JP2005268197A - X-ray image tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray image tube in which dust introduction, an unjust emission of light, and peeling off of a membrane can be prevented by finding out the composition ratio of chromium oxide membrane 11. <P>SOLUTION: The chromium oxide membrane 11 is formed at a site which has an electrical potential gradient in a vacuum envelope. A composition ratio of chromium oxide membrane 11 consists of Cr 25-40 atom%, silicon 1-8 atom%, and potassium 0.7-5 atom%, and the rest is substantially composed of oxygen. By the chromium oxide membrane 11, the dust introduction, the unjust emission of the light by obtaining a moderate conductivity and a low secondary electron emissive property, and peeling off of the membrane are prevented by obtaining adhesive force to a membrane formation site and binding capacity between particles. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an X-ray image tube in which a chromium oxide film is formed at a portion having a potential gradient such as an electrode in a vacuum envelope.

  In general, in medical X-ray diagnostic apparatuses and industrial non-destructive inspection apparatuses using an X-ray image tube, an X-ray image transmitted through a subject is converted into a visible light image by the X-ray image tube. An optical image is taken with an imaging camera, and this photographed image is displayed on a monitor for observation.

  The configuration of a conventional X-ray image tube will be described with reference to FIG. Reference numeral 1 denotes a vacuum envelope. An input window 3 is formed on the incident side of the X-ray 2 of the vacuum envelope 1, and an output window 4 is formed on the opposite side to the input window 3. In the vacuum envelope 1, an input surface 6 for converting the X-ray 2 into an electron beam 5 and emitting it is provided inside the input window 3, and the electron beam 5 is converted into a visible light image inside the output window 4. Thus, an output surface 7 for outputting is provided. An electron lens that accelerates or focuses the electron beam 5 is formed along the path of the electron beam 5 traveling from the input surface 6 toward the output surface 7, and this electron lens applies a negative voltage to the input surface 6. The cathode electrode K, the anode electrode A that applies a high positive voltage to the output surface 7, and a plurality of electrodes such as a plurality of grid electrodes G1, G2, and G3 between the cathode electrode K and the anode electrode A are configured.

  By applying a tube-driven high voltage to such an X-ray image tube, for example, there is a portion where the potential difference between the grid electrode G3 and the anode electrode A reaches 6 kV / mm or more. In a strong and high potential gradient portion, electrons are easily emitted from the grid electrode G3, and the probability of field emission is further increased when a metal foreign object is located on the grid electrode G3. Further, a gas is generated from the grid electrode G3 by heat accompanying the electron emission, and this gas is ionized and ionized by the electrons and collides with the grid electrode G3 to generate secondary electron emission. As a result, the local abnormal discharge is sustained, and the discharge reaches the input surface 6 to generate illegal photoelectrons from the photoelectric layer. The illegal photoelectrons cause the output surface 7 to fluoresce, which is the main cause of so-called illegal light emission of the X-ray image tube. Become. In addition, unauthorized photoelectrons change the potentials of various electrodes, and also make the operation of the X-ray image tube unstable.

As a countermeasure, it is effective to cover a portion having a potential gradient such as the grid electrode G3 with a material having a low secondary electron emission coefficient but also having a certain degree of conductivity. A typical material is a chromium oxide film. (For example, refer to Patent Document 1).
JP 58-5319 A (page 1-2, FIG. 1)

  However, the conventional chromium oxide film has poor adhesion and interparticle adhesion with electrodes and the like, and is easily peeled off due to vibrations and shocks during the manufacturing process, actual use, or sudden changes in the environment. When this chromium oxide film is peeled off, secondary electron emission occurs from the part where the chromium oxide film has been peeled off, causing not only the above-mentioned illegal light emission and unstable operation, but also the peeled film piece becomes a foreign substance in the tube. It becomes defective and causes a decrease in manufacturing yield and quality.

  Further, in order to increase the adhesion and interparticle binding force, it is known to contain, for example, water glass as a binder material, but the conductivity of the chromium oxide film is easily impaired, and the secondary electron emission property is Even if it is low, it is electrically insulative and causes dust attraction, and the potential distribution in the tube becomes unstable.

  The present invention has been made in view of these points, and provides an X-ray image tube that can prevent dust attraction and unauthorized light emission by finding the composition ratio of a chromium oxide film, and can prevent film peeling. For the purpose.

  The present invention provides a vacuum envelope in which an input window is formed on the X-ray incident side and an output window is formed on the opposite side of the input window, and the incident is provided on the input window side in the vacuum envelope. An input surface that emits an electron beam corresponding to X-rays to be emitted; an output surface that is provided on the output window side in the vacuum envelope and converts the electron beam into a visible light image; and between the input surface and the output surface A plurality of electrodes constituting an electron lens on the path of the electron beam, and an X-ray image tube in which a chromium oxide film is formed in a portion having a potential gradient in the vacuum envelope, The composition ratio of the chromium oxide film is such that chromium is 25 to 40 atomic%, silicon is 1 to 8 atomic%, alkali metal is 0.7 to 5 atomic%, and the balance is substantially composed of oxygen.

  And by setting it as the composition ratio of such a chromium oxide film | membrane, while obtaining moderate electroconductivity and low secondary electron emission property, dust attraction, unauthorized light emission, etc. are prevented, and also with a film formation site | part. Adhesive force and interparticle binding force are obtained, and film peeling is prevented, and defects due to secondary electron emission and foreign matter in the tube accompanying this film peeling are prevented.

  According to the present invention, the chromium oxide film has a composition ratio of chromium 25 to 40 atomic%, silicon 1 to 8 atomic%, alkali metal 0.7 to 5 atomic%, and the balance substantially composed of oxygen. In addition to being able to obtain low electrical conductivity and low secondary electron emission properties, it is possible to prevent dust attraction and unauthorized light emission, as well as adhesion to the film formation site and interparticle adhesion, thereby preventing film peeling. Defects due to secondary electron emission and foreign matter in the tube due to film peeling can be prevented.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  The basic configuration of the X-ray image tube is the same as the configuration shown in FIG. 4 described in the background art, and will be described using the same reference numerals. That is, in the basic configuration of the X-ray image tube, reference numeral 1 denotes a vacuum envelope, and an input window 3 is formed on the incident side of the X-ray 2 of the vacuum envelope 1 and on the opposite side to the input window 3. An output window 4 is formed. In the vacuum envelope 1, an input surface 6 for converting the X-ray 2 into an electron beam 5 and emitting it is provided inside the input window 3, and the electron beam 5 is converted into a visible light image inside the output window 4. Thus, an output surface 7 for outputting is provided. An electron lens that accelerates or focuses the electron beam 5 is formed along the path of the electron beam 5 traveling from the input surface 6 toward the output surface 7, and this electron lens applies a negative voltage to the input surface 6. The cathode electrode K and the anode electrode A for applying a high positive voltage to the output surface 7, and a plurality of electrodes such as a plurality of grid electrodes G 1, G 2, G 3 between the cathode electrode K and the anode electrode A are configured.

  FIG. 1 shows only a part of the X-ray image tube, that is, the vicinity of the anode electrode A and the grid electrode G3. Since the grid electrode G3 is closest to and faces the anode electrode A, the grid electrode G3 has the highest electric field strength and the highest potential gradient. The chromium electrode film 11 covers the front end portion of the grid electrode G3 closest to the anode electrode A where the electric field strength is highest and the surface in the vicinity thereof and the surface having the maximum electric field strength of at least 0.5 kV / mm. Is formed. Note that the chromium oxide film 11 shown in FIG. 1 is schematically shown.

  The composition ratio of the chromium oxide film 11 is 25 to 40 atomic% of chromium, 1 to 8 atomic% of silicon, 0.7 to 5 atomic% of potassium as an alkali metal, and the balance is substantially oxygen. This composition ratio is the composition ratio after the chromium oxide film 11 is formed. The average particle diameter of the chromium oxide particles in the chromium oxide film 11 is 0.5 to 1.5 μm. The film thickness of the chromium oxide film 11 is 5 to 100 μm.

An example of a method for forming the chromium oxide film 11 will be described. First, a water glass aqueous solution in which Cr ₂ O ₃ powder having an average particle size of 0.9 μm and SiO ₂ / K ₂ O have a molar ratio of 3 is weighed and mixed so that the composition ratio of the chromium oxide film 11 is within the above range. To do. At this time, ammonia may be added as a dispersion accelerator. Next, it is applied to the target site by spraying, brushing, or the like. Next, baking is performed at a temperature of 400 to 550 ° C. At this time, the atmosphere may be any of vacuum, air, hydrogen, etc., but the vacuum atmosphere can obtain the most stable conductivity.

  After firing, surface resistance, film thickness, and appearance are inspected as necessary, assembled with other components, input surface 6 and output surface 7 are sealed, evacuated to form a photocathode, and X-ray An image tube is formed.

  And the evaluation test was implemented about the composition ratio of the chromium oxide film | membrane 11, and the result is shown in FIG.

  In this evaluation test, the grids in which the chromium oxide films 11 were formed with the average particle diameter and film thickness of the chromium oxide particles being constant and the composition ratios of chromium (Cr), silicon (Si), and potassium (K) being different from each other were formed. Samples of the electrode G3 were prepared, and each sample was subjected to a peel resistance test, a surface resistance measurement, and a product vibration energization life test.

  In the peel resistance test, a tapping test, a dry US test, and a thermal shock test were performed in the state of the grid electrode G3 component, in the tape test, and in the product state of the X-ray image tube. Shows the number of delamination in 10 samples.

  In the tape test, a general-purpose adhesive tape is applied to the application site of the chromium oxide film 11 and then peeled off to evaluate whether or not the chromium oxide film 11 is peeled off.

  In the tapping test, whether or not the chromium oxide film 11 was peeled off by hitting the tube several hundred times in a state where the electrodes before the input surface 6 and the output surface 7 were installed in the tube of the vacuum envelope 1 Evaluate whether or not.

  In the dry US test, after the tapping test, an ultrasonic vibrator is directly applied to the tube in the air to evaluate whether or not the chromium oxide film 11 is peeled off.

  The thermal shock test evaluates whether or not the chromium oxide film 11 is peeled off by alternately exposing the upper and lower limit temperatures of the actual use environment several tens of times after the dry US test.

  Further, in the surface resistance measurement, the resistance value of the film surface is measured. If the resistance value is 1E12 or more, the electroconductivity is lacking, and it becomes easy to be charged and becomes defective.

  In the product vibration energization life test, the product was energized while applying vibration, and the occurrence of foreign object defects and improper light emission defects were tested by the predetermined life. In FIG. 2, 10 samples were tested for each sample. The number of defectives is shown.

  As shown in FIG. 2, when the chromium is less than 25 atomic% as a result of the evaluation test, not only the lack of conductivity but also the secondary electron emission suppressing function is impaired, and the irregular light emission increases. On the other hand, if the chromium content exceeds 40 atomic%, the adhesion to the film forming site and the interparticle bonding force are deficient, and the film is likely to be peeled off. Therefore, chromium is preferably in the range of 25 to 40 atomic%, and more preferably in the range of 32 to 36 atomic% in which conductivity, low secondary electron emission property and peeling resistance are surely obtained.

  If the silicon content is less than 1 atomic%, the adhesion to the film forming site and the interparticle bonding force are impaired, and film peeling is likely to occur, resulting in an increase in defect defects and defective light emission due to film peeling. On the other hand, if silicon exceeds 8 atomic%, the conductivity of the film becomes insufficient. For this reason, silicon is preferably in the range of 1 to 8 atomic%, and more preferably in the range of 3 to 6 atomic%, where conductivity, low secondary electron emission properties and peeling resistance can be reliably obtained.

  If the potassium content is less than 0.7 atomic%, the adhesion to the film forming site and the interparticle bonding force are impaired, and film peeling is likely to occur, resulting in an increase in foreign matter defects and improper light emission defects associated with film peeling. Moreover, when potassium exceeds 5 atomic%, the electroconductivity of a film | membrane will become inadequate. Therefore, potassium is preferably in the range of 0.7 to 5 atomic%, and more preferably in the range of 2 to 4 atomic%, where conductivity, low secondary electron emission property and peeling resistance are surely obtained. Moreover, the atomic ratio of potassium to silicon is preferably in the range of 0.6 to 0.7%.

  Thus, the composition ratio of the chromium oxide film 11 is found, the composition ratio of the chromium oxide film 11 is 25 to 40 atomic% of chromium, 1 to 8 atomic% of silicon, 0.7 to 5 atomic% of alkali metal, and the balance is substantially the same. By using oxygen as a constituent, moderate conductivity and low secondary electron emission properties can be obtained. In addition, illegal light emission and operational instability can be prevented, and adhesion to the film formation site and interparticle binding force can be prevented. Thus, film peeling can be prevented, and defects due to secondary electron emission and foreign matter in the tube accompanying this film peeling can be prevented.

  Further, on the premise of the composition ratio of the chromium oxide film 11, the average particle diameter of the chromium oxide particles is preferably in the range of 0.5 to 1.5 μm. If it is finer than 0.5 μm, it tends to agglomerate at the time of application, and the conductivity becomes too high, and if it is coarser than 1.5 μm, the conductivity is impaired and it becomes close to an insulating film.

  Furthermore, the film thickness of the chromium oxide film 11 is preferably in the range of 5 to 100 μm. When the thickness is less than 5 μm, the secondary discharge emission suppressing function is impaired, and illegal light emission defects increase. When the thickness is more than 100 μm, the film is easily broken. Therefore, the range of 5-100 micrometers is preferable, More preferably, it is 10-15 micrometers from which the low secondary electron emission property is acquired reliably and it can do not break easily.

  Next, a description will be given of a portion of the vacuum envelope 1 in a range where the chromium oxide film 11 is formed.

  Various experiments have revealed that when a metal foreign object is present in the tube, it can be a discharge source even at a location where the potential difference between the grid electrode G3 and the anode electrode A does not reach as much as 6 kV / mm, for example. In other words, metallic foreign matter is produced by various factors such as burrs generated during electrode processing, rubbing when welding electrodes into the tube, and welding, improving burr removal processing, assembling methods, welding Although it is possible to reduce the carry-in into the pipe by amending the conditions and to discharge to some extent by tapping and cleaning the pipe, it is not perfect and it is difficult to completely eliminate the metallic foreign matter in the pipe. The material of the metal foreign material is SUS, AL, Cu, or the like, and often has a needle shape of 50 to 200 microns. With this size, the electric field strength is 0.5 kV / mm or more. , The Coulomb force acts to move the metal foreign object around. During the actual operation of the X-ray image tube, if a metal foreign object that has been lurking in the tube is placed on the grid electrode G3, the Coulomb force acts on the metal foreign object and rises up to the anode electrode A. An X-ray image is generated by a process in which an electric field concentrates on the floating metal foreign object, a discharge occurs, a discharge current flows, the metal foreign object is welded to the grid electrode G3, and the discharge from the deposited metal foreign object continues. Experiments have shown that tubes often become unusable.

  FIG. 3 shows an example of the result of electric field intensity analysis of a part of the X-ray image tube, that is, the anode electrode A and the grid electrode G3 facing the anode electrode A. In this field strength analysis, analysis is performed using a finite element method or the like based on the actual electrode shape and applied voltage value, and the field strength of each part of the electrode is obtained. The arrow shown in FIG. 3 indicates an electric field at which the electric field strength is 0.5 kV / mm or more, and indicates that the electric field strength is higher as the length of the arrow is longer and the shade is darker.

  Then, the application range of the chromium oxide 11 to the grid electrode G3 is 3 of an electric field strength range of 3 kV / mm or more, an electric field strength range of 1 kV / mm or more, and an electric field strength range of 0.5 kV / mm or more. Samples of various types of X-ray image tubes were made respectively, and evaluation tests were conducted on these samples. The results are shown in FIG. In the evaluation test, a predetermined amount of metallic foreign matter was intentionally mixed in each tube in advance, and an energization rotation test was performed. This energization rotation test repeats the C-arm operation while applying a product drive voltage to each electrode, and is suitable as an accelerated life test.

  As shown in FIG. 4, when the chromium oxide film 11 was formed in the range of the electric field strength of 3 kV / mm or more as a result of the evaluation test, the improper sustained discharge caused by the metal foreign matter occurred in the total number of the five samples. . In addition, when the chromium oxide film 11 was formed in a range of electric field strength of 1 kV / mm or more, irregular sustained discharge caused by metallic foreign matter occurred in two of the ten samples. Further, when the chromium oxide film 11 was formed in a range of electric field strength of 0.5 kV / mm or more, the number of irregular sustained discharges caused by metallic foreign matter in 100 samples was zero. .

  Therefore, the chromium oxide film 11 having the above-mentioned predetermined composition, particle size, and film thickness is formed at a portion in a range where the electric field strength is at least 0.5 kV / mm or more particularly on the grid electrode G3 facing the anode electrode A. Thus, even if metal foreign matter is mixed in the tube and cannot be completely eliminated, the fatal problem of improper sustained discharge for the X-ray image tube is suppressed, and a high-quality X-ray image tube can be obtained. Can be provided.

  Note that the chromium oxide 11 is formed without leakage in a portion of the grid electrode G3 in a range where the electric field strength is 0.5 kV / mm or more, but even if it does not reach 0.5 kV / mm, it prevents improper discharge due to metallic foreign matter. In consideration of the margin, it is preferable to appropriately expand the formation range of the chromium oxide 11 within a range that does not hinder the assembly work.

  Further, the chromium oxide film 11 is formed on the grid electrode G3 as a portion having a potential gradient. However, the present invention is not limited to this, and other electrodes in the vacuum envelope 1 or glass disposed in the vacuum envelope 1 are used. The ceramic part is also a part having a potential gradient, and may be formed in these parts.

  In addition, as the alkali metal in the composition of the chromium oxide film 11, potassium is preferable, but it can be replaced with sodium, or both potassium and sodium can be used.

It is a partial expanded sectional view in which the chromium oxide film of the X-ray image tube which shows one embodiment of this invention was formed. It is explanatory drawing which shows the result of having performed the evaluation test about the composition ratio of a chromium oxide film | membrane same as the above. It is explanatory drawing which shows an example of the analysis result of the electrolytic strength of the anode electrode implemented when specifying the site | part which forms a chromium oxide film | membrane same as the above, and the grid electrode facing this anode electrode. It is explanatory drawing which shows the result of having performed the evaluation test about the range which forms a chromium oxide film | membrane same as the above. It is sectional drawing of an X-ray image tube.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vacuum envelope 2 X-ray 3 Input window 4 Output window 5 Electron beam 6 Input surface 7 Output surface
11 Chromium oxide film A Anode electrode
G3 grid electrode

Claims (6)

A vacuum envelope in which an input window is formed on the incident side of the X-ray and an output window is formed on the opposite side of the input window, and an incident X-ray provided on the input window side in the vacuum envelope. An input surface that emits a corresponding electron beam, an output surface that is provided on the output window side in the vacuum envelope and converts the electron beam into a visible light image, and the electron beam between the input surface and the output surface An X-ray image tube comprising a plurality of electrodes constituting an electron lens on the path of the electrode, and a chromium oxide film formed on a portion having a potential gradient in the vacuum envelope,
The composition ratio of the chromium oxide film is 25-40 atomic% chromium, 1-8 atomic% silicon, 0.7-5 atomic% alkali metal, and the balance is substantially composed of oxygen. Line image tube.   The X-ray image tube according to claim 1, wherein the chromium oxide film is formed at a portion having an electric field strength of at least 0.5 kV / mm.   3. An X-ray image tube according to claim 1, further comprising an anode electrode as an electrode and a grid electrode facing the anode electrode, wherein a chromium oxide film is formed on the grid electrode facing the anode electrode. .   4. The X-ray image tube according to claim 1, wherein the alkali metal is potassium.   The X-ray image tube according to any one of claims 1 to 4, wherein the average particle diameter of the chromium oxide particles in the chromium oxide film is 0.5 to 1.5 µm.   6. The X-ray image tube according to claim 1, wherein the chromium oxide film has a thickness of 5 to 100 [mu] m.