JP6734035B2 - Scintillator panel and manufacturing method thereof - Google Patents

Description

Embodiments of the present invention relate to a scintillator panel that converts radiation into light and a method for manufacturing the scintillator panel.

As a new-generation image detector for X-ray diagnosis, an X-ray detector, which is a flat-type radiation detector using an active matrix and a solid-state image sensor such as CCD and CMOS, has been attracting attention. By irradiating the X-ray detector with X-rays, an X-ray photographed 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 the light converted by the scintillator panel into an electric signal. Then, the light converted by the scintillator layer by the incident X-ray reaches the photoelectric conversion substrate and is converted into electric charges, which are read out as an output signal and converted into a digital image signal by a predetermined signal processing circuit or the like. To be done.

When CsI, which is a halide, is used for the scintillator layer, CsI alone cannot convert incident X-rays into visible light. An activator is contained in order to activate.

In the X-ray detector, since the peak wavelength of the photosensitivity of the photoelectric conversion substrate exists near 400 nm to 700 nm in the visible light region, when CsI is used for the scintillator layer, the light excited by the incident X-ray is detected. Tl having a wavelength near 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 characteristics of the scintillator layer are the concentration and concentration of Tl which is the activator, like 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 is not optimized, it will lead to deterioration of the characteristics of the scintillator layer, sensitivity related to the emission characteristics of the scintillator layer (emission Efficiency) and an afterimage (a phenomenon in which the subject image of the (n-1)th X-ray image before the (n-1)th time remains in the nth X-ray image) will be affected.

For example, in a diagnosis using an X-ray image, since the imaging conditions greatly vary depending on the subject {incident X-ray dose: about 0.0087 mGy to 0.87 mGy (because the X-ray transmittance varies depending on the site)}, (n -1) There may be a large difference in the incident X-ray dose between the X-ray image of the 1st time and the X-ray image of the n-th time, and the dose difference of the incident X-ray of the X-ray image of the (n-1)th time and the n-th time Is (n-1)>n, the emission characteristics of the scintillator layer in the non-subject part of the (n-1)th X-ray image changes due to the large energy of the incident X-rays, resulting in the nth X-ray image. The residual image causes an afterimage.

In the diagnosis using the X-ray image, the afterimage characteristic is an important characteristic compared with the sensitivity (luminous efficiency) and the resolution (MTF) which are the characteristics of other scintillator layers.

In a scintillator layer composed of a phosphor containing Ts as an activator in CsI, the higher the Tl concentration of the activator in the scintillator layer, the higher the X-ray resistance of the scintillator layer (the scintillator due to damage due to X-ray irradiation. It is shown in a paper (Non-Patent Document 1) and the like that deterioration of the layer sensitivity (reliability item)} is deteriorated. Furthermore, in general, when a substance is irradiated with high energy (such as X-rays), the bond between the atoms that form the substance is damaged (the bond is broken), and in particular, fluorescence that transmits light is used. It is described in a paper (Non-patent document 2) and the like that the body or the like is colored by damage (color center) when irradiated with high energy (X-ray or the like).

The scintillator layer composed of a phosphor containing Ts as an activator in CsI has a problem in further improvement of characteristics.

Conventionally, regarding the improvement of the characteristics of the scintillator layer, there are many things relating to the improvement of individual characteristics such as sensitivity (luminous efficiency), resolution (MTF), and afterimage, and the overall characteristics including afterimage characteristics and X-ray resistance There was nothing to improve.

JP, 2008-51793, A JP, 2015-38459, A

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 and a method for manufacturing the scintillator panel, which can improve the overall characteristics of the scintillator layer including afterimage characteristics and radiation resistance.

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 that 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. Assuming that the incident side of the radiation in the film thickness direction of the scintillator layer is the incident side area and the side opposite to the incident side area is the non-incident side area, the concentration of the activator in the incident side area of the phosphor is 1.6 mass% ± 0.4 mass%, the concentration of the activator in the phosphor at the non-incident side region Ri 0.2 mass% ± 0.15 mass% der thicker than the thickness of the film thickness of the incident side regions serial non-incident side region ..

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. FIG. 3 is a cross-sectional view of an image pickup apparatus using the same scintillator panel. 6 is a graph showing the correlation between the Tl concentration of the scintillator layer of the scintillator panel and the sensitivity ratio. 6 is a graph showing the correlation between the Tl concentration of the scintillator layer and the MTF ratio. 6 is a graph showing the correlation between the Tl concentration of the scintillator layer and the afterimage ratio. 3 is a graph showing the correlation between the lamination period of the scintillator layers and the sensitivity ratio. 6 is a graph showing the correlation between the stacking period of scintillator layers and the MTF ratio. 6 is a graph showing the correlation between the stacking period of scintillator layers and the afterimage ratio. 7 is a graph showing the correlation between the film thickness of the scintillator layer and the afterimage ratio. 6 is a graph showing the correlation between the Tl concentration of the scintillator layer and X-ray resistance (sensitivity attenuation ratio). Same as above, showing a scintillator layer, (a) is a schematic diagram showing a scintillator layer, (b) is a schematic diagram showing an X-ray absorption amount when the quality of X-rays incident on the scintillator layer is hard, (c) is a scintillator layer It is a schematic diagram which shows the X-ray absorption amount when the quality of the X-rays which injects into is soft. 6 is a graph showing the correlation between the film thickness of the scintillator layer and the tube voltage. 6 is a graph showing the correlation between the film thickness of the scintillator layer and the X-ray absorption rate. It is a schematic diagram which shows the general formation method of a scintillator layer same as the above. FIG. 5 is a schematic view showing a method of forming a scintillator layer according to the present embodiment in (a) and (b). It is a schematic diagram which shows the same scintillator layer of samples I, II, III, IV, and V of a scintillator panel same as the above, and (a)(b)(c)(d)(e) is a schematic view for every sample. Same as above, X-ray images acquired using samples I, II, III, IV, and V of the scintillator panel, and (a)(b)(c)(d)(e) are X-ray images for each sample. 9 is a table showing each characteristic obtained by using samples I, II, III, IV, and V of the same scintillator panel.

Hereinafter, one 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 has 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 to 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 supporting substrate 11 is mainly composed of a light element rather than a transition metal element and is made of a material having a high X-ray transmittance.

The reflection layer 12 reflects the light generated in the scintillator layer 13 in the direction opposite to the support substrate 11 to improve the light utilization efficiency.

The scintillator layer 13 is, for example, a vapor deposition method such as a vacuum vapor deposition method, a sputtering method, or a CVD method, and is a halogen compound such as cesium iodide (CsI) which is a high-intensity fluorescent substance, or an oxide such as gadolinium sulfate (GOS). A phosphor such as a compound is columnarly deposited on the support substrate 11 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 as described above, 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 are supported. Visible light 17 is emitted from the surface of the scintillator layer 13 (the surface of the protective layer 14) opposite to the substrate 11.

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

Further, 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 columnar crystals 13a, but the other structure is the same.

Further, 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 scintillator layer 13 does not form columnar crystals 13a, but the other structure is the same.

Further, FIG. 5 shows, for example, a CCD-DR type photographing device 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, and the other of the housing 21. A light receiving element 24 such as a CCD is installed at the end. Then, the X-rays 16 emitted from the X-ray generation source (X-ray tube) 25 enter the scintillator panel 10, and the 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, and the X-ray image is reflected by the reflection plate 22 and is condensed by the optical lens 23 to irradiate the light receiving element 24. Convert to a signal and output.

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

Then, in the scintillator panel 10 having the structure shown in FIGS. 1 to 4, the scintillator layer 13 is a phosphor containing Tl in CsI which is a halide as an activator, and further 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, the concentration of the activator in the phosphor in the incident side area A is 1.6 mass%±0.4 mass%, and the concentration of the activator in the phosphor in the non-incident side area B is 0.2 mass%±0. It is 15 mass%. Further, the scintillator layer 13 is composed of only the activator concentration regions of the incident side region A and the non-incident side region B, and there is no activator concentration region other than the incident side region A and the non-incident side region B.

(2): The proportion of the incident side region A in the film thickness direction of the scintillator layer 13 is 50% or more.

(3): The scintillator layer 13 has a concentration distribution of the activator of ±15% or less in the in-plane direction and the film thickness direction in a region having a unit film thickness of 200 nm or less in the incident side region A and the non-incident side region B. , Uniformity is maintained.

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

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

FIG. 6 shows the correlation between the Tl concentration in the scintillator layer 13 and the sensitivity ratio. The test conditions are as follows: incident X-ray: 70 kV-0.0087 mGy, sensitivity ratio: sensitivity with the Tl concentration in the scintillator layer 13 being 0.1 mass% as a reference (1.0). The scintillator layer forming conditions (excluding the Tl concentration in the scintillator layer 13) are the same. Then, 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 which is the resolution. The test conditions are as follows: 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%, based on the ratio (1.0). Therefore, the scintillator layer forming conditions (excluding 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 became 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 of the incident X-rays of the (n-1)th and the nth 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 in the nth X-ray image : Set to 60 seconds. Further, the afterimage ratio is a ratio with the afterimage when the Tl concentration in the scintillator layer 13 is 0.1 mass% as a reference (1.0), and is the scintillator layer forming condition (Tl concentration in the scintillator layer 13) of each test sample. Are the same). Then, as shown in FIG. 8, the afterimage reached the minimum level when the Tl concentration in the scintillator layer 13 was around 1.6 mass%. Further, no afterimage was observed in the region where the afterimage ratio was 0.5 (preferably 0.4) or less and the Tl concentration in the scintillator layer 13 was 1.6 mass%±0.4 mass%.

Then, as shown in FIG. 8, the afterimage becomes a minimum level when the concentration of the activator in the phosphor that is the scintillator layer 13 is around 1.6 mass%, and the afterimage ratio is 0.5 (preferably 0.4) or less. In the area of 1.6 mass%±0.4 mass%, the afterimage is not confirmed, and as shown in FIGS. 6 and 7, the characteristics of sensitivity and MTF are also in the area of 1.6 mass%±0.4 mass%. Since it is good, the concentration of the activator is preferably in the range of 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: 350 μm, the base material of the scintillator layer 13: CsI, the activator: Tl, and the Tl concentration in the scintillator layer 13 is 9 to 11 show the results of testing the correlation between the lamination period of the scintillator layer 13 (formation period of unit film thickness (formed film thickness per one rotation of the substrate)) and each characteristic when the scintillator layer 13 is kept constant.

FIG. 9 shows the correlation between the lamination period of the scintillator layer 13 and the sensitivity ratio. The test conditions are as follows: incident X-ray: 70 kV-0.0087 mGy, Tl concentration in scintillator layer 13: 0.1 mass%, sensitivity ratio: sensitivity when the stacking period of the scintillator layer 13 is 200 nm as a standard (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 stacking period of the scintillator layer 13 and the MTF ratio. The test conditions are: incident X-ray: 70 kV-0.0087 mGy, Tl concentration in the scintillator layer 13: 0.1 mass%, MTF ratio: MTF (at 2 Lp/mm) when the stacking period of the 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 of the incident X-rays of the (n-1)th and the nth 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 in the nth X-ray image : Set to 60 seconds. Furthermore, the Tl concentration in the scintillator layer 13 is 0.1 mass%, the afterimage ratio is a ratio based on (1.0) the afterimage when the stacking period of the scintillator layer 13 is 200 nm, and the scintillator layer forming condition of each test sample. (Excluding the Tl concentration in the scintillator layer 13) is the same.

Then, as shown in FIGS. 9 to 11, in the region where the stacking period of the scintillator layer 13 is 200 nm or more, the respective characteristics tend to deteriorate.

This is because the peak wavelength of the emission wavelength of the scintillator layer 13 is around 550 nm, but the refractive index of CsI, which is the base material of the scintillator layer 13, is 1.8, so the peak emission wavelength of light that propagates in the scintillator layer 13 If the wavelength is λ1, it can be regarded as λ1=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 λ1, the scintillator layer 13 has a variation in crystallinity. , And the possibility of being affected by deterioration (scattering, attenuation, etc.) of optical characteristics due to variations in Tl concentration in the scintillator layer 13 and the like increases.

Further, as shown in FIGS. 6 to 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, and therefore, the Tl concentration in the scintillator layer 13 is 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 there is a large deviation in the concentration distribution of the activator in the in-plane direction and the film thickness direction of the phosphor, each characteristic Is likely to fluctuate greatly, so 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 the 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. The activator concentration distribution in the thickness direction is preferably within ±15%. Furthermore, in at least the unit film thickness of the phosphor of 200 nm or less, if there is a large deviation in the concentration distribution of the activator in the in-plane direction and the film thickness direction of the phosphor, each characteristic is likely to change greatly, Even in the region where the film thickness is 200 nm or less, the concentration distribution of the activator in the in-plane direction and the film 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 period 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. 12 and 13.

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 of the incident X-rays of the (n-1)th and the nth 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 in the nth X-ray image : Set to 60 seconds. Further, the Tl concentration in the scintillator layer 13 is 0.1 mass %, and the afterimage ratio is a ratio with the afterimage when the film thickness of the scintillator layer 13 is 600 μm as a reference (1.0), and scintillator layer formation of each test sample. The conditions (excluding the Tl concentration in the scintillator layer 13) are the same. Then, as shown in FIG. 12, the thinner the scintillator layer 13, the smaller the afterimage. This is because when the thickness of the scintillator layer 13 becomes thin, the sensitivity lowers as the X-ray absorptance (DQE) lowers, but the afterimage characteristic is one of the light emission characteristics of the scintillator layer 13, and thus the sensitivity lowering ( It is considered that the afterimage relatively decreases with the decrease in the light excited by the incident X-ray.

FIG. 13 shows the correlation between the Tl concentration in the scintillator layer 13 and X-ray resistance (sensitivity decay of the scintillator layer 13 due to damage due to X-ray irradiation). The test conditions are: incident X-ray: 70 kV-0.0087 mGy, cumulative irradiation dose for X-ray resistance: equivalent to 3 years use in normal X-ray image diagnosis, sensitivity attenuation ratio: 0.1 mass Tl concentration in the scintillator layer. In the case of %, it is a ratio based on the sensitivity decay rate after X-ray resistance as 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. Then, as shown in FIG. 13, when the Tl concentration in the scintillator layer 13 is less than a constant threshold value of 0.4 mass%, the X-ray resistance is less deteriorated, and the Tl concentration in the scintillator layer 13 is constant. When the threshold value is 0.4 mass% or more, the deterioration of the X-ray resistance becomes remarkable, and when the Tl concentration is 1.0 mass% or more, which is a constant threshold value, the deterioration tendency of the X-ray resistance becomes slower.

This is because, in general, when a substance is irradiated with high energy (such as X-rays), the bond between the atoms constituting the substance is damaged (the bond is broken), and the light is transmitted particularly. It is considered that the phosphor or the like is colored (color center) due to damage when it is irradiated with high energy (X-ray or the like) (see Non-Patent Document 2). Further, in general, when a substance is irradiated with high energy (such as X-ray), the damage due to the high energy irradiation depends on the crystal state of the substance, and when the impurity concentration is high or the strain of the crystal is large. It is conceivable that the damage becomes large when the impurity concentration is low or when the crystal strain is small.

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

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, but as shown in FIGS. 6 and 8, the activator in the phosphor is When the density is less than 0.05 mass% (no light emission at 0 mass%), the sensitivity and the residual image are prone to deteriorate. That is, in order to improve the X-ray resistance without causing the characteristic deterioration of the scintillator layer 13, the concentration of the activator in the phosphor is preferably 0.2 mass%±0.15 mass% or less.

Next, FIG. 14(a) is a schematic diagram showing the scintillator layer 13, and FIG. 14(b) is a schematic diagram showing the X-ray absorption amount when the quality of the X-rays 16 incident on the scintillator layer 13 is hard, FIG. (c) is a schematic diagram showing an X-ray absorption amount 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 film thickness of the scintillator layer 13 and each characteristic when the base material of the scintillator layer 13 is CsI.

As shown in FIGS. 14(a)(b)(c), 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 emission level of the scintillator layer 13 is sequentially attenuated along the film thickness direction z, the light emission level of the scintillator layer 13 is also sequentially attenuated along the film thickness direction z.

Therefore, when the X-rays 16 are incident on the scintillator layer 13, the 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 between the film thickness of the scintillator layer 13 at an X-ray absorption rate of 50% and the X-ray quality {tube voltage of the X-ray source (X-ray tube)} {NIST (National Institute of Standards and Technology) Approximate from material data}. The test conditions are: incident X-ray: single ray (X-ray formed with a single radiation quality), 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.

As can be seen from FIGS. 14(b) and (c), FIGS. 15 and 16, the higher the X-ray quality, the higher the tube voltage of the X-ray generation source (X-ray tube). Therefore, when X-rays are incident on the scintillator layer 13, the harder the quality of the X-rays, 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 source, the generated X-rays are not single rays, and the softness is softer than the set quality (the tube voltage of the X-ray source (X-ray tube) is low. } Is included in a large amount, the light emission characteristic of the scintillator layer 13 depends more on the characteristic of the scintillator layer 13 on the X-ray incident side in a diagnosis using a general X-ray image.

For example, in the case where the base material of the scintillator layer 13 is CsI, the film thickness of the scintillator layer 13 is 500 μm, and the tube voltage of the incident X-ray is 70 kV (single line), the X-ray absorption rate of the scintillator layer 13 is about 50%. In the region of the scintillator layer 13 on the X-ray incidence side (half the film thickness of the scintillator layer 13), 60% or more of the entire X-rays absorbed by the scintillator layer 13 is absorbed. The Rukoto.

Further, since the X-rays generated from the X-ray tube, which is the X-ray generation source, are not single rays and contain a lot of softer quality than the set quality, in the case of the above case, the X-rays of the scintillator layer 13 are included. It is considered that at least 80% or more of the entire X-rays absorbed by the scintillator layer 13 is absorbed in the incident side region (a region of about 1/2 the film thickness of the scintillator layer 13).

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

Therefore, in the general indirect X-ray plane image detector and the CCD-DR type imaging device 20 shown in FIG. 5, the X-ray incident side region of the scintillator layer 13 (the film thickness of the scintillator layer 13 It is considered that 80% or more of the entire light emission of the scintillator layer 13 occurs in the area of about 1/2).

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

At this time, by controlling the rotation cycle of the support substrate 11 and the evaporation of CsI and TlI, the Tl concentration distribution in the in-plane direction and the film thickness direction per stacking cycle 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 the film thickness direction per stacking period of the scintillator layer 13 is ensured, the entire in-plane direction and the film thickness direction of the scintillator layer 13 are ensured. The uniformity of the Tl concentration distribution of is also secured.

Further, FIGS. 18(a) and 18(b) are schematic views showing a method of forming the scintillator layer 13 of this embodiment. In the vacuum chamber 30, a CsI evaporation source 31 and two TlI evaporation sources 32-1 and 32-2 corresponding to a required Tl concentration are arranged. Then, the supporting substrate 11 is placed in the vacuum chamber 30, and while the supporting substrate 11 is rotated, the evaporation particles 31a from the evaporation source 31 of CsI and the evaporation source 32-1 of TlI which is switched depending on the required Tl concentration. The scintillator layer 13 is laminated by a vacuum vapor deposition method in which vaporized particles 32a-1 and 32a-2 from 1 and 32-2 are vapor-deposited on the laminated surface of the support substrate 11. This makes it possible to change the Tl concentration distribution in the thickness direction of the scintillator layer 13. That is, when the incident side region of the scintillator layer 13 is A 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 A>B, and the incident side region A and the non-incident side region It is possible to form only the concentration region of the activator in the incident side region B and to form the concentration region of the activator other than the incident side region A and the non-incident side region B so as not to exist.

From the above, in the scintillator layer 13 composed of a phosphor containing Tl as an activator in CsI which is a halide, the Tl concentration in the incident side region A of the scintillator layer 13 is optimized, and the remaining non-incident side When the region B has a Tl concentration with good X-ray resistance, it is possible to improve both the afterimage characteristics and the X-ray resistance. That is, the concentration of the activator in the phosphor in the incident side area A is 1.6 mass%±0.4 mass%, and the concentration of the activator in the phosphor in the non-incident side area B is 0.2 mass%±0.15 mass% By so doing, it is possible to achieve both improvement in afterimage characteristics and improvement in X-ray resistance.

In addition, in the concentration region between the concentration of the activator in the phosphor in the incident side area A and the concentration of the activator in the phosphor in the non-incident side area B, the afterimage characteristic is lower than that in the incident side area A. Since the X-ray resistance is lower than that in the non-incident side region B, the activator concentration regions of the incident side region A and the non-incident side region B are only configured, and the regions other than the incident side region A and the non-incident side region B are formed. By making the concentration region of the activator nonexistent, it becomes possible to improve the afterimage characteristic at a high level and the X-ray resistance at a high level.

Further, if the proportion of the incident side region A in the film thickness direction of the scintillator layer 13 is set to 50% or more, it is possible to improve both the afterimage characteristics and the X-ray resistance. For example, if the proportion of the incident side region A in the film thickness direction of the scintillator layer 13 is smaller than 50%, the balance of improvement of each characteristic will be lost.

Furthermore, the scintillator layer 13 has a uniform concentration distribution of the activator of ±15% or less in the in-plane direction and the film thickness direction in the unit film thickness 200 nm or less in the incident side region A and the non-incident side region B. By maintaining the property, stable characteristics can be obtained.

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

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

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

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 activator concentration 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 activator concentration in the scintillator layer 13 is 1.2 mass %.

In Sample III, the incident side region of the scintillator layer 13 is A, and the non-incident side region is B. The incident side region A has a film thickness of 175 μm and an activator concentration of 1.2 mass%. In B, the film thickness is 175 μm, and the activator concentration is 0.1 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 activator concentration in the scintillator layer 13 is 1.6 mass %.

Sample V has an incident side area of the scintillator layer 13 as A and a non-incident side area as B, and has a film thickness of 175 μm and an activator concentration of 1.6 mass% in the incident side area A. In B, the film thickness is 175 μm, and the activator concentration is 0.1 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, and the predetermined image processing conditions are set. 20(a)(b)(c)(d)(e) shows the X-ray image (n-th time) when the photographed image is processed by the above, and the result of the characteristic is shown in the table of FIG.

In FIG. 21, the sensitivity ratio, the MTF ratio, and the afterimage ratio are ratios when the Tl concentration in the scintillator layer 13 is 0.1 mass% as a reference (1.00). The sensitivity attenuation ratio is a ratio based on the sensitivity attenuation ratio 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-ray: 70 kV-0.0087 mGy. The test condition of the afterimage ratio is that the dose difference between the incident X-rays of the (n-1)th and the nth X-ray images is (n-1)>n, and the incident X-ray is the incident X-ray image in the (n-1)th X-ray image. Line: 70 kV-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 in the nth X-ray image Image acquisition interval: 60 sec. The test conditions for X-ray resistance are: incident X-ray: 70 kV-0.0087 mGy, cumulative irradiation dose: equivalent to 3 years of use in normal X-ray image diagnosis.

The image processing conditions are flat field correction: Yes, window processing: Yes (image histogram average value ±10%).

Then, as shown in FIG. 20(a), in Sample I having a concentration of the activator of 0.1 mass%, an afterimage was confirmed in a range surrounded by a broken line in the figure. On the other hand, as shown in FIGS. 20(b)(c)(d)(e), in Samples II, III, IV and V, an afterimage was not confirmed in the range surrounded by the broken line in the figure.

As shown in FIG. 21, the 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.

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

It was confirmed that Sample III was improved in X-ray resistance (sensitivity attenuation ratio), although the sensitivity ratio and the afterimage ratio were slightly reduced as compared with Sample II.

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

In Sample V, the X-ray resistance (sensitivity attenuation ratio) was almost the same as that of Sample III, and it was confirmed that the sensitivity ratio and the afterimage ratio were improved. Further, in the sample V, although the sensitivity ratio and the afterimage ratio are slightly reduced as compared with the sample IV, it is confirmed that the X-ray resistance (sensitivity attenuation ratio) is improved.

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

Although some embodiments of the present invention have been described, these embodiments are presented as examples 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 spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the scope of equivalents thereof.

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

Claims (6)

A support substrate that transmits radiation,
A scintillator layer formed on the support substrate and converting 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, and the side opposite to the incident side region is the non-incident side region, the concentration of the activator in the phosphor in the incident side region. 1.6mass% ± 0.4mass%, the concentration of the activator of the phosphor in the non-incident side region Ri 0.2 mass% ± 0.15 mass% der, the film thickness of the incident-side region is the A scintillator panel, which is thicker than the non-incident side region . The scintillator panel according to claim 1, wherein the scintillator layer includes only the concentration regions of the activator in the incident side region and the non-incident side region . The scintillator layer has a concentration distribution of the activator of ±15% or less 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 the incident side region and the non-incident side region. The scintillator panel according to claim 1 or 2, wherein: The scintillator panel according to any one of claims 1 to 3 , wherein the scintillator layer has a columnar crystal structure. The scintillator panel according to any one of claims 1 to 4 , wherein the supporting substrate is made of a substance containing a light element as a main component rather than a transition metal element. A method of manufacturing a scintillator panel, 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,
When the incident side of the radiation in the film thickness direction of the scintillator layer is an incident side region, and the side opposite to the incident side region is a non-incident side region, the concentration of the activator in the phosphor in the incident side region. Is 1.6 mass% ± 0.4 mass% , the concentration of the activator in the phosphor in the non-incident side region is 0.2 mass% ± 0.15 mass% , and the film thickness of the incident side region is A method of manufacturing a scintillator panel, characterized in that the scintillator layer is formed by a vapor phase growth method using the CsI and Tl as material sources so that the scintillator layer is thicker than the incident side region .