JP2006092879A - X-ray tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray tube capable of improving manufacturability and miniaturizable. <P>SOLUTION: A vacuum capacitor 8 in a vacuum envelope 2 is serially connected between a filament 6 and a focusing electrode 7. Metallic coating layers 14 having a low work function are formed on the inside surfaces of a pair of parallel flat plates 11 and 12 of the vacuum capacitor 8. A bias voltage applied to the focusing electrode 7 is generated by charge left in the vacuum capacitor 8 in dropping the voltage of the filament 6. A laser beam is radiated from an optical fiber 15 to the inside surfaces of the parallel flat plates 11 and 12 in turning off the bias voltage. The vacuum capacitor 8 is discharged by using photoelectrons generated by a photoelectric effect to control the potential of the focusing electrode 7. This X-ray tube 1 capable of generating a pulse-shaped X-ray while cutting off a soft X-ray wave tail can be realized. The X-ray tube 1 can be reduced in cost and size. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an X-ray tube that generates X-rays when electrons emitted from a cathode enter an anode.

  Conventionally, this type of lattice-controlled X-ray tube is mainly used in a medical X-ray apparatus, and includes a vacuum container in which an anode and a cathode are accommodated. A control grid for controlling electrons emitted from the cathode is disposed in the vacuum vessel. A power source dedicated to lattice control for controlling the generation of pulsed X-rays by applying a bias voltage to the control lattice is provided outside or inside the vacuum vessel. However, in this lattice control type X-ray tube, since the power source for lattice control becomes large, it causes the increase in size and the manufacturing cost.

Further, in the case of an X-ray tube having three focal points that is frequently used for medical treatment and diagnosis as a medical X-ray tube, when a common electrode for supplying a filament current and a lattice electrode are combined, 5 There is known a configuration in which the cathode side high-voltage introduction terminal is required for the X-ray tube container (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 7-240296 (page 3-4, FIG. 1)

  However, a high voltage cable for a cathode having a 4-pin lead terminal generally used for an X-ray tube having three focal points requires two high voltage cables and a socket, and the X-ray tube container is enlarged. Is invited. In addition, the two cathode high-voltage cables become an obstacle, and it is not easy to mount the X-ray tube on the arm that supports the X-ray tube, or the volume of the high-voltage cable that runs through this arm is obstructive. Since restrictions are imposed on the design, there is a problem that it is not easy to improve the manufacturability of the entire X-ray apparatus.

  The present invention has been made in view of these points, and an object of the present invention is to provide an X-ray tube capable of improving manufacturability and miniaturizing.

  The present invention includes a container, a cathode that emits electrons, an anode that is provided in the container and generates X-rays upon incidence of electrons emitted from the cathode, and is emitted from the cathode toward the anode. An X-ray tube comprising a control electrode for controlling electrons, a capacitor having one electrically connected to the cathode and the other electrically connected to the control electrode, and charge control means for controlling the charge of the capacitor Are provided.

  Then, by controlling the charge of the capacitor by the charge control means, photoelectrons are generated in the capacitor, and the photoelectrons are supplied to the control electrode through the capacitor. As a result, the potentials of the control electrode and the cathode become equal, the potential of the control electrode becomes stable, electrons are emitted from the cathode toward the anode, and X-rays are generated. Next, when the application of high voltage from the high voltage power supply is stopped in order to stop the emission of X-rays, the potential of the cathode is lowered due to the discharge of the charge. By stopping, the capacitor remains in a state where charges are stored. Since the potential difference is generated in the capacitor due to the decrease in the potential of the cathode, the voltage of the control electrode with respect to the cathode becomes negative. Therefore, the emission of electrons from the cathode is suppressed by the electric field of the control electrode, and a cut-off state is established. Therefore, the voltage between the control electrode and the cathode can be controlled off by controlling the charge of the capacitor by the charge control means without providing a power source for applying a voltage to the control electrode, thereby improving productivity. Since the configuration is simplified, the size can be reduced.

  According to the present invention, by controlling the charge of the capacitor by the charge control means, the potentials of the control electrode and the cathode become equal, and the potential of the control electrode is stabilized. Further, by stopping the charge control of the capacitor by the charge control means as the cathode potential decreases, a potential difference is generated in the capacitor, and the emission of electrons from the cathode is suppressed by the electric field of the control electrode, and the blocking state is established. Become. For this reason, it is possible to control the voltage between the control electrode and the cathode by controlling the charge of the capacitor by the charge control means without providing a power source for applying a voltage to the control electrode in the container. Since it can improve and a structure becomes simple, it can reduce in size.

  The configuration of the first embodiment of the X-ray tube of the present invention will be described below with reference to the drawings.

  In FIG. 1, reference numeral 1 denotes an X-ray tube. The X-ray tube 1 is a grid control type X-ray tube mainly used in a medical X-ray apparatus or the like. And this X-ray tube 1 is equipped with the vacuum envelope 2 which is a tube as a vacuum vessel with the inside maintained in a high vacuum state. The vacuum envelope 2 holds the inside in a vacuum. Furthermore, a pair of vacuum introduction terminals 3 and 4 are provided on one side surface of the vacuum envelope 2 to energize the vacuum envelope 2 from the outside.

  And in this vacuum envelope 2, the anode 5 as an anode which produces | generates an X-ray by the incidence | injection of the thermoelectron as an electron is provided and accommodated. The anode 5 is housed in the vacuum envelope 2 and on the other side located on the opposite side of one side surface of the vacuum envelope 2 where the pair of vacuum introduction terminals 3 and 4 are provided. Further, a 4-pin high voltage cable (not shown) is electrically connected to the anode 5, and a high voltage is applied from the high voltage cable.

  The vacuum envelope 2 is provided with a filament 6 for thermionic emission as a cathode structure that is insulated from the anode 5 and serves as an electron emission source of the cathode. Further, the vacuum envelope 2 is provided with a focusing electrode 7 serving as a control electrode that also serves as a control grid. The converging electrode 7 converges the thermoelectrons emitted from the filament 6 by an electric field. That is, the focusing electrode 7 is disposed so as to be separated from the filament 6 and is electrically insulated from the filament 6.

  Here, each side of the filament 6 is electrically connected to the vacuum introduction terminals 3 and 4. The filament 6 is provided at a position where the thermoelectrons can be emitted facing the anode 5. Further, the filament 6 is electrically connected to a cathode high-voltage power source (not shown), and emits thermoelectrons when energized by the cathode high-voltage power source and reaches a high temperature. The thermoelectrons are accelerated by an electric field generated by a high bias voltage applied by an external power source (not shown) between the anode 5 and the filament 6 while being converged by the focusing electrode 7, and are directed toward the anode 5. X-rays are generated by braking radiation when the anode 5 is impacted. In other words, the thermoelectrons emitted from the filament 6 are accelerated by a high voltage applied between the anode 5 and the filament 6 from an external power source, collide with the anode 5, and enter the anode 5 of the thermoelectrons. X-rays are generated by the impact.

  Further, a vacuum capacitor 8 is accommodated and installed in the vacuum envelope 2. The vacuum capacitor 8 is electrically connected in series between the focusing electrode 7 and the filament 6. The vacuum capacitor 8 is configured by arranging parallel plates 11 and 12 as electrodes as a pair of conductors while maintaining a space in a vacuum. In other words, the pair of parallel flat plates 11 and 12 are arranged to face each other with a gap. That is, the pair of parallel plates 11 and 12 face each other with a vacuum gap (Gap). In this vacuum capacitor 8, the filament 6 and the focusing electrode 7 are electrically coupled via a capacitance generated between the pair of parallel plates 11 and 12.

  One parallel plate 11 of the vacuum capacitor 8 is a converging power supply side electrode and is electrically connected to the converging electrode 7. For this reason, the converging electrode 7 is in an electrically floating state with respect to the potential of the filament 6. The other parallel plate 12 of the vacuum capacitor 8 is a filament side electrode and is electrically connected to the common electrode 13 which is one electrode of the filament 6.

  The pair of parallel flat plates 11 and 12 of the vacuum capacitor 8 are arranged such that inner surfaces as surfaces that face each other with a predetermined gap therebetween are parallel to each other. Further, the inner surface of each of the pair of parallel plates 11 and 12 of the vacuum capacitor 8 is coated with a metal having a low work function and a high photoemission coefficient, for example, an alkali metal such as cesium (Cs). A coating layer 14 is provided as a layer.

  Further, an optical fiber 15 for introducing light into the vacuum envelope 2 is introduced and installed in the vacuum envelope 2. This optical fiber 15 is provided in a light irradiation means as a charge control means for controlling the charge of the vacuum capacitor 8. The proximal end of the optical fiber 15 is connected to a semiconductor laser light source (not shown) installed outside the vacuum envelope 2. The tip of the optical fiber 15 is disposed to face the inner surfaces of the pair of parallel plates 11 and 12 of the vacuum capacitor 8 facing each other. Are arranged so that the inner surface of the parallel plate 11 on the side electrically connected to the laser beam can be irradiated. That is, the optical fiber 15 irradiates the laser beam toward the inner surface of the parallel plate 11 on the side electrically connected to the focusing electrode 7. In other words, the optical fiber 15 is arranged at a position where the light introduced into the vacuum envelope 2 from the outside of the vacuum envelope 2 can be irradiated between the pair of parallel plates 11 and 12 of the vacuum capacitor 8. It is installed.

  In the vacuum envelope 2, an X-ray shielding cover 16 is installed as a shielding plate as a shielding means. The X-ray shielding cover 16 is made of a shielding metal having a large atomic number that emits less gas, such as tungsten (W) or molybdenum (Mo). Further, the X-ray shielding cover 16 surrounds the vacuum capacitor 8 and the optical fiber 15 in the vacuum envelope 2. That is, the X-ray shielding cover 16 is configured so as not to hit the vacuum capacitor 8 or the optical fiber 15 such as direct X-rays, scattered X-rays, and out-of-focus X-rays generated in the vacuum envelope 2. In other words, in this X-ray shielding cover 16, the optical fiber 15 is deteriorated due to coloring by the color center due to irradiation of X-rays generated in the vacuum envelope 2, or malfunction of the vacuum capacitor 8 is caused by photoelectric effect due to X-rays. To prevent it from occurring. Further, the X-ray shielding cover 16 is configured to perform a pulsed X-ray generation operation by light control.

  Next, the operation of the X-ray tube of the first embodiment will be described.

  First, when the filament 6 is energized by a cathode high voltage power source and the filament 6 becomes high temperature, thermoelectrons are emitted from the filament 6.

  The thermoelectrons are accelerated by a bias electric field formed by a high voltage applied from an external power source between the anode 5 and the filament 6 while being converged by the focusing electrode 7, and directed toward the anode 5. And collides with the anode 5.

  At this time, X-rays are generated from the anode 5 by bremsstrahlung due to impact when the thermoelectrons collide with the anode 5.

  Next, an operation when X-rays are exposed will be described.

  First, by applying a tube voltage for X-ray exposure to the filament 6 from the cathode high voltage power source, the potential Vc of the filament 6 rises with the cathode potential from the cathode high voltage power source.

  At this time, the focusing electrode 7 is floated in potential by the pair of parallel plates 11 and 12 of the vacuum capacitor 8. For this reason, the potential Vg of the converging electrode 7 does not increase following the potential increase of the filament 6.

  Therefore, as shown in FIG. 2, the laser beam L is irradiated to the mutually facing inner surfaces of the pair of parallel plates 11 and 12 of the vacuum capacitor 8 by the optical fiber 15 introduced from the outside to the inside of the vacuum envelope 2. To do.

  At this time, the inner surface of the pair of parallel flat plates 11 and 12 is coated with a material having a low work function to form a coating layer 14. Therefore, as shown in FIG. 3, photoelectrons e are generated by irradiating the coating layer 14 with the laser light L.

  Then, as shown in FIG. 4, the photoelectrons e emitted from the parallel plate 12 on the filament 6 side electrically connected to the filament 6 converge through a vacuum gap between the pair of parallel plates 11 and 12. It is supplied to the parallel plate 11 on the side of the focusing electrode 7 that is electrically connected to the electrode 7.

  As a result, as shown in FIG. 5, the potential Vc of the parallel plate 12 on the filament 6 side of the vacuum capacitor 8 is equal to the potential Vg of the parallel plate 11 on the focusing electrode 7 side of the vacuum capacitor 8. Therefore, electric charges are discharged to the focusing electrode 7, the electric potential of the focusing electrode 7 is stabilized, and thermoelectrons are emitted from the filament 6 toward the anode 5 to generate X-rays.

  Next, the operation when X-rays are blocked by the focusing electrode 7 will be described.

  First, when the high voltage application output from the cathode high voltage power supply is stopped to stop the generation of X-rays, the cathode potential of the filament 6 starts to decrease. Along with this, the potential Vc of the parallel plate 12 on the filament 6 side of the vacuum capacitor 8 decreases.

  At this time, as shown in FIG. 6, when the supply of the laser light L from the optical fiber 15 is stopped in synchronization with the stop of the output from the cathode high voltage power source, the parallel plate 11 on the converging electrode 7 side of the vacuum capacitor 8 is stopped. However, since it is electrically insulated by the gap of the vacuum capacitor 8, the charge when a high voltage is applied to the anode 5 is left behind, and this charge remains stored.

  Then, as shown in FIG. 7, the potential Vc of the filament 6 is lowered to the ground potential, so that a potential difference is generated between the potential Vg of the focusing electrode 7 and the potential Vc of the filament 6.

  That is, as shown in FIGS. 8 and 9, the voltage of the focusing electrode 7 with respect to the filament 6 of the vacuum capacitor 8 becomes negative. Accordingly, a reverse bias voltage is applied to the convergence electrode 7.

  When this voltage exceeds the lattice cutoff voltage (the voltage at which Vc is reduced by about 1 kV or more and 3 kV or less), thermionic emission from the filament 6 is suppressed by the electric field from the focusing electrode 7 and enters a cutoff state. The charge discharge of the stray capacitance of the high voltage cable that is not performed is stopped, and the soft X-ray wave tail due to this stray capacitance is cut off and cut off.

  As a result, by irradiating the vacuum condenser 8 with a laser beam from the optical fiber 15 in a pulsed manner in synchronization with the power on / off, the pulsed X-ray on / off control is repeated while repeatedly blocking the soft X-ray wave tail. Is possible.

  As described above, according to the first embodiment, the focusing electrode 7 is insulated from the anode 5, the vacuum capacitor 8 is built in the vacuum envelope 2, and the vacuum capacitor 8 is connected to the filament 6. And the focusing electrode 7 are connected in series. Further, an optical fiber 15 for irradiating the laser beam L between the pair of parallel plates 11 and 12 of the vacuum capacitor 8 is introduced into the vacuum envelope 2 and the pair of parallel plates of the vacuum capacitor 8 is introduced. A coating layer 14 is formed by coating the inner surfaces of 11 and 12 with a metal having a low work function.

  Then, the bias voltage applied to the focusing electrode 7 is generated by the charge left in the vacuum capacitor 8 when the voltage of the filament 6 decreases. Further, when this bias voltage is turned off, laser light is irradiated from the optical fiber 15 between the vacuum gap between the pair of parallel plates 11 and 12 of the vacuum capacitor 8 to use photoelectrons e generated by the photoelectric effect. Then, the vacuum capacitor 8 is discharged to control the potential of the focusing electrode 7.

  As a result, pulse X-rays can be generated while blocking the soft X-ray wave tail by controlling the optical fiber 15 and one 4-pin high-voltage cable electrically connected to the anode 5. A grid control type X-ray tube 1 having a focal point can be realized. Therefore, it is not necessary to provide a control power source on the system side (not shown) for driving the X-ray tube 1, and the bias voltage can be turned off using the laser light L.

  For this reason, since the configuration of the X-ray tube container is simplified by using one high-voltage cable on the cathode side of the X-ray tube container (not shown), the X-ray tube container can be downsized. Furthermore, since the space required for the passage of the high voltage cable of the arm (not shown) that supports the X-ray tube container can be reduced, the arm can be reduced in size and the work of mounting the X-ray tube 1 on the arm is easy. Therefore, the volume of the high-voltage cable that runs through the arm does not get in the way, and the design restrictions of the arm are reduced. Therefore, the cost and size of the X-ray tube 1 can be reduced, and design restrictions can be reduced. That is, it is possible to reduce the size while improving the manufacturability of the X-ray tube 1.

  In the first embodiment, since the electric charge stored in the vacuum capacitor 8 is gradually discharged by the release of thermoelectrons from the filament 6 and the leakage current from the insulating portion of the filament 6, X A capacity is needed to maintain the grid cut-off voltage within the time to cut off the line. In order to secure this capacity, the shape of the pair of parallel plates 11 and 12 constituting the vacuum capacitor 8 may be a structure in which pipe-like electrodes having different diameters are arranged concentrically or in multiple layers. .

  In addition, instead of using the photoelectric effect as a discharge in the vacuum capacitor 8 when X-rays are exposed, a discharge gap switch (not shown) is provided outside or inside the vacuum envelope 2 and a pair of vacuum capacitors 8 is provided. A charge control means in which a discharge gap as a spark gap is provided between the parallel plates 11 and 12 can also be used. In this case, when the voltage of the focusing electrode 7 rises above a specified level, the discharge gap switch is turned on, and electrons are collided between the pair of parallel plates 11 and 12 of the vacuum capacitor 8 to cause a spark to discharge.

  In this case, the laser light L was irradiated between the pair of parallel plates 11 and 12 of the vacuum capacitor 8 with the optical fiber 15 introduced into the vacuum envelope 2. An optical window (not shown) may be attached, and the laser beam L may be irradiated between the pair of parallel plates 11 and 12 of the vacuum capacitor 8 from the outside of the vacuum envelope 2 through the optical window. Here, the optical window is configured such that the laser light L can be transmitted from the outside of the vacuum envelope 2 toward the inside thereof. Further, the optical axis of the optical window is set so that laser light can be irradiated between the pair of parallel plates 11 and 12 of the vacuum capacitor 8.

  Further, even when the photoelectric effect is used, in order to protect the filament 6 and the vacuum capacitor 8 from a surge voltage generated due to a sudden change in unintended impedance that occurs when the operation of the X-ray tube 1 is unstable, FIG. As shown in the second embodiment, each of the pair of parallel plates 11 and 12 of the vacuum capacitor 8 is mainly composed of a metal having a high melting point and a low outgassing, such as tungsten (W) or molybdenum (Mo). A spherical portion 21 can be provided as an enlarged portion made of metal.

  These spherical portions 21 are circular circular structure portions provided at one end in the longitudinal direction of each of the pair of parallel flat plates 11 and 12. The spherical portions 21 are formed in a spherical shape having a diameter larger than the thickness of the pair of parallel plates 11 and 12. The spherical portions 21 cause the discharge gap, which is a gap between the spherical portions 21, to be smaller than the vacuum gap, which is a gap between the pair of parallel plates 11 and 12.

  In other words, the spherical portions 21 are arranged to face each other through a gap smaller than the gap between the pair of parallel flat plates 11 and 12. Therefore, the discharge gap between the spherical portions 21 is a spatial distance shorter than the vacuum gap of the pair of parallel plates 11 and 12 constituting the capacitance.

  Therefore, when a voltage exceeding a specified voltage, which is an assumed voltage between the pair of parallel plates 11 and 12 of the vacuum capacitor 8, is generated, the spherical portion 21 formed of a refractory metal is operated as a spark gap, By adopting a configuration in which the vacuum capacitor 8 is discharged by discharging at the discharge gap between the spherical portions 21, the vacuum capacitor 8 can be operated more stably. At this time, the discharge gap between the spherical portions 21 can be used as a vacuum gap, and the laser light L can be irradiated from the optical fiber 15 to the vacuum gap.

It is explanatory drawing which shows 1st Embodiment of the X-ray tube of this invention. It is explanatory drawing which shows the state which irradiated the laser beam to the capacitor | condenser at the time of exposure of an X-ray tube same as the above. It is explanatory drawing which shows the generation state of the photoelectron in a capacitor | condenser at the time of the laser beam irradiation of a X-ray tube same as the above. It is explanatory drawing which shows the supply state of the photoelectron in the capacitor | condenser of an X-ray tube same as the above. It is a graph which shows the change of the electric potential (Vc) of the cathode at the time of exposure of an X-ray tube same as the above, and the electric potential (Vg) of a control electrode. It is explanatory drawing which shows the state which stopped irradiation of the laser beam to a capacitor | condenser at the time of interruption | blocking of an X-ray tube same as the above. It is explanatory drawing which shows the state of the capacitor | condenser at the time of the laser beam stop of an X-ray tube same as the above. It is explanatory drawing which shows the state which the electric potential Vc of the capacitor | condenser of the X-ray tube same as the above fell. It is a graph which shows the change of the electric potential (Vc) of the cathode at the time of interruption | blocking of an X-ray tube same as the above, and the electric potential (Vg) of a control electrode. It is explanatory drawing which shows a part of X-ray tube of the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray tube 2 Vacuum envelope as a container 5 Anode 6 Filament as a cathode 7 Focusing electrode as a control electrode 8 Vacuum capacitor as a capacitor
14 Covering layer as high photoemission coefficient layer
15 Optical fiber as charge control means
16 X-ray shielding cover as shielding means

Claims (4)

A container,
A cathode that emits electrons;
An anode that is provided in the container and generates X-rays upon incidence of electrons emitted from the cathode;
A control electrode for controlling electrons emitted from the cathode toward the anode;
A capacitor having one electrically connected to the cathode and the other electrically connected to the control electrode;
An X-ray tube comprising: charge control means for controlling the charge of the capacitor. The X-ray tube according to claim 1, wherein the charge control means includes an optical fiber that irradiates light to the capacitor. The X-ray tube according to claim 1, wherein a high photoelectron emission coefficient layer having a high photoelectron emission coefficient is provided on one side surface of the electrodes that constitute the capacitor and face each other. The X-ray tube according to any one of claims 1 to 3, wherein the capacitor is covered with shielding means so that X-rays generated in the X-ray tube do not hit.

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