JPS60170145A - X-ray image tube - Google Patents

Abstract

PURPOSE:To allow the whole image-forming screen of a photoelectric cathode to approach a flat plane further and expand an effective visual field by decreasing the meridian radius of curvature of the photoelectric cathode from the center toward the periphery. CONSTITUTION:The meridian radius of curvature at the cross section of a photoelectric cathode 35 is decreased from the center toward the periphery. For example, if part of an elliptic face centering a point where an ellipse 23 crosses its minor axis 22 is used as the shape of the photoelectric cathode 35, the meridian radius of curvature is decreased from the center toward the periphery of the photoelectric cathode 35 as shown by a curve 42. Accordingly, the image-forming point of the whole photoelectric cathode further approaches a plane formed by the central image-forming point of the photoelectric cathode and the tube axis, i.e., fluorescent screen, the displacement of image formation is reduced, and as a result, an X-ray image tube with a large effective visual field can be obtained.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention provides a vacuum envelope with a curvature that differs from the center toward the periphery on the input side, and an opening on the output side of the vacuum envelope. The present invention relates to an X-ray image tube having a spherical cap-shaped cathode facing toward a provided fluorescent surface.

[Technical background of the invention]

In general, X-ray image tubes are used for medical X-ray diagnosis.
It is often used to obtain line images. In known X-ray image tubes based on electro-optical imaging, a spherical or hyperbolic spherical cap photocathode is used. The imaging surface of the electrons emitted from this photocathode is not a flat surface,
It will be quite curved. However, the fluorescent surface is flat because the image on the fluorescent surface of the X-ray image tube is captured by a television camera or optical camera through a lens system, and because the fluorescent surface can be easily formed. Therefore, as the image forming surface of the photocathode deviates from the plane, the image forming becomes worse and the resolution of the image obtained on the fluorescent surface becomes worse.

In other words, when the photocathode has a spherical cap shape, electrons emitted from the periphery of the photocathode pass through the periphery of the electron lens system and are more strongly focused than electrons emitted from the center of the photocathode. Therefore, the image forming point is closer to the photocathode side with respect to the fluorescent surface, and therefore the image forming surface of the entire photocathode is not flat but deviates by a large width.

[Problems with background technology]

This is because the image plane of the entire photocathode is not a single plane.

The entire image forming surface is aligned on the fluorescent surface, so the image obtained on the fluorescent surface is partially blurred.For example, when the image forming point of the central image is aligned, the peripheral portion is blurred. In this way, the entire surface of the photocathode cannot be made into an effective field of view, and the functionality of the conventional X-ray image pickup apparatus using an X-ray image tube is greatly degraded.

[Purpose of the invention]

An object of the present invention is to provide an X-ray image tube in which the entire image forming surface of the photocathode is brought closer to a flat surface and the effective field of view is expanded.

[Summary of the invention]

The present invention relates to an X-ray image tube having a fluorescent surface and a concave photocathode facing the fluorescent surface.

This is an X-ray image tube in which the meridian radius of curvature of the photocathode decreases from the center toward the periphery.

[Embodiments of the invention]

According to the invention, a spherical cap-shaped photocathode;

This X-ray image tube having a fluorescent surface facing the photocathode is characterized in that the meridional radius of curvature of the cross section of the photocathode decreases from the center toward the periphery of the photocathode. As an example, a part of the surface intersecting the short axis of the ellipsoid is used. The radius of meridional curvature decreases from the point of intersection with the short axis of the ellipsoid to the point of intersection with the long axis.

In such a new type of photocathode, the perpendicular line of the periphery is oriented toward the central axis of the electron lens system rather than when the photocathode is spherical, so the electrons emitted from the periphery are It passes through the center of the electron lens and therefore the focusing effect on this electron is weakened. Therefore, the imaging point moves away from the photocathode, and as a result approaches the plane of the fluorescent surface that exists at the imaging point of the electrons emitted from the center of the photocathode.
The imaging surface of the entire photocathode becomes more planar, and the effective field of view of the X-ray image tube using this new type of photocathode becomes wider.

Next, the present invention will be described in detail with respect to a specific embodiment. That is, the X-ray image tube of the present invention is constructed as shown in FIG. 1, and the input window 1 of the vacuum envelope has a convex shape and is usually made of an aluminum alloy material. Alternatively, the concave shape may be formed of titanium material.

The body 13 is made of a sufficiently strong material such as stainless steel or copper that can be sealed to the glass of the output window 14. The body part 3 and the output window part 14 constitute a vacuum envelope.

An input surface board 2 usually made of aluminum material is disposed on the input window section 1 side in such a vacuum envelope, and this board 2
A vapor-deposited fluorescent surface 3 made of Cs I /NA is formed on the vapor-deposited fluorescent surface 3, and A-1tos'f In2O is formed on this vapor-deposited fluorescent surface 3.
3 is formed, and a photocathode 5 is formed on this intermediate layer 4.
is formed. In addition, 6.7.8 in the figure is a focusing electrode, and there may be one to several focusing electrodes.
7.8, the photocathode 5, and the anode 9 provided on the output window 14 side form an electron lens system. A fluorescent surface (output fluorescent surface) 1 is provided near the end of the anode 9, and this fluorescent surface 1 is placed on the glass substrate 10 disposed on the glass surface of the output window 14. A metal glue layer 12 made of aluminum is formed on the fluorescent surface 11.

FIG. 3 shows an enlarged cross section of the electrode portion from the tube axis 31 to the periphery. In the figure, 35 corresponds to the photocathode 5;
6.37.38.39 correspond to focusing electrodes 6, 7.8,
4θ corresponds to the anode 9. In this embodiment, the shape of the photocathode 35 is a part of an ellipsoid whose center is at a point that intersects with the short axis 22 of the ellipse 23 shown in FIG. 2 (21 in the figure is the long axis). . In this case, the photocathode 35
From the center to the periphery, the meridional radius of curvature decreases as shown by the curve 42 shown in FIG. Moreover, straight line 4 indicates the case of a spherical surface.

That is, in this embodiment, for the R-Z coordinate system shown in FIG. 3, the ellipse equations Z-A, R.

(-) + (-) = 1 In A B, person = 180, B = 212.4909, the diameter of the photocathode is 334 mm, and the length of the electron lens is 406.6 mx.
A photocathode with a diameter of 25M on the surface was fabricated. Also, for comparison, we fabricated a spherical surface with the same dimensions in place of the ellipsoid, and compared the range of good focus, and found that the method of the present invention was better. In order to understand this quantitatively, we simulated the electron trajectory and calculated the variation of the imaging point in the direction of the tube axis.The result was 1.9B for the conventional spherical surface, but 1.9B for the ellipsoidal surface of this invention. .611, an improvement of about 15 points.

〔Effect of the invention〕

According to this invention, the image-forming point of the entire photocathode is brought closer to the plane formed by the image-forming point at the center of the photocathode and the tube axis, that is, the fluorescent surface, and the deviation in image formation is reduced, resulting in an effective field of view. A large X-ray image tube is obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an X-ray image tube according to an embodiment of the present invention, FIG. 2 is a plan view showing the shape of a photocathode used in the X-ray image tube of the present invention, and FIG. 3 is a view similar to that shown in FIG. FIG. 4 is an explanatory diagram showing the distribution of the meridian radius of curvature of the cross section of the photocathode in the conventional example and the invention. 5.35...Photocathode 1.91, 32, J3
...Electron orbit principal axis, 31...Tube axis (aligned with center electron orbit principal axis), 6, 7, 8, 36, 37, 3
B, ? 9... Focusing electrode, 9, 40... Anode, 22... Ellipse short axis, 21... Ellipse long axis, 41...
・Curve of meridian curvature radius in conventional example, 42...
Curve of meridian radius of curvature in this invention. Patent attorney Suzue Takehiko Figure 1 Figure 2 Figure 4 Identification on the electronic form

Claims (1)

[Claims] In an X-ray image tube, a photocathode is provided on the input side in a vacuum envelope, and a fluorescent surface is provided on the output side on which electrons emitted from the photocathode are electro-optically imaged by a high accelerating voltage. . An X-ray image tube, wherein the meridional radius of curvature of the cross section of the photocathode decreases from the center toward the periphery.