JP2004059382A - Rare earth silicate single crystal - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、シンチレータ等に用いられる希土類珪酸塩単結晶に関する。
【０００２】
【従来の技術】
珪酸ガドリニウム単結晶等の希土類珪酸塩単結晶は、シンチレータ、蛍光体等として広く用いられている。この珪酸ガドリニウム単結晶等は、希土類酸化物の酸化ガドリニウムと珪素酸化物の二酸化珪素を原料として、チョクラルスキー法等の原料融液から単結晶を育成する方法によって製造される。更に、一般には希土類珪酸塩単結晶に蛍光中心としてＣｅ等の添加物をドープしている。蛍光減衰時間等のシンチレータ特性には、構成元素以外の希土類元素及び遷移金属等の不純物が悪影響を与えると考えられ、それらの不純物元素を低減した９９．９９重量％以上の高純度原料（Ｇｄ２Ｏ３、ＳｉＯ２等）を使用して結晶育成が行なわれている。
【０００３】
【発明が解決しようとする課題】
従来の珪酸ガドリニウム単結晶等の希土類珪酸塩単結晶をシンチレータとして用いた場合の発光減衰曲線は２成分からなり、減衰の速い成分（Ｆａｓｔ成分）は３０〜６０ｎｓ、遅い成分（Ｓｌｏｗ成分）は４００〜６００ｎｓであり、その減衰の速い成分（Ｆａｓｔ成分）と遅い成分（Ｓｌｏｗ成分）の出力比（存在比）はそれぞれ７０〜８０％：３０〜２０％程度であった。このため蛍光減衰時間の短縮化が望まれるＰＥＴ（陽電子放出核種断層撮像装置、Ｐｏｓｉｔｒｏｎｅｍｉｓｓｉｏｎ ｃｏｍｐｕｔｅｄ ｔｏｍｏｇｒａｐｈｙ）用シンチレータでは発光減衰曲線の遅い成分（Ｓｌｏｗ成分）のみを高速化させ、その出力比（存在比）を低減することが望まれていた。
本発明は発光減衰曲線の遅い成分（Ｓｌｏｗ成分）を低減し、蛍光減衰時間を短縮化することを特徴とする希土類珪酸塩単結晶を提供するものである。
【０００４】
【課題を解決するための手段】
本発明は、特定の不純物を添加した希土類珪酸塩単結晶、すなわちＡｌを０．４ｐｐｍを超えて５０ｐｐｍ以下含有させることにより蛍光減衰時間を短縮化することを特徴とする希土類珪酸塩単結晶である。希土類成分がガドリニウムであると好ましく、またＣｅをドープした珪酸ガドリニウム単結晶であることが好ましい。
【０００５】
【発明の実施の形態】
本発明者らは、希土類珪酸塩単結晶の発光減衰曲線の２成分：減衰の速い成分（Ｆａｓｔ成分）及び遅い成分（Ｓｌｏｗ成分）とそれぞれの出力比（存在比）と、その原料である希土類珪酸塩単結晶中の不純物濃度について検討した結果、特定の不純物元素を含有させることが、育成した単結晶の特性に影響することを見いだし本発明に達した。すなわち珪酸ガドリニウム単結晶中にＡｌを０．４ｐｐｍを超えて５０ｐｐｍ以下含有させることによって発光減衰曲線の遅い成分（Ｓｌｏｗ成分）を低減し、蛍光減衰時間の短縮化が図られ、シンチレータ特性を向上できることがわかった。
【０００６】
本発明における希土類珪酸塩単結晶中のＡｌの含有量は０．４ｐｐｍを超えて５０ｐｐｍ以下であることが必要であり、好ましくは５ｐｐｍ〜４０ｐｐｍの範囲、最も好ましくは１０〜３０ｐｐｍの範囲である。
【０００７】
不純物Ａｌの含有量が０．４ｐｐｍ以下の場合、発光減衰曲線における遅い成分（Ｓｌｏｗ成分）は低減されず、蛍光減衰時間は短縮化されない。一方、不純物Ａｌの含有量が０．４ｐｐｍを超えると、発光減衰曲線における遅い成分（Ｓｌｏｗ成分）が低減され、蛍光減衰時間は短縮化される。しかし、不純物Ａｌの含有量が５０ｐｐｍを超えると、蛍光出力が急激に減少し劣化する。このため、本発明における不純物Ａｌの含有量は０．４ｐｐｍを超えて５０ｐｐｍ以下であることが必要である。
【０００８】
本発明の希土類珪酸塩単結晶は、珪酸ガドリニウム単結晶以外の、一般式Ｌｎ２−ｘＣｅｘＳｉＯ５（但し、Ｌｎ＝Ｓｃ、Ｙ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ及びＬｕからなる群より選ばれる少なくとも１種の元素を表し、ｘ＝０〜２の値である）で示される希土類珪酸塩単結晶についても、同様の結果となる。以上の希土類珪酸塩単結晶は、珪酸ガドリニウム単結晶の結晶構造と同じ結晶構造を持ち、その構造は空間群Ｐ２１／ｃに属する。
【０００９】
【実施例】
本発明を実施例に基づいて具体的に説明する。原料として酸化ガドリニウム（Ｇｄ２Ｏ３、９９．９９重量％）、二酸化珪素（ＳｉＯ２、９９．９９重量％）、酸化セリウム（ＣｅＯ２、９９．９９重量％）、及び酸化アルミニウム（Ａｌ２Ｏ３、９９．９９重量％）を使用して、チョクラルスキー法によって単結晶を育成した。単結晶から１０×１０×１０ｍｍ３の試料を採取して、シンチレータのエネルギースペクトル（１３７Ｃｓ）及びデジタルオシロにより発光減衰曲線を測定し、蛍光減衰時間、減衰成分の存在比（Ｆａｓｔ成分／Ｓｌｏｗ成分）、及び蛍光出力をまとめて表１に示した。ただし、それぞれの実施例について３本の単結晶を育成し、その平均値を示した。なお、本実施例は好適な一例を示すもので、本発明はこれらの実施例に限定されるものではない。
【００１０】
（実施例１）
Ｃｅ濃度０．４８ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを５．９ｇ、そして酸化アルミニウムを０．００７５ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、原料融液１９５０℃、種結晶の回転数３０ｒｐｍ、引き上げ速度２ｍｍ／ｈの条件で、原料の８０重量％が結晶化した段階で引き上げを完了し、直径５０ｍｍの単結晶を育成した。作製した結晶中のＡｌ濃度測定を、誘導結合プラズマ（ＩＣＰ：Ｉｎｄｕｃｔｉｖｅｌｙ Ｃｏｕｐｌｅｄ Ｐｌａｓｍａ）質量分析法を用いて測定した結果、０．６ｐｐｍであった。
【００１１】
（実施例２）
Ｃｅ濃度０．４８ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを５．９ｇ、そして酸化アルミニウムを０．３ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、原料融液１９５０℃、種結晶の回転数３０ｒｐｍ、引き上げ速度２ｍｍ／ｈの条件で、原料の８０重量％が結晶化した段階で引き上げを完了し、直径５０ｍｍの単結晶を育成した。作製した結晶中のＡｌ濃度測定を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、２４ｐｐｍであった。
【００１２】
（実施例３）
Ｃｅ濃度０．４８ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを５．９ｇ、そして酸化アルミニウムを０．５６２５ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、原料融液１９５０℃、種結晶の回転数３０ｒｐｍ、引き上げ速度２ｍｍ／ｈの条件で、原料の８０重量％が結晶化した段階で引き上げを完了し、直径５０ｍｍの単結晶を育成した。作製した結晶中のＡｌ濃度測定を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、４５ｐｐｍであった。
【００１３】
比較例として、実施例と同様にＣｅ濃度０．４８ｍｏｌ％の珪酸ガドリニウム単結晶の場合の例を説明する。原料として実施例で使用したものと全く同じ（精製ロット番号も同じ）酸化ガドリニウム（Ｇｄ２Ｏ３、９９．９９重量％）と、二酸化珪素（ＳｉＯ２、９９．９９重量％）、酸化セリウム（ＣｅＯ２、９９．９９重量％）及び酸化アルミニウム（Ａｌ２Ｏ３、９９．９９重量％）を使用して、チョクラルスキー法によって単結晶を育成した。単結晶から１０×１０×１０ｍｍ３の試料を採取して、シンチレータのエネルギースペクトル（１３７Ｃｓ）及びデジタルオシロにより発光減衰曲線を測定し、蛍光減衰時間、減衰成分の存在比（Ｆａｓｔ成分／Ｓｌｏｗ成分）、及び蛍光出力をまとめて表１に示した。ただし、それぞれの条件について３本の単結晶を育成し、その平均値を示した。
【００１４】
（比較例１）
Ｃｅ濃度０．４８ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、そして酸化セリウムを５．９ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、原料融液１９５０℃、種結晶の回転数３０ｒｐｍ、引き上げ速度２ｍｍ／ｈの条件で、原料の８０重量％が結晶化した段階で引き上げを完了し、直径５０ｍｍの単結晶を育成した。作製した結晶中のＡｌ濃度測定を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、０ｐｐｍであった。
【００１５】
（比較例２）
Ｃｅ濃度０．４８ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを５．９ｇ、そして酸化アルミニウムを０．００２５ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、原料融液１９５０℃、種結晶の回転数３０ｒｐｍ、引き上げ速度２ｍｍ／ｈの条件で、原料の８０重量％が結晶化した段階で引き上げを完了し、直径５０ｍｍの単結晶を育成した。作製した結晶中のＡｌ濃度測定を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、０．２ｐｐｍであった。
【００１６】
（比較例３）
Ｃｅ濃度０．４８ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを５．９ｇ、そして酸化アルミニウムを０．６５ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、原料融液１９５０℃、種結晶の回転数３０ｒｐｍ、引き上げ速度２ｍｍ／ｈの条件で、原料の８０重量％が結晶化した段階で引き上げを完了し、直径５０ｍｍの単結晶を育成した。作製した結晶中のＡｌ濃度測定を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、５２ｐｐｍであった。
【００１７】
（比較例４）
Ｃｅ濃度０．４８ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを５．９ｇ、そして酸化アルミニウムを０．８７５ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、原料融液１９５０℃、種結晶の回転数３０ｒｐｍ、引き上げ速度２ｍｍ／ｈの条件で、原料の８０重量％が結晶化した段階で引き上げを完了し、直径５０ｍｍの単結晶を育成した。作製した結晶中のＡｌ濃度測定を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、７０ｐｐｍであった。
【００１８】
【表１】
比較例１、２に示したように、不純物Ａｌの濃度が低いと発光減衰曲線の遅い成分（Ｓｌｏｗ成分）は低減されず、蛍光減衰時間は短縮化されない。一方、実施例１〜３に示したように、不純物Ａｌ濃度が０．４ｐｐｍを越すとＳｌｏｗ成分の存在比は低減し、その結果蛍光減衰時間は大きく短縮化される。しかし、比較例３、４に示したように、不純物Ａｌの濃度が５０ｐｐｍを越すと蛍光減衰時間は短縮化されるが、蛍光出力が急激に低下し、シンチレータ特性が劣化する。不純物Ａｌ濃度を０．４ｐｐｍを超えて５０ｐｐｍ以下の範囲に存在させることにより、シンチレータ特性を保ちながら蛍光減衰時間を短縮化させることができ、これによりＰＥＴ装置の高速診断化を図ることができる。
【００２０】
【発明の効果】
本発明による希土類珪酸塩単結晶は発光減衰曲線の遅い成分（Ｓｌｏｗ成分）を低減し、蛍光減衰時間の短縮化を図ることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to rare earth silicate single crystals used for scintillators and the like.
[0002]
[Prior art]
Rare earth silicate single crystals such as gadolinium silicate single crystals are widely used as scintillators, phosphors and the like. The gadolinium silicate single crystal and the like are manufactured by using a rare earth oxide gadolinium oxide and a silicon oxide silicon dioxide as raw materials and growing the single crystal from a raw material melt such as the Czochralski method. Further, in general, a rare earth silicate single crystal is doped with an additive such as Ce as a fluorescent center. It is considered that impurities such as rare earth elements and transition metals other than the constituent elements have an adverse effect on the scintillator characteristics such as the fluorescence decay time, and a high-purity raw material (Gd 2 ) of 99.99% by weight or more in which those impurity elements are reduced. O 3 , SiO 2, etc.) are used for crystal growth.
[0003]
[Problems to be solved by the invention]
When a rare earth silicate single crystal such as a conventional gadolinium silicate single crystal is used as a scintillator, an emission decay curve is composed of two components, a fast-decay component (Fast component) is 30 to 60 ns, and a slow-decay component (Slow component) is 400. The output ratio (existence ratio) of the fast-decay component (Fast component) and the slow-decay component (Slow component) was about 70 to 80%: 30 to 20%, respectively. For this reason, in a scintillator for PET (Positionemission Computed Tomography), for which it is desired to shorten the fluorescence decay time, only the slow component (Slow component) of the emission decay curve is speeded up and its output ratio (existence ratio). It has been desired to reduce this.
The present invention provides a rare earth silicate single crystal characterized by reducing a slow component (Slow component) of an emission decay curve and shortening a fluorescence decay time.
[0004]
[Means for Solving the Problems]
The present invention is a rare earth silicate single crystal to which specific impurities are added, that is, a rare earth silicate single crystal characterized by shortening the fluorescence decay time by containing Al in excess of 0.4 ppm and 50 ppm or less. . The rare earth component is preferably gadolinium, and is preferably a gadolinium silicate single crystal doped with Ce.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
The present inventors have proposed two components of a luminescence decay curve of a rare-earth silicate single crystal: a fast-decay component (Fast component) and a slow-decay component (Slow component), their respective output ratios (existence ratio), and a rare-earth element as a raw material thereof. As a result of studying the impurity concentration in the silicate single crystal, it has been found that the inclusion of a specific impurity element affects the characteristics of the grown single crystal, and the present invention has been achieved. That is, by adding Al in the gadolinium silicate single crystal in an amount of more than 0.4 ppm and 50 ppm or less, a slow component (Slow component) of the emission decay curve is reduced, the fluorescence decay time is shortened, and the scintillator characteristics can be improved. I understood.
[0006]
The content of Al in the rare earth silicate single crystal in the present invention needs to be more than 0.4 ppm and 50 ppm or less, preferably in the range of 5 ppm to 40 ppm, and most preferably in the range of 10 to 30 ppm.
[0007]
When the content of the impurity Al is 0.4 ppm or less, the slow component (Slow component) in the emission decay curve is not reduced, and the fluorescence decay time is not shortened. On the other hand, when the content of the impurity Al exceeds 0.4 ppm, the slow component (Slow component) in the emission decay curve is reduced, and the fluorescence decay time is shortened. However, when the content of the impurity Al exceeds 50 ppm, the fluorescent output sharply decreases and deteriorates. Therefore, the content of the impurity Al in the present invention needs to be more than 0.4 ppm and 50 ppm or less.
[0008]
Rare earth silicate single crystal of the present invention, other than gadolinium silicate single crystal, the formula Ln 2-x Ce x SiO 5 ( where, Ln = Sc, Y, La , Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu represent at least one element selected from the group consisting of x = 0 to 2). Results. The above rare earth silicate single crystal has the same crystal structure as the gadolinium silicate single crystal, and the structure belongs to the space group P21 / c.
[0009]
【Example】
The present invention will be specifically described based on examples. Gadolinium oxide (Gd 2 O 3 , 99.99% by weight), silicon dioxide (SiO 2 , 99.99% by weight), cerium oxide (CeO 2 , 99.99% by weight), and aluminum oxide (Al 2 O) as raw materials 3 , 99.99% by weight) to grow a single crystal by the Czochralski method. A 10 × 10 × 10 mm 3 sample was collected from the single crystal, and the emission spectrum of the scintillator ( 137 Cs) and the emission decay curve were measured using a digital oscilloscope. The fluorescence decay time and the abundance ratio of the decay component (Fast component / Slow component) ) And the fluorescence output are summarized in Table 1. However, three single crystals were grown for each example, and the average value was shown. Note that the present embodiment shows a preferred example, and the present invention is not limited to these embodiments.
[0010]
(Example 1)
A gadolinium silicate single crystal having a Ce concentration of 0.48 mol% was produced as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 5.9 g of cerium oxide, and 0.0075 g of aluminum oxide were weighed and mixed, fired at 1200 ° C., charged into an Ir crucible having a diameter of 100 mm, and charged as raw materials. The pulling was completed at a temperature of 1950 ° C., a rotation speed of the seed crystal of 30 rpm, and a pulling speed of 2 mm / h at the stage when 80% by weight of the raw material was crystallized, and a single crystal having a diameter of 50 mm was grown. As a result of measuring the concentration of Al in the produced crystal by using inductively coupled plasma (ICP) mass spectrometry, the result was 0.6 ppm.
[0011]
(Example 2)
A gadolinium silicate single crystal having a Ce concentration of 0.48 mol% was produced as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 5.9 g of cerium oxide, and 0.3 g of aluminum oxide were weighed and mixed, and fired at 1200 ° C., and then charged into an Ir crucible having a diameter of 100 mm. The pulling was completed at a temperature of 1950 ° C., a rotation speed of the seed crystal of 30 rpm, and a pulling speed of 2 mm / h at the stage when 80% by weight of the raw material was crystallized, and a single crystal having a diameter of 50 mm was grown. As a result of measuring the Al concentration in the produced crystal by using inductively coupled plasma (ICP) mass spectrometry, the result was 24 ppm.
[0012]
Example 3
A gadolinium silicate single crystal having a Ce concentration of 0.48 mol% was produced as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 5.9 g of cerium oxide, and 0.5625 g of aluminum oxide were weighed and mixed, and fired at 1200 ° C., and then charged into an Ir crucible having a diameter of 100 mm. The pulling was completed at a temperature of 1950 ° C., a rotation speed of the seed crystal of 30 rpm, and a pulling speed of 2 mm / h at the stage when 80% by weight of the raw material was crystallized, and a single crystal having a diameter of 50 mm was grown. As a result of measuring the Al concentration in the produced crystal by using inductively coupled plasma (ICP) mass spectrometry, the result was 45 ppm.
[0013]
As a comparative example, an example of a gadolinium silicate single crystal having a Ce concentration of 0.48 mol% as in the example will be described. Gadolinium oxide (Gd 2 O 3 , 99.99% by weight), silicon dioxide (SiO 2 , 99.99% by weight), cerium oxide Single crystals were grown by Czochralski method using CeO 2 , 99.99% by weight) and aluminum oxide (Al 2 O 3 , 99.99% by weight). A 10 × 10 × 10 mm 3 sample was collected from the single crystal, and the emission spectrum of the scintillator ( 137 Cs) and the emission decay curve were measured using a digital oscilloscope. The fluorescence decay time and the abundance ratio of the decay component (Fast component / Slow component) ) And the fluorescence output are summarized in Table 1. However, three single crystals were grown under each condition, and the average value was shown.
[0014]
(Comparative Example 1)
A gadolinium silicate single crystal having a Ce concentration of 0.48 mol% was produced as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide and 5.9 g of cerium oxide are weighed and mixed, fired at 1200 ° C., charged into an Ir crucible having a diameter of 100 mm, and a raw material melt at 1950 ° C. and a seed crystal Under the conditions of a rotation speed of 30 rpm and a pulling speed of 2 mm / h, 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. As a result of measuring the Al concentration in the produced crystal by using inductively coupled plasma (ICP) mass spectrometry, the result was 0 ppm.
[0015]
(Comparative Example 2)
A gadolinium silicate single crystal having a Ce concentration of 0.48 mol% was produced as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 5.9 g of cerium oxide, and 0.0025 g of aluminum oxide were weighed and mixed, fired at 1200 ° C., and then charged into an Ir crucible having a diameter of 100 mm. The pulling was completed at a temperature of 1950 ° C., a rotation speed of the seed crystal of 30 rpm, and a pulling speed of 2 mm / h at the stage when 80% by weight of the raw material was crystallized, and a single crystal having a diameter of 50 mm was grown. As a result of measuring the Al concentration in the produced crystal by using inductively coupled plasma (ICP) mass spectrometry, it was 0.2 ppm.
[0016]
(Comparative Example 3)
A gadolinium silicate single crystal having a Ce concentration of 0.48 mol% was produced as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 5.9 g of cerium oxide, and 0.65 g of aluminum oxide were weighed and mixed, fired at 1200 ° C., and charged into an Ir crucible having a diameter of 100 mm. The pulling was completed when 80% by weight of the raw material was crystallized under the conditions of a melt of 1950 ° C., a rotation speed of the seed crystal of 30 rpm, and a pulling speed of 2 mm / h, and a single crystal having a diameter of 50 mm was grown. As a result of measuring the Al concentration in the produced crystal by using inductively coupled plasma (ICP) mass spectrometry, the result was 52 ppm.
[0017]
(Comparative Example 4)
A gadolinium silicate single crystal having a Ce concentration of 0.48 mol% was produced as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 5.9 g of cerium oxide, and 0.875 g of aluminum oxide were weighed and mixed, fired at 1200 ° C., and charged into an Ir crucible having a diameter of 100 mm. The pulling was completed when 80% by weight of the raw material was crystallized under the conditions of a melt of 1950 ° C., a rotation speed of the seed crystal of 30 rpm, and a pulling speed of 2 mm / h, and a single crystal having a diameter of 50 mm was grown. As a result of measuring the Al concentration in the produced crystal by using inductively coupled plasma (ICP) mass spectrometry, the result was 70 ppm.
[0018]
[Table 1]
As shown in Comparative Examples 1 and 2, when the concentration of the impurity Al is low, the slow component (Slow component) of the emission decay curve is not reduced, and the fluorescence decay time is not shortened. On the other hand, as shown in Examples 1 to 3, when the impurity Al concentration exceeds 0.4 ppm, the abundance ratio of the Slow component decreases, and as a result, the fluorescence decay time is greatly shortened. However, as shown in Comparative Examples 3 and 4, when the concentration of the impurity Al exceeds 50 ppm, the fluorescence decay time is shortened, but the fluorescent output sharply decreases, and the scintillator characteristics deteriorate. When the impurity Al concentration is in the range of more than 0.4 ppm and not more than 50 ppm, the fluorescence decay time can be shortened while maintaining the scintillator characteristics, whereby high-speed diagnosis of the PET apparatus can be achieved.
[0020]
【The invention's effect】
The rare-earth silicate single crystal according to the present invention can reduce the slow component (Slow component) of the emission decay curve and shorten the fluorescence decay time.
Claims (3)
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| JP2002221536A JP4228609B2 (en) | 2002-07-30 | 2002-07-30 | Cerium-activated gadolinium silicate single crystal |
| US10/621,350 US6926847B2 (en) | 2002-07-30 | 2003-07-18 | Single crystals of silicates of rare earth elements |
| DE10334513A DE10334513B4 (en) | 2002-07-30 | 2003-07-29 | A process for producing a single crystal of a cerium-doped gadolinium silicate |
| FR0309375A FR2843131B1 (en) | 2002-07-30 | 2003-07-30 | RARE EARTH ELEMENTS SILICATE MONOCRYSTAL AND SCINTILLATOR CONTAINING SAME |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7282161B2 (en) | 2004-01-20 | 2007-10-16 | Hitachi Chemical Co., Ltd. | Inorganic scintillator |
| JP2008007393A (en) * | 2006-05-30 | 2008-01-17 | Hitachi Chem Co Ltd | Single crystal for scintillator and manufacturing method for the same |
| US8999281B2 (en) * | 2007-06-01 | 2015-04-07 | Hitachi Chemical Company, Ltd. | Scintillator single crystal, heat treatment method for production of scintillator single crystal, and method for production of scintillator single crystal |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7282161B2 (en) | 2004-01-20 | 2007-10-16 | Hitachi Chemical Co., Ltd. | Inorganic scintillator |
| JP2008007393A (en) * | 2006-05-30 | 2008-01-17 | Hitachi Chem Co Ltd | Single crystal for scintillator and manufacturing method for the same |
| US7749323B2 (en) | 2006-05-30 | 2010-07-06 | Hitachi Chemical Company, Ltd. | Single crystal for scintillator and method for manufacturing same |
| US8999281B2 (en) * | 2007-06-01 | 2015-04-07 | Hitachi Chemical Company, Ltd. | Scintillator single crystal, heat treatment method for production of scintillator single crystal, and method for production of scintillator single crystal |
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