JP2009210415A - Radiation detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a loss caused by reflection of light generating in a scintillator element at an emitting surface of the scintillator element, increase incident light to a semiconductor photodetection element, and improve an output. <P>SOLUTION: An antireflection coating of alternate multi-laminates of two different metal oxide coatings is directly formed in vacuum on a surface of the scintillator element facing the semiconductor photodetection element, thereby the loss caused by reflection of light generating at the surface of the scintillator element facing the semiconductor photodetection element is reduced, and the light amount incident to the semiconductor photodetection element can be increased by 10% and the radiation detector can be provided to obtain images with high resolution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a radiation detector, and more particularly to a radiation detector used in a computed tomography (CT) apparatus that uses radiation such as X-rays and γ-rays.

In a radiation CT apparatus, a large number of radiation detectors are arranged next to each other at a position symmetrical to a radiation source (for example, an X-ray tube) with respect to the object to be imaged, and the radiation intensity at the position of each detector is measured. The structure is to be observed. The detection elements of the radiation detectors arranged next to each other correspond to each pixel, so they are made as small as possible and the distance between adjacent detection elements is narrowed to increase the resolution and resolution. .

The radiation detector includes a radiation scintillator element and a semiconductor photodetector element (hereinafter referred to as PD).
The scintillator element opens to the radiation source side and receives radiation such as X-rays by the scintillator element. The scintillator element is disclosed in Patent Document 1.
To CdWO ₄ (hereinafter referred to as CWO) or Gd ₂ O ₂ S: P
It is made of r (Ce, F) (hereinafter referred to as GOS), (Y, Gd) ₂ O ₃ : Eu (hereinafter referred to as YGO), and generates visible light when radiation is incident thereon. The visible light is incident on a PD attached to the scintillator element and converted into an electric signal.

JP 56-151376 JP-A-11-172343 Japanese Patent Laid-Open No. 10-213665

The scintillator element irradiated with radiation generates visible light in the direction of all solid angles. It is necessary to efficiently guide light generated in the directions of all solid angles to the PD attached to the scintillator element. Therefore, the scintillator element has a structure in which the periphery is covered with a light reflecting material except for the surface facing the PD. Gold (Au), aluminum (Al), silver (light reflector)
Ag), a metal such as copper (Cu) is deposited to a thickness of 0.1 to 5 μm by vapor deposition or sputtering, and as disclosed in Patent Document 4, titanium dioxide (TiO ₂ ), zinc white (ZnO), A white powder of a metal compound such as lead white (PbO) or zinc sulfide (ZnS) is kneaded and applied to an epoxy resin or the like. The light reflectance of the metal film at a wavelength of around 600 nm is 90 to 95.
%. Aluminum which is low in price and has a small atomic weight and close to white is a preferable material. The light reflectance of the metal compound at a wavelength of around 500 nm is about 94 to 96% for titanium dioxide, 93 to 94% for zinc white, 90 to 91% for lead white, and about 95% for zinc sulfide. Titanium dioxide is often used as a light reflecting material because it has higher chemical stability to acids and alkalis than zinc white, lead white, and zinc sulfide.

JP 2000-180554 A

A radiation detection apparatus in which a scintillator element, a semiconductor light detection element, and a light reflecting material are combined is described in Patent Document 5. FIG. 6 shows a perspective view and a cross-sectional view of the radiation detector. The radiation detector 1 in FIG. 6a) is called a multi-slice type, and scintillator elements 2 are arranged in a grid pattern. FIG. 6B) is a cross-sectional view taken along the line j ′ of FIG. PD on substrate 5
4, wiring 6, and terminal 7 are formed. One end of the wiring 6 is connected to the terminal 7 and the other end is P
Connected to D4. The PD 4 is also formed in a grid pattern, and the scintillator element 2 is arranged facing the PD 4. The PD 4 and the scintillator element 2 are fixed with an adhesive 9. A surface of the scintillator element 2 other than the PD facing surface is coated with a light reflecting material 3 so that the light from the scintillator element is not leaked to the outside. The light reflecting material 3 includes an inter-element light reflecting material 32 filled between the scintillator elements, an element end surface light reflecting material 33 coated on the side surface of the scintillator element located at the end, and a scintillator element surface on which radiation is incident. The element upper surface light reflecting material 31 is applied. The light reflecting material 3 reflects light in the directions of all solid angles generated by the scintillator element and guides it to the PD 4, and blocks incident light from the outside to the scintillator element 2.

Visible light having an intensity proportional to the intensity of radiation incident on the scintillator element 2 through the element upper surface light reflecting material is emitted in the direction of all solid angles. Light other than the direction of the PD 4 is repeatedly reflected by the light reflecting material 3 and enters the PD. Since the light reflecting material 3 is required to have a high light reflectance, a material obtained by kneading white powder such as titanium dioxide or barium oxide with an epoxy resin is used, and the light reflectance is 95% to 98% at the emission wavelength of the scintillator. It is.

JP 2000-346948 A

In order to identify and observe thin blood vessels and small abnormalities, higher resolution images have been demanded. To obtain a high-resolution image, it is necessary to increase the number of scintillator elements corresponding to the number of pixels.
In order to increase, it is necessary to reduce the radiation incident area of the scintillator elements 2 arranged in a grid pattern shown in FIG. If the scintillator element 2 is made small, the amount of emitted light is also reduced, and it becomes difficult to obtain a high resolution image. Therefore, it is required to increase the light emission efficiency of the scintillator material and to efficiently guide the emitted light to the PD 4. It has been studied to increase the light transmittance of the scintillator material to reduce the attenuation of light in the scintillator material, to increase the light reflectance of the light reflecting material, etc., but the value to be improved is slight.

A detailed examination of what percentage of the amount of light generated by radiation irradiation was incident on the PD 4 revealed that a loss of about 15% occurred while entering the PD 4 from the scintillator element 2. Since the light refractive index of the scintillator materials GOS, CWO, and YGO is about 2.5,
This is because when light exits into the atmosphere, the light is reflected by the outgoing light surface of the scintillator element due to a difference in refractive index from the atmosphere. FIG. 7 illustrates the amount of light generated by the scintillator element entering the PD. The light reflectance of the light reflecting material is 95%, and the light reflectance on the scintillator element surface is 15%. In addition, the attenuation of light in the scintillator material is ignored, and the number of times of reflection by the light reflecting material is set to one. The light L1 emitted to the PD side is reduced to 85% due to loss due to reflection on the scintillator element surface. The light L2 emitted on the opposite side of the PD has a loss of 5% when reflected by the light reflecting material, and the light that has reached 95% further generates a loss of 15% on the surface of the scintillator element. It becomes. The value of the light L3 emitted in the lateral direction is also 80.
8%. Actually, it is conceivable that the value is smaller than these values due to multiple reflections by the light reflecting material and attenuation within the scintillator element. The light reflected by the scintillator element surface is again reflected by the light reflector and reflected by the scintillator element surface, and enters the PD. If the loss due to reflection on the surface of the scintillator element can be suppressed to, for example, several percent, it is considered that the emitted light from the scintillator element can be increased by 10% or more. However, lowering the refractive index of the scintillator material has been difficult to realize because it is necessary to change the composition and the like.

An object of the present invention is to provide a radiation detector capable of reducing a loss caused by reflection of light emitted in a scintillator element on an outgoing light surface of the scintillator element and obtaining a high-resolution image.

The radiation detector of the present invention is a radiation detector in which a scintillator element and a PD are stacked, and the other surface except the PD facing surface of the scintillator element is covered with a light reflecting material, and the PD facing surface of the scintillator element It is preferable that an antireflection film is formed on the surface.

Light generated by the scintillator element when irradiated with radiation travels in the direction of all solid angles. Light emitted in a direction other than the PD facing surface needs to be reflected to change the direction and guided to the PD facing surface. Therefore, light can be incident on the PD with high efficiency by forming a light reflecting material having a high light reflectance on the surface other than the PD facing surface. In addition, since the light reflectance is high, the amount of leaked light can be suppressed, and leakage light entering adjacent scintillator elements can be suppressed from becoming noise. From the PD facing surface of the scintillator element, it is required to leak light with high efficiency and enter the PD. Although the scintillator element and the PD are bonded with resin, light is reflected on the surface of the scintillator element due to the difference in refractive index between the scintillator element and the adhesive. Although it depends on the refractive index of the material in contact with the scintillator element surface, the amount of reflected light on the scintillator element surface is as large as about 15%. The light reflected by the PD facing surface is reflected by the light reflecting material and enters the PD facing surface again, and a part of the light is reflected again. Each time reflection is repeated, a reflection loss occurs in the light reflecting material, and attenuation occurs when the light passes through the scintillator element. Therefore, most of the light reflected initially on the PD facing surface is lost. For this reason as well, the amount of light emitted from the scintillator element can be increased by forming a light reflection preventing film on the PD facing surface to lower the light reflectance. A radiation detector capable of increasing the amount of light incident on the PD, improving the sensitivity, and obtaining a high-resolution image can be realized.

As the scintillator material, ceramics such as CWO, GOS, and YGO can be used. Since it is ceramic, it can be machined with a diamond grindstone or the like, and a small and highly accurate scintillator element can be obtained. The light reflecting material can also be formed by vacuum film formation or application of a white metal compound powder and resin kneading material. A thin film such as aluminum can be formed by vacuum deposition or sputtering, or a white powder of a metal compound such as titanium oxide, zinc white, lead white, or zinc sulfide can be kneaded into an epoxy resin, and then applied and dried. . P of scintillator element
It is important that the antireflection film on the D-facing surface is formed directly on the scintillator element surface. If a light reflection preventing film made separately on the PD facing surface of the scintillator element is pasted with resin or the like, the light reflectance on the PD facing surface cannot be lowered. It is desirable to form a light reflection preventing film on the PD facing surface in a vacuum so that there is no space between the PD facing surface of the scintillator element and the light reflection preventing film. The light reflection preventing film and the PD can be fixed with a phenol resin or the like. As the PD, a silicon photodiode, a GaAsP photodiode, or a Ge photodiode can be used. Since the emission center wavelength varies depending on the scintillator material, it is preferable to select a highly sensitive photodiode near the emission center wavelength.

The light reflection preventing film of the radiation detector of the present invention preferably has a light reflectance of 2% or less in a wavelength region of 400 nm to 800 nm.

The emission center wavelength of the scintillator material is 480 nm for CWO, 520 nm for GOS, YG
O is 610 nm. A Gd ₃ Ga ₅ O ₁₂ : Ce material having a longer wavelength has also been put into practical use, and its emission center wavelength is 730 nm. Since the emission center wavelength of the scintillator material used mainly is 480 nm to 730 nm, considering the wavelength range, the antireflection film formed on the PD facing surface of the scintillator element is low in the wavelength region of 400 nm to 800 nm. Reflection is preferred.

Ideally, the light reflectance of the antireflection film is 0%, but many of the manufactured films exhibit a light reflectance of several percent. In addition, there is a restriction that the antireflection film formed on the scintillator element needs to be formed directly on the surface of the scintillator element in a vacuum. Different refractive index 2
The light reflectance can be reduced to 2% or less by alternately stacking the metal oxide films of different types with high precision. The light reflectivity is about 15% when light is emitted from the scintillator element into the atmosphere.
Therefore, by setting the light reflectance to 2%, the amount of emitted light can be increased by approximately 10%.

The thickness of the antireflection film of the radiation detector of the present invention is preferably 0.2 μm or more and 2.0 μm or less.

The light reflection preventing film of the radiation detector of the present invention is preferably a multilayer film in which two kinds of films having different refractive indexes are alternately laminated.

A light reflection preventing film in which two types of oxide films having different refractive indexes are laminated reduces reflected light by utilizing light interference caused by a phase difference that occurs while light passes through the film. If the thickness of the antireflection film is too thin, the effect of the antireflection film cannot be obtained. Since the antireflection film itself does not have a light transmittance of 100%, the loss due to attenuation increases as the thickness of the antireflection film increases. The thickness of the antireflection film varies depending on the material of the film, the number of laminated layers, and the wavelength of light. The approximate film thickness when a four-layer film is formed using silicon dioxide and tantalum pentoxide is about 0.3 μm. Even if the material of the film, the number of stacked layers, and the wavelength of light change, the light reflectance can be reduced to 2% or less by setting the thickness of the antireflection film to 0.2 μm or more and 2.0 μm or less. The thickness of the antireflection film refers to a physical film thickness unless otherwise specified, and is not an optical film thickness obtained by multiplying the physical film thickness by a refractive index.

The light intensity reflected on the surface of the scintillator element depends on the refractive index of the scintillator material, and the light intensity reflected on the surface of the antireflection film depends on the refractive index of the antireflection film. For example, 1/4 of the light wavelength
In the case of a single-layer antireflection film having an optical film thickness, the light intensity reflected on the surface is different on the side opposite to the scintillator element side, so it is difficult to reduce the light reflectance to 2% or less. By alternately laminating two types of films with different optical refractive indexes, a plurality of interfaces with different refractive indexes can be formed, and the phase and intensity of the reflected light can be offset. Therefore, the light reflection on the PD facing surface of the scintillator element Can be suppressed.

The antireflection film is preferably formed by alternately laminating a plurality of films having a high refractive index of about 2.2 to 2.7 and a film having a low refractive index of about 1.4.

In the radiation detector of the present invention, it is preferable that the two types of films having different refractive indexes of the light reflection preventing film are a combination of silicon dioxide and tantalum pentoxide or a combination of silicon dioxide and titanium dioxide.

In order to transmit light having a predetermined wavelength λ as the center, it is necessary to form an optical thin film having a thickness of λ / 4. Therefore, it is necessary to control the film thickness with high accuracy. It is preferable to use a vacuum vapor deposition method or a sputtering method in which a metal oxide film can be formed and the film thickness can be easily controlled. Since the vacuum deposition method or the sputtering method forms a film in a vacuum apparatus, no space is generated between the scintillator element surface and the light reflection preventing film. There is a relationship of optical film thickness = physical film thickness × refractive index, and the film thickness of each metal oxide film indicates the physical film thickness. Silicon dioxide is preferable as the low refractive index oxide film of the antireflection film.
Since the refractive index of the silicon dioxide film is about 1.4, the film thickness at the center wavelength of 500 nm is about 0.08.
9 μm. For the high refractive index film, tantalum pentoxide or titanium dioxide can be used. Tantalum pentoxide has a refractive index of about 2.2, and titanium dioxide has a refractive index of about 2.3. The film thickness at the central wavelength of 500 nm is about 0.057 μm for tantalum pentoxide and about 0.07 for titanium dioxide.
054 μm. By forming a laminated film of a combination of silicon dioxide and tantalum pentoxide or silicon dioxide and titanium dioxide in a plurality of stages, an antireflection film having an optical reflectance of 2% or less can be obtained.

The light reflecting material of the radiation detector of the present invention is a kneaded material of resin and metal compound powder, and the metal compound is preferably titanium dioxide or magnesium oxide, zinc white, lead white, or zinc sulfide. Further, a metal thin film such as aluminum may be used.

The scintillator element upper surface light-reflecting material facing the radiation source is required to have a high radiation transmittance so that not only high light reflectance but also radiation can be efficiently incident on the scintillator element. However, the inter-element light reflecting material and the element end surface light reflecting material on the side surface of the scintillator element are required to have high light reflectance and low radiation transmittance in order to reduce the amount of radiation incident from the side surface of the scintillator element. Since it is difficult to satisfy the requirement of completely opposite radiation transmittance with one light reflecting material, a method of using a material with high radiation transmittance and inserting a heavy metal plate between elements is often used. Using ceramics such as CWO, GOS, YGO for the scintillator material,
Many methods have been adopted in which grooves are formed in a grid pattern by machining with a diamond grindstone or the like and a light reflecting material is filled in the grooves. A material obtained by kneading a white powder of a metal compound such as titanium dioxide, zinc white, lead white, or zinc sulfide in an epoxy resin has fluidity and is suitable for filling in a groove.

When the metal compound powder of titanium dioxide or magnesium oxide, zinc white, lead white, zinc sulfide and resin are in a weight ratio and the metal compound powder is 0.5 or more with respect to the resin 1, the light reflectance is 95.
% Or more is obtained. The upper limit of the mixing ratio may be any ratio as long as it can be molded as a light reflecting material. However, when the metal compound powder is 5 or 6 or more in comparison with the resin, the fluidity is lowered and the scintillator elements cannot be filled. Or metal compound powder may fall off.
. 5 to 3 is a preferable mixing ratio range. As much as possible, it is preferable to use fine powder as the metal compound powder, and the average particle diameter is preferably 0.15 μm to 1.0 μm. Since the size between the scintillator elements is 50 μm to 150 μm, the metal compound powder having an average particle diameter of 1 μm or less can be used so that the metal compound powder can be arranged in at least 50 layers in the groove. It is possible to prevent light from entering the adjacent scintillator element through the light reflecting material.

It is difficult to use a metal film for the inter-element light reflecting material in a state in which scintillator elements are formed in a grid pattern. Since the thickness of the scintillator element is 1 mm to 1.5 mm, it is impossible to form a metal film over the entire side surface of the scintillator element facing each other at an interval of 50 μm to 150 μm by sputtering or vacuum deposition. Therefore, a kneading material of resin and metal compound powder is preferably used as the inter-element light reflecting material. Since the element upper surface light reflecting material is formed on the flat scintillator element surface, a metal film can be formed by sputtering or vacuum deposition. By forming the element upper surface light reflecting material with an aluminum metal film, the radiation detector can be thinned. An aluminum film having a thickness of 0.1 μm or more does not transmit light and is a light metal, and therefore has high radiation transmittance. Aluminum has a light reflectance of about 95% in the visible light region and is a suitable light reflecting material for the upper surface of the element. The kneading material of resin and metal compound powder is required to have a thickness of 50 μm or more in order to obtain light reflectance. Further, the kneaded material cannot be uniformly formed with a thickness of 0.1 μm. For this reason, it is possible to reduce the thickness of the element upper surface light reflecting material by at least 50 μm or more by forming it with an aluminum metal film. When using gold or copper as the metal film,
Since the light reflectance at a wavelength of 600 nm or less is low, applicable scintillator materials are limited. Silver has a high light reflectance in the visible light region, but is not preferable because it is a heavy element metal and absorbs much radiation. Further, since silver easily oxidizes, it is necessary to form a film that blocks air from the film surface.

The light reflecting material provided on the surface of the scintillator element facing the radiation source of the radiation detector of the present invention is a combination of two kinds of metal oxide films having different refractive indexes of silicon dioxide and tantalum pentoxide or silicon dioxide and titanium dioxide. Preferably there is.

Since the element upper surface light reflecting material is formed on the surface on which the radiation is incident, the element upper surface light reflecting material is required not only to have a high light reflectivity and a high radiation transmittance, but also to be a stable material that does not deteriorate due to radiation exposure. Since the metal oxide film of titanium dioxide, tantalum pentoxide, or silicon dioxide used for the light reflection preventing film of the present invention has high exposure resistance, it can be used as an element upper surface light reflecting material. A light reflecting film formed by alternately laminating two kinds of metal oxide films having different refractive indexes of silicon dioxide and tantalum pentoxide or silicon dioxide and titanium dioxide can obtain a high light reflectance of 98% or more. When a large number of two types of metal oxide films with different refractive indexes are stacked with an optical film thickness that is ¼ of the emission center wavelength λ, many interfaces with different refractive indexes are formed, so incident light is reflected at the interface of each film. Therefore, incident light can be reflected efficiently. In order to efficiently reflect the light in the generated wavelength range, it is also possible to adopt a configuration in which a laminated portion that is thicker than an optical film thickness that is 1/4 of the emission center wavelength λ and a thin laminated portion are incorporated. Even a heavy metal such as titanium or tantalum can be made to have higher radiation transparency than a pure metal by forming a metal oxide film combined with light element oxygen atoms. PD
Since the same material as the light reflection preventing film formed on the opposite surface can be used, the apparatus and the material can be used efficiently and the cost can be reduced.

It is preferable that the light reflectance is 95% or more in the wavelength region of 400 nm to 800 nm of the light reflecting material provided on the scintillator element surface facing the radiation source of the present invention. More preferably, the light reflectance is 98% or more. By using a light reflecting film in which a large number of two types of metal oxide films having different refractive indexes are alternately laminated, a light reflectance of 98% or more can be obtained.

As described above, the radiation detector of the present invention directly forms an antireflection film in which a number of different two kinds of metal oxide films are alternately laminated on the PD facing surface of the scintillator element in a vacuum, and the PD facing the scintillator element. The loss due to light reflection generated on the surface was reduced, and the amount of light incident on the PD could be increased by about 10%. Thereby, the radiation detector which can obtain a high-resolution image was able to be provided.

Hereinafter, the present invention will be described in detail based on examples with reference to the drawings. In order to make the explanation easy to understand, the same reference numerals are used for the same parts and parts.

The radiation detector according to the first embodiment of the present invention will be described below. FIG. 1 shows a radiation detector 1 of the present invention. FIG. 1a) is a perspective view of the radiation detector 1, and FIG. 1b) is a kk ′ cross section of FIG. 1a). The scintillator elements 2 arranged in a grid pattern in this embodiment are 16 × 16, but the number is abbreviated as 4 × 4 for easy understanding of the drawing. Similarly, the number of wirings 6 and terminals 7 is also omitted.
A light reflection preventing film 8 is formed on the PD facing surface 14 side of the scintillator element 2 and a light reflecting material 3 is formed on the other surface to form an element assembly 10. The light reflecting material 3 includes an element upper surface light reflecting material 31, an inter-element light reflecting material 32, and an element end surface light reflecting material 33. A PD 5, wiring 6, and terminals 7 corresponding to the position and size of the scintillator element 2 are formed on the substrate 5. The element assembly 10 and the substrate 5 are fixed by a transparent resin adhesive 9 to form the radiation detector 1.

2A and 2B, the manufacturing method and material of the radiation detector 1 of the present embodiment, and the detailed dimensional relationship will be described in detail. 2A) to FIG. 2F) show the manufacturing process of the radiation detector 1, and each figure shows a perspective view and a mm ′ cross-sectional view. FIG. 2 a) shows a GOS having a light emission center wavelength of 520 nm in the scintillator plate 11 before being processed into the scintillator element 2. The scintillator plate 11 is 2
A 2 mm × 18.5 mm × 1.8 mm thickness machined to a surface roughness Ra of several nm or less was used. In FIG. 2b), the groove 12 is formed in a lattice pattern with a diamond grindstone on the side of the scintillator plate 11 that becomes the radiation incident surface 13, and the width w1 and the depth d1 of the scintillator element 2 are formed. w1 is 1.0 mm and d1 is 1.2 mm. The depth of the groove 12 is 1.5 mm.
The scintillator element 2 is connected at the bottom of 3 mm. For the surface roughness Ra, a center line average surface roughness Ra was determined according to JISB0601 using a non-contact type surface roughness meter.

FIG. 2 c) shows the light reflecting material 3 formed. The scintillator plate with the groove produced in FIG. 2b) was placed in a fluororesin jig, and the light reflecting material 3 was filled while degassing. The light reflecting material 3 is an epoxy resin obtained by kneading a rutile type titanium dioxide powder having an average particle size of 0.3 μm with the epoxy resin 1 in a weight ratio of 1.5. After filling, it was cured by heating to 80 ° C. while degassing. The light reflectance after curing was about 96% at a wavelength of 520 nm. FIG. 2d) shows the groove 12
Since the scintillator element 2 is connected to the bottom of the scintillator element, the scintillator element is singulated by grinding using a diamond grindstone. The scintillator element 2 has a thickness h1 of 1.3 mm, a light reflecting material of 0.4 mm, and an overall thickness h2 of 1.7 mm. The reason why the jig made of fluororesin is used is that the cured light reflecting material 3 does not adhere to the jig and can be easily removed.

FIG. 2e) shows the element assembly 10 in which the light reflection preventing film 8 is formed on the PD facing surface 14 side. The antireflection film 8 was formed by alternately stacking tantalum pentoxide having a refractive index of 2.2 and silicon dioxide having a refractive index of 1.4 alternately four times. On the surface of the scintillator element 2, tantalum pentoxide having a thickness of 0.059 μm and silicon dioxide having a thickness of 0.093 μm were successively formed in the order of tantalum pentoxide-silicon dioxide-tantalum pentoxide-silicon dioxide. The light reflection preventing film 8 is formed on the PD facing surface 1 of the scintillator element 2.
4, it was also formed on the light reflecting materials 32 and 33 on the PD facing surface side. Ion gun gas flow rate 50 (sccm), ion gun beam voltage 700 (V) using an ion beam assisted vapor deposition machine
Under the conditions of ion gun beam current 300 (mA) and ion gun acceleration voltage −400 (V), tantalum pentoxide is produced at a rate of 0.25 (nm / s) and silicon dioxide is produced at a rate of 0.70 (nm / S). Membrane was performed. Silicon dioxide and tantalum pentoxide were used as the evaporation source. FIG. 2f) shows the radiation detector 1 of this example. The radiation detector 1 was obtained by fixing the PD 4, the wiring 6, the substrate 5 having the terminals 7, and the element assembly 10 with an adhesive 9. The adhesive layer thickness of the adhesive 9 is several μm or less.

The radiation detector according to the second embodiment of the present invention will be described below. The main difference from the first embodiment is that the element upper surface light reflecting material 31 of the light reflecting material 3 is changed from a kneaded material of resin and metal compound powder to an aluminum film. The inter-element light reflecting material 32 and the element end surface light reflecting material 33 use the same resin and metal compound powder kneading material as in the first embodiment.

3A and 3B, the manufacturing method and material of the radiation detector 1 according to the second embodiment, and the detailed dimensional relationship will be described in detail. 3A) to 3F) show the manufacturing process of the radiation detector 1, and each figure shows a perspective view and an nn 'sectional view. FIG. 3 a) is a scintillator plate 11 before being processed into the scintillator element 2, and is a GOS having an emission center wavelength of 520 nm. Scintillator plate 11
Was 22.0 mm × 18.5 mm × 1.6 mm thick and machined to a surface roughness Ra of several nm or less. FIG. 3 b) shows the width w 1 ′ and depth d of the scintillator element 2 by placing grooves 12 in a lattice pattern with a diamond grindstone on the side of the scintillator plate 11 that becomes the radiation incident surface 13.
1 'was formed. w1 ′ is 1.0 mm and d1 ′ is 1.2 mm. The depth of the groove 12 is 1.
The scintillator element 2 is connected at the bottom of 0.2 mm thickness. The scintillator element 2 is 16 × 16, but the number is abbreviated as 4 × 4 for easy understanding of the drawing. Similarly, the number of wirings 6 and terminals 7 is also omitted.

FIG. 3 c) shows a state where the inter-element light reflecting material 32 and the element end surface light reflecting material 33 are formed and the scintillator elements are separated. The grooved scintillator plate produced in FIG. 3b) was placed in a fluororesin jig and filled with the light reflecting material 3 while degassing. The light reflecting material 3 is a rutile type titanium dioxide powder having an average particle size of 0.3 μm in an epoxy resin, and is 1 in weight ratio to the epoxy resin 1.
. 5 kneaded. After filling, it was cured by heating to 80 ° C. while degassing. The light reflectance after curing was about 96% at a wavelength of 520 nm. After the light reflecting material 3 is cured, the element upper surface light reflecting material 31 adhering to the radiation incident surface side is removed, and the connecting portion on the PD facing surface 14 side is ground with a diamond grindstone, and then removed by polishing to remove the scintillator element. 2 singulation and thickness h1
'I got. h1 ′ is 1.3 mm, and the surface roughness Ra is 3 nm. In FIG. 3c), the scintillator elements 2 are arranged in a grid pattern of 16 columns × 16 rows, the inter-element light reflecting material 32 is filled between the scintillator elements, and the element end surface light reflecting material 33 is formed on the outer side surface of the scintillator element. Assembly.

FIG. 3 d) shows a state in which the light reflecting film 16 and the protective film 17 are formed on the radiation incident surface side 13.
Sputtering 99.99% purity aluminum to a thickness of 0.35 μm, the light reflecting film 16
Formed. The light reflectance of the aluminum film was about 95%. The light reflecting film 16 was shielded from the outside air, and an aluminum oxide film was continuously formed to a thickness of 0.1 μm in order to prevent a decrease in light reflectance due to oxidation. FIG. 2e) shows the element assembly 10 in which the light reflection preventing film 8 is formed on the PD facing surface 14 side. The antireflection film 8 was formed by alternately stacking tantalum pentoxide having a refractive index of 2.2 and silicon dioxide having a refractive index of 1.4 alternately four times. 0.059 tantalum pentoxide on 2 scintillator elements
The film was continuously formed in the order of tantalum pentoxide-silicon dioxide-tantalum pentoxide-silicon dioxide with a thickness of .mu.m and silicon dioxide of 0.093 .mu.m. The light reflection preventing film 8 is formed from the scintillator element 2.
It was formed not only on the PD facing surface 14 but also on the light reflecting materials 32 and 33 on the PD facing surface side. Using an ion beam assisted deposition apparatus, an ion gun gas flow rate of 50 (sccm), an ion gun beam voltage of 700 (V), an ion gun beam current of 300 (mA), and an ion gun acceleration voltage of -400 (
V), tantalum pentoxide is 0.25 nm / s, and silicon dioxide is 0.70 nm.
The film was formed at a film forming speed of / S). Silicon dioxide and tantalum pentoxide were used as the evaporation source.
The total thickness of the light reflection preventing film 8 is about 0.3 μm, and the total thickness of the light reflection film 16 and the protective film 17 is about 0.
. Since the thickness h2 ′ of the element assembly 10 was 1.304 mm because it was 14 μm, the thickness was reduced by about 0.4 mm compared to 1.7 mm in Example 1, and a thickness reduction of about 25% was achieved.

FIG. 3f) shows the radiation detector 1 of this example. The radiation detector 1 was obtained by fixing the PD 4, the wiring 6, the substrate 5 having the terminals 7, and the element assembly 10 with an adhesive 9. The adhesive layer thickness of the adhesive 9 is several μm or less.

The radiation detector according to the third embodiment of the present invention will be described below. The main difference from the first embodiment is that the structure of the light reflection preventing film 8 is replaced with a titanium dioxide film and a silicon dioxide film. The manufacturing method and schematic dimensions are the same as in FIG. Since the refractive index of titanium dioxide is 2.3, which is larger than 2.2 of tantalum pentoxide of Example 1, the film thickness is 0.056 μm, which is about 0.
The thickness was 003 μm. On the surface of the scintillator element 2, titanium dioxide was 0.056 μm thick and silicon dioxide was 0.093 μm thick, and titanium dioxide-silicon dioxide-titanium dioxide-silicon dioxide was successively formed in this order.

The radiation detector according to the fourth embodiment of the present invention will be described below. Light reflecting film 16 on the upper surface of the element
The main difference from the second embodiment is that the aluminum film is replaced with a multilayer film of a tantalum pentoxide film and a silicon dioxide film. The light reflecting film has a three-unit, twelve-layer film configuration in which one unit is a four-layer film formed in the order of tantalum pentoxide-silicon dioxide-tantalum pentoxide-silicon dioxide. When a multilayer film is used, a large number of interfaces having different refractive indexes are formed, and incident light is reflected at the interfaces of the respective films, so that incident light can be efficiently reflected. Furthermore, in order to reflect all the light in the wavelength range emitted by GOS, the first unit is -10 of the emission center wavelength of GOS.
The film thickness was determined at 468 nm of the% wavelength, the second unit was 520 nm of the emission center wavelength of GOS, and the third unit was 572 nm of the wavelength + 10% of the emission center wavelength of GOS. The tantalum pentoxide film thickness of the first unit is 0.053 μm, the silicon dioxide film thickness is 0.084 μm, the tantalum pentoxide film thickness of the second unit is 0.059 μm, the silicon dioxide film thickness is 0.093 μm, The tantalum pentoxide film thickness was 0.065 μm, and the silicon dioxide film thickness was 0.102 μm. A light reflection film formed of a multilayer film of a tantalum pentoxide film and a silicon dioxide film has a light reflectance of 99.5% or more.

Since the light reflection film 16 is an oxide film, oxidation does not proceed due to the outside air, but since it is transparent, external light enters and becomes noise, so that a protective film 17 having a light shielding property is formed. A black paint was applied to the protective film 17 to a thickness of about 50 μm.

The radiation detector according to the fifth embodiment of the present invention will be described below. The main difference from the first embodiment is that the material of the scintillator element is changed to CWO. Since the emission center wavelength of CWO is 480 nm, the antireflection film was made as follows. On the scintillator element 2 surface, tantalum pentoxide is 0.055 μm thick, silicon dioxide is 0.086 μm thick,
Films were successively formed in the order of silicon dioxide-tantalum pentoxide-silicon dioxide.

The radiation detector according to the sixth embodiment of the present invention will be described below. The main difference from the second embodiment is that the material of the scintillator element is changed to CWO. The material and film thickness of the light reflecting film 16 and the protective film 17 were the same as those in Example 2. The light reflection preventing film is formed in the order of tantalum pentoxide, silicon dioxide, tantalum pentoxide, and silicon dioxide in the order of 0.055 μm tantalum pentoxide and 0.086 μm silicon dioxide on the scintillator element 2 surface. Went.

A radiation detector according to the seventh embodiment of the present invention will be described below. The difference from the fourth embodiment is that the material of the scintillator element 2 is changed to CWO and that titanium dioxide and silicon dioxide are used for the light reflection preventing film 8 and the light reflection film 31. The antireflection film 8 has a titanium dioxide thickness of 0.052 μm and a silicon dioxide thickness of 0.086 μm on the scintillator element 2 surface.
Films were successively formed in the order of titanium dioxide-silicon dioxide-titanium dioxide-silicon dioxide. The light reflecting film 16 has a three-unit, twelve-layer film configuration in which one unit is a four-layer film formed in the order of titanium dioxide-silicon dioxide-titanium dioxide-silicon dioxide. The first unit is CWO
The film thickness was determined such that the emission center wavelength was 432 nm, which was -10% of the emission center wavelength, the second unit was 480 nm of the emission center wavelength of CWO, and the third unit was 528 nm of the wavelength of + 10% of the emission center wavelength of CWO. The first unit has a titanium dioxide film thickness of 0.047 μm and a silicon dioxide film thickness of 0
. 077μm, second unit titanium dioxide film thickness is 0.052μm, silicon dioxide film thickness is 0
. 086μm, titanium dioxide film thickness of the third unit is 0.057μm, silicon dioxide film thickness is 0
. 094 μm.

The radiation detector according to the eighth embodiment of the present invention will be described below. The main point different from the first embodiment is that the formation of the antireflection film 8 is limited to the surface of the scintillator element. When the antireflection film 8 in FIG. 2e) is formed, a SUS mask having an opening in the scintillator element portion is used, and light is applied to the inter-element light reflecting material 32 surface and the element end surface light reflecting material 33 surface on the PD facing side. Antireflection film 8
Is not formed. Since the SUS mask can be used as a holder, the element assembly can be easily held in the ion beam assisted deposition apparatus.
Further, the element assembly 10 and the substrate 5 can be formed without applying the adhesive 9 between the light reflection preventing film 8 and the PD 4.
Can be fixed, and attenuation of light generated in the adhesive 9 can be eliminated, so that the selection range of the adhesive 9 is expanded.

The result of measuring the output of the radiation detector produced in Examples 1 to 7 is shown in FIG. For comparison, the output of the conventional radiation detector shown in FIG. Since the output is different between GOS and CWO, the output ratio was determined by setting the output of GOS of Comparative Example as Example 1 to Example 4 and the output of CWO of Comparative Example as 1 in Examples 5 to 7. Since the radiation detector is a scintillator element having 256 elements of 16 × 16, the average value of the output of the 256 elements was used as the output value of the radiation detector. The output value was obtained by dividing the average output value of each of the 20 radiation detectors of Examples 1 to 7 by the average output value of each of the 20 radiation detectors of the comparative examples. Radiation was generated with a tungsten X-ray tube under the conditions of an acceleration voltage (tube voltage) of 120 KV and an electric current (tube current) of 4 mA. As can be seen from FIG. 5, the output of the radiation detector having the antireflection film of Examples 1 to 7 is 10% to 12% higher than that of the conventional product. Even if the light reflecting material 31 on the upper surface of the element is changed, the light reflectance only changes in the range of about 96% to about 99%. Therefore, it is determined that the contribution to the output ratio is small compared to the light reflection preventing film. Is done. In other words, it has been found that the application of the antireflection film is great for improving the output.

It is the perspective view and sectional drawing of the radiation detector of 1st Example of this invention. It is a figure explaining the manufacturing process of the radiation detector of 1st Example of this invention. It is a figure explaining the manufacturing process of the radiation detector of 2nd Example of this invention. It is sectional drawing of the radiation detector of 8th Example of this invention. It is a figure explaining the output of the radiation detector produced in Example 1-7 of this invention. It is the perspective view and sectional drawing of the conventional radiation detector. It is the figure which expressed image-wise until the light generate | occur | produced with the scintillator element entered PD.

Explanation of symbols

1 radiation detector,
2 scintillator elements,
3 Light reflector,
4 Semiconductor photo detector (PD),
5 substrates,
6 Wiring,
7 terminals,
8 anti-reflection film,
9 Adhesive,
10 element assembly,
11 Scintillator plate,
12 grooves,
13 radiation incident surface,
14 Semiconductor photodetecting element facing surface (PD facing surface),
16 light reflecting film,
17 Protective film 31 Inter-element light reflecting material,
32 element upper surface light reflecting material,
33 Element end face light reflecting material.

Claims (8)

A scintillator element and a semiconductor light detection element are stacked, and the other surface of the scintillator element except the surface facing the semiconductor light detection element is a radiation detector covered with a light reflecting material. The scintillator element faces the semiconductor light detection element. A radiation detector, characterized in that an antireflection film is formed on the surface. The radiation detector according to claim 1, wherein the light reflection preventing film has a light reflectance of 2% or less in a wavelength region of 400 nm to 800 nm. The radiation detector according to claim 1 or 2, wherein the thickness of the light reflection preventing film is 0.2 µm or more and 2.0 µm or less. 4. The radiation detector according to claim 1, wherein the light reflection preventing film is a multilayer film in which two types of films having different refractive indexes are alternately laminated. 2 kinds of films having different refractive index of the light reflection preventing film, combination or silicon dioxide, silicon dioxide (SiO ₂₎ and tantalum pentoxide _(Ta 2 _{O 5)} (SiO ₂₎ and titanium dioxide _(TiO 2)
The radiation detector according to claim 4, which is a combination of metal oxide films. The light reflecting material is a kneading material of resin and metal compound powder, and the metal compound is titanium dioxide (TiO ₂ ).
Or magnesium oxide (MgO), zinc white (ZnO), lead white (PbO), zinc sulfide (
The radiation detector according to claim 1, wherein the radiation detector is ZnS). The light reflecting material provided on the surface of the scintillator element facing the radiation source is a combination of two kinds of metal oxide films having different refractive indexes of silicon dioxide and tantalum pentoxide, silicon dioxide and titanium dioxide, or an aluminum film. The radiation detector according to claim 1. The light reflecting material provided on the scintillator element surface facing the radiation source has a wavelength region of 400 n.
The radiation detector according to claim 6 or 7, wherein the light reflectance is 95% or more from m to 800 nm.

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