TW201338001A - Electric field emission type X-ray generator - Google Patents

Abstract

The subject of the present invention is to prevent the discharging between a glass tube accommodating a cold cathode elements and a frame body located on the outer side within the X-ray generator using the electric field emission type cold cathode elements, which may further extend the service life of the cold cathode elements and the X-ray generator than the prior art to realize the stable operation. The solution of the present invention is to ground the frame body (2); accommodating the cold cathode elements (5) for discharging electrons by applying a voltage from a DC power supply (7) within the glass tube (4); and, supporting the lower end (4a) of the glass tube (4) within the frame body (2) with insulation material (3). The upper end of the glass tube (4) is configured with a target (8) and a window portion (9) for emitting X-ray generated by the target (8) to the outside. The periphery (4b) of the lower end (4a) of the glass tube (4) is covered by insulation material (3), and the surface of insulation material (3) is coated with grounded conductor (21).

Description

Electric field discharge type X-ray generating device

The present invention relates to an X-ray generator using an electric field discharge type cold cathode element.

An X-ray tube (hereinafter referred to as an "electric field discharge type X-ray tube") using an electric field discharge type cold cathode element can emit electrons at a normal temperature, and has a small amount of heat generation, and can be easily improved in performance even if it is small. Therefore, a high-output light source of an X-ray tube is proposed as an alternative to a conventional filament method (a heated filament is used as an electron emission source). However, the amount of electron emission of the electron emission element (cold cathode element) as the electron source is within the range of the operating voltage or more, and tends to increase exponentially as the applied voltage rises.

For example, when an operating voltage of -13.5 kV is applied, an X-ray tube of 300 μA (current flowing between the cold cathode element and the ground target electrode inside the X-ray tube) is generated, and if it is applied higher than the aforementioned operating voltage, At a voltage of -14.5 kV, the tube current system also becomes 3000 μA, and the tube current system is suddenly increased by a factor of 10. The increase in the rapid current as described above is likely to induce a local discharge phenomenon in the tube, which causes breakage of the cold cathode element and the target as an electron emission source, deterioration of the vacuum level in the tube, and the like. As a result, a decrease in the X-ray output in the rated voltage range, that is, a shortened life is caused. As a result of the inventors' knowledge, the cause of fluctuations in the tube voltage which is the cause of abnormal discharge is listed as being stored in the cold cathode. The discharge from the charge on the inner wall surface of the glass tube of the element.

This situation is detailed in accordance with Figure 6. The conventional electric field discharge type X-ray tube 101 is grounded and has a frame 102 on which an opening is formed. In the casing 102, one end portion of the glass tube 104 is supported by the insulator 103. The glass tube 104 is housed in the casing 102. A cold cathode element 105 is provided on the insulator 103 side of the glass tube 104, and a cylindrical metal electrode 106 is provided around the cold cathode element 105. The cold cathode element 105 is connected in parallel with the metal electrode 106, and a negative voltage is applied to the electrodes by the DC power source 107. A target 108 made of a metal material having good conductivity is formed on the inner surface of the other end side of the glass tube 104. The target portion 108 is joined to the window portion 109 which is at the ground potential, and is exposed to the outside. The window portion 109 is made of a material having a function of emitting X-rays generated on the target material 108 to the outside, and is made of, for example, beryllium having excellent X-ray permeability. The glass tube 104 is airtight, and a fixing member (hereinafter referred to as a "fixing member") 110 that surrounds the frame 102 between the glass tube 104 and the upper end portion of the frame 102 is attached. With this configuration, a space S is formed between the casing 102 and the glass tube 104.

Next, when a predetermined high voltage is applied to the cold cathode element 105, for example, -13.5 kV, and the electric field discharge type X-ray tube 101 is actuated, electrons are emitted from the cold cathode element 105 toward the target 108, and are discharged by the window portion 109. X line.

At this time, since an electric field is formed between the metal electrode 106 of the same potential around the cold cathode element 105 and the grounded frame 102, a part of the electrons are supplied toward the casing 102 by the electric field. But in metal electricity A glass tube 104 as an insulator is present between the electrode 106 and the housing 102, and electrons emitted toward the housing 102 are accumulated on the inner surface of the glass tube 104. The accumulation of electrons continues until the potential difference between the glass tube 104 and the metal electrode 106 disappears. In other words, at the time of becoming the same potential (-13.5 kV at this time), the increase due to the electron accumulation on the inner wall surface of the glass tube 104 disappears, and an equilibrium state is reached.

As a result, there is a potential difference of -13.5 kV between the cold cathode element 105 and the frame 102 after the actuation, and the air layer S between the glass tube 104 and the frame 102 in the equilibrium state after the actuation. A potential difference of -13.5 kV occurs, and the risk of partial discharge becomes high. In particular, in the vicinity of the lower end portion A of the glass tube 104, electric field concentration is more likely to occur, and it is easy to form a starting point at which discharge occurs. When this discharge occurs, the voltage applied to the cold cathode element 105 is also affected by the change in the electric field that is violently in the periphery, and is changed. The change in the applied voltage is a cause, and in particular, when the applied voltage is increased (in the case of an absolute voltage, for example, -13.5 kV → -14 kV), the amount of electron emission is rapidly increased, and the electron of the cold cathode element 105 is caused by the overcurrent. The damage of the surface is released, which causes a large deterioration in life.

In this regard, a content of a resistive film having a high resistance value is fixed to the outside of the insulating member in the inside of the X-ray tube using the conventional hot electron method as the electron source (Patent Document 1).

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2009-245806

However, the conventional technique described in Patent Document 1 is based on the problem of discharge inside the X-ray tube, and it is not clear how the discharge occurring between the frame body 102 and the glass tube 104 as described above is handled. Further, the above-mentioned conventional technique has a limitation in the resistance value of the resistive film, and it is not limited to have a resistance value higher than that of the X-ray tube and lower than that of the insulating portion. Versatility. Further, in addition, in the above-mentioned conventional technique, as to how the discharge phenomenon occurs, not only is there no explanation, but also why the discharge can be prevented by the resistive film coating, and no explanation is given. Therefore, the specific effect of the countermeasure cannot be understood, and how the partial discharge phenomenon occurring between the glass tube 104 and the frame 102 is applied, and there is no suggestion as to the effect at the time of application.

The present invention has been made in view of the circumstances, and in the X-ray generator using an electric field discharge type cold cathode element, it is possible to prevent the glass tube containing the cold cathode element from being placed and located without applying the high resistance film as described above. The micro-discharge between the outer casings can extend the life of the cold cathode element and the X-ray generator more than conventional techniques, and can achieve stable operation.

In order to achieve the above object, the present invention is an electric field discharge type X-ray generating device which is supported in a frame which is grounded and which is supported by an insulating member. One end portion of the glass tube is provided to support an electron-emitting cold cathode element or the like on the one end side of the glass tube, and the other end portion side of the glass tube, that is, the side opposite to the cold cathode element An X-ray target which generates an X-ray by irradiation of electrons emitted from the cold cathode element, and an electric field discharge type X-ray generator which emits an X-ray generated in the target to an external window, and is characterized by Therefore, at least one end surface of the glass tube is covered with an insulating material.

According to the present invention, the peripheral surface of the one end portion which is easily started as the discharge starting point by the electric field concentration is covered with the insulating material, so that the electric field strength in the air can be prevented from rising, the charge accumulation can be suppressed, and the discharge as described above can be prevented. occur.

In the present invention, at least the peripheral surface of the end portion of the glass tube on the cold cathode element side which is likely to be the starting point of discharge by the electric field concentration may be covered, but of course, the entire surface of the glass tube may be covered.

Further, the surface of the glass tube which is not covered with the insulating material may be coated with a conductor (conductor), and the conductive system is grounded.

Further, the surface of the insulating member covering the surface of the glass tube as described above may be covered with a conductor, and the conductor may be grounded. The guiding system in this case includes, for example, a mesh made of a conductor, a gold mesh, a conductive coil, and a conductor film.

The above-mentioned conductive system may, for example, be any one of silver paste, nickel paste, gold paste, palladium paste, or carbon paste, or a conductor film composed of the above.

According to the present invention, it is possible to prevent discharge between the glass tube in which the cold cathode element is housed and the frame body outside the frame without applying a high-resistance film, and it is possible to extend the life of the cold cathode element and the X-ray generation device more than the prior art. A stable action can be achieved.

Embodiments of the present invention will be described below. 1 is a schematic view showing a configuration of an electric field emission type X-ray generator 1 according to an embodiment, and an electric field emission type X-ray generator 1 is grounded, and is passed through an insulating material 3 in a substantially cubical frame 2 having an opening formed thereon. One end portion of the glass tube 4 is supported, and the glass tube 4 is housed in the casing 2.

The insulating material 3 is provided between the lower end portion 4a of the glass tube 4 and the bottom surface portion 2a of the frame body 2, and the insulating material 3 covers the peripheral edge portion 4b of the lower end portion 4a of the glass tube 4 to the glass tube 4 The middle of the side covers its surroundings. In the range covered by the insulating material 3, the inventors have found that the intended purpose can be achieved by covering the lower end portion 4a of the glass tube 4 toward the upper end portion by at least 3 mm. The material of the insulating material 3 is made of, for example, silicone rubber.

A cold cathode element 5 is provided on the insulating material 3 side of the glass tube 4, and a cylindrical metal electrode 6 is provided around the cold cathode element 5. The cold cathode element 5 is connected in parallel with the metal electrode 6, and a negative voltage is applied to the electrodes through the high voltage cable from the DC power source 7. The penetration portion of the high-voltage cable to the insulating material 3 is the lower end portion 4a side of the glass tube 4.

A target material 8 made of a metal material having good conductivity such as tungsten or copper is formed on the inner surface of the upper end portion of the glass tube 4. A window portion 9 that becomes a ground potential is joined to the target 8, and the window portion 9 is exposed to the outside. The window portion 9 is made of a material having a function of releasing the X-ray generated in the target 8 to the outside, and is made of, for example, a ray having excellent X-ray permeability.

The glass tube 4 is airtight, and a fixing member 10 is provided between the glass tube 4 and the upper end portion of the frame 2. With this configuration, a space S is formed between the casing 2 and the glass tube 4.

The electric field emission type X-ray generator 1 of the embodiment has the above configuration. When a predetermined high voltage is applied to the cold cathode element 5, for example, -13.5 kV, electrons are emitted from the cold cathode element 5 toward the target 8, and the target is placed on the target. In the case of 8, an X-ray is generated due to an electronic collision, and an X-ray is emitted from the window portion 9.

At this time, an electric field is still formed between the metal electrode 6 of the same potential around the cold cathode element 5 and the grounded frame 2, so that a part of the electrons are supplied toward the casing 2 by the electric field, as described above. Electrons are accumulated on the inner surface of the glass tube 4. However, in the present embodiment, the peripheral edge portion 4b of the lower end portion 4a of the glass tube 4 in which the electric field is concentrated and the discharge is likely to be generated is also covered with the insulating material 3, so that a strong electric field portion can be formed in the insulating material 3, which can be reduced. The small peripheral portion 4b becomes a risk of starting the discharge in the space S. Therefore, damage or deterioration of the cold cathode element 5 due to discharge can be prevented, and the life of the X-ray generator 1 itself can be made longer than that of the prior art, and a stable operation can be realized.

In the meantime, from the viewpoint of avoiding the concentration of the electric field, the end portion 3a of the insulating material 3 covering the middle of the side surface of the glass tube 4 is preferably formed into a convex shape which is curved outward as shown in FIG. .

In the above-described embodiment, the peripheral portion 4b of the lower end portion 4a of the glass tube 4 is covered with the insulating material 3, and the periphery thereof is covered until the middle of the side surface of the glass tube 4, thereby suppressing the occurrence of discharge, but as shown in Fig. 2, After the formation of the insulating material 3 is shown, the surface of the insulating material 3 is additionally covered with the conductor 21. The conductor 21 is grounded. When grounding, it can be electrically connected to the frame 2 that has been grounded.

Thereby, a positive electric charge of opposite polarity to the electrons accumulated in the wall surface of the glass tube 4 is induced (inductive charge), and a strong electric field formed externally by the induced electric charge can be reduced to almost zero. As a result, the aforementioned discharge phenomenon can be surely prevented. On the other hand, on the wall surface of the glass tube 4, a potential difference of -13 kV occurs on the inner surface and the outer surface, but the discharge breakdown voltage of the glass material having a thickness of 1 to 2 mm is about 20 to 30 kV/mm, and is formed to be 1 mm or more. The glass wall, the discharge due to this potential difference can be surely prevented.

As the conductor 21, for example, a conductive material such as a mesh made of a metal, a gold mesh, or a conductive coil can be used. The material and thickness thereof are not particularly limited, and may be a condition having a property of rapidly forming an induced charge by grounding. Further, the film may be a flat film, such as a gold mesh, or may be a wire wound only at predetermined intervals. In this case, it is preferable to set the distance from the adjacent conductive line to 2 mm or less. If the distance is too long, the electric field formed between the frame 2 and the frame 2 will gradually change. High reason.

From this point of view, in place of the above-mentioned gold mesh or the like, the conductor 21 is formed by any one of silver paste, nickel glue, gold glue, palladium glue, or carbon glue, or by such combination. The conductor film is preferably coated.

Further, not only the surface of the insulating material 3 covered by the conductor 21 but also the region thereof may be enlarged to the surface of the glass tube 4 not covered with the insulating material 3.

Further, as shown in FIG. 3, the region covered by the insulating material 3 and the peripheral edge portion 4b of the lower end portion 4a of the glass tube 4 can be extended to all around the side surface of the glass tube 4. Thereby, the portion of the wall surface of the glass tube 4 exposed to the space S can be set to zero, and the dielectric breakdown strength of the surface of the glass tube 4 can be improved throughout. In this case as well, the conductor 21 may be grounded by covering the surface of the insulating material 3 that enlarges the covered region with the conductor 21 as described above. Thereby, the discharge between the glass tube 4 and the frame 2 can be made zero, and the strength of the glass tube 4 itself can be improved.

As described above, the peripheral portion 4b of the lower end portion 4a of the glass tube 4 is covered with the insulating material 3, thereby eliminating the risk that the peripheral portion 4b becomes the starting point of discharge in the space S, and the cold cathode element due to discharge can be prevented. The damage, deterioration, and life of the X-ray generator 1 itself are longer than those of the prior art, but the conductor 21 may cover the portion of the glass tube 4 that is not covered with the insulating material 3.

4 shows an X-ray generator 1 having such a configuration. In this example, with respect to the example shown in FIG. 1, the conductor 21 covers a portion of the glass tube 4 that is not covered with the insulating material 3, and the conductor 21 is covered. Ground it. among them, When the portion covered with the conductor 21 is located on the surface of the glass tube 4 when the boundary portion between the conductor 21 and the insulating material 3 is located, the electric field concentrates in this portion. Therefore, it is preferable that the boundary portion between the conductor 21 and the insulating material 3 is not located on the surface of the glass tube 4 and is located on the surface portion of the insulating material 3 shown in FIG. In other words, the portion covered with the conductor 21 may be a portion of the glass tube 4 that is not covered with the insulating material 3, and a portion that is the entire circumference of the end portion 3a of the insulating material 3 and that is not in contact with the surface of the glass tube 4. Since the casing 2 is already grounded, for example, the conductor 21 may be electrically connected to the casing 2 through the window portion 9.

By adopting this configuration, the damage and deterioration of the cold cathode element 5 due to the discharge can be more reliably prevented than in the example shown in Fig. 1, and the life of the X-ray generator 1 itself can be extended more than the prior art. Further, as described above, by covering the portion of the glass tube 4 that is not covered with the insulating material 3 with the conductor 21, the heat of the glass tube 4 can be released to the outside through the conductor 21, and the glass tube 4 and the inside thereof can be suppressed. Heat storage. Therefore, in this respect, the life of the cold cathode element 5 and the like inside the glass tube 4 and the glass tube 4 can be extended.

Further, when a cube or a frame having a square cross section is used as the frame 2, the distance between the frame 2 and the surface of the cylindrical glass tube 4 is not the same. That is, the distance between the center of the side surface of the frame 2 and the surface of the glass tube 4 is the shortest, and insulation breakdown occurs in this portion, and discharge is likely to occur. Therefore, when a frame having a square horizontal cross section is used as the frame 2, it is preferable to cover the circumferential surface of the glass tube 4 with the conductor 21 in order to prevent the occurrence of discharge in the portion.

Further, when there is no convex portion where electric field concentration occurs at the periphery of the lower end portion of the glass tube 4, the possibility that discharge occurs at the shortest portion between the center of the side surface of the frame body 2 and the surface of the glass tube 4 high. In the case of the above, the peripheral portion 4b of the lower end portion 4a of the glass tube 4 may not be covered with the insulating material 3, and the entire surface of the glass tube 4 may be covered with the conductor 21 to ground the conductor 21.

Next, the results of performing the four consecutive lighting tests of the electric field discharge type X-ray generator 1 of the embodiment shown in Fig. 2 and the conventional X-ray tube shown in Fig. 6 will be described. In the electric field discharge type X-ray generator 1 used in the test, a conductive film made of silver paste was used as the conductor 21, and the thickness thereof was set to about 20 μm.

In this test, an ON-OFF (about 1 minute)-ON operation with a higher probability of occurrence of a phenomenon that is predicted to be a problem of the present technology is performed for about 10 minutes. The rated applied voltage of each of the cold cathode elements 5, 105 is set to a higher potential of -14 kV in such a manner that the effectiveness of the present invention can be more clearly evaluated. Further, in the case of observing a minute discharge phenomenon, since a minute discharge occurs, emphasis is placed on the tendency of the electron emission characteristics of the cold cathode elements 5 and 105 to deteriorate, and a method of continuously observing an electron current is employed. The results after 150 hours of carrying out the test are shown in Fig. 4. In Fig. 4, X1 and X2 respectively show the results of two sets of the electric field discharge type X-ray generators 1 of the embodiment, and Y1 and Y2 show the results of two conventional X-ray tubes.

Therefore, the initial tube current system has some variation (variation) from 490 to 500 μA, but the change in the tube current is compared. In comparison, a clear difference is confirmed. In other words, in the electric field discharge type X-ray generator 1 of the embodiment, both of the tubes have a tube current of 150 hours, and are almost stable without any change. On the other hand, with respect to the conventional X-ray tube, both of them are found to have a rapid decrease in the plurality of portions, and Y1 is about 30 μA and Y2 is about 60 μA, which is also lower than the initial current, and the electrons of the cold cathode element 105 are clearly known. Release performance degradation. Among them, in the conventional X-ray tube, it is found that the rapid reduction of the 5 to 6 portions is presumed to be a deterioration of the cause of the partial discharge phenomenon. In addition, the decrease in the amplitude shows a tendency to increase the number of repetitions.

In the X1 and X2 of the electric field emission type X-ray generator of the embodiment used in the test, it was confirmed that the X1 and X2 were continuously turned on, and the output of the stable operation for 3000 hours was maintained.

[Industrial availability]

The present invention relates to an X-ray generating apparatus for using an electric field discharge type cold cathode element.

1‧‧‧Electric field discharge type X-ray generator

2‧‧‧ frame

2a‧‧‧ bottom part

3‧‧‧Insulation

3a‧‧‧End

4‧‧‧ glass tube

4a‧‧‧Bottom

4b‧‧‧The Peripheral Department

5‧‧‧Cold cathode components

6‧‧‧Metal electrodes

7‧‧‧DC power supply

8‧‧‧ Target

9‧‧‧ Window Department

10‧‧‧Fixed components

21‧‧‧Conductor

S‧‧‧ Space

Fig. 1 is an explanatory view showing a schematic side cross section of a configuration of an electric field emission type X-ray generator according to an embodiment.

Fig. 2 is an explanatory view showing a side cross section of an example in which the surface of the insulating material is covered with a conductor in the electric field discharge type X-ray generator of Fig. 1;

Figure 3 is a schematic view showing the entire circumference of the glass tube covered with an insulating material, An explanatory view of a side cross section of an example in which a surface of the insulating material is covered with a conductor.

Fig. 4 is an explanatory view showing a side cross section of an example of a surface of a glass tube which is not covered with an insulating material by a conductor in the electric field discharge type X-ray generator of Fig. 1;

Fig. 5 is a graph showing temporal changes of tube current in the electric field discharge type X-ray generator of the embodiment and the electric field discharge type X-ray generator of the prior art.

Fig. 6 is an explanatory view showing a schematic side cross-sectional view showing a configuration of an electric field emission type X-ray generating device of a conventional technique.

1‧‧‧Electric field discharge type X-ray generator

2‧‧‧ frame

2a‧‧‧ bottom part

3‧‧‧Insulation

3a‧‧‧End

4‧‧‧ glass tube

4a‧‧‧Bottom

4b‧‧‧The Peripheral Department

5‧‧‧Cold cathode components

6‧‧‧Metal electrodes

7‧‧‧DC power supply

8‧‧‧ Target

9‧‧‧ Window Department

10‧‧‧Fixed components

S‧‧‧ Space

Claims (5)

An electric field emission type X-ray generating device is provided in a frame to be grounded, and supports one end portion of the glass tube through an insulating member, and a cold cathode element for emitting electrons is provided on the one end side of the glass tube. On the other end side of the tube, there is a target in which X-rays are generated by irradiation of electrons emitted from the cold cathode element, and an electric field is emitted from a window portion in which X-rays generated by the target are emitted to the outside. A type X-ray generating device is characterized in that at least one end surface of the glass tube is covered with an insulating material. The electric field discharge type X-ray generator according to claim 1, wherein a surface of the glass tube not covered with the insulating material and an end portion of the insulating material are covered with a conductor, and the guiding system is grounded. . The electric field discharge type X-ray generator according to claim 1, wherein the surface of the insulating material is covered with a conductor, and the conductive system is grounded. An electric field discharge type X-ray generator according to the second aspect of the invention, wherein the surface of the insulating material is covered with a conductor, and the conductive system is grounded. The electric field emission type X-ray generating device according to any one of claims 2, 3, and 4, wherein the guiding system is any one of silver paste, nickel gel, gold gel, palladium gel, or carbon gel, or A conductor film composed of these combinations.