JPH10160852A - Radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve sensitivity and to miniaturize a detector by combining a ceramic scintillator and a single-crystal scintillator as a scintillator. SOLUTION: A single-crystal scintillator 2 and a photo detector 3 such as silicon photodiode 3 are buried in a substrate 7 made of epoxy resin containing glass and ceramic scintillators 1 are adjacently arranged directly above the single-crystal scintillator 2. A light reflection plate 5 such as Mo plate is provided in parallel between the ceramic scintillators 1, thus constituting a radiation detector. The single-crystal scintillator 2 functions as the light guide of the ceramic scintillator 1 and at the same time functions as a scintillator that absorbs X rays through the ceramic scintillator 1 and emits light. In this case, in terms of utilization efficiency, the light transmission rate of the single-crystal scintillator 2 is approximately 30% or higher. With this structure, a radiation detector which is compact, and has an improved sensitivity and a high utilization efficiency can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detector used in, for example, an X-ray CT apparatus for detecting X-rays.

[0002]

2. Description of the Related Art One of typical X-ray inspection apparatuses, which is a radiation inspection apparatus, is a computed tomography apparatus (Computed).
Tomography: hereinafter referred to as a CT apparatus). This C
The T apparatus is configured by arranging an X-ray tube for irradiating a fan-shaped fan beam X-ray and a radiation detector having a large number of radiation detection elements in such a manner that a tomographic plane to be measured is opposed to the center of the X-ray tube. X-ray absorption data is collected by irradiating a fan beam X-ray from the X-ray tube and changing the angle of the object to be measured each time irradiation is performed, and then analyzing this data with a computer to obtain a tomographic image. The X-ray absorptance of each position is calculated, and an image corresponding to the absorptivity is formed. Conventionally, a detector combining a CdWO ₄ single crystal scintillator and a silicon photodiode or a detector combining a Bi ₆ Ge ₄ O ₁₂ single crystal scintillator and a photomultiplier tube has been used for this CT apparatus.

[0003]

However, since the CdWO ₄ single crystal scintillator has a low luminous efficiency with respect to X-rays, it is difficult to measure a tomographic image of an object having a large X-ray absorption coefficient or a large mechanical structure. As a result, the / N ratio became small, and it was difficult to obtain a high-resolution tomographic image. By the way, in addition to CdWO ₄ , NaI and Cs
Some scintillators have high sensitivity to X-rays such as I, but they have deliquescence and large afterglow.
It was difficult to apply. Further, ceramic scintillators such as Gd ₂ O ₂ S: Pr are examples of scintillators having high luminous efficiency with respect to X-rays, low afterglow, and having no deliquescence. However, the ceramic scintillator has a lower light transmittance for visible light than a single crystal scintillator.
For this reason, when using X-rays having a large energy, if the thickness of the ceramic scintillator is increased in order to increase the utilization efficiency of the X-rays, the luminous efficiency is large but the light transmittance is small, so that the light actually reaching the photodetector is small. Of the CdWO ₄ single crystal scintillator, and the same problem remains.

On the other hand, in the radiation detector that combines Bi ₆ Ge ₄ O ₁₂ single crystal scintillator and photomultiplier, Bi ₆ Ge ₄ O
_{Although the} luminous efficiency of the _12- single-crystal scintillator for X-rays is small, the sensitivity of the photomultiplier to light is very high, so that the detector sensitivity can be increased. But this
In a radiation detector that combines a Bi ₆ Ge ₄ O ₁₂ single crystal scintillator and a photomultiplier tube, it is difficult to reduce the size of the photomultiplier tube, so the detection element becomes large, and it is difficult to increase the resolution of the tomographic image. there were. Therefore, the object of the present invention is to
Radiation detectors (for example, X-rays and the like) that have high sensitivity to radiation, can be miniaturized, and can obtain high-resolution tomographic images of objects and large mechanical structures having a large radiation absorption coefficient. X-ray CT etc.).

[0005]

Means for Solving the Problems The present inventors have proposed a structure in which a ceramic scintillator having a high luminous efficiency and a single-crystal scintillator having a large light transmittance in the visible region are combined, so that the luminous efficiency particularly for X-rays is improved. high,
It has been found that a radiation detector that can be downsized and has high X-ray utilization efficiency can be obtained. That is,
The present invention provides a radiation detector comprising a combination of a scintillator capable of emitting light by radiation and a photodetector for converting light of the scintillator into an electric signal, wherein a ceramic scintillator and a single crystal scintillator are used in combination as the scintillator. A radiation detector characterized in that: As the ceramic scintillator, polycrystalline body (e.g. ceramic powder as by sintering or the like) and a by e.g. _{Gd 2 O 2 S: Pr,} Gd 2 O 2 S: Eu, Gd 2 O 2 S: Tb
It is preferable to use any one or more of these. Further, either or both of Gd ₃ Ga ₅ O ₁₂ : Cr and (Y, Gd) ₂ O ₃ : Eu can be used as the polycrystalline ceramic scintillator. Further, it is preferable to use one or both of CdWO ₄ and Bi ₆ Ge ₄ O ₁₂ as the single crystal scintillator. In the present invention, by arranging the single crystal scintillator between the ceramic scintillator and the photodetector, high sensitivity to X-rays and imaging with high resolution are possible. Further, since the ceramic scintillator and the single-crystal scintillator are arranged adjacent to each other on the photodetector, the sensitivity to X-rays is particularly high, the size can be reduced, and high-resolution imaging can be performed as described above. .

In the present invention, the use of the above-mentioned ceramic scintillator has a particularly high luminous efficiency for X-rays.
The sensitivity of the radiation detector can be increased and the size can be reduced as compared with the related art. In addition, when the above-mentioned single crystal scintillator is used, the light emitted from the ceramic scintillator functions as a waveguide for efficiently guiding the light to the photodetector, and the single crystal scintillator itself emits light. It is possible to increase.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The radiation detector of the present invention will be described below in detail. There are basically two types of combinations of the ceramic scintillator and the single crystal scintillator of the present invention. X-rays, which are typical as radiation, decrease exponentially in a scintillator according to Lambert's law. At this time, the scintillator emits light in proportion to the X-ray intensity at each position, and the light emission output is the integrated value.

FIG. 1 is a partially broken external view showing one embodiment of the radiation detector of the present invention, and shows one of the combinations of the ceramic scintillator and the single crystal scintillator of the present invention. In FIG. 1, a single-crystal scintillator 2 (not shown) and a photodetector 3 (for example, a silicon photo dye), which are not shown, are embedded on a substrate 7 (for example, made of epoxy resin containing glass). 1 are arranged adjacently. As an example, this ceramic scintillator 1 has a length in the x direction of 10 to 10.
It is formed in a rectangular plate shape having a width of 50 mm, a width in the y direction of 0.5 to 3 mm, and a thickness in the z direction of 1 to 3 mm. The single crystal scintillator 2 is formed in a rectangular plate shape having a width in the y direction of 0.5 to 3 mm and a thickness in the z direction of 0.2 to 10 mm. In addition,
An amorphous silicon photo diode other than the silicon photo diode may be used as the photodetector 3. A light reflection plate 5 (for example, a Mo plate) is juxtaposed between the ceramic scintillators 1 and 1 to constitute a radiation detector 11 of the present invention. The length of the light reflecting plate 5 in the x direction is 10 to 50 mm, which is the same as that of the ceramic scintillator 1, and the width in the y direction is 0.2 to 2 m.
m. The light reflecting plate 5 may be formed of any of W, Cu, brass, and the like other than Mo. The light reflection plate 5 is also disposed on the rear and front side surfaces 11a, 11a of the radiation detector 11, and the left and right side surfaces 11b, 1
In 1b, an end reflector 6 (for example, made of TiO ₂ ) is arranged. The end reflector 6 is made of Mg other than TiO _2.
O or BaSO ₄ may be used. Radiation detector 1
A light reflecting material 4 made of, for example, TiO ₂ powder is applied on the upper surface of the first member 1. The light reflecting material 4 may be formed of any powder other than the TiO ₂ powder, such as MgO, BaSO ₄ , Al, an Al alloy, or Ag.

Next, FIG. 2 is a sectional view taken in the direction of the arrow y--y in FIG. In FIG. 2, a ceramic scintillator 1 having a high luminous efficiency is arranged on the X-ray incident side having a large X-ray intensity, and a single crystal scintillator 2 is arranged on a silicon photo diode 3 side. The single crystal scintillator 2 functions as a light guide of the ceramic scintillator 1 and also functions as a scintillator that absorbs X-rays transmitted through the ceramic scintillator 1 and emits light. Here, if the light transmittance of the single crystal scintillator 2 is less than 30%, the use efficiency and sensitivity of X-rays are reduced to a level that cannot be practically used. Therefore, the light transmittance is preferably set to 30% or more. Further, it is preferable that the ratio (t2 / t1) of the thickness (t1) of the ceramic scintillator 1 and the thickness (t2) of the single crystal scintillator 2 in FIG. 2 be t2 / t1 = 0.2 to 10. This ratio (t2 / t1) is 0.2
If it is less than 10, almost no increase in output due to the lamination of the single crystal scintillator 2 on the ceramic scintillator 1 is observed, and if it exceeds 10, the light transmittance of the single crystal scintillator 2 becomes too small and the output decreases to the conventional level. It is. According to the structure of FIG. 2, a radiation detector with high X-ray utilization efficiency, small size, and high sensitivity can be realized.

A second embodiment of the combination of the ceramic scintillator and the single-crystal scintillator of the present invention is shown in a sectional view of a main part in FIG. The only difference between FIG. 3 and FIG. 2 is the combination of the ceramic scintillator and the single crystal scintillator. In FIG. 3, the ceramic scintillator 10 and the single-crystal scintillator 20 are combined with a silicon photo dye # 3.
Since the structure is arranged adjacently on the upper side, light emitted from the ceramic scintillator 10 passes through the adjacent single crystal scintillator 20 and is guided to the silicon photo diode # 3. Light also directly enters the silicon photodiode 3 from the ceramic scintillator 10. Further, the light emitted from the single crystal scintillator 20 naturally enters the silicon photo diode # 3. With this structure as well, a radiation detector having a small size, a high X-ray utilization efficiency, and a high sensitivity can be realized as in FIG. 2, the ceramic scintillator 10 and the single crystal scintillator 20 are formed in a rectangular plate shape. Here, the ratio of the dimension in the y direction between the ceramic scintillator 10 and the single crystal scintillator 20 in FIG. 3 can be appropriately determined depending on the required resolution of the radiation detector. In the present invention, the ratio (m / l) of the dimension (m) of the single crystal scintillator 20 in the y direction to the dimension (l) of the ceramic scintillator 10 in the y direction is represented by m / l.
= 0.1 to 2.0 is preferable. This is (m /
If l) is less than 0.1, the optical waveguide action of the single crystal scintillator 20 will be small, and if it exceeds 2.0, the X-ray receiving area of the ceramic scintillator 10 will be small, and the output will be reduced to the conventional level. is there. here,
In order to improve the relative output and reduce the size of the radiation detector of the present invention having the structure shown in FIG. 2 or 3, the ceramic scintillator and the single crystal scintillator have a dimension in the y direction of 0.5 to 3 mm. Is preferred. If the size is less than 0.5 mm, the number of steps for processing to a predetermined size increases, and the processing cost tends to increase. As the size increases beyond 3 mm, it becomes more difficult to meet the needs for miniaturization.

Next, the radiation detector of the present invention will be further described with reference to examples. Example 1 As a ceramic scintillator 1, a rectangular plate-shaped polycrystalline Gd ₂ O ₂ S: Pr ceramic scintillator having a size of 1.6 mm in the y direction × 30 mm in the x direction × 1.2 mm in thickness, and a size of 1.6 mm × x in the y direction 30mm x 1.8mm thick rectangular plate
The CdWO ₄ single crystal scintillator 2 was bonded to the structure shown in FIG. 2 with an epoxy adhesive for optical use, and then bonded to a silicon photo diode 3. TiO ₂ powder was applied as a light reflecting material 4 on the upper surface of the scintillator, and a Mo plate 5 was adhered on the side surface as a light reflecting plate. Table 1 shows the relative output of the radiation detector of Example 1 when irradiating continuous X-rays with an X-ray tube voltage of 400 kV and a tube current of 4 mA. Here, the relative output in Table 1 is defined assuming that the output value from the silicon photo dye auto # 3 in Comparative Example 1 below is 1,
This is a value relatively representing the output value from the silicon photo diode # 3 in each of the examples and comparative example 2.

[0012]

[Table 1]

(Example 2) Ceramic scintillator 1
As a rectangular plate-shaped polycrystalline Gd ₂ O ₂ S: Eu ceramic scintillator with a size of 1.6 mm in the y direction × 30 mm in the x direction × 1.2 mm in thickness, and a size of 1.6 mm in the y direction × 30 mm in the x direction × 1.8 mm in thickness, The rectangular plate-shaped CdWO ₄ single-crystal scintillator 2 and FIG.
After bonding to the structure (1) with an epoxy adhesive for optics, it was bonded to a silicon photo tire (# 3). On top of this scintillator, TiO ₂
The powder was applied as a light reflecting material 4, and a Mo plate 5 was adhered to the side surface as a light reflecting plate. Table 1 shows the characteristics of the radiation detector of Example 2 when irradiated with continuous X-rays at an X-ray tube voltage of 400 kV and a tube current of 4 mA.

(Embodiment 3) Ceramic scintillator 1
As a rectangular plate-shaped polycrystalline Gd ₂ O ₂ S: Tb ceramic scintillator with a size of 1.6 mm in the y direction × 30 mm in the x direction × 1.2 mm in thickness, and a size of 1.6 mm in the y direction × 30 mm in the x direction × 1.8 mm in thickness The rectangular plate-shaped CdWO ₄ single-crystal scintillator 2 and FIG.
After bonding to the structure (1) with an epoxy adhesive for optics, it was bonded to a silicon photo tire (# 3). On top of this scintillator, TiO ₂
The powder was applied as a light reflecting material 4, and a Mo plate 5 was adhered to the side surface as a light reflecting plate. Table 1 shows the characteristics of the radiation detector of the third embodiment when irradiated with continuous X-rays having an X-ray tube voltage of 400 kV and a tube current of 4 mA.

(Example 4) Ceramic scintillator 1
Assuming 0, the size is 1.0 mm in the y direction x 30 mm in the x direction x 3.0 mm in thickness
Rectangular plate-shaped polycrystalline Gd ₂ O ₂ S: Pr ceramic scintillator with a size of 0.6 mm in the y direction x 30 mm in the x direction x 3.0 mm in thickness
After bonding the rectangular plate of the CdWO ₄ single crystal scintillator 20 with optical epoxy adhesive to the structure of FIG. 3, adhered to the silicon photo data Bu Ioto Bu 3. On the top of this scintillator,
TiO ₂ powder was applied as a light reflecting material 4, and a Mo plate 5 was adhered to a side surface as a light reflecting plate. X-ray tube voltage 400kV, tube current 4mA
Table 1 shows the characteristics of the radiation detector of Example 4 when the continuous X-ray was irradiated.

(Embodiment 5) Ceramic scintillator 1
Assuming 0, the size is 1.0 mm in the y direction x 30 mm in the x direction x 3.0 mm in thickness
Rectangular plate-shaped polycrystalline Gd ₂ O ₂ S: Eu ceramic scintillator with a size of 0.6 mm in the y direction x 30 mm in the x direction x 3.0 mm in thickness
After bonding the rectangular plate of the CdWO ₄ single crystal scintillator 20 with optical epoxy adhesive to the structure of FIG. 3, adhered to the silicon photo data Bu Ioto Bu 3. On the top of this scintillator,
TiO ₂ powder was applied as a light reflecting material 4, and a Mo plate 5 was adhered to a side surface as a light reflecting plate. X-ray tube voltage 400kV, tube current 4mA
Table 1 shows the characteristics of the radiation detector of Example 5 when the continuous X-ray was irradiated.

(Embodiment 6) Ceramic scintillator 1
Assuming 0, the size is 1.0 mm in the y direction x 30 mm in the x direction x 3.0 mm in thickness
Rectangular plate-shaped polycrystalline Gd ₂ O ₂ S: Tb ceramic scintillator with a size of 0.6 mm in the y direction x 30 mm in the x direction x 3.0 mm in thickness
After the rectangular plate-shaped CdWO ₄ single crystal scintillator 20 adhered by optical epoxy adhesive as the structure of FIG. 3, adhered to the silicon photo data Bu Ioto Bu 3. TiO ₂ powder was applied as a light reflecting material 4 on the upper surface of the scintillator, and a Mo plate 5 was adhered on the side surface as a light reflecting plate. Table 1 shows the characteristics of the radiation detector of the sixth embodiment when irradiated with continuous X-rays having an X-ray tube voltage of 400 kV and a tube current of 4 mA.

(Comparative Example 1) Next, as Comparative Example 1, evaluation results of a radiation detector having the following conventional structure configured as shown in a sectional view of a main part of FIG. 4 will be described. Size is in y direction
A rectangular plate-shaped CdWO ₄ single crystal scintillator 200 having a size of 1.6 mm × 30 mm in the x direction × 3.0 mm thickness was bonded to a silicon photo-diameter 3 with an epoxy adhesive for optical use. TiO ₂ powder was applied as a light reflecting material 4 on the upper surface of the scintillator, and a Mo plate 5 was adhered on the side surface as a light reflecting plate. Table 1 shows the characteristics of the radiation detector of Comparative Example 1 when irradiated with continuous X-rays at an X-ray tube voltage of 400 kV and a tube current of 4 mA. (Comparative Example 2) Next, as Comparative Example 2, evaluation results of a radiation detector having the following conventional structure configured as shown in a sectional view of a main part of FIG. 4 will be described. A rectangular plate-shaped polycrystalline Gd ₂ O ₂ S: Pr ceramic scintillator 300 having a size of 1.6 mm in the y direction × 30 mm in the x direction × 3.0 mm in thickness was bonded to a silicon photo dye auto 3 using an optical epoxy adhesive. TiO ₂ powder was applied as a light reflecting material 4 on the upper surface of the scintillator, and a Mo plate 5 was adhered on the side surface as a light reflecting plate. X-ray tube voltage 400kV,
Table 1 shows the characteristics of the radiation detector of Comparative Example 2 when irradiated with continuous X-rays having a tube current of 4 mA.

From Table 1 above, all of Examples 1 to 6 have the sensitivity to X-rays, that is, the relative output, that of Comparative Examples 1 and 2.
It can be seen that it is greatly improved as compared with.

Next, as shown in Table 2 below, Example 1 was used.
Instead of the CdWO ₄ single crystal scintillator used in to 6, Bi ₆ Ge formed in the CdWO ₄ single crystal scintillator of the same size
_{When a 4} O ₁₂ single crystal scintillator was used (Examples 7 to 1)
0) also showed that the relative output could be improved as compared with Comparative Examples 1 and 2, as in Examples 1 to 6 above.

[0021]

[Table 2]

Next, in the structure shown in FIG. 2, the ceramic scintillator 1 is made of polycrystalline (Y, Gd) ₂ O ₃ : Eu (Example 11) or polycrystalline Gd ₃ Ga ₅ O ₁₂ : Cr (Example 11). Good relative output was obtained as shown in Table 2 also when using (12). It should be noted that the ceramic scintillators 1 of Examples 11 and 12 are formed to have the same dimensions as the ceramic scintillator 1 of Example 1. In the configuration of FIG. 3, the ceramic scintillator 10 is made of polycrystalline (Y, G
d) Even when ₂ O ₃ : Eu (Example 13) was used, a good relative output was obtained as shown in Table 2. The ceramic scintillator 10 of the thirteenth embodiment has the same dimensions as the ceramic scintillator 10 of the fourth embodiment.

In the above embodiment, a rectangular plate-shaped ceramic scintillator and a single crystal scintillator were used. However, the present invention is not limited to this, and any shape and size capable of obtaining the same operation and effect as those of the above embodiment can be used. Of course, it can be adopted.

In the above embodiment, the radiation detector was constructed by combining one type of ceramic scintillator and one type of single crystal scintillator. However, two or more types of ceramic scintillators and two or more types of single crystal scintillators were used. Needless to say, a combination of the above may be adopted. In the above embodiment, the case where the radiation is continuous X-rays is described, but the present invention is also effective for γ-rays.

[0025]

As described above, the radiation detector of the present invention has particularly high sensitivity to X-rays, can be miniaturized, and is used for tomographic image measurement of objects having a large X-ray absorption coefficient and large mechanical structures. High resolution imaging is possible, for example, X-ray C
It is extremely useful for a high-performance radiation detector represented by a T device.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating one embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the y-direction of FIG. 1;

FIG. 3 is a sectional view of a main part showing another embodiment of the present invention.

FIG. 4 is a sectional view of a main part showing a conventional structure.

[Explanation of symbols]

1,10 ceramic scintillator, 2,20 single crystal scintillator, 3 light detector, 4 light reflection layer, 5 light reflection plate, 6 end reflector, 7 substrate, 11 radiation detector, 11a, 11b side surface, 200 single crystal Scintillator, 300 ceramic scintillator.

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI C09K 11/84 CQD C09K 11/84 CQD

Claims (6)

[Claims] 1. A radiation detector comprising a scintillator capable of emitting light by radiation and a photodetector for converting light from the scintillator into an electric signal, wherein a ceramic scintillator and a single crystal scintillator are used as the scintillator in combination. A radiation detector. 2. As the ceramic scintillator,
Gd ₂ O ₂ S: Re (where, Re is Pr, Eu, represents any one or more elements of Tb.) The radiation detector of claim 1, characterized in that use. 3. The ceramic scintillator,
_{(Y, Gd) 2 O 3} : Eu, Gd 3 Ga 5 O 12: radiation detector according to claim 1, characterized by using either or both of Cr. 4. A single crystal scintillator comprising: CdW
_4. The radiation detector according to claim 1, wherein one or both of O ₄ and Bi ₆ Ge ₄ O ₁₂ are used. 5. The radiation detector according to claim 1, wherein the single-crystal scintillator is disposed between the ceramic scintillator and a photodetector. 6. The radiation detector according to claim 1, wherein the ceramic scintillator and the single crystal scintillator are arranged adjacent to the photodetector.