JP2018185237A - Radiation detector and radiation measurement system - Google Patents

Abstract

An object of the present invention is to provide a radiation detector with improved spatial resolution in a low frequency region when using a scintillator plate configured to include phase-separated scintillator crystals. SOLUTION: A radiation detector including a scintillator plate and a photodetector, the scintillator plate including a plurality of columnar first phases extending in a uniaxial direction and surrounding the plurality of first phases. and a second scintillator layer in which scintillation light generated by radiation irradiation undergoes multiple scattering and is diffused, and the scintillator plate and The photodetector is arranged in the order of the second scintillator layer, the first scintillator layer, and the photodetector. [Selection diagram] Figure 1

Description

  The present invention relates to a radiation detector and a radiation measurement system.

  A flat panel detector (FPD) used for X-ray imaging at a medical site receives X-rays that have passed through a subject with a scintillator and detects light emitted by the scintillator with a light receiving element. As the scintillator, a powder-like structure or a needle-like structure is widely used. In particular, a scintillator layer having a needle-like structure formed by vapor deposition of cesium iodide (CsI) has an advantage that a high position resolution can be obtained because crosstalk is suppressed by optical waveguide in the needle-like crystal. Yes. However, in the CsI needle crystal, adjacent needle crystals easily adhere to each other, and this adhesion lowers the waveguiding property of the scintillation light and lowers the resolution of the radiation detector.

  Therefore, Patent Document 1 proposes a scintillator crystal body having a phase separation structure including two crystal phases having different refractive indexes. This phase-separated scintillator crystal body has a plurality of first phases (cylinder phases) having a unidirectionality functioning as a scintillator, and a second phase (matrix phase) located around the first phase. ing. Since the first phase has a higher refractive index than the second phase, the scintillation light generated isotropically in the first phase is expressed by Snell's law at the interface between the first and second phases. The scintillation light incident above the critical angle repeats total reflection and is guided in the direction of the cylinder while being confined in the first phase. Therefore, high resolution can be obtained by using this phase separation structure as a scintillator layer.

JP 2013-47334 A

  Although the technology described in Patent Document 1 greatly contributes to this technical field, the inventors have studied and found that there is room for improvement even with the technology described in Patent Document 1. Scintillation light that is incident on the interface between the first and second phases at a critical angle or less becomes light emitted from the first phase. Some of the leaked emission enters the adjacent first phase and is guided again by total reflection, but there is emission that does not take total reflection. Since the light emission that does not take total reflection spreads farther as the thickness of the scintillator layer increases, there is a problem that the spatial resolution in the low frequency region is lowered. The spatial resolution of the low frequency region here can be understood as whether or not the period of a plurality of adjacent relatively large objects can be resolved.

  An object of the present invention is to provide a radiation detector with improved spatial resolution in the low frequency region.

  A radiation detector provided by the present invention is a radiation detector having a scintillator plate and a light detection unit, and the scintillator plate includes a plurality of first phases extending in a uniaxial direction and forming a columnar shape. A first scintillator layer comprising: a second phase surrounding the first phase of the first scintillator; and a second scintillator layer in which scintillation light generated by radiation irradiation diffuses due to multiple scattering. The scintillator plate and the light detection unit are arranged in the order of the second scintillator layer, the first scintillator layer, and the light detection unit.

  In the present invention, the first scintillator layer is provided with the specific first phase and the second phase, and the scintillation light generated by radiation irradiation is subjected to multiple scattering as the second scintillator phase. The one that receives and spreads is adopted. And providing the radiation detector with which the spatial resolution of the low frequency area | region was improved by arrange | positioning a scintillator plate and a photon detection part in order of a 2nd scintillator layer, a 1st scintillator layer, and a photon detection part. Can do.

It is a 1st schematic diagram which shows the radiation detector which concerns on this invention. It is a schematic diagram which shows the conventional radiation detector. It is a mimetic diagram showing an example of the scintillator crystal concerning the present invention. It is a 2nd schematic diagram which shows the radiation detector which concerns on this invention. (A) is a radiographic image using the radiation detector according to the present invention. (B) is a radiographic image using a conventional radiation detector. (C) is a figure showing the relationship between a spatial frequency and CTF. It is a schematic diagram which shows the radiation measurement system provided with the radiation detector of this invention.

  The radiation detector of the present invention includes a scintillator plate having a plurality of scintillator layers that generate light upon incidence of radiation such as X-rays, and a light detection unit. Radiation includes α-rays, γ-rays, etc. in addition to X-rays. In the present specification, X-rays will be described as an example. The radiation detector of the present invention is a radiation detector having a scintillator plate and a light detection unit, and the scintillator plate includes a plurality of first phases extending in a uniaxial direction and forming a columnar shape, and the plurality of first phases. And a second scintillator layer in which scintillation light generated by radiation irradiation diffuses due to multiple scattering. The feature of the present invention is that the scintillator plate and the light detection unit are arranged in the order of the second scintillator layer, the first scintillator layer, and the light detection unit.

  Hereinafter, the present embodiment will be described more specifically with reference to the drawings.

  FIG. 1 shows a schematic diagram of a radiation detector 101 of the present invention. The radiation detector 101 includes a scintillator plate 102 that converts radiation into scintillation light, and a light detection unit 103 that detects scintillation light from the scintillator plate. The scintillator plate 102 includes a first scintillator layer 104 and a second scintillator layer 105, but another layer such as an adhesive layer may exist between the two layers. The first scintillator layer 104 includes a plurality of first phases that extend in a uniaxial direction to form a columnar shape, and a second phase that surrounds the plurality of first phases. On the other hand, the second scintillator layer 105 has a form in which scintillation light generated by radiation irradiation is diffused by receiving multiple scattering. The second scintillator layer in such a form can be configured to include particulate crystals.

  Here, the first scintillator layer 104 will be described in detail. As the first scintillator layer 104, a phase-separated crystal body 201 shown in FIG. 3 can be used. The phase-separated crystal body 201 can employ a phase-separated structure having a plurality of first phases 202 and a second phase 203 positioned around the first phase. The scintillator crystal 201 has a first surface 208 and a second surface 209, and the first phase 202 extends from the first surface 208 to the second surface 209. The first surface 208 is a radiation irradiation surface, the second surface 209 is a light extraction surface, radiation such as X-rays is incident from the first surface 208, and scintillation light is transmitted from the second surface 209. Incident on the light receiving element. At least one of the first phase and the second phase is a light emitting phase that converts at least part of incident radiation into scintillation light. The first phase 202 and the second phase 203 have different refractive indexes. Therefore, the scintillation light is confined in the high refractive index phase having a relatively high refractive index, while the thickness 207 direction of the scintillator crystal is changed from the first surface direction to the second surface direction. It is guided from the direction toward the first surface. Since the scintillation light is considered to have higher resolution when guided in the phase in which the scintillation light is generated, it is preferable that the high refractive index phase functions as the light emission phase. The low refractive index phase having a relatively low refractive index may function as a light emitting phase or may not function.

  Hereinafter, the case where the first phase 202 is a high refractive index phase and a light emitting phase will be described as an example. When the first phase 202 is a high refractive index phase, the scintillation light is guided between the first surface 208 and the second surface 209 while being confined in the first phase, like an optical fiber. Here, the first phase 202 has a cylindrical shape. Of the scintillation light generated in the first phase 202, the scintillation light 206 incident on the interface between the first and second phases at an angle larger than the critical angle passes through the first phase 202 while repeating total reflection. The light is guided in the waveguide direction 210 and is emitted from the first surface 208 or the second surface 209. Here, the waveguide direction 210 of the scintillation light is the extending direction (longitudinal direction) of the first phase 202 and is a direction parallel to the central axis of the cylinder. When the diameter of the first phase is smaller than the wavelength of the light emission to be guided, the component that the scintillation light does not reflect at the interface between the first phase 202 and the second phase 203 but passes through the interface increases. . Therefore, the diameter 205 of the first phase is desirably larger than the wavelength of the scintillation light. As a scintillator having a phase separation structure, a scintillator that emits light in the ultraviolet region from 300 nm is assumed to be used. Therefore, the diameter 205 of the first phase is desirably 300 nm or more. Further, the shape of the first phase 202 is not limited to a cylinder, and may be a polygonal column, for example.

As the scintillator crystal shown in FIG. 3, for example, a scintillator having a eutectic phase separation structure can be used. The eutectic phase separation structure refers to a structure in which a first phase and a second phase constitute a eutectic body in the phase separation structure shown in FIG. As an example of the material system of the eutectic phase separation structure, there is a eutectic phase separation structure of a perovskite oxide material (GdAlO ₃ ) containing Gd and alumina (Al ₂ O ₃ ). In the eutectic phase separation structure of this material system, the refractive index of the first phase (GdAlO ₃ : refractive index 2.05) is higher than that of the second phase (Al ₂ O ₃ : refractive index 1.79). High and the first phase functions as a scintillator. Therefore, the waveguide property is particularly high among the eutectic phase separation structures. In the case of the eutectic phase separation structure, the first phase is a crystal of the first material, and the second phase is a crystal of the second material. What is important in forming a eutectic phase separation structure having two phases of the first phase and the second phase located around the second phase and covering the side of the first phase is It is a composition ratio between the material constituting the first phase and the material constituting the second phase. In order to obtain a scintillator crystal having a phase separation structure, generally, the first phase material and the second phase material are a combination capable of forming a eutectic and have a good structure. In order to achieve this, it is desirable to use a eutectic composition ratio (for example, GdAlO ₃ : Al ₂ O ₃ = 46: 54 (mol%)). However, the composition ratio between the material of the first phase and the material of the second phase should not deviate from the eutectic composition, and the range of the eutectic composition ± 5 mol% with respect to this composition ratio is an allowable range. can do. That is, when it is desired to form a eutectic phase separation structure of GdAlO ₃ and Al ₂ O ₃ , the composition ratio of these materials is GdAlO ₃ : Al ₂ O ₃ = 41: 59 to 51:49 (mol%). It is preferable to do. More preferably, the composition ratio between the first phase material and the second phase material is in the range of eutectic composition ± 3 mol%. The high-quality phase shown in FIG. 3 is obtained by performing unidirectional solidification using a melt in which the material of the first phase and the material of the second phase are mixed in the vicinity of the eutectic composition ratio (± 5 mol%). A crystal having a separated structure can be obtained. As a specific method of unidirectional solidification, the Bridgman method or the like can be used. In the case of GdAlO ₃ described above, the emission wavelength changes depending on the type of element at the emission center. Specifically, for example, rare earth elements Tb ³⁺ , Eu ³⁺ , and Ce ³⁺ can be used as the emission center. In addition, the element containing these ions is not limited to a simple substance, these elements may be included, and a compound containing these elements may be added as a light emission center. In order to increase the luminous efficiency, it is preferable that 0.001 mol% or more of these luminescent centers are contained in GdAlO ₃ . When a plurality of types of emission centers are added, the total amount of emission centers may be 0.001 mol% or more. The additive element serving as the emission center is added so as to replace the Gd site of the first phase GdAlO _{3. When} the additive element is represented by the general formula RE, Gd _1-x RE _x AlO ₃ and Al ₂ O ₃ The composition ratio is 46:54 (mol%). When Tb ³⁺ is used as the emission center, a green emission peak is shown at around 545 nm. Further, when Eu ³⁺ is used, a red light emission peak is shown in the vicinity of 615 nm. In addition, when Ce ³⁺ is used, broad ultraviolet light emission is observed in the vicinity of 360 nm. Thus, scintillators with various emission wavelengths can be obtained by appropriately selecting the additive elements. Also, other rare earth elements (Pr, Nd, Pm, Sm, Dy, Ho, Er, Tm, Yb) can be selected as the additive element.

  Since the first phase 202 functions as an optical fiber, the phase-separated crystal 201 manufactured in this way functions as an FOP (Fiber Optical Plate) as an optical member formed by bundling a large number of optical fibers. The image incident on the first surface 208 is transmitted to the second surface 209 via the first phase 202.

  Next, the second scintillator layer 105 provided on the radiation incident surface side will be described with reference to FIG. The second scintillator layer 105 has a form in which scintillation light generated by irradiation of radiation is subjected to multiple scattering and diffuses, and the second scintillator layer can be configured to include particulate crystals. More specifically, it can be a powdery crystal or a structure containing a needle-like crystal (powder-like structure, needle-like structure). In these structures, since there are not a few optically non-uniform internal structures, light scattering occurs, and light emission generated in the second scintillator layer diffuses while receiving multiple scattering. As a result, the resolution in the high frequency region is reduced, but since the light emission is not spread far away spatially, if the second scintillator layer is thin, the resolution in the low frequency region is reduced. The resolution is maintained.

Here, first, consider the light emission 109 of the second scintillator layer disposed in a shallow region from the radiation incident surface. Of the light emission 109 of the second scintillator layer, the light diffused downward is incident on the first scintillator layer 104 and diffused as light 110 guided by total reflection by the FOP function of the first scintillator layer 104. Without being guided, the light is guided through the first scintillator layer 104 and detected by the light detection unit 103. On the other hand, the light 111 that diffuses at a high angle among the light emission 109 has a light component that diffuses downward due to multiple scattering, so the first scintillator layer is guided at the interface between the first and second scintillator layers. The wave 112 becomes a wave of light 112, is guided by the first scintillator layer 104 without being diffused by the FOP function, and is detected by the light detection unit 103. The light emission 113 of the first scintillator layer is emitted from a region relatively deep from the radiation incident surface. This is broadly classified into light 114 guided by total reflection and light 115 diffusing without entering total reflection. Specific materials constituting the second scintillator layer include Gd ₂ O ₂ S (GOS) powder, CsI acicular film, and the like.

  Next, as a comparison, a radiation detector that does not have the second scintillator layer corresponding to the conventional example and uses only the first scintillator layer 104 will be described with reference to FIG. In FIG. 2, when radiation 108 is incident on the first scintillator layer 104, light is absorbed exponentially from the incident surface in the depth direction, resulting in light emission. Therefore, light emitted from a region shallow from the radiation incident surface of the scintillator is deep. It becomes relatively large with respect to light emission from the region. In the figure, the difference in magnitude and width between the light emission from the shallow area from the radiation incident surface (117, 118, 119) and the light emission from the deep area from the radiation incident surface (120, 121, 122) and the width are schematically shown. It represents.

  Here, first, consider the light emission 117 of the first scintillator layer from a shallow region from the radiation incident surface. Of the emitted light 117, the light that is emitted almost directly below in the direction along the radiation 108 is incident on the interface between the first and second phases constituting the first scintillator layer at an angle larger than the critical angle. The light is guided by total reflection and guided as light 117 guided by total reflection in the first scintillator layer 104 without being diffused, and is detected by the light detection unit 103. On the other hand, in the light emission 117, light having a large angle formed with the radiation 108 so as to enter the boundary surface between the first and second phases at an angle less than the critical angle is diffused light without entering into total reflection. 119. Since the light 119 spreads farther as the thickness of the scintillator layer is increased, the spatial resolution in the low frequency region is consequently reduced.

  Next, consider light emission 120 of the first scintillator layer from a deep region from the radiation incident surface. As in the case of the light emission 117, there are light 121 guided by total reflection and light 122 that does not enter total reflection and diffuses, and the latter spreads far, so that the spatial resolution in the low frequency region is lowered. It leads to things. Here, when comparing 119 and 122, which are diffused light without entering into total reflection, the light 119 generated from a shallower region from the radiation incident surface spreads farther to the light 122, and further, The absolute value of light emission is also large. That is, as a factor for reducing the spatial resolution in the low frequency region, the influence of the light diffused without entering the total reflection from the shallow region from the radiation incident surface is great. Therefore, it is expected to suppress the reduction in spatial resolution in the low frequency region by guiding the light that diffuses without entering the total reflection particularly from the shallow area from the radiation incident surface to the light detection unit 103 without diffusing far away.

  Therefore, in the radiation detector 101 of the present invention, as described above, the second scintillator layer 105 is provided on the radiation incident surface side.

  Here, the radiation detector of the present invention shown in FIG. 1 is compared with the conventional radiation detector shown in FIG. Focusing on light diffusing far away from the shallow area from the radiation incident surface, in FIG. 2, the diffused light 119 that does not enter the total reflection is once again guided by total reflection once it deviates from the total reflection condition. The wave is basically not generated. On the other hand, in FIG. 1, the light 111 is diffused in the second scintillator layer 105 while the light emission undergoes multiple scattering, so that the light 111 is guided by total reflection at the interface between the first and second scintillator layers. There will be light having an angle, which makes it possible to guide the total reflection through the first scintillator layer 104. That is, the second scintillator layer that generates multiple scattering is caused to emit light from a region shallow from the radiation incident surface, which has been a factor in reducing the spatial resolution in the low frequency region. Then, the generated light emission is directly transmitted to the light detection unit 103 by the FOP function of the first scintillator layer 104, thereby improving the spatial resolution in the low frequency region. However, the powder-like structure and needle-like structure that cause light scattering will adversely affect the high-frequency region resolution of the intended first scintillator layer because the resolution in the high-frequency region will be significantly reduced as the thickness increases. It is necessary to use it as a thin film. From this viewpoint, the thickness of the second scintillator layer is preferably in the range of 10 μm to 100 μm. The layer thickness of the first scintillator layer is preferably in the range of 200 μm to 1000 μm.

  The spatial frequency required for the subject to be imaged is defined as a limit spatial frequency L (lp / mm). The sensor pixel size (μm) required at this time is calculated based on the sensor Nyquist frequency: [sensor pixel size (μm)] = [1000 (μm)] / [limit spatial frequency L (lp / mm) × 2].

  The combination of the first scintillator layer and the second scintillator layer is determined by the following procedure.

1. Set the required critical spatial frequency and x-ray energy.
(For example, a device having a limit spatial frequency of 4 lp / mm (corresponding to a pixel size of 125 μm) and an X-ray energy of W (tungsten) -100 kV).

2. The thickness of the eutectic phase-separated structure scintillator corresponding to the X-ray energy is set, and the resolution curve is determined.
(If it is W-100 kV, a phase separation scintillator needs to be 300 μm thick to prevent 80%.)

3. Combined with a second scintillator layer having a thickness that does not reduce resolution on the lower frequency side than the spatial frequency that intersects the limit spatial frequency set in 3.1.
(When a powdery structure is used as the second scintillator layer scintillator, referring to FIG. 5C described later, the resolution up to 4 lp / mm is not lowered if the thickness is 40 μm.)

  From the above, a scintillator panel in which a 40 μm thick powdery structure scintillator is provided on the radiation incident side of a 300 μm thick eutectic phase separation scintillator is obtained. Accordingly, the X-ray stopping power of the scintillator to be combined is weighted, and the resolution curve and brightness in the target spatial frequency region are improved as compared with the case of the eutectic phase separation structure scintillator alone.

  Here, assuming that the limit spatial frequency is 4 lp / mm, when the powder-like structure is used as the second scintillator layer, the thickness is about 40 μm, and the CsI needle-like structure is about 100 μm thick. Assuming that the limit spatial frequency is 10 lp / mm, the limit film thickness is about 10 μm when the powdered structure is used as the second scintillator layer and about 40 μm for the CsI needle structure. The above film thickness is only a guideline and may vary greatly depending on its configuration, so it needs to be determined by the resolution when an integrated scintillator panel is used.

  As described above, the first and second scintillator layers are used as one scintillator panel and a radiation detector for acquiring one radiation ray image is used. Is absorbed, and high-energy radiation is absorbed in the lower first scintillator layer. Therefore, as shown in FIG. 4, a color detector 123 and 124 is used to discriminate and detect each light emission. It can also be 125. In this case, it is possible to use it as an energy discrimination image by performing a weighting operation between the plurality of acquired radiation images.

  The radiation detector of the present invention can be used, for example, as a detector of an X-ray Talbot interferometer as a radiation measurement system. A schematic diagram of an X-ray Talbot interferometer is shown in FIG. The X-ray Talbot interferometer includes an X-ray source 70, an X-ray diffraction grating 73 that diffracts the X-ray 71 from the X-ray source to form an interference pattern, and an X-ray that detects the X-ray that forms the interference pattern. A detector 74 and a calculation device 75 that acquires information on the subject 72 using the detection result of the X-ray detector are provided.

  Since the details of the X-ray Talbot interferometer are described in many documents such as International Publication No. 2010/050484, the details are omitted. A general Talbot interferometer obtains information on an interference pattern having a period of about several μm by disposing a grating called a shielding grating or an absorption grating at a position where an interference pattern is formed and forming moire. . The interferometer shown in FIG. 6 includes the radiation detector of the present invention as the X-ray detector 74. By analyzing the change in the interference pattern by the subject 72 using the detection result by the X-ray detector 74, information on the phase, scattering, and absorption of the subject can be acquired. In addition, the analysis method of the interference pattern by the X-ray source, diffraction grating, and arithmetic unit is the same as that of a general Talbot interferometer. Note that the X-ray Talbot interferometer may include display means (not shown) for displaying information on the subject acquired by the arithmetic device 75. Further, the X-ray Talbot interferometer may not include the arithmetic device 75 and the X-ray source 70. In this case, it is possible to perform imaging (acquisition of interference pattern) with an X-ray Talbot interferometer by combining with an arbitrary X-ray source during imaging.

  Hereinafter, the present invention will be described in detail with specific examples.

(Examples and Comparative Examples)
In this example, a radiation imaging result when a eutectic phase separation structure is used as the first scintillator layer and a powdery structure is used as the second scintillator layer will be described.

The first scintillator layer of this example is composed of a phase-separated scintillator crystal having GdAlO ₃ as a plurality of first phase materials and Al ₂ O ₃ as a _second phase material, and emits Tb ³⁺ . Contains as a center. A method for producing this phase-separated scintillator crystal will be described. First, Gd ₂ O ₃ , Tb ₄ O ₇ , Al ₂ so that the composition ratio of Al ₂ O ₃ to a material obtained by adding 8 mol% of Tb ³⁺ to GdAlO _{3 is} 46:54 (mol%). O ₃ was weighed. These powders were sufficiently mixed to obtain a raw material powder. These raw material powders were put in an Ir crucible, and the crucible was heated to 1800 ° C. by induction heating to dissolve the entire sample. After the whole sample was dissolved, it was held for 30 minutes, and then the sample was grown by performing unidirectional solidification at a speed of 18 mm / h. The sample thus prepared was cut out at 5 mm × 5 mm × thickness 300 μm and polished on both sides. This sample showed a green emission peak around 545 nm by X-ray irradiation. A scintillator made of Gd ₂ O ₂ S (GOS) powder having a thickness of 40 μm was provided as a second scintillator layer on the cut scintillator crystal body to form a scintillator plate. The produced scintillator plate was disposed so as to face the two-dimensional light receiving element via the FOP, thereby forming a radiation detector. The FOP is used to prevent the X-rays from directly entering the light receiving element and forming noise. However, the scintillator may stop the X-rays depending on the energy of the X-rays.

  The limiting spatial frequency was set to 4 lp / mm, and a light receiving element having a pixel size of 125 μm was used. As a radiation source, a tungsten tube X-ray source was used. The X-rays were arranged so as to be perpendicularly incident on the scintillator crystal, and X-rays obtained under conditions of 40 kV, 0.5 mA, with an Al filter were used for imaging. .

FIG. 5 shows the imaging result of a 2 lp / mm line pattern of 50 μm thick lead. FIG. 5A shows an imaging result of the present invention when a phase separation structure is used as the first scintillator layer and a powder structure is provided as the second scintillator layer. For comparison, FIG. 5B also shows an imaging result when the first scintillator layer is composed only of the eutectic phase separation structure (300 μm thickness). The Contrast Transfer Function (CTF) value was calculated as CTF = (I _max −I _min ) / (I _max + I _min ) as the bright part (I _max ) and dark part (I _min ) of the line imaging region. FIG. 5C shows the relationship between the spatial frequency and the CTF when the GOS powder is not provided as the second scintillator layer for comparison with the scintillator plate of this example. FIG. 5C shows a resolution profile represented by spatial frequency and contrast. When a powdery structure was provided as the second scintillator layer, CTF was improved at a spatial frequency of 4 lp / mm or less. That is, the scintillator plate of the present invention has a resolution profile that exceeds the resolution profile in the low-frequency region as compared with the scintillator plate composed only of the first scintillator layer. As for the brightness of the bright part (I _max ) of the line patterns of FIGS. 5A and 5B, the configuration of the present invention shown in FIG. 5A is about about 4 lp / mm at a spatial frequency. 1.6 times brighter. As a factor for improving the luminance, firstly, a GOS powder having a large light emission amount is added to the phase-separated scintillator crystal. Secondly, among the light emitted from the shallow region from the radiation incident surface where the amount of light emission is large, in the case of only the phase-separated scintillator crystal, the light that has been diffused and quenched without entering the total reflection is converted into a scintillator having a powdery structure. By providing as the second scintillator layer, it can be considered that it was guided to the phase-separated scintillator crystal body without being diffused and detected as a signal. From this, it was confirmed that by providing a powdery structure as the second scintillator layer, both the CTF and the luminance were improved at the target spatial frequency up to 4 lp / mm.

DESCRIPTION OF SYMBOLS 101 Radiation detector 102 Scintillator plate 103 Photodetection part 104 1st scintillator layer 105 2nd scintillator layer 108 Radiation 109 Light emission of 2nd scintillator layer 202 1st phase 203 2nd phase

Claims (19)

A radiation detector having a scintillator plate and a light detection unit,
The scintillator plate includes a first scintillator layer including a plurality of first phases extending in a uniaxial direction and having a columnar shape, and a second phase surrounding the plurality of first phases, and radiation irradiation. A second scintillator layer in which the generated scintillation light is subjected to multiple scattering and diffuses, and
The radiation detector, wherein the scintillator plate and the light detector are arranged in the order of the second scintillator layer, the first scintillator layer, and the light detector.   The radiation detector according to claim 1, wherein the second scintillator layer includes a particulate crystal.   The radiation detector according to claim 2, wherein the particulate crystal is a powder crystal.   The radiation detector according to claim 2, wherein the particulate crystal is a needle crystal.   5. The scintillator plate according to claim 1, wherein the scintillator plate has a resolution profile expressed by a spatial frequency and a contrast that exceeds a resolution profile of only the first scintillator layer in a low frequency region. 6. Radiation detector.   The radiation detector according to claim 5, wherein the low frequency region indicates a region having a spatial frequency of 4 lp / mm or less.   The radiation detector according to any one of claims 1 to 6, wherein a layer thickness of the first scintillator layer is in a range of 200 µm to 1000 µm.   The radiation detector according to any one of claims 1 to 7, wherein a layer thickness of the second scintillator layer is in a range of 10 µm to 100 µm.   The radiation detector according to any one of claims 1 to 8, wherein another layer exists between the first scintillator layer and the second scintillator layer.   The radiation detector according to claim 9, wherein the another layer is an adhesive layer.   The radiation detector according to claim 1, wherein the first phase and the second phase have different refractive indexes with respect to scintillation light.   The first material forming the first phase and the second material forming the second phase are a combination capable of forming a eutectic. The radiation detector according to any one of 11.   The radiation detector according to claim 12, wherein the first material and the second material are within a range of ± 5 mol% of a eutectic composition.   The radiation detector according to claim 13, wherein the first material is a perovskite oxide material containing Gd, and the second material contains alumina.   The radiation detector according to any one of claims 12 to 14, wherein the first phase contains 0.001 mol% or more of a rare earth element as an emission center.   The radiation detector according to claim 15, wherein the rare earth element is at least one of Tb, Eu, and Ce. The radiation detector according to any one of claims 1 to 16, wherein the second scintillator layer includes Gd ₂ O ₂ S or CsI.   The radiation detection according to any one of claims 1 to 17, wherein the light detection unit discriminates and detects scintillation light from the first scintillator layer and the second scintillator layer. vessel. A diffraction grating that diffracts radiation from a radiation source to form an interference pattern, and a radiation detector that detects the interference pattern,
The radiation measurement system according to claim 1, wherein the radiation detector is the radiation detector according to claim 1.

Images