JPH0541190A - X-ray image tube - Google Patents

Abstract

PURPOSE:To provide an X-ray image tube such that its conversion efficiency, from X rays to electrons, is approximately uniform on its whole input surfaces. CONSTITUTION:An X-ray image tube provides input surfaces which comprises an input phosphor layer 12, consisting of a number of phosphor columner crystals 12a and 12b formed on a substrate 11, and photoelectric surfaces formed directly or indirectly on the input phosphor layer. Apex angles alpha1 and alpha2 of protrusions on the surfaces facing photoelectric surfaces of the columner crystals, vary extending from its peripheral parts to its central part, causing the accomplishment of the above purpose.

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 tube, and more particularly to improvement of its input surface.

[0002]

2. Description of the Related Art Generally, an X-ray image tube is constructed as shown in FIG. 2, in which the input side of the vacuum envelope 1 is opposed to the input window 1a, the input side 2 is on the output side, and the anode 3 is on the output side. Output surfaces 4 are respectively arranged, and focusing electrodes 5 are further provided along side walls inside the vacuum envelope 1. The input surface 2 is formed by sequentially stacking the input phosphor layer 7 and the photoelectric surface 8 on the substrate 6.

During operation, the X-ray from the X-ray tube 9 is the subject 1.
0, passes through the input window 1a and the substrate 6, and is converted into light at the input phosphor layer 7. This light reaches the photocathode 8 and is converted into electrons. The electrons are focused and accelerated by the focusing electrode 5 and the anode 3, and converted into a visible light image on the output surface 4.
In this way, the X-ray image is converted into a visible light image, and this visible light image is recorded by a TV camera, cine camera, spot camera, etc., and medical diagnosis is performed.

[0004]

When uniform X-rays are incident on the X-ray image tube, it is expected that the final image will also have uniform brightness or density. However, in reality, the brightness or the density may be different between the central part and the peripheral part of the image. For example, the distortion of the electron lens called the pincushion distortion of the X-ray image tube may reduce the electron density in the peripheral portion, and the brightness or density in the peripheral portion may become smaller than that in the central portion.

Another example is that the concentration of antimony on the photocathode differs between the central part and the peripheral part depending on the geometrical arrangement of the antimony evaporation source. In such a case, if the concentration of the central portion is appropriate, the peripheral portion of the photocathode has a lower ability to generate electrons than the central portion. Therefore,
The final image has a bright center. On the contrary, if the density of the peripheral portion is appropriate, the peripheral portion becomes bright in the final image. As described above, if there is a distribution in brightness or density, it may cause a problem in X-ray diagnosis, and a processing device or a program may be burdened during image processing in order to correct the density distribution. The present invention is an X-ray image in which the efficiency of converting X-rays into electrons is substantially uniform over the entire input surface.
The purpose is to provide the tube.

[0006]

The present invention is directed to an input phosphor layer formed of a large number of columnar crystals of a phosphor formed on a substrate, and a photocathode formed directly or indirectly on the input phosphor layer. In an X-ray image tube having an input surface consisting of and, the apex angle of the convex protrusion on the photocathode-side surface of the columnar crystal changes from the peripheral portion to the central portion of the input surface. Is.

[0007]

According to the present invention, the efficiency of converting X-rays into electrons is substantially uniform over the entire input surface.

That is, when the apex angle of the convex protrusions on the photocathode-side surface of the columnar crystals forming the input phosphor layer is close to 180 °, that is, when the surface is flat, the photocathode is the entire surface. Formed in. As the apex angle becomes smaller, irregularities appear on the surface. It is difficult for antimony and alkali metal, which are the components of the photocathode, to reach the concave portion, and the photocathode is not formed.

Therefore, the area of the photocathode formed in the portion having a small apex angle is smaller than the area of the input phosphor layer. Therefore, of the light that has been converted from X-rays and reached the surface of the input phosphor layer in the input phosphor layer, only a certain proportion is converted into electrons. Then, this ratio becomes smaller as the apex angle becomes smaller. In this way, by changing the apex angle, it is possible to change the rate at which light that is converted from X-rays and reaches the surface of the input phosphor layer is converted into electrons in the input phosphor layer.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. The present invention is an improvement of the input surface, and only the input surface will be described.

The input surface of the X-ray image tube according to the present invention is constructed as shown in FIG. 1, and the input phosphor layer 12 and the photocathode (not shown) are sequentially laminated on the substrate 11. There is. The input phosphor layer 12 is composed of many columnar crystals of phosphor.

In this case, the apex angle of the convex protrusion on the photocathode-side surface of the columnar crystal changes from the peripheral portion to the central portion of the input surface. That is, the apex angle α ₁ of the columnar crystal 12a in the central portion of the input surface is larger than the apex angle α ₂ of the columnar crystal 12b in the peripheral portion. That is, α ₁ > α ₂ is set.

Therefore, when the photocathode is formed on the surface of the peripheral columnar crystal 12b, the gap 13 between the columnar crystals 12b is formed.
In addition, the substance forming the photocathode, for example, an alkali metal hardly adheres, and as a result, the photocathode is formed only near the apex angle of the columnar crystal 12b. Therefore, a part of the light converted from the X-rays in the peripheral portion is converted into the light by the photocathode, and the efficiency of converting the X-rays into light can be suppressed more than that in the central portion.

Conversely, if the apex angle α ₂ of the columnar crystals 12b in the peripheral portion of the input surface is made larger than the apex angle α ₁ of the columnar crystals 12a in the central portion (α ₂ > α ₁ ) contrary to the above. , X in the center
The efficiency of converting rays into light can be suppressed to be lower than the efficiency of converting X-rays in the peripheral portion into light.

In the above embodiment, the photocathode is directly formed on the input phosphor layer 12, but even when the photocathode is formed on the input phosphor layer 12 via the transparent conductive film, This invention can be applied. Further, the present invention has the same structure as the X-ray image tube of FIG. 2 except for the above-mentioned input surface, and therefore detailed description thereof will be omitted.

[0016]

According to the present invention, the efficiency of converting X-rays into electrons is substantially uniform over the entire input surface. As a result, it is possible to solve the drawbacks that have been seen in the past, such that the X-ray diagnosis may be hindered and the processing device or the program may be burdened at the time of image processing in order to correct the density distribution.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view showing an input surface of an X-ray image tube according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view showing the whole of a general X-ray image tube.

[Explanation of symbols]

11 ... Substrate, 12 ... Input phosphor layer, 12a, 12b ... Columnar crystal, α ₁ , α ₂ ... Apex angle.

Claims (1)

[Claims] 1. An input surface comprising an input phosphor layer formed of a large number of columnar crystals of a phosphor formed on a substrate, and a photocathode formed directly or indirectly on the input phosphor layer. In the X-ray image tube, the apex angle of the convex protrusion on the photocathode-side surface of the columnar crystal changes from the peripheral portion to the central portion of the input surface. ..