JP2008134078A - Radiation detector and its component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiation detector and its component capable of increasing detection sensitivity. <P>SOLUTION: The detector comprises: a scintillator array 11 where a scintillator element 13 for converting a radiation into light is arranged one-dimensionally and a reflection thick film 15 is formed in a plane perpendicular to an incident direction of a radiation; and a photodiode array 12 having photodiodes 12a disposed corresponding to the arrangement positions of the respective scintillator elements 13 where the detection surface for detecting light outputted from the respective scintillator elements 13 is formed almost perpendicular to the incident direction and at least the detection surface of the photodiode 12a is fixed to the scintillator array 11. In the detector, a light detection area S2 of each of the photodiode elements 12a of the photodiode array 12 is smaller than a light output area S1 for outputting light from each of the scintillator elements 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radiation detector component and a radiation detector for capturing a radiation image by converting input radiation into light and detecting the converted light, and in particular, capturing a radiation image in a two-dimensional array. The present invention relates to a radiation detector component and a radiation detector.

  Conventionally, an X-ray CT apparatus used in a medical institution or the like images an internal structure of a subject by irradiating the subject with X-rays. Specifically, the X-ray CT apparatus includes an X-ray irradiation source, and a radiation detector having a structure in which an X-ray detection unit arranged to face the X-ray irradiation source via a subject is arranged in a one-dimensional array. Have Here, the detector has a function of converting received X-rays into electric signals, and includes a scintillator element that converts X-rays into visible light, and a photodiode that converts visible light into electric signals. X-rays that have passed through the subject are received by the radiation detector, and an electrical signal obtained based on the received X-rays is recorded. Then, while receiving the positional relationship between the X-ray irradiation source and the radiation detector, X-ray reception is repeated by changing the X-ray irradiation angle in various ways. Thereafter, the obtained electric signal is subjected to processing such as convolution (convolution) and back projection (back projection) to reconstruct an image of a cross section (slice) of the subject through which the X-rays have passed.

  In particular, in recent years, a multi-slice X-ray CT apparatus capable of imaging a plurality of slices simultaneously by a single X-ray irradiation has a plurality of array-shaped X-ray detection units arranged corresponding to the plurality of slices. X-rays that have passed through the slices are collected to reconstruct a slice image. Therefore, in the multi-slice X-ray CT apparatus, the detection unit includes a radiation detector arranged in a two-dimensional array instead of a one-dimensional array.

JP 2003-84066 A

  By the way, the light detection signal detected by the conventional radiation detector has a lot of noise and the light detection sensitivity is low, and particularly weak light may not be detected with high sensitivity.

  This invention is made in view of the above, Comprising: It aims at providing the component for radiation detectors and radiation detector which can make detection sensitivity high.

  In order to solve the above-described problems and achieve the object, a radiation detector component according to the present invention converts incident radiation into light, and outputs the converted light from a light output surface; A photodiode that is arranged corresponding to the arrangement position of the scintillator element and that is formed on the light output surface side of the scintillator element to detect light, and the photodetection region of the photodiode element includes a photodetection region of the scintillator element. It is smaller than the light output surface.

  In the radiation detector component according to the present invention as set forth in the invention described above, the light detection area is approximately 60% of the light output surface.

  According to another aspect of the present invention, there is provided a radiation detector, wherein the radiation detector component according to any one of the above inventions is arranged on a plane perpendicular to the incident direction of the radiation, and a one-dimensional array or a two-dimensional array is arranged. It is formed.

  The radiation detector component and the radiation detector according to the present invention include a photodiode in which a light detection region of a photodiode that detects light from a scintillator element is made smaller than a light output surface that outputs light from the scintillator element. This reduces the noise for the amplifier connected to the photodiode and reduces the dark current of the photodiode itself, so that a photodetection signal with less noise components can be obtained as a result. The detection sensitivity can be increased.

  Hereinafter, a radiation detector component and a radiation detector, which are the best mode for carrying out the present invention, will be described.

(Embodiment 1)
FIG. 1 is an exploded perspective view of a radiation detector component according to the first embodiment of the present invention. FIG. 2 is a perspective view showing a state in which the radiation detector parts shown in FIG. 1 are assembled. Further, FIG. 3 is a cross-sectional view showing a state in which the radiation detector parts shown in FIG. 1 are two-dimensionally arranged. FIG. 4 is a perspective view showing a schematic configuration of a radiation detector in which the radiation detector parts shown in FIG. 2 are arranged to form a two-dimensional array.

  1 to 3, the radiation detector component 1 has a scintillator array 11 and a photodiode array 12. In the scintillator array 11, a plurality of scintillator elements 13 that convert radiation such as X-rays or γ-rays into light are arranged one-dimensionally substantially perpendicular to the radiation incident direction A1. A separator 14 is provided between the scintillator elements 13. Further, a reflective thick film 15 having a thickness of about several hundreds of μm is formed on the surface perpendicular to the incident direction A1 of each scintillator element 13 and the side surface of the scintillator element 13 at the end to reflect the converted light.

  On the other hand, the photodiode array 12 corresponds to the position of each scintillator element 13 as a photoelectric conversion element that converts light converted by each scintillator element 13 into an electric signal on a semiconductor substrate such as Si. The scintillator elements 13 and the photodiode elements 12a are bonded with an optical bonding agent so that they correspond to each other. Therefore, the light receiving surface of each photodiode element 12a is disposed substantially horizontally with respect to the radiation incident direction A1. That is, the semiconductor substrate surface of the photodiode array 12 is substantially parallel to the incident direction A1.

  In addition, on the back surface of the photodiode array 12, that is, the surface opposite to the surface on which the photodiode elements 12a are formed, an Al reflective thin film 16 of about several μm formed by vapor deposition or sputtering is provided on the side surface of the scintillator array 11. It is provided with a positional relationship covering the area. When the Al reflective thin film 16 is formed on a Si semiconductor substrate, a reflectance of 80% or more can be obtained.

  In the photodiode array 12, terminals 26 for extracting detection signals of the respective photodiode elements 12a are formed on the semiconductor substrate, and wirings 25 connecting the photodiode elements 12a and the respective terminals 26 are formed on the semiconductor substrate. Is formed.

  Here, since the reflection film is not formed on the surface of each scintillator element 13 that is joined to the photodiode element 12a and the opposite surface, the light converted by each scintillator element 13 is emitted from these surfaces. Will be. Therefore, with the scintillator array 11 alone, the converted light is emitted to each photodiode element 12a side and the opposite side. However, as shown in FIGS. 3 and 4, the radiation detector parts 1 are arranged. When the detection cells including the pair of scintillator elements 13 and the photodiode elements 12a are two-dimensionally arranged, the surface on the opposite side of the photodiode elements 12a in the scintillator array 11 is formed by the reflective thin film 16 of the adjacent scintillator array 11. The light that is covered and converted by the scintillator element 13 is reflected, and eventually the converted light is emitted only to the photodiode element 12a side.

  As a result, the photodiode element 12a can efficiently receive the light converted by the scintillator element 13, and the reflective thin film 16 is significantly thicker than the reflective thick film 15 as shown in FIG. Can be reduced. Specifically, the thickness W1 of the reflective thick film 15 in FIG. 3 is 100 μm, the thickness W2 of the photodiode array 12 is 200 μm, and the thickness W3 of the reflective thin film 16 is 1 μm. Compared to the case where the surface of the scintillator element 13 other than the photodiode element 12a is formed thick, the thickness of the reflective thin film 16 on the two-dimensional arrangement surface of the detection cell is negligible.

  As a result, the receiving efficiency per unit area as seen from the incident direction A1 can be increased, and further, the detection cell interval can be shortened, so that the number of detection cells per unit area can be increased and the resolution can be increased. be able to.

Here, the light detection region S2 of each photodiode element 12a is smaller than the light output surface S1 of each scintillator element 13, and is preferably about 60% in area ratio. As described above, each photodiode element 12a and each scintillator element 13 are joined by the adhesive layer 12c formed of an optical binder, and the insulating film 12b is formed on the photodiode 12a side so as to cover the photodiode element 12a. Has been. In addition, each light detection region S2 is disposed substantially in the center with respect to each light output surface S1, but not limited to this, the light detection region S2 may be within a range corresponding to each light output surface S1. That's fine. Note that the bonding layer 12c and the insulating layer 12b function as a light guide, and light output from the scintillator element 13 and light input outside the light detection region S2 propagates or re-reflects in the light guide. Is transmitted to the light detection region S2 and light is detected. In the first embodiment described above, the radiation detector component has been described as a one-dimensional detection array formed by the scintillator array 11 and the photodiode array 12. However, the radiation detector component in the claims is described below. It is shown as including a basic detection cell consisting of a pair of scintillator elements 13 and a photodiode element 12a. When the radiation detector component 1 is used as a one-dimensional array detector, it corresponds to the radiation detector in the claims.

  In the first embodiment, the light detection region S2 of each photodiode element 12a is made smaller than the light output surface S1 of each scintillator element 13, so that the light detection region S2 and the light output surface S1 are substantially reduced. Compared to the same case, the capacitor capacity of each photodiode element 12a is reduced. As a result, the influence on the amplification function of an amplifier (not shown) connected to each photodiode element 12a is reduced, and the noise component during amplification is reduced. In addition, the capacitance of the capacitor itself is reduced, so that the dark current is also reduced. As a result, the noise component of the light detection signal detected by the photodiode element 12a is reduced, the signal-to-noise ratio is improved, and the light detection is Sensitivity will increase. In particular, since the signal-to-noise ratio is reduced, even a weak light detection signal can be detected.

  Further, in the first embodiment, the light detection region S2 of each photodiode element 12a is made smaller than the light output surface S1 of each scintillator element 13, so that each photodiode element 12a and each scintillator element 13 are Positioning at the time of joining is facilitated.

Note that the reflective thin film 16 is not limited to Al, and may be formed of a metal such as Ag. Furthermore, it is not limited to metal, and may be realized by, for example, titanium oxide (TiO ₂ ) or a multilayer film using the same. The thin film of the reflective thin film 16 may be formed by a semiconductor manufacturing apparatus such as sputtering, or may be coated by plating. Further, in the first embodiment, when the mechanical strength and reliability of the photodiode array 12 are taken into consideration, the thickness of the photodiode array 12 is limited to about several hundreds μm. The thickness of the reflective thin film 16 that can be formed is preferably 10 μm or less.

  The detection wavelength region of the photodiode element 12a is not limited to visible light. That is, the detection wavelength region of the photodiode element 12a may have a detection capability corresponding to the wavelength of light converted and output by the scintillator element 13, and may be capable of detecting ultraviolet light or infrared light. .

Further, the material of the scintillator element 13 is CdWO ₂ , but other CsI, NaI, Bi ₄ Ge ₃ O ₁₂ , BaF ₂ , Gd ₂ SiO ₅ , Lu ₂ SiO ₅ and various ceramic scintillators can also be used. good.

  In the first embodiment described above, the reflective thin film 16 is provided on the adjacent photodiode array 12. However, the present invention is not limited to this, and a reflective film corresponding to the reflective thin film 16 is provided on the scintillator array 11 itself. May be.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. In the first embodiment described above, the detection signal from each photodiode element 12a is extracted from each terminal 26. However, in this second embodiment, each photodiode element 12a is placed on the photodiode array 12. A wiring pattern for extracting the detection signals is formed, and all the detection signals are extracted from one end of the photodiode array 12.

  FIG. 5 is an exploded perspective view of a radiation detector component according to the second embodiment of the present invention. 6 is a perspective view of the radiation detector component shown in FIG. FIG. 7 is a perspective view showing a schematic configuration of a radiation detector in which the radiation detector parts shown in FIG. 6 are two-dimensionally arranged.

  5 to 7, terminals 36 corresponding to the terminals 26 are collectively provided at one end of the photodiode array 33, and each terminal 36 and each photodiode element are electrically connected by a wiring 35. One end of the photodiode array 33 is further provided with a substrate 37 that overlaps at the one end portion, and a lead terminal provided on the substrate 37 and each terminal 36 are electrically connected.

  This simplifies the configuration for extracting the detection signal output from each photodiode element, and facilitates the assembly of the radiation detector 20.

(Embodiment 3)
Next, a third embodiment of the present invention will be described. In the first and second embodiments described above, the scintillator array 11 has a light output surface in a direction perpendicular to the radiation incident direction, and the photodiode array 12 is disposed on the light output surface side. In the third embodiment, the scintillator array 11 has a light output surface on the output side in the radiation incident direction, and the photodiode array 12 is arranged on the light output surface side.

  That is, as shown in FIG. 8, the scintillator elements 13 delimited by the separator 14 are arranged perpendicular to the incident line direction A1 of radiation, and have a light output surface on the output side of the incident line direction A1. Each photodiode element 12 a is provided on the output surface corresponding to each scintillator element 13. In this case, as in the first and second embodiments, the light detection area of each photodiode element 12 a is made smaller than the light output surface of each scintillator element 13. An insulating film 12b is formed on the upper surface of each photodiode element 12a, and an adhesive film 12c is formed on the upper surface of the insulating film 12b. A reflective film is formed in each of the upper and lower directions in FIG.

  In this third embodiment, as in the first and second embodiments described above, the photodetection region of the photodiode element group is made smaller than the light output surface that outputs light from each scintillator element, and Since the capacitor is made small and the noise for the amplifier connected to the photodiode is reduced, and the dark current of the photodiode itself is reduced, a photodetection signal with less noise component can be obtained as a result. , The detection sensitivity can be increased.

  The radiation detector component and the radiation detector are applicable not only to X-rays but also to those that detect various types of radiation, and not only to X-ray CT apparatuses but also to PETCT apparatuses, for example. .

It is a disassembled perspective view of the components for radiation detectors which are Embodiment 1 of this invention. It is a perspective view of the components for radiation detectors shown in FIG. It is sectional drawing at the time of arranging the radiation detector components shown in FIG. 2 two-dimensionally. FIG. 3 is a perspective view showing a schematic configuration of a radiation detector in which the radiation detector parts shown in FIG. 2 are two-dimensionally arranged. It is a disassembled perspective view of the components for radiation detectors which are Embodiment 2 of this invention. It is a perspective view of the components for radiation detectors shown in FIG. It is a perspective view which shows schematic structure of the radiation detector which arranged the components for radiation detectors shown in FIG. 6 two-dimensionally. It is a fragmentary sectional view of the radiation detector component which is Embodiment 3 of this invention.

Explanation of symbols

1, 2 Radiation detector parts 10, 20 Radiation detector 11, 34 Scintillator array 12, 33 Photodiode array 12a Photodiode element 12b Insulating film 12c Adhesive layer 13 Scintillator element 14 Separator 15 Reflective thick film 16, 16a, 46 Reflective thin film 25, 35, 38 Wiring 26, 36 Terminal 37 Substrate S1 Light output surface S2 Light detection area

Claims (3)

A scintillator element that converts incident radiation into light and outputs the converted light from the light output surface;
A photodiode that is arranged corresponding to the arrangement position of the scintillator element and is formed on the light output surface side of the scintillator element to detect light;
A radiation detector component comprising: a light detection region of the photodiode element that is smaller than a light output surface of the scintillator element.   The radiation detector component according to claim 1, wherein the light detection region is approximately 60% of the light output surface.   The radiation detector according to claim 1, wherein the radiation detector parts are arranged on a plane perpendicular to the radiation incident direction to form a one-dimensional array or a two-dimensional array.

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