JP2006016251A - METHOD FOR MANUFACTURING Lu3Al5O12 CRYSTAL MATERIAL FOR DETECTING RADIATION - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an Lu<SB>3</SB>Al<SB>5</SB>O<SB>12</SB>crystal material for detecting radiation having high fluorescence intensity. <P>SOLUTION: The Lu<SB>3</SB>Al<SB>5</SB>O<SB>12</SB>crystal is manufactured by using a garnet seed crystal which is expressed by general formula: A<SB>3</SB>B<SB>2</SB>D<SB>3</SB>O<SB>12</SB>(wherein A is one kind of rare earth elements; B is one kind selected from rare earth elements, Al and Ga; and D is Al or Ga) and which is different from the Lu<SB>3</SB>Al<SB>5</SB>O<SB>12</SB>crystal but has the same melting point as that of the Lu<SB>3</SB>Al<SB>5</SB>O<SB>12</SB>crystal or a melting point lower by ≤150°C than that of the Lu<SB>3</SB>Al<SB>5</SB>O<SB>12</SB>crystal. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method for producing a radiation-detecting Lu ₃ Al ₅ O ₁₂ crystal material, and in particular, mainly an X-ray computed tomography (X-ray CT), a positron emission computed tomography (Positron Emission computed). Of Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection used in medical diagnostic devices such as Tomography (PET), Time-of-Flight Positron Emission Tomography (TOF-PET) It relates to a manufacturing method.

  Conventionally, radiation has been used for medical diagnosis, industrial nondestructive inspection, and the like. For example, X-ray CT and PET have been put to practical use as medical devices. In such an apparatus using radiation, a radiation detector for detecting radiation such as gamma rays and X-rays, for example, a scintillator is used.

  A scintillator is a substance that emits visible light or electromagnetic waves with a wavelength close to visible light upon stimulation of radiation such as gamma rays and X-rays, and has high density, short fluorescence decay time, and excellent radiation resistance. And good workability is required.

Conventionally, Bi ₄ Ge ₃ O ₁₂ single crystal (BGO) has been used as such a scintillator material for PET, but cerium-doped Gd ₂ SiO ₅ (Ce: GSO) is required for high performance characteristics. ) A single crystal was developed and put into practical use (for example, see Patent Document 1).

After that, various studies were conducted to obtain higher performance characteristics, and a cerium-doped lutetium oxyorthosilicate crystal (Ce: Lu ₂ SiO ₅ (Ce: LSO)) was developed, which is currently the most powerful. It has been put into practical use (see, for example, Patent Documents 2, 3, 4, etc.).

  However, such rare earth orthosilicate single crystals have strong cleaving properties and are easily cracked during growth or cracked during cutting, and are difficult to control during processing.

In addition to such rare earth orthosilicate single crystals, garnet crystals such as Lu ₃ Al ₅ O ₁₂ and Y ₃ Al ₅ O ₁₂ are also radiation detection crystals (see, for example, Patent Document 5) that have a light emission amount and a fluorescence lifetime. Although many studies have been made, compared to BGO, GSO, and LSO, which are currently mainstream, characteristics such as light emission amount and fluorescence lifetime are greatly inferior, so that they are not put into practical use (for example, non-patent documents). 1, 2, 3 etc.).

In addition to such single crystals, various ceramic materials have been studied as scintillators, and polycrystalline bodies (ceramics) such as BaFCl: Eu, LaOBr: Tb, CsI: Tl, CaWO ₄ , CdWO ₄ (CWO) (for example, patents) Reference 6), polycrystals (ceramics) of rare earth oxides having a cubic structure such as (Gd, Y) ₂ O ₃ : Eu (see, for example, Patent Document 7), Gd ₂ O ₂ S: Pr Such rare earth oxysulfide polycrystals (ceramics) (see, for example, Patent Document 8) are known.

Since such a ceramic scintillator material is manufactured by sintering powder, various proposals have been made regarding improvement of transparency (translucency), improvement of sintering property, and the like. For example, there is a proposal to improve the light output of the scintillator by setting the amount of impurities in phosphor ceramics such as Gd ₂ O ₂ S: Pr, particularly the content of phosphate (PO ₄ ) to 100 ppm or less ( For example, see Patent Document 9). Also, fluorides such as LiF, Li ₂ GeF ₆ , and NaBF ₄ are added to the rare earth oxysulfide powder as a sintering aid, and these mixed powders are sintered by hot isostatic pressing (HIP). A phosphor ceramic having a high density has been proposed (see, for example, Patent Document 10).

Japanese Examined Patent Publication No. 62-8472 (Claims) US Pat. No. 4,958,080 (I CLAIM) US Pat. No. 5,025,151 (WHAT IS CLAIMED IS) JP-A-9-118593 (Claims) U. S. P. 5,057,692 (Japanese Patent Publication No. 6-7165) Japanese Patent Publication No.59-45022 (Claims) JP 59-27283 A (Claims) JP 58-204088 A (Claims) JP-A-7-188655 (Claims) JP-A-5-016756 (Claims) M.M. Moszynski, IEEE Trans. , On Nucl. , Sci. , 44 (1997) 1052 A. Lempicki, IEEE Trans. , On Nucl. , Sci. , 42 (1995) 280 C. W. E. van Eik, Nucl. , Instr. and Meth. , A460 (2001) 1.

In view of such circumstances, and an object thereof is to provide a method of manufacturing the radiation detection Lu ₃ Al ₅ O ₁₂ crystal material having a high fluorescence intensity.

According to a first aspect of the present invention for achieving the above object, in the method for producing a Lu ₃ Al ₅ O ₁₂ crystal material, the general formula A ₃ B ₂ D ₃ O ₁₂ (A is any one of rare earth elements, B rare earth element is one type or Al or Ga noise, D is a different but the melting point the _Lu 3 _Al 5 _{O 12} crystals and represented and the _Lu 3 _Al 5 _{O 12} crystal with a a) Al or Ga Production of the Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection, characterized in that the Lu ₃ Al ₅ O ₁₂ crystal is produced using a garnet seed crystal having a melting point that is the same or lower than 150 ° C. Is in the way.

According to a second aspect of the present invention, in the first aspect, in the first aspect, the garnet seed crystal is Er ₃ Al ₅ O ₁₂ , Tm ₃ Al ₅ O ₁₂ , Ho ₃ Al ₅ O ₁₂ , Dy ₃ Al. ₅ O _12, or the method of manufacturing the radiation detection _Lu 3 _Al 5 _{O 12} crystalline material, characterized in that _Y is 3 _Al 5 _{O 12.}

According to a third aspect of the present invention, in the first or second aspect, a part of Lu constituting the Lu ₃ Al ₅ O ₁₂ crystal is Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Garnet substituted with at least one element Z of Gd, Tb, Dy, Ho, Er, and Tm and represented by (Z _x Lu _1-x ) ₃ Al ₅ O ₁₂ (0 <x <0.5) The present invention resides in a method for producing a radiation-detecting Lu ₃ Al ₅ O ₁₂ crystal material characterized by producing a system crystal.

The Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection produced in the present invention has a garnet structure, but the Lu cation is octacoordinated by oxygen, and the Al cation is hexahedrally and tetrahedrally coordinated by oxygen. Preferably has a cubic structure with 160 ions per unit cell containing 8 chemical formula units. Note that the radiation-detecting Lu ₃ Al ₅ O ₁₂ crystal material produced in the present invention may be in any crystalline state such as ceramic, polycrystal, and single crystal as long as the crystal is transparent and has high fluorescence. Needless to say, a single crystal is preferable.

On the other hand, it is necessary to increase the intensity of fluorescence generated when such a Lu ₃ Al ₅ O ₁₂ crystal absorbs radiation, improve the characteristics as a scintillator, or shift the fluorescence peak. Accordingly, a part of Lu constituting the Lu ₃ Al ₅ O ₁₂ crystal may be replaced with another element. As such an element that can be substituted for Lu, it is preferable to use an element having no absorption at the fluorescence wavelength. As an element that can be substituted for Lu constituting such a Lu ₃ Al ₅ O ₁₂ crystal, for example, 0.01 to 10 mol% may be substituted at a molar ratio with Lu constituting the Lu ₃ Al ₅ O ₁₂ crystal. it can. If a part of Lu constituting the Lu ₃ Al ₅ O ₁₂ crystal is replaced with another element in this manner, the intensity of fluorescence increases, but the emission wavelength and fluorescence lifetime may change. It is necessary to select appropriately according to the characteristics.

Other elements used in the present invention to replace part of Lu constituting the Lu ₃ Al ₅ O ₁₂ crystal include cerium Ce, praseodymium Pr, samarium Sm, europium Eu, terbium Tb, dysprosium Dy, holmium Ho, and erbium. Examples include rare earth elements such as Er, thulium Tm, and ytterbium Yb. Ce is particularly preferable. Further, in order to shift the wavelength of light emitted when irradiated with gamma rays, a part of Lu composing the Lu ₃ Al ₅ O ₁₂ crystal is replaced with gadolinium Gd, yttrium Y, terbium Tb, dysprosium Dy, holmium Ho, erbium. Although it can be substituted with Er, thulium Tm, ytterbium Yb or the like, Gd is particularly preferable.

Since the Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection produced according to the present invention is used as a scintillator of a detector such as PET or TOF-PET, it is necessary to obtain high quality and homogeneous crystals. Therefore, examples of the crystal growth method used in the present invention include Bernoulli method, crystal pulling method (CZ method), Bridgman method, heat exchange method, cairoporous method, zone melting method (FZ method), etc. From the viewpoint of properties, the Bernoulli method and the CZ method are preferred. Further, the FZ method is preferable as a crystal growth method for further improving the quality of the crystal. Hereinafter, using the CZ method or FZ method, a method for manufacturing the radiation detection _Lu 3 _Al 5 _{O 12} crystalline material of the present invention.

In the crystal pulling method, a Lu ₃ Al ₅ O ₁₂ crystal material is heated from room temperature to a temperature equal to or higher than the melting point of the material in an oxidizing gas, inert gas or reducing gas atmosphere, and a garnet species is added to the melt. A Lu ₃ Al ₅ O ₁₂ crystal is produced by bringing the garnet seed crystal into contact with the crystal and pulling the garnet seed crystal at a predetermined rotational speed and speed.

On the other hand, in the zone melting method, after a Lu ₃ Al ₅ O ₁₂ crystal material is compression-molded, the material is heated from room temperature to a temperature equal to or higher than the melting point of the material in an oxidizing gas, inert gas or reducing gas atmosphere. A Lu ₃ Al ₅ O ₁₂ crystal is produced by using a melt, bringing the garnet seed crystal into contact with the melt, and moving the garnet seed crystal at a predetermined rotational speed and speed.

The garnet seed crystal used in these methods has a garnet structure represented by the general formula A ₃ B ₂ D ₃ O ₁₂ , but the Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection manufactured according to the present invention described above. It is preferable to have the same cubic system structure.

The element A constituting the garnet seed crystal of the present invention is preferably a rare earth element, the element B is preferably a rare earth element, Al or Ga, and the element D is preferably Al or Ga, but the garnet used in the present invention. As the seed crystal, Er ₃ Al ₅ O ₁₂ , Tm ₃ Al ₅ O ₁₂ , Ho ₃ Al ₅ O ₁₂ , Dy ₃ Al ₅ O ₁₂ , or Y ₃ Al ₅ O ₁₂ is particularly preferable.

Furthermore, when the melting point of the garnet seed crystal is lower than the melting point of the material of the Lu ₃ Al ₅ O ₁₂ crystal (particularly, the melting point of the garnet seed crystal is preferably in the range of 0 to 150 ° C. from the melting point of the material). Even so, the garnet seed crystal can be used in the present invention by controlling the growth rate of the Lu ₃ Al ₅ O ₁₂ crystal after the garnet seed crystal is brought into contact with the melt of the material.

Since the Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection produced according to the present invention has high fluorescence intensity, the radiation detector using the Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection has a high resolving power. Play.

Hereinafter, a manufacturing method of a radiation detecting _Lu 3 _Al 5 _{O 12} crystalline material of the present invention will be described in detail. The description of the present embodiment is an exemplification, and the present invention is not limited to the following description.

The method for producing the Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection of the present invention using the CZ method is as follows. Powder or polycrystalline rare earth oxide raw material, that is, powder raw material for matrix such as Lu ₂ O ₃ , Al ₂ O _3, etc., is filled with CeO ₂ or the like, if necessary, and oxidized such as air or oxygen Gas, N ₂ , He, Ne, Ar or other inert gas, or a mixture of them in a reducing gas atmosphere in which H ₂ is 1 to 20 mol% based on the total of N ₂ and H ₂ , from room temperature to about 2050 ° C. I.e., to a temperature at which the mixture melts. Next, after confirming that the mixture melted into a melt, while maintaining the temperature of the melt near the melting point of the mixture, Y ₃ Al ₅ O ₁₂ or Tm ₃ Al was added to the melt. Lu ₃ free from bubbles and scattering centers in the crystal by contacting a garnet seed crystal such as ₅ O ₁₂ and pulling the garnet seed crystal at 0.1 to 10 mm / h while rotating at 5 to 10 rpm. Al ₅ O ₁₂ crystals are obtained.

Similarly, the manufacturing method of the radiation detecting Lu ₃ Al ₅ O ₁₂ crystal material of the present invention using the FZ method is as follows. CeO ₂ or the like is added to a powder or polycrystalline rare earth oxide raw material, that is, a powder raw material for a matrix such as Lu ₂ O ₃ or Al ₂ O ₃ as necessary, and the mixture is filled into a rubber tube or the like. Then, after compression-molding to a diameter of 10 to 20 mm and a length of 50 to 200 mm by an isostatic press, firing is performed at a predetermined temperature. Next, in an reducing gas atmosphere in which H ₂ is 1 to 20 mol% based on an oxidizing gas such as air or oxygen, an inert gas such as N ₂ , He, Ne, Ar, or the total of N ₂ and H ₂ The mixture is heated to about 2050 ° C., that is, the temperature at which the materials melt, and after confirming that the mixture has melted into a melt, the temperature of the melt is brought to the vicinity of the melting point of the mixture. While maintaining, the garnet seed crystal such as Y ₃ Al ₅ O ₁₂ or Tm ₃ Al ₅ O ₁₂ is brought into contact with the melt, and the garnet seed crystal is rotated at 5 to 10 rpm, and the speed is 0.1 to 10 mm / h. By pulling down, a Lu ₃ Al ₅ O ₁₂ crystal free from bubbles and scattering centers in the crystal can be obtained.

The Lu ₃ Al ₅ O ₁₂ crystal thus obtained is useful as a scintillator for PET or TOF-PET.

In addition, a scintillator obtained by cutting such a Lu ₃ Al ₅ O ₁₂ crystal into a predetermined size is a photodetector that matches the wavelength of fluorescence generated by absorbing radiation, for example, gamma rays, such as visible light or ultraviolet light. A radiation detector can be obtained by combining with a photodetector such as a photomultiplier tube.

Example 1 Production of Lu ₃ Al ₅ O ₁₂ Crystal Material for Radiation Detection by CZ Method Molar ratio of Lu ₂ O ₃ , Al ₂ O ₃ and CeO ₂ , which is a commercially available bulk pulverized raw material with a purity of 99.99% Of 2.985 mol% vs. 5.00 mol% vs. 0.03 mol% was stirred and mixed and filled into a crucible. It was placed in a single crystal production furnace as it was, and the air in the furnace was sufficiently replaced with N ₂ gas, and then heated to 2000 ° C. over 12 hours. Subsequently, after the mixture was heated to 2050 ° C. in an N ₂ atmosphere to confirm that the mixture in the crucible melted into a melt, a garnet seed crystal composed of YAG ( A melting point of 1940 ° C.), the garnet seed crystal was quickly pulled up in the vertical direction at a pulling speed of 5 to 10 mm / h, and after confirming that the crystal was growing, a pulling speed of 1.5 mm / h, A crystal was grown and produced by pulling up at a rotation speed of 10 rpm. The produced crystal has a diameter of 30 mm, a length of about 50 mm, has no bubbles, cracks, and a scattering center, and is a yellow transparent, high-quality, Ce-activated Lu ₃ Al ₅ O ₁₂ (Ce: LuAG) crystal. Met.

Example 2 Production of Lu ₃ Al ₅ O ₁₂ Crystal Material for Radiation Detection by FZ Method A molar ratio of Lu ₂ O ₃ , Al ₂ O ₃ and CeO ₂ , which is a commercially available bulk pulverized raw material having a purity of 99.99% Was stirred and mixed with a mixture consisting of 2.985 mol% vs. 5.00 mol% vs. 0.03 mol%. The mixture was filled in a rubber tube, compression-molded to a diameter of 10 mm and a length of 80 mm by an isostatic press, and then fired at 1400 ° C. in the atmosphere. Next, the mixture was heated to 2050 ° C. in an N ₂ atmosphere, and after confirming that the mixture melted into a melt, a garnet seed crystal composed of YAG (melting point: 1940 ° C.) The garnet seed crystal was quickly pulled down in the vertical direction at a pulling speed of 5 to 10 mm / h. After confirming that the crystal was growing, the pulling speed was 1.5 mm / h and the rotation speed was 10 rpm. Pulled down to grow and produce crystals. The produced garnet crystal was a Ce: LuAG crystal having a diameter of 6 mm and a length of about 40 mm, free of bubbles, cracks, and a scattering center, and having a high quality and transparency.

(X-ray diffraction measurement)
The Ce: LuAG crystal obtained in Example 2 was powdered and subjected to X-ray diffraction measurement. 1 and 2 show the X-ray diffraction spectra obtained. Here, ● represents X-ray diffraction data of a LuAG single crystal published in JCPDS (Joint Committee on Powder Diffraction Standards). As shown in FIGS. 1 and 2, the X-ray diffraction data of the obtained Ce: LuAG crystal does not have a peak due to CeO ₂ , and agrees with the X-ray diffraction data of the LuAG single crystal published in JCPDS. Thus, it was confirmed that the obtained Ce: LuAG crystal was a Ce: LuAG single crystal.

Next, the scintillator characteristics of the Ce: LuAG crystals obtained in Examples 1 and 2 by gamma ray irradiation were measured. The light emission amount was measured using a photomultiplier tube (R2486, manufactured by Hamamatsu Photonics) using Cs ¹³⁷ as a radiation source. The obtained scintillator characteristics are shown in Table 1, and the emission spectrum of the Ce: LuAG crystal of Example 2 is shown in FIG.

  As shown in Table 1, the light emission amounts of the Ce: LuAG crystals obtained in Examples 1 and 2 were 430 ch and 442 ch, respectively. Further, as shown in FIG. 3, the emission spectrum of the Ce: LuAG crystal obtained in Example 2 was 510 nm, and the fluorescence lifetime was 0.1 μs.

The production method of the Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection according to the present invention mainly includes an X-ray computed tomography (X-ray computed tomography: X-ray CT), a positron emission computed tomography (PET). ), Time-of-flight positron emission tomography (TOF-PET), etc., used for the production of radiation-detecting Lu ₃ Al ₅ O ₁₂ crystal materials for medical diagnostic devices However, it is used for the production of a Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection for various uses for radiation detection.

4 is a diagram showing an X-ray diffraction spectrum of a Ce: LuAG crystal according to Example 2. FIG. 4 is a diagram showing an X-ray diffraction spectrum of a Ce: LuAG crystal according to Example 2. FIG. 6 is a graph showing an emission spectrum of a Ce: LuAG crystal according to Example 2. FIG.

Claims (3)

In the method for producing a Lu ₃ Al ₅ O ₁₂ crystal material, the general formula A ₃ B ₂ D ₃ O ₁₂ (A is one of the rare earth elements, and B is one of the rare earth elements, Al or Ga) , D is Al or Ga) and is different from the Lu ₃ Al ₅ O ₁₂ crystal, but has a melting point that is the same as that of the Lu ₃ Al ₅ O ₁₂ crystal or a lower melting point within 150 ° C. A method for producing a Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection, characterized in that the Lu ₃ Al ₅ O ₁₂ crystal is produced using a garnet seed crystal. In claim 1, said garnet seed _{crystal, Er 3 Al 5 O 12,} Tm 3 Al 5 O 12, Ho 3 Al 5 O 12, Dy 3 Al 5 O 12, or _Y 3 _Al 5 _{O 12} A method for producing a characteristic Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection. In Claim 1 or 2, a part of Lu constituting the Lu ₃ Al ₅ O ₁₂ crystal is Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, A garnet-based crystal represented by (Z _x Lu _1-x ) ₃ Al ₅ O ₁₂ (0 <x <0.5) is produced by substitution with at least one element Z of Tm. A method for producing a Lu ₃ Al ₅ O ₁₂ crystal material for radiation detection.

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