JPH0636714A - X-ray image tube - Google Patents

Abstract

(57) [Summary] [Object] To provide an X-ray image tube capable of improving the resolution. [Structure] On an aluminum (Al) substrate 11, in a plane direction,
A first discontinuous phosphor layer 12 of cesium iodide is formed as a fiber body 12a of a large number of discontinuous columnar crystals. A second discontinuous phosphor layer 13 of cesium iodide, such as a fiber body 13a having a large number of columnar crystals having a diameter smaller than that of the fiber body 12a, is laminated on the first discontinuous phosphor layer 12 in the plane direction. To form the input fluorescent screen 14. Fiber body 12a of first discontinuous phosphor layer 12 and fiber body 1 of second discontinuous phosphor layer 13
3a increases the number of interfaces, increases the attenuation rate, and suppresses light diffusion. Photocathode with low surface resistance
15 to improve the brightness of the input phosphor screen 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an X with improved resolution.
Regarding line image tubes.

[0002]

2. Description of the Related Art Conventionally, X-ray image tubes have been widely applied to medical X-ray image pickup devices and industrial X-ray industrial televisions for nondestructive inspection.

Further, the conventional X-ray image tube is equipped with a vacuum envelope having an input window for inputting X-rays. A curved substrate is arranged inside the vacuum envelope so as to face the input window, and an input fluorescent screen and a photoelectric surface are sequentially laminated on the surface of the curved substrate opposite to the input window. Further, an anode and a fluorescent screen are arranged on the output side of the vacuum envelope, and a focusing electrode is arranged along a side wall inside the vacuum envelope.

Then, the X-ray emitted from the X-ray tube passes through the subject, passes through the input window and the curved substrate, and is converted into light by the input fluorescent screen. This light is converted into electrons by the photocathode, accelerated and converged by an electron lens composed of a focusing electrode and an anode, and converted into a visible image by the output fluorescent screen.

Then, this visible image is displayed on a television camera,
It is developed by a cine camera or spot camera, and medical diagnosis is performed.

Next, an example of the input fluorescent screen used in the X-ray image tube will be described with reference to FIG.

In the input fluorescent screen shown in FIG. 9, a discontinuous phosphor layer 2 of cesium iodide (CsI) is formed on an aluminum substrate 1, and a continuous fluorescent layer of cesium iodide is formed on the discontinuous phosphor layer 2. The body layers 3 are stacked to form the photocathode 4 continuously.

Then, the above-mentioned input fluorescent screen is
First, it has a light guide effect. That is, cesium iodide has a refractive index of 1.84 with respect to light emission near a wavelength of 420 nm, and theoretically, the light emission generated in the crystal is observed as a crystal at an obtuse angle of 33 ° or more as shown in FIG. When it reaches the interface with the vacuum, it is totally reflected and cannot get out of the crystal. Therefore, part of the emitted light reaches the photocathode 4, and the light is forcibly transmitted in the crystal growth direction.

In addition, light is attenuated at the interface between the crystal and the vacuum. Therefore, the light emitted outside the crystal at an angle of the critical angle of 33 ° or less reaches another discontinuous phosphor layer 2 adjacent thereto again. At this time, most of the light is taken into the crystal, but part of it is returned to the original crystal by Fresnel reflection as shown in FIG. The same applies when the crystal is evacuated. In this way, the light that spreads in the lateral direction is gradually attenuated, and the more the light deviates from the crystal growth direction, the more times it passes through the interface and the greater the degree of attenuation. Therefore, the light emission reaches the photocathode 4 with a smaller amount of attenuation as it approaches the crystal growth direction.

As described above, the light emitted from the discontinuous phosphor layer 2 reaches the photocathode 4 which is not far from the light emitting point, so that the resolution of the input phosphor screen alone can be obtained.

In recent X-ray image tubes, the thickness of the input fluorescent screen is set to 400 μm or more to improve the X-ray absorption efficiency in order to pick up as many X-ray signals that have passed through the subject. ing.

Further, among the above actions, the light guide effect does not depend on the thickness of the input fluorescent screen, but the attenuation of light between the vacuum and the interface is attenuated by the interface when the input fluorescent screen becomes thicker. Effect is weakened and the resolution of the input phosphor screen is reduced.

In order to reinforce this resolution, it is conceivable to reduce the diameter of the discontinuous phosphor layer 2 to make the optical interface in the plane direction denser. Then, by making the optical interfaces dense in this way, it is considered that the proportion of light that spreads in the lateral direction is attenuated per unit optical path length.

Further, since the diameter of the discontinuous phosphor layer 2 depends on the substrate temperature in the screen vapor deposition process, the cesium iodide film is formed under the pressure of 4.5 Pa while maintaining the substrate temperature at 150 ° C. during the vapor deposition. When formed, a discontinuous phosphor layer 2 having a crystal column of 6 μm is formed, and the substrate temperature is set to 180.
When maintained at 0 ° C., a discontinuous phosphor layer 2 of 9 μm was formed.

When the resolution of the input phosphor screen on which these discontinuous phosphor layers 2 were formed was measured, it was 20 lp.
/ Cm, the CTF (Contrast Transfer Function) values are all about 24% and are approximately the same, and 6 at 50 lp / cm.
The μm input phosphor screen was only 1% better. With such a difference in CTF, when the input fluorescent screen is mounted inside the X-ray image tube, the difference that appears on the television screen via the imaging system is small.

As another means for improving the resolution characteristics of such an input fluorescent screen having a columnar structure, a layer of a light absorbing material or a light reflecting material is provided at the optical interface formed by the columnar structure. Conceivable.

In particular, as a means for improving light attenuation between a vacuum and an interface, a light absorption layer is provided between crystal columns of a discontinuous phosphor layer as described in, for example, Japanese Patent Application Laid-Open No. 62-43046. With the interposition of JP-A-59-12173
As described in Japanese Patent Laid-Open No. 3 (1993), it is known that powder of a light-reflecting substance is filled between columnar crystals of a discontinuous phosphor layer.

However, the distance between the crystal columns of the discontinuous phosphor layer is 1
It is about μm, and it is very difficult to process the gap between these crystal columns.

The structure disclosed in Japanese Patent Publication No. 54-40071 is known as the easiest and most mass-producible method for realizing such a structure. This Japanese Patent Publication Sho 54-40071
In the configuration described in the publication, a light absorbing material is mixed and annealed in an oxidizing atmosphere to precipitate an oxide of the light absorbing material at an optical interface.

However, this Japanese Patent Publication No. 54-4007
In the structure described in Japanese Patent Laid-Open No. 1, the impurities contained in the crystal are
In order to deposit on the optical interface, the impurities can diffuse and move, and if the crystal structure and the annealing conditions where oxidation progresses at the optical interface are not in order, the input phosphor screen of any columnar structure can be used. It cannot always be realized.

[0021]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
As described in JP-A No. 3046 or JP-A No. 59-121733, a light absorbing layer is interposed between crystal columns of a discontinuous phosphor layer to improve the attenuation of light between a vacuum and an interface. , Or filling the powder of the light reflecting substance, the distance between the crystal columns of the discontinuous phosphor layer is about 1 μm,
There is a problem that it is very difficult to process the gap between these crystal columns.

Further, as described in JP-A-62-43046, a light absorbing substance is interposed between crystal columns of the discontinuous phosphor layer, and light from the phosphor is interposed between the crystal columns of the discontinuous phosphor layer. In the case of absorbing the light, there is a problem that the resolution cannot be improved sufficiently.

Further, in the structure described in Japanese Patent Publication No. 54-40071, since the impurities contained in the crystal are deposited at the optical interface, the impurities can diffuse and move, and at the optical interface. If the crystal structure in which oxidation progresses and the annealing conditions are not set, there is a problem that it cannot be realized for an input fluorescent screen having an arbitrary columnar structure.

The present invention has been made in view of the above problems, and it is possible to improve the resolution with a simple structure.
The purpose is to provide a line image tube.

[0025]

The X-ray image tube of the present invention comprises a columnar crystal containing a substrate and a light-absorbing substance which is formed on the substrate and absorbs the light emitted by the phosphor upon incidence of X-rays. The first discontinuous phosphor layer and a light absorbing substance that is formed on the first discontinuous phosphor layer and absorbs light emitted by the phosphor upon incidence of X-rays. The second discontinuous phosphor layer comprises columnar crystals having a diameter smaller than that of the columnar crystals of the continuous phosphor layer.

[0026]

In the X-ray image tube of the present invention, the first discontinuous phosphor layer made of columnar crystals containing a light absorbing substance which absorbs the light emitted by the phosphor upon incidence of X rays is formed on the substrate. , A columnar crystal having a diameter smaller than that of the columnar crystal of the first discontinuous phosphor layer, the light-absorbing substance absorbing the light emitted by the phosphor upon incidence of X-rays on the first discontinuous phosphor layer. Second
Since the discontinuous phosphor layer of was formed, the number of interfaces passing through before reaching it increased and the attenuation rate increased,
The scattering of light is suppressed and the brightness is improved.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the X-ray image tube of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a cesium iodide (CsI) first layer consisting of a large number of columnar crystal fiber bodies 12a of discontinuous fiber columns is first formed on an aluminum (Al) substrate 11 as a substrate in the plane direction. Forming a discontinuous phosphor layer 12 of
On the first discontinuous phosphor layer 12, a plurality of columnar crystal fiber bodies 13a of discontinuous fiber pillars having a diameter smaller than that of the fiber body 12a of the first discontinuous phosphor layer 12 are formed in the surface direction. A second discontinuous phosphor layer 13 of cesium chloride is laminated to form an input phosphor screen 14, and a photocathode 15 is formed continuously.

The first discontinuous phosphor layer 12 has an average concentration of 0.1 wt% or less, more preferably 0.01-.
Copper iodide (CuI) of 0.1 wt% is mixed and the transparency is low, and a black film 16 of copper oxide (CuO) is formed on the surface of the crystal of the first discontinuous phosphor layer 12. Has been done. In the first discontinuous phosphor layer 12, the concentration of the light absorbing substance is high near the substrate.

In addition, the first discontinuous phosphor layer 12 and the second discontinuous phosphor layer 12
The discontinuous phosphor layer 13 of contains thallium ions (Tl ⁺ ),
Sodium ion (Na ⁺ ), potassium ion (K ⁺ )
Is contained in an appropriate concentration to improve the luminous efficiency.

The distance between the adjacent fiber bodies 12a of the first discontinuous phosphor layer 12, that is, the distance between the optical interfaces is
0.1 to 40 μm is preferable, and 0.1 to 40 μm is more preferable.
3 μm, formed to 0.1 μm, fiber body 12a
The diameter is preferably 40 μm or less, more preferably 5 to 1
5 μm, set to 20 μm, film thickness is 200-400
It is set to μm.

On the other hand, the diameter of the fiber body 13a of the second discontinuous phosphor layer 13 is set to 3 to 6 μm and the film thickness is set to 20 to 50 μm.

Since the aluminum substrate 11 supports columnar crystals, another substance such as titanium (T
i) or, in some cases, beryllium (Be) or the like having a small X-ray transmittance.

Next, the manufacturing apparatus of the X-ray image tube will be described with reference to FIG.

FIG. 2 shows an apparatus for manufacturing an input fluorescent screen. Reference numeral 21 denotes a vacuum tank, and the aluminum substrate 11 is placed inside the vacuum tank 21. The heater 22 is provided above the aluminum substrate 11, and the boats 23 and 24 are provided below the aluminum substrate 11.
Are arranged respectively. Further, one boat 23 was filled with cesium iodide (CsI) mixed with 0.1 wt% of iron iodide (FeI ₂ ), and the other boat 24 was filled with cesium iodide (CsI). There is.

First, the heater 22 heats the aluminum substrate 11 to 180 ° C., and the pressure in the vacuum chamber 21 is increased to 4.
While maintaining the pressure at 5 × 10 ⁻¹ Pa, one boat 23 is heated to form the first discontinuous phosphor layer 12 made of a columnar fiber body 12a having a film pressure of 380 μm on the aluminum substrate 11. Once the discontinuous phosphor layer 12 is annealed in air at 280 ° C., it is returned to the vacuum chamber 21 again, the aluminum substrate 11 is heated to 180 ° C., and the pressure in the vacuum chamber 21 is set to 10 ⁻³ P.
In the state of a or less, the other boat 24 is heated, and the fiber body 12 having a thickness of about 20 μm is formed on the first discontinuous phosphor layer 12.
A second discontinuous phosphor layer 13 composed of a columnar fiber body 13a having a diameter smaller than a is formed. Then, the aluminum substrate 11 on which the first discontinuous phosphor layer 12 and the second discontinuous phosphor layer 13 are formed is exposed to the air at 280 ° C. for 5 hours.
Bake for hours.

Further, the function of forming the first discontinuous phosphor layer 12 and the second discontinuous phosphor layer 13 will be described.

First, cesium iodide (CsI), which is a substance constituting the input fluorescent screen 14 of the X-ray image tube, is used.
Since is an ionic crystal, the cesium ion (Cs ⁺ ) or iodine ion (I ⁻ ) in the lattice can easily replace other chemical species ions. For example,
In the input fluorescent screen 14, as shown in Chemical Formula 1, thallium ions (T
1 ⁺ ) and sodium ion (Na ⁺ ) are added in trace amounts.

[0039]

[Chemical 1] By utilizing this property, the light absorbing substance can be mixed into the first discontinuous phosphor layer 12 while maintaining the crystal lattice. This is also possible with polyvalent ions, and when the amount of addition is small, the original physical properties of the phosphor of the first discontinuous phosphor layer 12 are less likely to be impaired. Further, for example, in the case of monovalent copper ions (Cu ⁺ ), the chemical formula 2 is obtained.

[0040]

[Chemical 2] In this way, pure cesium iodide (CsI) or sodium cation (Na ⁺ ) added cesium iodide (CsI) is added to a crystal mixed with ions of a certain kind of chemical species.
The input fluorescent screen 14 which originally has a light absorption characteristic which is not present in I) and which was originally substantially transparent to light emission, also has a low light transmittance.

Therefore, the emission is the first discontinuous phosphor layer.
The light traveling in a direction deviating from the crystallographic direction of 12 has a longer distance to reach the photocathode 15, and the smaller the transmittance of the input fluorescent screen 14, the smaller the attenuation reaching at a position away from the light emitting point on the photocathode 15. As a result, the resolution of the input fluorescent screen 14 is improved.

The distribution of the contaminant can be changed by selecting the substance to be injected into the crystal.
For example, when a crystal of copper iodide (CuI) in which copper ions (Cu ⁺ ) are uniformly mixed is heated in an oxygen atmosphere, the surface of the crystal of the first discontinuous phosphor layer 12 is expressed by Chemical Formula 3 and Chemical Formula 4. Copper (Cu) near the optical interface
The oxide of is precipitated.

[0043]

[Chemical 3]

[Chemical 4] At this time, since the cesium ion (Cs ⁺ ) is more inactive with respect to oxygen (O ₂ ) than the copper ion (Cu ⁺ ), it is difficult to form an oxide of cesium (Cs), and the first discontinuous phosphor layer There is little deterioration of the 12 fluorescent films.

Furthermore, although copper ions (Cu ⁺ ) are deficient as the oxidation reaction near the surface of the first discontinuous phosphor layer 12 progresses, copper ions (Cu ⁺ ) in the bulk are heated by heating.
Are diffused and replenished, the reaction further progresses, and a layer of higher concentration copper oxide (CuO) is formed closer to the crystal surface of the first discontinuous phosphor layer 12, that is, the optical interface.

In the input fluorescent screen 14 purified by such a reaction, the concentration of the light absorbing ions as the light absorbing substance in the crystal bulk becomes low, and the luminous efficiency of the phosphor of the first discontinuous phosphor layer 12 is increased. Can be minimized,
Furthermore, when an oxide such as iron which is a light absorbing substance is selected, the light attenuating function can be kept the same.

Under the above conditions, the diameter of the columnar crystals was 12 μm on average, and the width of the optical interface was 0.3 to 1 μm.

When the reaction for forming the black film 16 is performed, the temperature for obtaining a sufficient reaction rate is iodine gas (I ₂ ) when copper iodide is oxidized to form copper oxide. Can be determined by monitoring the amount of

That is, as shown in FIG. 3, the horizontal axis represents time, the vertical axis represents the total amount of iodine gas generated, and the measured values are plotted. When the temperature is raised to 280 ° C., Since the amount of iodine gas rapidly increases, it can be said that the temperature of 280 ° C. is sufficient to cause the reactions of Chemical Formula 3 and Chemical Formula 4.

Regarding the precipitation of the impurities in the crystal as described above by heating in oxygen,
Journal of Crystal Growth 7 (1970), pages 259-26
“GROWTH OF Mn ₂ O ₃ THIN FILMS BY IMPURITY” on page 0
DIFFUSION FROM VOLUME TOSURFACE IN IMPURE NaCl CR
YSTALS ”and so on.

Therefore, in the above embodiment, a mixture of cesium iodide (CsI) powder and copper iodide powder is used to form the first discontinuous phosphor layer 12 comprising the fiber body 12a, and then the iodide Second discontinuous phosphor layer composed of columnar crystal fiber body 13a by vapor deposition of cesium (CsI) powder
It is possible to easily form the black film 16 of high concentration copper oxide (CuO) on the optical interface of the fiber body 12a by forming 13 and then heating in air at 280 ° C. for 5 hours. . In this case, since the surface of the fiber body 12a in contact with the second discontinuous phosphor layer 13 is not in contact with air, the black film 16 of high concentration copper oxide (CuO) is not formed.

On the other hand, the relationship between the heating conditions and the crystal size and the state of precipitation of impurities on the crystal surface is as follows:
de Fisica 30 (4) (1984) pp. 685-692. According to this description, assuming that the heating time is t and the crystal size is 1, t / l ² is a parameter indicating the progress of precipitation. In other words, when the crystal size is increased by n times, the heating time required for the precipitation of impurities on the crystal surface must be n ² , and the distance that impurities in the crystal reach the surface becomes long. That is the cause.

From the above, when the diameter of the fiber body 12a constituting the first discontinuous phosphor layer 12 is large,
Extremely long heating times are required. When the heating time becomes long, not only the mass productivity is deteriorated, but also the crystal is broken due to heat. When fiber bodies 12a having various diameters were actually manufactured, and the diameter of the fiber body 12a exceeded 50 μm,
It was found that the amount of the CuO black film 16 was extremely reduced by heating for 24 hours.

The optical interface of the fiber body 12a serves as an oxygen supply source in the annealing process. Therefore, if the distance between the fiber bodies 12a is small, oxygen will be insufficient during the annealing process and the reaction rate will be slow. According to experiments, if the thickness is smaller than 0.1 μm, it becomes difficult to form an oxide film having a thickness of about several tens of angstroms.

In consideration of the above, the heating temperature in air is preferably 60 to 350 ° C, more preferably 260 to 3 ° C.
The temperature is 00 ° C., and the heating time is preferably 24 hours or less, more preferably 3 to 5 hours.

The interval between the optical interfaces of the adjacent fiber bodies 12a serves as an oxygen supply source in the heating process. Therefore, if this interval is too narrow, the amount of oxygen will be insufficient during heating and the reaction rate will be slow. All the widths of the actually formed films were 0.3 μm or more, and there was no problem. However, if the width is smaller than 0.1 μm, it becomes difficult to form an oxide film of several tens of angstroms.

Next, a 12 μm columnar crystal fiber body 12
The effect of a will be described in the case of using the following three types of embodiments.

Sample A: A conventional input fluorescent screen heated in vacuum at 260 ° C. Sample B: The input fluorescent screen 14 containing 0.02 wt% of copper iodide was omitted at 260 ° C. by omitting the annealing step.
Sample C: 0.02 wt% of copper iodide was mixed to form an input fluorescent screen by the method shown in the example.
Vacuum heating at 260 ° C The vacuum heating at 260 ° C of samples A, B, and C is as follows.
This is a process for activating the phosphor.

When the sample C was heated in the air, copper oxide was formed and turned into gray.

As shown in FIG. 4, the sample C has a CTF curve significantly improved as compared with the sample A. Although the appearance of the sample C is gray, the amount of light emission reaches 36% of that of the sample A, although not shown. The reason why the decrease in the amount of emitted light is small even though the appearance is gray is considered to be that copper ions are not included in the bulk crystal and that the crystal is transparent as shown in FIG. .

On the contrary, the CTF curve of sample B is not different from that of sample A. Moreover, although sample B is transparent, since a large amount of copper ions are contained in the bulk crystal, it interferes with the light emission of the phosphor CsI / Na ⁺ , and the light emission amount is 29% of that of sample A though not shown. Fell to.

When the input fluorescent screen manufactured as described above was mounted on an X-ray image tube having an input field of view of 9 inches and an output diameter of 25 mm, the effect of improving the CTF curve was obtained as shown in FIG. At this time, as in the case of the experiment of the screen alone, sample C has a lower luminance ((cd / m ² ) / mRisec) than sample A, but in order to prevent the lowering of the luminance, It is only necessary to reduce the concentration of the absorbing material or to limit the part including the light absorbing material to a part in the thickness direction of the input fluorescent screen, and to adjust the concentration and structure according to the brightness required for each application of the X-ray image tube. You should consider.

As in the above embodiment, 0.02 wt.
% Of copper iodide, a sufficient transparency is obtained and it contributes to the emission of light from the photocathode 16, which is an important performance factor of the X-ray image tube. Is reduced as little as possible as an effective signal.

As described above, a series of steps of once mixing the ions as the source of the light absorbing material into the crystal and precipitating the source of the light absorbing material at the crystal interface by the subsequent oxidization process is high. By combining it with the process of forming an input fluorescent screen having a fiber structure of an X-ray image tube that requires disassembly performance, a great effect can be exhibited and a very simple desired structure can be obtained. It is also useful as a means of production.

As another example, a structure using iron oxide instead of copper oxide will be described.

Then, in the first discontinuous phosphor layer 12 of the embodiment shown in FIG. 1, instead of copper, an average concentration of 0.1 wt% or less,
More preferably, 0.01 to 0.1 wt% of iron (Fe) is mixed, and iron oxide (Fe ₂ O ₃ ) is added to the surface of the crystal of each fiber body 12a of the first discontinuous phosphor layer 12 from iron oxide (Fe ₂ O ₃ ). Black film
16 is coated.

The element iron is a phosphor mainly composed of, for example, sodium-activated cesium iodide (Cs).
(I: Na), which is more active than oxygen as an element ion, and is present as an oxide outside the crystal than when it is present as a metal ion in the crystal of the second discontinuous phosphor layer 13. In this case, the light emitted from the phosphor is effectively absorbed.

Similarly, the distance between the adjacent fiber bodies 12a, that is, the distance between the optical interfaces is 0.1 to 40 μm.
Is more preferable, 0.1 to 3 μm is more preferable, and the diameter of the fiber body 12a is preferably 40 μm or less, and more preferably 5 to 15 μm.

Thus, even when iron is used, the apparatus for manufacturing the input fluorescent screen shown in FIG. 2 is used.

When iron is used as described above, one boat is used.
Cesium iodide (CsI) mixed with 0.02 wt% of iron iodide (FeI ₂ ) and a trace amount of sodium iodide (NaI) were used for 23, and cesium iodide (CsI) was used for the other boat 24. And a small amount of sodium iodide (Na
I) is included. And the first containing copper iodide
The discontinuous phosphor layer 12 and the second discontinuous phosphor layer 13 are subjected to the same operations, and finally, the aluminum substrate 11 is exposed to the air and baked at 280 ° C. for 5 hours to be formed.

Further, the reason why the structure of the input fluorescent screen is obtained will be described.

Since cesium iodide (CsI), which is a substance constituting the input fluorescent screen of the X-ray image tube, is an ionic crystal, cesium ions (Cs ⁺ ) or iodine ions (I ⁻ ) in the lattice are It can easily replace other species ions. For example, in the input fluorescent screen, in order to increase the luminous efficiency, the chemical formula 5
As shown in (3), a trace amount of thallium ion (Tl ⁺ ) and sodium ion (Na ⁺ ) is added.

[0072]

[Chemical 5] By utilizing this property, the light absorbing substance can be mixed into the first discontinuous phosphor layer 12 while maintaining the crystal lattice. This is also possible with polyvalent ions, and when the amount of addition is small, the original physical properties of the phosphor of the first discontinuous phosphor layer 12 are less likely to be impaired. Further, for example, in the case of divalent iron ion (Fe ⁺⁺ ), the chemical formula 6 is obtained.

[0073]

[Chemical 6] The crystal having such a structure can be obtained by vacuum-depositing a mixture of cesium iodide and copper iodide powder.

Further, the iron ion (Fe ⁺⁺ ) is more active against oxygen (O ₂ ) than the cesium ion (Cs ⁺ ) and iodine ion (I ⁻ ) which form the phosphor, It can be oxidized by exposing it to the inside.

At this time

[Chemical 7] It becomes the reaction formula of. Oxygen is supplied to the optical interface from the inside of the first discontinuous phosphor layer 12 in a large amount, so that the reaction occurs mainly at the optical interface.

[0076] Further, although the iron ions as an oxidation reaction in the vicinity of the surface of the discontinuous phosphor layer 12 progresses (Fe ⁺⁺⁾ is depleted, iron ions in the bulk (Fe ⁺⁺⁾ is replenished by diffusion by heating Therefore, the reaction proceeds further, and the black film 16 of iron oxide (Fe ₂ O ₃ ) having a higher concentration is formed closer to the crystal surface of the discontinuous phosphor layer 12, that is, closer to the optical interface.

As the light-absorbing substance contained in cesium iodide (CsI), chromium (Cr), strontium (Sr), magnesium other than iron ion (Fe ⁺⁺ ) and copper ion (Cu ⁺ ) can be used. (Mg), mercury (H
As shown in g), if it is a light-absorbing substance that exhibits a chemical property close to that of iron (Fe) and is incorporated into the crystal lattice of cesium iodide (CsI), the same effect can be obtained by using one or more elements. Is obtained. In the vapor deposition process,
It must be vaporized at a vapor pressure close to that of cesium iodide (CsI).

Further, a substance which is colored in a gas atmosphere other than oxygen (O ₂ ) such as nitrogen gas (N ₂ ) or ammonia gas is also effective. When heat treatment is performed in an atmosphere containing nitrogen, chromium, iron, etc. can be used.

Furthermore, since the second discontinuous phosphor layer 13 is close to the photocathode 15, it may be preferable that the second discontinuous phosphor layer 13 does not contain a light absorbing substance such as iron (Fe) in order to avoid alteration of the photocathode 15. is there.

The X-ray image tube described above can be used as an X-ray imaging system in combination with the X-ray tube and the image pickup device. For example, FIG. 7 shows a perspective system and an indirect imaging system X-ray imaging system. It is a figure which shows an example.

As shown in FIG. 7, with respect to the X-ray tube 31, X
The line image tube 32 is arranged, and the subject 34 is arranged so as to face the X-ray grid 33 of the X-ray image tube 32. On the other hand, a half mirror 35 is arranged on the output side of the X-ray image tube 32,
This half mirror 35 sends it to a television camera 37 via a television lens 36 and a television monitor 38.
And the cine camera 39 and the spot camera 40.

As shown in FIG. 8, the X-ray image tube 32 has a first discontinuous fluorescence on the aluminum substrate 11 on the inner side of the input window 42 formed on one surface of the vacuum envelope 41. Body layer
An input phosphor screen 14 consisting of 12 and a second discontinuous phosphor layer 13 is formed. Further, an output surface 43 is formed on the side of the vacuum envelope 41 opposite to the input window 42.
An anode 44 is provided on the inner surface side of 43. A plurality of focusing electrodes 45 are formed along the inner surface of the vacuum envelope 41 between the input fluorescent screen 14 and the anode 44.

Then, the X-ray tube 31 irradiates the subject 34 with X-rays and transmits the subject 34 to form an X-ray transparent image.
The X-ray fluoroscopic image passes through the X-ray grid 33, the scattered X-rays are removed, and the X-ray transparent image enters the X-ray image tube 32. In addition, the X-ray image tube 32 receives X-rays from the input window 42, converts the X-rays at the input fluorescent screen 14, and focuses them at the focusing electrode 45 to form an anode.
A visible light image is converted and output on the output surface 43 by 44. Then, in the case of the fluoroscopic system, it is transmitted through the television lens 36, imaged by the television camera 37, and an X-ray fluoroscopic image is output on the television monitor 38. In the case of indirect photography system, half mirror 35 is used for cine camera
The remaining 10% is sent to the television camera 37 and the X-ray fluoroscopic image is output on the television monitor 38. If necessary, the half mirror 35 can be inverted to
0% of the light is sent to the spot camera 40 side to print an X-ray fluoroscopic image on a roll film or a cut film.

As described above, according to the X-ray image tube of the above-described embodiment, the S
The / N ratio is the same as the conventional one, and it can have high decomposition performance.

Further, since the black film 16 is deposited on the fiber body 12a which is a columnar crystal, the light emitted at one point of the fiber body 12a does not pass through between the fiber bodies 12a, so that the brightness is not lowered and the contrast is reduced. , The resolution is improved.

Further, since the first discontinuous phosphor layer 12 and the second discontinuous phosphor layer 13 are formed of the fiber body 12a and the fiber body 13a, respectively, the aluminum substrate 11 side to the photocathode 15 are formed. The number of interfaces that pass through before being output increases, the attenuation rate improves, and light scattering is suppressed. Further, since the photocathode 15 has a small surface resistance, the brightness can be improved.

Since the phosphor columnar crystals constituting the input phosphor screen 14 are adjacent to each other on their side surfaces, a light absorption layer containing a compound of this element having a higher concentration of the light absorption element than the inside is formed. , Lateral light diffusion is suppressed,
Thereby, the resolution can be improved. Further, since there is no light absorption layer at the interface between the fiber body 12a and the second discontinuous phosphor layer 13, the luminous efficiency and the luminance are not significantly reduced.

[0088]

According to the X-ray image tube of the present invention, the first discontinuous phosphor made of a columnar crystal containing a light absorbing substance that absorbs the light emitted by the phosphor upon incidence of X rays on the substrate. Forming a layer, containing a light absorbing substance that absorbs the light emitted by the phosphor upon incidence of X-rays on the first discontinuous phosphor layer, and has a diameter smaller than that of the columnar crystals of the first discontinuous phosphor layer. Since the second discontinuous phosphor layer made of columnar crystals is formed, the number of interfaces that pass through the layer increases and the attenuation rate increases, so that light scattering is suppressed and brightness is improved. it can.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an input fluorescent screen of an X-ray image tube of the present invention.

FIG. 2 is an explanatory view showing an apparatus for manufacturing an input fluorescent screen of the X-ray image tube of the above.

FIG. 3 is a graph showing the relationship between the total amount of iodine gas generated and the time during the annealing process of the input surface.

FIG. 4 is a graph showing CTF values of the input fluorescent screen of the X-ray image tube and the input fluorescent screen of the conventional example.

FIG. 5 is a graph showing the amount of spectrally transmitted light on the input surface of the same.

FIG. 6 is a graph showing CTF values of the input fluorescent screen of the X-ray image tube and the input fluorescent screen of the conventional example.

FIG. 7 is an explanatory diagram showing a system using the X-ray image tube of the same as above.

FIG. 8 is an explanatory view showing the X-ray image tube of the same as above.

FIG. 9 is a sectional view showing an input fluorescent screen of an X-ray image tube of a conventional example.

FIG. 10 is an explanatory diagram showing a relationship between an incident angle and reflection.

[Explanation of symbols]

 11 Aluminum Substrate as Base 12 First Discontinuous Phosphor Layer 13 Second Discontinuous Phosphor Layer

Claims (1)

[Claims] 1. A base, a first discontinuous phosphor layer formed of a columnar crystal containing a light absorbing substance formed on the base and absorbing light emitted from the phosphor upon incidence of X-rays, and the first discontinuous phosphor layer. Columnar crystals having a diameter smaller than that of the columnar crystals of the first discontinuous phosphor layer, the columnar crystals being formed on the first discontinuous phosphor layer and containing a light absorbing substance that absorbs the light emitted by the phosphor upon incidence of X-rays. An X-ray image tube, comprising: