JP4605588B2 - Fluoride single crystal for radiation detection, method for producing the same, and radiation detector - Google Patents
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本発明は、新規な放射線検出用フッ化物単結晶及び放射線検出器に関し、特に、主として、Ｘ線断層撮影装置（Ｘ−ｒａｙ Ｃｏｍｐｕｔｅｄ Ｔｏｍｏｇｒａｐｈｙ：Ｘ線ＣＴ）、陽電子放射断層撮影装置（Ｐｏｓｉｔｒｏｎ Ｅｍｉｓｓｉｏｎ ｃｏｍｐｕｔｅｄ Ｔｏｍｏｇｒａｐｈｙ：ＰＥＴ）、タイム・オブ・フライト陽電子放射断層撮影装置（Ｔｉｍｅ−Ｏｆ−Ｆｌｉｇｈｔ Ｐｏｓｉｔｒｏｎ Ｅｍｉｓｓｉｏｎ ｃｏｍｐｕｔｅｄ Ｔｏｍｏｇｒａｐｈｙ：ＴＯＦ−ＰＥＴ）などの医療診断装置に用いられる放射線検出用フッ化物単結晶及び放射線検出器に関する。また、本発明の放射線検出用フッ化物単結晶は、ＰＣＥなどの発光材料としても使用することができる。 The present invention relates to a novel fluoride single crystal for radiation detection and a radiation detector. In particular, the present invention mainly relates to an X-ray computed tomography (X-ray CT), a positron emission computed tomography (Positron emission computed tomography). : PET), and a fluoride single crystal for radiation detection and a radiation detector used in medical diagnostic apparatuses such as Time-of-Flight Positron Emission Tomography (TOF-PET). Moreover, the fluoride single crystal for radiation detection of the present invention can also be used as a light emitting material such as PCE.
従来、医療診断や工業用非破壊検査などに放射線が利用され、例えば、医療装置として、Ｘ線ＣＴ、ＰＥＴが実用化されている。このような放射線を用いた装置には、γ線やＸ線などの放射線を検出するための検出器、例えば、シンチレータが使用されている。 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 detector for detecting radiation such as γ-rays and X-rays, for example, a scintillator is used.
ここで、シンチレータは、γ線やＸ線などの放射線の刺激により可視光線又は可視光線に近い波長の電磁波を放射する物質であり、密度が高いこと、蛍光の減衰時間が短いこと、及び耐放射線性に優れていることが要求される。 Here, the scintillator is a substance that radiates visible light or electromagnetic waves having a wavelength close to visible light by stimulation of radiation such as γ-rays or X-rays, and has a high density, a short fluorescence decay time, and radiation resistance. It is required to have excellent properties.
このようなＰＥＴ用のシンチレータ材料としては、従来、ビスマスジャーマネイト（Ｂｉ４Ｇｅ３Ｏ１２単結晶（ＢＧＯ））が使用されていたが、高性能な特性を求めてセリウムをドープしたガドリニウムシリケート（Ｃｅ：Ｇｄ２ＳｉＯ５（Ｃｅ：ＧＳＯ））単結晶が開発され、実用化された（特許文献１参照）。 As such a scintillator material for PET, bismuth germanate (Bi 4 Ge 3 O 12 single crystal (BGO)) has been conventionally used. However, cerium-doped gadolinium silicate ( A Ce: Gd 2 SiO 5 (Ce: GSO)) single crystal was developed and put to practical use (see Patent Document 1).
また、その後、さらに高性能な特性を求めて種々の検討が行われ、セリウムをドープしたルテチウムオキシオルトシリケート結晶（Ｃｅ：Ｌｕ２ＳｉＯ５：（Ｃｅ：ＬＳＯ））が開発され、現在最も高性能なものとして実用化されている（特許文献２、３、４等参照）。
After that, various studies were conducted to obtain higher performance characteristics, and cerium-doped lutetium oxyorthosilicate crystals (Ce: Lu 2 SiO 5 : (Ce: LSO)) were developed. (See
しかしながら、酸化物シンチレータは、融点が高いためチョクラルスキー法を用いた育成ではホットゾーンへダメージが大きくかつ融点が高い分エネルギーコストが高価になり、また、組成に含まれる元素の種類が多く結晶育成の組成ずれを防ぐため仕込み比をシビアに制御する必要があるという問題がある。 However, because oxide scintillators have a high melting point, growing using the Czochralski method causes significant damage to the hot zone and increases the energy cost due to the high melting point, and there are many types of elements included in the composition. There is a problem that it is necessary to severely control the charging ratio in order to prevent the composition deviation of the growth.
そこで、現在、酸化物以外では、光学レンズ用などとして製造されているＢａＦ２およびＣｓＦを併用したシンチレータがＴＯＦ−ＰＥＴへ応用検討されているがＣｓＦは潮解性があり問題がある。また、従来から検討されているＣｅＦ３は、蛍光寿命に優れているが蛍光強度はやや低いなどの課題がある（非特許文献１）。 Therefore, other than oxides, scintillators using BaF 2 and CsF, which are manufactured for optical lenses and the like, are currently being applied to TOF-PET, but CsF has a problem of deliquescence. Further, CeF 3 which has been studied conventionally has problems such as excellent fluorescence lifetime but slightly low fluorescence intensity (Non-patent Document 1).
このような単結晶以外に、各種のセラミック材料がシンチレータとして検討され、ＢａＦＣｌ：Ｅｕ、ＬａＯＢｒ：Ｔｂ、ＣｓＩ：Ｔｌ、ＣａＷＯ４、ＣｄＷＯ４などの多結晶体（セラミックス）（特許文献５等参照）、（Ｇｄ，Ｙ）２Ｏ３：Ｅｕのような立方晶構造を有する希土類酸化物の多結晶体（セラミックス）（特許文献６等参照）、Ｇｄ２Ｏ２Ｓ：Ｐｒのような希土類酸硫化物の多結晶体（セラミックス）（特許文献７等参照）などが知られている。 In addition to such single crystals, various ceramic materials have been studied as scintillators, and polycrystals (ceramics) such as BaFCl: Eu, LaOBr: Tb, CsI: Tl, CaWO 4 , and CdWO 4 (see Patent Document 5, etc.) , (Gd, Y) 2 O 3 : Polycrystalline rare earth oxide (ceramics) having a cubic structure such as Eu (see Patent Document 6), rare earth oxysulfide such as Gd 2 O 2 S: Pr Known are polycrystals (ceramics) of products (see Patent Document 7, etc.).
このようなセラミックシンチレータ材料は、粉末を焼結して製造されるため、透明性（透光性）の改良、焼結性の改良などに関して種々の提案がなされている。例えば、Ｇｄ２Ｏ２Ｓ：Ｐｒなどの蛍光体セラミックス中の不純物量、特に燐酸塩（ＰＯ４）の含有量を１００ｐｐｍ以下とすることによって、シンチレータの光出力を向上させるという提案がある（特許文献８参照）。また、希土類酸硫化物粉末にＬｉＦ、Ｌｉ２ＧｅＦ６、ＮａＢＦ４のようなフッ化物を焼結助剤として添加し、これらの混合粉末を熱間静水圧プレス（ＨＩＰ）で焼結することによって、高密度化させた蛍光体セラミックスが提案されている（特許文献９参照）。 Since such a ceramic scintillator material is manufactured by sintering powder, various proposals have been made regarding improvement of transparency (translucency), improvement of sinterability, 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 (patent) Reference 8). 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 highly densified phosphor ceramic has been proposed (see Patent Document 9).
なお、フッ化物単結晶は、その広範囲に亘る高い透過性、小さな結晶場、屈折率の温度係数が負であることから、レーザー用結晶として大きな期待を集めていたが、ＣｅＦ３、ＣｓＦおよびＢａＦ２以外の単結晶についてはシンチレータなどの放射線検出用材料として応用検討は殆どなされていない。一方、フッ化物単結晶は作製雰囲気、作製温度、原料の純度や組成の制御等、作製を困難にする要因が多数存在するので、大きなバルク結晶を製造すること自体困難であった。そこで本発明者は高品位な単結晶を安全かつ容易に作製する技術を開発し（特許文献１０参照）、レーザー用単結晶として、フッ化リチウムカルシウムアルミニウム（特許文献１１参照）、フッ化バリウムリチウム単結晶（特許文献１２参照）を製造している。さらに、フッ化リチウムカルシウムアルミニウムに関してはシンチレータとして使用できる特性を有していることを報告した（非特許文献２、非特許文献３参照）が、密度が２．９４ｇ／ｃｍ３と小さく、γ線の吸収係数が小さいという問題があった。 In addition, since fluoride single crystals have a high transmittance over a wide range, a small crystal field, and a negative temperature coefficient of refractive index, they have attracted great expectations as laser crystals. However, CeF 3 , CsF and BaF For single crystals other than 2 , almost no application studies have been made as radiation detection materials such as scintillators. On the other hand, since there are many factors that make it difficult to produce a fluoride single crystal, such as the production atmosphere, production temperature, purity of raw materials, and control of composition, it is difficult to produce a large bulk crystal. Therefore, the present inventor has developed a technique for producing a high-quality single crystal safely and easily (see Patent Document 10), and as a single crystal for laser, lithium calcium aluminum fluoride (see Patent Document 11), barium lithium fluoride. A single crystal (see Patent Document 12) is manufactured. Furthermore, it has been reported that lithium calcium aluminum fluoride has characteristics that can be used as a scintillator (see Non-Patent Document 2 and Non-Patent Document 3), but the density is as small as 2.94 g / cm 3, and γ rays There was a problem that the absorption coefficient of was small.
本発明は上述した事情に鑑み、従来の材料より容易に結晶育成ができ、放射線に対して応答性を有する放射線検出用フッ化物単結晶及びそれを用いた放射線検出器を提供することを課題とする。 In view of the circumstances described above, the present invention has an object to provide a radiation detection fluoride single crystal that can grow crystals more easily than conventional materials and has a response to radiation, and a radiation detector using the same. To do.
前記課題を解決する本発明の第１の態様は、軽希土類フッ化物単結晶であって、Ｐｒ、Ｌｕ及びＦを含有し、Ｐｒ１−ｘ Ｌｕ ｘＦ３（ｘ≦０．５）で表されることを特徴とする放射線検出用フッ化物単結晶にある。 A first aspect of the present invention to solve the above problems is a light rare earth fluoride single crystal, Pr, containing Lu及 beauty with F, Pr 1-x Lu x F 3 (x ≦ 0.5) It exists in the fluoride single crystal for radiation detection characterized by being represented.
本発明の第２の態様は、第１の態様の放射線検出用フッ化物単結晶からなるシンチレータと、このシンチレータからの発光を検出する光検出器とを具備することを特徴とする放射線検出器にある。
本発明の第３の態様は、１０−４〜１０−５ｔｏｒｒの高真空を保ちながら、粉末又はバルク状多結晶フッ化物原料を室温から原料の融点以下の温度まで加熱し、フロン系ガス及びアルゴンガスを導入してから温度を融点以上に上げ、融液あるいは溶液表面に発生する不純物および融液あるいは溶液内に存在する不純物とガスとを反応させて、不純物を除去し、得られた融液あるいは溶液から成長させることを特徴とする第１の態様の放射線検出用フッ化物単結晶の製造方法にある。
According to a second aspect of the present invention, there is provided a radiation detector comprising the scintillator made of the fluoride single crystal for radiation detection according to the first aspect and a photodetector for detecting light emitted from the scintillator. is there.
In the third aspect of the present invention, while maintaining a high vacuum of 10 −4 to 10 −5 torr, the powder or bulk polycrystalline fluoride raw material is heated from room temperature to a temperature not higher than the melting point of the raw material, After introducing argon gas, the temperature is raised to the melting point or higher, impurities generated on the surface of the melt or solution and impurities present in the melt or solution react with the gas to remove the impurities, and the resulting melt is obtained. The method for producing a fluoride single crystal for radiation detection according to the first aspect, characterized by growing from a liquid or a solution.
本発明の放射線検出用フッ化物単結晶は、従来の材料より容易に結晶育成ができ、放射線に対して応答性を有するという効果を奏する。 The fluoride single crystal for radiation detection according to the present invention has the effect of being able to grow crystals more easily than conventional materials and being responsive to radiation.
本発明の放射線検出用フッ化物単結晶は、軽希土類フッ化物単結晶であって、ＲＥＦ３（ＲＥは、ＮｄおよびＰｒから選択される少なくとも一種である）からなる。蛍光波長が可視領域にあり、かつ蛍光強度が大きいほど解像度向上に寄与するから、プラセオジムＰｒが特に好ましい。 The fluoride single crystal for radiation detection of the present invention is a light rare earth fluoride single crystal, and is composed of REF 3 (RE is at least one selected from Nd and Pr). Praseodymium Pr is particularly preferable because the fluorescence wavelength is in the visible region and the higher the fluorescence intensity, the more the resolution is improved.
かかるフッ化物単結晶は、軽希土類でも単結晶密度が高く、蛍光の減衰時間が短く、蛍光の強度も大きいので、シンチレータなどの放射線検出用材料として有用である。 Such a fluoride single crystal is useful as a radiation detection material such as a scintillator because it has a high single crystal density even in a light rare earth, has a short fluorescence decay time, and has a high fluorescence intensity.
本発明の放射線検出用フッ化物単結晶である軽希土類フッ化物単結晶は、γ線やＸ線などの放射線の刺激により可視光線又は可視光線に近い波長の電磁波を放射するシンチレータ等としての特性を有するものであれば、製造方法としては特に限定されない。 The light rare earth fluoride single crystal, which is a fluoride single crystal for radiation detection of the present invention, has characteristics as a scintillator that emits visible light or electromagnetic waves having a wavelength close to visible light upon stimulation of radiation such as γ-rays or X-rays. If it has, it will not specifically limit as a manufacturing method.
本発明の軽希土類フッ化物は、複数の希土類フッ化物が複合した単結晶でもよく、また、希土類元素の一部を他の元素で置換したものとしてもよい。希土類元素の一部を他の元素で置換することにより、発光量の調整や発光波長のシフトをすることができる。 The light rare earth fluoride of the present invention may be a single crystal in which a plurality of rare earth fluorides are combined, or a part of the rare earth element may be substituted with another element. By replacing a part of the rare earth element with another element, the light emission amount can be adjusted and the light emission wavelength can be shifted.
このような他の元素としては、ＲＥ及びＬａ以外の希土類元素、すなわち、セリウムＣｅ、プラセオジムＰｒ、ネオジムＮｄ、プロメチウムＰｍ、サマリウムＳｍ、ユウロピウムＥｕ、ガドリニウムＧｄ、テルビウムＴｂ、ジスプロシウムＤｙ、ホルミウムＨｏ、エルビウムＥｒ、ツリウムＴｍ、イッテルビウムＹｂ、ルテチウムＬｕから選択される少なくとも一種の元素Ｒを挙げることができるが、好ましくは、Ｎｄ、Ｐｒ、Ｌｕ、Ｇｄ、Ｓｍ、Ｅｕ、Ｔｍ、Ｈｏ、Ｅｒ、Ｔｂ、Ｄｙを挙げることができる。 Such other elements include rare earth elements other than RE and La, that is, cerium Ce, praseodymium Pr, neodymium Nd, promethium Pm, samarium Sm, europium Eu, gadolinium Gd, terbium Tb, dysprosium Dy, holmium Ho, erbium. Although at least one element R selected from Er, thulium Tm, ytterbium Yb, and lutetium Lu can be mentioned, Nd, Pr, Lu, Gd, Sm, Eu, Tm, Ho, Er, Tb, Dy are preferable. Can be mentioned.
このような元素は５０モル％程度まで置換することができる。すなわち、希土類フッ化物単結晶は、ＲＥ１−ｘＲｘＦ３で表され、ｘは０．５以下、好ましくは０．２以下、さらに好ましくは、０．０１〜０．１である。ｘが０．５より大きいと、希土類フッ化物単結晶の特性が置換した元素Ｒに大きく依存するため、発光量の低下およびホスト材と異なる性質になる場合がある。なお、このような置換元素は、１モル％程度まではドーパントともいう。 Such elements can be substituted up to about 50 mol%. That is, the rare earth fluoride single crystal is represented by RE 1-x R x F 3 , where x is 0.5 or less, preferably 0.2 or less, and more preferably 0.01 to 0.1. When x is larger than 0.5, the characteristics of the rare earth fluoride single crystal greatly depend on the substituted element R, so that the light emission amount may be reduced and the property may be different from that of the host material. Such a substitution element is also called a dopant up to about 1 mol%.
また、置換元素は、ランタンＬａであってもよい。Ｌａは、同じ軽希土類であるため、クラックおよびインクルージョンが少ない状態でＮｄ及びＰｒを置換することが可能であり、使用量に応じて発光量および発光波長を幅広く変化させることができる。なお、Ｌａは９５モル％程度まで置換することができる。Ｌａを含む希土類フッ化物単結晶は、（ＲＥ１−ｘＲｘ）１−ｙＬａｙＦ３（０≦ｘ≦０．５）で表され、ｙは０．９５以下、好ましくは０．７以下、さらに好ましくは０．２〜０．５である。ｙが０．２より小さいと特性が大きく変化せず、また、０．９５より大きいと添加したランタンに大きく依存してしまうためＲＥおよびＲの特徴が低下する。 Further, the substitution element may be lanthanum La. Since La is the same light rare earth, it is possible to replace Nd and Pr with few cracks and inclusions, and the emission amount and emission wavelength can be changed widely depending on the amount used. La can be substituted up to about 95 mol%. Rare earth fluoride single crystals containing La is represented by (RE 1-x R x) 1-y La y F 3 (0 ≦ x ≦ 0.5), y is 0.95 or less, preferably 0.7 Hereinafter, it is more preferably 0.2 to 0.5. If y is less than 0.2, the characteristics do not change significantly, and if it is greater than 0.95, the characteristics of RE and R deteriorate because it depends greatly on the added lanthanum.
一方、このようなフッ化物単結晶が放射線を吸収した際に発生する蛍光の強度を増大させ、シンチレータとしての特性を向上させるため、フッ化物単結晶の相転移を防止するため、又は蛍光ピークをシフトするためなどに、必要に応じて他のドーパントを添加してもよい。このようなドーパントは、好ましくはフッ化物で添加するが、蛍光の波長に吸収が存在しないものを用いるのが好ましい。このようなドーパントは、例えば、モル比で０．０１％〜１％程度添加することができる。なお、このようなドーパントを添加すると、蛍光の強度、発光波長や蛍光寿命が変化する場合があるので、所望の特性に併せて適宜選択する必要がある。 On the other hand, in order to increase the intensity of fluorescence generated when such a fluoride single crystal absorbs radiation and improve the characteristics as a scintillator, to prevent the phase transition of the fluoride single crystal, or to increase the fluorescence peak For shifting, other dopants may be added as necessary. Such a dopant is preferably added as a fluoride, but it is preferable to use a dopant having no absorption at the fluorescence wavelength. Such a dopant can be added, for example, in a molar ratio of about 0.01% to 1%. Note that when such a dopant is added, the fluorescence intensity, emission wavelength, and fluorescence lifetime may change, so it is necessary to select them appropriately in accordance with desired characteristics.
本発明の放射線検出用フッ化物単結晶は、ＰＥＴ又はＴＯＦ−ＰＥＴの検出器のシンチレータなどとして使用するので、高品質、かつ均質なバルク結晶を得る必要がある。このようなバルク結晶を得るためには、下記に示すような製造法によるのが好ましい。 Since the fluoride single crystal for radiation detection of the present invention is used as a scintillator for a PET or TOF-PET detector, it is necessary to obtain a high-quality and homogeneous bulk crystal. In order to obtain such a bulk crystal, it is preferable to use a production method as described below.
すなわち、本発明の放射線検出用フッ化物単結晶は、好適には、融液成長法、あるいは溶液成長法によって製造するが、本発明の希土類フッ化物を製造するためには、以下の条件によって融液成長法、あるいは溶液成長法により製造するのが好ましい。この条件は、１０−４〜１０−５ｔｏｒｒの高真空を保ちながら、粉末又はバルク状多結晶フッ化物原料を室温から原料の融点以下の温度、例えば、５００〜８００℃の温度まで加熱し、炉内にＣＦ４などのフロン系ガス及びアルゴンガスを導入してから（混合比、フロン系ガス：アルゴンガス＝１００：０〜０：１００、体積比）温度を融点以上に上げ、融液あるいは溶液表面に発生する不純物および融液あるいは溶液内に存在する不純物とガスとを反応させて、不純物を除去し、得られた融液あるいは溶液から成長させるようにする。 That is, the fluoride single crystal for radiation detection of the present invention is preferably produced by a melt growth method or a solution growth method, but in order to produce the rare earth fluoride of the present invention, it is melted under the following conditions. It is preferable to manufacture by a liquid growth method or a solution growth method. This condition is that while maintaining a high vacuum of 10 −4 to 10 −5 torr, the powder or bulk polycrystalline fluoride raw material is heated from room temperature to a temperature below the melting point of the raw material, for example, a temperature of 500 to 800 ° C., After introducing a fluorocarbon gas such as CF 4 and an argon gas into the furnace (mixing ratio, fluorocarbon gas: argon gas = 100: 0 to 0: 100, volume ratio), the temperature is raised above the melting point, The impurities generated on the solution surface and the melt or impurities present in the solution are reacted with the gas to remove the impurities and grow from the obtained melt or solution.
上記製造方法によって、例えば、純度９９．９重量％程度のフッ化物原料を使った場合でも、従来技術の方法に比してより簡便に、高品質な単結晶を製造することが可能となる。また、本発明のフッ化物単結晶は、不純物を除去して得た融液又は溶液からＡｒなどの不活性ガス雰囲気下で融液成長法、あるいは溶液成長法によってフッ化物単結晶を作製することが可能となる。 According to the above manufacturing method, for example, even when a fluoride raw material having a purity of about 99.9% by weight is used, it is possible to manufacture a high-quality single crystal more easily than the conventional method. The fluoride single crystal of the present invention can be prepared from a melt or solution obtained by removing impurities by a melt growth method or a solution growth method in an inert gas atmosphere such as Ar. Is possible.
以下に、本発明の放射線検出用フッ化物単結晶についてより詳細に説明する。 Hereinafter, the fluoride single crystal for radiation detection of the present invention will be described in more detail.
本発明の放射線検出用フッ化物単結晶は、粉末又は多結晶の希土類フッ化物原料、すなわち、フッ化プラセオジム（ＰｒＦ３）などのマトリックス用原料に、必要に応じてフッ化ネオジム（ＮｄＦ３）などの置換元素、さらにはドーパント用原料を坩堝内に充填し、炉内・原料内に含まれる水分および酸素の除去のため１０−４〜１０−５ｔｏｒｒ程度の高真空を保ちながら、上記フッ化物原料を室温から５００〜８００℃程度、すなわち、融点を超えない所定の温度まで加熱する。次に、作製炉内にＣＦ４などのフロン系ガス及びアルゴンガスを導入してから（混合比、フロン系ガス：アルゴンガス＝１００：０〜０：１００、体積比）温度を融点以上に上昇し、融液又は溶液表面に発生する不純物および融液又は溶液内に存在する不純物とフロン系ガスとを反応させ、不純物を除去するようにする。そして、得られた融液あるいは溶液から希土類フッ化物単結晶を製造する。なお、ドーパントを添加する場合には、例えば、ドーパントのフッ化物を適量添加すればよい。 The fluoride single crystal for radiation detection of the present invention is a powder or polycrystalline rare earth fluoride raw material, that is, a matrix raw material such as praseodymium fluoride (PrF 3 ), and neodymium fluoride (NdF 3 ) as required. The above-mentioned fluoride is maintained while maintaining a high vacuum of about 10 −4 to 10 −5 torr in order to remove moisture and oxygen contained in the furnace and the raw material. The raw material is heated from room temperature to about 500 to 800 ° C., that is, a predetermined temperature not exceeding the melting point. Next, after introducing a chlorofluorocarbon gas such as CF 4 and an argon gas into the production furnace (mixing ratio, chlorofluorocarbon gas: argon gas = 100: 0 to 0: 100, volume ratio), the temperature is raised to the melting point or higher. Then, impurities generated on the surface of the melt or solution and impurities present in the melt or solution are reacted with the fluorocarbon gas to remove the impurities. Then, a rare earth fluoride single crystal is produced from the obtained melt or solution. In addition, when adding a dopant, what is necessary is just to add the fluoride of a dopant, for example.
このようにして得られる融液又は溶液からの単結晶の製造方法は特に限定されず、引き上げ法やブリッジマン法等を用いればよい。例えば、引き上げ法によると、融液の温度を各化合物の融点近辺に保ち、種結晶を１〜５０ｒｐｍで回転させながら０．１〜１０ｍｍ／ｈの速度で引き上げることによって、結晶中に気泡やスキャッタリングセンターなどのない、透明な高品質単結晶が得られる。また、本発明のフッ化物単結晶は、融解後、徐冷するだけでも単結晶が得られ、条件を適宜設定すれば、種結晶を用いることなく、徐冷するだけで単結晶が得られるという特長を有する。 The method for producing a single crystal from the melt or solution thus obtained is not particularly limited, and a pulling method, a Bridgman method, or the like may be used. For example, according to the pulling method, the temperature of the melt is kept in the vicinity of the melting point of each compound, and the seed crystal is lifted at a speed of 0.1 to 10 mm / h while rotating at 1 to 50 rpm. A transparent high-quality single crystal without a ring center is obtained. In addition, the fluoride single crystal of the present invention can be obtained only by slow cooling after melting, and if the conditions are set appropriately, the single crystal can be obtained by slow cooling without using a seed crystal. Has features.
このようにして得られる希土類フッ化物単結晶は、ＰＥＴやＴＯＦ−ＰＥＴ用のシンチレータとして有用である。 The rare earth fluoride single crystal thus obtained is useful as a scintillator for PET or TOF-PET.
このような希土類フッ化物単結晶を所定の寸法に切り出したシンチレータは、放射線、例えば、Ｘ線又はγ線を吸収することにより発生する蛍光の波長に合わせた光検出器、例えば、可視光又は紫外線の光電子増倍管などの光検出器と組み合わせることにより、放射線検出器とすることができる。 A scintillator obtained by cutting such a rare earth fluoride single crystal into a predetermined size is a photodetector that matches the wavelength of fluorescence generated by absorbing radiation, for example, X-rays or γ-rays, such as visible light or ultraviolet light. By combining with a photodetector such as a photomultiplier tube, a radiation detector can be obtained.
（実施例１）
純度９９．９９％の市販のバルク粉砕原料であるＰｒＦ３を準備し、これを坩堝内に充填した。それをそのまま単結晶作製炉内に置き、１０−４〜１０−５ｔｏｒｒ程度まで真空に引き、そのまま約７００℃程度まで真空状態で加熱し炉内・原料中の水分・酸素を除去した。ここでＣＦ４及びアルゴンガスを単結晶作製炉内に導入し、混合ガス雰囲気中で原料を加熱融解し、そのまま１時間、液体状態で保った。このとき、液体表面に現れた不純物は、ＣＦ４ガスと反応することにより、全て消滅した。次に融液に種結晶を接触させ、ｃ軸方向に引き上げ速度２ｍｍ／ｈ、回転数１０ｒｐｍで引き上げ単結晶を成長・作製した。作製した結晶は、直径約１５ｍｍ、長さ約７０ｍｍで、気泡、クラックおよびスキャッタリングセンターなどの無く、緑色透明かつ高品質なフッ化プラセオジム（ＰｒＦ３）単結晶であった。得られたＰｒＦ３単結晶の密度は６．２９ｇ／ｃｍ３であった。
Example 1
PrF 3 , which is a commercially available bulk pulverized raw material with a purity of 99.99%, was prepared and filled in a crucible. It was placed in a single crystal production furnace as it was, evacuated to about 10 −4 to 10 −5 torr, and heated as it was in a vacuum state to about 700 ° C. to remove moisture and oxygen in the furnace and raw materials. Here, CF 4 and argon gas were introduced into the single crystal production furnace, the raw material was heated and melted in a mixed gas atmosphere, and kept in a liquid state for 1 hour. At this time, all impurities appearing on the liquid surface disappeared by reacting with CF 4 gas. Next, the seed crystal was brought into contact with the melt, and a single crystal was grown and produced in the c-axis direction at a pulling speed of 2 mm / h and a rotation speed of 10 rpm. The produced crystal was a green transparent, high-quality praseodymium fluoride (PrF 3 ) single crystal having a diameter of about 15 mm and a length of about 70 mm, without bubbles, cracks, and a scattering center. The density of the obtained PrF 3 single crystal was 6.29 g / cm 3 .
（実施例２）
純度９９．９９％の市販のバルク粉砕原料であるＮｄＦ３を準備し、これを坩堝内に充填したのち、実施例１と同様に、結晶を育成した。作製した結晶は、直径約２５ｍｍ、長さ約７０ｍｍで、気泡、クラックおよびスキャッタリングセンターなどの無く、緑色透明かつ高品質なフッ化ネオジム（ＮｄＦ３）単結晶であった。得られたＮｄＦ３単結晶の密度は６．５０ｇ／ｃｍ３であった。
(Example 2)
After preparing NdF 3 which is a commercially available bulk pulverized raw material having a purity of 99.99% and filling this into a crucible, crystals were grown in the same manner as in Example 1. The produced crystal was a green transparent and high-quality neodymium fluoride (NdF 3 ) single crystal having a diameter of about 25 mm and a length of about 70 mm, without bubbles, cracks, and a scattering center. The density of the obtained NdF 3 single crystal was 6.50 g / cm 3 .
（実施例３）
純度９９．９９％の市販のバルク粉砕原料であるＰｒＦ３を準備し、これを坩堝内に充填した。それをそのまま単結晶作製炉内に置き、１０−４〜１０−５ｔｏｒｒ程度まで真空に引き、そのまま約７００℃程度まで真空状態で加熱し炉内・原料中の水分・酸素を除去した。ここでＣＦ４ガス及びアルゴンガスを単結晶作製炉内に導入し、混合ガス雰囲気中で原料を加熱融解し、そのまま１時間、液体状態で保った。このとき、液体表面に現れた不純物は、ＣＦ４ガスと反応することにより、全て消滅した。次に融液を２４時間かけて徐々に冷却し、気泡、クラックなどの無く、緑色透明かつ高品質なフッ化プラセオジム（ＰｒＦ３）単結晶を作製した。作製した結晶は、直径約６０ｍｍ、長さ約１５ｍｍで、気泡およびクラックおよびスキャッタリングセンターなどの無く、緑色透明かつ高品質なフッ化プラセオジム（ＰｒＦ３）単結晶であった。
(Example 3)
PrF 3 , which is a commercially available bulk pulverized raw material with a purity of 99.99%, was prepared and filled in a crucible. It was placed in a single crystal production furnace as it was, evacuated to about 10 −4 to 10 −5 torr, and heated as it was in a vacuum state to about 700 ° C. to remove moisture and oxygen in the furnace and raw materials. Here, CF 4 gas and argon gas were introduced into the single crystal production furnace, the raw material was heated and melted in a mixed gas atmosphere, and kept in a liquid state for 1 hour. At this time, all impurities appearing on the liquid surface disappeared by reacting with CF 4 gas. Next, the melt was gradually cooled over 24 hours to produce a green transparent and high-quality praseodymium fluoride (PrF 3 ) single crystal without bubbles and cracks. The produced crystal was a green transparent and high-quality praseodymium fluoride (PrF 3 ) single crystal having a diameter of about 60 mm and a length of about 15 mm, without bubbles, cracks, and a scattering center.
（実施例４）
純度９９．９９％の市販のバルク粉砕原料であるＰｒＦ３を準備し、これを坩堝内に充填したのち、ドーパントとしてＮｄＦ３を１モル％坩堝内に充填し、実施例１と同様に、結晶を育成した。
Example 4
PrF 3 which is a commercially available bulk pulverized raw material with a purity of 99.99% was prepared, and this was filled in a crucible, and then NdF 3 was filled in a 1 mol% crucible as a dopant. Nurtured.
（実施例５）
ドーパントとしてＮｄＦ３の代わりに、ＴｂＦ３を１モル％用いた以外は実施例４と同様に、結晶を育成した。
(Example 5)
A crystal was grown in the same manner as in Example 4 except that 1 mol% of TbF 3 was used instead of NdF 3 as a dopant.
（実施例６）
ドーパントとしてＮｄＦ３の代わりに、ＤｙＦ３を１モル％用いた以外は実施例４と同様に、結晶を育成した。
(Example 6)
A crystal was grown in the same manner as in Example 4 except that 1 mol% of DyF 3 was used instead of NdF 3 as a dopant.
（実施例７）
ドーパントとしてＮｄＦ３の代わりに、ＥｕＦ３を１モル％用いた以外は実施例４と同様に、結晶を育成した。
(Example 7)
A crystal was grown in the same manner as in Example 4 except that 1 mol% of EuF 3 was used instead of NdF 3 as a dopant.
（実施例８）
ドーパントとしてＮｄＦ３の代わりに、ＥｒＦ３を１モル％用いた以外は実施例４と同様に、結晶を育成した。
(Example 8)
A crystal was grown in the same manner as in Example 4 except that 1 mol% of ErF 3 was used instead of NdF 3 as a dopant.
（実施例９）
ドーパントとしてＮｄＦ３の代わりに、ＴｍＦ３を１モル％用いた以外は実施例４と同様に、結晶を育成した。
Example 9
A crystal was grown in the same manner as in Example 4 except that 1 mol% of TmF 3 was used instead of NdF 3 as a dopant.
（実施例１０）
ドーパントとしてＮｄＦ３の代わりに、ＨｏＦ３を１モル％用いた以外は実施例４と同様に、結晶を育成した。
(Example 10)
A crystal was grown in the same manner as in Example 4 except that 1 mol% of HoF 3 was used instead of NdF 3 as a dopant.
（実施例１１）
ドーパントとしてＮｄＦ３の代わりに、ＣｅＦ３を１モル％用いた以外は実施例４と同
様に、結晶を育成した。
(Example 11)
A crystal was grown in the same manner as in Example 4 except that 1 mol% of CeF 3 was used instead of NdF 3 as a dopant.
（実施例１２）
ドーパントとしてＮｄＦ３の代わりに、ＬｕＦ３を１モル％用いた以外は実施例４と同
様に、結晶を育成した。
(Example 12)
A crystal was grown in the same manner as in Example 4 except that 1 mol% of LuF 3 was used instead of NdF 3 as a dopant.
（試験例）
実施例１及び実施例２のＰｒＦ３単結晶及びＮｄＦ３単結晶のＸ線回折プロファイルを図１に示す。この結果、実施例１及び実施例２の単結晶が、それぞれＰｒＦ３単結晶及びＮｄＦ３単結晶であることが確認された。
(Test example)
The X-ray diffraction profiles of the PrF 3 single crystal and the NdF 3 single crystal of Example 1 and Example 2 are shown in FIG. As a result, it was confirmed that the single crystals of Example 1 and Example 2 were a PrF 3 single crystal and an NdF 3 single crystal, respectively.
実施例１で得られたＰｒＦ３単結晶についてＸ線蛍光スペクトルを測定した結果を図２に示す。この結果、発光波長が緑−赤領域にピークがなく、４００ｎｍに鋭いピークがあることがわかった。 The result of measuring the X-ray fluorescence spectrum of the PrF 3 single crystal obtained in Example 1 is shown in FIG. As a result, it was found that the emission wavelength had no peak in the green-red region and a sharp peak at 400 nm.
また、実施例１で得られたＰｒＦ３単結晶について、Ｘ線照射で蛍光寿命を測定した結果を図３に示す。この結果、蛍光寿命が５１０ｎｓｅｃでアフターグローは見られなかった。 Further, the PrF 3 single crystal obtained in Example 1 shows the results of measurement of the fluorescence lifetime at X-ray irradiation in FIG. As a result, afterglow was not observed at a fluorescence lifetime of 510 nsec.
さらに、実施例１で得られたＰｒＦ３単結晶のＸ線蛍光強度をＢＧＯと比較した結果を図４に示す。この結果、蛍光強度はＢＧＯより僅かに低いが、ほぼ同等の値を示すことがわかった。 Furthermore, the results of comparison of X-ray fluorescence intensity of PrF 3 single crystal obtained in Example 1 and BGO in FIG. As a result, it was found that the fluorescence intensity was slightly lower than that of BGO, but showed almost the same value.
各種ドーパントを１モル％添加して得られた実施例４〜１０の単結晶のＸ線蛍光スペクトル測定した結果を図５に示す。この結果、実施例４〜１０の単結晶は実施例１と比較して蛍光強度が低くはなるが、約４００ｎｍにピークが得られることが確認された。したがって、各種ドーパントを添加することにより発光量を調整できることが分かった。 The result of having measured the X-ray fluorescence spectrum of the single crystal of Examples 4-10 obtained by adding 1 mol% of various dopants is shown in FIG. As a result, it was confirmed that the single crystals of Examples 4 to 10 had a fluorescence intensity lower than that of Example 1, but a peak was obtained at about 400 nm. Therefore, it was found that the light emission amount can be adjusted by adding various dopants.
実施例１、１１及び１２の単結晶のＸ線蛍光スペクトル測定した結果を図６に示す。実施例１１は、実施例４〜１０と同様に、実施例１と比較して４００ｎｍ付近のピークが小さくなるが、新しく３００ｎｍに発光ピークが得られることを確認した。したがって、実施例４〜１０では４００ｎｍの蛍光強度が低下し、かつ可視領域付近で新たな大きな発光ピークの発現が見られなかったが、Ｃｅをドーパントとした実施例１１では、ピークが３００ｎｍに発現しＣｅの添加量に応じて可視領域付近での発光量を増加させることが可能であることがわかった。また、Ｌｕをドーパントとした実施例１２では約４００ｎｍに大きなピークが得られ実施例１より蛍光強度が高くなることが確認された。 The results of measuring the X-ray fluorescence spectra of the single crystals of Examples 1, 11 and 12 are shown in FIG. In Example 11, as in Examples 4 to 10, it was confirmed that a peak near 400 nm was smaller than that in Example 1, but a new emission peak was obtained at 300 nm. Therefore, the fluorescence intensity at 400 nm decreased in Examples 4 to 10 and no new large emission peak was observed in the vicinity of the visible region, but in Example 11 using Ce as a dopant, the peak appeared at 300 nm. It was found that the amount of light emitted in the vicinity of the visible region can be increased according to the amount of Ce added. In Example 12 using Lu as a dopant, a large peak was obtained at about 400 nm, and it was confirmed that the fluorescence intensity was higher than that in Example 1.
本発明の放射線検出用フッ化物単結晶は、主として、Ｘ線断層撮影装置（Ｘ−ｒａｙ Ｃｏｍｐｕｔｅｄ Ｔｏｍｏｇｒａｐｈｙ：Ｘ線ＣＴ）、陽電子放射断層撮影装置（Ｐｏｓｉｔｒｏｎ Ｅｍｉｓｓｉｏｎ ｃｏｍｐｕｔｅｄ Ｔｏｍｏｇｒａｐｈｙ：ＰＥＴ）、タイム・オブ・フライト陽電子放射断層撮影装置（Ｔｉｍｅ−Ｏｆ−Ｆｌｉｇｈｔ Ｐｏｓｉｔｒｏｎ Ｅｍｉｓｓｉｏｎ ｃｏｍｐｕｔｅｄ Ｔｏｍｏｇｒａｐｈｙ：ＴＯＦ−ＰＥＴ）などの医療診断装置に用いられるが、その他、放射線検出用の各種用途に用いられる。 The fluoride single crystal for radiation detection of the present invention is mainly composed of an X-ray computed tomography (X-ray CT), a positron emission computed tomography (PET), a time of flight. Although it is used for medical diagnostic apparatuses such as a positron emission tomography apparatus (TOF-PET), it is used for various other purposes for radiation detection.
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| JP2004137489A (en) * | 2002-09-24 | 2004-05-13 | Hokushin Ind Inc | Fluoride single crystal material for radiation detection and radiation detector |
| JP2005001933A (en) * | 2003-06-11 | 2005-01-06 | Fujikura Ltd | Metal fluoride body and its manufacturing method |
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| JP2004137489A (en) * | 2002-09-24 | 2004-05-13 | Hokushin Ind Inc | Fluoride single crystal material for radiation detection and radiation detector |
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