JP7571249B2 - Electron gun, X-ray generating tube, X-ray generating device, and X-ray imaging system - Google Patents

Description

The present invention relates to an X-ray generating device that can be used for non-destructive X-ray photography in the fields of medical equipment and industrial equipment, and an X-ray photography system equipped with the X-ray generating device.

In recent years, semiconductor devices have become increasingly miniaturized and multi-layered, and X-ray inspection equipment equipped with X-ray generating tubes is now used to inspect electronic devices, such as semiconductor integrated circuit boards, in the industrial field.

As an electron source that irradiates an electron beam onto a target, an X-ray generating tube equipped with an electron gun that protrudes toward the target along the tube axis is known.

Patent Document 1 discloses that by using an electron gun with multiple grid electrodes on the target side, it is possible to achieve high positional accuracy and microfocusing of the focal spot formed on the target.

In addition, the multiple grid electrodes of this electron gun are each supported by an insulating member, so that the distance between the electrodes is defined and a predetermined potential is applied to each electrode.

Patent document 2 discloses an X-ray generating tube equipped with an electron gun in which multiple grid electrodes are supported at intervals on insulating supports extending in the axial direction of the tube, with the aim of achieving a fine focus.

JP 2002-298772 A JP 2007-66694 A

In an X-ray imaging system using an X-ray generating tube with an electron gun having multiple grid electrodes supported by an insulating member, there have been cases where the quality of captured images has deteriorated.

The inventors' research has revealed that fluctuations in focal position or shape that occur due to the operating history of the X-ray generating tube are related to the deterioration of imaging quality.

The present invention aims to provide a highly reliable X-ray generating tube and X-ray generating device that includes an electron gun having a grid electrode supported by an insulating member and suppresses fluctuations in the position or shape of the focal spot. The present invention also aims to provide an X-ray imaging system that is equipped with the X-ray generating device according to the present invention and is capable of taking high-quality X-ray images.

An electron gun comprising: an anode including a target which generates X-rays by irradiating electrons thereon and which is grounded; a cathode which irradiates the target with electrons; and an insulating tube which insulates the anode and the cathode and constitutes a vacuum vessel together with the anode and the cathode; and which is applied to the cathode of an X-ray generating tube in which a tube voltage is applied between the anode and the cathode and which irradiates an electron beam toward the target,
an electron emitting section that emits electrons; an extraction electrode and a focusing electrode , each of which has an electron passing hole through which the electrons emitted from the electron emitting section pass and which are arranged in this order in a direction toward the target; and a plurality of insulating support members that are discretely provided in a tube circumferential direction to electrically insulate and support the extraction electrode and the focusing electrode ,
The present invention is characterized in that each of the extraction electrode and the focusing electrode has a conductive shielding portion that blocks the multiple insulating support members so that none of the multiple insulating support members has a portion where the insulating support member is directly viewed when viewed outside in the tube diameter direction from the electron passage, which is the path along which the emitted electrons pass from the electron emission portion to the focusing electrode.

A second electron gun according to an embodiment of the present invention is an electron gun that is applied to a vacuum tube in which a tube voltage is applied between the anode and the cathode, the electron gun comprising a grounded anode, a cathode, and an insulating tube that insulates the anode and the cathode and constitutes a vacuum container together with the anode and the cathode, the electron gun constituting the cathode,
an electron emitting section which emits electrons; an extraction electrode and a focusing electrode, each of which has an electron passing hole through which the electrons emitted from the electron emitting section pass and which are arranged in this order in a direction toward the anode; and a plurality of insulating support members which are discretely provided in a tube circumferential direction for electrically insulating and supporting the extraction electrode and the focusing electrode,
Each of the extraction electrode and the focusing electrode has a conductive shielding portion that blocks the multiple insulating support members so that none of the multiple insulating support members has a portion where the insulating support member is directly viewed when viewed outside in the tube radial direction from the electron passage, which is the path along which the emitted electrons pass from the electron emission portion to the focusing electrode.

According to the present invention, the electron gun of the X-ray generating tube has a conductive portion that blocks the insulating support member from being viewed directly from the electron passage, making it possible to provide a highly reliable X-ray generating tube and X-ray generating device in which fluctuations in the position or shape of the focal spot are suppressed.

1A to 1H are schematic configuration diagrams showing an X-ray generating tube according to a first embodiment of the present invention. 1A to 1I are schematic configuration diagrams showing an X-ray generating tube according to a reference embodiment. 1A to 1F are schematic diagrams of a presumed deposition process of scattered metal particles onto an insulating support member according to the subject matter of the present invention. 5A to 5J are schematic configuration diagrams showing an X-ray generating tube according to a second embodiment of the present invention. 5A to 5H are schematic configuration diagrams showing an X-ray generating tube according to a third embodiment of the present invention. FIG. 13 is a schematic configuration diagram showing an X-ray generating device according to a fourth embodiment of the present invention. FIG. 13 is a schematic configuration diagram showing an X-ray imaging system according to a fifth embodiment of the present invention.

Below, preferred embodiments of the present invention are described in detail with reference to the drawings. The dimensions, materials, shapes, relative positions, etc. of the components described in these embodiments are not intended to limit the scope of this invention. Furthermore, for parts not specifically shown or described in this specification, well-known or publicly known techniques in the relevant technical field are applied.

<X-ray generating tube>
1 shows an X-ray generating tube 1 according to a first embodiment of the present invention. The X-ray generating tube 1 is a transmission type X-ray generating tube having a conductive portion, which is a basic feature of the present invention.

Figures 1(a) and (b) are two-sided views showing the basic configuration of the X-ray generating tube 1, and Figure 1(b) is a front view of the X-ray generating tube 1 of Figure 1(a) seen from the anode side. Figure 1(c) is a partially enlarged view of Figure 1(b) showing the focal spot formed on the target when the X-ray generating tube 1 of this embodiment is driven. Figure 1(d) is an enlarged cross-sectional view of the electron gun 4b of the X-ray generating tube 1 shown in Figure 1(a). Figures 1(e) to (h) are cross-sectional views showing the cross sections of the electron gun 4b in the imaginary planes A-A, B-B, C-C, and D-D shown in Figure 1(d).

In this embodiment, X-rays are generated from the target 5b by irradiating the target layer 5c with the electron beam emitted from the electron emitter 40. For this reason, the target layer 5c is disposed on the surface of the support substrate 5d facing the electron gun 4b. In other words, the electron emitter 40 is disposed on the cathode 4 so as to face the target 5b. The electrons emitted from the electron emitter 40 are accelerated to the incident energy required to generate X-rays in the target layer 5c by the accelerating electric field formed between the cathode 4 and the anode 5 by the tube voltage applied to the X-ray generating tube 1.

The anode 5 comprises a target 5b and an anode member 5a connected to the target 5b, and functions as an electrode that determines the anode potential of the X-ray generating tube 1.

The anode member 5a is made of a conductive material and is electrically connected to the target layer 5c. As shown in FIG. 1, the anode member 5a is connected to the periphery of the support substrate 5d and holds the target 5b.

The target layer 5c contains target metals such as tantalum, molybdenum, and tungsten as metal elements with high atomic numbers, high melting points, and high specific gravity. On the other hand, the support substrate 5d is preferably made of a material that has high X-ray transparency and high thermal conductivity, such as diamond, silicon nitride, silicon carbide, aluminum nitride, graphite, and beryllium. Diamond is particularly preferable as a support substrate material for a transmission type target because it has high thermal conductivity due to sp3 bonds and high transparency to radiation.

The inside of the X-ray generating tube 1 is in a vacuum state in order to ensure the mean free path of the electron beam. The degree of vacuum inside the X-ray generating tube 1 is preferably 1×10 ⁻⁴ Pa or less, and from the viewpoint of stabilizing the electron emission characteristics of the electron emitting section 40, is even more preferably 1×10 ⁻⁶ Pa or less. In this embodiment, the electron emitting section 40 and the target layer 5c are disposed in the internal space or on the inner surface of the X-ray generating tube 1, respectively.

The vacuum inside the X-ray generating tube 1 is created by evacuating the air using an exhaust tube and vacuum pump (not shown) and then sealing the exhaust tube. A getter (not shown) may be placed inside the X-ray generating tube 1 to maintain the degree of vacuum.

In the X-ray generating tube 1, an insulating tube 2 is sandwiched between an anode member 5a and a cathode member 4a for the purpose of providing electrical insulation between an electron emitter 40, which is determined by a cathode potential, and a target layer 5c, which is determined by an anode potential. That is, one end and the other end of the insulating tube 2 are connected to the anode member 5a and the cathode member 4a, respectively, in the tube axial direction.

The insulating tube 2 is made of an insulating material such as glass or ceramic. The outer surface of the insulating tube 2 made of ceramics is protected by a glass layer 0.1 μm to 100 μm thick to ensure strength.

In this embodiment, the insulating tube 2, the cathode 4 with the electron emitter 40, and the anode 5 with the target 5b constitute an envelope that is airtight to maintain a vacuum and robust enough to withstand atmospheric pressure. The cathode 4 and the anode 5 are connected to both ends of the insulating tube 2 in the tube axis direction, respectively, to form part of the envelope. Similarly, the support substrate 5d serves as a transmission window that extracts the X-rays generated in the target layer 5c to the outside of the X-ray generating tube 1, and can be said to form part of the envelope.

<Electron gun>
Next, the electron gun, which is a feature of the X-ray generating tube of the present invention, will be described with reference to FIGS.

The cathode 4 comprises an electron gun 4b and a cathode member 4a, each of which comprises an electron emitter 40, a grid electrode 42, and an insulating support member 41 that supports the grid electrode, and is arranged so that the target 5b and the electron emitter 40 face each other.

The electron emission section 40 may be a hot cathode electron source such as a tungsten filament, an impregnated cathode, or an oxide cathode, or a cold cathode electron source such as a Spindt-type cathode made of molybdenum.

As shown in FIG. 1(a), the electron gun 4b in this embodiment protrudes from the cathode member 4a toward the anode 5. The purpose of arranging the electron gun 4b to protrude toward the anode 5 in this manner is to ensure the accuracy of the focal position without reducing the dielectric strength. In other words, by setting the creeping path of the insulating tube 2 connecting the cathode 4 and the anode 5 at a distance greater than a predetermined distance, while setting the distance between the electron gun 4b and the target 5b at a predetermined distance or less, the electron beam emitted from the electron emitter 40 is less susceptible to the effects of the electric field in the tube diameter direction.

The electron gun 4b has an electron emitter 40 and a grid electrode 42 arranged on the part that protrudes toward the anode 5; this part is referred to as the head part. The part that supports the head part against the cathode member 4a is referred to as the neck part. In this embodiment, the neck part is provided with a cathode support part 45 that supports the electron emitter 40, a power supply part 43d that supplies an extraction potential to the extraction grid electrode 43, and a power supply part 44d that supplies a focus potential to the focus grid electrode 44, as shown in Figures 1(d) to (h).

As shown in Figures 1(d) to (h), the electron gun 4b includes an extraction grid electrode 43 with electron passing holes 43f and a focusing grid electrode 44f, and an insulating support member 41 that supports the grid electrode 43 and the focusing grid electrode 44. The electron passing holes 43f and 44f in the grid electrode 43 and the focusing grid electrode 44 define an electron passage path 7 in the direction from the electron emitter 40 toward the target 5b.

The extraction grid electrode 43 and the focusing grid electrode 44 have in common the fact that they regulate the movement of electrons passing through the electron passage 7 and determine the beam diameter of the electron beam, and therefore in this invention, they are collectively referred to as the grid electrode 42.

The extraction grid electrode 43 is provided with the intention of controlling the amount of electrons emitted from the electron emitter 40 passing through the electron passage hole 43f over time, and multiple potentials are applied to it by a voltage source (not shown) in a switched manner. On the other hand, the focusing grid electrode 44 is provided with the intention of forming a focusing electric field for the electrons and defining the size of the focal spot 8 formed on the target 5b, and a focusing grid potential having a predetermined potential difference is applied to the electron emitter 40 by a voltage source (not shown).

In this specification, the electron passage 7 corresponds to the path along which the electrons emitted from the electron emitter 40 pass before passing through the focusing grid electrode 44.

The extraction grid electrode 43 has an annular portion 43a with electron passage holes 43f extending in the tube radial and circumferential directions, and is supported at the outer edge of the annular portion 43a by four insulating support members 41a to 41d arranged at 90 degree intervals around the electron passage 7.

The insulating support members 41a to 41d are matched in linear expansion coefficient to the grid electrode 42 in order to relieve thermal stress at the connection portion with the grid electrode 42. When the grid electrode 42 is made of molybdenum (α=4.8×10 ⁻⁶ K ⁻¹ at 300 K), alumina (α=7.0×10 ⁻⁶ K ⁻¹ at 300 K) is used. The grid electrode 42 and the insulating support members 41a to 41d are joined via a brazing material (not shown).

The embodiment of the present invention (not shown) also includes a configuration in which multiple grid electrodes 43 and multiple focusing grid electrodes 44 are arranged. Therefore, the embodiment of the present invention (not shown) also includes a configuration in which there are three or more grid electrodes 42. In such a configuration, the insulating support member 41 electrically insulates and supports at least two of the multiple grid electrodes 42.

As shown in Figs. 1(d) and (h), the focusing grid electrode 44 has an annular portion 44a extending in the tube radial and circumferential directions and provided with electron passing holes 44f through which electrons that have passed through the electron passing holes 43f of the extraction grid electrode 43 can pass.

The annular portions 43a and 44a do not need to be parallel to the tube diameter direction (yz plane), and may be cone-shaped as long as they form an electric field sufficient to define the electron passage 7. The annular portions 43a and 44a may also be discontinuous in shape, such as a mesh grid, a spiral grid electrode, or a multiple annular electrode.

First Embodiment
Next, an X-ray generating tube according to a first embodiment having a conductive portion that is a feature of the present invention will be described in more detail with reference to FIGS.

The grid electrode 42 of this embodiment includes an extraction grid electrode 43 on the side closer to the electron emitter 40, and a focusing grid electrode 44 on the side farther from the electron emitter 40. The extraction grid electrode 43 further includes tubular portions 43b and 43c extending in the tube axis direction. It can also be said that the tubular portions 43b and 43c extend in a direction intersecting the tube diameter direction. The tubular portions 43b and 43c are tubular protrusions protruding from the annular portion 43a on the electron emitter 40 side and the focusing grid electrode 44 side, respectively. The tubular portions 43b and 43c are part of the extraction grid electrode 43, and together with the annular portion 43a, are electrically connected to a voltage source (not shown) to regulate the potential.

The focusing grid electrode 44 is supported at the outer edge of the annular portion 44a by four insulating support members 41a to 41d arranged at 90 degree intervals around the electron passage 7. The annular portion 44a is arranged to face the target 5b.

In addition, like the annular portion 43a, the annular portion 44a may be in the shape of a cone or a mesh, as long as it generates an electric field sufficient to define the electron passage 7.

The focusing grid electrode 44 of this embodiment further includes tubular portions 44b and 44c extending in the tube axis direction. It can also be said that the tubular portions 44b and 44c extend in a direction intersecting the tube diameter direction. The tubular portions 44b and 44c are tubular protrusions that protrude toward the electron emission portion 40 side and the adjacent anode 5 side, respectively. The tubular portions 44b and 44c are part of the focusing grid electrode 44, and together with the annular portion 44a, are electrically connected to a voltage source (not shown) to regulate the potential.

As shown in Figures 1(d) and (e), the tubular portion 43b protrudes toward the cathode member 4b so that the insulating support member 41 is not directly viewed from the electron passage 7. Here, the tubular portion 43b is spaced apart from the electron emission portion 40 in the tube diameter direction so that the extraction grid electrode 43 and the electron emission portion 40 are not short-circuited.

As shown in Figs. 1(d) and (g), the tubular portions 43c and 44b protrude in opposite directions so as to overlap in the tube axial direction, so that the insulating support member 41 is not directly seen from the electron passage 7. That is, the annular portions 44a and 43a, and the tubular portions 43c and 44b are spaced apart from each other, so that the grid electrodes 42 (43, 44) are not short-circuited.

As shown in Figures 1(d) and (g), the extraction grid electrode 43 and the focusing grid electrode 44 can be considered to be a pair of grid electrodes 42 in which the annular portions 43a, 44a face each other in the tube axis direction, and the tubular portions 43c, 44b face each other in the tube diameter direction. By providing such annular portions 43a, 44a (conductive portion 6), the electron gun 4b of this embodiment suppresses the deposition of scattered metal particles moving in the tube diameter direction on the insulating support members 41a to 41d.

The tubular portion 43c is located further inward in the tube diameter direction than the tubular portion 44b. In other words, the tubular portion 43c of the extraction grid electrode 43, in which the annular portion 43a is located closer to the electron emitter 40, can be said to be located further inward in the tube diameter direction than the tubular portion 44b of the focusing grid electrode 44, in which the annular portion 44a is located farther from the electron emitter 40.

The conductive portion 6 (tubular portions 43b, 43c, 44b) serves to prevent metal particles flying from the electron passage 7 from accumulating on the insulating support member 41, and to maintain the insulation of the insulating support member 41. This allows the electron emitter 40 and grid electrode 42 (43, 44) to be stably set to their respective predetermined potentials. Therefore, the X-ray generating tube 1 according to this embodiment has high reliability as fluctuations in the size, position, and shape of the focal spot 8 caused by the operating history are suppressed.

In this embodiment, the conductive portion 6 (tubular portion 43b, 43c, 44b) is a part of the grid electrode 42 (43, 44) and has conductivity. Therefore, even if metal particles are deposited on the conductive portion 6 (tubular portion 43b, 43c, 44b), the electric field regulation action of the grid electrode does not fluctuate, as long as the adjacent electron emitters 40 and grid electrodes 42 (43, 44) are not short-circuited.

According to the X-ray generating tube 1 of this embodiment, the electron gun 4b has a conductive portion 6 (tubular portions 43b, 43c, 44b) that blocks the insulating support member 41 from being viewed directly from the electron passage 7, thereby ensuring the insulation of the insulating support member 41. By providing an electron gun 4b with such a conductive portion 6 (tubular portions 43b, 43c, 44b), it is possible to provide a highly reliable X-ray generating tube 1 in which fluctuations in the size, position, and shape of the focal spot 8 are suppressed.

In this embodiment, the conductive portion 6 (43b, 43c, 44b) is part of the grid electrode 42 (43, 44), but the present invention also includes a form in which a metal material electrically isolated from the grid electrode 42 (43, 44) is arranged. On the other hand, in order to prevent a short circuit between the conductive portion 6 and the grid electrode 42 or between the conductive portion 6 and the electron emission portion 40 in the space where the grid electrode 42 (43, 44) is arranged, it is preferable that the conductive portion 6 is part of the grid electrode 42 as in this embodiment.

In this embodiment, as shown in Figs. 1(e) and (g), the conductive portion 6 (43b, 43c, 44b) has a tubular shape that blocks the insulating support members 41a to 41d from being viewed directly from the electron passage 7, but the tubular shape is not essential. For example, the present invention also includes a form (not shown) in which the conductive portions are arranged discretely in the circumferential direction in correspondence with each of the insulating support members 41a to 41d that are arranged discretely in the circumferential direction.

The mechanism by which metal particles fly from the electron passage 7 and accumulate on the insulating support members 41a to 41d will be described later.

<Reference form>
The present inventors have confirmed that in an X-ray generating tube having an electron gun with a grid electrode supported by an insulating support member, the focal spot diameter varies with the driving history of the X-ray generating tube.

Figures 2(a) to (e) show an X-ray generating tube 301 according to a reference embodiment that differs from the first embodiment in that the grid electrodes 42 and 43 do not have tubular portions (conductive portions).

2(a) to 2(h) are shown corresponding to Fig. 1(a) to 1(h) according to the first embodiment. On the other hand, Fig. 2(i) is a schematic diagram showing a focal spot 308 observed in the X-ray generating tube 304 after ¹⁰⁴ exposure operations, and shows an enlargement of the focal spot diameter, which is different from the first embodiment.

As a result of intensive investigations by the present inventors, the following five observational facts regarding the variation in focal spot diameter due to the driving history in an X-ray generating tube having an electron gun with a grid electrode supported by an insulating support member have been confirmed.
- The change in focal spot diameter was irreversible and did not recover after a rest period.
The squared correlation coefficient ^R2 for the amount of variation in focal spot diameter was in the following order: tube voltage < exposure intensity ≒ electron beam dose < filament current of electron emission source.
- When the electron gun of the X-ray generating tube, which had a large fluctuation, was analyzed, a decrease in the resistance between the nodes between the grid electrodes and between the grid electrode and the electron gun was confirmed.
- When the electron gun of the X-ray generating tube, which had experienced a large amount of fluctuation, was analyzed, an increase in a specific metal was found in the surface composition of the insulating support member.
The metal that showed an increase was predominantly Ba, a component derived from the electron-emitting portion.

Based on these observations, the inventors of the present application have concluded that the cause of the fluctuation in focal spot diameter is the accumulation of scattered metal particles on the insulating support member 341 caused by the operation of the X-ray generating tube.

<Elemental process of scattering metal particles generation>
Next, the elementary process that the inventors of the present invention have devised for the generation of scattered metal particles and their deposition on an insulating support member, which is the subject of the present invention, will be described with reference to FIGS.

Inside the X-ray generating tube 301, metal particles float along with the gas that inevitably remains. These metal particles are thought to be a part of the constituent materials of the electron emitting section 340 and the target layer 305c that have been emitted into the vacuum space. From the observation results that were based on the exposure operation of the X-ray generating tube and the electron emission operation of the electron gun, the metal particle emission process is thought to be evaporation from the electron emitting section 340, sputtering on the target layer 305c and grid electrode 342, etc., as shown in Figure 3 (a).

Since the kinetic energy of the floating metal particles is less than a few eV, most of them are captured at or near the point of generation, but the remainder are irradiated with electrons and X-rays and become positively ionized, as shown in Figures 3(b) and (c).

Taking the impregnated electron emitting portion 340 impregnated with barium oxide as an example, the ionization process of Ba particles evaporated from the electron emitting portion 340 is shown in [Chemical formula 1] and [Chemical formula 2].
Ba (X-ray incidence) → Ba ^{++ e-} [Chemical formula 1]
Ba (+e ^- incident) → Ba ^{++ 2e-} [Chemical formula 2]

On the other hand, the generated metal ions move to the side of the cathode member 304 as shown in Fig. 3(d) due to electrostatic force from the electric field inside the electron gun 304b or the X-ray generating tube 301, and most of them are captured by the cathode 304. It is considered that the captured metal ions receive electrons on the cathode 304 and are deposited as a metal layer, as shown in [Chemical formula 3].
Ba ⁺ + e ^- → Ba [Chemical formula 3]

The metal deposited on the cathode 304 is permissible because it does not affect the electric field regulation performance of the cathode member 304a constituting the cathode 304 and the electron emission section 340.

Meanwhile, the remaining metal ions recombine with the scattered electrons and electron beam before being captured by the cathode 304, as shown in FIG. 3(e), and receive part of the kinetic energy of the electron beam and scattered electrons, becoming neutral scattered metal particles.

Since these scattered metal particles are not affected by the electric field, they can move in the tube diameter direction (yz plane), and as shown in FIG. 3(f), the metal particles are fixed to the surface of the insulating support member 341, depositing a metal layer. As a result, in the X-ray generating tube 301 having the electron emitting portion 304b that does not have the conductive portion 6 (tubular portion), the electric field regulation performance of the grid electrodes 343, 344 decreases with the operating history. As a result, it is believed that the focal spot size changes from the initial focal spot 8 shown in FIG. 2(c) to the defocused focal spot 308 shown in FIG. 2(i) with the operating history of the X-ray generating tube 301.

Second Embodiment
Fig. 4 shows an X-ray generating tube 1 according to a second embodiment. Each of Fig. 4(a) to (h) is presented in the same manner as Fig. 1(a) to (h). As shown in Fig. 4(d) and Fig. 4(e) to (h), this embodiment differs from the first embodiment in that an outer circumferential tubular portion 44e that hides the insulating support members 41a to 41d when viewed from the outside of the insulating support member 41 is provided.

In this embodiment, the outer tubular portion 44e also serves as the power supply portion 44d of the focusing grid electrode 44, and can also be considered to be part of the focusing grid electrode 44 (grid electrode 42).

The conductive portion 6 (tubular portion 43b, 43c, 44b) located inside the electron gun 4b shields the insulating support members 41a to 41d when viewed from the electron passage 7. In contrast, the conductive portion 6 (tubular portion 44e) located outside the electron gun 4b shields the insulating support members 41a to 41d when viewed from the area between the electron gun 4b and the insulating tube 2.

The technical significance of the outer circumferential tubular portion 44e acting as a conductive portion is explained below using Figures 4(a) to (j).

<<Scattering Metal Particles for Backscattered Electrons>>
Electrons emitted from the electron emitter 40 at substantially an initial velocity of 0 pass through the electron passage 7, are accelerated by the electrostatic potential of the tube voltage Va, and are incident on the target 5b with kinetic energy Va (eV).

In the target 5b, the electrons are converted into thermal energy, secondary electrons, and Auger electrons inside the target layer 5c, and the remainder is converted into X-rays. The secondary electrons and Auger electrons, which are components that interact with the target metal inside the target layer 5c and are decelerated, have a kinetic energy of only 0-500 (eV) and are emitted behind the target layer 5c, so most of them re-enter the anode 5 and are captured.

On the other hand, about 20% to 40% of the incident electrons are elastically scattered at the surface of the target layer 5c. The backscattered electrons elastically scattered at the surface of the target layer 5c have kinetic energy Va (eV) and can reach the area on the equipotential surface of the electron emitter 40.

In an X-ray generating tube 1 equipped with an electron gun 4b protruding from a cathode member 4a on the anode 5 side, the electric field between the cathode 4 and anode 5 is deformed by the electron gun 4b on the cathode 4 side, as shown in FIG. 4(i).

The backscattered electrons elastically scattered from the target layer 5c have a scattering angle distribution, and not only are there components that scatter toward the electron gun 4b, but there are also components that reach the space between the electron gun 4b and the insulating tube 2.

Figure 4(i) shows the tube axis directions X0 (y = -Ψ/2), X1 (y = 0), and X2 (y = -Ψ/4) which have different Y coordinates in the tube diameter direction. Also, Figure 4(j) shows the imaginary linear potential distribution along the tube axis directions X0 (y = -Ψ/2), X1 (y = 0), and X2 (y = -Ψ/4). Here, Ψ is the diameter (m) of the anode member 5a.

Since the electrostatic potential of the electron emitter 40 is the cathode potential -Va (eV), the backscattered electrons moving along X2 (y = -Ψ/4) reach the cathode member 4a side of the electron emitter 40.

Therefore, the backscattered electrons that reach the space between the electron gun 4b and the insulating tube 2 recombine with metal (cation) ions contained in minute amounts in the internal space of the X-ray generating tube 1, and change into neutral scattered metal particles. In other words, the backscattered electrons that reach the space between the electron gun 4b and the insulating tube 2 are thought to generate scattered metal particles in the space between the electron gun 4b and the insulating tube 2, and are a cause of the deposition of metal particles on the insulating support member 41.

The outer tubular portion 44e (conductive portion) of this embodiment prevents scattered metal particles generated in the space between the electron gun 4b and the insulating tube 2 from accumulating on the insulating support members 41a to 41d and lowering the resistance of the insulating support member 41. This allows the electron emitter 40 and the grid electrodes 42 (43, 44) to be stably set at their respective predetermined potentials. Therefore, as shown in FIG. 4(c), the X-ray generating tube 1 of this embodiment has high reliability as the fluctuations in size, position, and shape of the focal spot 8 caused by the operating history are further suppressed.

The outer tubular portion 44e can also be considered a conductive portion provided on the outside of the insulating support members 41a to 41d to prevent scattered metal particles from accumulating on the insulating support members 41a to 41d from the outside in the tube diameter direction.

The X-ray generating tube according to the first and second embodiments is an example of application to a transmission type X-ray generating tube equipped with a transmission type target. However, the present invention also includes an application to an X-ray generating tube equipped with an electron gun in which a grid electrode is supported by an insulating support member, and a reflection type X-ray generating tube equipped with a reflection type target.

Third Embodiment
FIG. 5 shows an X-ray generating tube 1 according to a third embodiment. Each of FIGS. 5(a) to (h) is presented in the same manner as in FIGS. 1(a) to (h). As shown in FIGS. 5(d) and 5(g), this embodiment differs from the first and second embodiments in the positional relationship in the tube diameter direction of the annular portions 43c and 44b constituting the conductive portion. That is, in the tube diameter direction, the annular portions 43c and 44b facing each other are arranged such that the tubular portion 43c of the extraction grid electrode 43 located on the cathode 4 side is located outside the tubular portion 44b of the focus grid electrode 44 located on the anode 5 side in the tube diameter direction. It can also be said that the tubular portion 43c of the extraction grid electrode 43 located on the cathode 4 side is arranged so as not to be directly viewed from the electron passage 7 by the tubular portion 44b of the focus grid electrode 44 located on the anode 5 side.

By adopting such an arrangement, the phenomenon in which reflected electrons (not shown) that are backscattered by the annular portion 44a of the focusing grid electrode 44 are prevented from entering the tubular portion 43c of the extraction grid electrode 43 is suppressed, and the potential fluctuation of the extraction grid electrode 43 is suppressed.

The X-ray generating tube 1 of this embodiment not only suppresses the deterioration of the insulation of the insulating support members 41a-d due to the history of exposure operations, but also suppresses the influence of reflected electrons incident on the grid electrodes. As shown in Figures 5(b) and (c), it is possible to provide an X-ray generating tube with a higher reliability in which the position of the center 8c of the focal spot 8 is more stable.

<X-ray generator>
Next, an example of the configuration of an X-ray generating device equipped with the X-ray generating tube of the present invention will be described with reference to FIG.

Figure 6 shows an X-ray generating device 101 according to the fourth embodiment. The X-ray generating device 101 includes the X-ray generating tube 1 according to the first or second embodiment, a driving circuit 106 for driving the X-ray generating tube 1, and a storage container 107 for storing the X-ray generating device 102 and the driving circuit 106.

The drive circuit 106 has a tube voltage circuit 106a that applies a tube voltage between the cathode and anode, and an electron quantity control circuit 106b that controls the amount of electrons emitted by the electron gun 4b. The tube voltage circuit 106a creates an acceleration electric field between the target layer 5c and the electron emitter 40. By appropriately setting the tube voltage Va in accordance with the thickness and metal type of the target layer 5c, the line type required for imaging can be selected.

The container 107 that houses the X-ray generating tube 1 and the drive circuit 106 is preferably strong enough as a container and has excellent heat dissipation properties, and is made of a metal material such as brass, iron, or stainless steel.

The storage container 107 in this embodiment is electrically connected to the anode 5 of the X-ray generating tube 1 and is set to ground potential.

Meanwhile, the remaining space in the storage container 107 other than the X-ray generating tube 1 and the drive circuit 106 is filled with an insulating fluid 108, thereby ensuring electrical insulation between the components stored in the storage container 107 and the storage container 107. The components stored in the storage container 107 include the X-ray generating tube 1, the drive circuit 106, and wiring (not shown), etc.

The insulating fluid 108 is a liquid having electrical insulation properties, and has the role of maintaining the electrical insulation inside the storage container 107 and the role of acting as a cooling medium for the X-ray generating tube 1. As the insulating fluid 108, electrical insulating oils such as mineral oil, silicone oil, and perfluoro oil, insulating gases such as SF6, etc. are used.

The X-ray generating device 101 of this embodiment is equipped with an electron gun that ensures stability in the focusing performance of the electron beam by applying at least the X-ray generating tube 1 according to any one of the first to third embodiments, and therefore has high reliability with suppressed fluctuations in the focal spot 8.

<X-ray imaging system>
Next, an example of the configuration of an X-ray imaging system including the X-ray generating device of the present invention will be described with reference to FIG.

Figure 7 shows an X-ray imaging system 200 according to the fifth embodiment. The X-ray imaging system 200 includes an X-ray detection device 201 that detects X-rays emitted from an X-ray generation device 101 and transmitted through a subject 204, and a system control device 201 that controls the X-ray generation device 101 and the X-ray detection device 201 in cooperation with each other.

The drive circuit 106 outputs various control signals to the X-ray generating tube 1 under the control of the system control device 202. The control signals output by the drive circuit 106 control the emission state of the X-ray flux emitted from the X-ray generating device 101.

The X-ray beam emitted from the X-ray generator 101 passes through the subject 204 and is detected by the detector 206. The detector 206 converts the detected X-rays into an image signal and outputs it to the signal processing unit 205.

The signal processing unit 205 performs predetermined signal processing on the image signal under the control of the system control device 202, and outputs the processed image signal to the system control device 202.

Based on the processed image signal, the system control device 202 outputs a display signal to the display device 203 to cause the display device 203 to display an image. The display device 203 displays the image based on the display signal on a screen as a captured image of the subject 204.

The X-ray imaging system 200 of this embodiment is equipped with the X-ray generating device 101 according to the fourth embodiment, and thus the fluctuation of the focal point 8 is suppressed, and high-quality images can be obtained with good reproducibility. The X-ray imaging system is applied to non-destructive testing of industrial products and pathological diagnosis of the human body and animals.

REFERENCE SIGNS LIST 1 X-ray generating tube 2 Insulating tube 4 Cathode 4b Electron gun 5 Anode 5b Target 6 Conductive portion 7 Electron passage 40 Electron emitting portion 41 Insulating support member 42 Grid electrode 43 Extraction grid electrode 44 Focusing grid electrode

Claims (19)

An electron gun comprising: an anode including a target which generates X-rays by irradiating electrons thereon and which is grounded; a cathode which irradiates the target with electrons; and an insulating tube which insulates the anode and the cathode and constitutes a vacuum vessel together with the anode and the cathode; and which is applied to the cathode of an X-ray generating tube in which a tube voltage is applied between the anode and the cathode and which irradiates an electron beam toward the target,
an electron emitting section that emits electrons; an extraction electrode and a focusing electrode, each of which has an electron passing hole through which the electrons emitted from the electron emitting section pass and which are arranged in this order in a direction toward the target; and a plurality of insulating support members that are discretely provided in a tube circumferential direction to electrically insulate and support the extraction electrode and the focusing electrode,
an electron gun in which the extraction electrode and the focusing electrode each have a conductive shielding portion that blocks the plurality of insulating support members so that none of the plurality of insulating support members has a portion where the insulating support member is directly visible when viewed radially outward from an electron passage, which is the path along which the emitted electrons pass from the electron emission portion until they pass through the focusing electrode. the X-ray generating tube includes an anode member electrically connected to the anode and to one end of the insulating tube in an airtight manner, and a cathode member connected to the cathode in an airtight manner to the other end of the insulating tube;
2. The electron gun according to claim 1, further comprising: an electron gun electrically connected to said cathode member, said electron gun constituting said cathode together with said cathode member. The electron gun according to claim 2, characterized in that the focusing electrode is at a potential regulated by a voltage source. The electron gun according to any one of claims 1 to 3, characterized in that the focusing electrode includes the conductive shielding portion. The electron gun according to claim 1, characterized in that the conductive shielding portion is arranged so that the insulating support members do not have any portions that are directly visible from the electron passage. the focusing electrode has an annular portion having an electron passing hole that defines the electron passage and extending in a tube radial direction, and a tubular portion that is connected to the annular portion and extends along the electron passage,
6. The electron gun according to claim 1, wherein the conductive shielding portion is at least a part of the tubular portion. The electron gun according to any one of claims 1 to 6, characterized in that the conductive shielding portion is configured to suppress a decrease in resistance of the insulating support member. The electron gun according to any one of claims 1 to 7, characterized in that the conductive shielding portion is configured to suppress deposition of metal particles originating from the electron emission portion that move toward the outside in the tube diameter direction on the insulating support member. An electron gun according to any one of claims 1 to 8, characterized in that the insulating support member has an outer tubular portion on the outside in the tube diameter direction so that the insulating support member cannot be viewed directly from the outside in the tube diameter direction. The electron gun according to claim 9, characterized in that the outer circumferential tubular portion constitutes a part of the focusing electrode. The electron gun according to any one of claims 1 to 10, wherein the anode has a target layer that generates X-rays when irradiated with the electron beam from the electron gun, and an accelerating electric field is formed between the target layer and the electron emission section. The electron gun according to claim 11, wherein the accelerating electric field is formed at least between the anode end of the electron gun and the target layer so that electrons emitted from the electron gun are accelerated by an electrostatic potential corresponding to the tube voltage and enter the target layer. 13. The electron gun according to claim 11, wherein the accelerating electric field is formed at least between the focusing electrode and the target layer such that electrons that have passed through the electron passage are accelerated by an electrostatic potential corresponding to the tube voltage and enter the target layer. 4. An X-ray generating tube comprising: an electron gun according to claim 2 or 3; the cathode member constituting the cathode together with the electron gun; the anode member constituting the anode together with the target ; and the insulating tube connected to the anode member and the cathode member at one end and the other end in a tube axial direction. 15. An X-ray generating device comprising: the X-ray generating tube according to claim 14 ; and a drive circuit electrically connected to each of the target and the electron emitter, the drive circuit outputting a tube voltage to be applied between the target and the electron emitter. An X-ray generating device according to claim 15 ,
an X-ray detection device that detects X-rays emitted from the X-ray generation device and transmitted through a subject;
a system control device that controls the X-ray generating device and the X-ray detecting device in cooperation with each other;
An X-ray imaging system comprising: An electron gun comprising an anode that is grounded, a cathode, and an insulating tube that insulates the anode and the cathode and constitutes a vacuum vessel together with the anode and the cathode, the electron gun being applied to a vacuum tube in which a tube voltage is applied between the anode and the cathode and constituting the cathode,
an electron emitting section which emits electrons; an extraction electrode and a focusing electrode, each of which has an electron passing hole through which the electrons emitted from the electron emitting section pass and which are arranged in this order in a direction toward the anode; and a plurality of insulating support members which are discretely provided in a tube circumferential direction for electrically insulating and supporting the extraction electrode and the focusing electrode,
an electron gun in which the extraction electrode and the focusing electrode each have a conductive shielding portion that blocks the plurality of insulating support members so that none of the plurality of insulating support members has a portion where the insulating support member is directly visible when viewed radially outward from an electron passage, which is the path along which the emitted electrons pass from the electron emission portion until they pass through the focusing electrode. 18. The electron gun according to claim 17 , wherein the anode has a target layer that generates X-rays when irradiated with the electron beam from the electron gun, and an accelerating electric field is formed between the target layer and the electron emission portion. 19. The electron gun according to claim 18, wherein the accelerating electric field is formed at least between an anode side end of the electron gun and the anode so that electrons emitted from the electron gun are accelerated by an electrostatic potential corresponding to the tube voltage and enter the target layer.

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