X-ray generation device

Abstract

To provide an X-ray generation device capable of avoiding a damage of a target even in the occurrence of discharge between a cathode electrode and an adjustment electrode.SOLUTION: An X-ray generation device 1 includes a cathode electrode 5 that emits an electron E, an adjustment electrode 7 that adjusts the amount of releasing electrons from the cathode electrode 5, a control electrode 8 that controls an orbit of the electron E from the cathode electrode 5, a target 9 that generates X-rays R by the incidence of the electron E, a discharge detection unit 21 that detects discharge between the cathode electrode 5 and the adjustment electrode 7, and a voltage switching unit 22 that switches the voltage difference between the cathode electrode 5 and the control electrode 8 so that the focal dimension of the electron E at the target 9 at the discharge detection becomes larger than the focal dimension of the electron E at the target 9 at the normal operation.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to x-ray generating devices. [Background technology]

[0002] An example of a conventional X-ray generating device is a radiation generating unit described in Patent Document 1. This conventional radiation generating unit includes a cathode electrode heated by a heater, an extraction electrode that extracts electrons from the heated cathode electrode, a heater power supply connected to the heater, an electrode power supply connected to the extraction electrode, and a target that receives electrons from the cathode electrode and generates radiation.

[0003] In the X-ray generator described above, discharges caused by various factors become a problem. For example, the X-ray generator described in Patent Document 2 focuses on discharges occurring within the casing. When a discharge occurs within the casing, the voltage (tube voltage) applied between the cathode electrode and the target drops instantaneously. At this time, if the bias voltage applied from the Wehnelt is kept at a constant value, the focal area of ​​the X-rays formed on the target is excessively narrowed, damaging the target. The X-ray generator of Patent Document 2 includes a means for detecting discharges occurring within the casing, and when a discharge is detected, the bias voltage applied from the Wehnelt is controlled so that the focal area of ​​the X-rays does not become smaller than the allowable limit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-130732 A [Patent Document 2] Japanese Patent Application Publication No. 8-94546 Summary of the Invention [Problem to be solved by the invention]

[0005] Discharge in the X-ray tube may also occur at a specific location in the casing. For example, when an adjustment electrode for adjusting the amount of electrons emitted from the cathode electrode is disposed in the X-ray tube, it is possible that a part of the material constituting the cathode electrode may fly from the cathode electrode heated by a heater and adhere to the adjustment electrode. When the adhesion accumulates on the adjustment electrode, the gap between the cathode electrode and the adjustment electrode narrows, and the inherent voltage resistance characteristic decreases, making it easier for discharge to occur. When discharge occurs between the cathode electrode and the adjustment electrode, the cathode electrode and the adjustment electrode have the same potential during discharge, so that the amount of electrons emitted from the cathode electrode, which was performed by the potential difference between the cathode electrode and the adjustment electrode, cannot be controlled temporarily. In this case, electrons from the cathode electrode are emitted without control according to the potential difference between the cathode electrode and the target, so there is a risk of excessive electron emission from the cathode electrode. When excessive electrons are emitted from the cathode electrode, excessive electrons are incident on the target, which may damage the target.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an X-ray generating device that can avoid damage to the target even if a discharge occurs between the cathode electrode and the adjustment electrode. [Means for solving the problem]

[0007] An X-ray generating device according to one aspect of the present disclosure includes a cathode electrode that emits electrons, an adjustment electrode that adjusts the amount of electrons emitted from the cathode electrode, a control electrode that controls the trajectory of electrons from the cathode electrode, a target that generates X-rays by the incidence of electrons, a discharge detection unit that detects discharge between the cathode electrode and the adjustment electrode, and a voltage switching unit that switches the voltage difference between the cathode electrode and the control electrode so that the focal size of the electrons at the target when the discharge is detected is larger than the focal size of the electrons at the target during normal operation.

[0008] In this X-ray generator, when a discharge between the cathode electrode and the adjustment electrode is detected, the voltage difference between the cathode electrode and the control electrode is switched to make the focal size of electrons on the target larger than the focal size of electrons on the target during normal operation. This makes it possible to suppress the concentration of excessive electrons on the target and avoid damage to the target even if excessive electrons are emitted from the cathode electrode due to a discharge between the cathode electrode and the adjustment electrode.

[0009] The voltage switching unit may reduce the voltage difference between the cathode electrode and the control electrode during discharge detection compared to during normal operation, thereby more reliably making the focal size of electrons on the target during discharge detection larger than the focal size of electrons on the target during normal operation.

[0010] The voltage switching unit may be configured by a resistor electrically connected to the cathode electrode. In this case, when electrons at a level that damages the target are emitted from the cathode electrode due to discharge between the cathode electrode and the adjustment electrode, a current larger than that during normal operation flows from the cathode electrode to the resistor. This causes the voltage of the cathode electrode to drop, and the focal size of the electrons on the target becomes larger than that during normal operation. With this configuration, a control unit or the like that controls the voltage switching unit is not required, and damage to the target can be avoided with a simple configuration.

[0011] The voltage switching unit may be configured with a variable power supply that applies a voltage to the cathode electrode. In this case, when a discharge between the cathode electrode and the adjustment electrode is detected, the voltage of the cathode electrode is varied by the variable power supply, so that the focal size of electrons on the target can be made larger than the focal size of electrons on the target during normal operation. With this configuration, the focal size of electrons can be freely adjusted by controlling the amount of variation in the voltage of the cathode electrode, and damage to the target can be more reliably avoided. Effect of the Invention

[0012] According to the present disclosure, even if a discharge occurs between the cathode electrode and the adjusting electrode, damage to the target can be avoided. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a configuration of an X-ray generating device according to an embodiment of the present disclosure. [Diagram 2] 6A and 6B are diagrams illustrating the operation of the voltage switching unit during normal operation and when detecting a discharge. [Diagram 3] FIG. 13 is a schematic diagram showing the configuration of an X-ray generating device according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a preferred embodiment of an X-ray generating device according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0015] 1 is a schematic diagram showing a configuration of an X-ray generator according to an embodiment of the present disclosure. As shown in the figure, the X-ray generator 1 includes an X-ray tube 2 and a driving circuit 3. The X-ray tube 2 is a transmission type X-ray tube, and includes a cathode electrode 5, a heater 6, an adjustment electrode 7, a control electrode 8, and a target 9 in a vacuum housing 4. The cathode electrode 5, the heater 6, the adjustment electrode 7, and the control electrode 8 constitute an electron gun EG.

[0016] The vacuum housing 4 is formed into a hollow cylinder by airtightly joining a head portion made of, for example, a metal material and a valve portion made of an insulating material. Examples of the metal material constituting the head portion include stainless steel, nickel alloy, copper, copper alloy, and iron alloy. Examples of the insulating material constituting the valve portion include glass and ceramic. A window member 10 is provided at the tip of the head portion. The window member 10 is formed into a plate shape with the tube axis as the center line, and is made of an X-ray transparent material such as beryllium, aluminum, or diamond.

[0017] The cathode electrode 5 is an electrode that emits electrons E. The cathode electrode 5 emits electrons E when heated by a heater 6 in an energized state. The heater 6 is a part that heats the cathode electrode 5. The heater 6 is composed of a filament that generates heat when energized. The electrons E emitted from the cathode electrode 5 pass through the electron passing hole 7a of the adjustment electrode 7 and the electron passing hole 8a of the control electrode 8, and proceed toward the target 9.

[0018] The adjustment electrode 7 is a first grid electrode that adjusts the amount of electrons emitted from the cathode electrode 5. The amount of electrons emitted from the cathode electrode 5 refers to the amount of electrons E that pass through the adjustment electrode 7 and proceed to the target 9, among the electrons E emitted from the cathode electrode 5 by the heating of the heater 6. The adjustment electrode 7 controls the amount of electrons emitted from the cathode electrode 5 based on the voltage applied to the adjustment electrode 7. The adjustment electrode 7 has an electron passing hole 7a having, for example, a circular cross section. The electron passing hole 7a allows the electrons E emitted from the cathode electrode 5 to pass to the control electrode 8 side.

[0019] The control electrode 8 is a second grid electrode that controls the trajectory of the electrons E from the cathode electrode 5 by forming an electrostatic lens. The control electrode 8 also functions as an extraction electrode that forms an electric field for extracting electrons from the cathode electrode 5. The control electrode 8 focuses the electrons E emitted from the cathode electrode 5 and passing through the adjustment electrode 7, and focuses them on the target 9 as an electron beam. The control electrode 8 has an electron passing hole 8a that has, for example, a circular cross section. The electron passing hole 8a is disposed coaxially with the electron passing hole 7a of the adjustment electrode 7, and allows the electrons E that have passed through the electron passing hole 7a to pass toward the target 9.

[0020] The target 9 is a portion that generates X-rays R by the incidence of electrons E. The target 9 is provided on the inner (vacuum side) surface of the window member 10 on the tube axis of the vacuum housing 4. The target 9 is, for example, a film formed on the inner surface of the window member 10. Examples of materials that make up the target 9 include tungsten, molybdenum, and copper. The target 9 is electrically connected to the head of the vacuum housing 4. The potential of the target 9 is, for example, ground potential.

[0021] 1, the drive circuit 3 includes a heater power supply 11, a cathode electrode power supply 12, an adjusting electrode power supply 13, and a control electrode power supply 14. The heater power supply 11 is electrically connected to the heater 6 and supplies a voltage to the heater 6. The cathode electrode power supply 12 is electrically connected to the cathode electrode 5 and supplies a voltage to the cathode electrode 5. The adjusting electrode power supply 13 is electrically connected to the adjusting electrode 7 and supplies a voltage to the adjusting electrode 7. The control electrode power supply 14 is electrically connected to the control electrode 8 and supplies a voltage to the control electrode 8.

[0022] In the X-ray generator 1 having the above configuration, during normal operation in which X-rays R are output from the target 9, a negative high voltage of, for example, about -100 kV is applied to the electron gun EG with the potential of the target 9 as a reference (ground potential). The X-ray tube 2 of this embodiment is a so-called triode X-ray tube that has, in addition to the above-mentioned cathode electrode 5 and target 9, electrodes such as the adjustment electrode 7 and control electrode 8 that control the electrons E emitted from the cathode electrode 5 and directed toward the target 9, and these electrodes 5, 7, and 8 control the parameters of the electrons E emitted from the cathode electrode 5 and the X-rays R generated from the target 9.

[0023] In the X-ray generating device 1, electrons E are emitted from the cathode electrode 5 by application of heat from the heater 6. The amount of electrons emitted from the cathode electrode 5 is controlled by the potential difference between the cathode electrode 5 and the adjustment electrode 7. The initial speed of the electrons E is controlled by the potential difference between the cathode electrode 5 and the control electrode 8. The electrons E that reach the control electrode 8 are accelerated by the potential difference between the control electrode 8 and a target 9 (here, ground potential) and collide with the target 9.

[0024] The potential of the control electrode 8 forms an electrostatic lens that controls the trajectory of the electrons E. The size (focal size) of the focal point F of the electrons E on the target 9 is controlled by the initial velocity of the electrons E and the action of the electrostatic lens. The focal size of the electrons E on the target 9 refers to the size of the incidence area of ​​the electrons E on the electron incidence surface 9a of the target 9. During normal operation, the potential difference between the cathode electrode 5 and the control electrode 8 is controlled so that the focal size of the electrons E on the target 9 is minimized. The X-rays R generated on the target 9 by the collision of the electrons E are emitted to the outside of the X-ray tube 2 through the window member 10. The brightness (tube current value) of the X-rays R is controlled by the potential of the adjustment electrode 7. The energy (acceleration voltage value) of the X-rays R is controlled by the potential of the control electrode 8.

[0025] In the above-mentioned X-ray generating device 1, discharge may occur inside the X-ray tube 2. In the X-ray generating device 1 in which the adjustment electrode 7 for adjusting the amount of electron emission from the cathode electrode 5 is arranged in the X-ray tube 2, it is considered that, for example, a part of the material constituting the cathode electrode 5 may fly from the cathode electrode 5 heated by the heater 6 and adhere to the adjustment electrode 7. In addition, various foreign matter such as the material constituting the heater 6 may adhere to the adjustment electrode 7, not limited to the material constituting the cathode electrode 5. When the adhesion accumulates on the adjustment electrode 7, the gap between the cathode electrode 5 and the adjustment electrode 7 is narrowed, and the inherent withstand voltage characteristics are reduced, making it easier for discharge to occur. When discharge occurs between the cathode electrode 5 and the adjustment electrode 7, the cathode electrode 5 and the adjustment electrode 7 have the same potential during the discharge, so that the amount of electron emission from the cathode electrode 5, which was performed by the potential difference between the cathode electrode 5 and the adjustment electrode 7, cannot be controlled temporarily. In this case, electrons from the cathode electrode 5 are emitted without control according to the potential difference between the cathode electrode 5 and the target 9, and there is a risk of excessive electron emission from the cathode electrode 5. If excessive electron emission from the cathode electrode 5 occurs, excessive electrons E will be incident on the target 9, and there is a risk of the target 9 being damaged.

[0026] Therefore, in the X-ray generating device 1, the drive circuit 3 is provided with a discharge detection unit 21 that detects discharge between the cathode electrode 5 and the adjustment electrode 7, and a voltage switching unit 22 that switches the voltage difference between the cathode electrode 5 and the control electrode 8 so that the focal spot size of the electrons E on the target 9 during discharge detection becomes larger than the focal spot size of the electrons E on the target 9 during normal operation. In this embodiment, as shown in FIG. 1, in the drive circuit 3, a resistor 23 is connected between the cathode electrode 5 and the cathode electrode power supply 12 (on the negative terminal side of the cathode electrode power supply 12), and this resistor 23 functions as the discharge detection unit 21 and the voltage switching unit 22.

[0027] When a discharge occurs between the cathode electrode 5 and the adjustment electrode 7, a current based on the discharge (discharge current) flows from the cathode electrode 5 to the resistor 23. The discharge current can be about 10 times larger than the current based on normal operation (normal current). When the discharge current flows through the resistor 23, the voltage of the cathode electrode 5 drops significantly compared to normal operation. This drop in the voltage of the cathode electrode 5 makes it possible to detect that a discharge has occurred between the cathode electrode 5 and the adjustment electrode 7.

[0028] The connection position of the resistor 23 may be any position where a current flows during discharge from the cathode electrode 5, and is not limited to the example of Fig. 1. In the example of Fig. 1, the resistor 23 is connected between the cathode electrode 5 and the cathode electrode power supply 12 (on the positive terminal side of the cathode electrode power supply 12), but the resistor 23 may be connected between the cathode electrode power supply 12 and the control electrode power supply 14 (on the negative terminal side of the cathode electrode power supply 12). The connection position of the resistor 23 may be between the control electrode power supply 14 and a reference potential (ground potential) (on the negative terminal side of the control electrode power supply 14).

[0029] When the voltage of the cathode electrode 5 drops during discharge detection, the voltage difference between the cathode electrode 5 and the control electrode 8 becomes smaller than that during normal operation, and the initial velocity of the electrons E emitted from the cathode electrode 5 decreases. As described above, the focal size of the electrons E on the target 9 is controlled by the initial velocity of the electrons E and the action of the electrostatic lens. When the initial velocity of the electrons E emitted from the cathode electrode 5 decreases, the focal position of the electrons E on the electron incidence surface 9a of the target 9 shifts along the orbital axis of the electrons E. For this reason, as shown in FIG. 2, the focal size of the electrons E on the target 9 becomes larger than the focal size of the electrons E on the target 9 during normal operation.

[0030] In this embodiment, the voltage of the cathode electrode 5 drops compared to that during normal operation due to the current flowing through the resistor 23 during discharge (see arrow F1 in FIG. 2), and the focal position of the electrons E shifts in front of the target 9, so that the focal size of the electrons E on the target 9 becomes larger than the focal size of the electrons E on the target 9 during normal operation. Therefore, even if the amount of electrons emitted from the cathode electrode 5 becomes temporarily uncontrollable due to the discharge occurring between the cathode electrode 5 and the adjustment electrode 7, damage to the target 9 caused by excessive electrons E being incident on the target 9 can be suppressed.

[0031] As described above, in the X-ray generating device 1, when a discharge between the cathode electrode 5 and the adjustment electrode 7 is detected, the voltage difference between the cathode electrode 5 and the control electrode 8 is switched to make the focal size of electrons on the target 9 larger than the focal size of electrons E on the target 9 during normal operation. This makes it possible to suppress the concentration of excessive electrons E on the target 9 and avoid damage to the target 9, even if excessive electrons are emitted from the cathode electrode 5 due to a discharge between the cathode electrode 5 and the adjustment electrode 7.

[0032] In this embodiment, the voltage switching unit 22 reduces the voltage difference between the cathode electrode 5 and the control electrode 8 during discharge detection compared to during normal operation. This makes it possible to more reliably make the focal size of the electrons E on the target 9 during discharge detection larger than the focal size of the electrons E on the target 9 during normal operation.

[0033] In this embodiment, the voltage switching unit 22 is configured by a resistor 23 electrically connected to the cathode electrode 5. In this case, when electrons E at a level that damages the target 9 are emitted from the cathode electrode 5 due to discharge between the cathode electrode 5 and the adjustment electrode 7, a current larger than that during normal operation flows from the cathode electrode 5 to the resistor 23. As a result, the voltage of the cathode electrode 5 drops, and the focal size of the electrons E on the target 9 becomes larger than the focal size of the electrons E on the target 9 during normal operation. According to this configuration, the resistor 23 itself functions as the discharge detection unit 21 and the voltage switching unit 22 by the discharge current flowing through the resistor 23, so that a control unit for controlling the voltage switching unit 22 is not necessary, and damage to the target 9 can be avoided with a simple configuration.

[0034] 3 is a schematic diagram showing the configuration of an X-ray generator according to a modified example. As shown in the figure, an X-ray generator 31 according to the modified example has a discharge detection unit 21 and a voltage switching unit 22 different in configuration from the X-ray generator 1 shown in FIG.

[0035] Specifically, in the X-ray generating device 31, a current detection unit 32 is provided as the discharge detection unit 21 instead of the resistor 23. The current detection unit 32 is configured, for example, by a current transformer or a resistor having a smaller electric resistance value than the resistor 23. In addition, as the voltage switching unit 22, the cathode electrode power supply 12 is configured by a variable power supply 33, and a control unit 34 is provided for controlling the operation of the variable power supply 33. The control unit 34 is physically configured to include, for example, a processor such as a CPU, and a storage medium such as a RAM or a ROM. The control unit 34 may be a smartphone or tablet terminal integrally provided with a display unit and an input unit, or may be configured by a microcomputer, an FPGA (Field-Programmable Gate Array), or the like.

[0036] In the X-ray generating device 31, when the current detection unit 32 detects a current during discharge from the cathode electrode 5, it outputs a signal indicating the detection result to the control unit 34. The control unit 34, which has received the signal from the current detection unit 32, controls the variable power supply 33 and switches the voltage difference between the cathode electrode 5 and the control electrode 8 so that the focal size of the electrons E on the target 9 becomes larger than the focal size of the electrons E on the target 9 during normal operation. This makes it possible to suppress the concentration of the excessive electrons E on the target 9, and to avoid damage to the target 9, even if excessive electrons are emitted from the cathode electrode 5 due to discharge between the cathode electrode 5 and the adjustment electrode 7.

[0037] In this embodiment, the voltage switching unit 22 is configured by a variable power supply 33. This makes it possible to freely adjust the focal size of the electrons E by controlling the amount of fluctuation in the voltage of the cathode electrode 5, and thus makes it possible to more reliably avoid damage to the target 9.

[0038] In addition, when the discharge detection unit 21 and the voltage switching unit 22 are configured with a resistor 23 as in the X-ray generating device 1 shown in Figure 1, the voltage of the cathode electrode 5 drops compared to normal operation when a discharge current flows through the resistor 23. However, in this embodiment, when the current detection unit 32 detects a discharge current, the voltage of the cathode electrode 5 may be lowered compared to normal operation by the variable power supply 33 (see arrow F1 in Figure 2) or may be increased compared to normal operation (see arrow F2 in Figure 2).

[0039] When the voltage of the cathode electrode 5 is increased compared to that during normal operation, the focal position of the electrons E shifts to the back of the target 9, and the focal size of the electrons E on the target 9 becomes larger than the focal size of the electrons E on the target 9 during normal operation. Therefore, similar to the case where the voltage of the cathode electrode 5 is decreased compared to that during normal operation, damage to the target 9 due to excessive concentration of the electrons E on the target 9 can be suppressed.

[0040] The present disclosure is not limited to the above embodiment. For example, in the above embodiment, a transmission type X-ray tube is exemplified as the X-ray tube 2, but the X-ray tube 2 may be a reflection type X-ray tube. In addition, in the above embodiment, a sealed tube structure in which the vacuum housing 4 is sealed as a vacuum tube is exemplified as the X-ray tube 2, but the X-ray tube 2 may be an open tube structure equipped with an exhaust pump or the like. In addition, in the above embodiment, a hot cathode structure equipped with a heater 6 is exemplified as the electron gun EG, but the electron gun EG may be a cold cathode structure. The potential relationship applied to the electron gun EG and the target 9 may be such that the electrons E are directed toward the target when X-rays are generated, and an electrode other than the target 9 may be a reference potential (ground potential).

[0041] The position of the discharge detection unit 21 is not limited to between the cathode electrode 5 and the cathode electrode power supply 12, and may be provided, for example, between the adjusting electrode 7 and the negative terminal of the adjusting electrode power supply 13. In this case, the discharge detection unit 21 detects the current flowing from the adjusting electrode 7 to the negative terminal of the adjusting electrode power supply 13 (the current flowing through the adjusting electrode 7) as the current during discharge. The discharge detection unit 21 may be provided between the positive terminal of the adjusting electrode power supply 13 and the cathode electrode 5. In this case, the discharge detection unit 21 detects the current flowing from the positive terminal of the adjusting electrode power supply 13 to the cathode electrode 5 as the current during discharge. The discharge detection unit 21 may be provided between the target 9 and a ground potential. In this case, the discharge detection unit 21 detects the current flowing through the target 9 as the current during discharge. [Explanation of symbols]

[0042] 1, 31...X-ray generator, 5...cathode electrode, 7...adjusting electrode, 8...control electrode, 9...target, 21...discharge detection unit, 22...voltage switching unit, 23...resistance, 33...variable power supply, 34...control unit, E...electrons, R...X-rays.

Claims

1. a cathode electrode that emits electrons; an adjustment electrode for adjusting the amount of electrons emitted from the cathode electrode; a control electrode for controlling a trajectory of the electrons from the cathode electrode; a target that generates X-rays when the electrons are incident on the target; a discharge detection unit that detects a discharge between the cathode electrode and the adjustment electrode; and a voltage switching unit that switches the voltage difference between the cathode electrode and the control electrode so that a focal size of the electrons on the target when a discharge is detected is larger than a focal size of the electrons on the target during normal operation.

2. 2. The X-ray generating device according to claim 1, wherein the voltage switching section reduces a voltage difference between the cathode electrode and the control electrode when the discharge is detected, compared to the voltage difference during the normal operation.

3. 3. The X-ray generating apparatus according to claim 1, wherein the voltage switching unit is configured by a resistor electrically connected to the cathode electrode.

4. 3. The X-ray generating apparatus according to claim 1, wherein the voltage switching unit is constituted by a variable power supply that applies a voltage to the cathode electrode.

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