X-ray generating device

Abstract

An X-ray generating device (1) is provided with: a cathode electrode (5) that releases electrons (E); an adjustment electrode (7) that adjusts the amount of electron emission from the cathode electrode (5); a control electrode (8) that controls the orbital of electrons (E) from the cathode electrode (5); a target (9) that generates X-rays (R) in response to the incidence of electrons (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) such that the focus size of the electrons (E) in the target (9) during discharge detection is larger than the focus size of the electrons (E) in the target (9) during normal operation.

Description

Technical Field

[0001] The invention relates to an X-ray generating device. Background Art

[0002] As an existing X-ray generating device, there is a radiation generating unit described in Japanese Patent Publication No. 2014-130732, for example. The existing radiation generating unit includes: a cathode electrode heated by a heater; an extraction electrode for extracting 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 to generate radiation.

[0003] In an X-ray generating device such as the one described above, discharges caused by various factors become a problem. For example, in the X-ray generating device described in Japanese Patent Publication No. 8-94546, attention is paid to the discharges generated in the shell. When a discharge occurs in the shell, the voltage (tube voltage) applied between the cathode electrode and the target will drop instantaneously. At this time, if the bias voltage applied from the Wehnelt electrode is maintained at a certain value, the focal area of ​​the X-rays formed on the target is excessively reduced, and the target is damaged. In the X-ray generating device of Patent Document 2, a unit for detecting the discharge generated in the shell is included. When a discharge is detected, the bias voltage applied from the Wehnelt electrode is controlled in such a way that the focal point of the X-rays is not less than the allowable limit. Summary of the invention

[0004] The discharge in the X-ray tube can also be generated at a more specific location inside the shell. For example, in the case where an adjustment electrode for adjusting the amount of electrons released from the cathode electrode is arranged in the X-ray tube, it is considered that a part of the material constituting the cathode electrode will fly from the cathode electrode heated by the heater and adhere to the adjustment electrode. When the attachment is deposited on the adjustment electrode, the gap between the cathode electrode and the adjustment electrode becomes narrower, the original withstand voltage characteristics decrease, and discharge is easy to occur. When a discharge occurs between the cathode electrode and the adjustment electrode, the cathode electrode and the adjustment electrode become the same potential during the discharge, so it is temporarily impossible to control the amount of electrons released from the cathode electrode by the potential difference between the cathode electrode and the adjustment electrode. In this case, the electrons from the cathode electrode are not released according to the potential difference control between the cathode electrode and the target, so there is a problem of excessive electron release from the cathode electrode. When excessive electrons are released from the cathode electrode, excessive electrons are incident on the target, and there is a risk of damage to the target.

[0005] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an X-ray generating device that can avoid damage to a target even when discharge occurs between a cathode electrode and an adjustment electrode.

[0006] An X-ray generating device involved in one aspect of the present invention includes: a cathode electrode that releases electrons; an adjusting electrode that adjusts the amount of electrons released from the cathode electrode; a control electrode that controls the orbit of electrons from the cathode electrode; a target that generates X-rays according to the incidence of electrons; a discharge detection unit that detects the discharge between the cathode electrode and the adjusting electrode; and a voltage switching unit that switches the voltage difference between the cathode electrode and the control electrode in such a way that the focal size of the electrons in the target during discharge detection becomes larger than the focal size of the electrons in the target during normal operation.

[0007] In the X-ray generating device, when the discharge between the cathode electrode and the adjustment electrode is detected, the voltage difference between the cathode electrode and the control electrode is switched so that the focal size of the electrons in the target is larger than the focal size of the electrons in the target during normal operation. Thus, even when excessive electrons are released from the cathode electrode due to the discharge between the cathode electrode and the adjustment electrode, the concentration of the excessive electrons in the target can be suppressed, and damage to the target can be avoided.

[0008] The voltage switching unit may make the voltage difference between the cathode electrode and the control electrode smaller during discharge detection than during normal operation. Thus, the focus size of electrons in the target during discharge detection can be made larger than the focus size of electrons in the target during normal operation more reliably.

[0009] The voltage switching unit may also be composed of a resistor electrically connected to the cathode electrode. In this case, when electrons of a level that damages the target are released from the cathode electrode through discharge between the cathode electrode and the adjustment electrode, a current larger than that in normal operation will flow from the cathode electrode to the resistor. As a result, the voltage of the cathode electrode drops, and the focal size of the electrons in the target becomes larger than the focal size of the electrons in the target during normal operation. With this structure, there is no need to set up a control unit for controlling the voltage switching unit, and damage to the target can be avoided with a simple structure.

[0010] The voltage switching unit may also be composed of a variable power supply that applies a voltage to the cathode electrode. In this case, when the discharge between the cathode electrode and the adjustment electrode is detected, the voltage of the cathode electrode can be varied by using the variable power supply, so that the focal size of the electrons in the target is larger than the focal size of the electrons in the target during normal operation. With this structure, the focal size of the electrons can be freely adjusted by controlling the variation of the voltage of the cathode electrode, and damage to the target can be more reliably avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram showing the structure of an X-ray generator according to one embodiment of the present invention. Figure 2 It is a diagram showing the operation of the voltage switching unit during normal operation and during discharge detection. Figure 3 It is a schematic diagram showing the structure of an X-ray generating device according to a modified example. DETAILED DESCRIPTION

[0012] Hereinafter, a preferred embodiment of an X-ray generating device according to one aspect of the present invention will be described in detail with reference to the accompanying drawings.

[0013] Figure 1 1 is a schematic diagram showing the structure of an X-ray generator according to an embodiment of the present invention. As shown in the figure, the X-ray generator 1 includes an X-ray tube 2 and a drive circuit 3. The X-ray tube 2 is a transmission type X-ray tube, and is composed of a cathode electrode 5, a heater 6, an adjustment electrode 7, a control electrode 8, and a target 9 provided in a vacuum box 4. The cathode electrode 5, the heater 6, the adjustment electrode 7, and the control electrode 8 constitute an electron gun EG.

[0014] The vacuum box 4 is formed in a hollow cylindrical shape, for example, by airtightly joining a head formed of a metal material and a tube body formed of an insulating material. Examples of the metal material constituting the head include stainless steel, nickel alloy, copper, copper alloy, iron alloy, etc. Examples of the insulating material constituting the tube body include glass, ceramics, etc. A window member 10 is provided at the front end of the head. The window member 10 is formed in a plate shape with the tube axis as the center line, for example, from an X-ray transmitting material such as beryllium, aluminum, diamond, etc.

[0015] The cathode electrode 5 is an electrode that releases electrons E. The cathode electrode 5 releases electrons E by being heated by the heater 6 in a powered state. The heater 6 is a portion that heats the cathode electrode 5. The heater 6 is composed of a filament that generates heat by being powered. The electrons E released from the cathode electrode 5 pass through the electron passage hole 7a of the adjustment electrode 7 and the electron passage hole 8a of the control electrode 8, and travel toward the target 9.

[0016] The adjustment electrode 7 is a first gate 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 emitted from the adjustment electrode 7 and traveling toward 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, for example, an electron passage hole 7a having a circular cross section. The electron passage hole 7a allows the electrons E emitted from the cathode electrode 5 to pass toward the control electrode 8 side.

[0017] The control electrode 8 is a second gate 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 released 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, for example, an electron passage hole 8a with a circular cross section. The electron passage hole 8a is coaxially arranged with the electron passage hole 7a of the adjustment electrode 7, so that the electrons E passing through the electron passage hole 7a pass toward the target 9 side.

[0018] The target 9 is a part that generates X-rays R in response to the incidence of electrons E. The target 9 is disposed on the inner (vacuum side) surface of the window member 10 on the tube axis of the vacuum box 4. The target 9 is, for example, a film formed on the inner surface of the window member 10. As constituent materials of the target 9, for example, tungsten, molybdenum, copper, etc. can be cited. The target 9 is electrically connected to the head of the vacuum box 4. The potential of the target 9 is, for example, a ground potential.

[0019] like Figure 1 As shown, the driving circuit 3 includes a heater power supply 11, a cathode electrode power supply 12, an adjustment 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 adjustment electrode power supply 13 is electrically connected to the adjustment electrode 7 and supplies a voltage to the adjustment 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.

[0020] In the X-ray generator 1 having the above-mentioned structure, when performing a normal operation of outputting X-rays R from the target 9, for example, a negative high voltage of 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 three-electrode X-ray tube that has not only the cathode electrode 5 and the target 9 described above, but also electrodes such as the adjustment electrode 7 and the control electrode 8 for controlling the electrons E emitted from the cathode electrode 5 to the target 9. The parameters of the electrons E released from the cathode electrode 5 and the X-rays R generated from the target 9 are controlled by these electrodes 5, 7, and 8.

[0021] In the X-ray generating device 1, electrons E are released from the cathode electrode 5 due to the addition of heat from the heater 6. The amount of electrons released from the cathode electrode 5 is controlled by the potential difference between the cathode electrode 5 and the adjustment electrode 7. The initial velocity of the electrons E is controlled by the potential difference between the cathode electrode 5 and the control electrode 8. The electrons E reaching the control electrode 8 are accelerated by the potential difference between the control electrode 8 and the target 9 (here, the ground potential), and collide with the target 9.

[0022] By controlling the potential of the control electrode 8, an electrostatic lens is formed to control the trajectory of the electron E. The size of the focus F of the electron E in the target 9 (focal point size) is controlled by the initial velocity of the electron E and the action of the electrostatic lens. The focal point size of the electron E in the target 9 refers to the size of the incident area of ​​the electron E on the electron incident surface 9a of the target 9. During normal operation, the potential difference between the cathode electrode 5 and the control electrode 8 is controlled in such a way that the focal point size of the electron E in the target 9 is minimized. The X-ray R generated by the impact of the electron E on the target 9 passes through the window member 10 and is emitted to the outside of the X-ray tube 2. The brightness of the X-ray R (tube current value) is controlled by adjusting the potential of the electrode 7. The energy (acceleration voltage value) of the X-ray R is controlled by the potential of the control electrode 8.

[0023] In the above-mentioned X-ray generator 1, discharge can be generated inside the X-ray tube 2. In the X-ray generator 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, for example, it is considered that a part of the material constituting the cathode electrode 5 flies from the cathode electrode 5 heated by the heater 6 and adheres to the adjustment electrode 7. In addition, not limited to the material constituting the cathode electrode 5, there is a possibility that various foreign matter such as the material constituting the heater 6 adheres to the adjustment electrode 7. When the attachment is deposited on the adjustment electrode 7, the interval between the cathode electrode 5 and the adjustment electrode 7 becomes narrower, and the withstand voltage characteristics originally possessed are reduced, and discharge is easy to occur. When discharge occurs between the cathode electrode 5 and the adjustment electrode 7, the cathode electrode 5 and the adjustment electrode 7 become the same potential in the middle of the discharge, so the control of the amount of electron emission from the cathode electrode 5 by the potential difference between the cathode electrode 5 and the adjustment electrode 7 cannot be performed temporarily. In this case, the electrons from the cathode electrode 5 are not released according to the potential difference control between the cathode electrode 5 and the target 9, so there is a possibility that excessive electrons are released from the cathode electrode 5. When excessive electrons are released from the cathode electrode 5 , excessive electrons E are incident on the target 9 , and there is a risk that the target 9 may be damaged.

[0024] Therefore, in the X-ray generator 1, the drive circuit 3 is provided with a discharge detection unit 21 for detecting the discharge between the cathode electrode 5 and the adjustment electrode 7 and a voltage switching unit 22 for switching the voltage difference between the cathode electrode 5 and the control electrode 8 in such a manner that the focal size of the electrons E in the target 9 during the discharge detection is larger than the focal size of the electrons E in the target 9 during the normal operation. In this embodiment, as Figure 1 As shown, in the drive circuit 3 , a resistor 23 is connected between the cathode electrode 5 and the cathode power supply 12 (on the negative terminal side of the cathode power supply 12 ), and the resistor 23 functions as a discharge detection unit 21 and a voltage switching unit 22 .

[0025] 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 the normal operation (normal current). By flowing the discharge current through the resistor 23, the voltage of the cathode electrode 5 drops significantly compared to the normal operation. By the drop in the voltage of the cathode electrode 5, it can be detected that a discharge has occurred between the cathode electrode 5 and the adjustment electrode 7.

[0026] The connection position of the resistor 23 is not limited to any position as long as it is a position where the discharge current from the cathode electrode 5 flows. Figure 1 of examples. exist Figure 1 In the example of , 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 also be between the control electrode power supply 14 and the reference potential (ground potential) (on the negative terminal side of the control electrode power supply 14).

[0027] When the voltage of the cathode electrode 5 decreases 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 released from the cathode electrode 5 decreases. As described above, the focal size of the electrons E in 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 released from the cathode electrode 5 decreases, the focal position of the electrons E on the electron incident surface 9a of the target 9 shifts along the orbital axis of the electrons E. Therefore, as Figure 2 As shown, the focal size of the electrons E in the target 9 becomes larger than the focal size of the electrons E in the target 9 during the normal operation.

[0028] In this embodiment, since the discharge current flows to the resistor 23, the voltage of the cathode electrode 5 decreases compared to the normal operation (see Figure 2 As a result, the focus position of the electron E is shifted toward the front of the target 9, and thus the focus size of the electron E in the target 9 becomes larger than the focus size of the electron E in the target 9 during normal operation. Therefore, even when the amount of electron emission from the cathode electrode 5 cannot be controlled temporarily due to the discharge generated between the cathode electrode 5 and the adjustment electrode 7, damage to the target 9 caused by excessive electrons E incident on the target 9 can be suppressed.

[0029] As described above, in the X-ray generating device 1, when the 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 so that the focal size of the electrons in the target 9 is larger than the focal size of the electrons E in the target 9 during normal operation. Thus, even when excessive electrons are released from the cathode electrode 5 due to the discharge between the cathode electrode 5 and the adjustment electrode 7, the concentration of the excessive electrons E in the target 9 can be suppressed, and damage to the target 9 can be avoided.

[0030] In this embodiment, the voltage switching unit 22 makes the voltage difference between the cathode electrode 5 and the control electrode 8 smaller during discharge detection than during normal operation. This can more reliably make the focal size of the electrons E in the target 9 larger during discharge detection than during normal operation.

[0031] In the present embodiment, the voltage switching unit 22 is composed of a resistor 23 electrically connected to the cathode electrode 5. In this case, when electrons E of a level that causes damage to the target 9 are released from the cathode electrode 5 by discharge between the cathode electrode 5 and the adjustment electrode 7, a current larger than that in 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 in the target 9 becomes larger than the focal size of the electrons E in the target 9 in normal operation. With this structure, by flowing the discharge current to the resistor 23, the resistor 23 itself functions as the discharge detection unit 21 and the voltage switching unit 22, so there is no need to set up a control unit for controlling the voltage switching unit 22, and damage to the target 9 can be avoided with a simple structure.

[0032] Figure 3 2 is a schematic diagram showing the structure of an X-ray generator according to a modified example. As shown in the figure, the structures of the discharge detection unit 21 and the voltage switching unit 22 of the X-ray generator 31 according to the modified example are similar to those of FIG. Figure 1 The X-ray generating device 1 shown is different.

[0033] Specifically, in the X-ray generating device 31, a current detecting unit 32 is provided as the discharge detecting unit 21 instead of the resistor 23. The current detecting unit 32 is composed of, for example, a current transformer or a resistor having a smaller resistance value than the resistor 23. In addition, as the voltage switching unit 22, the cathode electrode power supply 12 is composed of a variable power supply 33, and a control unit 34 for controlling the operation of the variable power supply 33 is provided. The control unit 34 physically includes, for example, a processor such as a CPU, and a storage medium such as a RAM and a ROM. The control unit 34 may be a smartphone or a tablet terminal in which a display unit and an input unit are integrally provided, or may be composed of a microcomputer, an FPGA (Field-Programmable Gate Array), or the like.

[0034] In the X-ray generator 31, when the current detection unit 32 detects the current during discharge from the cathode electrode 5, a signal indicating the detection result is output to the control unit 34. The control unit 34 receives the signal from the current detection unit 32 and controls the variable power supply 33 to switch the voltage difference between the cathode electrode 5 and the control electrode 8 so that the focal size of the electrons E in the target 9 becomes larger than the focal size of the electrons E in the target 9 during normal operation. Thus, even if excessive electrons are released from the cathode electrode 5 due to the discharge between the cathode electrode 5 and the adjustment electrode 7, the concentration of the excessive electrons E on the target 9 can be suppressed, and damage to the target 9 can be avoided.

[0035] In addition, in the present embodiment, the voltage switching unit 22 is constituted by a variable power supply 33. Thus, the focal size of the electrons E can be freely adjusted by controlling the amount of change in the voltage of the cathode electrode 5, and damage to the target 9 can be more reliably avoided.

[0036] In addition, in Figure 1 As in the X-ray generating device 1 shown in the figure, when the discharge detection unit 21 and the voltage switching unit 22 are composed of the resistor 23, the voltage of the cathode electrode 5 is reduced compared with the normal operation by flowing the discharge current to the resistor 23. In this embodiment, when the current detection unit 32 detects the discharge current, the voltage of the cathode electrode 5 can be reduced compared with the normal operation by the variable power supply 33 (refer to Figure 2 arrow F1), it can also rise compared to the normal action (refer to Figure 2 F2).

[0037] When the voltage of the cathode electrode 5 is increased compared to the normal operation, the focal position of the electrons E is shifted toward the depth of the target 9, so that the focal size of the electrons E in the target 9 becomes larger than the focal size of the electrons E in the target 9 during the normal operation. Therefore, as in the case where the voltage of the cathode electrode 5 is decreased compared to the normal operation, damage to the target 9 caused by the concentration of excessive electrons E in the target 9 can be suppressed.

[0038] The present invention is not limited to the above-mentioned embodiment. For example, in the above-mentioned embodiment, a transmission-type X-ray tube is exemplified as the X-ray tube 2, but the X-ray tube 2 may also be a reflection-type X-ray tube. In addition, in the above-mentioned embodiment, a sealed tube structure in which the vacuum box 4 is sealed as a vacuum tube is exemplified as the X-ray tube 2, but the X-ray tube 2 may also be an open tube structure having an exhaust pump or the like. In addition, in the above-mentioned embodiment, a hot cathode structure having a heater 6 is exemplified as the electron gun EG, but the electron gun EG may also be a cold cathode structure. The potential relationship applied to the electron gun EG and the target 9 only needs to be a relationship in which the electrons E go to the target when X-rays are generated, and the electrodes other than the target 9 may also be a reference potential (ground potential).

[0039] 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 can be, for example, set between the adjustment electrode 7 and the negative terminal of the adjustment electrode power supply 13. In this case, the discharge detection unit 21 detects the current flowing from the adjustment electrode 7 to the negative terminal of the adjustment electrode power supply 13 (the current flowing in the adjustment electrode 7) as the discharge current. The discharge detection unit 21 can also be set between the positive terminal of the adjustment 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 adjustment electrode power supply 13 to the cathode electrode 5 as the discharge current. The discharge detection unit 21 can also be set between the target 9 and the ground potential. In this case, the discharge detection unit 21 detects the current flowing in the target 9 as the discharge current.

Claims

1. An X-ray generating device, characterized in that: include: a cathode electrode that releases electrons; a regulating electrode for regulating the amount of electrons released from the cathode electrode; a control electrode for controlling the orbit of the electrons from the cathode electrode; a target that generates X-rays in response to the incidence of the electrons; a discharge detection unit for detecting a discharge between the cathode electrode and the adjustment electrode; and A voltage switching unit switches a voltage difference between the cathode electrode and the control electrode so that a focal size of the electrons in the target during discharge detection becomes larger than a focal size of the electrons in the target during normal operation.

2. The X-ray generating device according to claim 1, characterized in that: The voltage switching unit makes the voltage difference between the cathode electrode and the control electrode smaller during the discharge detection than during the normal operation.

3. The X-ray generating device according to claim 1 or 2, characterized in that: The voltage switching unit is composed of a resistor electrically connected to the cathode electrode.

4. The X-ray generating device according to claim 1 or 2, characterized in that: The voltage switching unit is composed of a variable power supply that applies a voltage to the cathode electrode.

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