Radiation image conversion panel

Abstract

This invention provides a radiation image conversion panel that can suppress the degradation of the brightness of a scintillator due to radiation irradiation by controlling the chromaticity of the scintillator's surface, etc. [Solution] The radiation image conversion panel 1A comprises a scintillator layer 40 that converts irradiated X-rays into visible light and emits light, and an element substrate 10 that includes a photoelectric conversion element that receives the visible light emitted by the scintillator layer 40 and converts the received visible light into an electrical signal. On at least one side of the scintillator layer 40, either the side facing the element substrate 10 or the opposite side, the chromaticity b in the CIELab color space is * A colored layer 400 is provided, in which the ratio is 30 or more.

Description

[Technical Field] 【0001】 This invention relates to a radiation image conversion panel. [Background technology] 【0002】 In recent years, flat panel detectors (FPDs), which can acquire high-quality radiation images by converting radiation that has passed through a subject into a digital signal, have become widely used. An FPD comprises a scintillator that converts irradiated X-rays into visible light and emits light, and an element substrate that includes a photoelectric conversion element that detects the light emitted by the scintillator as an electrical signal. 【0003】 Generally, scintillators have the problem of degrading when exposed to radiation for a long period of time, resulting in a decrease in the brightness of the light they emit. To solve this problem, the following technologies have been proposed. Patent Document 1 describes a scintillator in which the degradation of the scintillator's brightness due to long-term X-ray irradiation can be suppressed by setting the concentration of the activator contained in the scintillator to a predetermined value. [Prior art documents] [Patent Documents] 【0004】 [Patent Document 1] Japanese Patent Publication No. 2003-123456 [Overview of the project] [Problems that the invention aims to solve] 【0005】 Conventional technologies have disclosed that they focus on the concentration of the activator contained in the scintillator in order to suppress the degradation of the scintillator's brightness due to X-ray irradiation. However, conventional technologies do not disclose any techniques for controlling the durability due to radiation irradiation by focusing on an indicator other than the concentration of the activator. 【0006】 Therefore, the present invention aims to provide a radiation image conversion panel that can suppress the degradation of the brightness of a scintillator due to radiation irradiation by controlling the chromaticity of the surface side of the scintillator, etc., in order to solve the above problems. [Means for solving the problem] 【0007】 The radiation image conversion panel according to the present invention is A scintillator layer that converts irradiated radiation into visible light and emits light, The device substrate includes a photoelectric conversion element that receives the visible light emitted by the scintillator layer and converts the received visible light into an electrical signal, On the scintillator layer side of the element substrate, chromaticity b in the CIELab color space * A colored layer is provided in which the ratio is 30 or higher. [Effects of the Invention] 【0008】 According to the present invention, the chromaticity b in the CIELab color space of the colored layer formed on the scintillator layer side of the element substrate * By setting this value to 30 or higher, the element substrate side or the opposite side of the scintillator layer can be pre-colored yellow. This suppresses the degradation of the scintillator layer's brightness due to X-ray irradiation. [Brief explanation of the drawing] 【0009】 [Figure 1] This graph shows the relationship between the concentration of thallium in the scintillator layer during X-ray irradiation and the degradation rate of the scintillator layer due to X-ray irradiation. [Figure 2] This figure shows an example of the cross-sectional configuration of the radiation image conversion panel according to the first embodiment. [Figure 3] This figure schematically shows an example of the cross-sectional structure of a radiation image conversion panel according to the second embodiment. [Figure 4] This figure schematically shows an example of the cross-sectional structure of a radiation image conversion panel according to the third embodiment. [Figure 5]It is a diagram schematically showing an example of a cross-sectional structure of a radiation image conversion panel according to a fourth embodiment. 【Embodiments for Carrying out the Invention】 【0010】 Hereinafter, a radiation image conversion panel according to a preferred embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. 【0011】 <First Embodiment> [Relationship between Concentration of Activator in Scintillator Layer and Luminance Deterioration Rate of Scintillator Layer due to X-Ray Irradiation] First, the relationship between the concentration of the activator contained in the scintillator layer constituting the radiation image conversion panel 1A and the luminance deterioration rate of the scintillator layer when the scintillator layer is irradiated with X-rays will be described. For example, thallium is used as the activator. FIG. 1 is a graph showing the relationship between the concentration of thallium contained in the scintillator layer at the time of X-ray irradiation and the luminance deterioration rate of the scintillator layer due to X-ray irradiation. In FIG. 1, the horizontal axis represents the concentration of thallium contained in the scintillator, and the vertical axis represents the luminance deterioration rate due to X-ray irradiation. 【0012】 As shown in FIG. 1, as the concentration of thallium contained in the scintillator layer increases, the luminance deterioration rate of the scintillator layer due to X-ray irradiation gradually increases accordingly. On the other hand, when the concentration of thallium contained in the scintillator layer becomes a certain value or more, for example, about 1.5 mol% or more, the luminance deterioration rate of the scintillator due to X-ray irradiation decreases. Thus, the luminance deterioration rate of the scintillator layer due to X-ray irradiation does not follow a specific pattern of linearly increasing according to the concentration of thallium. 【0013】 Here, it is known that the chromaticity of the scintillator layer changes according to the concentration of thallium contained in the scintillator layer. For example, when the concentration of thallium contained in the scintillator is from 0 to about 1.5 mol%, the chromaticity of the scintillator layer becomes blue. Also, when the concentration of thallium contained in the scintillator layer exceeds about 1.5 mol%, the chromaticity of the scintillator layer becomes yellow. In this case, the chromaticity b* in the CIELAB color space is 30 or more. Thus, it can be seen that there is a correlation among the concentration of the activator contained in the scintillator layer, the luminance degradation rate of the scintillator layer due to X-ray irradiation, and the chromaticity of the scintillator layer. 【0014】 Therefore, in the present embodiment, attention was paid to the fact that by increasing the concentration of thallium contained in the scintillator layer and pre-coloring the chromaticity of the scintillator layer from blue to yellow, the luminance degradation rate of the scintillator layer due to X-ray irradiation can be reduced. Furthermore, attention was also paid to the fact that by coloring only the chromaticity of the surface side rather than the entire scintillator layer yellow, the luminance degradation rate of the scintillator layer due to X-ray irradiation can be reduced. In the first embodiment, the case where the layer on the surface side of the scintillator layer is made yellow in advance by controlling the concentration of the activator will be described. 【0015】 [Example of Cross-sectional Configuration of Radiation Image Conversion Panel 1A] FIG. 2 is a diagram showing an example of the cross-sectional configuration of the radiation image conversion panel 1A according to the first embodiment. The radiation image conversion panel 1A includes an element substrate 10, an adhesive layer 20, a protective layer 30, a scintillator layer 40, and a reflective substrate 50. In the present embodiment, X-rays, which are radiation, enter in the arrow direction from the side of the reflective substrate 50 constituting the radiation image conversion panel 1A. 【0016】 The element substrate 10 absorbs light generated in the scintillator layer 40 and converts it into an electrical signal by generating an amount of charge corresponding to the intensity of the light. The element substrate 10 has a substrate and photoelectric conversion elements etc. arranged on the substrate. The substrate is made of a material that can transmit radiation such as X-rays and light such as ultraviolet rays. The substrate material may be, for example, a glass substrate, or a resin plate or resin film such as polyimide such as PET (polyethylene terephthalate) or polyethylene naphthalate. The photoelectric conversion element may be, for example, a photodiode that, when irradiated with light from the scintillator layer 40 that has been irradiated with radiation, absorbs light energy and generates electron-hole pairs inside, thereby converting light energy into an electric charge. Each photoelectric conversion element is provided with one thin-film transistor. 【0017】 The adhesive layer 20 is placed between the element substrate 10 and the scintillator layer 40 covered by the protective layer 30, and bonds the element substrate 10 and the scintillator layer 40 via the protective layer 30. The adhesive layer 20 is made of, for example, an optical adhesive. Examples of optical adhesives include olefin-based, amide-based, ester-based, styrene-based, acrylic-based, urethane-based, vinyl-based, polycarbonate, or thermoplastic resins mainly composed of ABS resin. 【0018】 The protective layer 30 has the function of improving the moisture resistance of the scintillator layer 40. The protective layer 30 is formed to cover the surface of the scintillator layer 40 that faces the element substrate 10. For example, a polyparaxylylene film is used for the protective layer 30. In addition to the surface of the scintillator layer 40 that faces the element substrate 10, the protective layer 30 may also be formed to cover the side surfaces of the scintillator layer 40. 【0019】 The scintillator layer 40 is positioned between the element substrate 10 and the reflective substrate 50. The scintillator layer 40 converts X-rays incident from the reflective substrate 50 side into light of a different wavelength and emits the converted light towards the element substrate 10 side. Specifically, when X-rays are incident on the scintillator layer 40, it emits electromagnetic waves with wavelengths of 300 nm to 800 nm, that is, light ranging from ultraviolet to infrared, mainly visible light. The scintillator layer 40 is formed mainly of a light-emitting phosphor and includes, for example, an activator. Suitable materials for the scintillator include, for example, cesium iodide (CsI), gadolinium sulfate (GOS), cadmium tungstate (CWO), or gadolinium silicate (GSO). Examples of activators included in the phosphor matrix such as CsI include thallium (Tl), europium (Eu), indium (In), lithium (Li), potassium (K), rubidium (Rb), or sodium (Na). Various polymer materials such as cellulose acetate film, polyester film, polyethylene terephthalate film, and polyimide (PI) film are used for the support film. The scintillator layer 40 is formed by growing a phosphor consisting of columnar crystals on the support film, for example by vapor deposition or sputtering. 【0020】 The scintillator layer 40 has a chromaticity b in the CIELab color space on the side of the element substrate 10 opposite to the X-ray incident side. * The color of the scintillator layer 40 is 30 or more and has a yellow-colored colored layer 400. In other words, the colored layer 400 is formed on the scintillator layer 40 side of the element substrate 10. The colored layer 400 is formed by making the concentration of the activator it contains higher than the concentration of the activator contained in the parts of the scintillator layer 40 other than the colored layer 400. Thus, in the first embodiment, the colored layer 400 with a high concentration of activator is formed not on the entire scintillator layer 40, but only on the surface of the scintillator layer 40 on the element substrate 10 side. Note that the chromaticity b of the scintillator layer 40 itself in the CIELab color space before irradiation with X is *The color is less than 30 and, for example, is colored blue. The scintillator layer 40 including the colored layer 400 can be formed by using a phosphor material (cesium iodide) and an activator (thallium) as a deposition source and depositing the phosphor material and activator on, for example, a reflective substrate 50. At this time, the concentration of the activator, thallium, is controlled to a predetermined value and a scintillator layer 40 of a predetermined thickness is formed on the deposition substrate. 【0021】 The reflective substrate 50 is positioned on the side of the scintillator layer 40 opposite to the element substrate 10. The reflective substrate 50 has the function of efficiently reflecting the fluorescence (emitted light) converted by the scintillator layer 40 towards the element substrate 10. The material of the reflective substrate 50 is preferably a metallic material with high reflectivity, for example, at least one metal selected from the group of Al, Ag, Cr, Cu, Ni, Mg, Pt, and Au. Other materials for the reflective substrate 50 may be, for example, a resin mixed with particles such as titanium oxide or aluminum oxide. The reflective substrate 50 may be formed as a single layer or as two or more layers. The reflective substrate 50 is formed by methods such as vacuum deposition, sputter deposition, plating, or coating. 【0022】 According to the first embodiment, the chromaticity b in the CIELab color space is measured on the surface of the scintillator layer 40 on the element substrate 10 side. * This forms 30 or more colored layers 400. This allows the surface of the scintillator layer 40 on the element substrate 10 side to be pre-colored yellow. Conventionally, the chromaticity of the scintillator layer 40 changed due to X-ray irradiation, causing a degradation in the brightness of the scintillator layer 40. In contrast, according to the first embodiment, by eliminating the blue color in the colored layer 400 and making it yellow, the color change (difference) of the scintillator layer 40 due to X-ray irradiation can be reduced, and the degradation of the brightness of the scintillator layer 40 over time can be suppressed. Furthermore, since a colored layer 400 with a high concentration of thallium, which is an activator, is provided only on the surface side of the scintillator layer 40, the overall concentration of activators such as thallium can be suppressed. 【0023】 <Second Embodiment> In the radiation image conversion panel 1B according to the second embodiment, a color filter layer 60 that has been pre-colored yellow is used to prevent brightness degradation of the scintillator layer 40 due to X-ray irradiation. The following description will focus on the differences from the first embodiment, with the same reference numerals used for components that are substantially common to both the first embodiment and the first embodiment, and common descriptions will be omitted or simplified. 【0024】 Figure 3 is a schematic diagram showing an example of the cross-sectional structure of a radiation image conversion panel 1B according to the second embodiment. The radiation image conversion panel 1B comprises an element substrate 10, an adhesive layer 20, a color filter layer 60, a protective layer 30, a scintillator layer 40, and a reflective substrate 50. The color filter layer 60 is disposed between the adhesive layer 20 on the element substrate 10 side and the protective layer 30 on the scintillator layer 40 side. In the second embodiment, the color filter layer 60, which functions as a coloring layer, is disposed on the element substrate 10 side of the scintillator layer 40. The color filter layer 60 is pre-colored yellow, and the chromaticity b of the color filter layer 60 in the CIELab color space is * The value is 30 or more. The color filter layer 60 is formed by vapor deposition, sputtering, or inkjet using a material obtained by mixing a yellow pigment or dye with a resin material such as acrylic resin. Alternatively, a sheet-like film that has been pre-colored yellow may be used as the color filter layer 60. 【0025】 According to the second embodiment, the chromaticity b in the CIELab color space of the color filter layer 60 formed on the element substrate 10 side of the scintillator layer 40 * This is controlled to 30 or higher. This allows the colored layer 400 to be pre-colored yellow, thereby suppressing the degradation of the brightness of the light emitted by the scintillator layer 40. 【0026】 <Third Embodiment> In the radiation image conversion panel 1C according to the third embodiment, in order to prevent luminance degradation of the scintillator layer 40 due to X-ray irradiation, an adhesive layer 20a that is colored yellow in advance or the like is used. Hereinafter, the description will focus on the differences from the first embodiment, and components that are substantially common to the first embodiment will be denoted by the same reference numerals, and common descriptions will be omitted or simplified. 【0027】 FIG. 4 is a diagram schematically showing an example of a cross-sectional structure of a radiation image conversion panel 1C according to the third embodiment. The radiation image conversion panel 1C includes an element substrate 10, an adhesive layer 20a, a protective layer 30, a scintillator layer 40, and a reflective substrate 50. In addition to the adhesive function of bonding the scintillator layer 40 and the element substrate 10, the adhesive layer 20a functions as a coloring layer that prevents luminance degradation of the light emitted by the scintillator layer 40. In the third embodiment, the adhesive layer 20a as the coloring layer is disposed on the element substrate 10 side of the scintillator layer 40. The adhesive layer 20a is colored yellow in advance, and the chromaticity b in the CIELab color space of the adhesive layer 20a * is 30 or more. The adhesive layer 20a may be formed, for example, by mixing a yellow pigment or dye into a thermoplastic resin mainly composed of an olefin-based, amide-based, ester-based, styrene-based, acrylic-based, urethane-based, vinyl-based, polycarbonate, or ABS resin. 【0028】 In the third embodiment, the adhesive layer 20a is colored yellow to function as a coloring layer, but it is not limited thereto. For example, by coloring the protective layer 30 disposed between the adhesive layer 20 and the scintillator layer 40 yellow, the chromaticity b in the CIELab color space * may function as a coloring layer of 30 or more. 【0029】 According to the third embodiment, the chromaticity b in the CIELab color space of the adhesive layer 20a or the protective layer 30 formed on the element substrate 10 side of the scintillator layer 40 * is controlled to 30 or more. Thereby, the adhesive layer 20a or the protective layer 30 can be colored yellow in advance, and luminance degradation of the light emitted by the scintillator layer 40 can be suppressed. 【0030】 <Fourth Embodiment> In the radiation image conversion panel 1D according to the fourth embodiment, a reflective substrate 50a that has been pre-colored yellow is used to prevent brightness degradation of the scintillator layer 40 due to X-ray irradiation. The following description will focus on the differences from the first embodiment, with the same reference numerals used for components that are substantially common to both the first embodiment and the first embodiment, and common descriptions will be omitted or simplified. 【0031】 Figure 5 is a schematic diagram showing an example of the cross-sectional structure of a radiation image conversion panel 1D according to the fourth embodiment. The radiation image conversion panel 1D comprises an element substrate 10, an adhesive layer 20, a protective layer 30, a scintillator layer 40, and a reflective substrate 50a. In the fourth embodiment, X-rays, which are radiation, are incident on the radiation image conversion panel 1D from the element substrate 10 side in the direction of the arrow. The X-rays incident from the element substrate 10 side are converted into light such as visible light by the scintillator layer 40 and emitted, for example, on the reflective substrate 50a side. The reflective substrate 50a reflects the emitted light converted by the scintillator layer 40 back to the element substrate 10 side. 【0032】 In addition to reflecting the fluorescent light converted by the scintillator layer 40 back to the element substrate 10, the reflective substrate 50a functions as a colored layer that prevents degradation of the brightness of the emitted light from the scintillator layer 40. In the fourth embodiment, the reflective substrate 50a, as a colored layer, is positioned on the opposite side of the scintillator layer 40 from the element substrate 10. The reflective substrate 50a is pre-colored yellow, and the chromaticity b of the reflective substrate 50a in the CIELab color space is * The value is 30 or more. The reflective substrate 50a may be formed by mixing a yellow pigment or dye with a metallic material such as Al, Ag, or Cr. 【0033】 According to the fourth embodiment, the chromaticity b in the CIELab color space of the reflective substrate 50a formed on the element substrate 10 side of the scintillator layer 40 * The value is controlled to 30 or higher. This allows the reflective substrate 50a to be pre-colored yellow, thereby suppressing the degradation of the brightness of the light emitted by the scintillator layer 40. 【0034】 <Examples> The following describes examples of the present invention, but the present invention is not limited thereto. First, a scintillator layer including a colored layer constituting the radiation image conversion panel according to the first embodiment described above was created. In Examples 1 to 3 and Comparative Example 1, the chromaticity of the colored layer 400 was adjusted by varying the concentration of thallium contained in the colored layer of the scintillator layer. 【0035】 Specifically, a coating solution for forming a deposition substrate, which was a mixture of polyester resin and a solvent such as cyclohexanone, was applied to a polyimide film support, and then dried for a predetermined time to produce a deposition substrate consisting of a support and a reflective layer. Next, cesium iodide was filled into the first resistance heating crucible, and thallium was filled into the second resistance heating crucible. After that, the air inside the vacuum chamber of the deposition apparatus was temporarily evacuated using a vacuum pump, and Ar gas was introduced to adjust the vacuum level inside the vacuum chamber of the deposition apparatus to absolute pressure. 【0036】 Next, the deposition substrate was rotated at a predetermined speed, and the first and second resistance heating crucibles were heated to form a scintillator layer containing cesium iodide and thallium on the deposition substrate. Subsequently, the first and second resistance heating crucibles were heated to form a colored layer containing cesium iodide and thallium on one surface side of the previously formed scintillator layer. 【0037】 Next, the chromaticity b in the CIELab color space of the scintillator layers prepared in each of Examples 1-3 and Comparative Example 1. * Measurements were taken, the luminance degradation rate due to X-ray irradiation in the scintillator layer was calculated, and the durability of the X-rays was evaluated. First, the luminance M of the prepared scintillator layer before X-ray irradiation was determined. Next, 10R of X-rays was irradiated onto the entire surface of the scintillator layer from the opposite side of the colored layer, and the X-ray chromatogram recorded on the radiation image conversion panel was erased with halogen light. This process was repeated, and when the cumulative X-ray dose reached 2000R, the luminance N of the scintillator layer after X-ray irradiation was determined. 【0038】 Chromaticity b in the CIELab color space of the scintillator layer * The following measuring devices were used for the measurement. Measurement device: Konica Minolta CM-2600d spectrophotometer, wavelength of measured light: 350~750nm 【0039】 Next, for each scintillator layer prepared in Examples 1-3 and Comparative Example 1, the brightness degradation rate (N / M) of the scintillator layer due to X-ray irradiation was calculated before and after X-ray irradiation. Brightness degradation was evaluated according to the following criteria. • Evaluation criteria for determining brightness reduction A: Brightness degradation rate before and after X-ray irradiation is 89% or higher. B: Brightness degradation rate before and after X-ray irradiation is less than 89%. Chromaticity b in the CIELab color space of the scintillator layers of Examples 1-3 and Comparative Example 1 * Table 1 shows the measured values, the brightness degradation rate due to X-ray irradiation, and the brightness reduction judgment. 【0040】 [Table 1] 【0041】 As shown in Examples 1-3 and Comparative Example 1 in Table 1, chromaticity b in the CIELab color space * When the value is 30 or higher, the brightness degradation rate due to X-ray irradiation is 89% or higher, confirming that the decrease in brightness of the scintillator layer due to X-ray irradiation is suppressed. In contrast, as shown in Comparative Example 1 of Table 1, the chromaticity b in the CIELab color space * When the value is less than 30, the brightness degradation rate due to X-ray irradiation is less than 89%, confirming that the decrease in brightness of the scintillator layer due to X-ray irradiation is significant. 【0042】 Furthermore, using the radiation image conversion panels 1B, 1C, and 1D described in the second to fourth embodiments, the chromaticity b in the CIELab color space can be calculated in the same manner as in the first to third embodiments. * It was confirmed that even when the value was set to 30 or higher, the results were almost identical to those shown in Table 1. 【0043】 Although preferred embodiments of this disclosure have been described in detail above with reference to the attached drawings, the technical scope of this disclosure is not limited to these examples. Furthermore, various modifications and improvements naturally fall within the technical scope of this disclosure, within the scope of the technical ideas described in the claims for those skilled in the art. 【0044】 In the embodiments described above, chromaticity b in the CIELab color space * Although an example has been described in which 30 or more colored layers are arranged on either the element substrate 10 side or the opposite side of the scintillator layer 40, the method is not limited to this. For example, the chromaticity b in the CIELab color space may be arranged on both the element substrate 10 side and the opposite side of the scintillator layer 40. * Each of the 30 or more colored layers may be arranged. Also, the chromaticity b in the CIELab color space * A colored layer with 30 or more layers may be composed of multiple layers. [Explanation of Symbols] 【0045】 1A, 1B, 1C, 1D Radiation Image Conversion Panel 10-element substrate 20,20a Adhesive layer (colored layer) 30 Protective layer (colored layer) 40 Scintillator layer 50,50a Reflective substrate (colored layer) 60 color filter layers 400 colored layer

Claims

[Claim 1] A scintillator layer that converts irradiated radiation into visible light and emits light, The device substrate includes a photoelectric conversion element that receives the visible light emitted by the scintillator layer and converts the received visible light into an electrical signal, On the scintillator layer side of the element substrate, chromaticity b in the CIELab color space ＊ A colored layer is provided in which the ratio is 30 or more. Radiation image conversion panel. [Claim 2] The colored layer is formed on the surface of the scintillator layer on the element substrate side. The radiation image conversion panel according to claim 1. [Claim 3] chromaticity b of the scintillator layer in the CIELab color space ＊ This is controlled by the concentration of the activator. The radiation image conversion panel according to claim 2. [Claim 4] A color filter layer is provided between the scintillator layer and the element substrate and is colored to a predetermined color, The aforementioned color filter layer functions as the coloring layer, The radiation image conversion panel according to claim 1. [Claim 5] It has moisture resistance and comprises a protective layer that covers the surface of the scintillator layer on the element substrate side, The protective layer functions as the coloring layer. The radiation image conversion panel according to claim 1. [Claim 6] An adhesive layer is provided between the scintillator layer and the element substrate for bonding the scintillator layer and the element substrate, The adhesive layer functions as the coloring layer. The radiation image conversion panel according to claim 1. [Claim 7] The scintillator layer is provided on the side opposite to the element substrate and includes a reflective substrate for reflecting the light converted by the scintillator layer back towards the element substrate. The reflective substrate functions as the colored layer, The radiation image conversion panel according to claim 1.

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