JP2020197513A - Tritium detection element and detection method - Google Patents
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Description
本発明は、トリチウムの検出素子及び検出方法に関するものである。 The present invention relates to a tritium detection element and a detection method.
低エネルギーの放射線を放出する放射性物質の代表例としてトリチウムが挙げられる。トリチウムの放出するベータ線はエネルギーが低く（１８ｋｅＶ）、プラスチックフィルムなどで簡単に遮蔽されてしまうため、シンチレータと呼ばれる放射線を受けて発光する物質をトリチウムの近くに配置する必要がある。そのためトリチウムの検出には液体シンチレーションカウンターが頻繁に使われている。 Tritium is a typical example of a radioactive substance that emits low-energy radiation. Beta rays emitted by tritium have low energy (18 keV) and are easily shielded by a plastic film or the like. Therefore, it is necessary to place a substance called a scintillator that emits light by receiving radiation near tritium. Therefore, liquid scintillation counters are frequently used to detect tritium.
液体シンチレーションカウンターでの測定では、バイアル瓶と呼ばれる容器に有機シンチレータ、有機溶剤、界面活性剤、及びトリチウムを含む水を入れ混合して計測する方法が知られている（非特許文献１参照）。または樹脂材料の多孔質膜に無機シンチレータ粒子を固定化した検出体にトリチウムが含まれる水を接触させて測定する方法が知られている（特許文献１参照）。または棒状のファイバ状のプラスチックシンチレータを複数本まとめ、トリチウムが含まれる水に接触させて測定する方法が知られている（特許文献２参照）。また固体のシンチレータとしてケイ酸粒子にシンチレータを固定化された放射線検出材が報告されている（特許文献３参照）。 In the measurement with a liquid scintillation counter, a method is known in which an organic scintillator, an organic solvent, a surfactant, and water containing tritium are mixed and mixed in a container called a vial (see Non-Patent Document 1). Alternatively, a method is known in which water containing tritium is brought into contact with a detector in which inorganic scintillator particles are immobilized on a porous film of a resin material for measurement (see Patent Document 1). Alternatively, a method is known in which a plurality of rod-shaped fiber-shaped plastic scintillators are put together and brought into contact with water containing tritium for measurement (see Patent Document 2). Further, as a solid scintillator, a radiation detection material in which a scintillator is immobilized on silicic acid particles has been reported (see Patent Document 3).
トリチウムから放出されるベータ線は水中での平均自由行程が０．６μｍと短い。そのため液体シンチレータ法が用いられている。しかしながらこの方法では測定ごとに新たにバイアル瓶の中に溶液を調整する必要があり、放射性物質を含んだ廃液が膨大に生じることが問題となる。また樹脂材料の多孔質膜にシンチレータ粒子を固定化した検出体では多孔質の孔径がサブミクロン単位で大きいため透明性が劣り内部での発光の透過率が低いという問題があった。ファイバーシンチレータ法では廃液に含まれるトリチウムの大半がベータ線の届く距離に存在しないため、検出感度が低いことが問題となる。またシンチレータを固定したケイ酸粒子では廃棄物として有機溶液を排出しないが、繰り返し使用に問題があり、また透明で無いために、シンチレータ内部で発光した光の検出が出来ないという問題点がある。 Beta rays emitted from tritium have a short mean free path in water of 0.6 μm. Therefore, the liquid scintillator method is used. However, in this method, it is necessary to newly prepare the solution in the vial for each measurement, and there is a problem that a huge amount of waste liquid containing radioactive substances is generated. Further, in the detector in which the scintillator particles are immobilized on the porous film of the resin material, there is a problem that the transparency is poor and the transmittance of light emission inside is low because the pore size of the porous is large in the submicron unit. In the fiber scintillator method, most of the tritium contained in the waste liquid is not present within the reach of beta rays, so the problem is that the detection sensitivity is low. Further, the silicic acid particles having the scintillator fixed do not discharge the organic solution as waste, but there is a problem in repeated use, and there is a problem that the light emitted inside the scintillator cannot be detected because it is not transparent.
そのため安価に作製することができ、透明性があることで溶液に漬けて精度良く放射線の検出が可能で、且つ繰り返し使用できることで廃棄物が少なくなるトリチウムの検出素子及び検出方法が求められていた。 Therefore, there has been a demand for a tritium detection element and a detection method that can be manufactured at low cost, can be immersed in a solution to detect radiation with high accuracy due to its transparency, and can be used repeatedly to reduce waste. ..
本発明はこのような事情に鑑みてなされたものであって、透明かつ測定精度に優れ、安価に製造できて繰り返し使用可能な検出素子を提供することを目的とする。また、精度よく繰り返し検出可能であり、廃棄物が少ないトリチウムの検出方法を提供することを目的とする。 The present invention has been made in view of such circumstances, and an object of the present invention is to provide a detection element that is transparent, has excellent measurement accuracy, can be manufactured at low cost, and can be used repeatedly. Another object of the present invention is to provide a method for detecting tritium, which can be detected repeatedly with high accuracy and has a small amount of waste.
上記の課題を解決するため、本発明の第一の形態は、試料水に含まれるトリチウムを検出する検出素子であって、ガラスからなる多孔体である多孔質ガラスの孔内や表面に放射線を吸収して発光するシンチレータを設置することを特徴とする。本発明の形態において、多孔質ガラスの孔径が５０ｎｍ以下である構成としてもよい。 In order to solve the above problems, the first embodiment of the present invention is a detection element for detecting tritium contained in sample water, and emits radiation into or on the surface of a porous glass which is a porous body made of glass. It is characterized by installing a scintillator that absorbs and emits light. In the embodiment of the present invention, the porous glass may have a pore diameter of 50 nm or less.
また、本発明の第二の形態は、上記の検出素子と、前記検出素子を収容し、光透過性を有する容器とを備え、前記容器本体にトリチウムを含む試料水を収容し、前記検出素子に前記試料水を含浸させる工程と、前記試料水中のトリチウムから放出されるベータ線に起因して前記検出素子が放出する光を光検知器で受光する工程と、光検知器の信号からトリチウム濃度を算出する工程を有するトリチウムの検出方法を提供する。 A second embodiment of the present invention includes the above-mentioned detection element and a container containing the detection element and having light transmission, and the container body contains sample water containing tritium, and the detection element is contained. The step of impregnating the sample water with the sample water, the step of receiving the light emitted by the detection element due to the beta rays emitted from the tritium in the sample water with the photodetector, and the tritium concentration from the signal of the photodetector. Provided is a method for detecting tritium, which comprises a step of calculating.
本発明の形態においては前記のトリチウム検出後、前記容器に収容された前記試料水を排出するとともに、前記検出素子を乾燥する工程と、乾燥後の前記検出素子を収容した容器にトリチウムを含む第二の試料水を収容し、前記検出素子に第二の試料水を含浸させる工程と第二の試料水中のトリチウムから放出されるベータ線に起因して前記検出素子が放出する光を光検知器で受光する工程と、光検知器の信号からトリチウム濃度を算出する工程を有するトリチウムの検出方法としてもよい。In the embodiment of the present invention, after the tritium is detected, the sample water contained in the container is discharged, and the detection element is dried, and the container containing the dried detection element contains tritium. An optical detector that accommodates the second sample water and impregnates the detection element with the second sample water and emits light from the detection element due to beta rays emitted from tritium in the second sample water. The tritium detection method may include a step of receiving light in the light receiver and a step of calculating the tritium concentration from the signal of the light detector.
本発明によれば、透明かつ測定精度に優れ、安価に製造できて繰り返し使用可能なトリチウム検出素子を提供することができる。また、精度よく繰り返し検出可能であり、廃棄物が少ないトリチウムの検出方法を提供することができる。 According to the present invention, it is possible to provide a tritium detection element that is transparent, has excellent measurement accuracy, can be manufactured at low cost, and can be used repeatedly. In addition, it is possible to provide a method for detecting tritium, which can be detected repeatedly with high accuracy and has a small amount of waste.
［実施の形態１］はじめに、本発明の実施の形態１について説明する。[Embodiment 1] First, the first embodiment of the present invention will be described.
まず、検出素子の作製について説明する。図１Ａに示すように、シンチレータ混合物として安息香酸９．７１ｍｍｏｌ／Ｌ、２，５−ジフェニルオキサゾール（ＰＰＯ）１９．０ｍｍｏｌ／Ｌ、１，４−ビス（５−フェニル−２−オキサゾリル）ベンゼン（ＰＯＰＯＰ）０．２６ｍｍｏｌ／Ｌの混合トルエン溶液１０１を容器１０２中に作製する。次に、図１Ｂに示すように、混合トルエン溶液１０１に、平均孔径４ｎｍの多孔質ガラスである多孔体１０３を浸漬する。多孔体１０３は、例えば８（ｍｍ）×８（ｍｍ）で厚さ１（ｍｍ）のチップサイズである。なお、多孔体１０３は平均孔径が５０ｎｍ以下であるとより良い特性となる。また、ここでは多孔体を板状としたが、これに限るものではなく、ファイバ状に形成してもよい。 First, the production of the detection element will be described. As shown in FIG. 1A, as a scintillator mixture, benzoic acid 9.71 mmol / L, 2,5-diphenyloxazole (PPO) 19.0 mmol / L, 1,4-bis (5-phenyl-2-oxazolyl) benzene (POPOP). ) A 0.26 mmol / L mixed toluene solution 101 is prepared in the container 102. Next, as shown in FIG. 1B, the porous body 103, which is a porous glass having an average pore diameter of 4 nm, is immersed in the mixed toluene solution 101. The porous body 103 has a chip size of, for example, 8 (mm) × 8 (mm) and a thickness of 1 (mm). The porous body 103 has better characteristics when the average pore diameter is 50 nm or less. Further, although the porous body is formed in a plate shape here, the present invention is not limited to this, and the porous body may be formed in a fiber shape.
多孔体１０３をガラス（硼珪酸ガラス）から構成した場合、この平均孔径を５０ｎｍ以下とすることで、シンチレータの蛍光の波長領域の可視領域（４００から８００ｎｍ）では光が透過する。しかし、平均孔径が５０ｎｍを越えて大きくなると、図２に示すように可視領域で急激な透過率の減少が観測される。このことにより、多孔体は平均孔径が５０ｎｍ以下とした方が良い。なお、本実施の形態における多孔体１０３の比表面積は１ｇ当たり１００ｍ２以上である。When the porous body 103 is made of glass (borosilicate glass), light is transmitted in the visible region (400 to 800 nm) of the fluorescence wavelength region of the scintillator by setting the average pore diameter to 50 nm or less. However, when the average pore size exceeds 50 nm and becomes large, a sharp decrease in transmittance is observed in the visible region as shown in FIG. For this reason, it is preferable that the porous body has an average pore diameter of 50 nm or less. The specific surface area of the porous body 103 in the present embodiment is 100 m 2 or more per 1 g.
上述した多孔体１０３を混合トルエン溶液１０１に２４時間浸漬し、多孔体１０３の孔内にシンチレータを含浸させた後、シンチレータが含浸した多孔体を風乾し、図１Ｃに示すように、窒素ガス気流中に２４時間放置して乾燥し、検出素子１０３ａを作製する。この検出素子は厚さが１ｍｍであったが、シンチレータの蛍光の波長である４７０から４８０ｎｍにおいて透過率は９９％以上であり、透明性が高かった。 The above-mentioned porous body 103 is immersed in the mixed toluene solution 101 for 24 hours, the pores of the porous body 103 are impregnated with the scintillator, and then the porous body impregnated with the scintillator is air-dried, and as shown in FIG. The detection element 103a is produced by leaving it inside for 24 hours to dry. Although the detection element had a thickness of 1 mm, the transmittance was 99% or more at 470 to 480 nm, which is the wavelength of fluorescence of the scintillator, and the transparency was high.
またこのようにして含浸された検出素子に水溶液を含浸させ、その後最大で１４時間静置した時の、静置時間とＰＯＰＯＰの吸収である４３０ｎｍの吸光度の関係を示したものが図３である。吸光度は最初の６時間で減少するがその後は一定であり、これによりシンチレータであるＰＯＰＯＰは水につけることである程度は溶出するが、一定量溶出後は溶出せず多孔質ガラス表面上にとどまっていると考えられることが示された。また、同時に入れたＰＰＯ、安息香酸においても他の分析方法で確認したところ同様にとどまっていることが明らかになった。 Further, FIG. 3 shows the relationship between the standing time and the absorbance at 430 nm, which is the absorption of POPOP, when the detection element impregnated in this manner is impregnated with an aqueous solution and then allowed to stand for a maximum of 14 hours. .. The absorbance decreases in the first 6 hours but remains constant thereafter, so that the scintillator POPOP elutes to some extent when immersed in water, but does not elute after a certain amount of elution and remains on the porous glass surface. It was shown to be considered to be. In addition, it was revealed that PPO and benzoic acid, which were added at the same time, remained in the same manner as confirmed by other analytical methods.
次に、検出素子１０３ａを用いたトリチウムの測定方法について説明する。作製した検出素子１０３ａを前処理として純水に６時間含浸しその後乾燥窒素気流中で乾燥させる。その後測定対象のトリチウムを含む試料水（１０４）を液体シンチレーションカウンター用のバイアル瓶（１０５）に２ｍｌ入れる。その後図１Ｄに示すように検出素子１０３ａをバイアル瓶に入れて、測定対象の試料水を含浸する。これを図１Ｅに示すように液体シンチレーションカウンターで測定する。このようにして測定したところトリチウム濃度８ｋＢｑ／ｍＬの試料水に対して、１分間の計測で１００ｃｐｍの測定値が得られた。バックグランド値として同じ条件でトリチウムを含まない水を測定したところ３ｃｐｍであり、この濃度のトリチウム水を十分に測定できた。 Next, a method for measuring tritium using the detection element 103a will be described. The produced detection element 103a is impregnated with pure water for 6 hours as a pretreatment, and then dried in a dry nitrogen stream. Then, 2 ml of sample water (104) containing tritium to be measured is placed in a vial (105) for a liquid scintillation counter. Then, as shown in FIG. 1D, the detection element 103a is placed in a vial and impregnated with the sample water to be measured. This is measured with a liquid scintillation counter as shown in FIG. 1E. As a result of the measurement in this manner, a measured value of 100 cpm was obtained by measuring for 1 minute with respect to the sample water having a tritium concentration of 8 kBq / mL. When water containing no tritium was measured under the same conditions as the background value, it was 3 cpm, and tritiated water having this concentration could be sufficiently measured.
［実施の形態２］次に、本発明の実施の形態２について説明する。[Embodiment 2] Next, Embodiment 2 of the present invention will be described.
検出素子の作製について説明すると、図１Ａに示すように、シンチレータ混合物として安息香酸１６．３４ｍｍｏｌ／Ｌ、ＰＰＯ８．９５ｍｍｏｌ／Ｌ、ＰＯＰＯＰ０．５４ｍｍｏｌ／Ｌの混合トルエン溶液１０１を容器１０２中に作製する。次に、図１Ｂに示すように、混合トルエン溶液１０１に、平均孔径４ｎｍの多孔質ガラスである多孔体１０３を浸漬する。多孔体１０３は、例えば８（ｍｍ）×８（ｍｍ）で厚さ１（ｍｍ）のチップサイズである。なお、多孔体１０３は平均孔径が５０ｎｍ以下であるとよい。また、ここでは多孔体を板状としたが、これに限るものではなく、ファイバ状に形成してもよい。 To explain the preparation of the detection element, as shown in FIG. 1A, a mixed toluene solution 101 of benzoic acid 16.34 mmol / L, PPO 8.95 mmol / L, and POPOP 0.54 mmol / L is prepared in the container 102 as a scintillator mixture. Next, as shown in FIG. 1B, the porous body 103, which is a porous glass having an average pore diameter of 4 nm, is immersed in the mixed toluene solution 101. The porous body 103 has a chip size of, for example, 8 (mm) × 8 (mm) and a thickness of 1 (mm). The porous body 103 preferably has an average pore diameter of 50 nm or less. Further, although the porous body is formed in a plate shape here, the present invention is not limited to this, and the porous body may be formed in a fiber shape.
多孔体１０３をガラス（硼珪酸ガラス）から構成した場合、この平均孔径を５０ｎｍ以下とすることで、シンチレータの蛍光の波長領域の可視領域（４００から８００ｎｍ）では光が透過する。しかし、平均孔径が５０ｎｍを越えて大きくなると、図２に示すように可視領域で急激な透過率の減少が観測される。このことにより、多孔体は平均孔径が５０ｎｍ以下とした方が良い。なお、本実施の形態における多孔体１０３の比表面積は１ｇ当たり１００ｍ２以上である。When the porous body 103 is made of glass (borosilicate glass), light is transmitted in the visible region (400 to 800 nm) of the fluorescence wavelength region of the scintillator by setting the average pore diameter to 50 nm or less. However, when the average pore size exceeds 50 nm and becomes large, a sharp decrease in transmittance is observed in the visible region as shown in FIG. For this reason, it is preferable that the porous body has an average pore diameter of 50 nm or less. The specific surface area of the porous body 103 in the present embodiment is 100 m 2 or more per 1 g.
上述した多孔体１０３を混合トルエン溶液１０１に２４時間浸漬し、多孔体１０３の孔内にシンチレータを含浸させた後、シンチレータが含浸した多孔体を風乾し、図１Ｃに示すように、窒素ガス気流中に２４時間放置して乾燥し、検出素子１０３ａを作製する。この検出素子は厚さが１ｍｍであったが、シンチレータの蛍光の波長である４７０から４８０ｎｍにおいて透過率は９９％以上であり、透明性が高かった。 The above-mentioned porous body 103 is immersed in the mixed toluene solution 101 for 24 hours, the pores of the porous body 103 are impregnated with the scintillator, and then the porous body impregnated with the scintillator is air-dried, and as shown in FIG. The detection element 103a is produced by leaving it inside for 24 hours to dry. Although the detection element had a thickness of 1 mm, the transmittance was 99% or more at 470 to 480 nm, which is the wavelength of fluorescence of the scintillator, and the transparency was high.
次に、検出素子１０３ａを用いたトリチウムの測定方法について説明する。作製した検出素子１０３ａを前処理として純水に６時間含浸しその後乾燥窒素気流中で乾燥させる。その後測定対象のトリチウムを含む試料水（１０４）を液体シンチレーションカウンター用のバイアル瓶（１０５）に２ｍｌ入れる。その後図１Ｄに示すように検出素子１０３ａをバイアル瓶に入れて、測定対象の試料水を含浸する。これを図１Ｅに示すように液体シンチレーションカウンターで測定する。このようにして測定したところトリチウム濃度８ｋＢｑ／ｍＬの試料水に対して、９９ｃｐｍの測定値が得られた。バックグランド値として同じ条件でトリチウムを含まない水を測定したところ３ｃｐｍであり、この濃度のトリチウム水を十分に測定できた。 Next, a method for measuring tritium using the detection element 103a will be described. The produced detection element 103a is impregnated with pure water for 6 hours as a pretreatment, and then dried in a dry nitrogen stream. Then, 2 ml of sample water (104) containing tritium to be measured is placed in a vial (105) for a liquid scintillation counter. Then, as shown in FIG. 1D, the detection element 103a is placed in a vial and impregnated with the sample water to be measured. This is measured with a liquid scintillation counter as shown in FIG. 1E. As a result of the measurement in this manner, a measured value of 99 cpm was obtained with respect to the sample water having a tritium concentration of 8 kBq / mL. When water containing no tritium was measured under the same conditions as the background value, it was 3 cpm, and tritiated water having this concentration could be sufficiently measured.
その後バイアル瓶より検出素子を取り出し、乾燥させたところ検出素子に含まれていた水は蒸発して、検出素子内の水及びトリチウム水は無くなった。これは多孔質ガラスの水に起因する近赤外領域の吸収での吸光度差が乾燥状態に比較して非常に小さいことで確認した。またこの状態の検出素子にはＦＴ−ＩＲ及び蛍光分析によりシンチレータ混合物が含まれていることが明らかになった。そのため、この検出素子に再びトリチウムを含む試料水を含浸させることで、トリチウムの測定が可能である。 After that, when the detection element was taken out from the vial and dried, the water contained in the detection element evaporated, and the water in the detection element and the tritiated water disappeared. This was confirmed by the fact that the difference in absorbance in absorption in the near-infrared region caused by water in the porous glass was very small compared to the dry state. Further, it was revealed by FT-IR and fluorescence analysis that the detection element in this state contained a scintillator mixture. Therefore, tritium can be measured by impregnating the detection element with sample water containing tritium again.
１０１・・・シンチレータ混合トルエン溶液
１０２・・・容器
１０３・・・多孔体
１０３ａ・・・検出素子
１０４・・・トルエンを含む試料水
１０５・・・バイアル瓶101 ... Scintillator mixed toluene solution 102 ... Container 103 ... Porous body 103a ... Detection element 104 ... Sample water containing toluene 105 ... Vial bottle
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