JP2017134883A - Image tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image tube which can improve resolution.SOLUTION: An image tube comprises: a vacuum envelope which has an input window and an output window facing the input window; and an input surface 17 which is arranged inside the input window. The input surface 17 comprises: a substrate 30 having a plurality of recesses 33 formed on a surface 30a; an input fluorescent surface 31 which is a columnar crystal structure formed on the surface 30a of the substrate 30; and a photoelectric surface 32 formed on the input fluorescent surface 31.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to an image tube having an input surface disposed within a vacuum envelope.

  Conventionally, image tubes have been used for medical diagnosis and industrial nondestructive inspection. In order to improve the sensitivity of the photographing system, this image tube usually uses a system that combines an image tube and a CCD camera for imaging. In the imaging, X-rays transmitted through the subject are converted into visible light on the input fluorescent screen provided on the input surface of the image tube, and the visible light is converted into electrons on the photocathode to electrically amplify the electrons. A fluoroscopic image of the subject is obtained by converting electrons into visible light on the output phosphor screen and photographing the visible image with a CCD camera.

  In the case of an image tube, in the case of medical use, performance is important, and it is necessary to improve resolution and luminance. Furthermore, for the purpose of reducing X-ray exposure, a film thickness of 300 to 500 μm is frequently used for the input phosphor screen in order to increase the X-ray absorption on the input phosphor screen.

  The input surface of the image tube is formed by depositing a cesium iodide (CsI) phosphor on a smooth surface of the substrate.

  The input phosphor screen has a columnar crystal structure due to low-vacuum vapor deposition and oblique deposition techniques, and minute gaps are formed between the columnar crystals. Even if it is formed, the resolution has a certain level of performance. However, the resolution performance is limited, and the resolution is about 0.1 mm to 0.2 mm in an image tube with a variable field of view. The main cause is that the crystal growth of the phosphor starts from the smooth surface side of the substrate, but the temperature of the substrate and the phosphor rises during the growth process, so that the columnar crystal grows as the columnar crystal grows. This is because the diameter of each book gradually increases.

  Therefore, the reflection of light due to the critical angle in the columnar crystal is reduced, the scattered light in the lateral direction is increased, and the light converted in the input phosphor screen is easily diffused widely. In addition, since there is no gap between the columnar crystals, the thicker the film, the more scattered light increases. As a result, the effect of the light guide is lost, and the light in the columnar crystal diffuses in the lateral direction, so the resolution decreases. This is a factor that hinders improvement in resolution, and makes observation of a minute subject difficult.

  Such a problem is considered not only in X-ray imaging for medical diagnosis but also in industrial nondestructive inspection. For industrial use, a film thickness of about 10 μm to about 2 mm is applied depending on the application, and thus the above-described phenomenon occurs in the same manner.

JP 2011-44385 A

  As described above, it is difficult to improve the resolution in the conventional image tube.

  The problem to be solved by the present invention is to provide an image tube capable of improving the resolution.

  The image tube of the present embodiment includes a vacuum envelope having an input window and an output window facing the input window, and an input surface disposed inside the input window. The input surface includes a substrate having a plurality of concave portions formed on the surface, a fluorescent surface having a columnar crystal structure formed on the surface of the substrate, and a photoelectric surface formed on the fluorescent surface.

It is sectional drawing of the input surface of the image tube which shows one Embodiment. It is sectional drawing of an image tube same as the above. It is explanatory drawing which compares the propagation of the light in an input surface same as the above, (a) is explanatory drawing in the case of the input surface of this embodiment, (b) is explanatory drawing in case the surface of a board | substrate is a smooth input surface It is. It is a block diagram of the radiography apparatus using an image tube same as the above.

  Hereinafter, an embodiment will be described with reference to FIGS. 1 to 4.

  FIG. 2 shows a cross-sectional view of the image tube. The image tube 10 includes a vacuum envelope 11. The vacuum envelope 11 includes a cylindrical body portion 12, an input window 13 on one end side of the body portion 12, and an output window 14 facing the input window 13 on the other end side of the body portion 12. The input window 13 is formed in a convex curved shape that protrudes outward, and allows X-rays 15 as radiation to enter and transmit.

  In the vacuum envelope 11, an input surface 17 that converts X-rays 15 incident from the input window 13 into electrons 16 and emits the electrons is disposed inside the input window 13, and the input surface 17 is disposed inside the output window 14. An output surface 19 for converting the electrons 16 from the output 16 into a visible light image 18 and outputting it from the output window 14 is formed. Further, in the vacuum envelope 11, a focusing electrode 21 that constitutes an electron lens that accelerates and focuses the electrons 16 along the path of the electrons 16 traveling from the cathode 20 including the input surface 17 toward the output surface 19, and A plurality of electrodes 23 including the anode 22 are provided. The input surface 17 is formed in a convex curved surface shape that protrudes toward the input window 13 corresponding to the shape of the input window 13. The output surface 19 includes an output phosphor that converts the electrons 16 into visible light.

  Next, FIG. 1 shows a cross-sectional view of the input surface 17. The input surface 17 includes a substrate 30, an input phosphor screen 31 as a phosphor screen formed on the surface 30a of the substrate 30, and a photocathode 32 formed on the input phosphor screen 31. The X-ray 15 incident from the input window 13 and transmitted through the substrate 30 is converted into light at the input phosphor screen 31, and the light from the input phosphor screen 31 is converted into electrons at the photocathode 32 and emitted toward the output surface 19. To do.

  The substrate 30 is an aluminum substrate, for example, and is formed in a convex curved shape that protrudes toward the input window 13. A plurality of concave portions (concave surfaces) 33 are formed on the surface 30a of the substrate 30 on the opposite side to the input window 13, that is, the concave curved surface 30a. In the present embodiment, the concave inner surface of the concave portion 33 is formed on the concave curved reflecting surface 34, and the concave portion 33 is formed in a circular shape when viewed from the direction perpendicular to the surface 30a of the substrate 30, A plurality of recesses 33 are formed continuously. Between the adjacent recesses 33, a top 35 protruding from the surface 30a of the substrate 30 is formed. Depending on the formation method, the recesses 33 may have a shape other than a circle such as an ellipse, or the recesses 33 may not be continuous with each other and there may be a gap between the recesses 33.

  The input phosphor screen 31 has a plurality of columnar crystals on the surface 30a of the substrate 30 by depositing cesium iodide (CsI) phosphor on the plurality of recesses 33 by low-vacuum deposition or high-vacuum oblique deposition. A CsI film 38 as a phosphor film having a columnar crystal structure having 36 is formed.

  Minute gaps are formed between the plurality of columnar crystals 36. Therefore, the light generated in the columnar crystal 36 reaches the surface of the columnar crystal 36 while repeating total reflection at the boundary between the columnar crystal 36 and the gap.

  In one recess 33, a plurality of columnar crystals 36 are formed. A columnar crystal 36 is not formed at the top 35 which is a boundary between the concave portion 33 and the concave portion 33 adjacent to each other, and a gap 37 formed by the columnar crystals 36 competing with each other corresponding to the top portion 35 is formed. . The gap 37 extends in the direction of the surface of the input phosphor screen 31 together with the columnar crystal 36, and becomes a shape such that the gap 37 is filled very close on the surface side of the input phosphor screen 31.

  By forming the gap 37 around the recess 33 for each recess 33, the columnar crystal 36 in the recess 33 exhibits a function like a pixel.

  Therefore, in the input phosphor screen 31, the scattering of light in the lateral direction is reduced by the columnar crystal 36 and the gap 37, and the contrast is increased by the boundary between the recess 33 and the recess 33, so that the resolution is improved overall. Will contribute.

  Since the depth of the recess 33 is smaller than the entire film thickness of the CsI film 38, the surface unevenness of the CsI film 38 is not greatly affected. If the surface of the CsI film 38 is gently uneven due to the influence of the recess 33, it becomes concave due to the effect of the electric field that can make the direction of electron emission from the photocathode 32 formed on the surface close to it. Sharp electron emission contributes to improved resolution.

  On the columnar crystal 36, a cesium iodide (CsI) phosphor layer that is grown in multiple directions by high vacuum is formed.

  The activator of the input phosphor screen 31 is preferably sodium iodide or thallium iodide.

  The photocathode 32 is formed on the input phosphor screen 31 by vacuum evaporation of alkali metal.

  Next, FIG. 3 shows an explanatory diagram for comparing the propagation of light within the input surface 17. FIG. 3A is an explanatory diagram in the case of the input surface 17 of the present embodiment, and FIG. 3B is an explanatory diagram in the case of the input surface 17 where the surface 30a of the substrate 30 is smooth.

  The light path 41 that does not satisfy the critical angle emitted from the light emission point 40 in the CsI film 38 propagates in the CsI film 38 in the lateral direction.

  At this time, as shown in FIG. 3B, if the surface 30a of the substrate 30 is smooth, the light path 41 is reflected by the surface 30a of the substrate 30 and diffuses in a wide range in the lateral direction in the CsI film 38. I will do it.

  On the other hand, as shown in FIG. 3A, when the concave portion 33 is formed on the surface 30a of the substrate 30, the light path 41 hits the inclined surface of the concave portion 33 and reflects toward the surface of the CsI film 38. The spread of light in the lateral direction of the CsI film 38 can be suppressed.

  Therefore, coupled with the light guide effect in the columnar crystal 36 and the light guide effect at the boundary between the recess 33 and the recess 33, light is collected by the effect of suppressing the spread of light in the lateral direction of the CsI film 38. Since the light is emitted, the resolution is greatly improved.

  The recess 33 has, for example, a diameter of 20 μm and a depth of 3 μm. In this case, since the number of the concave portions 33 is equivalent to 50 per 1 mm scale, the resolution is 20 μm, and the resolution is improved much more than the conventional one.

  When the CsI film 38 is thick, the resolution can be prevented from decreasing by increasing the diameter of the recess 33 to, for example, 50 μm and the depth to 15 μm.

  When the CsI film 38 is as thin as 100 μm or less, the diameter of the recess 33 is reduced to 20 μm and the depth is reduced to 3 μm, which contributes to the improvement of resolution.

  Therefore, the recess 33 is preferably in the range of 20 to 50 μm in diameter and 3 to 15 μm in depth depending on the film thickness of the CsI film 38.

  The film thickness of the CsI film 38 can be selected according to the application, and can be adapted from 10 μm to about 2 mm. The image tube 10 of the input surface 17 with the CsI film 38 thicker from about 1 mm is for high-energy X-rays. The tube voltage of the X-ray tube covers the range of 200 kV to 1 MV, such as the structure and composition in the metal. Often used for inspection.

  Although the depth of the recess 33 depends on the formation method described later, about 10 to 20 μm is effective in consideration of the formation of the columnar crystals 36 and the mirror effect of light from the substrate 30. Furthermore, in order to enhance the mirror effect and reflect light efficiently, the surface 30a of the substrate 30 is preferably a surface having a metallic luster of aluminum.

  Next, a method for forming the recess 33 of the substrate 30 will be described.

  The concave portion 33 of the substrate 30 can be formed by, for example, shot blasting. In shot blasting, a plurality of particle bodies are sprayed onto the surface 30a of the substrate 30 to form a plurality of recesses 33. For shot blasting, a shot blast machine capable of high-speed, short-time irradiation with a large impact is used. As the particle body, a particle body having a particle size that does not include a particularly small particle of metal oxide such as ZrO having a high hardness is used, and the particle diameter is, for example, 7 to 10 μm.

  In this shot blasting process, if the particle body is sprayed many times on the surface 30a of the substrate 30, the boundary position of the concave portion 33 is lowered, so it is necessary to select spraying conditions. In order to form the particles with a small number of sprays, the substrate 30 is preferably heat-treated and softened in advance. In general, since an alumina layer having hardness is formed on the aluminum surface used for the substrate 30, removing the alumina layer with an alkali or the like is effective for improving workability.

In such a forming method, the recesses 33 are not circular in shape when viewed from the direction perpendicular to the surface 30a of the substrate 30, or the recesses 33 are not continuous with each other and there is a gap between the recesses 33. In some cases, it may be a crater-shaped recess 33. In addition, the shape of the concave portion 33 due to the collision of the particle bodies,
Therefore, even if there are non-circular portions in the large number of recesses 33, the effect is the same.

  FIG. 4 shows a configuration diagram of a radiation imaging apparatus 50 using the image tube 10.

  The radiation imaging apparatus 50 is, for example, an X-ray apparatus. Reference numeral 51 in FIG. 4 denotes a subject such as a human body or various articles, and the subject 51 is irradiated with X-rays 15 from a radiation source 52.

  The X-ray 15 absorbed or scattered by the subject 51 enters the input surface 17 from the input window 13 of the image tube 10. The X-ray 15 is converted into light at the input phosphor screen 31 of the input surface 17 and the light is converted into electrons 16 at the photocathode 32. The electrons 16 are accelerated and focused, and enter the output phosphor screen of the output surface 19. The electrons 16 are converted into visible light on the output phosphor screen of the output surface 19, and a visible light image 18 is output to the output window 14.

  The visible light image 18 in the output window 14 is picked up by the CCD camera 54 through the optical system 53 and displayed on the monitor 55.

  The image tube 10 of the present embodiment is configured such that an image with an appropriate resolution can be obtained by one imaging by adjusting the thickness of the input phosphor screen 31 according to the subject and the subject. . For medical use, both a thick film with enhanced X-ray absorption by the CsI film 38 and a high resolution enabling fine angiography can be achieved. For industrial use, the incident energy can be applied to a wide range of applications such as soft X-rays, high energy X-rays, and neutron beams. An image obtained with a neutron beam that requires observation and analysis of a fine part has a higher resolution, and is suitable for realizing a resolution of about 10 μm.

  As described above, because the image tube 10 has a higher resolution than the conventional image tube, the amount of information from the obtained image is large, and the part of the subject with different thickness and the minute part are reproduced on the image. can do. For this reason, in medical applications, the necessary input X-rays can be reduced to the required amount by using a thick film while maintaining a higher resolution than before in the same subject, which is effective in reducing the exposure X-ray dose to the subject and the operator. Become. Therefore, in various types of radiography including medical diagnostic radiography and wide industrial examination, it is possible to increase examination information and improve examination accuracy.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

10 Image tube
11 Vacuum envelope
13 Input window
14 Output window
17 Input side
30 substrates
30a surface
31 Input phosphor screen as phosphor screen
32 photocathode
33 recess
35 Top
36 columnar crystals
37 Clearance

Claims (4)

An image tube comprising: a vacuum envelope having an input window and an output window facing the input window; and an input surface disposed inside the input window,
The input surface includes a substrate having a plurality of recesses formed on the surface, a fluorescent surface having a columnar crystal structure formed on the surface of the substrate, and a photoelectric surface formed on the fluorescent surface. Image tube to do. The substrate is formed with a top portion protruding from the surface of the substrate between the adjacent recesses,
2. The image tube according to claim 1, wherein a gap is formed between the columnar crystals on the phosphor screen in correspondence with the top portion. The image tube according to claim 1, wherein the recess has a diameter of 20 to 50 μm and a depth of 3 to 15 μm. The image tube according to claim 1, wherein the recess is formed by blasting.

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