JPH0516756B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a scintillator material for radiation detection that is incorporated into medical equipment, scientific analysis equipment, etc., and is particularly suitable for use as a scintillator for X-ray CT. This invention relates to a scintillator material whose main component is rare earth oxysulfide. [Prior Art] Conventionally, a xenon (Xe) ionization chamber has been used as a scintillation detector. Although the Xe ionization chamber has been highly praised for its practicality,
It required an expensive low-vibration scanner and also had the problem of becoming unstable during continuous use. For this reason, in recent years, devices using so-called solid-state detection elements such as single-crystal scintillator materials, resin/powder composites in which scintillator material powder is dispersed and solidified in resin, and even translucent scintillator sintered bodies have appeared. In particular, these solid-state detection elements are mainly used in recent detectors that are capable of high-accuracy and high-speed scintillation detection. FIG. 2 is an explanatory diagram of a schematic configuration of a solid state detection element using a single crystal scintillator material. In the figure, 1 is a scintillator member made of a single crystal such as BGO, and incident X-rays are transmitted through the scintillator member 1 and sent to a photodiode 2.
It has an extremely simple configuration that can be detected. However, the conventionally used BGO,
It has been pointed out that single crystal scintillator materials such as CWO, NaI/Tl, CaF ₂ /Eu, and CsI/Tl all have problems. In other words, BGO has low luminous efficiency and is expensive, CWO (CdWO ₄ ) is expensive, highly toxic, and difficult to process due to its cleavability.
NaI/Tl and CsI/Tl tend to absorb moisture and have a relatively large afterglow, and CaF ₂ /Eu has problems such as poor wavelength matching with silicon photodiodes and the like. In particular, in the solid-state detection element having the above configuration, the light emitting output of the scintillator material has an important meaning because the amplification effect of the photodiode that receives light is small. For this reason, elements have been proposed that combine a photodiode with a scintillator material that has higher luminous efficiency than the single crystals mentioned above, such as a resin/powder composite made by dispersing fine powder such as oxysulfide in a resin and solidifying it. (Japanese Unexamined Patent Publication No. 1983-7861). FIG. 3 is a schematic structural explanatory diagram of a solid state detection element using a resin/powder composite. In the figure, 3 is a resin/powder composite. For example, powder of a scintillator material with high luminous efficiency such as Gd ₂ O ₂ S is dispersed in a resin and solidified. 3, the transmitted X-rays are absorbed by lead glass 4, and the photodiode 5 captures the emitted light. However, in such a structure, since the resin/powder composite 3 has low translucency,
This part has no choice but to be made of a relatively thin member. For this reason, it is essential to provide lead glass 4 in the middle for the purpose of absorbing the X-rays so that the incident X-rays do not directly reach the photodiode 5 and have any adverse effects, which has the disadvantage of complicating the structure. be. Furthermore, the emission intensity of the resin/powder composite is considerably lower than the theoretical value, and deformation during processing is also an obstacle to device development. [Problems to be solved by the invention] In view of the above-mentioned circumstances, the inventor of the present application previously proposed an element that combines a translucent rare earth oxysulfide and a photodiode (Japanese Patent Application No. 59-247467, (No. 191951). FIG. 4 is a schematic diagram illustrating the configuration of a solid-state detection element using a translucent rare earth oxysulfide sintered body previously proposed by the present inventors. In the figure, 6 is a sintered body for a scintillator, and for example, a sintered body of Gd ₂ O ₂ S-Pr, Ce, F is used. The sintered body is irradiated with X-rays, and the transmitted X-rays are exposed to lead glass 7.
The structure is such that the emitted light is absorbed by the photodiode 8 and the emitted light is captured by the photodiode 8. If the sintered body layer is thick, the absorption of X-rays in this layer is large and lead glass is not required. However, although the luminous output of the sintered body specifically disclosed in the previously proposed invention can be obtained up to about 1.5 times that of the resin/powder composite material, the thickness of the sintered body is made larger and the luminous output is higher than that of the lead glass. It has been found that this is not necessarily sufficient when eliminating the need or increasing resolution. As mentioned above, rare earth oxysulfides sintered using the HIP method can provide higher luminous output than resin/powder composite materials, but efforts have been made to significantly improve their performance as scintillator elements. It is insufficient if In view of the above circumstances, the present invention aims to realize a rare earth oxysulfide sintered body having high luminous output. [Means for Solving the Problems] In order to achieve the above object, the present invention adds a sintering aid to rare earth oxysulfide powder and processes it using a hot isostatic pressing method (hereinafter referred to as HIP method). ) is characterized in that it is a scintillator material made into a translucent and high-density sintered body by sintering. In the present invention, the rare earth oxysulfide has a composition known from, for example, Japanese Patent Application Laid-Open No. 55-62930 or Japanese Patent Application No. 56-151376, that is, the composition formula (Ln ₁ -x-yMxCey ) ₂ O ₂ S: (F) or (Cl) However, in the formula, Ln is at least one element selected from Gd, La, Y, and Lu. M is one or two of Pr and Tb. The amount of seed element x is 3×10 ^-6 ≦x≦0.2 The amount of y is 1×10 ^-6 ≦y≦5×10 ^-3 The amount of F or Cl is expressed as 0 to 1000 ppm by weight. or compositional formula (Ln ₁ -a-bEuaMb) ₂ O ₂ S However, in the formula, Ln is at least one element selected from Gd, La, Y, and Lu. M is at least one element selected from Pr and Tb. The amount of one or two elements a can be expressed as 1×10 ⁻³ ≦a≦0.1 and the amount of b can be expressed as 2×10 ⁻⁶ ≦b≦1×10 ⁻⁴ . Also,
In the present invention, among these, (Gd ₁ −x−yPrxCey) ₂ O ₂ S: (F) or (Cl) However, 3×10 ⁻⁶ ≦x≦0.2, 1×10 ⁻⁶ ≦y A scintillator material with a formula of ≦5×10 ^-3 is preferable. Further, in the present invention, the sintering aid may be any substance that has the effect of promoting densification and improving the luminous output of the rare earth oxysulfide sintered body by adding it. for example,
LiF, Li ₂ GeF ₆ , Li ₂ B ₄ O ₇ , Na ₃ AlF ₆ , NaPF ₆ ,
One or more compounds selected from NaBF ₄ , LiBF ₄ , (NH ₄ ) ₂ GeF ₆ and MgSiF ₆ can be used. In addition, the effect can be seen even if the addition amount is as small as 0.001%, but if it is added too much, the scintillator material will not be able to obtain the original light emission output, so it should be kept at most 10% by weight or less. is desirable. However, since the present invention contains a sintering aid, it has a much higher density than the previously proposed sintered material, and has an excellent property of high density with a relative density of 96% or more. scintillator materials can be realized. Furthermore, the shape of the crystal grains observed in a certain cross section of the sintered material according to the present invention is different from that proposed previously, and the shape of the crystal grains according to the present invention is different from that proposed previously.
All of them are characterized by containing a relatively large amount of crystal grains that have a columnar appearance. The presence of these columnar particles can be observed using a microscope on the cross section of the sintered body, but the relationship between their amount and the properties of the sintered body is currently under investigation and is not necessarily clear. However, it has been confirmed that if the area ratio on a microscopic photograph of a cut surface is about 10% or more, it exhibits the excellent properties aimed at by the present invention. Figure 1a shows the shape of the particles without the sintering aid, and Figure 1b shows the shape of the particles with the addition of the sintering aid. [Examples] Hereinafter, the present invention will be explained in more detail based on Examples. Example 1 (Gd _0.997 Pr _0.003 Ce _6×10 ^-6 ) Powder obtained by adding 90 ppm of F to ₂ O ₂ S and various sintering aids shown in Table 1 were placed in a stainless steel container. After vacuum sealing, this container was subjected to HIP treatment for 3 hours in argon gas at 1300° C. and 1000 atm. Table 1 shows the relative density, area ratio of columnar crystals in any cross section, and luminous output ratio of the obtained sintered body in comparison with the HIP sintered body to which no additives were added.

[Table] Example 2 (Gd _0.997 Pr _0.003 Ce _6×10 ^-6 ) Powder obtained by adding 90 ppm of F to ₂ O ₂ S and various sintering aids shown in Table 2 were added to stainless steel. After vacuum-sealing the container, the container was subjected to HIP treatment for 1.5 hours in argon gas at 1300° C. and 1500 atm. Table 2 shows the relative density, area ratio of columnar crystals in any cross section, and luminous output ratio of the obtained sintered body in comparison with the HIP sintered body to which no additives were added.

【table】

[Table] Example 3 A powder prepared by adding a sintering aid to the rare earth oxysulfide powder shown in Table 3 was vacuum sealed in a stainless steel container, and then the container was placed in argon gas at 1300°C and 1250 atm for 2 hours. I performed HIP processing.

[Table] Table 4 shows the relative density of the obtained sintered body, the area ratio of columnar crystals in any cross section, and the luminous output ratio in comparison with the HIP sintered body to which no additives were added.

[Table] *No. indicates the scintillator composition in Table 3.
[Effects of the Invention] As detailed above, according to the present invention, a sintered body of rare earth oxysulfide having a higher luminous output than the conventional sintered body of rare earth oxysulfide can be obtained, and as a result, (1) (2) Solid-state detection elements for radiation detection with high luminescence output can be obtained for use in scintillator elements for X-ray CT. Eliminating the need for glass or making it a thin layer can reduce device costs; (3) High light output increases signal-to-noise ratio (S/N ratio) and reduces the aperture angle of the device. By doing so, it becomes possible to improve spatial and gradation resolution, and the detection limits of conventional radiation detection elements can be exceeded. Furthermore, the sintered body produced according to the present invention is
Of course, it can be used as a linear CT element, but also as a translucent light emitter,
Since it can also be applied to target materials, it has great industrial effects.

[Brief explanation of the drawing]

Fig. 1 is an observation diagram showing the structures of the scintillator material of the present invention and comparative materials, Fig. 2 is a schematic illustration of the structure of a solid-state detection element using a single-crystal scintillator material, and Fig. 3 is an illustration of a solid-state detection element using a resin/powder composite. FIG. 4 is a schematic diagram illustrating the configuration of a solid-state detection element using a translucent rare earth oxysulfide sintered body previously proposed by the present invention. 1...Single crystal scintillator material, 2,5,8...Photodiode, 3...Resin/powder composite, 4,7
...Lead glass, 6...Sintered body for scintillator.

Claims (1)

[Scope of Claims] 1. A high-density translucent scintillator material characterized in that it is made from rare earth oxysulfide powder containing a sintering aid and is sintered by hot isostatic pressing. 2 The amount of the sintering aid added is 0.001 to 10% by weight.
The high-density translucent scintillator material according to claim 1, characterized in that: 3 The above rare earth oxysulfide has the composition formula (Gd ₁ −x−yPrxCey) ₂ O ₂ S: (F) or (Cl) However, 3×10 ^-6 ≦x≦0.2, 1×10 ^-6 ≦y≦ 5×10 ⁻³ . The high-density translucent scintillator material according to claim 1 or 2, characterized in that it has a molecular weight of 5×10 −3 . 4. The high-density translucent scintillator material according to any one of claims 1 to 3, wherein the sintered material has a high density with a relative density of 96% or more. 5. The high-density translucent scintillator material according to any one of claims 1 to 4, wherein the crystal grains in a certain cross section of the sintered material have a columnar shape. 6. The high-density translucent scintillator material according to claim 5, wherein the shape of the crystal grains in a certain cross section of the sintered material is columnar for an area ratio of 10% or more. 7 The above sintering aid is LiF, Li ₂ GeF ₆ , Li ₂ B ₄ O ₇ ,
Na ₃ AlF ₆ , NaPF ₆ , NaBF ₄ , LiBF ₄ ,
(NH ₄ ) ₂ The high-density transparent material according to any one of claims 1 to 6, characterized in that it is one or more compounds selected from GeF ₆ and MgSiF ₆ . Photoactive scintillator material.