein the cooling medium is in contact with at least a part of the shield.   The radiation generating apparatus according to claim 1, wherein an opening area of the passage is gradually increased on a side opposite to the electron emission source from the transmissive substrate.   3. The radiation according to claim 1, wherein the centers of gravity of the openings of the passages coincide with each other on the electron emission source side with respect to the transmission substrate and on the side opposite to the electron emission source with respect to the transmission substrate. Generator.   The radiation generator according to any one of claims 1 to 3, wherein the heat insulating member includes a space lower than atmospheric pressure therein.   The radiation generator according to any one of claims 1 to 3, wherein the heat insulating member is configured of a gas inside. The inside of the heat insulating member communicates with the inside of the envelope through a hole,
The radiation generating apparatus according to claim 4, wherein the hole is provided in the shield.   The radiation generator according to any one of claims 1 to 3, wherein the heat insulating member is a solid made of a material having a lower thermal conductivity than a material constituting the shield.   The radiation generator according to any one of claims 1 to 3, wherein the heat insulating member is also provided between an inner wall of the passage and the cooling medium.   The radiation generating apparatus according to claim 1, wherein the cooling medium is an electrical insulating oil.   It further comprises voltage control means for setting the target voltage to + (Va−α) [V], the electron emission source voltage to −α [V] (where Va> α> 0), respectively. The radiation generating apparatus according to claim 1, wherein the radiation generating apparatus is characterized in that:   A radiation imaging apparatus comprising: the radiation generator according to any one of claims 1 to 10; and a radiation detector that detects radiation emitted from the radiation generator and transmitted through a subject. .

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