JP2017078635A - Scintilator panel and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scintillator panel capable of improving total characteristics including afterimage characteristics and radiation resistance on a scintillator layer.SOLUTION: A scintillator panel 10 includes: a support substrate 11 that transmits X-ray 16; and a scintillator layer 13 which is formed on the support substrate 11 to convert an X-ray 16 incident from outside into light. The scintillator layer 13 is a fluorescent body containing Tl as an activator in the halide CsI. Defining the incident side of the X-ray 16 in the film thickness direction of the scintillator layer 13 as the incident side area A; the opposite side of the incidence side area A as the non-incident side area B; and an area between the incident side area A and the non-incident side area B as an intermediate area C, the density of the activator in the fluorescent body at incident side area A and non-incident side area B is 0.2 mass%±0.15 mass%, and the density of the activator in the fluorescent body at the intermediate area C is 1.6 mass%±0.4 mass%.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a scintillator panel that converts radiation into light and a method for manufacturing the scintillator panel.

  As a new-generation X-ray diagnostic image detector, an X-ray detector, which is a planar radiation detector using an active matrix or a solid-state imaging device such as a CCD and a CMOS, has attracted attention. By irradiating the X-ray detector with X-rays, an X-ray image or a real-time X-ray image is output as a digital signal.

  The X-ray detector includes a scintillator panel having a scintillator layer that converts radiation into light, and a photoelectric conversion substrate that converts light converted by the scintillator panel into an electrical signal. The light converted in the scintillator layer by incident X-rays reaches the photoelectric conversion substrate and is converted into electric charge. This electric charge is read out as an output signal and converted into a digital image signal by a predetermined signal processing circuit or the like. Is done.

  In addition, when CsI, which is a halide, is used for the scintillator layer, since CsI alone cannot convert incident X-rays into visible light, excitation of light with respect to incident X-rays is performed in the same manner as general phosphors. An activator is contained in order to activate.

  In the X-ray detector, since the peak wavelength of the light receiving sensitivity of the photoelectric conversion substrate exists in the visible light region of 400 nm to 700 nm, when CsI is used for the scintillator layer, the light excited by the incident X-rays Tl having a wavelength of around 550 nm is used as an activator.

  When the scintillator layer is a phosphor containing Tl as an activator in CsI, which is a halide, the concentration and concentration of the activator Tl is similar to that of a phosphor containing a general activator. It will be greatly affected by the distribution.

  In a scintillator panel having a scintillator layer containing an activator, if the concentration and concentration distribution of the activator are not optimized, the characteristics of the scintillator layer will be deteriorated, and the sensitivity related to the light emission characteristics of the scintillator layer (light emission) Efficiency) and afterimage (a phenomenon in which the subject image of the X-ray image before the (n-1) -th X-ray image remains in the n-th X-ray image).

  For example, in diagnosis using an X-ray image, the imaging conditions vary greatly depending on the subject {incident X-ray dose: approximately 0.0087 mGy to 0.87 mGy (since X-ray transmittance varies depending on the region)}, (n -1) There may be a large difference in the dose of incident X-rays between the X-ray image and the n-th X-ray image, and the dose difference between incident X-rays between the (n-1) -th and n-th X-ray images. Is (n-1)> n, the light emission characteristic of the scintillator layer in the non-subject portion of the (n-1) th X-ray image is changed by the large energy of incident X-rays, and the nth X-ray image Up to this, an afterimage occurs due to the remaining effect.

  This afterimage characteristic is an important characteristic in diagnosis using an X-ray image as compared with sensitivity (light emission efficiency) and resolution (MTF) which are characteristics of other scintillator layers.

  Further, in a scintillator layer composed of a phosphor containing Tl as an activator in CsI, the higher the Tl concentration as the activator in the scintillator layer, the higher the Xl resistance of the scintillator layer {scintillator associated with damage caused by X-ray irradiation. It has been shown in a paper (Non-patent Document 1) and the like that the sensitivity reduction of the layer (reliability item)} deteriorates. Furthermore, in general, when a substance is irradiated with high energy (such as X-rays), the bond between the atoms constituting the substance is damaged (bonds are broken, etc.), and in particular fluorescence that transmits light. It has been described in a paper (Non-Patent Document 2) and the like that when a body or the like is irradiated with high energy (X-ray or the like), coloring (color center) due to damage occurs.

  And the scintillator layer comprised with the fluorescent substance which contains Tl as an activator in CsI has a subject in the further improvement of a characteristic.

  Conventionally, the improvement of the characteristics of the scintillator layer is mostly related to improvement of individual characteristics such as sensitivity (light emission efficiency), resolution (MTF), and afterimage, and has comprehensive characteristics including afterimage characteristics and X-ray resistance. There was nothing related to improvement.

JP 2015-17972 A Japanese Patent Laid-Open No. 2015-38458

Sara Bergenius, `` GLAST CsI (Tl) Crystal '', ROYAL INSTITUTE OF TECHNOLOGY, Stockholm 2004, ISBN: 91-7283-754-3 Simon Jolly, `` Radiation damage and afterglow in CsI (Tl) '', Brunel University, Institute of Physical and Environmental Sciences, Physics Unit

  The problem to be solved by the present invention is to provide a scintillator panel that can improve the overall characteristics including the afterimage characteristics and radiation resistance of the scintillator layer, and a method for manufacturing the scintillator panel.

  The scintillator panel of the present embodiment includes a support substrate that transmits radiation, and a scintillator layer that is formed on the support substrate and converts radiation incident from the outside into light. The scintillator layer is a phosphor containing Tl as an activator in CsI which is a halide. When the incident side of the radiation in the film thickness direction of the scintillator layer is the incident side region, the opposite side of the incident side region is the non-incident side region, and the intermediate region is between the incident side region and the non-incident side region. The concentration of the activator in each phosphor in the non-incident side region is 0.2 mass% ± 0.15 mass%, and the concentration of the activator in the phosphor in the intermediate region is 1.6 mass% ± 0.4 mass%. .

It is sectional drawing of the 1st structural example of the scintillator panel which shows one Embodiment. It is sectional drawing of the 2nd structural example of a scintillator panel same as the above. It is sectional drawing of the 3rd structural example of a scintillator panel same as the above. It is sectional drawing of the 4th structural example of a scintillator panel same as the above. It is sectional drawing of the imaging device using a scintillator panel same as the above. It is a graph which shows the correlation with Tl density | concentration of the scintillator layer of a scintillator panel same as the above, and a sensitivity ratio. It is a graph which shows the correlation with Tl density | concentration of a scintillator layer same as the above, and MTF ratio. It is a graph which shows the correlation with Tl density | concentration and a residual image ratio of a scintillator layer same as the above. It is a graph which shows the correlation with the lamination period of a scintillator layer, and a sensitivity ratio same as the above. It is a graph which shows the correlation with the lamination period of a scintillator layer, and MTF ratio same as the above. It is a graph which shows the correlation with the lamination period of a scintillator layer, and an afterimage ratio same as the above. It is a graph which shows the correlation with the film thickness of a scintillator layer, and an afterimage ratio same as the above. It is a graph which shows the correlation with Tl density | concentration of a scintillator layer same as the above, and X-ray tolerance (sensitivity attenuation ratio). The scintillator layer is shown, (a) is a schematic diagram showing the scintillator layer, (b) is a schematic diagram showing the amount of X-ray absorption when the quality of the X-ray incident on the scintillator layer is hard, and (c) is the scintillator layer. It is a schematic diagram which shows the X-ray absorption amount in case the quality of the X-ray which injects into is soft. It is a graph which shows the correlation with the film thickness of a scintillator layer, and a tube voltage. It is a graph which shows the correlation with the film thickness of a scintillator layer, and an X-ray absorption rate same as the above. It is a schematic diagram which shows the general formation method of a scintillator layer same as the above. It is a schematic diagram which shows the formation method of this embodiment of a scintillator layer same as the above (a) (b). It is a schematic diagram which shows the same scintillator layer of sample I, II, III, IV, V of a scintillator panel same as the above, and is a schematic diagram for every sample of (a) (b) (c) (d) (e). It is an X-ray image acquired using the samples I, II, III, IV, and V of the scintillator panel, and (a), (b), (c), (d), and (e) are X-ray images for each sample. It is a table | surface which shows each characteristic acquired using sample I, II, III, IV, V of a scintillator panel same as the above.

  Hereinafter, an embodiment will be described with reference to FIGS. 1 to 21.

  1 to 4 show first to fourth structural examples of the basic configuration of the scintillator panel 10.

  First, a first structural example of the scintillator panel 10 will be described with reference to FIG. The scintillator panel 10 includes a support substrate 11 that transmits X-rays as radiation. A reflection layer 12 that reflects light is formed on the support substrate 11, and the radiation is converted into visible light on the reflection layer 12. A scintillator layer 13 is formed, and a protective layer 14 that seals the scintillator layer 13 is laminated on the scintillator layer 13.

  The support substrate 11 is made of a substance that has a light element as a main component rather than a transition metal element and has a good X-ray transmittance.

  The reflective layer 12 reflects the light generated in the scintillator layer 13 in the direction opposite to the support substrate 11 to increase the light use efficiency.

  The scintillator layer 13 is formed by a vapor deposition method such as a vacuum deposition method, a sputtering method, or a CVD method, for example, a halogen compound such as cesium iodide (CsI), which is a high-intensity fluorescent material, or an oxide such as gadolinium sulfate (GOS). A phosphor such as a system compound is deposited on the support substrate 11 in a columnar shape to form a film. The scintillator layer 13 is formed in a columnar crystal structure in which a plurality of strip-shaped columnar crystals 13a are formed in the surface direction of the support substrate 11.

  Then, in the scintillator panel 10 configured in this way, X-rays 16 as radiation incident on the scintillator layer 13 from the support substrate 11 side are converted into visible light 17 by the columnar crystals 13a of the scintillator layer 13, and supported. Visible light 17 is emitted from the surface of the scintillator layer 13 opposite to the substrate 11 (the surface of the protective layer 14).

  FIG. 2 shows a second structural example of the scintillator panel 10. The first structure example of the scintillator panel 10 shown in FIG. 1 is the same as the other structure except that the reflective layer 12 is not provided. In this case, the support substrate 11 is made of a metal material such as Al, Ni, Cu, Pd, or Ag having a high reflectance.

  FIG. 3 shows a third structural example of the scintillator panel 10. In the first structural example of the scintillator panel 10 shown in FIG. 1, the scintillator layer 13 does not form the columnar crystal 13a, and the other configurations are the same.

  FIG. 4 shows a fourth structural example of the scintillator panel 10. In the second structural example of the scintillator panel 10 shown in FIG. 2, the other structures are the same except that the scintillator layer 13 does not form the columnar crystal 13a.

  FIG. 5 shows a CCD-DR type photographing apparatus 20 using the scintillator panel 10. The imaging device 20 has a housing 21, the scintillator panel 10 is installed at one end of the housing 21, a mirror-like reflector 22 and an optical lens 23 are installed inside the housing 21, A light receiving element 24 such as a CCD is installed at the end. X-rays 16 emitted from an X-ray generation source (X-ray tube) 25 enter the scintillator panel 10, and visible light 17 converted by the scintillator layer 13 is emitted from the surface of the scintillator layer 13. An X-ray image is projected on the surface of the scintillator layer 13, the X-ray image is reflected by the reflecting plate 22, condensed by the optical lens 23 and irradiated to the light receiving element 24, and the X-ray image is electrically converted by the light receiving element 24. Convert to signal and output.

  Since the light receiving element 24 used in the CCD-DR imaging device 20 exists in the visible light region where the peak wavelength of the light receiving sensitivity is 400 to 700 nm, when CsI is used for the scintillator layer 13, the X-ray 16 is incident. Tl having a wavelength of excited light in the vicinity of 550 nm is used as an activator.

  In the scintillator panel 10 having the structure shown in FIGS. 1 to 4, the scintillator layer 13 is a phosphor containing Tl as an activator in CsI, which is a halide, and the following (1) (2) ( 3) It has the characteristics of (4).

  (1): The concentration of the activator in the phosphor has a distribution in the film thickness direction of the scintillator layer 13. That is, the incident side of the X-ray 16 in the film thickness direction of the scintillator layer 13 is the incident side region A, and the side opposite to the incident side region A (the output side of the visible light 17 converted by the scintillator layer 13) is the non-incident side region B. , And the intermediate region C between the incident side region A and the non-incident side region B, the concentration of the activator in each phosphor in the incident side region A and the non-incident side region B is 0.2 mass% ± 0. .15 mass%, the concentration of the activator in the phosphor in the intermediate region C is 1.6 mass% ± 0.4 mass%. Further, the scintillator layer 13 is composed only of the concentration regions of the activator in the incident side region A, the intermediate region C, and the non-incident side region B, and the activator other than the incident side region A, the intermediate region C, and the non-incident side region B. There is no density region.

  (2): The ratio of the incident side region A and the non-incident side region B in the film thickness direction of the scintillator layer 13 is 10% or more.

  (3): The scintillator layer 13 has the concentration of each activator in the in-plane direction and in the film thickness direction in each of the unit film thicknesses of 200 nm or less in the incident side area A, intermediate area C, and non-incident side area B. The distribution is ± 15% or less, and uniformity is maintained.

  (4): The scintillator layer 13 is formed by a vacuum evaporation method using two evaporation sources (material sources) of CsI and TlI, and preferably has a structure of a strip-like columnar crystal 13a.

  Here, in the scintillator panel 10 of the first structural example shown in FIG. 1, the film thickness of the scintillator layer 13 is 350 μm, the base material of the scintillator layer 13 is CsI, and the activator is Tl, and the Tl concentration in the scintillator layer 13 FIG. 6 to FIG. 8 show the results of testing the correlation between the characteristics and each characteristic.

  FIG. 6 shows the correlation between the Tl concentration in the scintillator layer 13 and the sensitivity ratio. The test conditions are incident X-ray: 70 kV-0.0087 mGy, sensitivity ratio: ratio based on the sensitivity (1.0) when the Tl concentration in the scintillator layer 13 is 0.1 mass%, and each test sample The scintillator layer formation conditions (except for the Tl concentration in the scintillator layer 13) are the same. As shown in FIG. 6, the sensitivity was most improved when the Tl concentration in the scintillator layer 13 was in the vicinity of 1.4 mass% to 1.8 mass%.

  FIG. 7 shows the correlation between the Tl concentration in the scintillator layer 13 and the MTF ratio as the resolution. The test conditions are incident X-ray: 70 kV-0.0087 mGy, MTF ratio: MTF (at 2 Lp / mm) when the Tl concentration in the scintillator layer 13 is 0.1 mass% as a standard (1.0). Yes, the scintillator layer formation conditions (except for the Tl concentration in the scintillator layer 13) of each test sample are the same. Then, as shown in FIG. 7, the Tl concentration in the scintillator layer 13 was substantially constant up to around 2.0 mass%.

  FIG. 8 shows the correlation between the Tl concentration in the scintillator layer 13 and the afterimage ratio. The test condition is that the dose difference between the incident X-rays of the (n-1) th and n-th X-ray images is (n-1)> n, and the incident X-ray is 70 kV in the (n-1) th X-ray image. -0.87 mGy, subject: lead plate (thickness 3 mm), X-ray image acquisition interval: 60 sec, incident X-ray: 70 kV-0.0087 mGy, subject: none, X-ray image acquisition interval for the nth X-ray image : 60 sec. Further, the afterimage ratio: a ratio based on the afterimage when the Tl concentration in the scintillator layer 13 is 0.1 mass% as a reference (1.0), and the scintillator layer forming conditions of each test sample (Tl concentration in the scintillator layer 13) Are the same. As shown in FIG. 8, the afterimage was at the minimum level when the Tl concentration in the scintillator layer 13 was around 1.6 mass%. Further, in the region where the afterimage ratio is 0.5 (preferably 0.4) or less and the Tl concentration in the scintillator layer 13 is 1.6 mass% ± 0.4 mass%, no afterimage was confirmed.

  And as shown in FIG. 8, the afterimage becomes the minimum level when the concentration of the activator in the phosphor as the scintillator layer 13 is around 1.6 mass%, and the afterimage ratio is 0.5 (preferably 0.4) or less. In the region of 1.6 mass% ± 0.4 mass%, no afterimage is confirmed, and as shown in FIGS. 6 and 7, the characteristics of sensitivity and MTF are also obtained in the region of 1.6 mass% ± 0.4 mass%. Since it is good, the concentration of the activator is preferably 1.6 mass% ± 0.4 mass% in order to improve the overall characteristics including the afterimage characteristics of the scintillator layer 13.

  Further, in the scintillator panel 10 of the first structural example shown in FIG. 1, the film thickness of the scintillator layer 13 is 350 μm, the base material of the scintillator layer 13 is CsI, the activator is Tl, and the Tl concentration in the scintillator layer 13 is FIG. 9 to FIG. 11 show the results of testing the correlation between the stacking cycle of the scintillator layer 13 (the formation cycle of the unit film thickness (formed film thickness per one rotation of the substrate)) and each characteristic in a constant case.

  FIG. 9 shows the correlation between the lamination period of the scintillator layer 13 and the sensitivity ratio. The test conditions were as follows: incident X-ray: 70 kV-0.0087 mGy, Tl concentration in the scintillator layer 13: 0.1 mass%, sensitivity ratio: sensitivity when the lamination period of the scintillator layer 13 is 200 nm as a reference (1.0). The scintillator layer forming conditions (excluding the Tl concentration in the scintillator layer 13) of each test sample are the same.

  FIG. 10 shows the correlation between the lamination period of the scintillator layer 13 and the MTF ratio. Test conditions are based on incident X-ray: 70 kV-0.0087 mGy, Tl concentration in scintillator layer 13: 0.1 mass%, MTF ratio: MTF (at 2 Lp / mm) when the laminating period of scintillator layer 13 is 200 nm. The scintillator layer forming conditions (excluding the Tl concentration in the scintillator layer 13) of each test sample are the same.

  FIG. 11 shows the correlation between the lamination period of the scintillator layer 13 and the afterimage ratio. The test condition is that the dose difference between the incident X-rays of the (n-1) th and n-th X-ray images is (n-1)> n, and the incident X-ray is 70 kV in the (n-1) th X-ray image. -0.87 mGy, subject: lead plate (thickness 3 mm), X-ray image acquisition interval: 60 sec, incident X-ray: 70 kV-0.0087 mGy, subject: none, X-ray image acquisition interval for the nth X-ray image : 60 sec. Furthermore, the Tl concentration in the scintillator layer 13 is 0.1 mass%, the afterimage ratio is a ratio based on the afterimage when the stacking period of the scintillator layer 13 is 200 nm (1.0), and the scintillator layer formation of each test sample The conditions (except for the Tl concentration in the scintillator layer 13) are the same.

  As shown in FIGS. 9 to 11, each characteristic tends to deteriorate in the region where the lamination period of the scintillator layer 13 is 200 nm or more.

  This is because the peak wavelength of the emission wavelength of the scintillator layer 13 is around 550 nm, but the peak of the emission wavelength propagating in the scintillator layer 13 is because the refractive index of CsI which is the base material of the scintillator layer 13 is 1.8. If the wavelength is λ 1, it can be considered that λ 1 = 550 nm / 1.8 = 306 nm from the relationship between the refractive index and the wavelength. Therefore, when the stacking period of the scintillator layer 13 is larger than λ 1, the crystallinity variation of the scintillator layer 13 This is because the possibility of being affected by deterioration of optical characteristics (scattering, attenuation, etc.) due to variations in the Tl concentration in the scintillator layer 13 and the like is increased.

  Further, as shown in FIG. 6 to FIG. 8, in the region where the Tl concentration in the scintillator layer 13 is 1.6 mass% ± 0.4 mass%, each characteristic is close to a stable state, so the Tl concentration in the scintillator layer 13 Even if fluctuates (about ± 15%), the fluctuation of each characteristic is small.

  Even if the concentration of the activator in the phosphor is in the range of 1.6 mass% ± 0.4 mass%, if the concentration distribution of the activator in the in-plane direction and the film thickness direction of the phosphor is largely biased, each characteristic Therefore, the concentration distribution of the activator in the in-plane direction and the film thickness direction of the phosphor is preferably within ± 15%. If the concentration distribution of this activator is within the fluctuation range of about ± 15%, the fluctuation of each characteristic is small and the influence is small.

  Therefore, in order to improve the overall characteristics including the afterimage characteristics of the scintillator layer 13, the concentration of the activator in the phosphor is 1.6 mass% ± 0.4 mass%, and the in-plane direction of the phosphor and the film It is preferable that the concentration distribution of the activator in the thickness direction is within ± 15%. Further, if there is a large bias in the concentration distribution of the activator in the in-plane direction and the film thickness direction of the phosphor in at least the region of the unit film thickness of 200 nm or less, each characteristic is likely to fluctuate greatly. Even in a region having a thickness of 200 nm or less, the concentration distribution of the activator in the in-plane direction and the thickness direction of the phosphor is preferably within ± 15%.

  Next, in the scintillator panel 10 of the first structural example shown in FIG. 1, the base material of the scintillator layer 13: CsI, the activator: Tl, the lamination cycle of the scintillator layer 13: 150 nm, and the film thickness of the scintillator layer 13 The results of testing the correlation with each characteristic are shown in FIGS.

  FIG. 12 shows the correlation between the film thickness of the scintillator layer 13 and the afterimage ratio. The test condition is that the dose difference between the incident X-rays of the (n-1) th and n-th X-ray images is (n-1)> n, and the incident X-ray is 70 kV in the (n-1) th X-ray image. -0.87 mGy, subject: lead plate (thickness 3 mm), X-ray image acquisition interval: 60 sec, incident X-ray: 70 kV-0.0087 mGy, subject: none, X-ray image acquisition interval for the nth X-ray image : 60 sec. Further, the Tl concentration in the scintillator layer 13 is 0.1 mass%, and the afterimage ratio is a ratio based on the afterimage when the film thickness of the scintillator layer 13 is 600 μm (1.0), and the scintillator layer formation of each test sample The conditions (except for the Tl concentration in the scintillator layer 13) are the same. And as shown in FIG. 12, the afterimage became small, so that the film thickness of the scintillator layer 13 was thin. This is because, when the film thickness of the scintillator layer 13 is reduced, the sensitivity decreases with a decrease in the X-ray absorption rate (DQE). However, since the afterimage characteristic is one of the light emission characteristics of the scintillator layer 13, the sensitivity decreases ( It is considered that the afterimage is relatively reduced with a decrease in light excited by incident X-rays.

  FIG. 13 shows a correlation between the Tl concentration in the scintillator layer 13 and X-ray resistance (sensitivity attenuation of the scintillator layer 13 due to damage caused by X-ray irradiation). Test conditions are incident X-ray: 70 kV-0.0087 mGy, integrated irradiation dose in X-ray resistance: equivalent to use for 3 years in normal X-ray imaging diagnosis, sensitivity attenuation ratio: Tl concentration in scintillator layer is 0.1 mass% In this case, the ratio of the sensitivity attenuation rate after X-ray resistance is a reference (1.0), and the scintillator layer forming conditions (excluding the Tl concentration in the scintillator layer 13) of each test sample are the same. As shown in FIG. 13, when the Tl concentration in the scintillator layer 13 is less than the constant threshold of 0.4 mass%, the X-ray resistance is less deteriorated, and the Tl concentration in the scintillator layer 13 is constant. When the T value was 0.4 mass% or more, the X-ray resistance was significantly deteriorated, and when the Tl concentration was 1.0 mass% or more, which was a constant threshold, the X-ray resistance was deteriorated.

  This is because, in general, when a substance is irradiated with high energy (such as X-rays), the bonds between the atoms constituting the substance are damaged (bonds are broken, etc.), and particularly light is transmitted. It is considered that phosphors and the like are colored due to damage (color center) when irradiated with high energy (such as X-rays) (see Non-Patent Document 2). In general, when a substance is irradiated with high energy (such as X-rays), the damage caused by irradiation with high energy depends on the crystal state of the substance, and when the impurity concentration is high or the distortion of the crystal is large It is conceivable that the damage is increased when the impurity concentration is low or when the crystal distortion is small.

  Here, in the scintillator layer 13 composed of a phosphor containing Tl as an activator in CsI, which is a halide, the activator is an impurity. Therefore, the higher the Tl concentration in the scintillator layer 13, the more incident X Since the damage due to the line becomes remarkable, the correlation between the Tl concentration in the scintillator layer 13 and the X-ray resistance (sensitivity attenuation ratio) shown in FIG.

  Therefore, in order to improve the X-ray resistance of the scintillator layer 13, the concentration of the activator in the phosphor is preferably 0.4 mass% or less. However, as shown in FIGS. 6 and 8, the activator in the phosphor. When the density of the light is 0.05 mass% or less (no light emission at 0 mass%), the deterioration tendency of sensitivity and afterimage becomes remarkable. That is, in order to improve the X-ray resistance without causing significant deterioration in the scintillator layer 13, the concentration of the activator in the phosphor is preferably within 0.2 mass% ± 0.15 mass%.

  14A is a schematic diagram showing the scintillator layer 13, FIG. 14B is a schematic diagram showing the amount of X-ray absorption when the quality of the X-ray 16 incident on the scintillator layer 13 is hard, and FIG. (c) is a schematic diagram showing the amount of X-ray absorption when the quality of X-rays 16 incident on the scintillator layer 13 is soft. 15 and 16 show the results of testing the correlation between the thickness of the scintillator layer 13 and each characteristic when the base material of the scintillator layer 13 is CsI.

  As shown in FIGS. 14A, 14B and 14C, the X-rays 16 incident on the scintillator layer 13 are absorbed by the scintillator layer 13 and converted into visible light. Since the light is sequentially attenuated along the film thickness direction z of 13, the light emission level of the scintillator layer 13 is also attenuated sequentially along the film thickness direction z.

  For this reason, when X-rays 16 are incident on the scintillator layer 13, the light emission characteristics of the scintillator layer 13 depend on the characteristics of the scintillator layer 13 on the X-ray incident side.

  FIG. 15 shows the correlation {NIST (National Institute of Standards and Technology)) between the film thickness of the scintillator layer 13 and the X-ray quality {X-ray generation source (X-ray tube) tube voltage} at an X-ray absorption rate of 50%. Approximate from material data}. The test conditions are incident X-ray: single ray (X-ray formed with a single radiation quality), and X-ray absorption rate of the scintillator layer 13: 50%.

  FIG. 16 shows the correlation between the film thickness of the scintillator layer 13 and the X-ray absorption rate at a tube voltage of 70 kV. The test conditions are incident X-ray: single ray, X-ray quality (tube voltage): 70 kV.

  14 (b) (c), FIG. 15 and FIG. 16, the X-ray has a harder quality (the higher the tube voltage of the X-ray generation source (X-ray tube)), the more transparent the substance. Therefore, when X-rays enter the scintillator layer 13, the harder the X-ray quality, the smaller the attenuation that occurs along the film thickness direction z of the scintillator layer 13.

  However, due to the characteristics of the X-ray tube that is the X-ray generation source, the generated X-ray is not a single line, but a softer quality than the set quality {the tube voltage of the X-ray generation source (X-ray tube) is low } In the diagnosis using a general X-ray image, the light emission characteristic of the scintillator layer 13 is more dependent on the characteristic of the scintillator layer 13 on the X-ray incident side.

  For example, in the case where the base material of the scintillator layer 13 is CsI, the thickness of the scintillator layer 13 is 500 μm, and the tube voltage of incident X-rays is 70 kV (single line), the X-ray absorption rate of the scintillator layer 13 is about 50%. 15% or more of the entire X-ray absorbed in the scintillator layer 13 is absorbed in the region on the X-ray incident side of the scintillator layer 13 (region of 1/10 of the film thickness of the scintillator layer 13). The Rukoto.

  Furthermore, since the X-rays generated from the X-ray tube, which is the X-ray generation source, are not a single line and contain a lot of softer quality than the set quality, the X-rays of the scintillator layer 13 are used in the above case. It is considered that at least 25% or more of the entire X-ray absorbed by the scintillator layer 13 is absorbed in the incident side region (region of about 1/10 of the thickness of the scintillator layer 13).

  In a general indirect X-ray planar image detector and the CCD-DR imaging apparatus 20 shown in FIG. 5, the X-ray absorption rate of the scintillator layer 13 is at least 50% or more in order to reduce unnecessary exposure. For example, in the case of an X-ray planar image detector for general radiography that is often used with a tube voltage of around 70 kV, the film thickness of the scintillator layer 13 is selected. Is generally 500 μm or more.

  For this reason, a general indirect X-ray plane image detector and a CCD-DR imaging apparatus 20 shown in FIG. 5 are used in the X-ray incident side region of the scintillator layer 13 (the film thickness of the scintillator layer 13). It is considered that 25% or more of the total light emission of the scintillator layer 13 occurs in the region of about 1/10.

  Therefore, in the scintillator layer 13 composed of a phosphor containing Tl as an activator in CsI which is a halide, the region on the X-ray incident side of the scintillator layer 13 has a Tl concentration with good X-ray resistance, and the remaining If the Tl concentration in the X-ray non-incident side region is optimized, it is possible to improve both the afterimage characteristics and the X-ray resistance.

  In crystal formation by a general vapor phase growth method, the better the crystallinity of the whole crystal, the better the crystal characteristics.

  For example, in the scintillator layer 13 made of a phosphor containing Tl as an activator in CsI which is a halide, the activator is an impurity. Therefore, the lower the Tl concentration in the scintillator layer 13, the more the CsI single crystal becomes. It becomes a close crystal state (a state with good crystallinity).

  In general, the better the crystallinity of the scintillator layer 13, the better the optical characteristics (transmission, attenuation, etc.) of the scintillator layer 13, but a general indirect X-ray planar image detector or CCD shown in FIG. In the scintillator panel 10 incorporated in the -DR imaging device 20, the optical characteristics of the scintillator layer 13 in the X-ray non-incident side region, which is the output side of light excited by incident X-rays, is an X-ray planar image detector. And the characteristics (particularly the resolution) of the CCD-DR imaging device 20 are greatly affected. Therefore, the better the crystallinity of the scintillator layer 13 in the X-ray non-incident side region, the more the X-ray planar image detector and the CCD-DR. The characteristic deterioration (especially resolution) of the imaging device 20 of the type is less likely to occur.

  However, the region on the X-ray incident side of the scintillator layer 13 (region about 1/10 of the film thickness of the scintillator layer 13) has a Tl concentration with good X-ray resistance, and the remaining Tl of the region on the non-X-ray incident side. When the concentration is optimized, the Tl concentration in the X-ray non-incident side region becomes high, so that the crystallinity of the X-ray non-incident side region of the scintillator layer 13 deteriorates and the characteristics of the scintillator panel 10 deteriorate (resolution, etc.) May occur.

  Since the energy of incident X-rays attenuates sequentially along the film thickness direction of the scintillator layer 13, the light emission level of the scintillator layer 13 also attenuates sequentially along the film thickness direction. It is considered that the region (region of about 1/10 of the thickness of the scintillator layer 13) has almost no influence on the afterimage characteristics and the X-ray resistance.

  Therefore, the region on the non-incident side of the scintillator layer 13 (region about 1/10 of the film thickness of the scintillator layer 13) is changed to the region on the X-ray incident side of the scintillator layer 13 (1 / th of the film thickness of the scintillator layer 13). If the Tl density with good X-ray resistance is optimized and the Tl density in the remaining area is optimized, the afterimage characteristics and the X-ray resistance can be compatible, and the characteristics of the scintillator panel 10 deteriorate. (Resolution etc.) can be prevented.

  Next, FIG. 17 shows a schematic diagram of a general method for forming the scintillator layer 13. The support substrate 11 is arranged in the vacuum chamber 30 and the support substrate 11 is rotated while the evaporation particles 31a from the CsI evaporation source 31 and the evaporation particles from the TlI evaporation source 32 are installed in the vacuum chamber 30. The scintillator layer 13 is laminated by a vacuum vapor deposition method in which 32a is vapor-deposited on the laminated surface of the support substrate 11.

  At this time, if the rotation period of the support substrate 11 and the evaporation of CsI and TlI are controlled, the in-plane direction and the film thickness direction Tl concentration distribution per stacking period of the scintillator layer 13 can be arbitrarily controlled. Therefore, when the scintillator layer 13 is formed, if the uniformity of the Tl concentration distribution in the in-plane direction and film thickness direction per stacking period of the scintillator layer 13 is ensured, the entire in-plane direction and film thickness direction of the scintillator layer 13 The uniformity of the Tl concentration distribution is also ensured.

  Further, FIGS. 18 (a) and 18 (b) are schematic views showing a method of forming the scintillator layer 13 according to this embodiment. In the vacuum chamber 30, a CsI evaporation source 31 and two TlI evaporation sources 32-1 and 32-2 corresponding to the required Tl concentration are arranged. Then, the support substrate 11 is disposed in the vacuum chamber 30 and the TlI evaporation source 32 − is switched according to the required Tl concentration and the evaporated particles 31 a from the CsI evaporation source 31 while rotating the support substrate 11. The scintillator layer 13 is laminated by a vacuum vapor deposition method in which the vaporized particles 32a-1 and 32a-2 from 1 and 32-2 are vapor-deposited on the laminated surface of the support substrate 11. As a result, the Tl concentration distribution in the film thickness direction of the scintillator layer 13 can be changed. That is, assuming that the incident side region of the scintillator layer 13 is A, the intermediate region is C, and the non-incident side region is B, the concentration and concentration distribution of the activator in the phosphor in the film thickness direction are C> A and C> B. And the concentration region of the activator other than the incident side region A, the intermediate region C, and the non-incident side region B is composed of only the concentration region of the activator in the incident side region A, the intermediate region C, and the non-incident side region B. It can be formed so that it does not exist.

  From the above, in the scintillator layer 13 composed of a phosphor containing CsI as a halide and containing Tl as an activator, the incident side region A and the non-incident side region B of the scintillator layer 13 have good X-ray resistance. If the Tl density is set and the remaining intermediate region C is optimized to a Tl density with good afterimage characteristics, both improvement in afterimage characteristics and improvement in X-ray resistance can be achieved. That is, the concentration of the activator in the phosphor in the incident side region A and the non-incident side region B is 0.2 mass% ± 0.15 mass%, and the concentration of the activator in the phosphor in the intermediate region C is 1.6 mass% ±. By setting the mass to 0.4 mass%, it is possible to improve both the afterimage characteristics and the X-ray resistance.

  Moreover, the concentration region between the concentration of the activator in the phosphor in the incident side region A and the non-incident side region B and the concentration of the activator in the phosphor in the intermediate region C is the incident side region A and the non-incident side. Since the X-ray resistance is reduced compared to the region B and the afterimage characteristics are reduced compared to the intermediate region C, it is composed only of the concentration regions of the activator in the incident side region A, the intermediate region C, and the non-incident side region B. By having no concentration region of the activator other than the incident side region A, the intermediate region C, and the non-incident side region B, it is possible to achieve both improvement in afterimage characteristics at a high level and improvement in X-ray resistance. Become.

  Furthermore, if the ratio of the incident side region A and the non-incident side region B in the film thickness direction of the scintillator layer 13 is 10% or more, it is possible to achieve both improvement in afterimage characteristics and improvement in X-ray resistance. For example, if the ratio of the incident side area A and the non-incident side area B in the film thickness direction of the scintillator layer 13 is smaller than 10%, the improvement balance of each characteristic is lost.

  Furthermore, the scintillator layer 13 has a concentration distribution of each activator in the in-plane direction and in the film thickness direction in each of the unit film thicknesses of 200 nm or less in the incident side area A, the intermediate area C, and the non-incident side area B. Each of the stable characteristics can be obtained by maintaining the uniformity within ± 15%.

  Further, the scintillator layer 13 is formed by a vacuum evaporation method using two evaporation sources 32-1 and 32-2 of CsI and TlI, and preferably has a structure of a strip-like columnar crystal 13a.

  Therefore, if the characteristics (1) to (4) are added to the scintillator layer 13 composed of a phosphor containing Tl as an activator in CsI which is a halide, the characteristics of the scintillator layer 13 can be improved (afterimage characteristics and Comprehensive improvement including X-ray resistance) becomes possible.

  An embodiment of the scintillator panel 10 of the first structural example shown in FIG. 1 will be described. In this example, the base material of the scintillator layer 13: CsI, the activator: Tl, the lamination period of the scintillator layer 13: 150 nm, the concentration distribution of the activator in the in-plane direction and the film thickness direction of the scintillator layer 13: ± 15% Samples I, II, III, IV, and V, each having a different concentration distribution in the film thickness direction of the scintillator layer 13 and different concentrations of the activator in the scintillator layer 13 are prepared. FIGS. 19 (a), (b), (c), (d), and (e) are schematic views of the scintillator layers 13 of Samples I, II, III, IV, and V. FIG.

  In sample I, the concentration distribution in the film thickness direction of the scintillator layer 13 is constant, the film thickness of the scintillator layer 13 is 350 μm, and the concentration of the activator in the scintillator layer 13 is 0.1 mass%.

  In Sample II, the concentration distribution in the film thickness direction of the scintillator layer 13 is constant, the film thickness of the scintillator layer 13 is 350 μm, and the concentration of the activator in the scintillator layer 13 is 1.2 mass%.

  In Sample III, the incident side region of the scintillator layer 13 is A, the non-incident side region is B, and the intermediate region is C. In the incident side region A and the non-incident side region B, the film thickness is 35 μm, and the concentration of the activator is: In the intermediate region C, the film thickness is 280 μm, and the concentration of the activator is 1.2 mass%.

  In sample IV, the concentration distribution in the film thickness direction of the scintillator layer 13 is constant, the film thickness of the scintillator layer 13 is 350 μm, and the concentration of the activator in the scintillator layer 13 is 1.6 mass%.

  In sample V, the incident side region of the scintillator layer 13 is A, the non-incident side region is B, and the intermediate region is C. In the incident side region A and the non-incident side region B, the film thickness is 35 μm, and the concentration of the activator is: In the intermediate region C, the film thickness is 280 μm, and the concentration of the activator is 1.6 mass%.

  Each of these five samples I, II, III, IV, and V is combined with the CCD-DR type photographing device 20 shown in FIG. 6, and a subject is photographed under specific photographing conditions to satisfy predetermined image processing conditions. The X-ray image (n-th) when the captured image is processed is shown in FIGS. 20 (a) (b) (c) (d) (e), and the characteristic results are shown in the table of FIG.

  In FIG. 21, the sensitivity ratio, the MTF ratio, and the afterimage ratio are ratios based on the reference (1.00) when the Tl concentration in the scintillator layer 13 is 0.1 mass%. The sensitivity attenuation ratio is a ratio based on the sensitivity attenuation rate after X-ray resistance when the Tl concentration in the scintillator layer is 0.1 mass% as a reference (1.00).

  The test conditions for the sensitivity ratio and MTF ratio are incident X-rays: 70 kV-0.0087 mGy. The test conditions for the afterimage ratio are as follows: (n-1)> n is the dose difference between the incident X-rays of the (n-1) -th and n-th X-ray images, and the incident X in the (n-1) -th X-ray image. Line: 70 kV-0.87 mGy, subject: lead plate (plate thickness 3 mm), X-ray image acquisition interval: 60 sec. In the nth X-ray image, incident X-ray: 70 kV-0.0087 mGy, subject: none, X-ray Image acquisition interval: 60 sec. The X-ray resistance test conditions are incident X-ray: 70 kV-0.0087 mGy, cumulative irradiation dose: equivalent to use for 3 years in normal X-ray image diagnosis.

  The image processing conditions are: Flat Field Correction: Yes, Window Processing: Yes (Image histogram average value ± 10%).

  And as shown to Fig.20 (a), in the sample I whose activator density | concentration is 0.1 mass%, the afterimage was confirmed in the range enclosed with a broken line in the figure. On the other hand, as shown in FIGS. 20 (b), (c), (d), and (e), no afterimage was observed in the range surrounded by the broken line in the samples II, III, IV, and V.

  As shown in FIG. 21, sample I has the best X-ray resistance (sensitivity attenuation ratio), but the sensitivity ratio decreases, and the afterimage ratio increases and the afterimage is confirmed as described above.

  In Sample II, the sensitivity ratio and the afterimage ratio were improved as compared with Sample I, but a decrease in X-ray resistance (sensitivity attenuation ratio) was confirmed.

  Compared to sample II, sample III was confirmed to have improved X-ray resistance (sensitivity attenuation ratio) although the sensitivity ratio and afterimage ratio were slightly reduced.

  Sample IV was confirmed to have improved sensitivity ratio and afterimage ratio compared to samples I, II, and III, but a decrease in X-ray resistance (sensitivity attenuation ratio) was confirmed.

  Compared to sample III, sample V had almost no change in X-ray resistance (sensitivity attenuation ratio), and improved sensitivity ratio and afterimage ratio were confirmed. Furthermore, although the sensitivity ratio and the afterimage ratio of Sample V are slightly lower than those of Sample IV, an improvement in X-ray resistance (sensitivity attenuation ratio) was confirmed.

  Therefore, if the features (1) to (4) defined in the present embodiment are added to the scintillator layer 13, the improvement of the afterimage characteristics and the improvement of the X-ray resistance can be achieved with good sensitivity and MTF. Therefore, the scintillator panel 10 can be improved in performance and reliability.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

10 Scintillator panel
11 Support substrate
13 Scintillator layer
16 X-ray as radiation A Incident side area B Non-incident side area C Intermediate area

Claims (7)

A support substrate that transmits radiation;
A scintillator layer formed on the support substrate and converting radiation incident from the outside into light, and
The scintillator layer is
A phosphor containing Tl as an activator in CsI which is a halide,
The incident side of the radiation in the film thickness direction of the scintillator layer is an incident side region, the opposite side of the incident side region is a non-incident side region, and an intermediate region is between the incident side region and the non-incident side region. Then, the concentration of the activator in each phosphor in the incident side region and the non-incident side region is 0.2 mass% ± 0.15 mass%, and the concentration of the activator in the phosphor in the intermediate region The scintillator panel is characterized by 1.6 mass% ± 0.4 mass%. The scintillator panel according to claim 1, wherein the scintillator layer includes only the concentration region of the activator in the incident side region, the intermediate region, and the non-incident side region. 3. The scintillator panel according to claim 1, wherein a ratio of each of the incident side region and the non-incident side region in the film thickness direction of the scintillator layer is 10% or more. The scintillator layer has a concentration distribution of the activator in each of the in-plane direction and the film thickness direction in a region having a unit film thickness of 200 nm or less in each of the incident side region, the intermediate region, and the non-incident side region. The scintillator panel according to any one of claims 1 to 3, wherein the scintillator panel is 15% or less. The scintillator panel according to any one of claims 1 to 4, wherein the scintillator layer has a columnar crystal structure. The scintillator panel according to any one of claims 1 to 5, wherein the support substrate is made of a material whose main component is a light element rather than a transition metal element. A scintillator panel manufacturing method comprising: a support substrate that transmits radiation; and a scintillator layer that is formed on the support substrate and converts radiation incident from the outside into light,
The scintillator layer is a phosphor containing Tl as an activator in CsI which is a halide,
The incident side of the radiation in the film thickness direction of the scintillator layer is an incident side region, the opposite side of the incident side region is a non-incident side region, and an intermediate region is between the incident side region and the non-incident side region. Then, the concentration of the activator in each phosphor in the incident side region and the non-incident side region is 0.2 mass% ± 0.15 mass%, and the concentration of the activator in the phosphor in the intermediate region The scintillator layer is formed by a vapor phase growth method using the CsI and the Tl as material sources so as to be 1.6 mass% ± 0.4 mass%.