JPH0354417B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a fluorescent screen in which an optical fiber bundle plate is used as a substrate and a fluorescent layer is formed on the surface thereof. [Technical background and problems of the invention] In general, image tubes with a built-in fluorescent screen, such as X-ray fluorescence multiplier tubes, are widely used for medical purposes, mainly for industrial non-destructive testing, in conjunction with X-ray industrial televisions. It is applied. This type of X-ray fluorescence multiplier tube is constructed as shown in FIG. 1, and has an input surface 2 disposed inside the input side of a vacuum envelope 1 mainly made of glass. On the other hand, inside the output side of the vacuum envelope 1,
An anode 3 is provided and an output surface 4 is provided,
Furthermore, a focusing electrode 5 is provided along the side wall inside the vacuum envelope 1.
is located. The input surface 2 is made of spherical Al
An input phosphor layer 7 of _CSI is formed on the output side (concave side) of the substrate 6, and a photocathode 8 is further formed on the input phosphor layer 7. Also, output surface 4
The output phosphor layer 10 is formed on a substrate 9. In operation, the X-rays (not shown) are modulated by the X-ray transmittance of the object as they pass through the object (not shown) to excite the input phosphor layer 7. The excitation light of the input phosphor layer 7 gives energy to the photocathode 8 formed on the inner surface of the input phosphor layer 7, causing the photocathode 8 to emit electrons. These electrons are accelerated and focused onto the output phosphor layer 10 by the action of an electron lens constituted by the anode 3 and the focusing electrode 5, causing the output phosphor layer 10 to emit light. In this process, electrons are multiplied, and an image much brighter than the light image obtained in the input phosphor layer 7 is obtained in the output phosphor layer 10. By the way, as one example of using an optical fiber bundle board as a holding base for the output phosphor layer of the X-ray fluorophore multiplier tube as described above, an optical There have been proposals to improve contrast by forming an output phosphor layer on the fiber bundle plate. The outline of this proposal is shown in FIG .
6 is placed on the output side of the vacuum envelope 1. This proposal uses a conventionally well-known optical fiber bundle plate as part of the vacuum envelope, and the signal cannot be directly extracted outside the vacuum envelope, requiring a lens system. is the conventional X shown in Figure 1.
It has the advantage of being able to be used in the same way as a linear fluorescent multiplier tube. However, simply forming a phosphor on the optical fiber bundle 17 has a limit in contrast improvement, and the reason for this will be explained below. That is, although FIG. 3 shows an explanatory diagram of the optical fiber,
Now, for convenience of explanation, the glass refractive index n ₁ of the core portion 101 of the optical fiber is 1.8, and the glass refractive index of the coating portion 102 is 1.8.
Let n ₂ be 1.49. Further, when the refractive index of vacuum is n ₀ and the angle of incidence on the optical fiber is θ ₀ , θ ₀ is expressed by the following equation. n ₀ sinθ ₀ = √ ₁ ² − ₂ ^2From this formula, θ ₀ is 90°. On the other hand, for light incident at 90°, the refraction angle θ ₁ at the glass core 101 is 33.7°.
becomes. On the other hand, the glass of the core part 101 and the covering part 10
The angle of total reflection at the interface with glass No. 2 is 55.9°. By the way, for light whose θ ₁ is 33.7°, the angle of incidence φ ₁ on the interface between the glass of the core part 101 and the glass of the covering part 102 is 56.3°, which is larger than the critical angle, so it passes through the main body while being totally reflected. It propagates and is transmitted to the other side.
What should be noted here is that the angle θ ₁ between the central axis of the glass of the core part 101 and the light is in the range of 0 to 33.7 degrees,
There is no light beyond 33.7°. Theoretically, therefore, light can be transmitted from the single fiber without leakage to the outside maintenance. In reality, some light directly enters the covering portion 102, but the effect of this is very small. However, when a fluorescent film is formed on an optical fiber bundle plate, the light transmission situation is drastically different. This explanation is shown in FIG. 4. Usually, when forming a phosphor layer,
Since the phosphor particles 201 are bonded using a glassy adhesive, the degree of optical contact between the phosphor particles 201 and the optical fiber bundle plate 17 is increased. Therefore,
As shown in FIG. 3, there are also cases where the angle between the central axis of the glass of the core portion 101 and the light emitted from the fluorescent film is 33.7° to 90°. Therefore, the core portion 101
There is an angle φ ₁ smaller than the total reflection angle determined by the refractive index of the glass and the glass of the coating 102, and this light propagates to the adjacent optical fiber. As shown in FIG. 4, for example, the light emitted in the directions (a) and (b) propagates through a single fiber, but as in the light (c), the glass of the core 101 and the glass of the coating 102 are separated. When incident on the boundary surface at an angle smaller than the total internal reflection angle,
The light propagates to the next neighbor and is reflected by the fluorescent film 10 of the optical fiber bundle plate 17 and the reflective surface, which illuminates another position of the fluorescent layer 10, thereby worsening the contrast. In actual optical fiber bundle plates, an absorption layer 103 is provided on the outside of the glass of the covering portion 102 to reduce the light propagating to the neighboring area. Since the number of times that the propagating light passes through the absorption layer 103 decreases, the contrast decreases significantly. In particular, when the thickness of the optical fiber bundle plate 17 becomes 1 mm or less, the contrast position becomes very large, and the advantage of using the optical fiber bundle plate 17 is lost. In addition, as another example of forming a fluorescent film on an optical fiber bundle board, see Utility Model Publication No. 40-19855, or
There is a technique disclosed in the specification of USP4264408.
These methods involve providing a recess in an optical fiber bundle plate and embedding a phosphor in the recess. However, this has poor contrast because the degree of contact between the phosphor and the optical fiber bundle plate is large. Furthermore, the technique for uniformly embedding the phosphor is difficult, and the brightness is low. [Object of the Invention] An object of the present invention is to provide a fluorescent screen that uses an optical fiber bundle plate as a substrate and can provide high-quality images with excellent contrast and brightness. [Summary of the Invention] This invention provides a recess in the end face of each single fiber core glass of an optical fiber bundle plate, and leaves the recess as a space without filling the recess with phosphor particles. A phosphor screen in which a phosphor layer is formed on the end surface of the single fiber coating glass of the plate, reducing the optical contact area between the phosphor layer and the optical fiber bundle plate and improving contrast and brightness. It is. [Embodiments of the Invention] An example in which the present invention is applied to the output surface of the image tube as described above will be described. That is, if a phosphor film is formed directly on an optical fiber bundle plate, optical contact with the phosphor layer increases, resulting in a decrease in contrast. Optical fiber bundle plates generally have optical defects, such as black spots, fiber devitrification, and disordered fiber bundles. This optical defect can be improved by polishing the optical fiber bundle plate to a thinner thickness, but on the other hand, the aforementioned decrease in contrast becomes even greater. Therefore, the embodiment of the invention is constructed as shown in FIG.
On the surface of 1, that is, on the side where the phosphor layer is formed, there is a recess 1, respectively.
8 is provided. In this case, the optical fiber bundle plate 1
The formation of the recess 18 in 7 is carried out by etching with acid. In general, glasses with high refractive indexes contain many metal components in addition to silicon, which is the main component, and are more susceptible to acids than glasses with low refractive indexes. Therefore, when the optical fiber bundle plate 17 is placed in an acid solution such as hydrochloric acid or nitric acid, the glass of the core portion 101 having a high refractive index corrodes faster than the glass of the coating portion 102 having a low refractive index, causing the dents 18. occurs. If the degree of this depression 18 is too small, no improvement in contrast will be seen, and if it is too large, the glass of the covering portion 102 will also be corroded.
No good effect was obtained, and good results were obtained at a depth of 1 to 20 μm. On the optical fiber bundle plate 17 provided with the recesses 18 in this way, the covering glass 1 of each single fiber is placed so that the phosphor particles 201 are hardly filled into the recesses 18.
The output phosphor layer 10 is formed by depositing it on the surface formed by the end surface of 02. In this case, either a method of depositing the phosphor particles by precipitation in a suspension, which is generally practiced in cathode ray tubes, or a method of forcibly depositing the phosphor particles using a centrifuge may be used. These methods are preferable because the inconvenience of the phosphor particles 201 being filled in the recesses 18 is hardly caused because the large particles are settled first. However, the selection of the particle size of the phosphor particles 201 is important. That is, if it is too thin, it will enter the recess 18 of the optical fiber bundle plate 17 and good results will not be obtained.
On the other hand, if it is too rough, the graininess will deteriorate. The optimum particle size of the phosphor particles 201 is determined by the optical fiber bundle plate 1.
Although it is also related to the diameter of the glass of the core portion 101 of No. 7, good results were obtained with an average diameter of 2 to 10 μm. Of course, it is acceptable for the phosphor particles to penetrate into the recesses to the extent that a sufficiently large space remains in each recess, that is, a space with a depth in the range of 1 to 20 μm, which is sufficiently larger than the emission wavelength of the phosphor layer. Not even. Further, in the optical fiber bundle plate 17, it is necessary to specify the diameter of the single fibers from the viewpoint of resolution. That is, the end fiber diameter is Dmm, the spatial frequency is flp/mm,
When the image transmission ability of the optical fiber bundle plate is expressed as F(f) as the degree of modulation for a sine wave input, F(f) is as follows. F(f)=[2J ₁ (2πfD)/2πfD] ² ×100 (%) Here, J ₁ is a first-order Betzel function. usually,
For image tubes, in order to obtain high-quality images, it is preferable that the modulation rate is 30lp/mm and the modulation depth is 50% or more. Calculating F(f) of the optical fiber bundle plate 17 from this point,
D, that is, the single fiber diameter needs to be 10 μm or less. Furthermore, as the output image diameter of the image tube increases, the brightness decreases and a large lens is required for image transmission.
Good effects were obtained with an effective diameter of 50 mm or less. [Effects of the Invention] According to the present invention, the performance of the optical fiber bundle plate can be further exhibited, and high-quality images with extremely excellent contrast characteristics can be obtained. To explain the reason why extremely excellent contrast characteristics are obtained, as shown in FIG.
01 is hardly in contact with the core portion 101 of the optical fiber bundle plate 17. Fluorescent particles 2 by electron beam
01 emits light, but the directionality of this light is almost close to that of a completely diffusing surface. Now, consider light in three directions (a), (b), and (c). The light in the direction of (a) passes through the glass of the core 101. The light in the direction (b) propagates through the optical fiber while being totally reflected, and is extracted from the opposite surface. Finally, the light in (c) is transmitted to the glass of the covering part 102 and the absorption layer 10.
3 and enters the adjacent optical fiber, but this is caught by the adjacent optical fiber and propagates therein. That is,
The operation shown in FIG. 4(c) is eliminated, and as a result, the song trust is significantly improved. For specific contrast values, an optical fiber bundle plate with a thickness of 0.5 mm was used, the emission diameter of the phosphor layer was 20 mm,
Place an electron beam and a light shield with an area ratio of 10% at the center of the emission diameter. When contrast is defined as the brightness ratio between when the light shielding plate is not placed and when it is placed, it is approximately 50:1 in the conventional method, but in this invention, it is approximately 50:1.
This was a remarkable improvement of 100:1. In the above embodiment, the image tube output surface was described, but the invention is not limited to the output surface, but can be widely applied to screens having a structure in which a phosphor layer is formed on the surface of an optical fiber bundle plate. .

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram showing a general image tube (X-ray fluorescence multiplier tube), Figure 2 is a sectional view showing the main parts of an image tube proposed in the past, and Figure 3 is an optical fiber FIG. 4 is a sectional view used to explain the drawbacks of the image tube shown in FIG. 2, and FIG. 5 is a sectional view showing essential parts of a fluorescent screen according to an embodiment of the present invention. It is a diagram. DESCRIPTION OF SYMBOLS 1... Vacuum envelope, 2 ... Input surface, 3... Anode, 5... Concentrating electrode, 10... Fluorescent layer, 16 ...
... Output surface, 17 ... Optical fiber bundle plate, 18 ... Recess, 101 ... Core glass of optical fiber, 102 ...
... optical fiber coating glass, 103 ... absorption layer,
201...fluorescent particles.

Claims (1)

[Scope of Claims] 1. In a fluorescent screen formed by forming a phosphor layer on the surface of an optical fiber bundle plate, an end surface portion of the single fiber core glass of the optical fiber bundle plate on the side of the phosphor layer. A fluorescent screen characterized in that a recess is formed in the optical fiber bundle plate, and the phosphor layer is formed on the end face of the monofilament-coated glass of the optical fiber bundle plate, leaving the recess as a space. 2 The optical fiber bundle plate has a single fiber diameter of 10 μm.
2. The fluorescent screen according to claim 1, wherein the depth of the recess is 1 to 20 μm. 3. The fluorescent screen according to claim 1 or 2, wherein the fluorescent particles have an average particle size of 2 to 10 μm.