X-ray generator

Abstract

To provide an x-ray generator capable of making an electron beam incident on a target at an appropriate position.SOLUTION: An x-ray generator 10 includes an electron gun 3 having a cathode 32 for emitting electrons and a first grid electrode 33 for extracting the electrons emitted from the cathode 32, a target 4 that generates X-rays upon incidence of electrons, and a power supply unit 11 that applies a tube voltage between the cathode 32 and the target 4. The thickness T4 of the target 4 has a distribution, and the target 4 is inclined with respect to a virtual plane perpendicular to the axis A3 of the electron gun 3, and the target 4 is arranged such that the thickness T4 of the target 4 is thinner at the electron incidence position when the extraction voltage is relatively low than at the electron incidence position when the extraction voltage applied to the first grid electrode 33 is relatively high.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Patent Document 1 describes a transmission type X-ray tube device. This device includes a vacuum envelope that constitutes an X-ray tube, an X-ray transmission window provided at one end of the vacuum envelope, a metal thin film that forms an X-ray target provided on the vacuum side of the X-ray transmission window, and an electron gun that generates an electron beam that irradiates the X-ray target. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-126650 Summary of the Invention [Problem to be solved by the invention]

[0004] In the device described in Patent Document 1, the metal thin film has a thickness that varies depending on the location, and a deflection electrode is provided to deflect the electron beam. The deflection electrode is composed of a pair of electrode plates arranged facing each other between the target and the focusing electrode. This allows the device to change the deflection voltage applied to the deflection electrode in response to changes in the acceleration voltage of the electron beam generated by the electron gun, thereby directing the electron beam to be incident on a location on the target with an appropriate thickness.

[0005] Thus, in the above technical field, there is a demand for making the electron beam incident on a position of the target having an appropriate thickness depending on the acceleration voltage.

[0006] Therefore, an object of the present disclosure is to provide an X-ray generating device that can cause an electron beam to be incident on an appropriate position on a target. [Means for solving the problem]

[0007] The X-ray generator according to the present disclosure comprises a housing, an electron gun having an electron emission unit that emits electrons within the housing and an extraction electrode for extracting the electrons emitted from the electron emission unit, a target that generates X-rays by the incidence of electrons within the housing, a window member that seals an opening in the housing and allows X-rays to pass through, and a tube voltage application unit that applies a tube voltage between the electron emission unit and the target, wherein the thickness of the target has a distribution, and the target is arranged so as to be inclined with respect to a virtual plane perpendicular to the axis of the electron gun and so as to be thinner at the electron incidence position when the extraction voltage applied to the extraction electrode is relatively low than at the electron incidence position when the extraction voltage is relatively high.

[0008] In this device, a tube voltage is applied between the electron exit part of the electron gun and the target by a tube voltage application unit, and the target is positioned at an inclination with respect to a virtual plane perpendicular to the axis of the electron gun. Therefore, the equipotential surface of the tube voltage between the electron exit part and the target is inclined with respect to the virtual plane. As a result, electrons are deflected when they pass through the region where this equipotential surface is inclined. The amount of electron deflection decreases as the electron initial velocity increases and increases as the electron initial velocity decreases. Therefore, the amount of electron deflection is adjusted according to the magnitude of the extraction voltage applied by the extraction electrode (the magnitude of the electron initial velocity). Therefore, the target thickness has a distribution, and the target thickness is thinner at the electron incident position when the extraction voltage is relatively low than at the electron incident position when the extraction voltage is relatively high. This allows electrons to be incident at an appropriate position on the target. Note that a high (or low) extraction voltage means a large (or small) potential difference between the extraction electrode and the electron exit part.

[0009] In the X-ray generator according to the present disclosure, the thickness of the target may be made thinner from the center to the periphery, and the target may be arranged so that electrons are incident on the periphery as the extraction voltage becomes relatively lower. In this case, it is easy to form the target so that the target has the above-mentioned thickness distribution.

[0010] The X-ray generator according to the present disclosure may include a magnetic field forming unit for deflecting electrons by forming a magnetic field between the electron emitter and the target, in which case the electrons can be further deflected by utilizing the magnetic field.

[0011] In the X-ray generator according to the present disclosure, the magnetic field generating unit may include a permanent magnet. In this manner, in this device, if a constant magnetic field is generated by the permanent magnet, the amount of electron deflection caused by the magnetic field is automatically adjusted. This reliably avoids complicating control.

[0012] In the X-ray generator according to the present disclosure, the window member may have a first surface opposite to the interior of the housing and a second surface on the interior side of the housing, and the target may be formed on the second surface, forming a so-called transmission type X-ray generator.

[0013] In the X-ray generator according to the present disclosure, the target may be supported in an inclined state so as to face both the electron gun and the window member, in which case a so-called reflection type X-ray generator is configured. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide an X-ray generating device that can cause an electron beam to be incident on an appropriate position on a target. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram of an X-ray generating device according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the X-ray tube shown in FIG. [Figure 3] FIG. 2 is a schematic diagram for explaining the relationship between an electron beam and a target. [Figure 4] FIG. 3 is a schematic side view showing an enlarged view of a part of FIG. 2. [Figure 5] FIG. 10 is a cross-sectional view of a modified X-ray tube. [Figure 6] FIG. 6 is a schematic side view showing an enlarged view of a part of FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted.

[0017] 1, an X-ray generator 10 includes an X-ray tube 1, a power supply unit 11, a deflection unit 12, and a control unit 13. The X-ray tube 1, the power supply unit 11, and the deflection unit 12 are supported in a case (not shown) made of metal. As an example, the X-ray tube 1 is a small focus X-ray source, and the X-ray generator 10 is a device used in X-ray nondestructive inspection for magnifying and observing the internal structure of an inspection object.

[0018] 2, the X-ray tube 1 includes a housing 2, an electron gun 3, a target 4, and a window member 5. As will be described below, the X-ray tube 1 is configured as a sealed transmission type X-ray tube that does not require replacement of parts.

[0019] The housing 2 has a head 21 and a bulb 22. The head 21 is formed of metal in a cylindrical shape with a bottom. The bulb 22 is formed of an insulating material such as glass in a cylindrical shape with a bottom. An opening 22a of the bulb 22 is airtightly joined to an opening 21a of the head 21. In the X-ray tube 1, the center line of the housing 2 is the tube axis A. An opening 23 is formed in the bottom wall portion 21b of the head 21. The opening 23 is located on the tube axis A. When viewed from a direction parallel to the tube axis A, the opening 23 has, for example, a circular shape with the tube axis A as its center line.

[0020] The electron gun 3 emits an electron beam B within the housing 2. The electron gun 3 includes a heater 31, a cathode 32, a first grid electrode 33, and a second grid electrode 34. The heater 31, the cathode 32, the first grid electrode 33, and the second grid electrode 34 are arranged on the tube axis A in this order from the bottom wall portion 22b side of the bulb 22. As an example, the axis A3 of the electron gun 3 (see FIG. 4) coincides with the tube axis A. The axis A3 of the electron gun 3 may be defined as, for example, the central axis of the electron gun 3 (e.g., the central axis of the cathode 32, the first grid electrode 33, and the second grid electrode 34), or as the trajectory of the electron beam B when the electron beam B is not deflected, as described below. The heater 31 is formed of a filament and generates heat when current is applied. The cathode 32 is heated by the heater 31 and emits electrons. That is, the cathode 32 is an electron emitting part that emits electrons within the housing 2.

[0021] The first grid electrode 33 is formed in a cylindrical shape and adjusts the amount of electrons emitted from the cathode 32. The first grid electrode 33 also serves as an extraction electrode for extracting electrons emitted from the cathode 32. The initial velocity of the electrons is determined according to the voltage (extraction voltage) applied to the first grid electrode 33. The second grid electrode 34 is formed in a cylindrical shape and focuses the electrons that have passed through the first grid electrode 33 onto the target 4. The heater 31, the cathode 32, the first grid electrode 33, and the second grid electrode 34 are electrically and physically connected to a plurality of lead pins 35 that penetrate the bottom wall portion 22b of the bulb 22. Each of the lead pins 35 is electrically connected to the power supply unit 11 of the X-ray generator 10.

[0022] The window member 5 seals the opening 23 of the housing 2. The window member 5 is formed in a plate shape from a material with high X-ray transparency, such as diamond or beryllium. The window member 5 has, for example, a disk shape with the tube axis A as its center line. The window member 5 has a first surface 51 and a second surface 52. The first surface 51 is the surface opposite to the interior of the housing 2, and the second surface 52 is the surface facing the interior of the housing 2. Each of the first surface 51 and the second surface 52 is, for example, a flat surface perpendicular to the tube axis A. The target 4 is formed on the second surface 52 of the window member 5. The target 4 is, for example, formed in a film shape from tungsten. The target 4 generates X-rays R when an electron beam B is incident on it within the housing 2. In this embodiment, the X-rays R generated in the target 4 pass through the target 4 and the window member 5 and are emitted to the outside.

[0023] The window member 5 is attached to a mounting surface 24 around the opening 23 in the housing 2. The mounting surface 24 is, for example, a flat surface perpendicular to the tube axis A and is formed on the head 21. The window member 5 can be hermetically joined to the mounting surface 24 via a joining member (not shown) such as brazing material. In the X-ray tube 1, the target 4 is electrically connected to the head 21, and the target 4 and the window member 5 are thermally connected to the head 21. As an example, the target 4 is set to ground potential via the head 21. As a result, a tube voltage is applied between the cathode 32 of the electron gun 3 and the target 4.

[0024] The tube voltage determines the acceleration of electrons emitted from the cathode 32 toward the target 4. In the X-ray generator 10, the power supply unit 11 supplies a negative voltage to the cathode 32 via the lead pin 35 and grounds the target 4 (anode), thereby applying a tube voltage between the cathode 32 and the target 4. In this manner, the power supply unit 11 constitutes a tube voltage application unit that applies the tube voltage in cooperation with the cathode 32 and the target 4. Meanwhile, the power supply unit 11 is also connected to the first grid electrode 33, which serves as an extraction electrode, and applies an extraction voltage to the first grid electrode 33. Therefore, the power supply unit 11 constitutes an extraction voltage application unit. Note that, as an example, heat generated in the target 4 due to the incidence of the electron beam B is transferred to the head 21 directly or via the window member 5, and is further dissipated from the head 21 to a heat dissipation unit (not shown). In this embodiment, the interior space of the housing 2 is maintained at a high vacuum by the housing 2, the target 4, and the window member 5.

[0025] In the X-ray generator 10 configured as described above, a negative voltage is applied to the electron gun 3 by the power supply unit 11, with the potential of the target 4 as a reference. As an example, the power supply unit 11 applies a negative high voltage (for example, −10 kV to −500 kV) to each part of the electron gun 3 via each lead pin 35, with the target 4 at ground potential. The electron beam B emitted from the electron gun 3 is focused on the target 4 along the tube axis A. The X-rays R generated in the area of the target 4 irradiated with the electron beam B are focused at the irradiated area and transmitted through the target 4 and the window member 5 to be emitted to the outside. Target Configuration

[0026] Next, the relationship between the electron beam and the target will be explained in conjunction with the description of the target configuration. In an X-ray generator, the energy of the generated X-rays varies depending on the tube voltage, so the tube voltage may be changed within a range of, for example, 40 kV to 130 kV. As shown in Figure 3, the penetration depth of the electron beam B1 into the target 4A when accelerated at a relatively high tube voltage is deeper than that of the electron beam B2 when accelerated at a relatively low tube voltage.

[0027] Therefore, as shown in FIG. 3(a), when the target 4A is relatively thick, the electron beam B1 at a high tube voltage penetrates into the target 4A so as to reach the vicinity of the boundary between the target 4A and the support 5A (corresponding to the window member 5 in this case) (the deepest part of the target 4A). That is, the penetration depth is appropriate for the thickness of the target 4A. In other words, because the thickness of the target 4A through which the X-rays generated by the target 4A must pass before reaching the support 5A is small, a decrease in X-ray output due to self-absorption by the target 4A is suppressed. On the other hand, the penetration depth of the electron beam B2 at a low tube voltage remains near the surface of the target 4A, and because the thickness of the target 4A through which the X-rays generated by the target 4A must pass before reaching the support 5A is large, there is a risk of a decrease in X-ray output due to self-absorption by the target 4A.

[0028] Furthermore, because most of the energy of the electron beam B is converted into heat, if the heat is accumulated in the target 4A, there is a risk of thermal damage to the target 4A. Therefore, by penetrating the target 4A near the boundary between the target 4A and the support 5A, as with the electron beam B1, the generated heat is easily transferred to the support 5A, thereby preventing thermal damage to the target 4A. On the other hand, the electron beam B2 at low tube voltage penetrates only near the surface of the target 4A, making it difficult to transfer the generated heat to the support 5A, which may result in thermal damage to the target 4A. Thus, a relatively thick target 4A is preferable for the electron beam B1 at high tube voltage but not for the electron beam B2 at low tube voltage. To efficiently dissipate the heat generated inside the target 4A, the support 5A is preferably made of a material with good thermal conductivity, such as diamond.

[0029] Furthermore, as shown in Figure 3(b), when the target 4B is relatively thin, even the electron beam B2 at a low tube voltage penetrates into the target 4B so as to reach the boundary between the target 4B and the support 5A (the deepest part of the target 4A). In other words, the penetration depth is appropriate for the thickness of the target 4B. On the other hand, the electron beam B1 at a high tube voltage penetrates the target 4B, resulting in a lower X-ray output compared to the case of Figure 3(a).

[0030] In response to this, it is possible to configure the target 4C to have a non-uniform thickness, as shown in FIG. 3(c). In other words, it is possible to create a distribution in the thickness of the target 4C. In this way, by making the electron beam B1 at a high tube voltage incident on a relatively thick position of the target 4C and the electron beam B2 at a low tube voltage incident on a relatively thin position of the target 4C, it is possible to make either electron beam penetrate into the target 4C so as to reach the vicinity of the boundary between the target 4C and the support 5A. Therefore, it is possible to suppress a decrease in X-ray output over a wide range of tube voltages and to suppress thermal damage to the target 4C.

[0031] 4, the X-ray generator 10 is configured so that the thickness T4 of the target 4 has a predetermined distribution. That is, the thickness T4 of the target 4 has a distribution that varies depending on the position in a plane intersecting with the axis A3 (tube axis A), which is the center line of the electron gun 3. Although the distribution may take any form, in the illustrated example, the thickness T4 of the target 4 becomes thinner from the central portion 4a to the peripheral portion 4b when viewed from the direction intersecting with the axis A3.

[0032] A target 4 having a thickness distribution as described above can be manufactured, for example, as follows. That is, when forming the target 4 by depositing a film on a support (here, the window member 5), a mask corresponding to the peripheral portion of the target 4 is used. The portion of the support that overlaps with the mask is poorly visible from the vapor deposition source, preventing film deposition, and the film is deposited thinner than in the central portion that does not overlap with the mask. In this way, the target 4 can be manufactured so that it is thicker in the center and thinner in the peripheral portion. The difference in thickness (aspect ratio) between the central portion and the peripheral portion can be controlled by the position where the mask is placed, the thickness of the mask, etc.

[0033] The target 4 as described above is arranged so as to be inclined with respect to an imaginary plane perpendicular to the axis A3 (tube axis A) of the electron gun 3. In other words, the target 4 is arranged so as to be inclined with respect to the direction from the cathode 32 toward the target 4. Here, this arrangement of the target 4 is achieved by tilting the window member 5 on which the target 4 is provided. More specifically, the bottom wall 21b of the head 21 extends so as to be inclined with respect to an imaginary plane perpendicular to the axis A3 (tube axis A) of the electron gun 3, and the window member 5 that seals the opening 23 provided in the bottom wall 21b and the target 4 provided on the window member 5 are arranged so as to extend along the bottom wall 21b, so that the target 4 is inclined with respect to the imaginary plane perpendicular to the axis A3 (tube axis A) of the electron gun 3.

[0034] The imaginary plane is, for example, a plane parallel to the surface of the cathode 32 facing the target 4 (electron emission surface). As a result, the equipotential surface CL of the tube voltage formed between the cathode 32 and the target 4 has a portion that is inclined with respect to the imaginary plane. In other words, the equipotential surface CL has a portion that is not orthogonal to the axis A3 of the electron gun 3. The electrons accelerate in a direction perpendicular to the equipotential surface CL. Therefore, the electrons are deflected by the inclined equipotential surface CL and are incident perpendicularly on the target 4. [Deflection section configuration]

[0035] As described above, the target 4 is formed so that its thickness T4 varies non-uniformly depending on the position (thickness T4 has a distribution), and the appropriate position (thickness T4) for the electron beam B to be incident varies depending on the tube voltage. Therefore, the deflection unit 12 deflects the electron beam B emitted from the cathode 32 in accordance with the tube voltage, thereby making the electron beam B incident on the appropriate position on the target 4.

[0036] Here, the deflection unit 12 includes a deflection unit 6 and a first grid electrode 33. An extraction voltage for extracting electrons emitted from the cathode 32 is applied to the first grid electrode 33 by the power supply unit 11. The magnitude of the extraction voltage applied to the first grid electrode 33 determines the initial velocity of the electrons traveling toward the target 4. More specifically, the initial velocity of the electrons increases as the potential difference between the cathode 32 and the first grid electrode 33 increases. Therefore, the velocity of the electrons depends on the velocity of the electrons at the time they pass through the first grid electrode 33, i.e., on the extraction voltage applied to the first grid electrode 33.

[0037] On the other hand, as described above, in the X-ray generator 10, the target 4 is tilted, and therefore the equipotential surface CL of the tube voltage is also tilted. Therefore, electrons that have passed through the first grid electrode 33 are deflected as they move toward the target 4, but the faster the electrons are, the less they are deflected, and the smaller the amount of deflection. Therefore, in the X-ray generator 10, the amount of electron deflection can be adjusted by adjusting the extraction voltage applied to the first grid electrode 33, and as a result, the position at which the electrons are incident on the target 4 can be adjusted. The adjustment of the extraction voltage is performed, for example, by the control unit 13 controlling the power supply unit 11. Therefore, a part of the deflection unit 12 (a part that uses the first grid electrode 33) also works in cooperation with the power supply unit 11 (in other words, it can be said that the power supply unit 11 is also part of the deflection unit 12).

[0038] In the X-ray generator 10, the target 4 is arranged so that its relationship with the incident positions of the electron beams B1 and B2 is appropriate. That is, the target 4 is arranged so that the thickness T4 of the target 4 is thinner at the incident position of electrons (electron beam B2) when the extraction voltage applied to the first grid electrode 33 is relatively low than at the incident position of electrons (electron beam B1) when the extraction voltage applied to the first grid electrode 33 is relatively high.

[0039] As a result, by the control unit 13 controlling the power supply unit 11, it is possible to set the extraction voltage high when the tube voltage is high, thereby reducing the amount of electron deflection and allowing electrons (electron beam B1) to be incident on a relatively thick portion of the target 4 (for example, the central portion 4a), and to set the extraction voltage low when the tube voltage is low, thereby increasing the amount of electron deflection and allowing electrons (electron beam B2) to be incident on a relatively thin portion of the target 4 (for example, the peripheral portion 4b).

[0040] In the X-ray generator 10, the amount of electron deflection can be adjusted simply by controlling the magnitude of the initial electron velocity by adjusting the extraction voltage, utilizing the slope of the equipotential surface CL of the tube voltage. That is, in the X-ray generator 10, there is no need to directly control the electron trajectory. Therefore, for example, if the amount of electron deflection is set to change from small to large as the extraction voltage changes from high to low, the control can be made less complicated than when the electron trajectory is controlled using electrodes extending along the electron trajectory.

[0041] A high (or low) extraction voltage means a large (or small) potential difference between the first grid electrode 33 and the cathode 32. In addition, in FIG. 4, various parts including the second grid electrode 34 of the electron gun 3 are omitted.

[0042] The deflection unit 12 further includes a deflection unit 6. The deflection unit 6 includes a permanent magnet 61. The permanent magnet 61 is made of, for example, a ferrite magnet, a neodymium magnet, a samarium-cobalt magnet, an alnico magnet, or the like.

[0043] The permanent magnet 61 is disposed outside the housing 2 and is fixed to a flange portion of the head 21 via, for example, a fixing portion (not shown). This allows the permanent magnet 61 to be attached to the outside of the housing 2. In particular, the permanent magnet 61 is disposed between the cathode 32 and the target 4 when viewed from a direction intersecting the tube axis A. As a result, a magnetic field including at least a component perpendicular to the direction of electron travel is formed between the cathode 32 and the target 4. In this way, the permanent magnet 61 functions as a magnetic field forming portion for deflecting electrons by forming a magnetic field between the cathode 32 and the target 4.

[0044] The deflection unit 6 deflects the electron beam B using a magnetic field generated by the permanent magnets 61, thereby changing the position of incidence of the electron beam B on the target 4. When viewed from a direction perpendicular to the path of the electron beam B emitted from the cathode 32 and traveling to the target 4 (i.e., a radial direction), the deflection unit 6 preferably includes a portion overlapping the path. This allows the magnetic field generated by the permanent magnets 61 to preferably apply a force to the electron beam B. In this example, the deflection unit 6 is disposed so that the entire deflection unit 6 is included in the path of the electron beam B when viewed from a radial direction. Note that the deflection unit 6 is not limited to being disposed so as to include a portion overlapping the path of the electron beam B when viewed from a radial direction, as long as it can generate a magnetic field that deflects the electron beam B. For example, in FIG. 2 , if the emission direction of the X-rays R is the upper side and the opposite side is the lower side in the direction along the tube axis A, the deflection unit 6 may be disposed below the bottom wall portion 22b of the bulb 22. The deflection unit 6 may be rotatable around the tube axis A. In this case, the position of incidence of the electron beam B on the target 4 can be adjusted by rotating the deflection unit 6. [Action and effect]

[0045] In the X-ray generator 10, a tube voltage is applied between the cathode 32 of the electron gun 3 and the target 4 by a tube voltage application unit (power supply unit 11), and the target 4 is disposed at an angle with respect to an imaginary plane perpendicular to the axis A3 of the electron gun 3. As a result, an equipotential surface CL of the tube voltage between the cathode 32 and the target 4 is inclined with respect to the imaginary plane. As a result, electrons are deflected by passing through a region where this equipotential surface CL is inclined. The amount of electron deflection at this time decreases as the initial velocity of the electrons increases, and increases as the initial velocity of the electrons decreases.

[0046] Therefore, the amount of deflection of electrons is automatically adjusted according to the magnitude of the extraction voltage (magnitude of the initial velocity of the electrons) by the first grid electrode 33. Therefore, by disposing the target 4 so that the thickness T4 of the target 4 has a distribution and the thickness T4 of the target 4 is thinner at the electron incidence position when the extraction voltage is relatively low than at the electron incidence position when the extraction voltage is relatively high, electrons can be made to be incident at an appropriate position on the target 4. Note that a high (and low) extraction voltage means a large (and small) potential difference between the extraction electrode and the cathode 32.

[0047] In the X-ray generator 10, the thickness T4 of the target 4 is set to become thinner from the central portion 4a to the peripheral portion 4b, and the target 4 is arranged so that electrons are incident on the peripheral portion 4b side as the extraction voltage becomes relatively lower. In this case, it is easy to form the target so that the thickness T4 of the target 4 has the above-mentioned distribution.

[0048] The X-ray generator 10 also includes a magnetic field forming unit (permanent magnet 61) for deflecting electrons by forming a magnetic field between the cathode 32 and the target 4. This makes it possible to further deflect electrons by utilizing the magnetic field.

[0049] Furthermore, the X-ray generator 10 includes, as a magnetic field forming unit, a permanent magnet 61 attached to the housing 2 between the cathode 32 and the target 4. In this way, in the X-ray generator 10, if a constant magnetic field is formed by the permanent magnet 61, the amount of electron deflection caused by the magnetic field is automatically adjusted. This reliably avoids complicating control.

[0050] Furthermore, in the X-ray generator 10, the window member 5 has a first surface 51 on the side opposite to the inside of the housing 2 and a second surface 52 on the inside side of the housing 2, and the target 4 is formed on the second surface 52. This forms a so-called transmission type X-ray generator 10. [Variations]

[0051] The present disclosure is not limited to the above-described embodiment. The X-ray tube 1 and the X-ray generator 10 may be configured as a sealed reflection type. As shown in FIG. 5 , the sealed reflection type X-ray tube 1 differs from the sealed transmission type X-ray tube 1 mainly in that the electron gun 3 is disposed in a housing portion 7 on the side of the head 21, and the target 4 is supported by a support member 8 rather than a window member 5. The housing portion 7 has a side tube 71 and a stem 72. The side tube 71 is joined to the side wall of the head 21 so that one opening 71a of the side tube 71 faces the interior of the head 21. The stem 72 seals the other opening 71b of the side tube 71.

[0052] The heater 31, cathode 32, first grid electrode 33, and second grid electrode 34 are arranged in this order from the stem 72 side inside the side tube 71. Multiple lead pins 35 penetrate the stem 72. The support member 8 penetrates the bottom wall 22b of the bulb 22. The target 4 is fixed to the tip 81 of the support member 8 in a state inclined so as to face both the electron gun 3 and the window member 5 on the tube axis A.

[0053] In this example, the deflection unit 6 is provided with respect to the side tube 71 of the accommodation unit 7. As a result, the permanent magnet 61 is disposed between the cathode 32 and the target 4 by the holding member 62. As a result, a magnetic field including at least a component perpendicular to the direction of electron travel is formed between the cathode 32 and the target 4. In this way, the permanent magnet 61 also functions as a magnetic field forming unit for deflecting electrons by forming a magnetic field between the cathode 32 and the target 4.

[0054] More specifically, as shown in Fig. 6, the permanent magnet 61 is disposed outside the side tube 71 of the housing unit 7. Therefore, the electrons emitted from the cathode 32 are deflected by the force of the magnetic field formed by the permanent magnet 61, at least within the side tube 71. Note that Fig. 6 does not show all components, including the second grid electrode 34 of the electron gun 3.

[0055] In particular, in this example, the target 4 is also disposed at an angle with respect to a virtual plane perpendicular to the axis A3 of the electron gun 3. As a result, the equipotential surface CL of the tube voltage between the cathode 32 and the target 4 is inclined with respect to the virtual plane. As a result, electrons are deflected as they pass through a region where this equipotential surface CL is inclined. The amount of electron deflection at this time decreases as the initial velocity of the electrons increases, and increases as the initial velocity of the electrons decreases.

[0056] Therefore, the amount of deflection of electrons is automatically adjusted according to the magnitude of the extraction voltage (magnitude of the initial velocity of the electrons) applied by the first grid electrode 33. Therefore, by disposing the target 4 so that the thickness T4 has a distribution and the target 4 is thinner at the electron incidence position when the extraction voltage is relatively low than at the electron incidence position when the extraction voltage is relatively high, electrons can be made to be incident at an appropriate position on the target 4 while avoiding complicated control. Note that a high (and low) extraction voltage means a large (and small) potential difference between the extraction electrode and the cathode 32.

[0057] In an X-ray generator 10 equipped with the sealed reflection type X-ray tube 1 configured as described above, for example, with the head 21 and side tube 71 held at ground potential, a positive voltage is applied to the target 4 by the power supply unit 11 via the support member 8, and a negative voltage is applied to each component of the electron gun 3 by the power supply unit 11 via multiple lead pins 35. The electron beam B emitted from the electron gun 3 is focused on the target 4 in a direction perpendicular to the tube axis A. X-rays R generated in the region of the target 4 irradiated by the electron beam B are focused at the irradiated region and transmitted through the window member 5 to be emitted to the outside. When X-rays are generated by electrons incident on the target 4, most of the incident energy is converted into heat. If heat is accumulated in the target 4, the target 4 may be thermally damaged. To prevent this, the support member 8 is made of a material with good thermal conductivity, such as copper, and the support 5A is made of a material with high thermal conductivity, such as diamond. In order to efficiently transfer the heat generated inside the target 4 from the support 5A to the support member 8, the electron beam B must penetrate the target 4A so as to reach the vicinity of the boundary between the target 4A and the support 5A. This makes it easier to transfer the generated heat to the support 5A and prevents thermal damage to the target 4A. Therefore, by controlling the electron beam B to be incident on a thick portion of the target 4 at a high tube voltage where the electron beam B1 penetrates deeply, and on a thin portion of the target 4 at a low tube voltage where the electron beam B2 penetrates only shallowly, the electron beam B can be incident on an appropriate position on the target 4, thereby preventing thermal damage to the target 4.

[0058] The X-ray tube 1 may be configured as an open transmission type X-ray tube or an open reflection type X-ray tube. The open transmission type or open reflection type X-ray tube 1 is an X-ray tube in which the housing 2 is configured to be openable, and parts (for example, the window member 5 and each part of the electron gun 3) can be replaced. In an X-ray generating device 10 equipped with an open transmission type or open reflection type X-ray tube 1, the degree of vacuum in the space inside the housing 2 is increased by a vacuum pump.

[0059] In a sealed transmission type or open transmission type X-ray tube 1, the target 4 may be formed on at least a region of the second surface 52 of the window member 5 that is exposed to the opening 23. In a sealed transmission type or open transmission type X-ray tube 1, the target 4 may be formed on the second surface 52 of the window member 5 via another film.

[0060] Furthermore, in the above example, the permanent magnet 61 is exemplified as the magnetic field forming unit. However, any configuration (for example, an electromagnet such as a coil) that can form a magnetic field between the cathode 32 and the target 4 may be employed as the magnetic field forming unit. Whichever configuration of magnetic field forming unit is employed, electrons can be automatically injected into an appropriate position on the target 4 according to the tube voltage without controlling the formation (magnitude) of the magnetic field, that is, while avoiding complex control.

[0061] In the above example, one permanent magnet 61 is exemplified as the magnetic field generating unit. However, the number of permanent magnets 61 is not limited to this, and there may be a plurality of permanent magnets 61, in which case they may be arranged to face each other. Alternatively, in the X-ray generating device 10, the first grid electrode 33 and the power supply unit 11 have the function of deflecting electrons. Therefore, in the X-ray generating device 10, the deflection unit 12 does not need to include the deflection unit 6 (the permanent magnet 61 is not essential).

[0062] Furthermore, as described above, the distribution of the thickness T4 of the target 4 can be any desired form, and is not limited to the distribution that becomes thinner from the central portion 4a toward the peripheral portion 4b as in the above example. For example, the distribution of the thickness T4 of the target 4 may be a distribution that becomes monotonically thinner from one end to the other. Even in this case, the same effect can be achieved by arranging the target 4 so that electrons (electron beam B) are incident on the relatively thinner portion when the tube voltage is relatively low rather than when the tube voltage is relatively high. [Explanation of symbols]

[0063] 2...housing, 3...electron gun, 4...target, 5...window member, 10...X-ray generator, 11...power supply unit (tube voltage application unit), 32...cathode (electron emission unit), 33...first grid electrode (extraction electrode), 61...permanent magnet (magnetic field formation unit).

Claims

1. The housing and an electron gun having an electron emission unit that emits electrons within the housing and an extraction electrode that extracts the electrons emitted from the electron emission unit; an extraction voltage application unit that applies an extraction voltage to the extraction electrode; a target that generates X-rays in response to the electrons incident thereon; a window member that seals the opening of the housing and allows the X-rays to pass through; a tube voltage application unit that applies a tube voltage between the electron emission unit and the target; Equipped with the target has a thickness distribution; the target is arranged so as to be inclined with respect to a virtual plane perpendicular to the axis of the electron gun, and so as to have a thickness smaller at the electron incidence position when the tube voltage and the extraction voltage are relatively low than at the electron incidence position when the tube voltage and the extraction voltage are relatively high. X-ray generator.

2. The thickness of the target is made to decrease from the center to the periphery, the target is disposed so that the electrons are incident on the peripheral portion side as the tube voltage and the extraction voltage become relatively lower.

2. The X-ray generating device according to claim 1.

3. a magnetic field forming unit for forming a magnetic field between the electron emission unit and the target to deflect the electrons, 3. The X-ray generating device according to claim 1 or 2.

4. The magnetic field forming unit includes a permanent magnet.

4. The X-ray generating device according to claim 3.

5. the window member has a first surface opposite to the interior of the housing and a second surface on the interior side of the housing; the target is formed on the second surface; The X-ray generating device according to any one of claims 1 to 4.

6. the target is supported in an inclined state so as to face both the electron gun and the window member; The X-ray generating device according to any one of claims 1 to 4.

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