JP2001229860A - X-ray image detector - Google Patents

Abstract

(57) [Problem] To provide a flat type X-ray image tube capable of obtaining an observation image with good resolution and contrast. An X-ray image detector according to the present invention includes a through-hole (4).
Regarding the metal veneers 41 and 42 in which 0 is formed, from the side facing the output fluorescent screen 51 (taper side) to the approximate center of the through hole 40 in the depth direction, the material is compared with the material of the metal veneer 42. And MgO which has a high secondary electron emission rate
The thin film 47 made of Al, which is 10% of gO, and the secondary electrons from the side of the single metal plate 41 facing the input phosphor screen 31 to the approximate center of the through hole 40 as compared with the material of the single metal plate 41. The electron multiplier 4 has a thin film 46 made of TiN (titanium nitride), TiNO, metal carbide, or a carbon-based compound or a nitrogen-based compound having a low emission rate. Is done.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a radiation X
The present invention relates to an X-ray image detector that converts an image obtained by a line into an optical or electrical image signal.

[0002]

2. Description of the Related Art In general, X-rays are useful for examining the internal structure of a human body or an object, and the transmission density distribution of X-rays irradiated on a human body or an object, that is, an X-ray intensity distribution or an X-ray image is visible light. Devices for converting an image or an electrical image signal corresponding to X-rays are widely used.

[0003] As devices for converting an X-ray image into a visible light image or an electric image signal, an X-ray image tube (X-ray image intensifier) and an X-ray vidicon (X-ray image detector) have been developed. .

[0004] Today, there have been reported examples of using an electron multiplier in a vacuum vessel to reduce the thickness, ie, depth, of an X-ray image tube.

For example, US Pat. No. 3,394,261 discloses a configuration in which a micro channel plate (MCP) having a function of amplifying electrons is added to an X-ray image tube. It should be noted that this type of thin X-ray image tube having a small depth using an MCP is a flat X-ray image tube.
It is called a line image tube.

The MCP, or electron multiplier, has a structure in which a plurality of metal plates having a predetermined thickness and a plurality of through holes formed at predetermined intervals in a plane direction are laminated via an insulating material. It is said that the S / N (signal-to-noise) ratio can be improved. JP-A-55-146854 (JP-B-62-41378) uses an oxide film formed by oxidizing a layer of Mg and Al on the wall surface of a hole of a metal plate in order to obtain secondary electrons. Examples are disclosed.

[0007]

By the way, in the MCP structure disclosed in U.S. Pat. No. 3,394,261 and a well-known similar planar electron multiplier, the wall surface of the hole of the metal plate is used. It is known that the angle at which the generated secondary electrons fly out and the emission energy are undefined, and the secondary electrons collide with the metal plate other than the wall surfaces of the holes. Secondary electrons that collide with the wall surface also newly emit secondary electrons, so that electrons are scattered, and there is a problem that the resolution of an image output, which is electrons traveling from the electron multiplier to the output phosphor screen, is reduced.

On the other hand, as disclosed in JP-A-55-146854 (JP-B-62-41378), the surface of a through-hole of a metal plate constituting an electron multiplier is made of Mg.
It has been confirmed by the present inventors that when covered with an oxide of Al and Al, the oxide functions as if it were a capacitor and the secondary electron emission rate is conversely reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a flat type X-ray tube capable of obtaining an image having a high resolution and a high contrast by reducing noise components in an output image.

[0010]

SUMMARY OF THE INVENTION The present invention has been made based on the above-mentioned problems, and has a vacuum vessel for holding a vacuum and an X-ray provided in the vacuum vessel and having X-rays incident from outside.
An input phosphor screen for converting a line into fluorescence, a photocathode arranged in the vacuum vessel to change the fluorescence generated by the input phosphor screen into photoelectrons, and a plurality of holes arranged in the vacuum vessel in a plane direction. An electron multiplier that amplifies the photoelectrons emitted from the photocathode by applying a predetermined voltage to each metal plate while insulating the opened metal plate with an insulating material and applying a predetermined voltage to each metal plate, An output fluorescent screen that is disposed in a vacuum vessel and converts the photoelectrons amplified by the electron multiplier into a visible light image, and an output window that holds the output fluorescent screen and transmits the visible light image. In the X-ray image detector, a low secondary electron emission rate layer whose secondary electron emission rate is lower than that of the material of the metal plate is formed on a photoelectron incidence side inner wall of each hole of the metal plate. The inner wall has a secondary electron emission rate of the material of the metal plate. There is provided an X-ray image detector, characterized in that remote high insulation layer high secondary electron emission coefficient layer with added conductive substance in is formed.

The inner wall of the photoelectron incident side refers to a portion closer to the input phosphor screen when viewed in the depth direction of the hole, and the inner wall of the photoelectron emission side refers to a portion closer to the output phosphor screen as viewed in the depth direction of the hole. Point out. Further, the electron multiplier may have a focusing metal electrode plate for focusing photoelectrons in addition to the metal electrode plate for amplifying photoelectrons. The focusing metal plate can be formed of a single metal plate formed such that the holes are aligned with the openings of the holes of the amplification metal plate.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing a configuration of an X-ray image-visible light image conversion section of a flat type X-ray image detector to which an embodiment of the present invention is applied.

In FIG. 1, an X-ray source (not shown) is emitted into a vacuum vessel (not shown) of the X-ray image detector 1,
An input window 2 to which X-rays transmitted through the observation target are input, and an input substrate provided at a predetermined position (in a vacuum vessel) inside the input window 2 and converting X-rays incident from the input window 2 into electrons. 3. An electron multiplier 4 provided at a predetermined position where electrons output from the input substrate 3 can reach, and an output substrate that converts the electrons amplified by the electron multiplier 4 into visible light and outputs the visible light. An output window 5 is provided. The electron multiplier 4 is provided with a power supply unit 6 to which a predetermined voltage is supplied from a power supply device described below with reference to FIG.

The input substrate 3 is a substrate 30 made of, for example, Al.
A CsI (a phosphor film formed of cesium iodide, hereinafter referred to as a Csl film) 31 having a predetermined thickness, a transparent conductive film 32 such as ITO (a thin film of indium-tin oxide) having a predetermined thickness, And K (potassium), Cs (cesium)
Or photoelectric surface 3 composed of Na (sodium) or the like
Three.

The electron multiplier 4 is formed by laminating single metal plates 41 and 42 each having a predetermined thickness in which a plurality of through holes 40 are formed at predetermined intervals in a plane direction, or a single metal single plate. A plurality of bead-shaped ceramics, preferably an insulator 44 made of zirconia, which has a lower cohesiveness than glass beads and is excellent in insulation, is provided between the metal plate 43 and the metal plate 43. Note that the insulators 44 may be provided, for example, in one or more rows. Also, the insulator 44
Is a low melting point frit glass 4 at a predetermined position on a metal plate.
5 are joined.

Single metal plates 41 and 42 and metal plate 4
For example, soft iron (Fe) or an invar alloy or the like is used for 3.

The distance between the metal plates is, for example, 1 to 100.
Within the range of 0 μm, the distance is set to be substantially constant between any of the conductor layers. In addition, a potential difference having a magnitude indicated by V _{2 to} V _n is given to each metal plate by the power supply device 11. The CsI of the input board 3
A potential difference indicated by V ₁ is given from the power supply device 11 between the film 31 and the first-stage metal plate of the electron multiplier 4.

The output substrate 5 includes a glass plate 50 and a glass plate 5.
The output fluorescent film 51 of a predetermined thickness provided on the side of the electron multiplier 4 and the light reflective metal film 5 provided on the electron multiplier 4 side of the output fluorescent film 51 and made of, for example, aluminum.
Two. Note that the n-th stage of the metal plate of the electron multiplier 4, between the output phosphor film 51 of the output board 5, from the power supply 11, a potential difference represented by V _a (acceleration voltage) is applied .

FIG. 2 is a schematic diagram illustrating a power supply device connected to the X-ray image detector shown in FIG.

As shown in FIG. 2, the power supply 10
A power transformer 11 that receives a commercial power supply (not shown) and outputs a 24 V DC voltage;
A first to a third D for converting the V voltage into a predetermined DC voltage
One of the C-DC converters 12 to 14 and the DC-DC converters 12 to 14 (here, the second DC-D
And a dividing resistor 15 for dividing the DC voltage from the C converter 13 into a predetermined voltage and supplying the divided voltage to each metal plate of the electron multiplier 5. The third DC-DC
The converter 14 serves as a power supply for driving an ion pump (not shown) for removing an impurity (element) gas generated in an envelope (not shown), and a first DC-DC converter.
DC converter 12 is adapted to the acceleration voltage V _a output, as a power supply device to the cathode which is not described in detail, is used independently.

The potential divider V ₁ to be applied between the CsI film 31 of the input substrate 3 and the first stage metal plate of the electron multiplier 4, the potential difference V ₁ from the first stage of the electron multiplier 4 potential difference to be applied to each of the metal plates of the n-2 stage _V 2 _{~V n-1}
And to generate a potential difference V _n to be applied between the electron multiplier n-1 stage 4 and the n-th stage of the metal plate, in which a combined plurality of resistive elements or variable resistive element .

[0023] Note that the resistive element and the potential difference _{V n-1} and the resistance element for generating a potential difference _{V n} to generate a potential difference _{V 1,} the variable resistor is used, the other potential _V 2 ~V
_A fixed resistor is used for the resistance element that generates _n−2 .

The potential difference V ₂ -V
V _n−2 and V _n−1 are both 300 V, the potential difference V ₁ is 200 V to ₁ kV, and the potential difference V _n is 1 to 30 V.
Each is set to 0V.

On the other hand, the acceleration voltage _{V a,} the first DC-DC
The voltage is set in the range of 0 to 25 kV by converter 12.

FIG. 3 is a partially enlarged view for explaining in detail a through hole in each conductor layer of the electron multiplier of the X-ray image detector shown in FIG.

As shown in FIG. 3, among the n-stage metal plates of the electron multiplier 4, the individual metal plates except for the (n−1) -th stage and the n-th stage are connected to the input fluorescent screen 31 side of the input substrate 3. And a single metal plate 42 directed to the output fluorescent screen 51 side of the output substrate 5.

The single metal plates 41 and 42 are formed by double side etching so that the through hole 40 on one side is tapered and the through hole 40 on the other side is defined by a radius r. Each is spherically etched. That is, in the through hole 40 of each of the metal veneers 41 and 42, one opening has a tapered shape and the other opening has a spherical cross-sectional shape in the depth direction. In this embodiment, two metal veneers 41 and 42 are laminated on each other such that the tapered portion of each through hole 40 faces outward. .

The inner surface of the through hole 40 of the metal plate 43 on which the metal single plates 41 and 42 are laminated is substantially at the center of the through hole 40 from the side facing the output fluorescent screen 51 (taper side) in the depth direction. Up to MgO (magnesium oxide), which has a high secondary electron emission rate as compared with the material of the metal single plate 42, a thin film (Al) having a weight ratio of Al (aluminum), which is approximately 10% of MgO, is added. (An emission rate layer) 47. In addition, Al is preferably located near the surface portion (the inner diameter side of the through hole 40) of the thin layer of MgO.

The inner surface of the through hole 40 is also provided with the input fluorescent screen 3.
1 from the side of the metal veneer 41 to the approximate center of the through hole 40, the secondary electron emission rate is lower than that of the metal veneer 41, such as TiN (titanium nitride), TiNO, metal carbide or carbon. It is covered with a thin film (low secondary electron emission rate layer) 46 made of a nitrogen-based compound or a nitrogen-based compound.

The above-mentioned metal plate 43 is tapered by double side etching into single metal plates 41 and 42 in which the shape of the through hole 40 in the depth direction is spherical and tapered, respectively. MgO from the side where
And a thin layer 47 of Al or a thin layer 46 of TiN or TiNO
Can also be obtained by aligning and bonding through holes to each other and growing them in the depth direction by a method such as sputtering or CVD.

On the other hand, the n-th stage and n-1
On the inner surface of the through hole 40 of the metal plate 43 of the step, for example, Ti
A thin layer (low secondary electron emission rate layer) 48 consisting only of N is formed. That is, the n-th and (n-1) -th metal plates 43 function as control electrodes capable of converging and accelerating the electrons directed to the output phosphor screen 51.

Next, the operation of the X-ray image detector 1 will be described with reference to FIGS. FIG. 4 is a partially enlarged view showing a part of the electron multiplier 4 of the X-ray image detector 1 shown in FIG.

The unshown X-ray source emitting X-rays R are observed object from, for example X-ray R ₁ concentration distribution is given by passing through the human body, the input surface 3 passes through the input window 2 CsI reaches the film 31, converted by the CsI film 31 to the fluorescent R _2, and reaches the photocathode 33 through the transparent conductive film 32, is converted into photoelectrons E by the photocathode 33, it is emitted into the vacuum.

At this time, the photoelectrons E are applied to Cs of the input substrate 3.
It is accelerated to reach the first stage of the metal plate by the potential difference V ₁ applied between the first-stage metal plates I film 31 and the electron multiplier 4.

The photoelectrons E reaching the electron multiplier 4 are guided to the through holes 40 of the metal plate, and the metal single plate 42 located on the side opposite to the input substrate 3 in the depth direction of the through holes 40. Collides with the inner wall on the side of, and one or more electrons E
₂ and the potential difference V ₂ applied between the respective metal plates
The accelerating voltage V _a between the output phosphor surface 51 of ~V _n-1 and the last stage the metal plate and the output substrate 5 (n-th stage), towards the output phosphor surface 51 of the metal plate or output board 5 of the next stage Te are accelerated sequentially, the new one or more electron E ₂ collides with the inner wall of the through hole 40 of one of the metal plate.

[0037] Incidentally, optoelectronic E and electronic E ₂ enters the through hole 40, as shown in FIG. 4, the input substrate 3 of the metal plate
When a collision occurs with the flat portion facing the side or the through-hole portion (the region where the thin layer 46 is formed) on the metal single plate 41 side in the depth direction of the through-hole 40, the secondary electrons E ₂ are newly added. Is unlikely to be released, and conversely, when it collides with the through-hole portion (the region where the thin layer 47 is formed) on the side of the single metal plate 42 in the depth direction of the through-hole 40, the efficiency is reduced. well, since new secondary electrons E ₂ is released, under the condition that the noise component is hardly generated, it is sequentially amplified.

[0038] Specifically, in the electron multiplier 4, in order to increase the contrast of the output image due to the influence of electron scattering, the through-hole of the electron E ₂ emitted in front of the metal plate next metal plate It is desirable that the surface of the metal plate 40 be surely reached only the portion (low secondary electron emission rate layer) 47 coated with MgO and Al, but actually, the flat portion of the metal plate (the surface on the input fluorescent surface side) is desired. ) And a portion of the wall surface of the through hole 40 in the depth direction of the through hole 40 (in a state where the two metal single plates 41 and 42 are laminated) to a portion where the inner diameter of the through hole 40 is minimized. it has been confirmed that the probability of the secondary electrons E ₂ generated by optoelectronic E or secondary electrons E ₂ having collided with the area scattered electrons collide with the surface of the next stage of the metal plate will occur is about 40% .

According to the computer simulation, the photoelectrons E or the secondary electrons E ₂ are taken into consideration even in consideration of the thickness and interval of the metal plate, the diameter of the through hole, the acceleration voltage, and the like.
Holes 4 secondary electrons E ₂ that occurred in the next stage of the metal plate by
0 predetermined position (MgO + A in this embodiment)
It is difficult to increase the probability of reaching only the I layer 47) to be higher than about 70% (the probability of generation of scattered electrons is 30).
% Is difficult to lower).

Therefore, even when the photoelectrons E or the secondary electrons E ₂ collide with the surface of the metal plate (here, the side facing the input fluorescent screen 31), the secondary electrons E ₂ are generated. with released structure difficult, it can be suppressed, which is an image secondary electrons E ₂ output from the electron multiplier 4 toward the output phosphor screen 51 is the contrast of the output image is scattered is reduced.

Thereafter, the photoelectrons E incident on the electron multiplier 4 are gradually amplified by repeating the collision of the electrons of the photoelectrons E against the through holes 40 of the metal plate and the generation of the secondary electrons. 4 is emitted toward the output fluorescent screen 51 of the output substrate 5.

At this time, the amount of the emitted electrons E ₂ is proportional to the amount of the incident photoelectrons E, and the single metal plate 4 constituting the metal plate
1, 42 and 43, the thickness of the metal veneers 41, 42 and 43, the shape (curvature r) of the metal veneers 41 and 42 and the through hole 40, and the mixing ratio of MgO and Al in the thin layer 47. determined secondary electron emission coefficient, between the thickness of the insulator 44 (the distance between the metal plate other), and the metal plate of the potential difference V ₂ ~V _n and the last stage is applied between the metal plate mutually the output board 5 It depends on the electric field distribution generated depending on the accelerating voltage V _a,
The amplification factor is determined by the number of layers on which the metal plates are stacked.

The electron multiplier 4 has a plurality of metal plates.
The last (n-th) metal plate and the previous (n-1) -th metal plate
The metal plate of the eye is charged by
Child E ₂Undesirably spreads in the plane direction of the output phosphor screen 51
Can be suppressed, the contrast of the output image and
Useful for accumulating resolution.

As described above, the X-ray (X-ray image) R ₁ incident from the outside on the input window 2 is amplified by the electron multiplier 4 and is visible on the output surface (substrate 50) of the output substrate 5. It is output as the light image _{R 3.}

The visible light image R ₃ is amplified by the electron multiplier 4 at the same magnification as that incident on the incident surface on the input window 2 side of the envelope 3 without being undesirably distorted. It is output to the output substrate 5 without blurring or bleeding, which is the effect of the spread of the electron orbit at the time.

In the above embodiment, by adding a small amount of an aluminum group element as an impurity to the high secondary electron emission rate layer, the charge generated when photoelectrons collide with the secondary electron emission rate layer is dispersed. Thus, secondary electrons can be efficiently generated. This aluminum group element
It is not necessary for the MgO layer to be uniformly contained in the MgO layer, and the MgO layer may be formed at a higher concentration in the vicinity of the surface of the secondary electron emitting layer where charges easily accumulate. Furthermore, on the surface of the secondary electron emission layer,
An extremely thin Al film may be formed. If you do this,
Since the charge accumulated in the secondary electron emission layer is quickly dissipated through the Al layer, secondary electrons can be emitted more efficiently.

The Al layer can be easily formed by, for example, depositing the Al material alone for a predetermined time after the simultaneous deposition of the MgO material and the Al material is completed. More specifically,
The shutter opening / closing time between the target provided in the sputtering apparatus and the film formation chamber is adjusted, the shutter on the MgO target side is closed and isolated from the film formation chamber, and a predetermined time A
l Keep the target side shutter open. According to this method, only the opening / closing sequence of the shutter needs to be changed, and the process control is facilitated.

If the thickness of the Al layer is less than 0.1 μm, the ability to dissipate the charge accumulated in the secondary electron emission layer is not sufficient, and if it exceeds 10 μm, the arrival of electrons to the lower MgO layer is hindered. Therefore, a sufficient secondary electron emission cannot be obtained, so that the range of 0.1 to 10 μm is preferable. As described above, in the X-ray image detector of the present invention, the Al layer is formed by optimally setting the distance between the conductor layers provided on the output side of the electron multiplier and the applied potential difference. An X-ray image detector capable of obtaining an observation image of an observation target without distortion, blur, or bleeding is provided.

[0049]

As described above, in the X-ray image detector according to the present invention, an X-ray image with no distortion can be obtained.
The line image detector is formed at low cost and small.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an X-ray image detector according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a power supply device that supplies a predetermined voltage to the electron multiplier shown in FIG.

FIG. 3 is a partially enlarged view for describing in detail a through hole in each conductor layer of the electron multiplier of the X-ray image detector shown in FIG. 1;

FIG. 4 is a schematic enlarged view illustrating a change in the trajectory of electrons amplified by a conductor layer of the electron multiplier shown in FIGS. 1 and 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... X-ray image detector, 2 ... Input window, 3 ... Input board, 4 ... Electron multiplier, 5 ... Output board, 6 ... Power supply part, 10. ..Power supply device, 30 ... substrate, 31 ... CsI film (input fluorescent film), 32 ... transparent conductive film, 33 ... photoelectric surface, 40 ... through hole, 41 ... metal Single plate (metal plate), 42: Single metal plate (metal plate), 43: Metal plate (single metal plate), 44: Glass beads (insulator), 45: Frit glass, 46 ... Low secondary electron emission rate layer, 47 ... High secondary electron emission rate layer, 48 ... Low secondary electron emission rate layer, 50 ... Glass substrate, 51 ... Output fluorescent film, 52 ... light reflection film.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroyuki Aida 1385-1 Shimoishigami, Otawara-shi, Tochigi Prefecture F-term in Toshiba Nasu Electronic Tube Factory (reference) 5C037 GG05 GH02 GH05 GH05 GH11

Claims (9)

[Claims] A vacuum vessel for holding a vacuum; an input phosphor screen provided in the vacuum vessel for converting X-rays incident from outside into fluorescent light; and an input phosphor screen disposed in the vacuum vessel. A photocathode which changes the fluorescence generated by the photoelectrons,
Arranged in the vacuum vessel, a metal plate having a plurality of holes formed in a plane direction is insulated by an insulating material, and a plurality of layers are stacked, and a predetermined voltage is applied to each metal plate, so that the metal plate is separated from the photoelectric surface. An electron multiplier that amplifies the emitted photoelectrons, an output phosphor screen that is arranged in the vacuum vessel and converts the photoelectrons amplified by the electron multiplier into a visible light image, and holds the output phosphor screen. An X-ray image detector comprising: an output window that transmits the visible light image; and an inner wall on the photoelectron incidence side of each hole of the metal plate, the secondary electron emission rate of which is lower than the material of the metal plate. A secondary electron emission layer is formed, and a high secondary electron emission layer formed by adding a conductive substance to an insulating layer having a higher secondary electron emission rate than the material of the metal plate is formed on the inner wall of the photoelectron emission side. An X-ray image detector, comprising: 2. The method according to claim 1, wherein the low secondary electron emission rate layer comprises TiN, Ti.
2. The X-ray image detector according to claim 1, wherein the X-ray image detector contains NO, a metal carbide, a carbon compound, or a nitrogen compound. 3. The X according to claim 1, wherein the insulating layer constituting the high secondary electron emission rate layer is an MgO layer.
Line image detector. 4. The X-ray image detector according to claim 1, wherein the conductive material contained in the high secondary electron emission layer contains an aluminum group element. 5. The X-ray image detection device according to claim 1, wherein a mixing ratio of the aluminum group element to MgO in the high secondary electron emission layer is 10% or less. vessel. 6. The X-ray image detector according to claim 5, wherein said aluminum group element is contained at a higher concentration near the surface of said high secondary electron emission rate layer. 7. An X-ray image detector according to claim 5, wherein a film made of an aluminum group element having a thickness of 0.1 to 10 μm is formed on a surface of said high secondary electron emission rate layer. . 8. The X-ray according to claim 1, wherein each of said metal plates is formed of two metal single plates which are formed with through holes and are superposed with their opening positions aligned. Image detector. 9. A low secondary electron emission rate whose secondary electron emission rate is lower than that of the material of the metal single sheet on the inner wall of each through hole of the single sheet on the photoelectron incidence side of the two metal single sheets. A layer is formed, and on the inner wall of each through hole of the single plate on the photoelectron emission side,
The X-ray image detector according to claim 8, wherein a high secondary electron emission rate layer having a higher secondary electron emission rate than the material of the single metal plate is formed.