JPS5916702B2 - image intensifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a special number input screen for an image intensifier ζζ which converts logarithmic ray images such as γ-rays and X-rays into visible images.

The image intensifier tube converts high-energy radiation such as gamma electrons and X-rays into light beams to produce a brighter visible image. It is equipped with an output screen that converts the photoelectronic image into a visible image.

It is desirable for such an image intensifier tube to be able to obtain a visible image with good resolution, but this depends on how faithfully the radiation image irradiated onto the input screen is photoelectrically converted.

Normally, an input screen uses aluminum as a substrate that easily transmits radiation images, and on this substrate, an alkali-ride phosphor layer that emits light efficiently by radiation is formed by vapor deposition, and then on this phosphor layer. Substances sensitive to the luminescence of this phosphor, such as antimony-cesium (
It is composed of a photocathode made of (Sb-Cs).

Conventionally, as a means to solve the above-mentioned technical problems, a large number of cracks are created in the phosphor layer that is deposited from the substrate toward the diode surface, and the phosphor layer is formed into an aggregate of phosphor blocks (bundles of columnar crystals). A method is known in which the resolution is improved by forming a phosphor layer between blocks and suppressing scattering of light emitted within the phosphor layer.

In other words, by scattering the light emitted from the phosphor layer only within the phosphor block, the light is guided to the photocathode and the phosphor block has a light guiding effect! :It's something.

FIG. 1 shows a portion of an input screen with such a phosphor layer.

That is, this input screen is made by depositing a phosphor layer 12 made of cesium iodide on an aluminum substrate 11, and then
This structure uses the difference in thermal expansion coefficient between the substrate 11 and the phosphor layer 12 to apply a thermal shock to create cracks 13 in the phosphor layer 12.

However, this input screen has the following drawbacks.

(1) Cracks are caused by strain caused by the difference between the substrate temperature and the upper surface temperature of the phosphor layer, which is higher than the substrate temperature, so cracks tend to occur from the upper surface of the phosphor layer and extend close to the substrate. It's difficult.

Therefore, phosphor blocks due to cracks from the substrate side, which contribute most to improving resolution, cannot be formed much, and for example, point A2
The light emitted at point B is scattered as shown by the arrow, and the light guiding effect becomes insufficient.

For example, the resolution of an X-ray fluorescence multiplier using this manual screen is 28 to 301 P/cIrL.

(2) Since the means for generating cracks is based on temperature control, the reproducibility of cracks is poor and it is difficult to obtain an input screen of stable quality.

Further, as a known technique for creating cracks in the phosphor layer, for example, a mesh made of metal wires such as copper wires woven vertically and horizontally is bonded to an aluminum substrate, and cesium iodide is deposited on the copper wires to form a phosphor block ( There is a method for obtaining a phosphor layer consisting of an aggregate of columnar crystals (bundles of columnar crystals), but it has the following drawbacks.

(1) Since the surface of the phosphor layer formed on the mesh is concave in the area corresponding to the space between the metal wires, the entire upper surface of the phosphor layer is uneven, which adversely affects the characteristics of the photocathode.

(2) The input screen usually uses a dome-shaped substrate in order to efficiently reproduce the photoelectronic image as a visible image on the output screen. It is difficult to do so.

Therefore, input screens having such drawbacks have not been put to practical use and have only been experimentally attempted.

Furthermore, as another known technique, as shown in FIG. 2, grid-like protrusions 22 and recesses 23 are alternately provided on a substrate 21 using a known photolithographic technique, and the protrusions 22 and recesses 23 are covered with an ink layer. There is a method of obtaining a phosphor layer 24 consisting of an aggregate of phosphor blocks (bundles of columnar crystals) 25a and 25b by vapor-depositing cesium oxide (y).

However, in this method, the division between the phosphor blocks 25a and 25b is unclear, so the light guiding effect is small, and the phosphor layer 25 is It has the disadvantage that it causes unevenness on the upper surface of the photocathode, which adversely affects the characteristics of the photocathode.

SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the above-mentioned drawbacks of the prior art and to provide an excellent image intensifier tube having a novel structure, greatly improving resolution, and having an input screen that provides high image quality. be.

FIG. 3 shows the present invention applied to an X-ray fluorescence multiplier tube that converts an X-ray image into a light image.

That is, this X-ray fluorescence multiplier tube includes an envelope 31 made of glass, and an input screen 32, an output screen 33, a focusing electrode 34, an accelerating electrode 35, etc. disposed within the glass envelope 31. Become.

Therefore, the X-ray 36 is irradiated onto the subject 37, and the subject 37
An X-ray image modulated two-dimensionally by the X-ray absorption ability of the input screen 32 passes through the envelope 31 and emits light at the phosphor layer 39 of the input screen 32.

This light passes through the protective film 40, and from the photocathode 41 the photoelectrons 4
Releases 2.

The photoelectrons 42 are accelerated by the focusing electrode 35 and reproduce on the output screen 33 an optical image several thousand times brighter than the optical image obtained on the input screen.

In the present invention, the input screen 32 has a structure as shown in FIG.

That is, a fine groove 32 that partitions a substrate 321 and a large number of mosaic structures 322 formed on one surface of this substrate 321 (the substrate structure above the position indicated by the two-dot chain line in the figure).
3, and 1 a first phosphor layer made of an alkali metal such as cesium iodide or potassium iodide in columnar crystals deposited on the mosaic structure surface and extending substantially perpendicular to the surface;
24, a light-transmissive intermediate thin film 325 deposited on the first phosphor layer 324, and columnar crystals of cesium iodide, potassium iodide, etc. extending substantially perpendicularly on the intermediate thin film 325. A second phosphor layer J consisting of an alkali halide of
λJ, and a photocathode 41 formed on the second phosphor layer 326 via a light-transmitting protective film 40 .

Thus, the first phosphor layer 324 has a crack 32 between the mosaic structures 322, 322 defined by the groove 323.
9, each optically independent phosphor block (
bundle of columnar crystals) 330.

The intermediate thin film 325 is formed over the cracks 329 between the phosphor blocks 330, 330 of the first phosphor layer 324 (but not on the substrate 3).
(21 side is the lower part) Part I enters into the hole and plays the role of isolating the phosphor blocks from each other.

Further, a wedge-shaped crack 331 exists in a portion of the second phosphor layer 326 near the intermediate thin film, but no crack exists on the surface side near the protective film 40.

By using an input screen having such a structure, the resolution characteristics are good and the photocathode 41 is formed uniformly, so that an X-ray fluorescence multiplier tube with good image quality can be stably obtained.

In general, alkali halide phosphors have a lower melting point (621°C in the case of cesium iodide) than other fluorescers, such as zinc sulfide phosphors and rare earth phosphors, and the X-ray fluorophor tube is evacuated. In the baking process when baking, if the baking temperature is high, crystal fusion will easily occur, and the phosphor block 330°3
Cracks between 30 and 30 degrees are easy to disappear.

When the crack disappears, the above-mentioned light guiding effect disappears and the resolution deteriorates.

The present invention provides an X-ray fluorophore multiplier having an input screen structured to prevent fusion of fluorophore blocks.

In particular, the purpose of the first phosphor layer is to improve resolution, and the purpose of the second phosphor layer is to improve the uniformity of the photocathode, combining these two purposes into the structure. It is possible to stably obtain good characteristics in terms of resolution and uniformity of the photocathode.

An embodiment of the present invention will be described below with reference to FIGS. 4 and 5.

First, the surface of the aluminum substrate 321 with a thickness of 0.5 mm on which the phosphor layer will be formed later is anodized.

For example, the anodization is carried out in a 3% acid aqueous solution with the substrate 321 as the substrate and aluminum as a counter electrode for about 2 hours at IA/am.
20 Electrification is carried out.

Then, the hole is opened in boiling water for about 2 hours.

Through this sealing treatment, an aluminum oxide layer containing crystal water is formed on the substrate surface.

By further subjecting this to heat treatment at 250° C. or higher, a surface having a mosaic structure 322 defined by fine grooves 323 is formed.

Under the above conditions, the groove width is about 3 to 7μ, and the groove depth is about 10μ.

A perspective view of the substrate thus obtained is shown in FIG.

In this case, the size of each mosaic structure is 50 to 10
Most of them have a value of 0μ.

Next, a cesium iodide phosphor is deposited on the surface of the substrate after the above treatment in vacuum at a rate of 3 to 6 μm, e.g., μmA'J-1.
The first phosphor layer 324 is deposited to a thickness of 150 μm at a substrate temperature of 40 to 150° C., for example, 100° C., and the first phosphor layer 324 is formed by growing columnar crystals with a diameter of 1 to 5 μm on the mosaic structure 322 surface of the substrate 321. Crack 32 formed in groove 323
9, a phosphor block 330 consisting of a bundle of columnar crystals
is formed substantially perpendicularly from the substrate.

Next, as an intermediate thin film, an aluminum oxide thin film is formed by vapor deposition.

The thickness is 100A to 1 μm, for example 500A.

At this time, aluminum oxide is formed to cover the upper surface of the phosphor block 330 and also enters the upper part 332 of the crack 329.

Next, a cesium iodide phosphor is deposited at a rate of 3 to 6μ, for example 5μ to a temperature of 200 to 300℃, for example 250℃.
The second phosphor layer 326 is deposited to a thickness of 50 μm at
shall be.

The second phosphor layer 326 has fine wedge-shaped cracks 3 in the portions corresponding to the cracks 329 in the first phosphor layer 324.
31 is formed, but it disappears as ζ moves towards the top.

There are therefore no cracks on top of the second phosphor layer.

On top of the second phosphor layer, a thin film of aluminum oxide is applied.
The protective film 40 is formed by vapor deposition to a thickness of 00A to 1 μm, for example, 500A.

A photocathode 41 is formed on the protective film 40 and becomes the input screen 32.

By arranging the input screen as described above inside the X-ray fluorescence multiplier tube, it is possible to stably obtain a resolution characteristic of 43 to 451P/CIrL and a good uniformity of the photocathode. Ta.

In particular, the purpose of the first phosphor layer is to improve resolution, and the second phosphor layer's purpose is to improve the uniformity of the photocathode, and their roles are clearly linked to the structure, resulting in excellent properties. You can get things stably.

Note that the block structure of the first phosphor layer used in the present invention is not necessarily limited to the above embodiments.

For example, among the conventional methods mentioned above, there is a method that takes advantage of the difference in thermal expansion coefficient between the substrate and the phosphor layer, but this method does not work well when the phosphor layer is thin (for example, 100 μm or less). Block structures can be created stably.

That is, as shown in FIG. 6, a first phosphor layer 624 having a block structure is formed on a substrate 621 without a mosaic structure.
An intermediate thin film 625 is formed thereon, and a second phosphor layer 626 is formed thereon.

Furthermore, a protective film 40 and a photocathode 41 are formed thereon.

It can be easily inferred that an input screen having such a structure has the same effect as the previously described embodiment.

Also included in the invention is an image intensifier tube having an input screen of the structure shown in FIG. 7 for purposes of photocathode uniformity and stability.

That is, in order to prevent the surface of the phosphor layer from deteriorating due to moisture absorption, a phosphor that does not easily absorb moisture is used as the second phosphor layer 726.

Next, examples will be described.

The first phosphor layer 725 has, for example, 2×10
The second phosphor layer 726 is made of a cesium iodide phosphor containing sodium iodide in a molar ratio of ˜10 as an activator.
For example, it is made of a cesium iodide phosphor containing sodium iodide in a molar ratio of 10 to 204 as an activator.

Although a large amount of sodium iodide tends to absorb moisture, the structure prevents moisture absorption, keeps the surface of the phosphor layer smooth, and contributes to the uniformity and stability of the photocathode.

Here, the intermediate thin film 725 serves to prevent mutual diffusion between the substance constituting the first phosphor layer and the substance constituting the second phosphor layer.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a part of a conventional human cover screen for an X-ray fluorescence multiplier tube, and FIG. 2 is a cross-sectional view showing a part of a conventional human cover screen for an X-ray fluorescence multiplier tube. FIG. 3 is a schematic diagram showing an X-ray fluorescence multiplier tube according to an embodiment of the present invention, FIG. 4 is a sectional view showing a part of an input screen according to the present invention, and FIG. 5 is an input screen according to the present invention. A perspective view showing one embodiment of the substrate in the screen, and FIGS. 6 and 7 are cross-sectional views showing other embodiments of the input screen according to the present invention. 32... Input screen, 321... Board, 324
... first phosphor layer, 325 ... intermediate thin film, 326
...Second phosphor layer, 40...Protective film, 41...
Photocathode.

Claims (1)

[Claims] 1. An input screen that converts a radiation image into an electron beam image;
The input screen includes a substrate, an electron optical system that accelerates and focuses the electron beam image, and an image intensifier tube that includes an output fluorescent surface that converts the accelerated and focused electron beam image into a visible image. a first phosphor layer formed on one surface of the substrate;
a transparent thin film formed on this first phosphor layer, a second phosphor layer formed on this transparent thin film, and a second phosphor layer formed on this second phosphor layer;
An image intensifier tube comprising a photocathode formed on a phosphor layer. 2. The image intensifier tube according to claim 1, wherein at least the first phosphor layer of the two phosphor layers constituting the input screen has a block structure. 3. One surface of the substrate has a mosaic structure, and the first
3. An image intensifier tube according to claim 2, wherein the phosphor layer has a block structure according to the mosaic structure. 4. Claim 3, characterized in that at least the upper layer of the second phosphor layer does not have a block structure.
Image intensifier tube as described in section. 5. The image intensifier tube according to claim 1, wherein the first phosphor layer and the second phosphor layer are made of materials with different compositions.