JP2015056247A - Radiation generation device and radiographic device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress occurrence of discharge due to a mismatch between a potential distribution ascribable to a radiation generation tube and a potential distribution ascribable to a step-up circuit substrate, and to achieve miniaturization of a radiation generation device.SOLUTION: A radiation generation device includes: a radiation generation tube 6 that includes an anode 2 having a target 5, a cathode 1 having an electron emission source 4, and an insulation tube 3 connected with the anode and the cathode; and a drive circuit substrate 31 obtained by mounting, on a substrate, an anode terminal 43 electrically connected with the anode, a cathode terminal 41 electrically connected with the cathode, and a step-up circuit, wherein the anode is a transmission-type target and constitutes an end window of the radiation generation tube, the anode terminal and the cathode terminal are positioned apart by a prescribed distance on the substrate, the step-up circuit of the drive circuit substrate is constructed so that a potential increases as a distance from the cathode terminal increases, and a position of a midpoint 65 in a tube axis direction of the insulation tube substantially coincides with a centroid position of a midpoint potential of the drive circuit substrate.

Description

  The present invention relates to a radiation generating apparatus and a radiation imaging apparatus that can be applied to X-ray imaging and the like in the fields of medical equipment and industrial equipment.

  In general, a radiation generator applies a high voltage between a cathode and an anode installed in a radiation generating tube to irradiate the anode with electrons emitted from the cathode and generate radiation such as X-rays. . In such a radiation generation apparatus, in order to ensure the pressure resistance performance of the apparatus, a structure in which the radiation generation tube and the drive circuit board are installed in a storage container filled with an insulating liquid is employed.

  Usually, a tube voltage of about 70 to 150 kV is applied between the drive circuit board and the anode and cathode of the radiation generating tube. Therefore, even in a state filled with an insulating liquid, in a portion where the electric field is strong, a discharge may occur between the storage container, the cathode, the anode or other stored items. In some cases, the operating characteristics of the drive circuit board are changed or damaged. In order to prevent these discharges, it was necessary to keep a sufficient distance between the storage container, the cathode, the anode or other stored items. Further, the radiation generating tube has a structure in which a heavy metal such as lead, barium, or tungsten is used as an outer shield to cover the periphery in order to shield leakage radiation. In the case of such a structure, it is necessary for the outer peripheral shield to further secure an insulation distance between the anode or cathode of the radiation generating tube and the anode terminal or cathode terminal of the drive circuit board.

  Patent Document 1 describes a small-sized radiation generating device provided with a reflection type radiation generating tube in a storage container. By disposing a heat radiating member between the storage container and the anode, the heat dissipation is improved. It is described that the device can be driven for a long time. In Patent Document 1, it is disclosed to secure electrical insulation between a reflective radiation tube or a drive circuit and a storage container by disposing an insulating plate 46 inside a storage container made of a conductive shield. Has been.

  On the other hand, Patent Document 2 includes a transmission radiation generating tube having a transmission target as an end window, and a transmission container in which the transmission radiation generating tube and a drive circuit are stored in a storage container filled with insulating oil. A type of radiation generator is disclosed.

JP 2007-80568 A JP2013-055041A

  The present invention realizes a structure in which no discharge occurs even when the radiation generator tube and the drive circuit board are brought close to each other by adjusting the relative arrangement of the radiation generator tube and the drive circuit board with the transmission target as an end window. is there.

  In the reflection-type radiation generating tube 96 as shown in FIG. 5 according to Patent Document 1 described above, the radiation 91 emitted from the target 5 is emitted over a wide range other than the radiation extraction window 87, so that lead or tungsten is used. A peripheral shield 81 containing a heavy metal element such as bismuth as a main component is provided. The outer shield 81 is usually a conductor and is grounded by a lead wire 82. Therefore, discharge may occur depending on the distance between the outer peripheral shield 81 and at least one of the cathode 1 and the anode 2 to which a tube voltage of about 70 to 150 kV is applied. Therefore, in order to ensure insulation, the structure which arrange | positions with sufficient space | interval, or provided the insulating member 83 between the cathode 1, the anode 2, and the shielding body 81, and ensure the withstand voltage was common. Furthermore, since there is a possibility that a region having a high electric field strength is generated between the outer peripheral shield 81 and the booster circuit 84, it is necessary to provide the insulating member 83 therebetween. These structures have been limited in reducing the size of the radiation generating device including the radiation generating tube 96, the booster circuit 84, and the outer shield 81.

  On the other hand, when a transmission type radiation generating tube is used, the amount of radiation leaking to the surroundings is reduced by providing a tubular shield 7 that holds the target 5 in its inner tube as shown in FIG. Is possible. Therefore, in the transmission type radiation generating tube having such a structure, it is not necessary to separately arrange a bulky shield surrounding the radiation generating tube, so that a unit including the radiation generating tube and the drive circuit board is provided as a reflection type radiation generating tube. There was a possibility that it would be smaller and lighter than that. However, discharge may occur depending on the mismatch between the potential distribution caused by the radiation generator tube and the potential distribution caused by the drive circuit board in the space (capacitor-divided space (insulating tube, insulating liquid)). It was an obstacle to realize.

  In the present invention, in order to solve the above-described problem, the circuit board includes a radiation generating tube to which an acceleration voltage is applied between the anode and the cathode, and the circuit board extends from the center to both ends in the circuit board. In the radiation generator equipped with a booster circuit that boosts the voltage in the positive voltage direction and the negative voltage direction according to the distance from the center of the device, the following method is used to achieve a reduction in size and weight.

That is, the radiation generator of the present invention includes an anode provided with a target, a cathode provided with an electron emission source that irradiates the target with an electron beam, and the anode and the cathode connected between the anode and the cathode. A drive circuit in which a radiation generating tube comprising: an insulated tube; an anode terminal electrically connected to the anode; a cathode terminal electrically connected to the cathode; and a booster circuit mounted on a substrate A radiation generator comprising: a substrate; and a storage container for storing the radiation generator tube and the drive circuit substrate,
The anode is a transmissive target, the transmissive target constitutes an end window of the radiation generating tube, and the booster circuit has a distance from the cathode terminal between the cathode terminal and the anode terminal. The drive circuit board is disposed on the substrate so that the potential increases in accordance with the increase, and the cathode terminal, the booster circuit, and the anode terminal are arranged in the tube axis direction of the radiation generating tube. It is characterized by being juxtaposed with the radiation generating tube so as to be arranged in this order along the direction from the cathode toward the anode.

  Furthermore, the present invention provides the radiation generator, a radiation detector that detects radiation emitted from the radiation generator and transmitted through the subject, and a system control device that integrally controls the radiation generator and the radiation detector. And a radiographic apparatus characterized by comprising:

  According to the present invention, a drive circuit board on which a booster circuit in which the potential is stepped up stepwise from a cathode terminal mounted on one end side of the board toward an anode terminal mounted on the other end side, In a radiation generating device including a radiation generating tube including a cathode, an insulating tube, and an anode in the tube axis direction, an effect of suppressing discharge between the drive circuit board and the radiation generating tube can be obtained.

  By using the present invention, the drive circuit board and the radiation generating tube can be arranged close to each other. As a result, the radiation generator unit can be made smaller and lighter.

It is a figure which shows 1st embodiment of this invention and an Example. It is a figure which shows the 1st Example of this invention. It is a figure which shows the 2nd Example of this invention. It is a figure which shows the generation frequency of the micro discharge in an Example. It is a figure which shows conventional embodiment as a comparative example. It is explanatory drawing of the radiography apparatus of this invention.

The basic configuration of the radiation generator of the present invention is as follows:
1) A radiation generating tube comprising an anode provided with a target, a cathode provided with an electron emission source for irradiating the target with an electron beam, and an insulating tube connected to both electrodes between the anode and the cathode;
2) A drive circuit board in which an anode terminal electrically connected to the anode, a cathode terminal electrically connected to the cathode, and a booster circuit are mounted on the board;
3) A storage container for storing the radiation generating tube and the drive circuit board;
The features of the present invention having this basic configuration will be described in detail along the embodiment shown in FIG. The dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention only to them.

  FIG. 1 is a diagram showing a configuration of a radiation generating apparatus according to a first embodiment of the present invention.

  The radiation generating apparatus in FIG. 1 includes a radiation generating tube 6 and a drive circuit board 31 connected to the radiation generating tube 6 by lead wires 42 and 44, and is disposed in an insulating liquid when in use. The drive circuit board 31 generates radiation so that the cathode terminal 41, the booster circuit, and the anode terminal 43 are arranged in this order along the direction from the cathode 1 to the anode 2 in the tube axis direction of the radiation generating tube 6. It is juxtaposed with respect to the tube 6. The booster circuit is configured such that the potential increases as the distance from the cathode terminal 41 increases. The anode potential and the cathode potential output from the anode terminal 43 and the cathode terminal 41 of the drive circuit substrate 31 are radiation generated. The potentials of the anode 2 and the cathode 1 of the tube 6 are defined. The insulating liquid has a role as a cooling medium for the radiation generating tube 6 that heats the radiation generating tube 6 and the drive circuit board 31 to ensure the withstand voltage and when the radiation is generated. As the insulating liquid, it is preferable to use an electric insulating oil, and mineral oil, silicone oil or the like is preferably used. Other insulating liquids that can be used include fluorine-based electrical insulating liquids.

  The storage container 10 is made of a metal such as brass or stainless steel, and has a size capable of storing the radiation generating tube 6 and the insulating liquid inside the container. The storage container 10 has functions such as supporting the radiation generating tube 6 or the drive circuit board 31, shielding leakage radiation, radiating heat through the insulating liquid, and regulating the potential of the outer peripheral surface of the radiation device in addition to the storage function. May be configured to express.

  The inside of the radiation generating tube 6 is kept in vacuum, and an electron gun 4 as an electron emission source is provided inside the cathode side, and a target 5 is provided inside the anode side. Electrons emitted from the electron gun 4 are accelerated by an electric field of ± 80 to 160 kV applied between the anode and the cathode, collide with the target 5, and radiation 91 is emitted to the outside through the window 8. The target 5 is a transmissive target, and is configured as an end window of the radiation generating tube 6, unlike the case of a reflective radiation generating tube.

  Furthermore, the main structure of this invention is demonstrated along FIG.

  The boundary of the joint between the cathode 1 of the radiation generating tube 6 and the electrode of the insulating tube 3 in the anode 2 is provided at a predetermined distance away from both ends of the cathode side joint 64, the anode side joint 66, and the drive circuit board 31. The output terminals for outputting the tube voltage to the radiation generating tube 6 are referred to as a cathode terminal 41 and an anode terminal 43, respectively.

  Hereinafter, the potential distribution in the circuit network including the wiring and electric circuit components mounted on the side facing the radiation generating tube 6 on the drive circuit board 31 is identified, and the region of the intermediate potential between the anode potential and the cathode potential is identified. The position of the area centroid is defined as the midpoint 35. That is, the potential at the midpoint 35 is an additive averaged potential (Va + Vc) / 2 where the potential defined by the anode terminal 43 is the anode potential Va and the potential defined by the cathode terminal 41 is the cathode potential Vc.

  Further, in the radiation generating tube 6, the boundaries of the anode 2 and the cathode 1 and the insulating tube 3 on the side facing the drive circuit board 31 are respectively joined portions 64 and 66, and the tube axis on the outer peripheral surface of the insulating tube 3 therebetween. The distance in the direction was L, and the midpoint of the length on the surface of the drive circuit board 31 between the anode and the cathode was the midpoint 65 of the radiation generating tube 6.

  At this time, regarding the positional relationship of the midpoint 35 on the drive circuit board side, a distance 68 from the junction position 64 at the boundary between the cathode 1 of the radiation generating tube and the insulating tube 3 is defined as M.

  With such a configuration, the position of the midpoint 35 is changed by shifting the arrangement of components on the drive circuit board, and a tube voltage of ± 40 to 80 kV is applied and held for a predetermined time, resulting in a minute discharge. The frequency with which the fluctuation rate ΔIa / Iave with respect to the average value of the anode current Ia exceeded the fluctuation value of ± 10% was compared. As a result, the frequency of the current fluctuation is the lowest in the vicinity of M = L / 2, which is a state where the midpoint 35 and the midpoint 65 coincide as shown in FIG. 2, but as shown in FIG. In a certain range, it has been found that even if the midpoints of both are shifted, the increase in current fluctuation due to the micro discharge is small.

As a result of performing an experiment by moving the position of the midpoint 35 from the position of the intermediate point 65 toward the anode as shown in FIG.
M ≦ 1.44 × L / 2
It was found that the frequency of current fluctuations suddenly increased beyond this range.

Next, FIG. 3 shows the configuration of the drive circuit board and the radiation generating tube when a similar experiment is performed by moving the position of the midpoint 35 toward the cathode. In this configuration, the arrangement of the components on the drive circuit board is changed, and the position of the midpoint 35 is shifted from the position of the intermediate point 65 of the radiation generating tube 6 to the cathode side. As a result of measuring the frequency of current fluctuation while changing the position of the midpoint 35 in such a configuration,
0.56 × L / 2 ≦ M
It was found that the frequency of current fluctuations suddenly increased beyond this range.

Therefore, it was found from the above results that in this configuration, the frequency of discharge can be effectively reduced by keeping the position of the midpoint 35 of the drive circuit board within the following range.
0.56 × L / 2 ≦ M ≦ 1.44 × L / 2

  An intermediate electrode defined by the midpoint potential of the anode potential and the cathode potential is provided at a position apart from each of the anode 2 and the cathode 1 of the insulating tube 3, and the intermediate potential point between the intermediate electrode and the drive circuit board 31 is Further, it can be configured to be connected to a common electrode defined by the ground potential. In this case, there is an advantage that the potential distribution along the surface of the insulating tube can be stabilized.

  Hereinafter, a configuration common to each embodiment will be described with reference to FIG.

For the radiation generating tube 6, glass, ceramic material, or the like is used. The degree of vacuum in the tube is normally maintained at about 10 ^{−4 to} 10 ⁻⁸ Pa. The radiation generating tube 6 is provided with an opening for extracting the radiation to the outside, and a rear shielding body 7 for shielding unnecessary radiation in the vicinity of the target 5. The rear shield 7 has a passage communicating with the opening of the radiation generating tube 6, and the support substrate of the target 5 is joined to the passage so that the inside is sealed in a vacuum. The radiation generating tube 6 may be provided with an exhaust pipe (not shown). When the exhaust pipe is provided, for example, after the inside is evacuated to vacuum through the exhaust pipe, the inside of the radiation generating pipe 6 can be evacuated by sealing a part of the exhaust pipe. In order to maintain the degree of vacuum inside the radiation generating tube 6, a getter (not shown) may be arranged.

  The electron gun 4 is disposed inside the radiation generating tube 6 so as to face the opening. The electron gun 4 can be a tungsten filament, a hot cathode such as an impregnated cathode, or a cold cathode such as a carbon nanotube. Electrons 90 emitted from the electron gun 4 enter the target 5 and generate radiation 91. As a material of the target 5, tungsten, tantalum, molybdenum or the like is used.

  The radiation generating tube 6 may be provided with an extraction electrode and a lens electrode (not shown). When these are provided, the electrons emitted from the electron gun 4 by the electric field formed by the extraction electrode are converged by the lens electrode and incident on the target 5. At this time, the voltage applied between the electron gun 4 and the target 5 is approximately 40 to 150 kV although it varies depending on the intended use of radiation.

  As the drive circuit board 31, a half-wave voltage doubler rectifier circuit or a Cockcroft-Walton circuit can be used. In the Cockcroft-Walton circuit, a voltage obtained by boosting an AC voltage from an external inverter power supply (not shown) to 10 to 20 kV by a transformer (not shown) is input to the central portion of the drive circuit board 31. Electric components and wiring are mounted so that the AC voltage input at this time is gradually boosted from the center of the drive circuit board 31 toward the outside, and ± 20 kV to ± 75 kV on the anode side and the cathode side. Is output as a direct current voltage.

  Between the radiation generating tube 6 and the drive circuit board 31, only insulating oil, insulating gas, and insulating resin are present as dielectrics, and there is no outer peripheral shielding metal or conductive member.

  FIG. 6 is a diagram illustrating an example of an embodiment of a radiation imaging apparatus. The system control apparatus 102 controls the radiation generation apparatus 100 and the radiation detection apparatus 106 described above in a coordinated manner. The tube driving unit 105 includes a drive circuit board 31 and outputs various control signals to the radiation tube 6 under the control of the system control device 102. The emission state of the radiation emitted from the radiation generation apparatus 100 is controlled by the control signal. The radiation emitted from the radiation generating apparatus 100 passes through the subject 104 and is detected by the radiation detector 108. The radiation detector 108 converts the detected radiation into an image signal and outputs the image signal to the signal processing unit 107. The signal processing unit 107 performs predetermined signal processing on the image signal under the control of the system control device 102 and outputs the processed image signal to the system control device 102. The system control apparatus 102 outputs a display signal for displaying an image on the display apparatus 103 to the display apparatus 103 based on the processed image signal. The display device 103 displays an image based on the display signal on the screen as a captured image of the subject 104. That is, the system control apparatus 102 controls the radiation generation apparatus 100 and controls the radiation detector 108 via the signal processing unit 107, thereby integrally controlling the radiation generation apparatus 100 and the radiation detector 107. . A typical example of radiation is X-rays, which can be used for non-destructive inspection of industrial products and pathological diagnosis of human bodies and animals.

<Example 1>
A first embodiment will be described with reference to FIG.

  The dimensions of the main part of the radiation generating tube 6 used in this example are as follows: the tube diameter: 50 mm, and the length L between the joints 64 and 66 of the insulating tube 3 between the cathode 1 and the anode 2 of the tube is 50 mm. The insulating tube 3 between the electrodes is made of alumina ceramics. The cathode 1 is composed of Kovar alloy, and the anode-side electrode 2 is composed of tungsten alloy, Kovar alloy and copper as main materials.

  The drive circuit board 31 is a cockcroft circuit composed of a capacitor and a diode of six stages on one side, but the component layout is changed on the positive and negative circuit boards in order to change the position of the electrical middle point. The total length of the drive circuit board 31 was 140 mm, and the length between the cathode terminal 41 and the anode terminal 43 was set to 135 mm.

  The midpoint 35 and the midpoint 65 of the potential distribution between the radiation generating tube 6 configured as described above and the positive and negative electrodes of the drive circuit board 31 were arranged so that M = 36 mm. When the line connecting the cathode terminals 41 and 43 on the drive circuit board 31 to the radiation generating tube 6 side is 37, the distance 70 between the radiation generating tube 6 and the adjacent line 67 is set to G = 12 mm and immersed in insulating oil. .

  At this time, the relationship is M = 1.44 × L / 2.

  In this state, ± 50 kV is generated at the anode and the cathode of the drive circuit board 31, and a tube voltage is applied from the cathode terminal 41 and the anode terminal 43 to the cathode 1 and the anode 2 at both ends of the radiation generating tube 6 through the lead wires 42 and 44. As a result of the withstand voltage test, there was no sudden increase in current fluctuation that was thought to be caused by minute discharges as compared with the case shown in FIG. 2 in which the midpoint 35 and the midpoint 65 were aligned. At this time, the operation was stable and no discharge occurred.

  As a comparison, as a result of increasing the position of M beyond 1.44 × L / 2 <M, it was confirmed that the frequency of occurrence of minute discharges increased rapidly as shown in FIG. At this time, the operation was unstable and in some rare cases, discharge occurred. For this reason, in this embodiment, the interval 70 should be at least G = 24 mm.

<Example 2>
A second embodiment will be described with reference to FIG.

  The dimensions of the main part of the radiation generating tube 6 used in this example were the same as those in Example 1. The drive circuit board 31 is a cockcroft circuit composed of six stages of capacitors and diodes, and the length between the cathode terminal 41 and the anode terminal 43 is the same as that of the first embodiment. Is moved to the cathode side. In this embodiment, M = 14 mm. At this time, the relationship is M = 0.56 × L / 2.

  In this state, it is immersed in insulating oil to generate ± 50 kV at the anode and cathode of the drive circuit board, and from the cathode terminal 41 and anode terminal 43 to the cathode 1 and anode 2 at both ends of the radiation generating tube 6 through lead wires 42 and 44. As a result of applying the tube voltage and monitoring the current, there was no significant increase in the frequency of occurrence of microdischarges within the scope of the present invention.

  As a comparison, as a result of shifting the position of M exceeding M <0.56 × L / 2, it was confirmed that the frequency of occurrence of minute discharges rapidly increased as shown in FIG. At this time, the operation was unstable, and in some rare cases, discharge occurred. For this reason, in this embodiment, the interval 70 should be at least G = 25 mm.

  1: cathode, 2: anode, 3: insulating tube, 4: electron gun, 5: target, 6: radiation generating tube, 8: window, 10: storage container, 31: drive circuit board, 35: midpoint position, 41 : Cathode terminal, 42: lead wire, 43: anode terminal, 44: lead wire, 64: position of junction (cathode side junction), 65: midpoint of radiation generating tube, 66: position of junction (anode side) (Joint part), 68: distance from the midpoint position to the joint part, 70: interval (G), 81: outer peripheral shield, 82: ground ground wire, 83: insulating member, 84: booster circuit, 85: electron gun, 87: Radiation extraction window, 86: Reflective target, 90: Electron beam, 91: Radiation, 96: Reflective radiation generator tube

Claims (9)

Radiation generation comprising an anode having a target, a cathode having an electron emission source for irradiating the target with an electron beam, and an insulating tube connected to the anode and the cathode between the anode and the cathode Tube,
An anode terminal electrically connected to the anode, a cathode terminal electrically connected to the cathode, and a drive circuit board on which a booster circuit is mounted on a substrate;
A storage container for storing the radiation generating tube and the drive circuit board;
A radiation generator comprising:
The anode is a transmission target, and the transmission target constitutes an end window of the radiation generating tube;
The booster circuit is disposed on the substrate such that the potential increases with an increase in the distance from the cathode terminal between the cathode terminal and the anode terminal,
The drive circuit board is arranged such that the cathode terminal, the booster circuit, and the anode terminal are arranged in this order along the direction from the cathode to the anode in the tube axis direction of the radiation generating tube. A radiation generating apparatus, wherein the radiation generating apparatus is juxtaposed with the radiation generating tube.   The position of the intermediate point in the tube axis direction of the insulating tube on the outer peripheral surface of the insulating tube substantially coincides with the position of the center of gravity of the midpoint potential of the drive circuit board. Radiation generator.   The intermediate point is an intermediate position in the distance between the anode side junction between the anode and the insulating tube and the cathode side junction between the cathode and the insulating tube. The radiation generator described in 1. The midpoint potential is an average potential (Va + Vc) / 2 between the anode potential Va defined by the anode terminal and the cathode potential Vc defined by the cathode terminal,
4. The radiation generating apparatus according to claim 1, wherein the center-of-gravity position is a position of a center of gravity of a region defined by the midpoint potential on the drive circuit board. 5.   When the distance from the cathode side junction in the tube axis direction of the center-of-gravity position of the midpoint potential is M and the length of the insulating tube in the tube axis direction is L, M is 0.56 × L. The radiation generator according to any one of claims 1 to 4, wherein a range of /2≦M≦1.44×L/2 is satisfied.   The radiation generating tube has an intermediate electrode defined by a midpoint potential of an anode potential and a cathode potential at a position separated from each of the anode and the cathode of the insulating tube, and an intermediate electrode between the intermediate electrode and the drive circuit board. The radiation generating apparatus according to claim 1, wherein the potential point is connected to the common electrode.   The radiation generating apparatus according to claim 6, wherein the common electrode is regulated to a ground potential.   The boost circuit includes a Cockcroft-Walton circuit that generates a positive voltage based on the midpoint potential and a Cockcroft-Walton circuit that generates a negative voltage based on the midpoint potential. Item 8. The radiation generator according to any one of Items 1 to 7.   A radiation generator according to any one of claims 1 to 8, a radiation detector that detects radiation emitted from the radiation generator and transmitted through a subject, the radiation generator and the radiation detector. A radiation imaging apparatus comprising: a system control device that performs integrated control.

Images