JP2006258618A - Phosphor sheet for radiation detector and radiation detector using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phosphor sheet for radiation detector which is stable in material properties without affecting to a human body as a specimen and can improve sharpness of image, and also to provide a radiation detector using it. <P>SOLUTION: The phosphor sheet 11 for radiation detector having a support 9 provided with a metal film 8 and at least a phosphor layer 10 formed on the support 9 surface uses a rare-earth oxisulfide as a phosphor layer 10 whose thickness is 50 to 300 μm as characteristics. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a phosphor sheet for a radiation detector and a radiation detector using the same, and in particular, when used for a radiation detector of a medical diagnostic apparatus and a non-destructive inspection apparatus using radiation, a radiation transmission image with high sharpness is obtained. The present invention relates to a phosphor sheet for a radiation detector and a radiation detector using the same.

  Conventionally, in the field of X-ray flat panel detectors for medical X-ray diagnostic equipment and industrial non-destructive inspection equipment, radiation intensity such as X-rays has been irradiated to diagnostic objects and inspection objects and transmitted through the objects. An apparatus that detects a radiation image of an object by detecting the above is widely used outside the field of the non-destructive inspection and medical diagnosis. An intensifying screen / film method is widely used as a general method for taking such an image. That is, a laminate is prepared in which a phosphor sheet (intensifying screen) that emits visible light when irradiated with X-rays is adhered to both sides of the photosensitive film, and the laminate is irradiated with radiation such as X-rays through the subject. It is a method to do. At this time, X-rays and the like transmitted through the subject are emitted by the phosphor, and the light is captured by the photosensitive film, and the latent image formed on the photosensitive film is developed and visualized by chemical processing to obtain an X-ray transmission image. Is obtained.

  On the other hand, with recent advances in digital technology, a method of obtaining a high-quality radiation image by converting a radiation image into an electrical signal, processing the electrical signal, and reproducing and displaying the image on a CRT or the like as a visible image has been tried. ing.

  As a method of converting such a radiation image into an electrical signal, a radiation transmission image is temporarily accumulated as a latent image in a phosphor, and then the latent image is photoelectrically irradiated by irradiating excitation light such as laser light later. A radiation image recording / reproducing system (CR) that reads out and outputs a visible image has been proposed.

  In addition, an image intensifier TV (II-TV) system that directly digitizes an image using a large vacuum tube provided with a photoelectric film, an accelerating electrode, and a fluorescent film and a CCD (solid-state imaging device) camera of about 1 inch. A diagnostic device is realized. However, for example, when diagnosing the lungs of a patient as a subject, a large optical device that collects light is indispensable for photographing a wide area of about 40 cm × 40 cm, and the enlargement of the diagnostic device is a problem. It has become.

  Further, along with recent progress in semiconductor process technology, an image apparatus system for taking a radiographic image using a semiconductor sensor has been developed. This type of system has an extremely wide dynamic range compared to a radiographic system using a conventional photosensitive film, and is advantageous in that it can obtain a radiographic image that is not easily affected by fluctuations in the exposure dose of radiation. have. Furthermore, there is an advantage that an output image can be obtained immediately without requiring chemical processing.

  In the medical field, in order to perform treatment quickly and accurately, progress is being made toward creating a database of patient medical data. In this background, patients often use multiple medical institutions, and in order to carry out more effective and accurate treatment, treatment progress data such as examination data at other medical institutions (treatment history) ) Is necessary. With respect to X-ray image data, there is a growing demand for a database that is unified for each individual patient, and accordingly, digitization of X-ray images is required.

As one of the digitization methods, in addition to a direct conversion method that converts an X-ray image directly into an electrical signal using an amorphous silicon thin film transistor (a-Si / TFT), the X-ray image is once converted into an optical signal, A so-called indirect conversion type X-ray flat panel detector that converts the converted optical signal into an electrical signal has also been proposed. In this conventional indirect conversion type X-ray flat panel detector, a phosphor sheet for radiation detector used for converting an X-ray image into an optical signal is used. This phosphor sheet is formed by integrally attaching a phosphor layer made of a phosphor such as Gd ₂ O ₂ S: Tb on a support made of a resin material or the like.

In addition, by arranging a plurality of detection elements such as photodiodes that convert X-rays into light, arranging separators that isolate adjacent detection elements, and increasing the reflectance of light on the surface of the separators, In order to improve the sharpness of an image by reducing the absorption of light and efficiently guiding light to a detection element (for example, Patent Document 1).
Japanese Patent Laid-Open No. 5-45468 JP 2004-335870 A

  However, the sharpness of the image of the image pickup device by the combination with the photoelectric conversion element as described above is equal to or less than that of the image of the image pickup device combining the conventional intensifying screen / film system and II-TV, and the high There was a problem that accuracy diagnosis and inspection could not be performed.

  In addition, an imaging apparatus using a CsI: Tl vapor deposition film instead of the radiation detector phosphor sheet has been put into practical use (for example, Patent Document 2). In this case, since the deposited film is a columnar crystal, it is preferable for improving the resolution. However, there is a problem that the deliquescence of the film component is high, and there is a possibility that the photographing sensitivity may be lowered with time. There was a problem that stable sensitivity characteristics could not be exhibited over a period of time. In addition, there is a problem that the imaging device becomes very expensive due to the complexity of the manufacturing method of the deposited film. Tl (thallium) is an environment-related substance, and the environmental standard is set to 0.6 ppm or less.

On the other hand, the direct conversion method for directly converting an X-ray image into an electric signal is a very advantageous method for improving the resolution from the principle. However, there are a-Se, PbI ₂ , HgI ₂ , CdTe, CdZnTe, etc. as materials of the X-ray charge conversion film currently being studied. However, since any substance adversely affects the human body, it is preferable to avoid use. There was also a request that it should be.

  As described above, the conventional phosphor sheet for radiation detectors has a problem that the sharpness of an image by an imaging device combined with a photoelectric conversion element is insufficient, and high-precision diagnosis and inspection cannot be performed.

  The present invention has been made to solve the above-mentioned problems of the prior art, has no adverse effect on the human body as a subject, has stable material characteristics, and can improve the sharpness of an image. An object of the present invention is to provide a phosphor sheet for a radiation detector and a radiation detector using the same.

  In order to achieve the above object, a radiation detector sheet according to the present invention comprises a support provided with a metal film and at least one phosphor layer formed on the support surface. In the sheet, the phosphor layer contains a rare earth oxysulfide phosphor and has a thickness of 50 to 300 μm.

  The phosphor layer-forming surface side of the support provided with the metal film preferably has a total light reflectance of 90% or more and a regular reflectance of 70% or more. The metal film is preferably an Ag or Al film.

  The rare earth oxysulfide phosphor preferably has an average particle diameter of 2 to 20 μm. The rare earth oxysulfide phosphor is preferably gadolinium oxysulfide. The phosphor layer preferably has a filling ratio of rare earth oxysulfide phosphor of 50 to 80% by volume.

  The radiation detector according to the present invention includes the phosphor sheet for radiation detector, and a plurality of photoelectric conversion films and pixel electrodes arranged in an array on the phosphor sheet. In addition, when the radiation detector is used as an X-ray flat detector of various imaging devices, an image having excellent sharpness can be obtained.

  According to the phosphor sheet for radiation detector and the radiation detector according to the above configuration, the phosphor layer contains a rare earth oxysulfide-based phosphor and has a thickness of 50 to 300 μm. A phosphor sheet and a radiation detector can be provided.

  Further, by adjusting the total reflectance and regular reflectance of light on the phosphor layer forming surface side of the support provided with the metal film, light emitted from the phosphor layer due to radiation incident from the support side is emitted. It is less scattered at the surface of the support and is efficiently emitted from the secondary side of the phosphor layer. Therefore, when the phosphor sheet is used in a radiographic imaging apparatus for diagnosis or inspection, an image with high sharpness can be obtained, and the accuracy of diagnosis and inspection can be greatly improved.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows an embodiment of a radiographic imaging apparatus incorporating a phosphor sheet and a radiation detector according to the present invention, and particularly shows a conceptual diagram of an X-ray imaging apparatus system using X-rays as radiation. The X-ray imaging apparatus 1 includes an X-ray flat panel detector 2 including a phosphor sheet. The X-ray 15 emitted from the X-ray generator 3 is irradiated to the subject 4 and transmitted through the subject 4. The line is detected by an X-ray flat detector 2 which is a photoelectric conversion element arranged in a two-dimensional lattice pattern. The image signal output from the photoelectric conversion element is subjected to digital image processing 5 in the image processing means 4 and is displayed on the monitor 6 as an X-ray image of the subject 4.

  FIG. 2 is a partially enlarged cross-sectional view showing the configuration of the X-ray flat panel detector 2 incorporating the radiation detector phosphor sheet 11 according to the present embodiment. A radiation detector phosphor sheet 11 that converts X-rays 15 as irradiated radiation into visible light is formed on a support body 7 made of plastic or nonwoven fabric, and on the surface of the support body 7 on the phosphor side. The metal film 8 is composed of an Ag film 8 and a phosphor layer 10. A support 9 is formed by the support body 7 and the metal film 8.

  A transparent protective film may be provided on the upper surface side of the phosphor layer 10, but the protective film may reduce sharpness, which is a characteristic of the phosphor sheet, and therefore requires a special protective function. Except in certain cases, it is preferable not to attach them. Further, the X-ray flat panel detector 2 is laminated with a photoelectric conversion element 12 arranged in a lattice shape for converting the converted visible light into an electric signal, and a substrate 13 for supporting the photoelectric conversion element 12. In addition, the photoelectric conversion element 12 is connected to a circuit board for processing an electric signal subjected to photoelectric conversion via a wiring 14.

  More specifically, the X-ray flat panel detector 2 includes a radiation detector phosphor sheet 11 that converts incident X-rays into visible light, a plurality of photoelectric conversion films and pixel electrodes arranged in an array, A switching element connected to the pixel electrode, a scanning line for sending a driving signal to each row of switching elements, a signal line connected to each row of switching elements, and a pixel electrode of the radiation detector phosphor sheet are provided. A common electrode provided on the surface opposite to the surface on which the light is applied, and the total reflectance of light on the surface of the support 9 in contact with the phosphor layer 10 is 90% or more and the regular reflectance is 70%. It is comprised so that it may become the above.

  As shown in FIG. 2, the radiation detector phosphor sheet 11 according to the present embodiment includes a support 9 and a phosphor layer 10 formed on one surface thereof. Furthermore, you may form a protective film on the fluorescent substance layer 10 as needed.

  Examples of the phosphor used for forming the phosphor layer 10 include rare earth oxysulfide phosphors. In particular, it is preferable to use a rare earth oxysulfide-based phosphor having a composition represented by the following general formula (1).

[Equation 1]
M ₂ O ₂ S: Z (1)

  Where M is at least one element selected from the group consisting of yttrium (Y), lanthanum (La), gadolinium (Gd) and lutetium (Lu), and O is oxygen, S is sulfur, and Z is It is at least one element selected from the group consisting of terbium (Tb) and europium (Eu).

Further, more preferable as the phosphor is a phosphor exhibiting light emission suitable for the light receiving sensitivity distribution of the photoelectric conversion element 12. FIG. 3 shows light receiving sensitivity distributions of a-Si and single crystal Si that are generally used as the constituent material of the photoelectric conversion element 12. As shown in FIG. 3, a-Si has a broad light receiving sensitivity distribution having a light receiving peak near 600 nm, and single crystal Si has a broad light receiving sensitivity distribution having a light receiving peak of 700 to 800 nm. Examples of the phosphor that matches the light receiving sensitivity distribution of the photoelectric conversion element 12 and exhibits high luminous efficiency include europium-activated rare earth oxysulfide phosphors, and more preferably europium-activated gadolinium oxysulfide phosphors, europium. Examples include activated lutetium oxysulfide phosphors and europium activated lanthanum oxysulfide phosphors. In particular, a terbium or europium activated gadolinium oxysulfide phosphor (Gd ₂ O ₂ S) is preferable because of its high luminous efficiency.

  In addition, two or more rare earth oxysulfide phosphors such as europium activated gadolinium oxysulfide phosphor, europium activated lutetium oxysulfide phosphor, and europium activated lanthanum oxysulfide phosphor can be used in combination. May be.

  In order to increase the sharpness of the transmitted image by setting the amount of light transmitted through the phosphor layer within an appropriate range, the thickness of the phosphor layer is preferably 50 to 300 μm. If the thickness of the phosphor layer is less than 50 μm, sufficient output for X-rays cannot be obtained, and if it exceeds 300 μm, the reflected light is scattered and absorbed in the phosphor layer, so that the amount of light that appears on the surface tends to be insufficient. The effect of providing a metal film on the support is difficult to obtain. Preferably it is the range of 100-250 micrometers.

  The phosphor layer is prepared by dispersing predetermined phosphor particles, a binder, a dispersing material, and a plasticizer in an organic component such as an organic solvent to prepare a phosphor coating solution, and applying the solution to a support surface. It is formed by drying. The thickness of the phosphor layer of the present invention indicates the distance from the upper end of the phosphor particles on the front surface side to the lower end of the phosphor particles on the back surface (support side).

  The binder used for the preparation of the phosphor coating solution is nitrified cotton, cellulose acetate, ethyl cellulose, polyvinyl butyral, cotton-like polyester, polyvinyl acetate, vinylidene chloride-vinyl chloride polymer, vinyl chloride-vinyl acetate copolymer, polyalkyl. (Meth) acrylate, polycarbonate, polyurethane, cellulose acetate butyrate, polyvinyl alcohol and the like. As the organic solvent, for example, ethanol, methyl ethyl ether, butyl acetate, ethyl acetate, ethyl ether, xylene and the like are used. If necessary, a dispersing agent such as phthalic acid or stearic acid or a plasticizer such as triphenyl phosphate or diethyl phthalate may be added to the phosphor coating solution.

  Furthermore, as described above, a protective film may be provided on the radiation detector phosphor sheet according to the present embodiment, if necessary. Various transparent resins are used as the constituent material of the protective film. Specifically, a transparent resin film made of polyethylene terephthalate (PET), polyethylene (PE), polyvinylidene chloride, polyamide or the like is laminated on the phosphor layer to form a protective film. Or dissolve cellulose derivatives such as cellulose acetate, ethyl cellulose, cellulose acetate butyrate, transparent resins such as polyvinyl chloride, polyvinyl acetate, vinyl chloride-vinyl acetate copolymer, polycarbonate, polyvinyl butyral, polymethyl methacrylate, polyvinyl formal, polyurethane, etc. Thus, a protective film coating solution having an appropriate viscosity is prepared, and this is coated on the phosphor layer and dried to form a protective film. In some cases, a protective film may be formed by kneading an appropriate amount of a light scattering agent such as titanium oxide. The thickness of the protective film is not included in the thickness of the phosphor layer.

  In order to increase the sharpness of the transmitted image by setting the amount of light transmitted through the phosphor layer within an appropriate range, the average particle size of the phosphor particles constituting the phosphor layer is preferably in the range of 2 to 20 μm. When the average particle diameter of the phosphor particles is too small, less than 2 μm, the density of the phosphor layer becomes excessive, and the light generated in the phosphor layer becomes difficult to transmit through the phosphor layer, and the transmission image Shooting sensitivity will decrease. On the other hand, if the average particle diameter of the phosphor particles is too large so as to exceed 20 μm, the light generated in the phosphor layer will pass through the phosphor layer too much, and the transmitted light will be blurred because the density of the transmitted light becomes unclear. The sharpness of the image is reduced.

  The filling rate of the rare earth oxysulfide phosphor in the phosphor layer is preferably 50 to 80% by volume. Furthermore, 60-75 volume% is preferable. Here, the filling rate of the rare earth oxysulfide phosphor in the phosphor layer is represented by (total volume of phosphor particles / volume of phosphor layer) × 100 (%). When the filling rate is less than 50% by volume, scattering of emitted light increases and sharpness cannot be obtained. On the other hand, a phosphor layer exceeding 80% by volume is difficult to manufacture when handling powder.

Instead of the plastic film or the nonwoven fabric described above, the phosphor layer may be formed by applying and drying a phosphor coating solution on a protective film laminated on a polyester film having a thickness of 250 μm, for example. In that case, a phosphor sheet for a radiation detector can also be formed by laminating a support coated with an adhesive or the like and a phosphor layer with a protective film.

  As the above support, for example, a resin such as cellulose acetate, cellulose propionate, cellulose acetate butyrate, polyethylene terephthalate (PET), polystyrene, polymethacrylate, polyamide, vinyl chloride-vinyl acetate copolymer, polycarbonate or the like is formed into a film. , Paper, aluminum plate, etc. are used. In addition, a sheet obtained by kneading a light-reflecting substance such as titanium dioxide and calcium carbonate or a light-absorbing substance such as carbon black into a plastic film or paper as described above, or a sheet containing bubbles can be used. . By containing the light reflecting material or the light absorbing material, a colored support such as white or black can be obtained.

  In this embodiment, a metal film is specifically provided on the surface of the support so that most of the light emitted from the phosphor layer is reflected without being scattered on the surface of the support. The metal film preferably has a total light reflectance of 90% or more and a regular reflectance of 70% or more.

  Examples of the metal film include metal films such as Al, Ag, Cr, Cu, Ni, Ti, Mg, Rh, Pt, and Au. Particularly preferred are Ag and Al films, and more preferred is an Ag film. In the case of an Ag film, it is easy to obtain a metal film having a total reflectance of 95% or more and a regular reflectance of 90% or more. Moreover, although the formation method of a metal film is not specifically limited, a vapor deposition method is preferable. In particular, Ag, Al, Cu, and the like can be deposited at a relatively low temperature by using a vacuum deposition method, so that the support is not damaged by the heat during film formation. The thickness of the metal film is preferably 0.01 to 3 μm. If the thickness is less than 0.01 μm, it is difficult to obtain the above reflectance, and if it exceeds 3 μm, no further effect can be obtained, which causes an increase in cost.

  If one of the total reflectance and regular reflectance does not satisfy the above condition, the amount of light emission scattered on the surface of the support increases, and the sharpness of a predetermined image cannot be obtained. Therefore, in order to obtain good image sharpness, it is necessary to ensure both a total reflectance of 90% or more and a regular reflectance of 70% or more on the reflecting surface.

  When the metal vapor deposition film 8 is formed integrally with the support body 7, the surface roughness of the metal vapor deposition film 8 becomes coarse depending on conditions such as the degree of vacuum of the vapor deposition apparatus and the surface roughness of the support, and the scattered light is scattered. Is likely to occur. Therefore, the total reflectance of light on the surface of the metal reflecting layer or the support 9 is 90% or more, and the regular reflectance is defined to be 70% or more. Further, the regular reflectance is preferably 90% or more.

  In the phosphor sheet 11 of the support 9 provided with such a metal vapor-deposited film (reflection layer) 8, light emitted from the phosphor layer 10 by the X-rays 15 is hardly scattered to the support 9 side, and the surface As a result of being incident on the photoelectric conversion element 12 on the back side from the side with high efficiency, the sharpness of the transmitted image is improved.

  As a method for measuring the reflectance, generally, at the stage of the support before forming the phosphor layer 8 or at the stage of forming the metal vapor-deposited film 8 on the support body 7, the Japanese Industrial Standard ( A method of performing measurement using a spectrophotometer in accordance with the regulations of JIS R3106 and Z8741 (45 °) is employed.

  Here, the regular reflection is a reflection form in which the reflection of light has an incident angle equal to the reflection angle, and the ratio of the luminous flux reflected as regular reflection when the incident luminous flux is 100 is defined as the regular reflectance. The other than regular reflectance is called diffuse reflectance, and the sum of regular reflectance and diffuse reflectance is called total reflectance.

  In the present embodiment, the thickness of the phosphor layer 10 is a factor that greatly affects the behavior of reflected light on the support 9. The phosphor layer 10 is composed of a phosphor and a binder excluding the protective film and the support, and the thickness thereof is defined in the range of 50 to 300 μm. When the thickness of the phosphor layer 10 is as thin as less than 50 μm, the light emission output of the phosphor layer for X-rays is insufficient.

  On the other hand, when the thickness of the phosphor layer 10 becomes excessive so as to exceed 300 μm, almost no light is emitted when the reflected light is emitted to the surface of the photoelectric conversion element while causing scattering and absorption in the phosphor layer 10. Since it is lost, the light reflection effect on the surface of the support becomes useless. Therefore, in order to increase the emission amount of light emission in synergy with the light reflection effect on the support surface, the thickness of the phosphor layer 10 is specified in the range of 50 to 300 μm.

  In the X-ray imaging apparatus incorporating the radiation detector phosphor sheet 11 and the radiation detector 2 according to the present embodiment as described above, the X-rays 15 emitted from the X-ray generator 3 are transmitted through the subject 4 to the X-ray. When incident on the line flat detector 2, the transmitted X-rays are converted into visible light by the phosphor layer 10 of the radiation detector phosphor sheet 11, and the visible light is converted into an electric signal by the photoelectric conversion element 12, and then by the circuit board. The processed electrical signal is displayed as an X-ray image on a monitor 6 such as a CRT.

  According to the X-ray imaging apparatus 1 incorporating the phosphor sheet for radiation detector and the radiation detector according to the above embodiment, the thickness of the phosphor layer 10 of the phosphor sheet 11 is 50 to 300 μm. Since the total reflectance of light on the surface of the metal vapor deposition film 8 of the support 9 in contact with the layer 10 is defined as 90% or more and the regular reflectance is defined as 70% or more, the light enters from the support 9 side. Light emitted from the phosphor layer 10 by the X-ray 15 is hardly scattered on the surface of the support 9 and is efficiently emitted from the secondary side of the phosphor layer 10. Therefore, when the phosphor sheet 11 is used in the radiographic imaging apparatus 1 for diagnosis or inspection, an image with high sharpness can be obtained and the accuracy of diagnosis or inspection can be greatly improved. .

  In particular, when the X-ray flat detector 2 using the phosphor sheet 11 for radiation detectors of the above-described embodiment is used for medical X-ray imaging and industrial nondestructive inspection, the sharpness is improved and the inspection accuracy is improved. It leads to improvement.

  Next, specific examples of the present invention will be described.

[Example 1]
Fluorescence is obtained by mixing 0.5 parts by weight of polyvinyl butyral resin as a binder and an appropriate amount of butyl acetate as an organic solvent with respect to 10 parts by weight of Gd ₂ O ₂ S: Tb phosphor powder having an average particle diameter of 8 μm. A body coating solution was prepared. This phosphor coating solution is uniformly applied on a sheet of a white polyethylene terephthalate film having a thickness of 250 μm with a knife coater so that the phosphor coating weight density (coating amount) after drying is 90 mg / cm ² . The phosphor layer was formed by drying. Moreover, the fluorescent substance sheet for Example 1 was produced by pressing a fluorescent substance layer to the support body in which the Ag vapor deposition film whose thickness is 1 micrometer was formed. The total reflectance of the Ag vapor deposition film on the surface of the support was 98%, and the regular reflectance was 95%. The filling rate of the phosphor in the phosphor layer was 69% by volume.

  Using the thus prepared phosphor sheet 11 for a radiation detector, an X-ray imaging system as shown in FIG. 1 was constructed, and the sharpness was measured.

[Example 2]
The phosphor for a radiation detector according to Example 2 is processed in the same manner as in Example 1 except that an Al deposited film having a total light reflectance of 92% and a regular reflectance of 70% is provided on the support surface. A sheet was produced.

[Example 3]
A phosphor sheet for a radiation detector according to Example 3 is processed in the same manner as in Example 1 except that phosphor particles having an average particle diameter of 2 μm are used and a phosphor layer having a thickness of 50 μm is formed. Was made.

[Example 4]
A phosphor sheet for a radiation detector according to Example 4 processed in the same manner as in Example 1 except that phosphor particles having an average particle diameter of 20 μm were used and a phosphor layer having a thickness of 300 μm was formed. Was made.

[Example 5]
A phosphor sheet for a radiation detector according to Example 5 was produced in the same manner as in Example 1 except that the average particle diameter of the phosphor particles was 25 μm and the thickness of the phosphor layer was 300 μm.

[Example 6]
A phosphor sheet for a radiation detector according to Example 6 was prepared by treating in the same manner as in Example 1 except that the phosphor was changed to Gd ₂ O ₂ S: Eu.

[Example 7]
A phosphor sheet for a radiation detector according to Example 7 was prepared by treating in the same manner as in Example 1 except that the phosphor was replaced with Lu ₂ O ₂ S: Eu.

[Example 8]
A phosphor sheet for a radiation detector according to Example 8 was produced by performing the same process as in Example 1 except that the filling rate of the phosphor in the phosphor layer was changed to 60% by volume.

[Example 9]
A phosphor sheet for a radiation detector according to Example 9 was produced by performing the same treatment as in Example 1 except that the phosphor filling rate in the phosphor layer was changed to 75% by volume.

[Comparative Example 1]
A phosphor sheet for a radiation detector according to Comparative Example 1 was prepared in the same manner as in Example 1 except that a white PET film support having a total reflectance of 85% and a regular reflectance of 20% without a metal layer was used. . Moreover, the filling rate of the phosphor in the phosphor layer was 71% by volume.

[Comparative Example 2]
Fluorescence for a radiation detector according to Comparative Example 2 in the same manner as in Example 1 except that fine phosphor particles having an average particle diameter of 1 μm are used and a phosphor layer having a thickness of 40 μm is formed. A body sheet was prepared. Moreover, the filling rate of the phosphor in the phosphor layer was 71% by volume.

[Comparative Example 3]
Radiation detection according to Comparative Example 3 in the same manner as in Example 1 except that coarse phosphor particles having an average particle size of 30 μm are used and a phosphor layer having an excessive thickness of 350 μm is formed. A device phosphor sheet was prepared. Moreover, the filling rate of the phosphor in the phosphor layer was 71% by volume.

The sharpness of the transmission image was measured for the phosphor sheets for radiation detectors according to the examples and comparative examples prepared as described above. In the evaluation of the sharpness, the phosphor sheet of Comparative Example 1 was used as a standard (100), and the improvement rate of the sharpness with respect to the standard value was relatively measured and evaluated. Each measurement result is shown in Table 1 below.

  As is clear from the results shown in Table 1 above, the thickness of the phosphor layer 10 of the phosphor sheet 11 is in the range of 50 to 300 μm, and the surface of the metal vapor deposition film 8 of the support 9 in contact with the phosphor layer 10. In the X-ray imaging apparatus using the phosphor sheet 11 according to each example in which the total reflectance of light is defined as 90% or more and the regular reflectance is defined as 70% or more, the support 9 side The light emitted from the phosphor layer 10 by the X-rays 15 incident thereon from the phosphor layer 10 is effectively reflected from the secondary side of the phosphor layer 10 with little scattering on the surface of the Ag vapor deposition film 8 of the support 9. Therefore, it is possible to obtain an image with high sharpness and to greatly improve the accuracy of diagnosis and inspection.

  In addition, even when the total reflectance and regular reflectance of light on the support surface satisfy the specified values, X using the phosphor sheet according to Comparative Examples 2 and 3 in which the thickness of the phosphor layer is outside the predetermined range In the line image photographing apparatus, it has been found that the image sharpness is lowered because the difference in light intensity emitted from the phosphor layer is reduced.

  As described above, an X-ray flat panel detector with improved sharpness is provided by defining the thickness of the phosphor layer, the total reflectance of light on the support surface, and the regular reflectance within a predetermined range. Is possible.

The block diagram which shows the system configuration | structure of the radiographic imaging apparatus incorporating the radiation detector using the fluorescent substance sheet which concerns on this invention. Sectional drawing which shows schematic structure of the X-ray flat panel detector which uses the fluorescent substance sheet for radiation detectors concerning this invention. The graph which shows the light reception sensitivity distribution of a-Si and single crystal Si which comprise a light receiving element.

Explanation of symbols

1 Radiation imaging equipment (X-ray imaging equipment)
2 Radiation plane detector (X-ray plane detector)
3 Radiation generator (X-ray generator)
4 Subject 5 Digital image processing means 6 Monitor (CRT)
7 Support body 8 Metal film (Ag vapor deposition film, reflective layer)
DESCRIPTION OF SYMBOLS 9 Support body 10 Phosphor layer 11 Phosphor sheet for radiation detector 12 Photoelectric conversion element (photodiode)
13 Substrate 14 Wiring 15 Radiation (X-ray)

Claims (8)

In a phosphor sheet for a radiation detector having a support provided with a metal film and at least one phosphor layer formed on the surface of the support, the phosphor layer contains a rare earth oxysulfide phosphor. And the thickness is 50-300 micrometers, The fluorescent substance sheet for radiation detectors characterized by the above-mentioned. 2. The radiation detection according to claim 1, wherein the phosphor layer-forming surface side of the support provided with the metal film has a total light reflectance of 90% or more and a regular reflectance of 70% or more. A phosphor sheet for dexterity. The phosphor sheet for a radiation detector according to claim 1, wherein the metal film is an Ag or Al film. The phosphor sheet for a radiation detector according to any one of claims 1 to 3, wherein the rare earth oxysulfide phosphor has an average particle diameter of 2 to 20 µm. The phosphor sheet for a radiation detector according to any one of claims 1 to 4, wherein the phosphor layer has a rare earth oxysulfide-based phosphor filling ratio of 50 to 80% by volume. The phosphor sheet for a radiation detector according to any one of claims 1 to 5, wherein the rare earth oxysulfide-based phosphor is gadolinium oxysulfide. A phosphor sheet for a radiation detector according to any one of claims 1 to 6, and a plurality of photoelectric conversion films and pixel electrodes arranged in an array on the phosphor sheet. A radiation detector. The radiation detector according to claim 7, wherein the radiation detector is an X-ray flat panel detector.

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