JP2008288159A - X-ray tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray tube having a new structure used for medical, industrial and analytic applications. <P>SOLUTION: This X-ray tube is provided, in a vacuum tube 11, with: a positive electrode 12 having a conical shape having a tip side 12a extended onto an X-ray radiation direction line L1 with a conical top part 12a1 thereof located on the X-ray radiation direction line L1; a field emission type annular negative electrode 14 annularly surrounding the radial outside of the positive electrode tip part 12a coaxially with the positive electrode tip part 12a, and having an outer peripheral surface formed of a nano-carbon film; and an electron screening member 16 arranged on both sides of the annular negative electrode 14 in the X-ray radiation direction, and screening electrons emitted by the annular negative electrode 14; and is structured such that an X-ray extraction window 11a formed of an X-ray-permeable thin film is arranged on a tube wall of the vacuum tube in front of the positive electrode tip part 12a on the X-ray radiation direction line L1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an X-ray tube that emits electrons by field emission from a field emission type cathode and collides the emitted electrons with an anode to generate X-rays. In particular, the tube diameter is extremely small, for example, about several mm. The present invention relates to an X-ray tube that can be made into a laser.

  X-rays are used in many fields such as medical, industrial, and analytical purposes (Patent Documents 1, 2, etc.). For medical use, for example, radiotherapy, endovascular irradiation, diagnostic X-ray source, etc., for industrial use, nondestructive inspection, surface treatment, physics, etc.

  It is well known that such X-rays are generated when electrons collide with an X-ray target (anode) such as a metal or a fluorescent material (Patent Document 3).

  Incidentally, a hot cathode method has been proposed in which thermoelectrons generated by filament heating collide with an anode to generate X-rays (Patent Document 4).

  However, in the case of using thermoelectrons, it is difficult to reduce the size of the X-ray tube, and when thermoelectrons are beamed, there is a problem of heat generation and electrons are emitted in a wide range and collide with the anode. The bundle diameter of the X-ray bundle generated from the anode cannot be reduced.

  Therefore, in the case of a hot cathode type X-ray tube, the X-ray irradiation spot cannot be made small to irradiate the X-ray irradiation target, which is unsuitable for the above-mentioned use.

  Further, there is an X-ray tube that emits electrons from a field emission type cold cathode by field emission and collides the emitted electrons with an anode to generate X-rays.

  In the case of this cold cathode type X-ray tube, there is no problem of heat generation. However, in the case of the conventional cold cathode type X-ray tube, electrons are emitted from the cathode in a wide range and collide with the anode, and thus are generated from the anode. The X-ray flux to spread also spreads, and it is difficult to reduce the X-ray irradiation spot.

  For this reason, in the case of a conventional cold cathode type X-ray tube, the X-ray irradiation spot cannot be irradiated with an X-ray irradiation target by making the X-ray irradiation spot smaller and clearer.

  In particular, when the X-ray irradiation target for medical treatment or analysis is small, the X-ray density from the inner periphery to the outer periphery of the spot is large and the spot diameter of the X-ray irradiation spot is large as in the conventional X-ray tube. If it is not uniform, it is difficult to obtain a clear X-ray image with respect to the X-ray irradiation target, and it becomes impossible to carry out highly accurate medical treatment and analysis.

On the other hand, although it is possible to narrow down the X-ray bundle diameter and reduce the X-ray irradiation spot, it should be adopted for small or ultra-compact X-ray tubes as the structure becomes complicated and large. I can't.
Japanese Patent Laid-Open No. 08-167497 Special table 2004-505421 Special Table 2002-517882 Special table 2006-514421

  The present invention provides an X-ray tube capable of irradiating an X-ray bundle with high accuracy and high density with a simple structure even when an X-ray irradiation target is small.

  An X-ray tube according to the present invention includes a vacuum tube having a conical shape whose tip side extends on the X-ray irradiation direction line and a conical top portion directed forward in the X-ray irradiation direction line, and a radially outer side of the anode tip portion. A field emission type annular cathode which is concentrically enclosed with the tip of the anode and whose outer peripheral surface is made of a nanocarbon film, and electrons which are arranged at least on both sides in the X-ray irradiation direction of the annular cathode and shield electrons emitted from the annular cathode And an X-ray derivation window made of a thin film capable of transmitting X-rays on the vacuum tube wall in front of the anode tip on the X-ray irradiation direction line.

  The cone shape includes a cone shape and a pyramid shape. In this case, the entire circumference is not limited to the conical shape, and may be partially conical. The profile of the conical slope is not limited to a linear shape with a constant reduction ratio toward the tip, but has a shape (parabolic shape, etc.) in which the reduction ratio changes continuously or stepwise toward the tip. Alternatively, even a needle shape with a reduced diameter toward the tip can be included in the cone shape.

  The ring is not limited to a completely closed ring, and includes a partial ring.

  The conical top is not limited to a sharp top and may include some rounding or the like.

  In the above, the shape of the anode is not limited to the linear axis shape except for the tip.

  In the above, it is preferable that the electron shielding member includes a pair of annular plate portions arranged annularly around the X-ray irradiation direction on both sides of the annular cathode in the X-ray irradiation direction. By arranging the two annular plate portions independently of each other, the electron shielding member may control the emission electrons emitted from the annular cathode.

  In the above, the angle with respect to the X-ray irradiation direction line of the outer peripheral slope of the anode tip is adjusted to an angle that makes the bundle diameter of the X-ray bundle generated from the anode tip smaller than the beam diameter of the electron beam from the annular cathode. It is preferable that the X-ray irradiation spot on the X-ray irradiation target is controlled.

  In the present invention, in addition to the fact that the tip of the anode is conical, an annular cathode is disposed around the anode tip, and an electron shielding member that partially shields electrons emitted from the annular cathode is disposed. The X-ray lead-out window is disposed in front of the anode tip, and the X-ray can be substantially linearly advanced. Therefore, a high electric field is applied between the anode tip and the annular cathode, Electrons generated from the electron shielding member are shielded by an electron shielding member so as to be focused on an electron beam having a predetermined beam diameter toward the anode tip slope, and the electron beam collides with the anode tip slope to cause the anode tip slope to An X-ray bundle can be generated, and the X-ray bundle can be made to travel straight toward the X-ray derivation window ahead of the X-ray irradiation direction line to irradiate the X-ray irradiation target outside the window in a spot shape.

  As described above, in the present invention, it is possible to irradiate an X-ray irradiation target with an X-ray irradiation spot whose X-ray density from the inner periphery to the outer periphery of the spot is uniform and the spot diameter is controlled to be small. It is suitable for use as an ultra-small X-ray tube.

  In the present invention, it is preferable that the anode has a heat conducting portion that is coupled to the tip portion and has a heat capacity larger than that of the tip portion and is used for conducting heat generated at the tip portion. In this aspect, even if the tip portion generates heat due to the electron beam collision, the generated heat is conducted to the heat conducting portion, so that the tip portion is cooled and the generation efficiency of the X-ray flux can be improved.

  In the present invention, the rear end portion of the heat conducting portion of the anode is preferably led out of the vacuum tube and used as a vacuum sealed portion of the vacuum tube. In this aspect, since the heat conducting portion is led out of the vacuum tube, the heat conducted is radiated to the outside of the vacuum tube, the heat radiation effect of the tip portion is further improved, and as a result, the generation efficiency of the X-ray flux can be further improved. become able to.

  The present invention can be configured such that the angle of the slope of the anode tip portion is made smaller in a continuous exponential function or stepwise as the tip of the anode tip portion. In this configuration, by shifting the facing position between the annular cathode and the slope of the tip of the anode in the axial direction, the bundle diameter of the X-ray bundle can be converged smaller, or conversely, the bundle diameter can be increased.

  An electron acceleration means may be disposed between the anode tip and the annular cathode. The annular cathode may be solid or hollow. The anode may be solid or hollow. The electron shielding member may be capable of adjusting the distance from the annular cathode and / or adjusting the inner diameter.

  In the present invention, the bundle diameter of the X-ray bundle may be arbitrarily controlled by making the anode tip and the annular cathode relatively movable in the X-ray irradiation direction.

  According to the present invention, it is possible to provide an X-ray tube having a novel structure for medical use, industrial use, analysis use and the like.

  Hereinafter, an X-ray tube according to an embodiment of the present invention will be described with reference to the accompanying drawings. 1 is an external perspective view of the X-ray tube, FIG. 2 is a cross-sectional view of the X-ray tube, FIG. 3 is a diagram showing a cross-sectional configuration along the line AA in FIG. 2, and FIG. FIG. 5 is an enlarged view showing a cross section of the main part (axial anode, annular cathode, electron shielding member, X-ray extraction window) of the ray tube, and FIG. 5 is an enlarged view showing the appearance of the main part. 6 is a diagram for explaining the operation state of the entire X-ray tube, FIG. 7 is a diagram for explaining the relationship in which electrons emitted from the annular cathode are shielded by the shielding member in the overall operation of FIG. FIG. 7 is a diagram for explaining the relationship between the electron beam diameter and the X-ray bundle diameter depending on the angle of the conical slope at the tip of the anode in the overall operation of FIG. 6.

  First, referring to FIG. 1, an X-ray tube 10 of the embodiment includes an X-ray extraction window 11a made of a thin film having a thickness of about several μm, for example, a beryllium film, which can transmit X-rays. A flexible coaxial cable 11b is connected to the rear portion of the X-ray tube 10. A control device with a drive power supply (not shown) is connected to the coaxial cable 11b, and, for example, a pulse voltage is applied from the drive power supply under the control of the control device. The X-ray irradiation target 11c can be irradiated with X-rays as an X-ray irradiation spot 11d from the X-ray extraction window 11a.

  2 to 5, the vacuum tube 11 is a cylindrical straight tube that is long in the direction of the X-ray irradiation direction line L1, and the inside thereof is evacuated. Inside, the axial anode 12, the annular cathode 14, the electron shield A member 16 is provided.

  The axial anode 12 is disposed so as to extend linearly in the X-ray irradiation direction line L1. An X-ray derivation window 11a is positioned in front of the X-ray irradiation direction line L1 of the tip end portion 12a of the axial anode 12.

  The tip portion 12a of the axial anode 12 has a conical slope 12a2 shape and becomes a target for generating X-rays by electron beam collision. The target material is not particularly limited. The rear side of the anode tip portion 12a of the shaft-like anode 12 has a large heat capacity and becomes a heat conducting portion 12b that conducts heat generated at the tip portion 12a, and the rear side of the heat conducting portion 12b is led out of the rear portion of the vacuum tube 10 and is connected to the vacuum tube 11. It becomes the part 12c to be vacuum-sealed and is connected to the coaxial cable 11b so that a high voltage can be applied.

  The anode tip portion 12a has a conical shape in which the top portion 12a1 is located on the X-ray irradiation direction line L1 and the cone center line coincides with the X-ray irradiation direction line L1, and the conical slope 12a2 is located on the X-ray irradiation direction line L1. On the other hand, the slope has a predetermined angle.

  The annular cathode 14 surrounds the X-ray irradiation direction line of the anode tip portion 12a in an annular shape, and a nanocarbon film 14b is formed on the outer peripheral surface of the annular conducting wire 14a.

  The nanocarbon film 14b has fine nanometer-order projections such as carbon nanotubes, carbon nanowalls, carbon nanofibers, diamond-like carbon, amorphous diamond, crystalline diamond, graphite, fullerene, and acicular carbon films.

  The applicant has filed several applications for acicular carbon films. For example, the acicular carbon film includes the carbon film disclosed in the SEM photographs of FIGS. 8 to 12 in the specification of Japanese Patent Application No. 2005-232017 (Japanese Patent Application Laid-Open No. 2007-048603: published on February 22, 2007). Can be used.

  The annular cathode 14 emits an electric field by applying an electric field to the axial anode 12 and emits electrons toward the axial anode 12 on the radially inner side. The electric field is applied by applying a high potential to the shaft-like anode 12 from, for example, the drive power supply 18. There are various potential application modes, and this embodiment mode is not particularly limited.

  For example, the drive power supply 18 may be constituted by a pulse power supply controlled by the microcomputer 20, and an extremely short pulse may be applied to the shaft-like anode 12 from the pulse power supply under the control of the microcomputer 20. For example, a positive pulse voltage + V is applied to the axial anode 12 and a negative pulse voltage -V having the same absolute value as the positive pulse voltage + V is applied to the annular cathode 14 in synchronization with the positive pulse voltage + V. Thus, the voltage of the pulse power supply may be controlled in half. The waveform of the pulse voltage may be a rectangular wave, a sawtooth wave, or other waveform shapes.

  The electron shielding member 16 is an electron shielding member that is arranged on both sides of the annular cathode 14 in the X-ray irradiation direction and shields electrons emitted from the annular cathode 14 in both axial directions. Annular plate portions 16a and 16b and a cylindrical portion 16c connecting both the annular plate portions 16a and 16b. The electron shielding member 16 is applied with the same or substantially the same potential as the annular cathode 14.

  Referring to FIG. 6, when a high pulse voltage is applied to the axial anode 12, a high electric field is applied between the anode tip 12 a and the annular cathode 14. As a result, electrons are emitted from the annular cathode 14 toward the anode tip 12a by field emission, and the emitted electrons collide with the conical slope 12a2 of the anode tip 12a.

  When electrons collide with the conical slope 12a2, X-rays are generated from the conical slope 12a. This X-ray goes straight in the X-ray irradiation direction line L1, and irradiates the X-ray irradiation target 11c outside the window in a spot shape from the X-ray derivation window 11a.

  In this case, the electrons emitted from the annular cathode 14 are shielded by the electron shielding member 16 so that the electrons collide with the anode tip portion 12a. At this time, the opposing distance and the inner diameter of the annular plate portions 16a and 16b are adjusted. , The electrons in the orbits indicated by broken lines are shielded, and only the electrons in the orbits indicated by solid lines are caused to collide with the anode tip 12a as a narrow electron beam.

  Thereby, the bundle diameter of the X-ray bundle generated from the conical slope 12a2 of the anode tip 12a can be narrowed down, and the X-ray irradiation target 11c can be irradiated with X-rays in the form of an X-ray irradiation spot 11d.

  Further, by adjusting the angle of the conical slope 12a2 of the anode tip portion 12a, X generated from the conical slope 12a2 of the anode tip portion 12a even when the beam diameter of the electron beam colliding with the cone slope 12a2 of the anode tip portion 12a is the same. The bundle diameter of the wire bundle can be narrowed down.

  Next, the relationship in which electrons emitted from the annular cathode 14 are shielded by the electron shielding member 16 will be described with reference to FIG.

  FIG. 7A1 shows a case where the opposing distance between the two annular plate portions 16a and 16b of the electron shielding member 16 is D1, and the spread angle of electrons emitted from the annular cathode 14 at this time is θ1.

  FIG. 7A2 shows the case where the opposing distance between the two annular plate portions 16a and 16b of the electron shielding member 16 is D2 (<D1), and the spread angle of electrons emitted from the annular cathode 14 at this time is θ2 (< θ1). That is, if the opposing distance between the annular plate portions 16a and 16b is reduced, the electrons emitted from the annular cathode 14 can be effectively focused on the anode tip portion 12a.

  FIG. 7B1 shows the case where the inner diameters of the two annular plate portions 16a and 16b of the electron shielding member 16 are R1, and the spread angle of electrons emitted from the annular cathode 14 at this time is θ1.

  FIG. 7B2 shows the case where the inner diameters of both the annular plate portions 16a and 16b of the electron shielding member 16 are R2 (<R1), and the spread angle of electrons emitted from the annular cathode 14 at this time is θ2 (<θ1). ). That is, if the inner diameters of both the annular plate portions 16a and 16b are reduced, the electrons emitted from the annular cathode 14 can be effectively focused on the anode tip portion 12a.

  Next, the relationship between the electron beam diameter and the X-ray flux diameter according to the angle of the conical slope 12a2 of the anode tip 12a will be described with reference to FIG.

  In FIG. 8A, the angle of the conical inclined surface 12a2 is θ1, and the bundle diameter r2 of the X-ray bundle B2 generated from the conical inclined surface 12a2 is larger than the beam diameter r1 of the electron beam B1 colliding with the conical inclined surface 12a2. The spot diameter r3 of the X-ray irradiation spot irradiated to the X-ray irradiation target in front of the irradiation direction line L1 is large.

  In FIG. 8B, the angle of the cone slope is θ2 (<θ1), and the bundle diameter r2 of the X-ray bundle B2 generated from the cone slope 12a2 is smaller than the beam diameter r1 of the electron beam B1 colliding with the cone slope 12a2. The spot diameter r3 of the X-ray irradiation spot irradiated to the X-ray irradiation target in front of the X-ray irradiation direction line L1 is small. That is, by reducing the angle of the conical inclined surface 12a2, the X-ray irradiation spot can be reduced by reducing the bundle diameter of the X-ray bundle even if the beam diameter of the electron beam B1 is the same.

  As described above, in the embodiment, the electrons generated from the annular cathode 14 by the application of an electric field between the anode tip 12a and the annular cathode 14 are shielded by the electron shielding member 16, and the cone of the anode tip 12a on the radially inner side thereof. It is focused on a predetermined electron beam toward the inclined surface 12a2.

  As a result, the electron beam collides with the conical slant surface 12a2 of the anode tip 12a, and the X-ray flux generated from the conical slant surface 12a2 goes straight toward the X-ray derivation window 11a ahead of the X-ray irradiation direction line L1 and out of the window 11a. Can be irradiated in a spot shape.

  As a result, the X-ray irradiation spot for the X-ray irradiation target has a uniform X-ray density from the inner periphery to the outer periphery of the spot, and the slope angle of the conical slope 12a2 of the anode tip 12a is reduced to reduce the spot diameter. Therefore, it is suitable for use as an ultra-small X-ray tube in medical use, industrial use, and the like.

  The present invention is not limited to the above-described embodiments, and includes various changes or modifications within the scope described in the claims.

FIG. 1 is a perspective view showing an appearance of an X-ray tube according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the X-ray tube of FIG. 3 is a cross-sectional view taken along line AA in FIG. FIG. 4 is an enlarged cross-sectional view showing a main part of the X-ray tube shown in FIG. FIG. 5 is an enlarged perspective view showing the main part. FIG. 6 is a diagram for explaining the entire operation state. FIG. 7 is a view for explaining the relationship in which electrons emitted from the annular cathode are shielded by the shielding member in the overall operation of FIG. FIG. 8 is a diagram for explaining the relationship between the electron beam diameter and the X-ray bundle diameter depending on the angle of the conical slope at the tip of the anode in the overall operation of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray tube 11 Vacuum tube 11a X-ray extraction window 12 Axial anode 12a Anode tip part 14 Annular cathode 16 Electron shielding member

Claims (3)

  Inside the vacuum tube, an anode whose tip side extends in the X-ray irradiation direction line and whose apex is directed forward in the X-ray irradiation direction line, and a radially outer side of the anode tip portion are concentric with the anode tip portion. A field emission type annular cathode having an annular outer peripheral surface made of a nanocarbon film, and an electron shielding member arranged at least on both sides of the annular cathode in the X-ray irradiation direction and shielding electrons emitted from the annular cathode; An X-ray tube characterized in that an X-ray derivation window made of a thin film capable of transmitting X-rays is provided on the vacuum tube wall in front of the anode tip on the X-ray irradiation direction line.   2. The X-ray tube according to claim 1, wherein the electron shielding member includes a pair of annular plate portions that are annularly arranged around the X-ray irradiation direction on both sides of the annular cathode in the X-ray irradiation direction.   The angle with respect to the X-ray irradiation direction line of the outer peripheral slope of the anode tip is adjusted to an angle that makes the bundle diameter of the X-ray bundle generated from the anode tip smaller than the beam diameter of the electron beam from the annular cathode. The X-ray tube according to claim 1 or 2, wherein

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