JPH0794114A - X-ray image pickup tube - Google Patents

Abstract

PURPOSE:To make the collision angle of an electron beam perpendicular to the screen even in the case of a large diameter by forming a target for forming a charge pattern corresponding to a X-ray pattern into a curved face, protrusion- curved in the moving direction of the electron beam. CONSTITUTION:A target 2 is formed into a curved face, protrusion-curved to the moving direction of electron beam from an electron gun 3, and a field mesh 6 at plus-potential on the target 2 is provided near the electron beam entry side of the target 2. As a result, a deceleration field for the electron beam is created between both of them to reduce the speed and bend the path with potential distribution forming an equipotential surface. By properly setting the plus potential given to the mesh 6 and the curved shape of the target 2, the electron beam can be directed at right angles to the target 2 and landed perpendicularly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray image pickup tube used in place of an image intensifier, an X-ray vidicon or the like in the field of medical treatment or general industry.

[0002]

2. Description of the Related Art An X-ray image pickup tube forms a charge image corresponding to an incident X-ray image on a photoconductive film and scans the charge image with an electron beam to extract it as a video signal. In this case, there are a structure in which X-rays are received by a fluorescent screen to generate light and the light is guided to a photoconductive film, and a structure in which X-rays are directly incident on the photoconductive film to form a charge image. . This X-ray image pickup tube is configured, for example, as shown in FIG. A target (photoconductive film) 2 is arranged in a vacuum glass envelope 1 so that X-rays are incident thereon, an electron gun 3 and an electrode 4 are provided, and the electron gun 3 is directed toward the target 2. To emit an electron beam, and the deflection coil 5
The electron beam is deflected to scan. As the photoconductive film forming the target 2, an amorphous selenium film that generally causes an avalanche effect in a high electric field therein and increases the charge exponentially is used, and X-rays are converted into light and guided to the target. In this case, a fluorescent film such as CsI is brought into close contact with the X-ray incident side of the amorphous selenium film.

In this X-ray image pickup tube, the target 2
It is necessary to land the electron beam vertically with respect to. If this is not done, secondary electron emission will increase due to electron collisions, and the function as an image pickup tube will not be obtained.
As a configuration therefor, conventionally, a field mesh 6 is arranged on the front surface of the target 2 (on the side where the electron beam is incident), and a positive high potential is applied to the electron gun 3.
The collimation action is performed so that the electrons passing through the field mesh 6 are perpendicular to the target 2. The collimation is on the side of the electron gun 3 of the field mesh, and the equipotential surface that is concavely curved toward the side of the electron gun 3 causes the electron beam passing therethrough to have a central axis (center toward the target 2 from the electron gun 3). It is made by bending in the (axis) direction. The curved shape of the equipotential surface is determined by the potential difference and shape of the electrode 4 and the field mesh 6.

[0004]

However, such a field mesh 6 has an insufficient collimation action, and since the electron beam is deflected at a large angle especially when the diameter becomes large, the direction thereof is the central axis. There is a problem in that it cannot be returned to the direction parallel to and land vertically on the target 2, that is, the angle θ between the electron beam and the field mesh 6 does not become 90 °.

In view of the above, it is an object of the present invention to provide an X-ray image pickup tube improved so that vertical landing of an electron beam on a target can be easily achieved even with a large diameter.

[0006]

In order to achieve the above object, in an X-ray image pickup tube according to the present invention, a target on which a charge image corresponding to an X-ray image is formed is directed toward an electron beam from an electron gun. It is characterized in that it is formed into a curved surface that is convexly curved toward and the field mesh having a positive potential with respect to the target is provided close to the electron beam incident side of the target.

[0007]

Since the field mesh has a positive potential with respect to the target, a deceleration field between the two becomes an electron beam deceleration field, and the equipotential surface between the two is convex so that the target is convex in the traveling direction of the electron beam. Because it is curved,
It becomes convex as shown in. Therefore, when the electron beam generated from the electron gun passes through the deceleration field between the field mesh and the target, it is decelerated and its orbit is bent by the potential distribution forming the equipotential surface.

As shown in FIG. 2, the equipotential surface has a large inclination toward the periphery of the target, and since the distance between the field mesh and the target is small, the equipotential surface also becomes dense, so that it is deflected at a large angle. The higher the electron beam, the greater the bending action due to the equipotential surface. Therefore, by appropriately setting the positive potential applied to the field mesh and the curved shape of the target, it is possible to make the electron beam trajectory close to ideal, direct the electron beam at a right angle to the target, and direct the electron beam to the target. Can be landed vertically.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the drawings. In FIG. 1, a glass envelope 1 is kept in a vacuum, and a target (photoconductive film) 2 is placed therein. X-rays are incident from the right side of the figure, and a charge image corresponding to the incident X-ray image is formed on the target 2. In this glass envelope 1, an electron gun 3 is arranged at the end portion (on the left side) opposite to the target 2. A deflection coil 5 for deflecting an electron beam generated from the electron gun 3 and directed toward the target 2 is arranged around the glass envelope 1.

A field mesh 6 is arranged in the glass envelope 1 near the electron gun 3 side of the target 2, and the target 2 is directed toward the traveling direction side of the electron beam generated from the electron gun 3. It is formed into a curved surface that is convexly curved. A potential is applied to each of the target 2, the electron gun 3, the electrode 4, and the field mesh 6. That is, when the potential of the target 2 is used as a reference, the potential of the electron gun 3 is a negative high potential,
The field mesh 6 has a positive potential with respect to the target 2. Further, a deflection current is applied to the deflection coil 5 to scan the electron beam.

The electron beam generated from the electron gun 3 travels to the target 2 and is deflected by the deflection coil 5 during that time to scan the surface of the target 2. In the space between the electron gun 3 and the target 2, a potential distribution is formed by the electrode 4, the field mesh 6, the target 2 and the like. The trajectory of the electron beam can be changed according to the shape of this potential distribution. Of the space to reach this target 2,
Since the field mesh 6 close to the target 2 has a positive potential with respect to the target 2, both spatial regions serve as a deceleration field for the electron beam, and the potential distribution in this deceleration field region is the positive potential of the field mesh 6, that is,
It is determined by the potential difference between the target 2 and the field mesh 6 and the curved surface shape of the target 2. Since the target 2 is formed in a curved surface that is convexly curved toward the traveling side of the electron beam generated from the electron gun 3, the equipotential surface is forcibly defined along this curved surface.

The equipotential surface in the deceleration area is the target 2
In the same manner as described above, the electron beam generated from the electron gun 3 has a curved surface that is convexly curved toward the traveling side, so that the electron beam passing therethrough has a central axis (from the electron gun 3 toward the target 2). Since the potential gradient of the equipotential surface is larger in the vicinity of the target 2 and the density of the equipotential surface is larger, the electron beam deflected at a larger angle is bent in the central axis direction. Furthermore, since it is made to act by the field mesh 6, the electron beam lands vertically on the target 2. In addition,
Since the plus potential of the field mesh 6 with respect to the target 2 and the curved surface shape of the target 2 forcefully determine the potential distribution of the deceleration field in both spaces, the trajectory of the electron beam is corrected to achieve vertical landing.
It is necessary to properly determine the position, shape, and electric potential.

[0013]

As described in the above embodiments, according to the X-ray image pickup tube of the present invention, the electron beam can be landed perpendicularly to the target even when the deflection angle is large, and particularly in the case of a large aperture. It is effective for X-ray imaging tubes.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining the operation.

FIG. 3 is a schematic cross-sectional view of a conventional example.

[Explanation of symbols]

1 ... Glass envelope 2 ... Target 3 ... Electron gun 4 ... Electrode 5 ... Deflection coil 6 ... Field mesh

Claims (1)

[Claims] 1. A target on which a charge image corresponding to an X-ray image is formed, an electron gun for generating an electron beam toward the target, and a deflection coil for deflecting the electron beam to scan the target surface. The target is formed of a field mesh having a positive potential with respect to the target provided close to the electron beam incident side of the target, and the target is formed in a curved surface that is convexly curved toward the electron beam traveling direction side. X-ray image pickup tube.