JPH10319126A - Radiation detector and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the reflection efficiency and the radiation utilization efficiency of visible light and at the same time improve detection sensitivity by providing a reflection layer being formed by electroless plating on a surface other than a connection surface with the photoelectric transducer of a scintillator and providing a screening layer to the adjacent scintillator. SOLUTION: A scintillator 1 absorbs X rays and converts to visible light. Then, for guiding visible light that is emitted after applying X rays to and absorbing them from the scintillator 1 after the scintillator 1 is cut to a desired shape and is subjected to polishing machining, a reflection layer 2 is formed on a surface other than the optical connection surface with the photoelectric transducer 6 using a silver mirror reaction. When the film thickness of the reflection layer 2 causes void when the Ag film is thin and transmits visible light being emitted in the scintillator 1 and decreases efficiency. Further, a shielding film for reducing crosstalk due to X rays is formed on the side surface of the scintillator 1 where the reflection layer 2 is formed by forming, for example, gold and lead.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to radiation detection using a digital X-ray imaging apparatus and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventional radiation detectors are roughly classified into three types: an ionization chamber system utilizing gas ionization, a solid state detection system utilizing scintillation scintillation light, and a semiconductor detection system such as CdTe. Since the present invention is a radiation detector relating to a combination of a scintillator and a photoelectric conversion element, a conventional solid-state detector will be described here.

FIG. 2 is a sectional view showing an example of a basic structure of a conventional solid-state detector. After a photoelectric conversion element array 24 composed of a plurality of photoelectric conversion elements is optically placed and fixed on the surface of a printed wiring board 25 made of glass epoxy or the like with an adhesive mainly composed of epoxy or the like, the printing is performed from each photoelectric conversion element. A bonding process for extracting a photocurrent signal from a substrate is performed by bonding using a gold wire or the like.

Further, in order to protect the bonding portion, a sealing material mainly composed of epoxy, acrylate, silicone, or the like is used to seal a bonding wire or a pad portion for short-circuit protection. Also scintillator 2
1 is cadmium tungstate (CdWO ₄ ),
Bi ₄ Ge ₃ O ₁₂ , thallium-added sodium iodide <Na
I (TI)> or Gd ₂ O ₂ S: P
r. Ce. A ceramic body such as F is selected and used according to the purpose, and the shape of the scintillator 21 also varies depending on the purpose, and is determined and cut and polished.

The scintillator 21 cut and polished.
Are fixed to each pixel of the photoelectric conversion element array 24 with high precision by being arranged with an acrylic or epoxy adhesive 23 having excellent light transmittance. However, to prevent crosstalk between channels, the distance between scintillators is 300
A dead area of μm or more is required.

[0006] The fixed surface of the scintillator further arranged.
White pigment such as TiO. _TwoAnti-based
Having the above-described configuration having the radiation layer 22,
The translator 21 absorbs incident X-rays and converts them into visible light to emit light.
You. The visible light emitted inside the scintillator 21 is
2 and efficiently guided to the photoelectric conversion element array 24
And photoelectrically converted. Photocurrent increases in proportion to the amount of X-rays incident
I do.

[0007]

SUMMARY OF THE INVENTION Conventional multi-element solid-state detection
The crosstalk between each element was reduced
Therefore, a gap of about 300 μm is required,
The inter-use efficiency was poor, causing the sensitivity to deteriorate.
TiO used for the reflective layer_TwoIs a metal film such as Ag
Reflectivity is lower than that of
You. Further TiO _TwoHas a reflective layer because it is in powder form
It is difficult to fix as
There was a problem to say.

[0008]

According to the present invention, in order to solve the above-mentioned problems, a plurality of photoelectric conversion elements and a scintillator arranged opposite to each other transmit X-rays,
The structure has a reflecting means for reflecting visible light emitted inside the scintillator and a closing means for absorbing X-rays on a side face between adjacent scintillators.

[0009] Further, a protection means for protecting the reflection means and the closing means is provided. Further, the reflection means had a structure in which Ag was formed into a film having a thickness of 1 μm to 5 μm by a silver mirror reaction. Further, the shielding means has a configuration in which a metal film mainly containing a metal such as lead, bismuth, tantalum, or tungsten is formed by electrolytic plating. Therefore, in a radiation detector using a combination of a photoelectric conversion element and a scintillator, an Ag film using a silver mirror reaction is formed on the scintillator interface, so that visible light generated in the scintillator can be efficiently guided to the photoelectric conversion element. it can. Furthermore, since a metal film mainly composed of a metal material having a large X-ray absorption coefficient was formed on the side surface of the scintillator using an electrolytic plating method,
Crosstalk between scintillators was reduced, and X-ray space utilization efficiency could be improved.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.
It will be explained. FIG. 1 shows an embodiment of the solid-state detector according to the present invention.
1 shows a cross-sectional structure. The scintillator 1 absorbs X-rays (radiation)
Anything that can be collected and converted to visible light can be used.
No. For example, the known cadmium tungstate
(CdWO _Four), Bi_FourGe_ThreeO₁₂, Thallium added iodide
A single crystal such as sodium <NaI (TI)> or
Is Gd_TwoO_TwoS: Pr. Ce. Ceramic body such as F
Is raised. The characteristics of radiation used from these
The selection may be made in consideration of the light emission characteristics of the scintillator.

The thickness and shape of the scintillator 1 may be varied depending on the purpose. Here, since X-ray CT is assumed, cadmium tungstate (CdWO ₄ ) having excellent afterglow characteristics is used. The shape of the scintillator was 2.7 mm thick × 0.93 mm wide × 25 mm long. Further, the surface of the scintillator 1 was mirror-finished (polishing) in order to form a metal film that reflects light later and to prevent irregular reflection at the interface of the reflection film.

After the scintillator 1 has been cut and polished into a desired shape as described above, the visible light emitted after X-ray incidence and absorption into the scintillator 1 is efficiently guided to the photoelectric conversion element 6. The Ag layer is formed on the five surfaces other than the surface optically connected to the reflective layer 2 using a silver mirror reaction. When the thickness of the reflective layer 2 is small, voids are generated when the Ag film is thin, and visible light emitted in the scintillator 1 is transmitted, which causes a reduction in efficiency. Also, this A
If the g film is thick, it absorbs X-rays, and the X-ray utilization efficiency of the scintillator is reduced, which causes a decrease in sensitivity. Here, the film was formed with a thickness of about 1 to 5 μm.

Further, in order to reduce X-ray crosstalk between elements on the side surface of the scintillator 1 on which the reflective layer 2 is formed, X-ray absorption is provided on a surface other than the optical junction surface between the X-ray incident surface and the photoelectric conversion element 6. A material having a large coefficient, for example, a metal mainly composed of a metal such as gold, lead, bismuth, tantalum, or tungsten is formed to a thickness of about 1 μm to 100 μm by electrolytic plating to form the shielding layer 3. The thickness of the shielding layer 3 here is determined by the characteristics of the radiation used and the like. Although it depends on the material to be plated, it is also possible to form a film on Ni or the like as a base in order to improve adhesion.

Further, a protective layer 4 is formed to prevent corrosion of the reflection layer 2 and the shielding layer 3 due to oxidation and the like. The protective layer 4 is made of a material mainly containing Teflon, fluorine and the like. As described above, the scintillator 1 having each functional layer has excellent light transmittance on each element of the photoelectric conversion element array 6 composed of a plurality of photoelectric conversion elements, and has a refractive index of 1.
About 5 epoxy or acrylic adhesives 5 are used to face each other and fixed. Further, needless to say, the thickness of the adhesive 5 has a predetermined ratio in accordance with the emission wavelength characteristics of the scintillator 1. Here, since CdWO ₄ (cadmium tungstate) is used for the scintillator 1, there is a peak wavelength around 520 nm, and λ / 4
And a thickness of 130 nm.

The adhesive material 5 was applied to the photoelectric conversion surface of the photoelectric conversion element array 6 by a known coating method using a dispenser, and the film thickness was controlled by controlling the coating amount.
In order to further improve the film thickness accuracy, a more accurate film thickness can be controlled by adding a gap material such as micropearl to the adhesive 5 and controlling the film thickness. Next, FIG. 3 shows the structure and manufacturing method of each functional layer on the scintillator in detail.

In the step 1, a masking tape 12 is used in a step of first performing a masking process on the bonding surface of the scintillator 11 with the PIN photodiode (FIG. 3).
(A)). Step 2 is to add a reflective layer 1 to the scintillator 11.
In the step of forming the film No. 3, silver nitrate was first added to 100 parts by weight of pure water.
Dissolve 0 parts by weight to prepare an aqueous silver nitrate solution. While stirring the aqueous silver nitrate solution with a stirrer, aqueous ammonia is added little by little. When the aqueous solution of silver nitrate starts to be added with aqueous ammonia, turbidity due to precipitation occurs. Further addition of ammonia eliminates turbidity and forms a complexed solution.

The scintillators 11 masked in the above step 1 on a petri dish or the like are lined up with a masking tape below.
The complexed solution is added until the scintillator is completely immersed. When a Rochelle salt is added to the dish, a silver mirror reaction starts and a silver thin film is formed on the scintillator. It goes without saying that the thickness of this film is determined by the Rochelle salt concentration, the reaction time and the like. Here,
The reaction time and the Rochelle salt concentration were set so as to obtain a film thickness of about 5 μm (FIG. 3B).

Step 3 is a step of masking the X-ray irradiation surface of the scintillator 11 in a step before forming the shielding layer 15 and applying and masking the resist material 14 on the X-ray incidence surface using a brush and brush. (FIG. 3 (c)). In step 4, a material mainly composed of a heavy metal having a high X-ray absorption coefficient, such as lead, bismuth, tantalum, or tungsten, is formed on a surface other than the masking by electrolytic plating to a thickness of about 1 μm to 100 μm.
Further, in order to increase the adhesion strength, it is possible to apply Ni on the Ag film by electrolytic plating to a thickness of about 100 to 5000 (FIG. 3D).

Step 5 is a step of removing the masking applied in step 3, using a developing solution of the resist material usually used in the step of peeling off the masking material with an etchant or the like. However, if the absorption of X-rays is negligible depending on the X-ray used, the resist material can be left without peeling the resist material (FIG. 3E). Step 6 is a process for forming the reflective layer 1
3. In the step of forming the protective layer 16 in order to prevent corrosion such as oxidation of the metal film of the shielding layer 15, the protective layer 16 is made of, for example, a material mainly composed of Teflon or fluorine based on IPA (isopropyl alcohol). The scintillator 11, which has been completed up to the step 5, is immersed in a solution dissolved in an organic solvent such as the above, immersed in the solution, pulled up, dried in a drying furnace, and dried to form a film. The above process assumes the experimental stage, but the process at the time of commercialization also includes
Except for changing the device, the content can be the same.

[0020]

Since the present invention has been described above, it has the following effects. The radiation detector of the present invention has excellent reflection efficiency in visible light because Ag is used for the reflective layer, and has radiation utilization efficiency superior to that of the conventional solid state detector. Therefore, a radiation detector excellent in detection sensitivity can be obtained.

Further, since the reflection layer of the present invention is formed by an electroless plating method, it can be easily performed as compared with other thin film processes such as a vacuum deposition method, a sputtering method and an ion plating method, and the equipment cost is low. It is possible to reduce costs. In addition, since the shielding layer can be made of a metal having a large X-ray absorptivity, the gap between scintillators can be reduced, so that the X-ray space utilization efficiency of the scintillator is improved, and a radiation detector excellent in detection sensitivity can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional structural view showing an embodiment of a radiation detector of the present invention.

FIG. 2 is a sectional structural view showing one embodiment of a conventional radiation detector.

FIG. 3 is a schematic view of a process for forming a reflective layer, a shielding layer, and a protective layer on the scintillator of the present invention.

[Explanation of symbols]

 1, 11, 21 Scintillator 2, 13, 22 Reflective layer 3, 15 Sealing layer 4, 16 Protective layer 5, 23 Adhesive 6, 24 Photoelectric conversion element array 7, 25 Printed wiring board 12 Masking tape 14 Resist material

Claims (6)

[Claims] 1. A radiation detector comprising a plurality of scintillators for converting radiation into visible light, a photoelectric conversion element optically connected to each of the scintillators, and a circuit board supporting the whole. In the container, a reflection layer that reflects visible light generated in the scintillator on a surface other than the connection surface of the scintillator with the photoelectric conversion element,
A radiation detector, comprising: a shielding layer that shields radiation on a surface between adjacent scintillators. 2. The radiation detector according to claim 1, wherein the scintillator having the reflection layer and the shielding layer is further provided with a protective layer for preventing oxidation and the like. 3. The radiation detector according to claim 1, wherein the reflection layer is formed by electroless plating Ag on the surface of the scintillator by silver mirror reaction. 4. The radiation detector according to claim 1, wherein the shielding layer is formed of a metal film containing a heavy metal such as lead, bismuth, tantalum, and tungsten as a main component. 5. A method of manufacturing a radiation detector using a scintillator, comprising the steps of: a) performing a masking process on a joint surface between the scintillator and the photoelectric conversion output stage; Forming a silver thin film on the portion; c) masking the X-ray irradiated surface of the scintillator; and d) forming a heavy metal having a high X-ray absorption coefficient on portions of the scintillator other than the masked in step c). And a method for manufacturing a radiation detector. 6. The method for manufacturing a radiation detector according to claim 5, further comprising: e) forming a protective film for preventing corrosion after step d). Production method.