JPH09142994A - Method for growing single crystal of silicate of rare earth element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain a single crystal free from voids and having satisfactory performance as a scintillator by specifying the concn. of Al as an impurity in a stock melt contg. oxide of a rare earth element and silicon oxide. SOLUTION: Characteristics of a grown single crystal are affected by a specified impurity element in stock. In the case of growth of a gadolinium silicate single crystal, gadolinium oxide having a low concn. of Al as an impurity is used as stock. By this low concn. of Al, the occurrence of voids in the resultant crystal is prevented and characteristics as a scintillator can be improved. Since the crystal is free from voids, fluorescence generated in the crystal by irradiation efficiently reaches a photomultiplier brought into contact with one face of the crystal and the fluorescence output and energy resolving power of the photomultiplier are enhanced. As a result, characteristics of the crystal as a scintillator are improved. When stock having <=0.4ppm concn. of Al as an impurity is used, oxide of a rare earth element having <=0.4ppm concn. of Al is preferably used.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for growing a rare earth silicate single crystal used in scintillators and the like.

[0002]

2. Description of the Related Art Rare earth silicate single crystals such as gadolinium silicate single crystals are widely used as scintillators, phosphors and the like. This gadolinium silicate single crystal or the like is grown by a method of growing a single crystal from a raw material melt such as the Czochralski method using gadolinium oxide of a rare earth oxide and silicon dioxide of silicon oxide as a raw material. Generally, scintillator characteristics such as fluorescence output are considered to be adversely affected by impurities such as rare earth elements other than the constituent elements and transition metals,
Crystal growth is performed using high purity raw materials (Gd ₂ O ₅ , SiO ₂ etc.) of 4N or more (99.99% by weight or more) in which those impurity elements are reduced.

[0003]

However, when the conventional raw materials are used, there is a problem that voids are generated in the crystal and stable scintillator characteristics cannot be obtained. The present invention provides a method for growing a rare earth silicate single crystal in which a rare earth silicate single crystal having good scintillator performance in which no void is generated in the crystal is stably obtained when growing the rare earth silicate single crystal. It is provided.

[0004]

The present invention uses a raw material such as a rare earth oxide reduced in a specific impurity element when growing a rare earth silicate single crystal. In a method of growing a rare earth silicate single crystal from a melt of a raw material containing a substance, the Al impurity concentration is 0.
It is a method for growing a rare earth silicate single crystal, characterized by using 4 ppm or less of a raw material.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have examined the void generation and scintillator characteristics of rare earth silicate single crystals, and the impurity concentration relations in the rare earth oxides and the like as the raw material.
As a result, by finding that the difference in the content of a specific impurity element affects the characteristics of the grown single crystal,
The present invention has been made. It has been found that, when a gadolinium silicate single crystal is grown, by using a rare earth oxide having a low Al impurity concentration as a raw material, void generation in the crystal is eliminated and the scintillator characteristics can be improved. That is, when the generation of voids in the crystal disappears, the fluorescence generated in the crystal by irradiating the crystal with radiation such as γ-rays efficiently reaches the photomultiplier tube provided in contact with one surface of the crystal, The fluorescence output and energy resolution are improved, and as a result, the scintillator characteristics are improved. When using a raw material having an Al impurity concentration of 0.4 ppm or less, it is preferable to use a rare earth oxide having an Al impurity concentration of 0.4 ppm or less.

Other than gadolinium silicate single crystal, the general formula R SiO, where R = La, Ce, Pr, Nd, Pm, Sm, Eu,
With respect to the rare earth silicate single crystal represented by Tb, Dy, Ho, Er, Tm, and Yb, the influence of impurities in the raw material is similar, and the same result is obtained. Further, generally, a rare earth silicate single crystal is doped with an additive such as Ce as a fluorescent center, but in that case, the effect is similar. The above rare earth silicate single crystal has the same crystal structure as that of the gadolinium silicate single crystal, and the structure is the space group P2.
Belongs to ₁ / c.

[0007]

【Example】

Comparative Example Cerium Activated Gadolinium Silicate Single Crystal (Ce: Gd ₂ S
An example in the case of iO ₅ and Ce concentration of 0.5 mol%) will be described. Gadolinium oxide (Gd ₂ O ₃ ) 4N (A
Seed) Silicon dioxide (SiO ₂ ) 4N and cerium oxide (CeO ₂ ) 4N were used to grow a single crystal by the Czochralski method. Gadolinium oxide 2573.
5 g of silicon dioxide, 426.5 g of silicon dioxide, and 5.9 g of cerium oxide were weighed and mixed, fired at 1200 ° C., and then charged into an Ir crucible having a diameter of 100 mm to obtain a raw material melt 1
950 ° C., seed crystal rotation speed 30 rpm, pulling speed 2
Under the condition of mm / h, the pulling was completed when 80% by weight of the raw material was crystallized, and a single crystal having a diameter of 50 mm was grown. The grown single crystal had many voids in the lower part of the ingot. The degree of occurrence of voids varied depending on the growing (ingot). Table 1 shows the results of measuring the characteristics when a sample of 10 × 10 × 30 mm ³ was collected from the grown crystal and was irradiated with γ-ray.
Stable and good results were not obtained. As a result of measuring Al impurities in gadolinium oxide, silicon oxide, and cerium oxide, 13.0 ppm, 0.016 ppm,
It was less than 3.5 ppm. Al impurity in raw material is 1
It exceeds 1.1 ppm.

EXAMPLE An example in the case of a cerium activated gadolinium silicate single crystal (Ce: Gd ₂ SiO ₅ , Ce concentration 0.5 mol%) will be described as in the comparative example. Gadolinium oxide (Gd) as a raw material
₂ O ₅ ) 4N (B type) and silicon dioxide (SiO ₂ ) 4 which is exactly the same as that used in the comparative example (same refining lot number)
A single crystal was grown by the Czochralski method using N and cerium oxide (CeO ₂ ) 4N. 2573.5 g of gadolinium oxide, 426.5 g of silicon oxide, and 5.9 g of cerium oxide were weighed, mixed and fired, then put in an Ir crucible and grown in the same manner as in the comparative example. As a result of the growth, a stable crystal without coloring or generation of voids was obtained. Table 1 also shows the results of measurement of the characteristics when a sample of 10 × 10 × 30 mm ³ was taken from the grown crystal and was irradiated with γ-ray, but the characteristics were stable and good. It was clearly observed that the crystal characteristics were improved by reducing the Al impurities. As a result of measuring Al impurities in gadolinium oxide, the result was 0.35 ppm, which was significantly smaller than that of the gadolinium oxide raw material used in the comparative example. The Al impurity in the raw material is less than 0.31 ppm.

[0009]

[Table 1] Table 1 Void generation and light transmittance ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Comparative example Example ───── ──────────────────────── Void generation (book / book) 3/6 0/5 Transmittance (%) 430 nm 60 80 ━━━━ ━━━━━━━━━━━━━━━━━━━━━━━━━

[0010]

According to the method of growing a rare earth silicate single crystal of the present invention, it is possible to grow a rare earth silicate single crystal having stable and good scintillator performance without generation of voids in the crystal.

Claims (3)

[Claims] 1. A method for growing a rare earth silicate single crystal from a melt of a raw material containing a rare earth oxide and a silicon oxide,
A method for growing a rare earth silicate single crystal, which comprises using a raw material having an Al impurity concentration of 0.4 ppm or less. 2. The method for growing a rare earth silicate single crystal according to claim 1, wherein a rare earth oxide having an Al impurity concentration of 0.1 ppm or less is used. 3. The method for growing a rare earth silicate single crystal according to claim 1, wherein the rare earth oxide is gadolinium oxide.