JP4216394B2 - X-ray tube device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray tube apparatus that generates X-rays.
[0002]
[Prior art]
An X-ray tube apparatus is an apparatus that generates X-rays and is used in many applications such as medical diagnostic apparatuses.
[0003]
Here, a conventional X-ray tube apparatus will be described with reference to FIG. Reference numeral 31 denotes a vacuum envelope constituting an X-ray tube, and a cathode 32 is disposed on one side of the vacuum envelope 31. The cathode 32 includes a filament 32a that emits electrons, a grid electrode 32b that focuses the electrons e emitted from the filament 32a, and the like. In addition, an anode 33 that generates X-rays by collision of electrons e is disposed at a position facing the cathode 32. Both the cathode 32 and the anode 33 are mechanically supported by the vacuum envelope 31 and are electrically insulated.
[0004]
The cathode 32 is connected to the negative terminal of the first power supply 34. The positive terminal of the first power supply 34 is connected to the ground GND, and is simultaneously connected to the ammeter 35. The ammeter 35 is connected to the negative terminal of the second power source 36, and the positive terminal of the second power source 36 is connected to the anode 33.
[0005]
In the above configuration, when the X-ray tube enters the operating state, a high voltage is applied between the cathode 32 and the anode 33 by the first power source 34 and the second power source 36. At this time, electrons e are emitted from the filament 32e, converged by the grid electrode 32b, and collide with the anode 33. X-rays are generated from the anode 33 by the collision of electrons e.
[0006]
Further, the tube current flowing through the anode 33 of the X-ray tube is measured by an ammeter 35, and X-ray energy and X-ray dose generated from the X-ray tube are controlled by controlling the tube voltage and tube current.
[0007]
[Problems to be solved by the invention]
In the case of the conventional X-ray tube apparatus, in its operating state, a predetermined tube voltage is applied between the cathode 32 and the anode 33, and the wall surface of the vacuum envelope 31 has a certain potential distribution. Then, the electrons e emitted from the cathode 32 collide with the anode 33 and X-rays are generated from the anode 33. At this time, a part of the electron flux reaches the surface of the vacuum envelope 31 as shown by the dotted arrow Y due to scattering when colliding with the anode 33, and the vacuum envelope 31 is charged.
[0008]
The charging of the vacuum envelope 31 is stable under certain operating conditions. However, if the tube voltage is changed to change the generated X-ray energy or X-ray dose, the charged state becomes unstable. The unstable state continues for a certain period of time, and during that time, for example, the charge moves along the inner wall surface of the vacuum envelope 31 and may reach the anode 33.
[0009]
At this time, the current value (ie + ia) is added to the ammeter 35 by adding the current (ie) due to the electric charge moving along the inner wall surface of the vacuum envelope 31 and the tube current (ia) of the X-ray tube. Is detected. In this case, the current (ie) due to the charge does not contribute to the generation of X-rays. Therefore, when the operation of the X-ray tube is controlled based on the tube current measured by the ammeter 35, the current (ie) due to the charge is affected, and a predetermined X-ray output such as X-ray energy and X-ray dose is generated. It can no longer be obtained.
[0010]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described drawbacks and to provide an X-ray tube apparatus capable of obtaining a stable X-ray output.
[0011]
[Means for Solving the Problems]
This invention includes a cathode for emitting electrons, X-rays generated in the irradiation of the electron, and an anode connected to ground, mechanically supporting said cathode and said anode, and electrically insulates the anode A vacuum envelope having a small diameter on the side supporting the negative electrode, a negative terminal connected to the cathode, a positive terminal connected to ground, and a voltage applied between the cathode and the anode In an X-ray tube apparatus having a power source, an ammeter is connected between the anode and the ground, and a metal annular capture electrode is provided in the small diameter portion of the vacuum envelope, and the capture electrode is connected to the ammeter. It is characterized by being connected to the ground without being interposed .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIG.
[0013]
Reference numeral 11 denotes a vacuum envelope constituting the X-ray tube, and the vacuum envelope 11 is substantially entirely formed of an insulator such as glass. A cathode 12 is disposed on one side of the vacuum envelope 11. The cathode 12 includes a filament 12a that emits electrons, a grid electrode 12b that focuses the electrons e emitted from the filament 12a, and the like. An anode 13 that generates X-rays by collision of electrons e is disposed at a position facing the cathode 12. Both the cathode 12 and the anode 13 are mechanically supported by the vacuum envelope 11 and are electrically insulated. The vacuum envelope 11 has a small diameter portion 11a having a small diameter on the side supporting the anode 13. A metal capture electrode 14 is annularly provided at a position close to the portion that supports the anode 13, for example, at a small diameter portion 11 a that is a side portion of the anode 13. Therefore, the glass part constituting the vacuum envelope 11 is divided into two by the capture electrode 14 on the cathode 12 side and the anode 13 side.
[0014]
The cathode 12 is connected to the negative terminal of the first power supply 15. The positive terminal of the first power supply 15 is connected to the ground GND and simultaneously connected to the ammeter 16. The ammeter 16 is connected to the anode 13. The capture electrode 14 is connected to the positive terminal of the first power supply 15, and is connected to the ground GND without passing through the ammeter 16.
[0015]
In the above configuration, when the X-ray tube enters the operating state, a high voltage is applied between the cathode 12 and the anode 13 by the first power supply 15. At this time, electrons e are emitted from the filament 12a, converged by the grid electrode 12b, and irradiated to the anode 13. X-rays are generated from the anode 13 by irradiation with electrons e.
[0016]
At this time, in the X-ray tube, the tube current flowing through the anode 13 is measured by the ammeter 16, and the generated X-ray energy and X-ray dose are controlled.
[0017]
In the X-ray tube apparatus having the above-described configuration, a predetermined tube voltage is applied between the cathode 12 and the anode 13 in the operating state. At this time, the inner wall surface of the vacuum envelope 11 has a certain potential distribution. When the electrons e emitted from the cathode 12 collide with the anode 13, a part of the electrons e is scattered, and a part of the electron flux reaches the surface of the vacuum envelope 11 as shown by the dotted arrow Y, and the vacuum The envelope 11 is charged.
[0018]
In this state, for example, if the tube voltage is changed in order to change the energy or amount of X-rays, the charged state of the vacuum envelope 11 becomes unstable, and the charge along the inner wall surface of the vacuum envelope 11 becomes unstable. However, it moves toward the anode 13 having a high potential.
[0019]
However, in the case of the configuration described above, the capture electrode 14 is provided in a part of the vacuum envelope 11. Therefore, the current (ie) due to the electric charges moving along the inner wall surface of the vacuum envelope 11 is captured by the capture electrode 14 and flows in the direction of the ground GND without passing through the ammeter 16. Therefore, the current (ie) due to charge transfer is not measured by the ammeter 16.
[0020]
As a result, the ammeter 16 measures only the tube current (ia), the tube current stabilization control of the X-ray tube is correctly performed, and a desired X-ray output is obtained.
[0021]
Further, the capture electrode 14 is provided in a small diameter portion 11 a of the vacuum envelope 11 that is a side portion of the anode 13. In this case, the capture electrode 14 is located near the anode 13. Therefore, many charges moving on the inner wall surface of the vacuum envelope 11 can be captured by the capture electrode 14, and correct tube current stabilization control of the X-ray tube is performed.
[0022]
In the configuration described above, a power source is not connected between the anode 13 and the capture electrode 14. In this case, the potential difference between the anode 13 and the capture electrode 14 is small, and discharge between the anode 13 and the capture electrode 14 is prevented. Therefore, this configuration is suitable when the anode 13 is operated while being grounded.
[0023]
Next, another embodiment of the present invention will be described with reference to FIG. 2, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted.
[0024]
In this embodiment, the anode 13 is connected to the positive terminal of the second power supply 21, and the negative terminal of the second power supply 21 is connected to the ammeter 16. Further, the ammeter 16 and the first power supply 15 are connected to the ground GND. A resistor 22 and a smoothing capacitor 23 are connected in parallel between the capture electrode 14 and the positive terminal of the second power supply 21. Note that the current (ie) flowing through the capture electrode 14 due to the movement of the electric charge charged on the inner wall surface of the vacuum envelope 11 is normally generated in a pulse shape when the charge is accumulated to some extent. According to the configuration described above, the current (ie) due to the movement of charges is smoothed by the action of the smoothing capacitor 23. Therefore, a change in current measured by the ammeter 16 is suppressed to a small level, tube current stabilization control of the X-ray tube is correctly performed, and a desired X-ray output is obtained.
[0025]
In the case of the configuration described above, the capture electrode 14 is connected to the positive terminal of the second power supply 21 via the resistor 22 and the smoothing capacitor 23. For this reason, the potential difference between the anode 13 and the capture electrode 14 is reduced, and the occurrence of discharge between the anode 13 and the capture electrode 14 is prevented.
[0026]
Therefore, this configuration is suitable when a power source is connected between the anode 13 and the ground.
[0027]
According to the configuration described above, fluctuations in the X-ray output due to the movement of charges on the wall surface of the vacuum envelope, which occurs when the operating conditions of the X-ray tube such as the tube voltage are changed, can be prevented.
[0028]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the X-ray tube apparatus which can obtain a stable X-ray output is realizable.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining an embodiment of the present invention and showing a schematic electrical connection configuration;
FIG. 2 is a diagram for explaining another embodiment of the present invention and showing a schematic electrical connection configuration;
FIG. 3 is a diagram showing a schematic electrical connection configuration of a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Vacuum envelope 12 ... Cathode 12a ... Filament 12b ... Grid electrode 13 ... Anode 14 ... Capture electrode 15 ... 1st power supply 16 ... Ammeter 21 ... 2nd power supply 22 ... Resistance 23 ... Capacitor e ... Electron GND ... Ground ie ... Current ia due to charge transfer ... Tube current

Claims (3)

A cathode that emits electrons, an X-ray generated by irradiation of the electrons, and a grounded anode, and the side that mechanically supports and electrically insulates the cathode and the anode and supports the anode A vacuum envelope having a small diameter and a small diameter portion , a negative terminal connected to the cathode, a positive terminal connected to ground, and a power source for applying a voltage between the cathode and the anode. In the X-ray tube apparatus, an ammeter is connected between the anode and the ground, and a metal annular capture electrode is provided in the small diameter portion of the vacuum envelope, and the capture electrode is grounded without passing through the ammeter. An X-ray tube device connected to the X-ray tube. A cathode that emits electrons, an anode that generates X-rays upon irradiation of the electrons, a mechanically supporting and electrically insulating cathode and anode, and a side that supports the anode having a small diameter A vacuum envelope that is a small portion, a first power source with a negative terminal connected to the cathode, a positive terminal connected to ground, and a second power source with a positive terminal connected to the anode ; In the X-ray tube device comprising an ammeter connected between the negative terminal of the second power source and the ground , a metal annular capture electrode is provided in the small diameter portion of the vacuum envelope, and the capture electrode Is connected to the positive terminal of the second power supply through a parallel circuit of a resistor and a capacitor . The X-ray tube apparatus according to claim 1 or 2, wherein the capture electrode is provided so as to divide the insulating portion of the vacuum envelope supporting the cathode and the anode into two parts on the cathode side and the anode side .

Images