JP2016033450A - Radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation detector capable of accurately identifying scintillator cells that generated scintillation light.SOLUTION: A radiation detector 1 includes; a scintillator array 2 comprising a plurality of two-dimensionally arrayed scintillator cells 6, each having a cell incident surface 7a and a cell coupling surface 8a; and a photodetector 3 having a photoreceiver unit optically coupled with the cell coupling surfaces 8a. The scintillator array 2 has light reflective surfaces 9 that act as a light diffusion limiter surrounding the plurality of scintillator cells 6, and light scattering surfaces 11 that optically separate each of the scintillator cells 6 surrounded by the light diffusion limiter from others. Each light scattering surface 11 contains one or more modified quality areas formed through irradiation of laser light.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radiation detector capable of specifying a position where radiation is detected.

  Radiation detectors are used for positron emission tomography (PET). This radiation detector includes a scintillator and a position detection type photodetector. The scintillator absorbs radiation and generates scintillation light. The position detection type photodetector detects the position where the scintillation light is generated and the light intensity. As technologies in such a field, technologies described in Patent Documents 1 to 4 are known.

  The radiation detector of Patent Document 1 includes a scintillator having a plurality of light scattering surfaces and two photodetectors. At least one of the photodetectors captures the scintillation light whose light intensity has been attenuated after passing through one or more light scattering surfaces. Since the amount of attenuation of light intensity corresponds to the number of light scattering surfaces that have passed, the region where scintillation light is generated can be specified using the light intensity. The three-dimensional radiation position detector of Patent Document 2 includes a scintillator unit having a plurality of scintillator cells and a light receiving element. Between the scintillator cells, only one of the reflective material and the transmissive material is disposed. The radiation position detector of Patent Document 3 includes a multilayer scintillator and a light receiving element. This radiation position detector has a light reflecting material installed between scintillator cells as one of means for equalizing the light intensity incident on the light receiving element. The detector component of Patent Document 4 includes a scintillator. A plurality of voids are formed in this scintillator. This void is for defining an optical boundary for controlling the scintillation light, and is formed by focusing the laser beam on a focal point set in the scintillator.

International Publication 2012/105292 Patent No. 4338177 Japanese Patent No. 4333213 Japanese Patent No. 5013864

  By the way, in the radiation detector provided with the scintillator and the light detector described above, the position where the scintillation light is generated is set as the center of gravity of the light intensity distribution using the two-dimensional light intensity distribution output from the light detector. The cell where the scintillation light is generated is specified by calculation. Therefore, it is necessary to diffuse the scintillation light within a certain range before the scintillation light reaches the photodetector. As a configuration for diffusing light, for example, there is a configuration in which a light guide is sandwiched between a scintillator and a photodetector. There is also a configuration in which the scintillator is divided into a plurality of optically separated cells using a light scattering surface. Since the light scattering surface transmits a certain amount of light, the light can be diffused without using a light guide.

  However, when the scintillator becomes thicker, the distance from the position where the scintillation light is generated to reach the photodetector becomes longer, so that the scintillation light may be excessively diffused. In this case, it may be difficult to obtain the light intensity distribution with high accuracy, and there is a possibility that the scintillator cell in which the scintillation light is generated cannot be specified with high accuracy.

  Therefore, an object of the present invention is to provide a radiation detector capable of accurately identifying a scintillator cell in which scintillation light is generated.

  A radiation detector according to an aspect of the present invention includes a scintillator cell having a cell incident surface that intersects the incident direction of radiation and a cell coupling surface parallel to the cell incident surface, and the scintillator cells are arranged in a two-dimensional manner. A scintillator array, and a light detection unit having a light receiving unit optically coupled to a plurality of cell coupling surfaces. The scintillator array is parallel to the normal direction of the cell incident surface, and is parallel to the normal direction of the cell incident surface and the light reflecting surface surrounding the plurality of scintillator cells to form a light diffusion limiting portion. A light scattering surface that optically separates the scintillator cell included in the light diffusion limiting unit, and the light scattering surface includes one or a plurality of modified regions formed by laser light irradiation.

  In this radiation detector, radiation is absorbed by the scintillator array, and scintillation light having a light intensity corresponding to the dose is generated. The scintillation light propagates while diffusing from the generation position toward the light detection unit. The diffused scintillation light enters the light receiving unit. Then, using the signal output from the light receiving unit on which the scintillation light is incident, the center of gravity is calculated to calculate the position where the scintillation light is generated. That is, the calculation of the position where the scintillation light is generated is affected by the diffusion range of the scintillation light. Here, the scintillator array has a light reflecting surface, and this light reflecting surface surrounds a plurality of scintillator cells to form a light diffusion limiting portion. When scintillation light is generated in the scintillator cell included in the light diffusion restriction unit, the light reflection surface restricts the diffusion of the scintillation light to the outside of the light diffusion restriction unit. A light scattering surface including a modified region formed by laser light irradiation is formed in the light diffusion limiting portion. In the light diffusion limiting unit, the scintillation light diffuses while passing through the light scattering surface. This scintillation light can be detected as a light intensity distribution capable of accurately calculating the light emission position. Therefore, the scintillator cell in which the scintillation light is generated can be specified with high accuracy.

  The light diffusion limiting unit may be provided at the peripheral edge of the scintillator array. Here, when scintillation light is generated in the scintillator cells arranged at the peripheral edge of the scintillator array, the light intensity distribution acquired by the light detection unit is obtained because the diffusion range of the scintillation light is biased to the inside of the scintillator array. The center of gravity of the center of the scintillator is shifted toward the center of the scintillator array. Therefore, there is a possibility that the light detection position corresponding to the inner scintillator cell is close to and overlapped. According to this configuration, the light reflection surface restricts the scintillation light from diffusing inside the light diffusion limiting portion. Therefore, it is possible to avoid the overlap between the scintillator cells arranged at the peripheral edge of the scintillator array and the inner scintillator cells, and to further suppress the deterioration of the separation characteristics.

  Further, the scintillator array has a plurality of light diffusion limiting portions. The light receiving unit of the light detection unit may be optically coupled to the scintillator array so as to straddle adjacent light diffusion units. Here, the separation characteristics of the scintillator cells arranged on the light receiving parts tend to be lower than the separation characteristics of the scintillator cells arranged on the light receiving parts. According to such a configuration, when scintillation light is generated in any one of the light diffusion limiting units adjacent to each other, the scintillation light is prevented from diffusing to the other light diffusion limiting unit. Therefore, even when scintillation light is generated in the scintillator cell arranged on the light receiving unit, it is possible to suppress a decrease in the separation characteristics of the scintillator cell. Therefore, the scintillator cell in which the scintillation light is generated can be specified with high accuracy.

  In addition, the light receiving unit of the light detecting unit may be optically coupled to the scintillator array so as to straddle each of the light diffusion limiting units that are two-dimensionally arranged in two rows and two columns. According to such a configuration, even when scintillation light is generated in the scintillator cell arranged on the light receiving unit, it is possible to suppress a decrease in the separation characteristics of the scintillator cell. That is, the separation characteristic of the scintillator cell arranged on the light receiving unit can be further improved.

  According to the radiation detector of the present invention, a scintillator cell in which scintillation light is generated can be specified with high accuracy.

It is a perspective view of the radiation detector concerning a 1st embodiment of the present invention. FIG. 2 is a plan view of the radiation detector shown in FIG. 1. FIG. 2 is an exploded perspective view of the scintillator array shown in FIG. 1. It is a figure which shows typically distribution of the detection point obtained by the radiation detector shown by FIG. It is a top view of the radiation detector concerning a 2nd embodiment of the present invention. It is a figure which shows typically distribution of the detection point obtained by the radiation detector shown by FIG. It is a top view of the radiation detector concerning a modification. It is a figure which shows typically distribution of the detection point obtained by the radiation detector shown by FIG. (A) is a top view of the radiation detector which concerns on the comparative example 1, (b) is a figure which shows typically distribution of the detection point obtained by the radiation detector shown by (a). (A) is a top view of the radiation detector which concerns on the comparative example 2, (b) is a figure which shows typically distribution of the detection point obtained by the radiation detector shown by (a).

[First Embodiment]
DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. As shown in FIG. 1, the radiation detector 1 detects radiation by detecting light generated by incidence of radiation such as gamma rays.

  The radiation detector 1 includes a scintillator array 2 and a photodetector (light detector) 3. The scintillator array 2 generates radiation called scintillation light by absorbing radiation. The scintillation light diffuses two-dimensionally while traveling from the generated position toward the photodetector 3. The scintillation light is detected by the photodetector 3 as a light intensity distribution. By calculating the center of gravity of the two-dimensional light intensity distribution, two-dimensional position information where the scintillation light is generated can be obtained.

  The scintillator array 2 is optically coupled to the light receiving unit 4 of the photodetector 3. The scintillator array 2 includes 121 scintillator cells 6 arranged two-dimensionally. The scintillator array 2 has a block incident surface 7 on which radiation is incident and a block coupling surface 8 on the opposite side of the block incident surface 7. An optical member that is transparent to the scintillation light is filled between the scintillator array 2 and the photodetector 3. Examples of such optical members include silicone oil, air, and optical transparent adhesive.

The scintillator array 2 is composed of crystal lumps that generate scintillation light upon incidence of radiation. This scintillation light has a light intensity corresponding to the absorbed dose of radiation. The crystal mass has a substantially rectangular parallelepiped outer shape. For example, the scintillator array 2 has one side A1 of 50 mm, the other side A2 of 50 mm, and a height A3 of about 20 mm. The crystal mass is, for example, Bi ₄ Ge ₃ O ₁₂ (BGO), Ce ₂ doped Lu ₂ SiO ₅ (LSO), Lu _{2 (1-X)} Y _2X SiO ₅ (LYSO), Gd ₂ SiO ₅ (GSO). ), PrAG-doped LuAG (Lu ₃ Al ₅ O ₁₂ ), Ce-doped LaBr ₃ (LaBr ₃ ), Ce-doped LaCl ₃ (LaCl ₃ ), Ce-doped Lu _0.7 Y _0.3 AlO ₃ (LuYAP), Luthenium Fine Silicate (LFS), or any other suitable crystal is preferably used.

  In the scintillator array 2, a light reflecting surface 9 and a light scattering surface 11 are formed. The light reflecting surface 9 and the light scattering surface 11 optically separate the crystal lump into a plurality of scintillator cells 6. The specific arrangement of the light reflecting surface 9 and the light scattering surface 11 will be described later. The optical separation means that when light is incident on the scintillator cells 6 adjacent to each other, light is scattered by the light scattering surface 11 and light whose intensity is weakened is propagated. And the case where the light reflecting surface 9 reflects a predetermined ratio of light and transmits the remaining light.

  The light reflecting surface 9 inhibits the diffusion of scintillation light and has a light transmittance lower than that of the light scattering surface 11. That is, the light reflecting surface 9 is more hindered from light diffusion than the light scattering surface 11. Therefore, since the light transmittance is only required to be lower than that of the light scattering surface 11, the reflectance of the light reflecting surface 9 may be approximately 100% or 100% or less. As the light reflecting surface 9, for example, any member such as Teflon tape (Teflon is a registered trademark), barium sulfate, aluminum oxide, titanium oxide, an ESR (Enhanced Specular Reflector) film, and a polyester film can be used. .

  The light scattering surface 11 is constituted by a modified region (not shown). The modified region is a region formed so that, for example, void-shaped modified spots overlap each other. The plurality of modified spots form an optical scattering surface. The modified spot is formed by condensing laser light inside the crystal mass. That is, the light scattering surface 11 is not obtained by mechanically or chemically treating the surface of the crystal mass forming the scintillator. The modified region does not block or absorb scintillation light. Therefore, even if the modified region is formed on the entire surface of the light scattering surface 11, a part of the scintillation light is transmitted to the adjacent scintillator cell 6. Further, the light scattering surface 11 has different light transmittance depending on the incident angle of light to the light scattering surface 11. For example, when the incident angle is vertical, the light transmittance increases. That is, the incident scintillation light is almost transmitted. On the other hand, when the incident angle is increased, the light transmittance is reduced as compared with the case where the incident angle is perpendicular.

  As shown in FIG. 3, the scintillator array 2 first forms a light scattering surface 11 by irradiating a plate-shaped crystal block with laser light. Therefore, the formation of the light scattering surface 11 is not accompanied by a step of cutting the crystal mass forming the scintillator. Next, a light reflecting material forming the light reflecting surfaces 9a to 9d is disposed between the crystal blocks on which the light scattering surfaces 11 are formed by the laser light, and optically joined again. Finally, the light reflecting surface 9e is formed on the side surface. The scintillator array 2 is obtained by the above process. In short, the scintillator array 2 is formed by a laser beam irradiation process on the crystal mass and a bonding process between the crystal masses.

  The photodetector 3 is a so-called position detection type photodetector. The photodetector 3 has a light receiving unit 4. The photodetector 3 outputs an electrical signal corresponding to the incident position of light incident on the light receiving unit 4 and the light intensity. The photodetector 3 is preferably composed of, for example, a position detection type photomultiplier tube or a semiconductor photodetector.

  Next, the arrangement of the light reflecting surface 9 and the light scattering surface 11 will be described in detail. In the following description, “row” and “column” may be used. As shown in FIG. 1, the “column” is a direction (direction D3) along the other side A2. The “row” is a direction (direction D2) along one side A1. Then, the scintillator cell 6r arranged at the uppermost left in the plan view is defined as a cell arranged in one row and one column. This definition is for convenience of explanation.

  The plurality of light reflecting surfaces 9 are parallel to the normal direction (direction D1) of the block incident surface 7 and are orthogonal to the block incident surface 7. That is, the light reflecting surface 9 is formed between the block incident surface 7 and the block coupling surface 8. Therefore, the scintillator light may reach the photodetector 3 without passing through the light reflecting surface 9. The light reflecting surfaces 9 a and 9 b are formed between the side surface 12 and the side surface 13 of the scintillator array 2. Specifically, the light reflecting surface 9a is formed between the scintillator cells 6 in the first row and the scintillator cells 6 in the second row. The light reflecting surface 9b is disposed between the 10th row of scintillator cells 6 and the 11th row of scintillator cells 6. The light reflecting surfaces 9 c and 9 d are formed between the side surface 14 and the side surface 16 of the scintillator array 2. Specifically, the light reflecting surface 9c is formed between the scintillator cells 6 in the first row and the scintillator cells 6 in the second row. The light reflecting surface 9d is disposed between the scintillator cells 6 in the 10th row and the scintillator cells 6 in the 11th row. Further, the light reflecting surface 9 e is disposed on each of the side surfaces 12, 13, 14, 16 of the scintillator array 2.

  As shown in FIG. 2, these light reflecting surfaces 9 a to 9 d are combined in a lattice shape and surround one or more scintillator cells 6. A region surrounded by these light reflecting surfaces 9 is called a light diffusion limiting unit 17. That is, the light diffusion limiting unit 17 includes the light reflecting surface 9 and one or a plurality of scintillator cells 6. The scintillator array 2 has nine light diffusion limiting portions 17a to 17c. The scintillator array 2 has four light diffusion limiting portions 17a formed at each corner. These light diffusion limiting portions 17 a include one scintillator cell 6. The scintillator array 2 has four light diffusion limiting portions 17b formed between the respective light diffusion limiting portions 17a. These light diffusion limiting portions 17b include nine scintillator cells 6 separated along the direction D2 or the direction D3. Further, the scintillator array 2 has one light diffusion limiting portion 17c surrounded by the light diffusion limiting portions 17a and 17b. The light diffusion limiting portion 17c includes 81 scintillator cells 6 that are divided into nine along the direction D2 and divided into nine along the direction D3.

  A plurality of light scattering surfaces 11 are formed in the light diffusion limiting portions 17b and 17c. The light scattering surface 11 is parallel to the normal direction (direction D1) of the block incident surface 7. That is, the light scattering surface 11 intersects, more specifically, is orthogonal to the block incident surface 7. Therefore, the scintillator light may reach the photodetector 3 without passing through the light scattering surface 11. For example, in the light diffusion limiting portion 17b, nine light scattering surfaces 11 orthogonal to the row direction (direction D3) or the column direction (direction D2) are formed at equal intervals. That is, the scintillator cells 6 are arranged one-dimensionally in the light diffusion limiting unit 17b. In the light diffusion limiting unit 17c, eight light scattering surfaces 11 orthogonal to the row direction (direction D3) are formed at equal intervals, and eight light scattering surfaces 11 orthogonal to the column direction (direction D2) are equal to eight. Is formed. That is, in the light diffusion limiting portion 17 c, the light reflection surface 9 is formed in a lattice shape, so that 64 scintillator cells 6 are two-dimensionally arranged along the block incident surface 7.

  The scintillator cell 6 has a cell incident surface 7a and a cell coupling surface 8a (see FIG. 1). The cell incident surface 7 a is a surface that intersects the radiation incident direction (direction D <b> 1), and is included in the block incident surface 7. The cell coupling surface 8 a is a surface parallel to the cell incident surface 7 a and is included in the block coupling surface 8. In addition, the cell coupling surface 8 a is optically coupled to the photodetector 3.

  The scintillator cell 6 is optically separated from another adjacent scintillator cell 6 by the light reflecting surface 9 or the light scattering surface 11. For example, the scintillator cells 6 a and 6 r are optically separated from other adjacent scintillators by the light reflecting surface 9. The scintillator cell 6b is optically separated by a pair of light reflecting surfaces 9 facing each other and a pair of light scattering surfaces 11 orthogonal to the light reflecting surfaces 9 and facing each other. The scintillator cell 6c is optically separated by a light reflecting surface 9 orthogonal to each other and a light scattering surface 11 orthogonal to each other. The scintillator cell 6 d is optically separated by one light reflecting surface 9 and three light scattering surfaces 11. The scintillator cell 6 e is optically separated by the light scattering surface 11.

  Hereinafter, the operation effect of the radiation detector 1 will be described in comparison with the operation effect of the radiation detector according to the comparative example 1.

  As shown in FIG. 9A, the radiation detector 100 according to the comparative example 1 is different from the radiation detector 1 in that the crystal lump is separated into a plurality of scintillator cells 106 only by the light scattering surface 101. . That is, the radiation detector 100 does not have the light reflecting surface 9 in the scintillator array. A light reflecting surface 9 is provided on the side surface of the scintillator array 102.

  FIG. 9B is a diagram schematically illustrating the distribution of the detection points P1. The detection point P1 corresponds to the scintillator cell 106 where scintillation light is generated in the radiation detector 100. For example, the detection point P1a corresponds to the scintillator cell 106a. That is, when the detection point P1a is included in the data obtained using the radiation detector 100, it indicates that radiation has entered the scintillator cell 106a.

  As shown in FIG. 9B, the interval between the detection points P <b> 1 becomes narrower as it approaches the peripheral edge of the scintillator array 102. For example, it is assumed that scintillation light is generated in the scintillator cell 106a. Assuming that the scintillation light is evenly diffused two-dimensionally, the light is not diffused outside the scintillator array 102, but diffuses inward. When the center of gravity is calculated based on such a light intensity distribution, the position of the detection point P1 is calculated as a position that is shifted to the center of the scintillator array 2 with respect to an accurate position. In short, the closer to the periphery, the more the symmetry of the light intensity distribution is broken and the distribution is biased toward the center, and the position of the detection point P1 is shifted to the center of the scintillator array 2. The degree of deviation of the detection point P1 depends on the diffusion range of the scintillation light. The factors that determine the diffusion range of the scintillation light are the light transmittance of the light scattering surface 101 and the distance from the position where the scintillation light is generated to the photodetector 3.

  Basically, it is desirable that the detection point P1a corresponding to the scintillator cell 106a and the detection point P1b corresponding to another scintillator cell 106b adjacent to the scintillator cell 106a are completely separated. On the other hand, the detection points P1a and P1b are allowed to approach to some extent as long as they can be discriminated by image processing. However, for example, when the detection points P1a and P1b are close to each other until they come into contact with each other or further overlap, it is difficult to determine which scintillator cell 106 the detection points P1a and P1b correspond to. There is a case.

  In the radiation detector 1 according to the present embodiment, the scintillator array 2 absorbs radiation, and scintillation light having light intensity corresponding to the dose is generated. The scintillation light propagates while diffusing from the generation position toward the photodetector 3. The scintillation light is incident on the photodetector 3. Then, the position where the scintillation light is generated is calculated by calculating the center of gravity using the light intensity distribution output from the light detector 3. That is, the calculation of the position where the scintillation light is generated is affected by the light intensity distribution of the scintillation light.

  Here, the scintillator array 2 has a light reflecting surface 9, and the light reflecting surface 9 surrounds the scintillator cell 6 and forms a light diffusion limiting portion 17. When scintillation light is generated in the scintillator cell 6 included in the light diffusion restriction unit 17, the light reflection surface 9 restricts the diffusion of the scintillation light to the outside of the light diffusion restriction unit 17. That is, since the scintillation light stays in the light diffusion limiting unit 17 including the scintillator cell 6 where the scintillation light is generated, the diffusion of the scintillation light to the adjacent light diffusion limiting unit 17 is limited. According to the scintillation light diffused in the light diffusion limiting unit 17, the light detector 3 can detect the light emission position as a light intensity distribution that can be calculated with high accuracy. Therefore, since the separation characteristic between the adjacent light diffusion limiting portions 17 is improved, the scintillator cell 6 in which the scintillation light is generated can be specified with high accuracy.

  That is, in the scintillator array 2 of the radiation detector 1, the separation characteristics in the scintillator cell 6 are improved by combining optical separation via the light reflecting surface 9 and the light scattering surface 11.

  A predetermined amount of scintillation light is transmitted between the scintillator cells 6 included in the light diffusion limiting unit 17. Accordingly, the scintillator cell 6 in the light diffusion limiting unit 17 can function as a light guide. Therefore, since the light reflection surface 9 and the light scattering surface 11 are formed in the scintillator array 2 of the radiation detector 1, a light guide can be omitted.

  Further, according to the light diffusion limiting unit 17b formed at the peripheral edge of the scintillator array 2, when scintillation light is generated in the scintillator cell 6b or the like in the light diffusion limiting unit 17b, the scintillation light is converted into the light diffusion limiting unit 17b. Diffusion inside is limited. Specifically, diffusion to the inside of the scintillator array 2 is limited. Accordingly, it is possible to further suppress the deterioration of the separation characteristics of the scintillator cells 6b and the like arranged at the peripheral edge of the scintillator array 2.

  Further, according to the light reflecting surface 9 formed on the scintillator array 2, the diffusion range of the scintillation light can be limited, so that the distance from the position where the scintillation light is generated to the photodetector 3 can be increased. Therefore, the scintillator array 2 having a large thickness can be employed for the radiation detector 1.

  The operational effects of the radiation detector 1 will be specifically described with reference to FIG. FIG. 4 is a diagram schematically showing the distribution of the detection points P1, P2. The detection point P2 corresponds to the scintillator cell 6 where scintillation light is generated in the radiation detector 1. The detection point P1 corresponds to the scintillator cell 106 where scintillation light is generated in the radiation detector 100 according to the comparative example 1. A broken line L1 indicates that the scintillator cell 6 is optically separated by the light scattering surface 11. An alternate long and short dash line L2 indicates that the scintillator cell 6 is optically separated by the light reflecting surface 9. As shown in FIG. 4B, the interval between the detection point P2a corresponding to the scintillator cell 6 arranged at the peripheral edge of the scintillator array 2 and the detection point P2b corresponding to the adjacent scintillator cell 6 is increased. Yes.

  When scintillation light is generated in the scintillator cell 6r (see FIG. 2) located at the peripheral edge of the scintillator array 2 of the present embodiment, the scintillator cell 6r in which the scintillation light is generated has a light reflecting surface 9 (dashed lines L2a to L2d). Is surrounded by Therefore, the diffusion of the scintillation light in the direction orthogonal to the light reflecting surface 9 (dashed line L2a) is limited. Similarly, diffusion of scintillation light in a direction orthogonal to the light reflecting surface 9 (dashed line L2d) is limited. This limits the diffusion of scintillation light into the scintillator array 2. Therefore, for example, the position of the detection point P2a is suppressed from shifting inward from the accurate position (see FIG. 4B).

  In the radiation detector 1, all the scintillator cells 6 are optically coupled to the light receiving unit 4 of the photodetector 3. That is, the light incident surface 3a of the photodetector 3 does not include a dead area that does not contribute to detection of scintillator light. Thus, even with the photodetector 3 that does not include a dead area, the scintillator array 2 can suitably calculate the position where the scintillator light is generated.

[Second Embodiment]
A radiation detector according to the second embodiment will be described. As shown in FIG. 5, the radiation detector 1A is different from the scintillator array 2 of the first embodiment in the arrangement of the light reflecting surfaces 9 formed on the scintillator array 2A. That is, in the radiation detector 1A, the configuration of the light diffusion limiting unit 18 formed in the scintillator array 2A is different from the configuration of the light diffusion limiting unit 17 of the first embodiment. The radiation detector 1 </ b> A is different from the photodetector 3 of the first embodiment in that the photodetector 3 </ b> A has an array configuration including the light receiving unit 5.

  In the scintillator array 2A of the radiation detector 1A, four light diffusion limiting portions 18a, eight light diffusion limiting portions 18b, and four light diffusion limiting portions 18c are formed. The scintillator array 2A has a light diffusion limiting portion 18a formed at each corner. These light diffusion limiting portions 18 a include one scintillator cell 10. The scintillator array 2A has a light diffusion limiting portion 18b formed between the light diffusion limiting portions 18a. Each of these light diffusion limiting portions 18b includes four scintillator cells 10 separated along the direction D2 or the direction D3. Further, the scintillator array 2A has four light diffusion limiting portions 18c surrounded by the light diffusion limiting portions 18a and 18b. The light diffusion limiting unit 18c includes 16 scintillator cells 10 that are divided into four along the direction D2 and divided into four along the direction D3.

  Further, the scintillator array 2A has a light reflection surface intersection 20 in which the light reflection surfaces 9 are combined in a cross shape. Each of the light diffusion limiting portions 18 a to 18 c is in a two-dimensional and two-column two-dimensional array via the light reflecting surface intersecting portion 20. For example, the four light diffusion limiting portions 18c are arranged in a secondary arrangement of 2 rows and 2 columns via the light reflection surface intersecting portion 20a. Further, the two light diffusion limiting portions 18b and the two light diffusion limiting portions 18c are arranged in a secondary arrangement of 2 rows and 2 columns via the light reflection surface intersecting portion 20b.

  The photodetector 3A has nine light receiving portions 5 that are spaced apart from each other. Such a photodetector 3A is preferably configured by a semiconductor photodetector such as an avalanche photodiode (APD: Avalance Photo Diode) or MPPC (Multi-Pixel Photon Counter). The MPPC is a photon counting device composed of a plurality of Geiger mode APD pixels. The scintillator array 2A is optically coupled to the photodetector 3A so that the light reflecting surface intersecting portions 19 are arranged on the respective light receiving portions 5. The coupling area where the light receiving unit 5 and the scintillator array 2A are optically coupled is smaller than the block coupling surface 8 of the scintillator array 2A. For example, the light receiving unit 5a of the photodetector 3A is optically coupled to the scintillator array 2A so as to straddle four light diffusion limiting units 18a, 18b, and 18c arranged in a two-dimensional arrangement of two rows and two columns. ing.

  Hereinafter, the operation effect of the radiation detector 1 </ b> A will be described in comparison with the operation effect of the radiation detector according to the comparative example 2.

  As shown in FIG. 10A, the radiation detector 200 according to the comparative example 2 has scintillator cells 206 that are the same number of divisions as the scintillator array 2A of the present embodiment and are arranged in 10 rows and 10 columns. ing. On the other hand, the scintillator array 202 is different from the scintillator array 2A of the radiation detector 1A in that the scintillator array 202 is separated into a plurality of scintillator cells 206 only by the light scattering surface 211. That is, the radiation detector 200 according to the comparative example 2 is not provided with the light reflecting surface 9 and is not provided with the light diffusion limiting unit 18. A light reflecting surface 9 is provided on the side surface of the scintillator array 2. Moreover, since the light detector 200 of the comparative example 2 is not provided with the light reflecting surface 9, the light reflecting surface intersection 19 is not provided. Accordingly, the light receiving unit 5 is disposed across the four scintillator cells 206 that are arranged in a two-dimensional array of two rows and two columns. Each scintillator cell 206 is optically separated by the light scattering surface 211. Has been. The photodetector 203 has the same configuration as the photodetector 3A of the present embodiment. The relationship between each light receiving unit 5 and the scintillator cell 206 optically coupled is also the same as that of the radiation detector 1A of the present embodiment.

  FIG. 10B is a diagram schematically showing the distribution of the detection points P3. The detection points P3a to P3d correspond to the scintillator cell 206 in which scintillation light is generated in the radiation detector 200 according to the comparative example 2. As shown in FIG. 10B, for example, the detection point P3a corresponds to the scintillator cell 206a. The intervals between the detection points P3a to P3d corresponding to the scintillator cells 206a to 206d on the light receiving unit 5a are narrow. That is, the separation characteristics of the scintillator cells 206a to 206d arranged on the light receiving unit 5a tend to be lower than, for example, the separation characteristics of the scintillator cells 206e arranged between the light receiving unit 5a and the light receiving unit 5b. is there.

  As an example, when scintillation light is generated in the scintillator cell 206a, most of the scintillation light is detected by the light receiving unit 5a. The same applies when scintillation light is generated in the scintillator cell 206b adjacent to the scintillator cell 206a. That is, even if scintillation light is generated in any of the four scintillator cells 206a to 206d on the light receiving unit 5a, the obtained light intensity distribution may be approximated. When the light intensity distribution is approximate, the positions of the detection points P3a to P3d obtained from the light intensity distribution tend to approach each other.

  FIG. 6 is a diagram schematically showing the distribution of the detection points P3 and P4. The detection point P4 corresponds to the scintillator cell 10 in which scintillation light is generated in the radiation detector 1A of the present embodiment. A broken line L3 indicates that the scintillator cell 10 of the present embodiment is optically separated by the light scattering surface 11. An alternate long and short dash line L4 indicates that the scintillator cell 10 of this embodiment is optically separated by the light reflecting surface 9.

  As shown in FIG. 6A, according to the radiation detector 1A, the intervals between the detection points P4a to P4d corresponding to the scintillator cells 10a to 10d on the light receiving unit 5a are enlarged. For example, when scintillation light is generated in the scintillator cell 10a, the scintillation light is diffused in the light diffusion limiting unit 18c and diffused to the light diffusion limiting unit 18c including the adjacent scintillator cells 10b, 10c, and 10d. Limited. Therefore, according to the radiation detector 1A of the present embodiment, the separation characteristics of the scintillator cells 10a to 10d arranged on the light receiving unit 5a are improved as compared with the light intensity distribution according to the comparative example 2.

  In addition, the light incident surface 3 a of the photodetector 3 </ b> A includes a light receiving unit 5 that detects scintillator light, and a dead area 3 b formed between the light receiving units 5. That is, the radiation detector 1A includes a scintillator cell optically coupled to the light receiving unit 5 and a scintillator cell coupled to the insensitive region 3b. Since the radiation detector 1A has the light scattering surface 11, even if the scintillator cell in which the scintillator light is generated is optically coupled to the insensitive region 3b, the scintillator light is coupled to the scintillator cell coupled to the light receiving unit 5. Diffuses. Therefore, even with the photodetector 3A having the insensitive region 3b, the position where the scintillator light is generated can be suitably calculated.

  As mentioned above, although one form of this invention was demonstrated, this invention is not limited to the said embodiment, A various deformation | transformation is possible in the range which does not deviate from the summary of this invention.

  For example, as shown in FIG. 7, the radiation detector 1B according to the modification may be a combination of the photodetector 3 of the first embodiment and the scintillator array 2A of the second embodiment. FIG. 8 is a diagram schematically showing the distribution of the detection points P1 and P5. The detection point P5 corresponds to the scintillator cells 6g, 6h, etc. in which scintillation light is generated in the radiation detector 1B of the modification. The detection point P1 corresponds to the scintillator cell 106 in which scintillation light is generated in the radiation detector 100 of Comparative Example 1. A broken line L5 indicates that the scintillator cell 6g or the like of the modification is optically separated by the light scattering surface 11. An alternate long and short dash line L6 indicates that the scintillator cells 6g, 6h and the like of the modification are optically separated by the light reflecting surface 9.

  As shown in FIG. 8, the interval between the detection point P5a corresponding to the scintillator cell 6g arranged at the peripheral edge of the scintillator array 2 and the detection point P5b corresponding to the adjacent scintillator cell 6h is enlarged. Therefore, even in the radiation detector 1B of the modified example, the interval between the detection points P5a and P5b in the peripheral portion can be increased. Therefore, it is possible to further suppress the deterioration of the separation characteristics of the scintillator cells 6g, 6h and the like arranged at the peripheral edge of the scintillator array 2.

  In the radiation detector 1 described above, the diffusion range of the scintillation light is based on the light reflection surface 9 and the light scattering surface 11 that form the light diffusion limiting portions 17 and 18. More specifically, it is based on the light transmittance of the light reflecting surface 9 and the light scattering surface 11. For this reason, the diffusion range of the scintillation light may be set to an arbitrary range using the light transmittances of the light reflecting surface 9 and the light scattering surface 11 as parameters. That is, the position of the detection point P2 corresponding to the scintillator cell 6 can be set to a desired position using the light transmittances of the light reflecting surface 9 and the light scattering surface 11 as parameters.

  In the radiation detector 1 </ b> A described above, the light receiving unit 5 of the photodetector 3 </ b> A does not necessarily need to be arranged at the peripheral edge of the scintillator array 2. The optical coupling configuration of the photodetector 3A to the scintillator array 2 can be appropriately set depending on the arrangement of the light diffusion limiting portions 18 included in the scintillator array 2, the number of the light receiving portions 5a, and the like.

1, 1A, 1B, 100, 200 ... radiation detectors, 2, 2A, 102, 202 ... scintillator arrays, 3, 3A, 203 ... photodetectors, 4, 5, 5a, 5b ... light receiving parts, 6, 106, 206 ... scintillator cell, 7 ... block incident surface, 7a ... cell incident surface, 8 ... block coupling surface, 8a ... cell coupling surface, 9 ... light reflecting surface, 11, 101, 211 ... light scattering surface, 17, 18 ... light Diffusion limiting part, 19 ... light reflection surface crossing part, P1, P2, P3, P4, P5 ... detection point.

Claims (4)

A scintillator cell having a cell incident surface intersecting with the incident direction of radiation and a cell coupling surface parallel to the cell incident surface; and a scintillator array in which the scintillator cells are arranged two-dimensionally;
A light detection unit having a light receiving unit optically coupled to the plurality of cell coupling surfaces;
With
The scintillator array is
A light reflecting surface that is parallel to the normal direction of the cell incident surface and surrounds the plurality of scintillator cells to form a light diffusion limiting portion;
A light scattering surface that is parallel to a normal direction of the cell incident surface and optically separates the scintillator cell included in the light diffusion limiting unit,
The light scattering surface is a radiation detector including one or more modified regions formed by laser light irradiation.   The radiation detector according to claim 1, wherein the light diffusion limiting unit is provided at a peripheral portion of the scintillator array. The scintillator array has a plurality of the light diffusion limiting portions,
The radiation detector according to claim 1, wherein the light receiving unit of the light detecting unit is optically coupled to the scintillator array so as to straddle the light diffusion limiting units adjacent to each other.   The light receiving unit of the light detection unit is optically coupled to the scintillator array so as to straddle each of the light diffusion limiting units two-dimensionally arranged in 2 rows and 2 columns. Radiation detector.