JP2005294680A - Optical conductive layer for constituting radiant-ray photographing panel, and same panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make out of a highly sensible optical conductive material having a small environmental load an optical conductive layer for constituting a radiant-ray photographing panel which records a radiant-ray image information as an electrostatic latent image. <P>SOLUTION: The optical conductive layer is the one for constituting a radiant-ray photographing panel which records a radiant-ray image information as an electrostatic latent image, and it is made of Bi<SB>2</SB>Ti<SB>2</SB>O<SB>7</SB>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radiation imaging panel suitable for application to a radiation imaging apparatus such as an X-ray, and more particularly to a photoconductive layer constituting the radiation imaging panel.

  Conventionally, in medical X-ray photography, a photoconductive layer sensitive to X-rays has been used as a photoconductor to reduce the exposure dose received by subjects and improve diagnostic performance. An X-ray imaging panel that reads and records a recorded electrostatic latent image with light or multiple electrodes is known. These are superior in that the resolution is higher than the indirect photographing method using a TV image pickup tube which is a well-known photographing method.

The X-ray imaging panel described above generates charges corresponding to X-ray energy by irradiating the charge generation layer provided in the imaging panel with X-rays, and reads the generated charges as an electrical signal. The photoconductive layer functions as a charge generation layer. Conventionally, materials such as amorphous selenium (a-Se), PbI ₂ , HgI ₂ , and Cd (Zn) Te have been used for this photoconductive layer (Patent Documents 1 and 2).

However, among the radiation conductive materials described in Patent Documents 1 and 2, amorphous selenium is inferior in radiation absorption efficiency, so it is necessary to increase the thickness of the film and to apply a high electric field. There is. PbI ₂ , HgI ₂ , and Cd (Zn) Te have a problem that the dark current is high and the S / N ratio is poor.

From such a viewpoint, for example, Patent Document 3 describes BiI ₃ as a radiation conductive material that replaces these. BiI ₃ has an advantage that the environmental load is small. However, when formed by a coating method, the effect of collecting generated charges is low and the electric noise is increased, so that the graininess of the image is deteriorated. is there. Further, ZnO described in Patent Document 2 also has an advantage that the environmental load is small, but there is a problem that sensitivity is low because radiation absorption efficiency is inferior.
JP 2000-105297 A JP-A-11-211832 JP 2001-221894 A

  None of the above photoconductive materials can be said to be sufficiently satisfactory in terms of radiation absorption efficiency, trapping effect of generated charges, dark current, and environmental load.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a photoconductive layer made of a novel conductive material having high sensitivity and low environmental load, and a radiation imaging panel including the photoconductive layer. It is what.

The photoconductive layer of the present invention is a photoconductive layer constituting a radiation imaging panel for recording radiographic image information as an electrostatic latent image, and the photoconductive layer is made of Bi ₂ Ti ₂ O _7. Is.

  The photoconductive layer may be a layer containing a binder provided by coating, or may be a layer containing no binder such as a sintered film.

The radiation imaging panel of the present invention includes a photoconductive layer made of Bi ₄ MO _{12 that} records radiation image information as an electrostatic latent image.

The photoconductive layer of the present invention is a photoconductive layer constituting a radiation imaging panel that records radiation image information as an electrostatic latent image, and since this photoconductive layer is made of Bi ₂ Ti ₂ O ₇ , The collection effect can be increased and the sensitivity can be improved. In addition, since electric noise can be reduced, an image with good graininess can be obtained. In addition, the photoconductive layer made of Bi ₂ Ti ₂ O ₇ is advantageous in that it has excellent durability, is not toxic, and has a low environmental load.

In particular, BiI _{3 and the} like, which are conventionally known as photoconductive materials, have a problem that when formed by a coating method, the effect of collecting generated charges is low due to carbonization of the impurities of the binder, and the graininess of the image is poor However, in the photoconductive layer made of Bi ₂ Ti ₂ O _{7 of} the present invention, the sensitivity can be increased even if it is formed by a coating method. In addition, since the photoconductive layer by the coating method can be manufactured at low cost, the manufacturing cost of the radiation imaging panel can be reduced.

On the other hand, when the photoconductive layer made of Bi ₂ Ti ₂ O ₇ and sintered membrane, it is possible to increase the filling factor of Bi ₂ Ti ₂ O _7, therefore, the photoconductive layer becomes dense layer, The X-ray absorption rate can be improved, and the effect of collecting generated charges can be increased to greatly improve the sensitivity.

The photoconductive layer made of Bi ₂ Ti ₂ O _{7 of the} present invention can be formed first by a coating method. Specifically, for example, Bi ₂ O ₃ and TiO ₂ are mixed and stoichiometrically mixed and fired to obtain Bi ₂ Ti ₂ O ₇ powder, and this Bi ₂ Ti ₂ O ₇ powder is mixed with a binder to support it. It can be applied to the body and dried after application to form a photoconductive layer made of Bi ₂ Ti ₂ O ₇ .

Further, Bi nitrate, acetate or alkoxide as Bi source is reacted with ammonium titanate or Ti alkoxide (eg, titanium tetraisopropoxide) as Ti source, and Bi _{2 is obtained by} hydrothermal reaction or baking reaction. A Ti ₂ O ₇ powder can be obtained, and this Bi ₂ Ti ₂ O ₇ powder can be mixed with a binder, applied to a support, and dried after application to form a photoconductive layer made of Bi ₂ Ti ₂ O _7. .

  As the binder, known binders can be used. For example, nitrocellulose, ethyl cellulose, cellulose acetate, vinylidene chloride / vinyl chloride copolymer, polyalkyl methacrylate, polyurethane, polyvinyl butyral, polyester, polythylene, polyamide, polyethylene, polychlorinated Vinyl, polyvinyl acetate, vinyl chloride / vinyl acetate copolymer, cellulose acetate, polyvinyl alcohol, linear polyester, nylon, carboxymethyl cellulose and the like can be preferably used.

The photoconductive layer made of Bi ₂ Ti ₂ O _{7 of the} present invention can be secondly formed as a sintered film. Specifically, Bi ₂ O ₃ and TiO ₂ described above are mixed at stoichiometric ratio and fired to obtain Bi ₂ Ti ₂ O ₇ powder (or Bi nitrate, acetate or alkoxide as Bi source, Reaction with ammonium salt of titanate or Ti alkoxide as Ti source, and Bi ₂ Ti ₂ O ₇ powder is obtained by hydrothermal reaction or baking reaction), and this Bi ₄ M ₃ O ₁₂ powder is carrier gas in vacuum in rolled up, the Bi ₂ Ti ₂ O ₇ powder of mixed carrier gas and the blowing to a support in a vacuum Bi ₂ Ti ₂ O ₇ powder aerosol deposition method of depositing (AD method), the Bi ₂ The Ti ₂ O ₇ powder is formed into a film by pressing at a high pressure using a press machine, and the above-mentioned Bi ₂ Ti ₂ O ₇ powder is applied using a binder, and the resulting film is sintered. Green sheet (binder And a known method such as a method of baking the green sheet to remove the binder and sinter the powder (hereinafter referred to as the green sheet method).

  In the green sheet method, a binder is used. Preferred examples of the binder include cellulose acetate, polyalkyl methacrylate, polyvinyl alcohol, and polyvinyl butyral.

  In the radiation imaging panel, a direct conversion method in which radiation is directly converted into charges and stored, and radiation is converted into light once by a scintillator such as CsI, and the light is converted into charges by an a-Si photodiode and stored. Although there is an indirect conversion method, the photoconductive layer of the present invention is used for the former direct conversion method. In addition to X-rays, γ rays, α rays, etc. can be used as radiation.

  In addition, the photoconductive layer of the present invention accumulates charges generated by radiation irradiation in a so-called optical reading system that reads by a radiation image detector using a semiconductor material that generates charges by light irradiation. It can also be used for a method (hereinafter referred to as “TFT method”) in which the charges are read by turning on and off an electrical switch such as a thin film transistor (TFT) one pixel at a time.

  First, a radiation imaging panel used for the former optical reading method will be described as an example. FIG. 1 is a sectional view showing an embodiment of a radiation imaging panel having a photoconductive layer according to the present invention.

  The radiation imaging panel 10 includes a first conductive layer 1 that is transparent to a recording radiation L1, which will be described later, and a recording radiation that exhibits conductivity when irradiated with the radiation L1 transmitted through the conductive layer 1. The conductive layer 2 and the charge charged on the conductive layer 1 (latent image polar charge; for example, negative charge) act as an insulator and have a charge opposite to the charge (transport polar charge; in the above example) Is a positive charge), a charge transport layer 3 acting as a substantially conductive material, a read photoconductive layer 4 that exhibits conductivity when irradiated with a read light L2 for reading, which will be described later, and a light-transmitting electromagnetic wave L2. The second conductive layer 5 having the property is laminated in this order.

  Here, as the conductive layers 1 and 5, for example, a transparent glass plate in which a conductive substance is uniformly applied (nesa film or the like) is suitable. As the charge transport layer 3, the larger the difference between the mobility of the negative charge charged in the conductive layer 1 and the mobility of the positive charge having the opposite polarity, the better, poly N-vinylcarbazole (PVK), N, N Organic compounds such as' -diphenyl-N, N'-bis (3-methylphenyl)-[1,1'-biphenyl] -4,4'-diamine (TPD) and discotic liquid crystals, or TPD polymers ( Polycarbonate, polystyrene, PVK) dispersion, semiconductor materials such as a-Se doped with 10 to 200 ppm of Cl are suitable. In particular, organic compounds (PVK, TPD, discotic liquid crystal, etc.) are preferable because they have light insensitivity, and since the dielectric constant is generally small, the capacitance of the charge transport layer 3 and the photoconductive layer 4 for reading is reduced, and thus reading is performed. The signal extraction efficiency can be increased.

  The reading photoconductive layer 4 includes a-Se, Se-Te, Se-As-Te, metal-free phthalocyanine, metal phthalocyanine, MgPc (Magnesium phtalocyanine), VoPc (phase II of Vanadyl phthalocyanine), CuPc (Cupper phtalocyanine), and the like. Among them, a photoconductive material mainly containing at least one of them is preferable.

For the recording radiation conductive layer 2, a photoconductive layer made of Bi ₂ Ti ₂ O ₇ of the present invention is used. That is, the photoconductive layer of the present invention is a recording radiation conductive layer.

  Next, a system that uses light to read an electrostatic latent image will be briefly described. FIG. 2 is a schematic configuration diagram of a recording / reading system using the radiation imaging panel 10 (integrated electrostatic latent image recording device and electrostatic latent image reading device). This recording / reading system comprises a radiation imaging panel 10, a recording irradiation means 90, a power source 50, a current detection means 70, a reading exposure means 92, and connection means S1, S2. The panel 10, the power supply 50, the recording irradiation means 90, and the connection means S 1, and the electrostatic latent image reading device portion includes the radiation imaging panel 10, the current detection means 70, and the connection means S 2.

  The conductive layer 1 of the radiation imaging panel 10 is connected to the negative electrode of the power source 50 through the connection means S1, and is also connected to one end of the connection means S2. One end of the connection means S2 is connected to the current detection means 70, and the conductive layer 5 of the radiation imaging panel 10, the positive electrode of the power supply 50, and the other end of the connection means S2 are grounded. The current detection means 70 includes a detection amplifier 70a made of an operational amplifier and a feedback resistor 70b, and constitutes a so-called current-voltage conversion circuit.

  A subject 9 is disposed on the upper surface of the conductive layer 1, and the subject 9 has a portion 9a that is transparent to the radiation L1 and a blocking portion (light-shielding portion) 9b that is not transparent. The recording irradiation means 90 uniformly exposes the radiation L1 to the subject 9, and the reading exposure means 92 scans and exposes the reading light L2 such as infrared laser light, LED or EL in the direction of the arrow in FIG. Therefore, it is desirable that the reading light L2 has a beam shape converged to a small diameter.

  Hereinafter, an electrostatic latent image recording process in the recording / reading system having the above configuration will be described with reference to a charge model (FIG. 3). In FIG. 2, the connection means S2 is opened (not connected to either the ground or current detection means 70), the connection means S1 is turned on, and the DC voltage Ed from the power source 50 is applied between the conductive layer 1 and the conductive layer 5. Then, a negative charge is applied to the conductive layer 1 and a positive charge is applied to the conductive layer 5 from the power source 50 (see FIG. 3A). Thereby, a parallel electric field is formed between the conductive layers 1 and 5 in the radiation imaging panel 10.

  Next, the radiation L1 is uniformly irradiated toward the subject 9 from the recording irradiation means 90. The radiation L1 passes through the transmission part 9a of the subject 9, and further passes through the conductive layer 1. The radiation conductive layer 2 receives the transmitted radiation L1 and exhibits conductivity. This is understood by acting as a variable resistor that shows a variable resistance value according to the dose of radiation L1, and the resistance value is caused by the generation of a charge pair of electrons (negative charge) and holes (positive charge) by radiation L1. The resistance value is large if the dose of the radiation L1 transmitted through the subject 9 is small (see FIG. 3B). The negative charge (−) and the positive charge (+) generated by the radiation L1 are represented by enclosing − or + in circles in the drawing.

  The positive charge generated in the radiation conductive layer 2 moves at high speed in the radiation conductive layer 2 toward the conductive layer 1, and the negative charge is charged in the conductive layer 1 at the interface between the conductive layer 1 and the radiation conductive layer 2. And disappear due to charge recombination (see FIGS. 3C and 3D). On the other hand, the negative charges generated in the radiation conductive layer 2 move in the radiation conductive layer 2 toward the charge transfer layer 3. Since the charge transfer layer 3 acts as an insulator for charges having the same polarity as the charges charged in the conductive layer 1 (in this example, negative charges), the negative charges that have moved through the radiation conductive layer 2 are radiation. It stops at the interface between the conductive layer 2 and the charge transfer layer 3 and accumulates at this interface (see FIGS. 3C and 3D). The amount of charge accumulated is determined by the amount of negative charge generated in the radiation conductive layer 2, that is, the dose of radiation L1 transmitted through the subject 9.

  On the other hand, since the radiation L1 does not pass through the light shielding part 9b of the subject 9, no change occurs in the portion corresponding to the lower part of the light shielding part 9b of the radiation imaging panel 10 (see FIGS. 3B to 3D). In this way, by exposing the subject 9 to the radiation L1, charges corresponding to the subject image can be accumulated at the interface between the radiation conductive layer 2 and the charge transfer layer 3. The subject image based on the accumulated charges is called an electrostatic latent image.

  Next, an electrostatic latent image reading process will be described with reference to a charge model (FIG. 4). The connection means S1 is opened to stop the power supply, and S2 is temporarily connected to the ground side, and the conductive layers 1 and 5 of the radiation imaging panel 10 on which the electrostatic latent image is recorded are charged to the same potential to recharge the charge. After the arrangement (see FIG. 4A), the connection means S2 is connected to the current detection means 70 side.

  When the reading light L2 is scanned and exposed to the conductive layer 5 side of the radiation imaging panel 10 by the reading exposure means 92, the reading light L2 passes through the conductive layer 5, and the photoconductive layer 4 irradiated with the transmitted reading light L2 is Conductivity is exhibited according to scanning exposure. This is dependent on the fact that the radiation conductive layer 2 is irradiated with the radiation L1 to generate positive and negative charge pairs, and has a positive and negative charge pair upon irradiation with the reading light L2. (See FIG. 4B). As in the recording process, negative charges (−) and positive charges (+) generated by the reading light L2 are represented by enclosing − or + in circles in the drawing.

  Since the charge transport layer 3 acts as a conductor for positive charges, the positive charge generated in the photoconductive layer 4 rapidly moves in the charge transport layer 3 so as to be attracted to the accumulated charges, The accumulated charge and charge recombination disappear at the interface between the radiation conductive layer 2 and the charge transport layer 3 (see FIG. 4C). On the other hand, the negative charge generated in the photoconductive layer 4 disappears by recombining with the positive charge of the conductive layer 5 (see FIG. 4C). The photoconductive layer 4 is scanned and exposed with a sufficient amount of light by the reading light L2, and the accumulated charges accumulated at the interface between the radiation conductive layer 2 and the charge transport layer 3, that is, the electrostatic latent image are all recombined. Will be extinguished. Thus, the disappearance of the charges accumulated in the radiation imaging panel 10 means that the current I has flowed through the radiation imaging panel 10 due to the movement of charges, and this state is the radiation imaging panel 10. Can be expressed by an equivalent circuit as shown in FIG. 4D, in which the current amount is expressed by a current source whose amount depends on the accumulated charge amount.

  In this way, by detecting the current flowing out from the radiation imaging panel 10 while scanning and exposing the reading light L2, it is possible to sequentially read the accumulated charge amount of each scanning-exposed part (corresponding to the pixel). The electrostatic latent image can be read. The operation of the radiation detection unit is described in Japanese Patent Application Laid-Open No. 2000-105297.

  Next, the latter TFT type radiation imaging panel will be described. This radiation imaging panel has a structure in which a radiation detection unit 100 and an active matrix array substrate (hereinafter referred to as an AMA substrate) 200 are joined as shown in FIG. As shown in FIG. 6, the radiation detection unit 100 is roughly divided into a common electrode 103 for applying a bias voltage and light that generates carriers that are electron-hole pairs in response to the radiation to be detected in order from the radiation incident side. The conductive layer 104 and the detection electrode 107 for collecting carriers are stacked. The upper layer of the common electrode may have a radiation detection unit support.

The photoconductive layer 104 is a photoconductive layer made of Bi ₂ Ti ₂ O ₇ of the present invention. The common electrode 103 and the detection electrode 107 are made of a conductive material such as ITO (indium tin oxide), Au, or Pt, for example. Depending on the polarity of the bias voltage, a hole injection blocking layer and an electron injection blocking layer may be attached to the common electrode 103 and the detection electrode 107.

  The configuration of each part of the AMA substrate 200 will be briefly described. As shown in FIG. 7, the AMA substrate 200 is provided with a capacitor 210 as a charge storage capacitor and a TFT 220 as a switching element for each of the radiation detection portions 105 corresponding to pixels. In the support 102, the radiation detection units 105 corresponding to the pixels are two-dimensionally arranged in a matrix configuration of about 1000 to 3000 × 1000 to 3000 in accordance with the required pixels, and the AMA substrate 200 also has pixels. The same number of capacitors 210 and TFTs 220 are two-dimensionally arranged in the same matrix configuration. The electric charge generated in the photoconductive layer is accumulated in the capacitor 210 and becomes an electrostatic latent image corresponding to the optical reading method. In the TFT method of the present invention, an electrostatic latent image generated by radiation is held in a charge storage capacitor.

  Specific configurations of the capacitor 210 and the TFT 220 in the AMA substrate 200 are as shown in FIG. That is, the AMA substrate support 230 is an insulator, and the connection side electrode 210b of the capacitor 210 and the TFT 220 are formed on the ground electrode 210a of the capacitor 210 and the gate electrode 220a of the TFT 220 formed on the surface thereof via the insulating film 240. In addition to the source electrode 220b and the drain electrode 220c being stacked, the outermost surface side is covered with a protective insulating film 250. Further, the connection side electrode 210b and the source electrode 220b are connected to each other and are formed simultaneously. As the insulating film 240 constituting both the capacitor insulating film of the capacitor 210 and the gate insulating film of the TFT 220, for example, a plasma SiN film is used. The AMA substrate 200 is manufactured by using a thin film forming technique or a fine processing technique used for manufacturing a liquid crystal display substrate.

  Subsequently, the joining of the radiation detection unit 100 and the AMA substrate 200 will be described. With the detection electrode 107 and the connection side electrode 210b of the capacitor 210 aligned, both substrates 100 and 200 are made of anisotropic conductive film (ACF) containing conductive particles such as silver particles and having conductivity only in the thickness direction. The substrates 100 and 200 are mechanically combined by heating and pressurizing and bonding together, and at the same time, the detection electrode 107 and the connection side electrode 210b are electrically connected by the interposition conductor 140. .

  Further, the AMA substrate 200 is provided with a read drive circuit 260 and a gate drive circuit 270. As shown in FIG. 7, the read drive circuit 260 is connected to a read wiring (read address line) 280 in the vertical (Y) direction that connects the drain electrodes of the TFTs 220 having the same column, and the gate drive circuit 270 has a row. A horizontal (X) direction read line (gate address line) 290 connecting the gate electrodes of the same TFT 220 is connected. Although not shown, one preamplifier (charge-voltage converter) is connected to one readout wiring 280 in the readout drive circuit 260. As described above, the read driving circuit 260 and the gate driving circuit 270 are connected to the AMA substrate 200. However, an integrated circuit in which the read drive circuit 260 and the gate drive circuit 270 are integrally formed in the AMA substrate 200 is also used.

The radiation detection operation by the radiation imaging apparatus in which the radiation detector 100 and the AMA substrate 200 are joined and combined is described in, for example, Japanese Patent Application Laid-Open No. 11-287862.
Examples of the photoconductive layer constituting the radiation imaging panel of the present invention are shown below.

(Example 1)
Bi (NO) ₃ powder · 5H ₂ O was dissolved in a 10% nitric acid solution to prepare a 0.2M aqueous solution (hereinafter, this aqueous solution is referred to as a B-1 solution). Titanium peroxosodium citrate tetrahydrate (manufactured by Furuuchi Chemical Co., Ltd .: TAS-Fine) was dissolved in water to prepare a 0.2 M aqueous solution (hereinafter, this aqueous solution is referred to as T-1 solution). The B-1 solution and the T-1 solution were mixed at a ratio of 1: 1, and a 28% aqueous ammonia solution was added with stirring to obtain a white precipitate. The washing operation of washing with water and discarding the supernatant was repeated five times by centrifugation, and then recovered and dried. This powder was dispersed in water and aged in a PRR pressure vessel Parr Acid Digestion Bombs at 180 ° C. for 48 hours to obtain Bi ₂ Ti ₂ O ₇ powder particles having an average particle diameter of about 1 μm. When the crystal phase of the obtained Bi ₂ Ti ₂ O ₇ powder particles was confirmed with an X-ray analyzer (RINT-ULTIMA +: manufactured by Rigaku Corporation), it was a Bi ₂ Ti ₂ O ₇ single phase. The obtained Bi ₂ Ti ₂ O ₇ powder and polyester binder (Byron 300: Toyobo) were mixed and dispersed in a methyl ethyl ketone solvent at a weight ratio of 9: 1, and this was applied to an Al substrate by the doctor blade method and dried. A coating film (photoconductive layer) having a thickness of about 200 μm was obtained.

(Example 2)
Bismuth trioxide (Bi ₂ O ₃ ) powder and titanium dioxide (TiO ₂ ) powder were blended at a molar ratio of 1: 2, and ball mill mixing was performed in ethanol using zirconium oxide balls. This was recovered and dried, and then calcined at 800 ° C. for 6 hours in a muffle furnace to obtain Bi ₂ Ti ₂ O ₇ powder by a solid phase reaction between bismuth trioxide and titanium dioxide. When the crystal phase of the obtained Bi ₂ Ti ₂ O ₇ powder particles was confirmed with an X-ray analyzer, it was a Bi ₂ Ti ₂ O ₇ single phase. The Bi ₂ Ti ₂ O ₇ powder was pulverized and passed through a mesh of 150 μm or less, and then pulverized and dispersed in ethanol using a zirconium oxide ball in ethanol. At this time, 0.4% by weight of polyvinyl butyral (PVB) was added as a dispersant. Thereafter, 0.7% by weight of PVB as a binder and 0.8% by weight of dioctyl phthalate as a plasticizer were added, and ball milling was further performed to prepare a sheet molding slurry. The recovered slurry was defoamed and concentrated by vacuum defoaming to adjust the viscosity to 50 poise.

The slurry whose viscosity was adjusted was applied onto a film base with a release agent using a coater so that the film thickness after firing was about 200 μm and molded into a sheet. The molded body was left to dry at room temperature for 24 hours, and then peeled off from the film base to produce a green sheet film. This green sheet film was placed on an aluminum oxide sintered body as a setter and sintered at a sintering temperature of 800 ° C. This sintered Bi ₂ Ti ₂ O ₇ was bonded to an Al substrate using conductive paste dotite (manufactured by Fujikura Kasei) to obtain a photoconductive layer.

(Comparative example)
Bismuth trioxide (Bi ₂ O ₃ ) powder and germanium dioxide (GeO ₂ ) powder were blended at a molar ratio of 6: 1, and ball mill mixing was performed in ethanol using zirconium oxide balls. This was recovered and dried, and then calcined at 800 ° C. for 6 hours in a muffle furnace to obtain Bi ₁₂ GeO ₂₀ powder by a solid phase reaction between bismuth trioxide and germanium dioxide. This Bi ₁₂ GeO ₂₀ powder was pulverized in a mortar, passed through a mesh of 150 μm or less, pulverized and dispersed in ethanol using a zirconium oxide ball in a ball mill, and dried. The obtained powder had an average particle size of about 4 μm. The obtained Bi ₁₂ GeO ₂₀ powder and a polyester binder (Byron 300: Toyobo) were mixed and dispersed in a methyl ethyl ketone solvent at a weight ratio of 9: 1, and this was applied to an Al substrate by a doctor blade method and dried to about 200 μm. A thick coating film (photoconductive layer) was obtained.

  Gold was sputtered to a thickness of 60 nm as the upper electrode on the photoconductive layers obtained in Examples 1 and 2 and the comparative example. A pulse generated under the condition that X-ray photocurrent signal is irradiated with 10mR X-ray for 0.1 second under the condition of voltage 80kV and voltage is applied (applied voltage is applied to correspond to electric field 2.5V / μm). The above photocurrent was converted to voltage with a current amplifier and measured with a digital oscilloscope. From the obtained current / time curve, integration was performed in the range of the X-ray irradiation time, and the amount of generated charge was measured. Further, the dark current was measured as a current value by the same method as the photocurrent measurement in a dark place not irradiated with X-rays.

The results are shown in Table 1. The amount of generated charge was represented by a relative value with the amount of generated charge of the comparative example measured by the above method as 100, and the dark current was represented by a relative value with the dark current of the comparative example measured by the above method as 1.

As is clear from Table 1, the photoconductive layer made of Bi ₂ Ti ₂ O _{7 according} to the present invention is a photoconductive layer provided by a coating method as compared with the photoconductive layer made of Bi ₁₂ GeO ₂₀ (Example 1). ) Was 1.2 times, and the photoconductive layer (Example 2) of the sintered film was 42 times higher, and the generated charge collecting effect was high. Further, in the photoconductive layer provided by the coating method, the dark current is reduced by half compared to the photoconductive layer made of Bi ₁₂ GeO ₂₀ and the electric noise is small, so that an image with good graininess can be obtained. . In the sintered photoconductive layer, although the dark current was large, the magnitude thereof was small compared to the sensitivity, and therefore, a remarkable SN ratio improvement and sensitivity improvement were achieved.

As described above, the photoconductive layer made of Bi ₂ Ti ₂ O _{7 according} to the present invention has high sensitivity due to the large effect of collecting generated charges, and can obtain an image with good graininess because of low electric noise. It is. In addition, it has advantages of excellent durability, non-toxicity, and low environmental load.

Sectional drawing which shows one Embodiment of the radiation imaging panel which has a photoconductive layer manufactured with the manufacturing method of this invention Schematic configuration diagram of a recording and reading system using a radiation imaging panel Diagram showing the electrostatic latent image recording process in a recording and reading system using a charge model Diagram showing the electrostatic latent image reading process in the recording and reading system using a charge model Schematic diagram showing the combined state of the radiation detector and the AMA substrate Electrical circuit diagram showing equivalent circuit of AMA substrate Schematic cross-sectional view showing the pixels of the radiation detector

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Conductive layer 2 Recording radiation conductive layer 3 Charge transport layer 4 Recording photoconductive layer 5 Conductive layer 10 Radiation imaging panel 70 Current detection means

Claims (4)

A photoconductive layer constituting a radiation imaging panel for recording radiation image information as an electrostatic latent image, wherein the photoconductive layer is made of Bi ₂ Ti ₂ O ₇ .   The photoconductive layer according to claim 1, wherein the photoconductive layer is provided by coating.   The photoconductive layer according to claim 1, wherein the photoconductive layer is a sintered film. A radiation imaging panel comprising a photoconductive layer made of Bi ₂ Ti ₂ O _{7 according} to claim 1, 2 or 3, which records radiation image information as an electrostatic latent image.

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