JP2008209124A - Scintillator panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scintillator panel having high emission light extraction efficiency and high sharpness, with reduced deterioration in sharpness between flat light-receiving element faces. <P>SOLUTION: A scintillator panel 10 has on a substrate 1 a reflection layer 3 and a scintillator layer 2 formed by vapor deposition, wherein the reflection layer is composed of a white pigment and a binder resin. A surface of the reflection layer is preferably smoothed by calender processing, and the white pigment is preferably at least one white pigment selected from alumina, yttrium oxide, zirconium oxide, and titanium oxide. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a scintillator panel used when a radiographic image of a subject is formed.

  Conventionally, radiographic images such as X-ray images have been widely used for diagnosis of medical conditions in the medical field. In particular, radiographic images using intensifying screen-film systems are still the world as an imaging system that combines high reliability and excellent cost performance as a result of high sensitivity and high image quality in the long history. Used in the medical field. However, the image information is so-called analog image information, and free image processing and instantaneous electric transmission cannot be performed like the digital image information that has been developed in recent years.

  In recent years, digital radiological image detection apparatuses represented by computed radiography (CR), flat panel type radiation detectors (FPD), and the like have appeared. In these, since a digital radiographic image is directly obtained and an image can be directly displayed on an image display device such as a cathode tube or a liquid crystal panel, image formation on a photographic film is not necessarily required. As a result, these digital X-ray image detection devices reduce the need for image formation by the silver halide photography method, and greatly improve the convenience of diagnosis work in hospitals and clinics.

  Computed radiography (CR) is currently accepted in the medical field as one of the digital technologies for X-ray images. However, the sharpness is insufficient and the spatial resolution is insufficient, and the image quality level of the screen / film system has not been reached. As a new digital X-ray image technology, for example, a flat plate X-ray detector (FPD) using a thin film transistor (TFT) has been developed (for example, see Non-Patent Documents 1 and 2).

  In order to convert radiation into visible light, a scintillator panel made of an X-ray phosphor having a characteristic of emitting light by radiation is used. In order to improve the S / N ratio in low-dose imaging, luminous efficiency is used. It is necessary to use a high scintillator panel. In general, the light emission efficiency of a scintillator panel is determined by the thickness of the scintillator layer (phosphor layer) and the X-ray absorption coefficient of the phosphor. The thicker the phosphor layer, the light emission in the phosphor layer. Light scattering occurs and sharpness decreases. Therefore, when the sharpness necessary for the image quality is determined, the film thickness is determined.

  In particular, cesium iodide (CsI) has a relatively high rate of change from X-rays to visible light, and phosphors can be easily formed into a columnar crystal structure by vapor deposition. Therefore, it was possible to increase the thickness of the phosphor layer.

  However, since the luminous efficiency is low only with CsI, for example, a mixture of CsI and sodium iodide (NaI) at an arbitrary molar ratio is used as sodium-activated cesium iodide (CsI: Na) on the substrate by vapor deposition. Deposition, or in recent years, a mixture of CsI and thallium iodide (TlI) mixed in an arbitrary molar ratio deposited on a substrate as a thallium-activated cesium iodide (CsI: Tl) by vapor deposition. As a result of annealing, the visible conversion efficiency is improved and used as an X-ray phosphor.

  As another means for increasing the light output, a method for making the substrate on which the scintillator is formed reflective (for example, refer to Patent Document 1), a method for providing a reflective layer on the substrate (for example, Patent Document 2), A method of forming a scintillator on a reflective metal thin film and a transparent organic film covering the metal thin film (see, for example, Patent Document 3) has been proposed, but these methods increase the amount of light obtained, but are sharp. There is a drawback that the performance is significantly reduced.

  Further, although there is a method of arranging the scintillator panel on the surface of the planar light receiving element (for example, see Patent Documents 4 and 5), the production efficiency is poor, and the sharpness deterioration on the surface of the scintillator panel and the planar light receiving element is inevitable.

  Conventionally, as a manufacturing method of a scintillator by a gas layer method, a phosphor layer is formed on a rigid substrate such as aluminum or amorphous carbon, and the entire surface of the scintillator is covered with a protective film (see, for example, Patent Document 6). It is common. However, when a phosphor layer is formed on these substrates that cannot be bent freely, the flat panel device is affected by the deformation of the substrate and the warpage during vapor deposition when the scintillator panel and the planar light receiving element surface are bonded together. There is a drawback that uniform image quality characteristics cannot be obtained within the light receiving surface of the taker. This problem has become more serious with the recent increase in the size of flat panel detectors.

In order to avoid this problem, it is common to use a scintillator as a substitute for a scintillator panel, such as a method of forming a scintillator directly by vapor deposition on an image sensor, or a medical intensifying screen with low sharpness but flexibility. Has been done. In addition, an example in which a flexible protective layer such as polyparaxylylene is used as the protective layer is shown (for example, see Patent Document 7). However, aluminum and amorphous carbon used as a substrate are rigid, and the substrate Uniform contact between the scintillator panel surface and the planar light receiving element surface is difficult to achieve due to the effects of unevenness and warpage of the surface.

Under such circumstances, it is desired to develop a radiation flat panel detector that is excellent in the amount of emitted light and sharpness, and has little deterioration in sharpness between the scintillator panel and the plane light receiving element surface.
Japanese Patent Publication No. 7-21560 Japanese Patent Publication No. 1-240887 JP 2000-356679 A Japanese Patent Laid-Open No. 5-312961 JP-A-6-331749 Japanese Patent No. 3669926 JP 2002-116258 A Physics Today, November 1997, page 24, John Laurans' paper "Amorphous Semiconductor User in Digital X-ray Imaging" SPIE, Vol. 32, 1997, E. Antonuk's paper “Development of a High Resolution, Active Matrix, Flat-Panel Imager with Enhanced Fill Factor”

  The present invention has been made in view of the above situation, and its object is to provide a scintillator panel that has high light emission extraction efficiency and sharpness of the scintillator, and has little deterioration in sharpness between plane light receiving element surfaces. .

  The above object of the present invention can be achieved by the following configuration.

  1. A scintillator panel having a reflective layer and a scintillator layer formed by vapor deposition on a substrate, wherein the reflective layer comprises a white pigment and a binder resin.

  2. 2. The scintillator panel according to 1 above, wherein the surface of the reflective layer is smoothed by a calendar process.

  3. 3. The scintillator panel according to 1 or 2, wherein the white pigment is at least one white pigment selected from alumina, yttrium oxide, zirconium oxide, and titanium oxide.

  4). 4. The scintillator panel according to 3 above, wherein the white pigment is a white pigment having an average particle size of 0.1 to 3.0 μm.

  5. 5. The scintillator panel as described in 4 above, wherein the white pigment having an average particle size of 0.1 to 3.0 μm is titanium dioxide.

  6). The scintillator panel according to any one of 1 to 5, wherein the substrate is made of a flexible polymer film having a thickness of 50 μm to 500 μm.

  7. 7. The scintillator panel according to 6, wherein the polymer film is a polyimide (PI) or polyethylene naphthalate (PEN) film.

  8). The scintillator panel according to any one of 1 to 7, wherein the scintillator layer is formed by a vapor phase method using an additive containing cesium iodide and at least one kind of thallium as a raw material.

  9. 9. The scintillator panel according to any one of 1 to 8, wherein the reflective layer has a thickness of 0.2 to 3.0 [mu] m.

  By the above-mentioned means of the present invention, it is possible to provide a scintillator panel that has high emission extraction efficiency and sharpness of the scintillator, and little deterioration of sharpness between plane light receiving element surfaces.

  The scintillator panel of the present invention is a scintillator panel in which a reflective layer and a scintillator layer are provided on a substrate, and the reflective layer is made of a white pigment and a binder resin.

  The “scintillator” according to the present invention absorbs the energy of incident radiation such as X-rays and has an electromagnetic wave with a wavelength of 300 nm to 800 nm, that is, an electromagnetic wave ranging from ultraviolet light to infrared light centering on visible light. A phosphor that emits (light).

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have formed a reflective layer with a white pigment and a binder resin by the above-mentioned characteristic technical means, and hardly reduced the high light emission extraction efficiency. It was found that sharpness improved dramatically.

  Hereinafter, the present invention and its components will be described in detail.

(Configuration of scintillator panel)
The scintillator panel according to the present invention is a scintillator panel in which a reflective layer and a scintillator layer are provided on a substrate, and the reflective layer is formed of a white pigment having an average particle diameter of 0.1 to 3.0 μm and a binder resin. It is preferable.

  In this invention, it is preferable to provide the protective layer mentioned later other than a reflection layer and a scintillator layer. Hereinafter, each constituent layer and constituent elements will be described.

(Reflective layer)
The reflective layer according to the present invention is present between the substrate and the scintillator layer, and preferably comprises a white pigment and a binder resin.

  The reflective layer preferably contains at least one selected from the group consisting of alumina, yttrium oxide, zirconium oxide and titanium oxide as a white pigment. The thickness of the reflective layer is preferably 0.2 to 3.0 μm from the viewpoint of emission light extraction efficiency.

  Hereinafter, components of the reflective layer will be described.

<White pigment>
Examples of white pigments include Al ₂ O ₃ , ZrO ₂ , TiO ₂ , MgO, BaSO ₄ , SiO ₂ , ZnS, ZnO, CaCO ₃ , Sb ₂ O ₃ , Nb ₂ O ₅ , 2PbCO ₃ · Pb (OH) ₂ , mention may be made of _{PbF 2, BiF 3, Y 2} O 3, YOCl, magnesium silicate, basic silicate lead sulfate, basic lead phosphate, white pigments such as aluminum silicate. These substances may be used alone or in combination. Among these, preferable materials having a high refractive index are Al ₂ O ₃ , Y ₂ O ₃ , ZrO ₂ , and TiO ₂ , and the effect of the present invention can be enhanced by the high refractive index. Particularly preferred is TiO ₂ .

<Binder resin>
In the present invention, the white pigment is used by being dispersed in a binder resin. Various dispersants can be used according to the binder and white pigment to be used. The binder is preferably a polymer having a glass transition temperature (Tg) of 30 to 100 ° C. from the viewpoint of attaching a film between the deposited crystal and the substrate, and particularly preferably a polyester resin.

  Examples of the dispersant include phthalic acid, stearic acid, caproic acid, and a lipophilic surfactant.

  As a method for dispersing the white pigment in the binder, a known dispersion technique used in ink production or toner production can be used. Examples of the disperser include a sand mill, an attritor, a pearl mill, a super mill, a ball mill, an impeller, a disperser, a KD mill, a colloid mill, a dynatron, a three-roll mill, and a pressure kneader. Details are described in "Latest Pigment Application Technology" (CMC Publishing, 1986).

  The reflective layer according to the present invention is preferably formed by applying and drying a resin dissolved in a solvent. Specific examples of the resin include polyurethane, vinyl chloride copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer. , Polyamide resin, polyvinyl butyral, polyester, cellulose derivative (nitrocellulose, etc.), styrene-butadiene copolymer, various synthetic rubber resins, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic Resin, urea formamide resin, and the like. Of these, polyurethane, polyester, vinyl chloride copolymer, polyvinyl butyral, and nitrocellulose are preferably used. In particular, it is preferable to contain a binder resin having a glass transition temperature of 30 to 100 ° C. Usually, when forming a scintillator by vapor deposition, the substrate temperature is 150 ° C. to 250 ° C. When the glass transition temperature is 30 to 100 ° C. in the reflective layer, the light reflective layer becomes the adhesive layer. Will function effectively as well.

  Solvents used for preparing the reflective layer include lower alcohols such as methanol, ethanol, n-propanol and n-butanol, hydrocarbons containing chlorine atoms such as methylene chloride and ethylene chloride, ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone, toluene , Aromatic compounds such as benzene, cyclohexane, cyclohexanone, xylene, esters of lower fatty acids and lower alcohols such as methyl acetate, ethyl acetate, butyl acetate, ethers such as dioxane, ethylene glycol monoethyl ester, ethylene glycol monomethyl ester and the like Can be mentioned.

(Scintillator layer)
As a material for forming the scintillator layer (also referred to as “phosphor layer”), various known phosphor materials can be used. In addition, since the phosphor can be formed into a columnar crystal structure, scattering of the emitted light within the crystal can be suppressed by the light guide effect, and the thickness of the scintillator layer (phosphor layer) can be increased. Cesium iodide (CsI) is preferred.

  However, since only CsI has low luminous efficiency, various activators are added. For example, as shown in Japanese Patent Publication No. 54-35060, a mixture of CsI and sodium iodide (NaI) at an arbitrary molar ratio can be mentioned. Also, for example, CsI as disclosed in Japanese Patent Application Laid-Open No. 2001-59899 is deposited, and indium (In), thallium (Tl), lithium (Li), potassium (K), rubidium (Rb), sodium (Na CsI containing an activating substance such as) is preferred.

  In the present invention, it is particularly preferable to use an additive containing one or more types of thallium compounds and cesium iodide as raw materials. That is, thallium-activated cesium iodide (CsI: Tl) is preferable because it has a broad emission wavelength from 400 nm to 750 nm.

  As the thallium compound as an additive containing one or more types of thallium compounds according to the present invention, various thallium compounds (compounds having oxidation numbers of + I and + III) can be used.

In the present invention, a preferable thallium compound is thallium bromide (TlBr), thallium chloride (TlCl), thallium fluoride (TlF, TlF ₃ ), or the like.

  The melting point of the thallium compound according to the present invention is preferably in the range of 400 to 700 ° C. If the temperature exceeds 700 ° C., the additives in the columnar crystals exist non-uniformly, resulting in a decrease in luminous efficiency. In the present invention, the melting point is a melting point at normal temperature and pressure.

  Moreover, it is preferable that the molecular weight of a thallium compound exists in the range of 206-300.

  In the scintillator layer of the present invention, the content of the additive is desirably an optimum amount according to the target performance and the like, but is 0.001 mol% to 50 mol% with respect to the content of cesium iodide, and further 0 It is preferable that it is 1-10.0 mol%.

  Here, when the additive is less than 0.001 mol% with respect to cesium iodide, the target light emission luminance cannot be obtained without much difference from the light emission luminance obtained by using cesium iodide alone. Moreover, when it exceeds 50 mol%, the property and function of cesium iodide cannot be maintained.

(Protective layer)
The protective layer according to the present invention focuses on protecting the scintillator layer. That is, cesium iodide (CsI) absorbs water vapor in the air and deliquesces when exposed to a high hygroscopic property, and therefore the main purpose is to prevent this.

  The protective layer can be formed using various materials. For example, a polyparaxylylene film is formed by a CVD method. That is, a polyparaxylylene film can be formed on the entire surface of the scintillator and the substrate to form a protective layer.

  Moreover, a polymer protective film can also be provided on a scintillator layer as a protective layer of another aspect.

  The thickness of the polymer protective film is preferably 12 μm or more and 60 μm or less, more preferably 20 μm in consideration of the formation of voids, scintillator (phosphor) layer protection, sharpness, moisture resistance, workability, and the like. As mentioned above, 40 micrometers or less are preferable. The haze ratio is preferably 3% or more and 40% or less, more preferably 3% or more and 10% or less in consideration of sharpness, radiation image unevenness, manufacturing stability, workability, and the like. A haze rate shows the value measured by Nippon Denshoku Industries Co., Ltd. NDH 5000W. The required haze ratio is appropriately selected from commercially available polymer films and can be easily obtained.

  The light transmittance of the protective film is preferably 70% or more at 550 nm in consideration of photoelectric conversion efficiency, scintillator emission wavelength, etc., but a film having a light transmittance of 99% or more is difficult to obtain industrially. Substantially 99% to 70% is preferable.

The moisture permeability of the protective film is preferably 50 g / m ² · day (40 ° C., 90% RH) (measured according to JIS Z0208) or less, more preferably 10 g / m, taking into account the protection and deliquescence properties of the scintillator layer. ² · day (40 ° C./90% RH) (measured according to JIS Z0208) or less is preferable, but a film with a water vapor transmission rate of 0.01 g / m ² · day (40 ° C./90% RH) or less is industrially used. Substantially 0.01 g / m ² · day (40 ° C, 90% RH) or more, 50 g / m ² · day (40 ° C, 90% RH) (measured according to JIS Z0208) The following are preferable, and more preferably 0.1 g / m ² · day (40 ° C. · 90% RH) or more and 10 g / m ² · day (40 ° C. · 90% RH) (measured according to JIS Z0208) or less.

(substrate)
When manufacturing the scintillator panel of the present invention, a wide variety of substrates can be used. That is, various glasses, polymer materials, metals, and the like that can transmit radiation such as X-rays can be used. For example, plate glass such as quartz, borosilicate glass, chemically tempered glass, sapphire, Ceramic substrates such as silicon nitride and silicon carbide, semiconductor substrates such as silicon, germanium, gallium arsenide, gallium phosphide, gallium nitrogen, cellulose acetate film, polyester film, polyethylene terephthalate film, polyamide film, polyimide film, triacetate film, polycarbonate A metal sheet such as a film, a polymer film (plastic film) such as a carbon fiber reinforced resin sheet, an aluminum sheet, an iron sheet, or a copper sheet, or a metal sheet having a coating layer of the metal oxide can be used. .

  In particular, a polymer film containing polyimide or polyethylene naphthalate is suitable when a columnar scintillator is formed by a vapor phase method using cesium iodide as a raw material. In particular, the substrate is preferably a flexible polymer film having a thickness of 50 to 500 μm.

Here, “a substrate having flexibility” means a substrate having an elastic modulus (E120) at 120 ° C. of 1000 to 6000 N / mm ² , and a polymer film containing polyimide or polyethylene naphthalate as such a substrate. Is preferred.

  Note that the “elastic modulus” means the slope of the stress with respect to the strain amount in a region where the strain indicated by the standard line of the sample conforming to JIS-C2318 and the corresponding stress have a linear relationship using a tensile tester. Is what we asked for. This is a value called Young's modulus, and in the present invention, this Young's modulus is defined as an elastic modulus.

Substrate used in the present invention, the elastic modulus at the 120 ° C. as described above (E120) is preferably a ^{1000N / mm 2 ~6000N / mm 2} . More preferably ^{1200N / mm 2 ~5000N / mm 2} .

Specifically, polyethylene naphthalate ^{(E120 = 4100N / mm 2)} , polyethylene terephthalate ^{(E120 = 1500N / mm 2)} , polybutylene naphthalate ^{(E120 = 1600N / mm 2)} , polycarbonate (E120 = 1700N / mm ²⁾ , Syndiotactic polystyrene (E120 = 2200 N / mm ² ), polyetherimide (E120 = 1900 N / mm ² ), polyarylate (E120 = 1700 N / mm ² ), polysulfone (E120 = 1800 N / mm ² ), polyethersulfone Examples thereof include a polymer film made of (E120 = 1700 N / mm ² ).

  These may be used singly or may be laminated or mixed. Among them, as a particularly preferable polymer film, a polymer film containing polyimide or polyethylene naphthalate is preferable as described above.

  In addition, when bonding the scintillator panel and the planar light receiving element surface, due to the influence of deformation of the substrate and warping during vapor deposition, it is not possible to obtain uniform image quality characteristics within the light receiving surface of the flat panel detector. By making the substrate into a polymer film having a thickness of 50 μm or more and 500 μm or less, the scintillator panel is deformed into a shape suitable for the shape of the planar light receiving element surface, and uniform sharpness is obtained over the entire light receiving surface of the flat panel detector. .

(Production method of scintillator panel)
A typical example of a method for manufacturing a scintillator panel of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of the radiation scintillator panel 10. FIG. 2 is an enlarged cross-sectional view of the radiation scintillator panel 10. FIG. 3 is a diagram showing a schematic configuration of the vapor deposition apparatus 61.

<Vapor deposition equipment>
As shown in FIG. 3, the vapor deposition apparatus 61 has a box-shaped vacuum vessel 62, and a vacuum vapor deposition boat 63 is disposed inside the vacuum vessel 62. The boat 63 is a member to be filled as an evaporation source, and an electrode is connected to the boat 63. When a current flows through the electrode to the boat 63, the boat 63 generates heat due to Joule heat. At the time of manufacturing the radiation scintillator panel 10, the boat 63 is filled with a mixture containing cesium iodide and an activator compound, and an electric current flows through the boat 63 so that the mixture can be heated and evaporated. It has become.

  As the member to be filled, an alumina crucible around which a heater is wound may be applied, or a refractory metal heater may be applied.

  A holder 64 for holding the substrate 1 is disposed inside the vacuum vessel 62 and immediately above the boat 63. The holder 64 is provided with a heater (not shown), and the substrate 1 mounted on the holder 64 can be heated by operating the heater. When the substrate 1 is heated, the adsorbate on the surface of the substrate 1 is removed or removed, and an impurity layer is formed between the substrate 1 and the scintillator layer (phosphor layer) 2 formed on the surface. Can be prevented, the adhesion between the substrate 1 and the scintillator layer 2 formed on the surface thereof can be strengthened, and the film quality of the scintillator layer 2 formed on the surface of the substrate 1 can be adjusted. It has become.

  The holder 64 is provided with a rotating mechanism 65 that rotates the holder 64. The rotating mechanism 65 is composed of a rotating shaft 65a connected to the holder 64 and a motor (not shown) as a driving source for the rotating shaft 65. When the motor is driven, the rotating shaft 65a rotates to displace the holder 64 in the boat. It can be rotated in a state of being opposed to 63.

  In the vapor deposition apparatus 61, in addition to the above configuration, a vacuum pump 66 is disposed in the vacuum container 62. The vacuum pump 66 exhausts the inside of the vacuum vessel 62 and introduces gas into the inside of the vacuum vessel 62. By operating the vacuum pump 66, the inside of the vacuum vessel 62 has a gas atmosphere at a constant pressure. Can be maintained below.

<Scintillator panel>
Next, a method for manufacturing the scintillator panel 10 according to the present invention will be described.

  In the manufacturing method of the said scintillator panel 10 for radiation, the evaporator 61 demonstrated above can be used suitably. A method for producing the radiation scintillator panel 10 using the evaporation device 61 will be described.

<Formation of reflective layer>
The reflective layer 3 is formed by applying and drying a composition obtained by dispersing and dissolving the above-described white pigment and binder resin in the organic solvent. The binder resin is preferably a hydrophobic resin such as a polyester resin or a polyurethane resin from the viewpoint of adhesiveness.

<Formation of scintillator layer>
The substrate 1 provided with the reflective layer 3 as described above is attached to the holder 64, and the boat 63 is filled with a powdery mixture containing cesium iodide and thallium iodide (preparation step). In this case, it is preferable that the distance between the boat 63 and the substrate 1 is set to 100 to 1500 mm, and the later-described vapor deposition process is performed within the set value range.

When the preparation process is completed, the vacuum pump 66 is operated to evacuate the inside of the vacuum vessel 62, and the inside of the vacuum vessel 62 is brought to a vacuum atmosphere of 0.1 Pa or less (vacuum atmosphere forming step). Here, “under vacuum atmosphere” means under a pressure atmosphere of 100 Pa or less, and preferably under a pressure atmosphere of 0.1 Pa or less.
afterwards. An inert gas such as argon is introduced into the vacuum vessel 62, and the inside of the vacuum vessel 62 is maintained in a vacuum atmosphere of 0.1 Pa or less. Next, the heater of the holder 64 and the motor of the rotation mechanism 65 are driven, and the substrate 1 attached to the holder 64 is rotated while being heated while facing the boat 63.

  In this state, a current is passed from the electrode to the boat 63, and the mixture containing cesium iodide and thallium iodide is heated at about 700 ° C. to 800 ° C. for a predetermined time to evaporate the mixture. As a result, innumerable columnar crystals 2a are sequentially grown on the surface of the substrate 1 to form a scintillator layer 2 having a desired thickness (evaporation process). Thereby, the scintillator panel 10 for radiation which concerns on this invention can be manufactured.

(Radiation image detector)
The configuration of the radiation image detector 100 including the radiation scintillator plate 10 will be described below as an application example of the radiation scintillator panel 10 with reference to FIGS. 4 and 5. FIG. 4 is a partially broken perspective view showing a schematic configuration of the radiation image detector 100. FIG. 5 is an enlarged cross-sectional view of the imaging panel 51.

  As shown in FIG. 4, the radiation image detector 100 includes an imaging panel 51, a control unit 52 that controls the operation of the radiation image detector 100, a rewritable dedicated memory (for example, a flash memory), and the like. A memory unit 53 that is a storage unit that stores the output image signal, a power supply unit 54 that is a power supply unit that supplies power necessary to obtain the image signal by driving the imaging panel 51, and the like 55 is provided inside. The housing 55 has a communication connector 56 for performing communication from the radiation image detector 100 to the outside as needed, an operation unit 57 for switching the operation of the radiation image detector 100, and completion of preparation for radiographic image capturing. In addition, a display unit 58 indicating that a predetermined amount of image signal has been written in the memory unit 53 is provided.

  Here, if the radiation image detector 100 is provided with the power supply unit 54 and the memory unit 53 for storing the image signal of the radiation image, and the radiation image detector 100 is detachable via the connector 56, the radiation image detector is provided. It can be set as the portable structure which can carry 100.

  As shown in FIG. 5, the imaging panel 51 includes a radiation scintillator panel 10 and an output substrate 20 that absorbs electromagnetic waves from the radiation scintillator panel 10 and outputs an image signal.

  The radiation scintillator panel 10 is disposed on the radiation irradiation surface side, and is configured to emit an electromagnetic wave corresponding to the intensity of incident radiation.

  The output substrate 20 is provided on the surface opposite to the radiation irradiation surface of the radiation scintillator panel 10, and in order from the radiation scintillator panel 10 side, the diaphragm 20a, the photoelectric conversion element 20b, the image signal output layer 20c, and the substrate 20d. It has.

  The diaphragm 20a is used to separate the radiation scintillator panel 10 from other layers.

  The photoelectric conversion element 20 b includes a transparent electrode 21, a charge generation layer 22 that is excited by electromagnetic waves that have passed through the transparent electrode 21 to enter the light, and generates a charge, and a counter electrode 23 that is a counter electrode for the transparent electrode 21. The transparent electrode 21, the charge generation layer 22, and the counter electrode 23 are arranged in this order from the diaphragm 20a side.

The transparent electrode 21 is an electrode that transmits an electromagnetic wave that is photoelectrically converted, and is formed using a conductive transparent material such as indium tin oxide (ITO), SnO ₂ , or ZnO.

  The charge generation layer 22 is formed in a thin film on one surface side of the transparent electrode 21 and contains an organic compound that separates charges by light as a compound capable of photoelectric conversion. Each of them contains a conductive compound as an electron acceptor. In the charge generation layer 22, when an electromagnetic wave is incident, the electron donor is excited to emit electrons, and the emitted electrons move to the electron acceptor, and charge, that is, holes in the charge generation layer 22. And electron carriers are generated.

  Here, examples of the conductive compound as the electron donor include a p-type conductive polymer compound. Examples of the p-type conductive polymer compound include polyphenylene vinylene, polythiophene, poly (thiophene vinylene), polyacetylene, polypyrrole, Those having a basic skeleton of polyfluorene, poly (p-phenylene) or polyaniline are preferred.

  Examples of the conductive compound as the electron acceptor include an n-type conductive polymer compound. As the n-type conductive polymer compound, those having a basic skeleton of polypyridine are preferable, and in particular, poly (p-pyridyl) Those having a basic skeleton of vinylene) are preferred.

  The film thickness of the charge generation layer 22 is preferably 10 nm or more (especially 100 nm or more) from the viewpoint of securing the amount of light absorption, and is preferably 1 μm or less (particularly 300 nm or less) from the viewpoint that the electric resistance does not become too large. .

  The counter electrode 23 is disposed on the side opposite to the surface on the side where the electromagnetic wave of the charge generation layer 22 is incident. The counter electrode 23 can be selected and used from, for example, a general metal electrode such as gold, silver, aluminum, and chromium, or the transparent electrode 21. Small (4.5 eV or less) metals, alloys, electrically conductive compounds and mixtures thereof are preferably used as electrode materials.

  In addition, a buffer layer may be provided between each electrode (transparent electrode 21 and counter electrode 23) sandwiching the charge generation layer 22 so as to act as a buffer zone so that the charge generation layer 22 and these electrodes do not react. Good. Examples of the buffer layer include lithium fluoride and poly (3,4-ethylenedioxythiophene): poly (4-styrenesulfonate), 2,9-dimethyl-4,7-diphenyl [1,10] phenanthroline. Formed using.

  The image signal output layer 20c performs accumulation of charges obtained by the photoelectric conversion element 20b and output of a signal based on the accumulated charges. Charge for accumulating the charges generated by the photoelectric conversion element 20b for each pixel. The capacitor 24 is a storage element, and the transistor 25 is an image signal output element that outputs the stored charge as a signal.

  As the transistor 25, for example, a TFT (Thin Film Transistor) is used. This TFT may be an inorganic semiconductor type used in a liquid crystal display or the like, or an organic semiconductor, and is preferably a TFT formed on a plastic film. As the TFT formed on the plastic film, an amorphous silicon type is known, but in addition, it was manufactured by FSA (Fluidic Self Assembly) technology developed by Alien Technology of the United States, that is, made of single crystal silicon. A TFT may be formed on a flexible plastic film by arranging micro CMOS (Nanoblocks) on an embossed plastic film. Furthermore, Science, 283, 822 (1999) and Appl. Phys. A TFT using an organic semiconductor as described in documents such as Lett, 771488 (1998), Nature, 403, 521 (2000) may be used.

  Thus, as the transistor 25 used in the present invention, a TFT manufactured by the FSA technique and a TFT using an organic semiconductor are preferable, and a TFT using an organic semiconductor is particularly preferable. If a TFT is formed using this organic semiconductor, equipment such as a vacuum deposition apparatus is not required as in the case where a TFT is formed using silicon, and the TFT can be formed by utilizing printing technology or inkjet technology. Cost is low. Furthermore, since the processing temperature can be lowered, it can also be formed on a plastic substrate that is vulnerable to heat.

  The transistor 25 accumulates electric charges generated in the photoelectric conversion element 20 b and is electrically connected to a collection electrode (not shown) that serves as one electrode of the capacitor 24. The capacitor 24 accumulates charges generated by the photoelectric conversion element 20 b and reads the accumulated charges by driving the transistor 25. That is, by driving the transistor 25, a signal for each pixel of the radiation image can be output.

  The substrate 20d functions as a support for the imaging panel 51, and can be made of the same material as the substrate 1.

  Next, the operation of the radiation image detector 100 will be described.

  First, the radiation incident on the radiation image detector 100 is incident from the radiation scintillator panel 10 side of the imaging panel 51 toward the substrate 20d.

  Then, the radiation incident on the radiation scintillator panel 10 is absorbed by the scintillator layer 2 in the radiation scintillator panel 10 and emits electromagnetic waves corresponding to the intensity thereof. Of the emitted electromagnetic wave, the electromagnetic wave incident on the output substrate 20 passes through the diaphragm 20 a and the transparent electrode 21 of the output substrate 20 and reaches the charge generation layer 22. Then, the electromagnetic wave is absorbed in the charge generation layer 22 and a hole-electron pair (charge separation state) is formed according to the intensity.

  Thereafter, the generated charges are transported to different electrodes (transparent electrode film and conductive layer) by the internal electric field generated by the application of a bias voltage by the power supply unit 54, and a photocurrent flows.

  Thereafter, the holes carried to the counter electrode 23 side are accumulated in the capacitor 24 of the image signal output layer 20c. The accumulated holes output an image signal when the transistor 25 connected to the capacitor 24 is driven, and the output image signal is stored in the memory unit 53.

  According to the radiation image detector 100 described above, since the radiation scintillator panel 10 is provided, the photoelectric conversion efficiency can be increased, the SN ratio at the time of low-dose imaging in the radiation image can be improved, and image unevenness and Generation of linear noise can be prevented.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

Example 1
(Preparation of reflection layer sample 1)
A reflective layer sample 1 was prepared on a 125 μm-thick polyimide film (UPILEX-125S manufactured by Ube Industries) by the following procedure.

  After adding 40 parts by mass of rutile titanium dioxide having an average particle size of 0.2 μm, 10 parts by mass of a polyester resin (Byron 630: manufactured by Toyobo Co., Ltd.), 25 parts by mass of toluene and 25 parts by mass of methyl ethyl ketone (MEK) were added as a solvent, and then a sand mill The coating for the reflective layer was prepared by dispersing with The coating material for the reflective layer was coated on a polyimide film substrate having a width of 500 mm with a micro gravure coater, dried, and then subjected to a total load of 2000 kg, an upper roll temperature of 40 ° C., a lower roll temperature of 40 ° C., and a speed of 0 using a calender device. Compressed at 1 m / min. Thereby, the surface property of the light reflection layer was improved, and a reflection layer sample 1 having the thickness shown in Table 1 was produced.

(Production of reflection layer samples 2 to 10)
In the same manner as in the reflective layer sample 1, a white pigment and a reflective layer coating material having an average particle diameter changed as shown in Table 1 were prepared, and this coating material was applied onto the polyimide film substrate in the same manner as in the reflective layer sample 1. After drying, calendering was performed to prepare reflective layer samples 2 to 10 having the thicknesses shown in Table 1.

(Preparation of reflective layer sample 11)
A reflective layer sample 11 was produced in the same manner as the reflective layer sample 1 except that the substrate was an aluminum plate having a thickness of 300 μm.

(Preparation of reflection layer sample 12)
After drying, a reflective layer sample 12 was produced in the same manner as the reflective layer sample 1 except that the calendar apparatus was not used.

(Preparation of reflective layer sample 13)
Reflective layer sample 1 except that a 125 μm thick polyimide film (UPILEX-125S manufactured by Ube Industries) was sputtered with aluminum to form a reflective layer (0.10 μm), and then a reflective layer coating containing no titanium dioxide was used. In the same manner, a reflective layer sample 13 having the thickness shown in Table 1 was produced on the reflective layer.

(Formation of scintillator layer)
A scintillator phosphor (CsI: TlI (0.3 mol%)) is vapor-deposited using the vapor deposition apparatus shown in FIG. 3 on the reflective layer side of the substrate on which the above-described reflective layer samples 1 to 13 are formed. Each layer was formed.

  That is, first, the resistance heating crucible was filled with the phosphor raw material as a vapor deposition material, and the support was placed on a rotating support holder, and the distance between the support and the evaporation source was adjusted to 400 mm.

  Subsequently, the inside of the vapor deposition apparatus was once evacuated, Ar gas was introduced and the degree of vacuum was adjusted to 0.5 Pa, and then the substrate temperature was maintained at 150 ° C. while rotating the support at a speed of 10 rpm. Subsequently, the resistance heating crucible was heated to deposit a phosphor, and when the scintillator layer had a thickness of 500 μm, the deposition was terminated to obtain a scintillator panel (radiation image conversion panel) shown in Table 1.

  In Table 1, the scintillator panel No. 11 is a base material of aluminum.

<Evaluation>
After sealing each obtained sample, set it to a CMOS flat panel (X-ray CMOS camera system Shad-o-Box4KEV manufactured by Radicon), and measure the sharpness from the 12-bit output data by the following method. Evaluation was performed by the following method.

  A sponge sheet was placed on the radiation incident side (the side without the phosphor) of the carbon plate of the radiation incident window and the scintillator panel, and both were fixed by lightly pressing the plane light receiving element surface and the scintillator panel.

<Evaluation method of sharpness>
X-rays having a tube voltage of 80 kVp were irradiated from the back surface (surface on which the scintillator layer was not formed) of each sample through a lead MTF chart, and image data was detected by a CMOS flat panel on which the scintillator was arranged and recorded on a hard disk. Thereafter, the recording on the hard disk was analyzed by a computer, and the modulation transfer function MTF (MTF value at a spatial frequency of 1 cycle / mm) of the X-ray image recorded on the hard disk was used as an index of sharpness. In the table, the higher the MTF value, the better the sharpness. MTF is an abbreviation for Modulation Transfer Function.

  The evaluation results are shown in Table 1.

  As is clear from the results shown in Table 1, it can be seen that the examples according to the present invention are superior in sharpness as compared with the comparative examples.

Sectional drawing which shows schematic structure of scintillator panel 10 for radiation Expanded sectional view of radiation scintillator panel 10 The figure which shows schematic structure of the vapor deposition apparatus 61 Partially broken perspective view showing a schematic configuration of the radiation image detector 100 Enlarged sectional view of the imaging panel 51

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Scintillator (phosphor) layer 3 Reflective layer 10 Radiation scintillator panel 61 Vapor deposition device 62 Vacuum vessel 63 Boat (filled member)
64 Holder 65 Rotating mechanism 66 Vacuum pump 100 Radiation image detector

Claims (9)

A scintillator panel having a reflective layer and a scintillator layer formed by vapor deposition on a substrate, wherein the reflective layer comprises a white pigment and a binder resin. The scintillator panel according to claim 1, wherein the surface of the reflective layer is smoothed by a calendar process. The scintillator panel according to claim 1 or 2, wherein the white pigment is at least one white pigment selected from alumina, yttrium oxide, zirconium oxide, and titanium oxide. The scintillator panel according to claim 3, wherein the white pigment is a white pigment having an average particle diameter of 0.1 to 3.0 μm. The scintillator panel according to claim 4, wherein the white pigment having an average particle diameter of 0.1 to 3.0 μm is titanium dioxide. The scintillator panel according to any one of claims 1 to 5, wherein the substrate is made of a flexible polymer film having a thickness of 50 µm to 500 µm. The scintillator panel according to claim 6, wherein the polymer film is a polyimide (PI) or polyethylene naphthalate (PEN) film. The scintillator panel according to any one of claims 1 to 7, wherein the scintillator layer is formed by a vapor phase method using an additive containing cesium iodide and at least one kind of thallium as a raw material. The scintillator panel according to claim 1, wherein the reflective layer has a thickness of 0.2 to 3.0 μm.

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