JP2015096820A - Radiation detector and radiation detector manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation detector capable of improving general characteristics including an afterimage characteristic of a scintillator layer.SOLUTION: An X-ray detector 1 includes: a photoelectric conversion substrate 2 converting light to an electric signal; and a scintillator layer 31 in contact with the photoelectric conversion substrate 2 for converting an X-ray 51 incident thereon from an outside to light. The scintillator layer 31 is a fluorescent substance containing Tl acting as an activator in CsI that is a halide. If it is defined that a central area of a formation area of the scintillator layer 31 is a central portion and an outer peripheral area thereof is a peripheral portion, a concentration of the activator in the fluorescent substance in an in-plane direction of the scintillator layer 31 satisfies a relation of (central portion)>(peripheral portion) and the concentration of the activator in the fluorescent substance is 1.6 mass% to 2.0 mass%.

Description

  Embodiments described herein relate generally to a radiation detector that detects radiation and a method for manufacturing the same.

  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 photoelectric conversion substrate that converts light into an electric signal, and a scintillator layer that converts X-rays incident from the outside in contact with the photoelectric conversion substrate into light. 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 an X-ray detector 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 (Luminescence 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} will be affected.

  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.

  Furthermore, in diagnosis using an X-ray image, since the diagnosis is usually performed in a state where a subject is arranged at the center of the X-ray image, the characteristics of the central region of the scintillator layer forming region are important.

  Conventionally, for the purpose of improving sensitivity (luminous efficiency) and resolution (MTF), there has been a proposal to define the concentration and concentration distribution of the activator of the scintillator layer.

JP 2007-232636 A

  Conventionally, many improvements in the characteristics of the scintillator layer are related to sensitivity (light emission efficiency) and resolution (MTF), and few are related to an improvement in overall characteristics including afterimage characteristics.

  The problem to be solved by the present invention is to provide a radiation detector capable of improving the overall characteristics including the afterimage characteristics of the scintillator layer and a method for manufacturing the same.

  The radiation detector of the present embodiment includes a photoelectric conversion substrate that converts light into an electrical signal, and a scintillator layer that converts radiation incident from the outside in contact with the photoelectric conversion substrate, and the scintillator layer includes: A phosphor containing Tl as an activator in CsI which is a halide, and when the central region of the scintillator layer forming region is a central portion and the outer peripheral region is a peripheral portion, the fluorescence in the in-plane direction of the scintillator layer The density | concentration of the said activator in a body has the relationship of a center part> peripheral part, and the density | concentration of the said activator in the said fluorescent substance is 1.6 mass%-2.0 mass%.

It is sectional drawing of the 1st structural example of the radiation detector which shows one Embodiment. It is sectional drawing of the 2nd structural example of a radiation detector same as the above. It is sectional drawing of the 3rd structural example of a radiation detector same as the above. It is sectional drawing of the 4th structural example of a radiation detector same as the above. It is an equivalent circuit diagram of a radiation detector same as the above. It is a graph which shows the correlation with Tl density | concentration of the scintillator layer of a radiation detector 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 side view which shows the arrangement | positioning relationship between a radiation detector same as the above and an X-ray generation source. It is a front view of a radiation detector same as the above. It is an X-ray image acquired using the radiation detector same as the above, (a) is an X-ray image without correction, and (b) is an X-ray image with correction. 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 an example of the formation method which changes the density | concentration of the activator in fluorescent substance by the center part and peripheral part of a scintillator layer same as the above. It is a schematic diagram which shows the other example of the formation method which changes the density | concentration of the activator in fluorescent substance by the center part and peripheral part of a scintillator layer same as the above. It is a table | surface which shows the samples A, B, C, D, and E of the radiation detector which changed the density | concentration of the activator in the fluorescent substance in the center part and peripheral part of a scintillator layer same as the above. It is an X-ray image acquired using samples A, B, C, D, and E of the radiation detector as described above. (A) (b) (c) (d) (e) is there. It is a table | surface which shows each characteristic acquired using sample A, B, C, D, E of a radiation detector same as the above. It is an X-ray image acquired using the samples D and E of the radiation detector as described above, (a) is an X-ray image of the sample D, and (b) is an X-ray image of the sample E.

  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 radiation detector, and FIG. 5 shows an equivalent circuit diagram of the basic configuration.

  First, with reference to FIG. 1 and FIG. 5, the 1st structural example of the X-ray detector 1 as a radiation detector is demonstrated. As shown in FIG. 1, the X-ray detector 1 is an indirect X-ray planar image detector. The X-ray detector 1 includes a photoelectric conversion substrate 2 that is an active matrix photoelectric conversion substrate that converts visible light into an electrical signal.

  The photoelectric conversion substrate 2 includes a support substrate 3 as an insulating substrate formed of a rectangular flat plate-shaped glass having translucency. On the surface of the support substrate 3, a plurality of pixels 4 are two-dimensionally arranged in a matrix and spaced from each other. For each pixel 4, a thin film transistor (TFT) 5 as a switching element and a charge storage capacitor 6. A pixel electrode 7 and a photoelectric conversion element 8 such as a photodiode are formed.

  As shown in FIG. 5, on the support substrate 3, control electrodes 11 are wired as a plurality of control lines along the row direction of the support substrate 3. The plurality of control electrodes 11 are located between the respective pixels 4 on the support substrate 3 and are separated from each other in the column direction of the support substrate 3. These control electrodes 11 are electrically connected to the gate electrode 12 of the thin film transistor 5.

  On the support substrate 3, a plurality of readout electrodes 13 are wired along the column direction of the support substrate 3. The plurality of readout electrodes 13 are located between the respective pixels 4 on the support substrate 3 and are separated from each other in the row direction of the support substrate 3. The source electrode 14 of the thin film transistor 5 is electrically connected to the plurality of readout electrodes 13. The drain electrode 15 of the thin film transistor 5 is electrically connected to the charge storage capacitor 6 and the pixel electrode 7, respectively.

  As shown in FIG. 1, the gate electrode 12 of the thin film transistor 5 is formed in an island shape on the support substrate 3. An insulating film 21 is laminated on the support substrate 3 including the gate electrode 12. This insulating film 21 covers each gate electrode 12. On the insulating film 21, a plurality of island-shaped semi-insulating films 22 are laminated. These semi-insulating films 22 are made of a semiconductor and function as a channel region of the thin film transistor 5. Each of these semi-insulating films 22 is disposed to face each gate electrode 12 and covers each gate electrode 12. That is, each of these semi-insulating films 22 is provided on each gate electrode 12 via the insulating film 21.

  On the insulating film 21 including the semi-insulating film 22, island-shaped source electrodes 14 and drain electrodes 15 are formed, respectively. The source electrode 14 and the drain electrode 15 are insulated from each other and are not electrically connected. The source electrode 14 and the drain electrode 15 are provided on both sides of the gate electrode 12, and one end portions of the source electrode 14 and the drain electrode 15 are stacked on the semi-insulating film 22.

  As shown in FIG. 5, the gate electrode 12 of each thin film transistor 5 is electrically connected to the common control electrode 11 together with the gate electrodes 12 of other thin film transistors 5 located in the same row. Further, the source electrode 14 of each thin film transistor 5 is electrically connected to the common readout electrode 13 together with the source electrodes 14 of other thin film transistors 5 located in the same column.

  As shown in FIG. 1, the charge storage capacitor 6 includes an island-shaped lower electrode 23 formed on the support substrate 3. An insulating film 21 is laminated on the support substrate 3 including the lower electrode 23. The insulating film 21 extends from the gate electrode 12 of each thin film transistor 5 to the lower electrode 23. Further, an island-shaped upper electrode 24 is laminated on the insulating film 21. The upper electrode 24 is disposed to face the lower electrode 23 and covers each lower electrode 23. That is, each upper electrode 24 is provided on each lower electrode 23 via the insulating film 21. A drain electrode 15 is laminated on the insulating film 21 including the upper electrode 24. The other end of the drain electrode 15 is stacked on the upper electrode 24 and is electrically connected to the upper electrode 24.

On the insulating film 21 including the semi-insulating film 22, the source electrode 14 and the drain electrode 15 of each thin film transistor 5 and the upper electrode 24 of each charge storage capacitor 6, an insulating layer 25 is laminated and formed. Yes. The insulating layer 25 is formed of silicon oxide (SiO ₂ ) or the like, and is formed so as to surround each pixel electrode 7.

  A part of the insulating layer 25 is formed with a through hole 26 as a contact hole communicating with the drain electrode 15 of the thin film transistor 5. On the insulating layer 25 including the through hole 26, an island-shaped pixel electrode 7 is laminated. The pixel electrode 7 is electrically connected to the drain electrode 15 of the thin film transistor 5 through the through hole 26.

  On each pixel electrode 7, a photoelectric conversion element 8 such as a photodiode for converting visible light into an electric signal is laminated.

  A scintillator layer 31 that converts X-rays as radiation into visible light is formed on the surface of the photoelectric conversion substrate 2 on which the photoelectric conversion elements 8 are formed. The scintillator layer 31 is formed by vapor deposition methods such as vacuum deposition, sputtering, and CVD, and is a high-luminance fluorescent material such as a halogen compound such as cesium iodide (CsI) or an oxide such as gadolinium sulfate (GOS). A phosphor such as a system compound is deposited on the photoelectric conversion substrate 2 in a columnar shape to form a film. The scintillator layer 31 is formed in a columnar crystal structure in which a plurality of strip-shaped columnar crystals 32 are formed in the surface direction of the photoelectric conversion substrate 2.

  In addition, a reflection layer 41 is formed on the scintillator layer 31 so as to increase the utilization efficiency of visible light converted by the scintillator layer 31, and the scintillator layer 31 is removed from moisture in the atmosphere on the reflection layer 41. A protective layer 42 for protection is laminated and formed, and an insulating layer 43 is laminated on the protective layer 42. A lattice-shaped X-ray grid 44 that shields between the pixels 4 is formed on the insulating layer 43.

  In the X-ray detector 1 configured as described above, X-rays (also referred to as incident X-rays) 51 as radiation incident on the scintillator layer 31 are converted into visible light 52 by columnar crystals 32 of the scintillator layer 31. Converted.

  The visible light 52 reaches the photoelectric conversion element 8 of the photoelectric conversion substrate 2 through the columnar crystal 32 and is converted into an electric signal. The electric signal converted by the photoelectric conversion element 8 flows to the pixel electrode 7 and is transferred to the charge storage capacitor 6 connected to the pixel electrode 7 until the gate electrode 12 of the thin film transistor 5 connected to the pixel electrode 7 is driven. Move and hold and accumulate.

  At this time, when one of the control electrodes 11 is in a driving state, the thin film transistors 5 in one row connected to the control electrode 11 in the driving state are in a driving state.

  Electric signals stored in the charge storage capacitors 6 connected to the respective thin film transistors 5 in this driving state are output to the readout electrode 13.

  As a result, since signals corresponding to the pixels 4 in a specific row of the X-ray image are output, signals corresponding to the pixels 4 of all X-ray images can be output by the drive control of the control electrode 11, and this output signal Is converted into a digital image signal and output.

  Next, a second structural example of the X-ray detector 1 will be described with reference to FIG. The same reference numerals as those in the first structural example of the X-ray detector 1 are used, and the description of the same configuration and operation is omitted.

  The structure and operation of the photoelectric conversion substrate 2 are the same as those in the first structure example.

  A scintillator panel 62 is bonded onto the photoelectric conversion substrate 2 via a bonding layer 61. The scintillator panel 62 has a support substrate 63 that transmits X-rays 51, a reflection layer 41 that reflects light is formed on the support substrate 63, and a plurality of strip-like columnar crystals 32 are formed on the reflection layer 41. A scintillator layer 31 is formed, and a protective layer 42 that seals the scintillator layer 31 is laminated on the scintillator layer 31. Further, a lattice-shaped X-ray grid 44 that shields between the pixels 4 is formed on the support substrate 63.

  In the X-ray detector 1 configured as described above, the X-ray 51 incident on the scintillator layer 31 of the scintillator panel 62 is converted into visible light 52 by the columnar crystal 32 of the scintillator layer 31.

  The visible light 52 reaches the photoelectric conversion element 8 of the photoelectric conversion substrate 2 through the columnar crystal 32 and is converted into an electric signal, and is converted into a digital image signal and output as described above.

  Next, a third structural example of the X-ray detector 1 will be described with reference to FIG. In the first structural example of the X-ray detector 1 shown in FIG. 1, the scintillator layer 31 does not form the columnar crystal 32, and the other configuration is the same.

  Next, a fourth structural example of the X-ray detector 1 will be described with reference to FIG. In the second structural example of the X-ray detector 1 shown in FIG. 2, the scintillator layer 31 does not form the columnar crystal 32, and the other configurations are the same.

  In the X-ray detector 1 having the structure shown in FIGS. 1 to 4, the scintillator layer 31 is a phosphor containing Tl as an activator in CsI, which is a halide, and the following (1) (2 ) (3) (4).

  (1): The central region of the formation region of the scintillator layer 31 is the central portion 31a (the inner region of the circular phantom line indicated by the two-dot chain line in FIG. 13), and the outer peripheral region is the peripheral portion 31b (the circular shape indicated by the two-dot chain line in FIG. 13). In the case of the outer region of the phantom line), the concentration of the activator in the phosphor in the in-plane direction of the scintillator layer 31 has a relationship of central portion> peripheral portion, and the concentration of the activator in the phosphor is 1. .6 mass% to 2.0 mass%.

  (2): The central portion 31a of the scintillator layer 31 is concentric or rectangular with respect to the center of the formation region of the scintillator layer 31, and occupies 50% or more of the formation region of the scintillator layer 31.

  (3): In the scintillator layer 31, the concentration distribution of the activator in the phosphor in the in-plane direction and the film thickness direction of the scintillator layer 31 is ± 15 in each region of the central portion 31a and the peripheral portion 31b of the scintillator layer 31. %, And the concentration distribution of the activator in the phosphor in the in-plane direction and the film thickness direction of the scintillator layer 31 in the region where the unit film thickness is 200 nm or less is ± 15% or less, and uniformity is maintained. ing.

  (4): The scintillator layer 31 is formed by a vacuum deposition method using two evaporation sources of CsI and TlI, and preferably has a structure of a strip-like columnar crystal 32.

  Here, in the X-ray detector 1 of the first structural example shown in FIG. 1, the film thickness of the scintillator layer 31 is 600 μm, the activator is Tl, and the correlation between the Tl concentration in the scintillator layer 31 and each characteristic is tested. The results are shown in FIGS. 6 to 8, and the laminating period of the scintillator layer 31 when the Tl concentration in the scintillator layer 31 is constant {the forming period of the unit film thickness (formed film thickness per one rotation of the substrate)} FIG. 9 to FIG. 11 show the results of testing the correlation of the characteristics.

  FIG. 6 shows the correlation between the Tl concentration in the scintillator layer 31 and the sensitivity ratio. The test conditions are incident X-ray: 70 kV-0.0087 mGy, sensitivity ratio: a ratio based on the sensitivity when the Tl concentration in the scintillator layer 31 is 0.1 mass%, and the scintillator layer formation conditions ( Except for the Tl concentration in the scintillator layer 31). As shown in FIG. 6, the sensitivity was most improved when the Tl concentration in the scintillator layer 31 was around 1.4 mass% to 1.8 mass%.

  FIG. 7 shows the correlation between the Tl concentration in the scintillator layer 31 and the MTF ratio as the resolution. Test conditions are incident X-ray: 70 kV-0.0087 mGy, MTF ratio: ratio based on MTF (at 2 Lp / mm) when the Tl concentration in the scintillator layer 31 is 0.1 mass%, and each test sample The scintillator layer forming conditions (except for the Tl concentration in the scintillator layer 31) are the same. As shown in FIG. 7, the Tl concentration in the scintillator layer 31 was substantially constant up to around 2.0 mass%.

  FIG. 8 shows the correlation between the Tl concentration in the scintillator layer 31 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 is a ratio based on the afterimage when the Tl concentration in the scintillator layer 31 is 0.1 mass%, and the scintillator layer forming conditions (excluding the Tl concentration in the scintillator layer 31) of each test sample are the same. It is. As shown in FIG. 8, the afterimage was at the minimum level when the Tl concentration in the scintillator layer 31 was around 1.6 mass%. Further, no afterimage was observed in an area where the afterimage ratio was 0.5 (preferably 0.4) or less and was an area of 1.6 mass% ± 0.4 mass%.

  FIG. 9 shows the correlation between the lamination period of the scintillator layer 31 and the sensitivity ratio. The test conditions are incident X-ray: 70 kV-0.0087 mGy, Tl concentration in the scintillator layer 31: 0.1 mass%, sensitivity ratio: a ratio based on the sensitivity when the lamination period of the scintillator layer 31 is 200 nm, The scintillator layer forming conditions (excluding the Tl concentration in the scintillator layer 31) of each test sample are the same.

  FIG. 10 shows the correlation between the lamination period of the scintillator layer 31 and the MTF ratio. Test conditions are based on incident X-ray: 70 kV-0.0087 mGy, Tl concentration in the scintillator layer 31: 0.1 mass%, MTF ratio: MTF (at 2 Lp / mm) when the lamination cycle of the scintillator layer 31 is 200 nm The scintillator layer forming conditions (excluding the Tl concentration in the scintillator layer 31) of each test sample are the same.

  FIG. 11 shows the correlation between the lamination period of the scintillator layer 31 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 31 is 0.1 mass%, the afterimage ratio is a ratio based on the afterimage when the lamination period of the scintillator layer 31 is 200 nm, and the scintillator layer formation conditions (scintillator layer 31 of each test sample) Except for the Tl concentration in it).

  As shown in FIGS. 9 to 11, each characteristic tends to deteriorate in the region where the lamination period of the scintillator layer 31 is 200 nm or more.

  This is because the peak wavelength of the emission wavelength of the scintillator layer 31 is around 550 nm, but the refractive index of CsI which is the base material of the scintillator layer 31 is 1.8, so the emission wavelength that propagates in the scintillator layer 31 If the peak wavelength of λ1 is λ1, it can be considered that 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 31 is larger than λ1, This is because the possibility of being affected by deterioration of optical characteristics (scattering, attenuation, etc.) due to variations in crystallinity and variations in Tl concentration in the scintillator layer 31 is matched.

  Further, as shown in FIG. 6 to FIG. 8, in the region where the Tl concentration in the scintillator layer 31 is 1.6 mass% ± 0.4 mass%, each characteristic is close to a stable state, so the Tl concentration in the scintillator layer 31 is Even if fluctuates (about ± 15%), the fluctuation of each characteristic is small.

  Further, from the correlation shown in FIGS. 6 to 8, the characteristic improvement effect (especially afterimage characteristics) of the scintillator layer 31 is greatest in the region where the Tl concentration in the scintillator layer 31 is 1.6 mass% ± 0.4 mass%, and The optimum value is around 1.6 mass%. However, in the case where the scintillator layer 31 is a phosphor containing Tl as an activator in CsI which is a halide, the following characteristics (a) (b) (c) is there.

  (a): CsI is highly hygroscopic and deliquesces by reacting with moisture in the atmosphere, but since TlI has no hygroscopicity, the higher the Tl concentration in the scintillator layer 31, the higher the moisture resistance of the scintillator layer 31. Will improve.

  (b): Since the atomic weight of Tl is larger than that of Cs, the higher the Tl concentration in the scintillator layer 31, the better the DQE (X-ray absorption rate) of the scintillator layer 31, so that the quantum noise in the X-ray image decreases. In addition, it is possible to obtain an X-ray image with a high S / N ratio.

  (c): Since the atomic weight of Tl is larger than Cs, the higher the Tl concentration in the scintillator layer 31 is, the higher the DQE (X-ray absorption rate) of the scintillator layer 31 is. And damage to the IC and the like on the photoelectric conversion substrate 2 are reduced.

  Thus, as the Tl concentration in the scintillator layer 31 is higher, the effects (a) to (c) are obtained.

  FIG. 12 shows the positional relationship between the X-ray detector 1 and the X-ray generation source (X-ray tube) 66, and FIG. 13 shows a front view of the X-ray detector 1. In this arrangement relationship, since the X-ray generation source 66 is usually installed on the central axis of the X-ray detector 1, the X-ray generation source 66 is arranged between the central portion 31a and the peripheral portion 31b of the X-ray detector 1. And the incident angle of the incident X-ray 51 are different.

Here, the distances from the X-ray generation source 66 at the S1 position of the central portion 31a and the S2 position of the peripheral portion 31b of the X-ray detector 1 are L1 and L2, and the angle of the incident X-ray 51 at the S2 position of the peripheral portion 31b. θ, M is the distance from the S1 position of the central portion 31a to the S2 position of the peripheral portion 31b, and the intensities (energy) of the incident X-rays 51 at the S1 position of the central portion 31a and the S2 position of the peripheral portion 31b are α and β, respectively. Then, since the intensity of the incident X-ray 51 attenuates in proportion to the square of the distance from the X-ray generation source 66,
β = α · cos θ · (L1 / L2) = α · cos θ · (cos θ) ² = α · (cos θ) ³
It becomes. Note that θ = tan ⁻¹ (M / L1).

  For example, when L1 = 1500 and M = 300 (arrangement of a general 17-inch X-ray detector 1 and X-ray generation source 66), the S2 position of the peripheral portion 31b with respect to the S1 position of the central portion 31a The intensity of the incident X-ray 51 is reduced by about 6%.

  Furthermore, since the X-ray generation source 66 also has an X-ray intensity distribution, the intensity of the incident X-ray 51 at the peripheral portion 31b with respect to the central portion 31a of the X-ray detector 1 is approximately several percent to several tens of percent. Will be reduced to a certain extent.

  Moreover, the X-ray image of a general X-ray detector is shown to Fig.14 (a) (b). Since the intensity of the incident X-ray 51 affects the light emission of the scintillator layer 31, the sensitivity also decreases as the intensity of the incident X-ray 51 decreases. Therefore, the incident X-ray 51 as shown in FIG. Concentric sensitivity spots (shading) associated with the intensity distribution or the like will occur.

  For this reason, generally, in a general X-ray detector, flat field correction for correcting sensitivity spots as shown in FIG. 14B is given to the X-ray image.

  However, when a flat field correction is applied to an X-ray image in a general X-ray detector, the noise component included in the image is also amplified along with the correction. The S / N of the image of the image is reduced, and the dynamic range of the image is also reduced.

  For this reason, in a general X-ray detector, the better the uniformity of sensitivity distribution of an X-ray image {BU (Brightness Uniformity)}, the higher the quality of the X-ray image (high S / N, wide dynamic range). Will be obtained.

  From the correlation between the Tl concentration in the scintillator layer 31 and the sensitivity ratio shown in FIG. 6, in the region where the Tl concentration in the scintillator layer 31 is 1.6 mass% or more, the sensitivity tends to decrease gradually as the Tl concentration increases. There is. Therefore, if the characteristic of (1) is given to the scintillator layer 31, the sensitivity distribution of the scintillator layer 31 can be set to the peripheral part> the central part. Therefore, the BU of the X-ray image in the X-ray detector 1 can be set. Therefore, it is possible to obtain a high-quality X-ray image as compared with the case where the Tl concentration distribution in the in-plane direction of the scintillator layer 31 is uniform.

  In diagnosis using an X-ray image, the diagnosis is usually performed with a subject placed at the center of the X-ray image. Therefore, as the feature of (1) above, when the central region of the scintillator layer 31 is the central portion 31a and the outer peripheral region is the peripheral portion 31b, the Tl concentration in the in-plane direction in the scintillator layer 31 is the central portion. > If the relationship between the peripheral parts and the Tl concentration in the phosphor is set to 1.6 mass% to 2.0 mass%, the improvement of the overall characteristics including the afterimage characteristics of the scintillator layer 31 and the X-ray detection The reliability of the device 1 can be improved.

  Further, as the feature (2) above, the central portion 31a of the scintillator layer 31 occupies 50% or more of the formation region of the scintillator layer 31, so that an X-ray detector suitable for diagnosis using an X-ray image or the like. 1 can be provided.

  Even if the concentration of the activator in the phosphor is in the range of 1.6 mass% to 2.0 mass%, the concentration distribution of the activator in the phosphor in the in-plane direction and the film thickness direction of the scintillator layer 31 is large. If there is a bias, each characteristic is likely to fluctuate greatly. Therefore, the concentration distribution of the activator in the phosphor in the in-plane direction and the film thickness direction of the scintillator layer 31 is preferably within ± 15%. If the concentration distribution of the activator in the phosphor is within a fluctuation range of about ± 15%, the fluctuation of each characteristic is small and the influence is small.

  Furthermore, if the concentration distribution of the activator in the phosphor in the in-plane direction and the film thickness direction of the scintillator layer 31 is largely biased in at least the region of the unit film thickness of 200 nm or less in the scintillator layer 31, each characteristic varies greatly. Therefore, the concentration distribution of the activator in the phosphor in the in-plane direction and the film thickness direction of the scintillator layer 31 is preferably within ± 15% even in a region where the unit film thickness is 200 nm or less.

  Therefore, as the feature of (3) above, a region in which the concentration distribution of the activator in the phosphor in the in-plane direction and the film thickness direction of the scintillator layer 31 is ± 15% or less and the unit film thickness is 200 nm or less. It is preferable that the concentration distribution of the activator in the phosphor in the in-plane direction and the film thickness direction of the scintillator layer 31 is within ± 15%.

  Here, a schematic diagram of a general method of forming the scintillator layer 31 is shown in FIG. FIG. 16 and FIG. 17 show schematic diagrams of a forming method in which the concentration of the activator in the phosphor is changed between the central portion 31a and the peripheral portion 31b of the scintillator layer 31. FIG.

  In FIG. 15, a substrate 72 (corresponding to the photoelectric conversion substrate 2 or the support substrate 63) is arranged in the vacuum chamber 71, and the CsI evaporation source 73 installed in the vacuum chamber 71 while rotating the substrate 72. A film of the scintillator layer 31 is laminated by a vacuum vapor deposition method in which the vaporized grains from the TlI and the vaporized grains from the TlI evaporation source 74 are deposited on the laminated surface of the substrate 72.

  At this time, if the rotation period of the substrate 72 and the evaporation of CsI and TlI are controlled, the Tl concentration distribution in the in-plane direction and the film thickness direction per stacking period of the scintillator layer 31 can be arbitrarily controlled. Therefore, when the scintillator layer 31 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 31 is ensured, the entire in-plane direction and film thickness direction of the scintillator layer 31 The uniformity of the Tl concentration distribution is also ensured.

  Furthermore, as shown in FIG. 16, one TlI evaporation source 74 is arranged so as to oppose the central axis (rotation center) of the substrate 72, or as shown in FIG. It is possible to change the Tl concentration distribution in the in-plane direction of the scintillator layer 31 by using the evaporation source 74 and placing one of the evaporation sources 74 so as to face the central axis (rotation center) of the substrate 72. Become. With this forming method, when the central region of the scintillator layer 31 is the central region 31a and the outer peripheral region is the peripheral region 31b, the concentration of the activator in the phosphor in the in-plane direction of the scintillator layer 31 is It is possible to form a relationship of parts.

  Therefore, the characteristics (1) to (4) are given to the scintillator layer 31 made of a phosphor containing Tl as an activator in CsI which is a halide in consideration of the characteristics (a) to (c). By doing so, it is possible to improve the overall characteristics including the afterimage characteristics of the scintillator layer 31 and the reliability of the X-ray detector 1.

  An embodiment of the X-ray detector 1 having the first structural example shown in FIG. 1 will be described. In this embodiment, the thickness of the scintillator layer 31 is 600 μm, the lamination period of the scintillator layer 31 is 150 nm, the activator is Tl, the formation region of the scintillator layer 31 is 432 mm × 432 mm, the central portion 31a of the scintillator layer 31 is the scintillator layer 31 A concentric region occupying 50% with respect to the center of the formation region of the substrate, a peripheral portion 31b of the scintillator layer 31: a region other than the central portion 31a of the formation region of the scintillator layer 31, a central portion 31a and a peripheral portion 31b of the scintillator layer 31 The concentration distribution of the activator in the phosphor in the in-plane direction and the film thickness direction of the scintillator layer 31 in each region: ± 15%, and the concentration of the activator in each region of the central portion 31a and the peripheral portion 31b of the scintillator layer 31 Samples A, B, C, D, and E of the X-ray detector 1 changed as shown in FIG. 18 are created.

  X-ray images of the samples A, B, C, D, and E of the X-ray detector 1 obtained by photographing a subject under predetermined imaging conditions and processing the captured images under predetermined image processing conditions (n-th time) 19 (a) (b) (c) (d) (e) and the characteristic results are shown in the table of FIG. In FIG. 20, the sensitivity ratio, MTF ratio, and afterimage ratio are values based on the case where the Tl concentration in the scintillator layer 31 is 0.1 mass%.

  The imaging condition is that the dose difference between the (n-1) th and nth X-ray images is (n-1)> n, and the (n-1) th X-ray image has an incident X-ray of 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 image acquisition interval for the nth X-ray image : 60 sec. The distance from the X-ray generation source 66 to the X-ray detector 1 is 1500 mm.

  The image processing conditions are flat field correction: yes, window processing: yes (image histogram average value ± 50%).

  As shown in FIGS. 19 (a) and 19 (b), the concentration of the activator in the phosphor in each region of the central portion 31a and the peripheral portion 31b of the scintillator layer 31 is 0.1 mass% of sample A and 1.0 mass%. In sample B, an afterimage was confirmed in a range surrounded by a rectangular broken line in FIGS. 19 (a) and 19 (b). On the other hand, as shown in FIGS. 19 (c) (d) (e), a sample C in which the concentration of the activator in the phosphor in each region of the central portion 31a and the peripheral portion 31b of the scintillator layer 31 is 1.2 mass%, Sample D in which the concentration of the activator in the phosphor in each region of the central portion 31a and the peripheral portion 31b of the scintillator layer 31 is 1.6 mass%, and the concentration of the activator in the phosphor in the central portion 31a of the scintillator layer 31 is 2. In sample E where the concentration of the activator in the phosphor at 0 mass% and the peripheral portion 31b is 1.6 mass%, no afterimage was confirmed in the range surrounded by the rectangular broken line in FIGS. 19 (c) (d) (e). . Note that the inner side of the circular phantom line indicated by the two-dot chain line in FIGS. 19A, 19B, 19C, 19D, and 19E corresponds to the imaging region in the central portion 31a of the scintillator layer 31, and The outer side corresponds to the imaging region in the peripheral portion 31b of the scintillator layer 31.

  For samples D and E, X-ray images when flat field correction is not performed are shown in FIGS. The sensitivity of the central part is measured at the position P1 of the diagonal line of the X-ray image shown in FIGS. 21 (a) and 21 (b), and 90% of the diagonal line from the central part is 90% (intersections between the circle and the diagonal line shown by the broken line). ) At the position P2, and the sensitivity of the X-ray image is uniformly distributed. BU {BU = b / a · 100, b: sensitivity at the center, a: sensitivity at the periphery (4 Average value of the portion)}.

  In the case of sample D shown in FIG. 21 (a), BU = 62%, whereas in the case of sample E shown in FIG. 21 (b), BU = 72%. Therefore, the BU of the X-ray image was improved in the sample E.

  Therefore, if the features (1) to (4) defined in the present embodiment are added to the scintillator layer 31, the afterimage characteristics and BU can be improved with good sensitivity and MTF, so that the X-ray detector 1 High performance and reliability can be improved.

  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.

1 X-ray detector as a radiation detector 2 Photoelectric conversion substrate
31 Scintillator layer
31a center
31b peripheral area

Claims (5)

A photoelectric conversion substrate that converts light into an electrical signal;
A scintillator layer that contacts the photoelectric conversion substrate and converts 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, and when the central region of the scintillator layer forming region is a central portion and the outer peripheral region is a peripheral portion, the surface of the scintillator layer The concentration of the activator in the phosphor in the inward direction has a relationship of center portion> peripheral portion, and the concentration of the activator in the phosphor is 1.6 mass% to 2.0 mass%. A radiation detector characterized by. The radiation detector according to claim 1, wherein a central portion of the scintillator layer occupies 50% or more of a formation region of the scintillator layer. In the scintillator layer, the concentration distribution of the activator in the phosphor in the in-plane direction and the film thickness direction of the scintillator layer is ± 15% or less in each region of the central portion and the peripheral portion of the scintillator layer. The concentration distribution of the activator in the phosphor in the in-plane direction and the film thickness direction of the scintillator layer in a unit film thickness of 200 nm or less is ± 15% or less. Or the radiation detector of 2. The radiation detector according to any one of claims 1 to 3, wherein the scintillator layer has a columnar crystal structure. A method for manufacturing a radiation detector comprising: a photoelectric conversion substrate that converts light into an electrical signal; and a scintillator layer that converts radiation incident from the outside in contact with the photoelectric conversion substrate;
The scintillator layer is a phosphor containing Tl as an activator in CsI which is a halide,
When the central region of the scintillator layer forming region is the central portion and the outer peripheral region is the peripheral portion, the concentration of the activator in the phosphor in the in-plane direction of the scintillator layer has a relationship of central portion> peripheral portion. And forming the scintillator layer by a vapor phase growth method using CsI and Tl as material sources so that the concentration of the activator in the phosphor is 1.6 mass% to 2.0 mass%. The manufacturing method of the radiation detector characterized by these.