JP6782879B2 - Radioactivity measuring device and radioactivity measuring method - Google Patents
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Description
本発明は、複雑な設備を用いることなく、短時間且つ正確に、土壌中の放射能分布を把握できる放射能測定装置及び放射能測定方法に関する。 The present invention relates to a radioactivity measuring device and a radioactivity measuring method capable of grasping the radioactivity distribution in soil in a short time and accurately without using complicated equipment.
平成23年3月11日に発生した東北地方太平洋沖地震及びそれに伴う津波によって引き起こされた東京電力福島第一原子力発電所の事故によって、福島県を中心に広範囲の土壌や、ため池、その他の施設が放射性物質によって汚染された。特に、福島県内には3400箇所以上のため池が存在し、農業用水源として利用されていたが、その多くの底質から放射性セシウムが検出された。 Due to the accident at TEPCO's Fukushima Daiichi Nuclear Power Station caused by the 2011 off the Pacific coast of Tohoku Earthquake and the accompanying tsunami, a wide range of soil, reservoirs, and other facilities centered on Fukushima Prefecture Was contaminated with radioactive material. In particular, there are more than 3,400 ponds in Fukushima Prefecture, which were used as water sources for agriculture, but radioactive cesium was detected in many of the sediments.
そのため、農林水産省をはじめとする各機関は、土壌等における放射性物質を除去又は低減するための作業や技術について検討を進めている。ここで、土壌等における放射性物質については、水平方向や、深さ方向に不均一に分布していることから、放射性物質の除去や低減を進めるためには、実際にどのように放射性物質の汚染が広がっているか（放射能の分布）を把握することが非常に重要となる。 Therefore, each organization including the Ministry of Agriculture, Forestry and Fisheries is studying work and technology for removing or reducing radioactive substances in soil and the like. Here, since radioactive substances in soil and the like are unevenly distributed in the horizontal direction and the depth direction, how to actually contaminate the radioactive substances in order to promote the removal or reduction of the radioactive substances. It is very important to understand whether or not (radioactivity distribution) is spreading.
従来、土壌における放射能濃度の分布を把握するための技術としては、ひも状のシンチレータであるプラスチック・シンチレーション・ファイバー（ＰＳＦ）を用いる方法（例えば、特許文献１を参照。）が一般的に知られている。ただし、これらのＰＳＦを用いた技術では、地表の放射能分布については有効に把握できるものの、土壌にＰＳＦを埋め込むことが困難であり、土壌の深さ方向の放射能分布については把握することができないという問題があった。 Conventionally, as a technique for grasping the distribution of radioactivity concentration in soil, a method using a plastic scintillation fiber (PSF), which is a string-shaped scintillator (see, for example, Patent Document 1) is generally known. Has been done. However, although the technology using these PSFs can effectively grasp the radioactivity distribution on the ground surface, it is difficult to embed PSF in the soil, and it is possible to grasp the radioactivity distribution in the depth direction of the soil. There was a problem that it could not be done.
そのため、土壌中の放射能分布を把握するための技術として、柱状採泥器を用いて土壌からコア（抜き出した土壌の柱状塊）を採取し、採取したコアについて、複数点の放射能を測定することで、土壌中の放射能分布を把握する方法が挙げられる（例えば、特許文献２を参照。）。
しかしながら、特許文献２に開示されているような柱状採泥については、比較的大きな設備、労力及び費用を必要とし、多くの調査に用いることが難しいという問題があった。また、土壌からコアを複数回採取した後に放射能の測定を行い、分布を調査するため、調査に時間を要するという問題もあった。
さらに、引用文献２に開示されているような、前記土壌に穴を開けて、該穴にＰＳＦを配備する方法についても、土壌中に適切な穴を形成し、ＰＳＦを適切な間隔で配備する必要があるため、調査実施のためには大きな労力や時間がかかるという問題があった。
Therefore, as a technique for grasping the radioactivity distribution in the soil, cores (columnar masses of extracted soil) are collected from the soil using a columnar mud sampler, and the radioactivity at multiple points is measured for the collected cores. By doing so, there is a method of grasping the radioactivity distribution in the soil (see, for example, Patent Document 2).
However, columnar mud collection as disclosed in Patent Document 2 requires relatively large equipment, labor and cost, and has a problem that it is difficult to use for many investigations. In addition, since the radioactivity is measured after the core is collected from the soil multiple times and the distribution is investigated, there is a problem that the investigation takes time.
Further, as for the method of making a hole in the soil and deploying the PSF in the hole as disclosed in Cited Document 2, an appropriate hole is formed in the soil and the PSF is deployed at an appropriate interval. Since it is necessary, there is a problem that it takes a lot of labor and time to carry out the survey.
本発明の目的は、複雑な設備を用いることなく、短時間且つ正確に、土壌中の放射能分布を把握できる放射能測定装置及び放射能測定方法を提供することにある。 An object of the present invention is to provide a radioactivity measuring device and a radioactivity measuring method capable of grasping the radioactivity distribution in soil in a short time and accurately without using complicated equipment.
本発明者らは、上記課題を解決すべく鋭意研究を行った結果、長手方向に複数の放射線受光素子を有する放射線検出プローブを用い、該複数の放射線受光素子が、土壌中で、それぞれ放射線のカウント数を取得することによって、複雑な設備や時間をかけることなく、土壌中の放射能分布を取得できることを見出した。
ただし、それぞれの放射線受光素子で取得したカウント数については、取得する必要のない位置の放射性物質からの放射線（例えば、１つの放射線受光素子が取得するべき深さ位置の放射性物質ではなく、上や下の深さ位置に存在する放射性物質からの放射線）についても取得しているため、そのままでは正確な放射能の分布を把握することができなかった。このため、本発明者らはさらに鋭意研究を行った結果、放射線受光素子ごとに取得したカウント数から不要なカウント数を除く処理を行うことによって、土壌中の放射能分布を正確に把握することが可能となり、本発明を完成するに至った。
As a result of diligent research to solve the above problems, the present inventors used a radiation detection probe having a plurality of radiation receiving elements in the longitudinal direction, and the plurality of radiation receiving elements each of the radiation receiving elements in the soil. It was found that by acquiring the count number, the radioactivity distribution in the soil can be acquired without complicated equipment and time.
However, regarding the count number acquired by each radiation receiving element, the radiation from the radioactive substance at the position that does not need to be acquired (for example, not the radioactive substance at the depth position that one radiation receiving element should acquire, but above or above. Since we also obtained radiation from radioactive substances that exist at the lower depths, we could not grasp the accurate distribution of radioactivity as it was. Therefore, as a result of further diligent research, the present inventors have performed a process of removing unnecessary counts from the counts acquired for each radiation receiving element to accurately grasp the radioactivity distribution in soil. Has become possible, and the present invention has been completed.
本発明は、このような知見に基づきなされたもので、その要旨は以下の通りである。
（１）長手方向に複数の放射線受光素子を有する放射線検出プローブと、該放射線受光素子ごとに検出した放射線のカウント数に基づいて解析を行う解析部とを備え、
前記放射線検出プローブが土壌に挿入された際、前記複数の放射線受光素子が、それぞれ放射線のカウント数を取得し、前記解析部が、前記放射線受光素子毎に取得したカウント数から不要なカウント数を除いた最尤カウント数を算出し、該最尤カウント数から前記土壌における放射能分布を導出することを特徴とする、放射能測定装置。
The present invention has been made based on such findings, and the gist thereof is as follows.
(1) A radiation detection probe having a plurality of radiation receiving elements in the longitudinal direction, and an analysis unit that performs analysis based on the count number of radiation detected for each radiation receiving element are provided.
When the radiation detection probe is inserted into the soil, the plurality of radiation receiving elements each acquire a radiation count number, and the analysis unit obtains an unnecessary count number from the count number acquired for each radiation receiving element. A radioactivity measuring apparatus, characterized in that the excluded most probable count is calculated and the radioactivity distribution in the soil is derived from the most probable count.
（２）前記放射線受光素子は、NaI(Tl)、CsI(Tl)、LnBr3又はCsIからなることを特徴とする、（１）に記載の放射能測定装置。 (2) The radioactivity measuring device according to (1), wherein the radiation receiving element is composed of NaI (Tl), CsI (Tl), LnBr 3 or CsI.
（３）前記不要なカウント数とは、前記各放射線受光素子が取得するべき深さ位置とは異なる深さ位置から取得したカウント数であり、前記解析部は、前記放射線受光素子毎に取得したカウント数の逆解析を行うことで前記不要なカウント数を除き、前記最尤カウント数を算出することを特徴とする、（１）又は（２）に記載の放射能測定装置。 (3) The unnecessary count number is a count number acquired from a depth position different from the depth position to be acquired by each radiation receiving element, and the analysis unit acquires each radiation receiving element. The radioactivity measuring apparatus according to (1) or (2), wherein the most probable count number is calculated by performing an inverse analysis of the count number to remove the unnecessary count number.
（４）各放射線受光素子は、前記放射線検出プローブの長手方向に10〜50mm程度の間隔で、10個以上配設されることを特徴とする、（１）〜（３）のいずれかに記載の放射能測定装置。 (4) The method according to any one of (1) to (3), wherein 10 or more of each radiation receiving element are arranged at intervals of about 10 to 50 mm in the longitudinal direction of the radiation detection probe. Radioactivity measuring device.
（５）前記放射線検出プローブは、外径が10〜50mmであることを特徴とする、（１）〜（４）のいずれかに記載の放射能測定装置。 (5) The radioactivity measuring device according to any one of (1) to (4), wherein the radiation detection probe has an outer diameter of 10 to 50 mm.
（６）前記プローブの外周にガイドロットをさらに備えることを特徴とする、（１）〜（５）のいずれかに記載の放射能測定装置。 (6) The radioactivity measuring apparatus according to any one of (1) to (5), further comprising a guide lot on the outer periphery of the probe.
（７）既知の汚染濃度の土壌から汚染成分ごとの換算式を算出し、前記導出された放射能分布に該換算式を適用することで、前記導出された放射能分布を汎用的なデータへと変更する、キャリブレーション手段をさらに備えることを特徴とする、（１）〜（６）のいずれかに記載の放射能測定装置。 (7) By calculating a conversion formula for each contaminated component from soil with a known pollution concentration and applying the conversion formula to the derived radioactivity distribution, the derived radioactivity distribution can be converted into general-purpose data. The radioactivity measuring apparatus according to any one of (1) to (6), further comprising a calibration means.
（８）長手方向に複数の放射線受光素子を有する放射線検出プローブを土壌に挿入し、前記複数の放射線受光素子が、それぞれ放射線のカウント数を取得し、前記放射線受光素子毎に取得したカウント数から不要なカウント数を除いた最尤カウント数を算出し、該最尤カウント数から前記土壌における放射能分布を導出することを特徴とする、放射能測定方法。 (8) A radiation detection probe having a plurality of radiation receiving elements in the longitudinal direction is inserted into the soil, the plurality of radiation receiving elements each acquire a radiation count number, and the count number acquired for each radiation receiving element is used. A method for measuring radioactivity, which comprises calculating the most likely count number excluding unnecessary counts and deriving the radioactivity distribution in the soil from the most likely count number.
（９）既知の汚染濃度の土壌から汚染成分ごとの換算式を算出し、前記導出された放射能分布に該換算式を適用することで、前記導出された放射能分布を汎用的なデータへと変更することを特徴とする、（８）に記載の放射能測定方法。 (9) By calculating a conversion formula for each contaminated component from soil with a known pollution concentration and applying the conversion formula to the derived radioactivity distribution, the derived radioactivity distribution can be converted into general-purpose data. The radioactivity measurement method according to (8), which comprises changing the method.
本発明によれば、複雑な設備を用いることなく、短時間且つ正確に、土壌中の放射能分布を把握できる放射能測定装置及び放射能測定方法を提供することが可能となる。 According to the present invention, it is possible to provide a radioactivity measuring device and a radioactivity measuring method capable of grasping the radioactivity distribution in soil in a short time and accurately without using complicated equipment.
＜放射能測定装置＞
本発明に従う放射能測定装置について、必要に応じて図面を用いて説明する。
本発明の放射能測定装置は、図１に示すように、長手方向に複数の放射線受光素子を有する放射線検出プローブ１０と、該放射線受光素子ごとに検出した放射線のカウント数に基づいて解析を行う解析部２０とを備える。
<Radioactivity measuring device>
The radioactivity measuring device according to the present invention will be described with reference to the drawings as necessary.
As shown in FIG. 1, the radioactivity measuring apparatus of the present invention performs analysis based on a radiation detection probe 10 having a plurality of radiation receiving elements in the longitudinal direction and a count number of radiation detected for each radiation receiving element. It includes an analysis unit 20.
そして、本発明の放射能測定装置は、図２（ａ）〜（ｃ）に示すように、に前記放射線検出プローブ１０が土壌１００に挿入された際（図２（ａ））、前記複数の放射線受光素子１１が、それぞれ放射線のカウント数を取得し（図２（ｂ））、前記解析部２０が、前記放射線受光素子１１毎に取得したカウント数から不要なカウント数を除いた最尤カウント数を算出し、該最尤カウント数から前記土壌における放射能分布を導出する（図２（ｃ））ことを特徴とする。
図２（ａ）及び（ｂ）に示すように、前記複数の放射線受光素子１１が、土壌１００で、それぞれ放射線のカウント数を取得することによって、複雑な設備や時間をかけることなく、土壌における深さ方向に沿った放射能の大まかな分布の取得が可能となり、さらに、前記解析部２０が、図２（ｃ）に示すように、放射線受光素子ごとに取得したカウント数（図２（ｂ））から不要なカウント数を除く処理を行うことによって、土壌１００における放射能分布を正確に予測することが可能となる。
Then, as shown in FIGS. 2A to 2C, the radioactivity measuring apparatus of the present invention has the plurality of radiation detection probes 10 when the radiation detection probe 10 is inserted into the soil 100 (FIG. 2A). The radiation receiving element 11 acquires the radiation count number (FIG. 2B), and the analysis unit 20 removes an unnecessary count from the count number acquired for each radiation receiving element 11. It is characterized in that the number is calculated and the radioactivity distribution in the soil is derived from the most probable count number (FIG. 2 (c)).
As shown in FIGS. 2A and 2B, the plurality of radiation receiving elements 11 acquire the count number of radiation in the soil 100, respectively, so that the soil can be used without complicated equipment or time. It is possible to acquire a rough distribution of radioactivity along the depth direction, and further, as shown in FIG. 2 (c), the number of counts acquired by the analysis unit 20 for each radiation receiving element (FIG. 2 (b). By performing the treatment of removing unnecessary counts from)), it becomes possible to accurately predict the radioactivity distribution in the soil 100.
ここで、前記放射線検出プローブが挿入される「土壌」とは、地面の下や、堆積された、水以外の無機物や有機物からなる物質層のことであり、岩石が風化して生成した粗粒の無機物（一次鉱物）やコロイド状の無機物（粘土鉱物あるいは二次鉱物）、生物の死骸などの粗大有機物、粗大有機物が微生物などの分解者の作用などによって変質して生じる有機物（腐植）を含むものである。 Here, the "soil" into which the radiation detection probe is inserted is a material layer under the ground or deposited, which is composed of inorganic substances or organic substances other than water, and is coarse particles generated by weathering of rocks. Inorganic substances (primary minerals) and colloidal inorganic substances (clay minerals or secondary minerals), coarse organic substances such as dead organisms, and organic substances (rotted plants) produced by the alteration of coarse organic matter by the action of decomposers such as microorganisms. It is a waste.
なお、本発明での「放射性物質」は、放射能を持った物質であれば特に限定はされず、核燃料物質や、放射性元素、又は、放射性同位体、中性子から生成された放射化物質などが挙げられる。その中でも、本発明では、特に、137Cs（セシウム）、134Cs（セシウム）、40K（カリウム）、214Bi（ビスマス）、228Ac（アクチニウム）、208Tl（タリウム）、212Pb（鉛）、235U（ウラン）等の放射性物質から放出される放射線が対象となる。これらの放射性物質は土壌中に含まれることが多く、本発明による効果が発揮されやすい。
また、本発明での「放射線」とは、α線、γ線、β線等の人体に与える影響の強い電離放射線のことであり、「放射能」とは、放射線を発する能力のことである。
The "radioactive substance" in the present invention is not particularly limited as long as it is a substance having radioactivity, and may be a nuclear fuel substance, a radioactive element, a radioisotope, an activated substance generated from a neutron, or the like. Can be mentioned. Among them, in the present invention, in particular, 137 Cs (cesium), 134 Cs (cesium), 40 K (potassium), 214 Bi (bismuth), 228 Ac (actinium), 208 Tl (talium), 212 Pb (lead). , 235 U (uranium) and other radioactive substances are targeted. These radioactive substances are often contained in soil, and the effects of the present invention are likely to be exhibited.
Further, the "radiation" in the present invention is an ionizing radiation having a strong influence on the human body such as α-rays, γ-rays and β-rays, and the "radioactivity" is the ability to emit radiation. ..
（放射線検出プローブ）
本発明の放射能測定装置は、図１に示すように、放射線検出プローブ１０を備える。該放射線検出プローブ１０は、図２（ａ）に示すように、その長手方向に複数の放射線受光素子１１を有し、図２（ｂ）に示すように、該放射線受光素子１１ごとに放射線のカウント数を検出する。
(Radiation detection probe)
As shown in FIG. 1, the radioactivity measuring device of the present invention includes a radiation detection probe 10. As shown in FIG. 2A, the radiation detection probe 10 has a plurality of radiation receiving elements 11 in the longitudinal direction thereof, and as shown in FIG. 2B, each of the radiation receiving elements 11 receives radiation. Detect the number of counts.
ここで、前記放射線受光素子１１とは、放射線を吸収し、吸収量の出力を行う素子のことである。
前記放射線受光素子１１については、放射線の有無及び吸収量を検出できるものであれば特に限定はされず、例えば、放射線のカウント数を取得する放射線受光素子が挙げられる。
その中でも、前記放射線受光素子１１は、NaI(Tl)、CsI(Tl)、LnBr3又はCsIからなることが好ましい。前記放射線量の検出精度が高く、正確に放射能分布を把握できるためである。さらに、NaI(Tl)、CsI(Tl)、LnBr3又はCsIを放射線受光素子として用いた場合、放射性物質の種類ごとにカウント数の検出を行うことができる（つまり、図２（ｂ）に示すようなカウント数のデータを、放射性物質の種類毎に得ることができる。）。
Here, the radiation receiving element 11 is an element that absorbs radiation and outputs an absorbed amount.
The radiation receiving element 11 is not particularly limited as long as it can detect the presence or absence of radiation and the amount of absorption, and examples thereof include a radiation receiving element that acquires a count number of radiation.
Among them, the radiation receiving element 11 is preferably composed of NaI (Tl), CsI (Tl), LnBr 3 or CsI. This is because the detection accuracy of the radiation amount is high and the radioactivity distribution can be grasped accurately. Furthermore, when NaI (Tl), CsI (Tl), LnBr 3 or CsI is used as the radiation receiving element, the count number can be detected for each type of radioactive substance (that is, as shown in FIG. 2B). Data on such counts can be obtained for each type of radioactive material.)
なお、前記放射線受光素子１１の設けられる箇所については、前記放射線のカウント数を検出できる位置であれば特に限定はされない。ただし、前記放射線受光素子１１の破損を防ぐ観点からは、図２（ａ）に示すように、前記放射線検出プローブ１０の内部に設けられることが好ましい。 The location where the radiation receiving element 11 is provided is not particularly limited as long as it is a position where the count number of the radiation can be detected. However, from the viewpoint of preventing damage to the radiation receiving element 11, it is preferable that the radiation detecting probe 10 is provided inside the radiation detecting probe 10 as shown in FIG. 2A.
また、前記各放射線受光素子１１は、前記放射線検出プローブ１０の長手方向に10〜50mm程度の間隔で、10個以上配設されることが好ましい。短い間隔で配設されることで、前記放射線のカウント数の検出精度が高くなり、放射能分布のより正確な把握が可能となるからである。また、前記放射線受光素子１１の配設間隔については、50mmを超える場合には、間隔が大きくなりすぎるために正確な放射能分布の把握が難しくなるおそれがあり、一方、配設間隔が10mm未満の場合には、配設間隔が近く、前記放射線のカウント数の検出精度についてもそれ以上の向上が望めないことから、経済的に好ましくないためである。 Further, it is preferable that 10 or more of the radiation receiving elements 11 are arranged at intervals of about 10 to 50 mm in the longitudinal direction of the radiation detecting probe 10. This is because the arrangement at short intervals improves the detection accuracy of the count number of the radiation and enables more accurate grasp of the radioactivity distribution. Further, when the arrangement interval of the radiation receiving element 11 exceeds 50 mm, the interval becomes too large, which may make it difficult to grasp the accurate radioactivity distribution, while the arrangement interval is less than 10 mm. In the case of, the arrangement interval is close, and the detection accuracy of the radiation count number cannot be expected to be further improved, which is economically unfavorable.
さらに、前記放射線受光素子１１のサイズについては、特に限定はされず、前記放射線検出プローブ１０の大きさに応じて適宜変更することができる。ただし、高い検出精度を実現し、より正確な放射能分布の把握を可能とする点からは、前記放射線受光素子１１のサイズが0.5cm3以上であることが好ましく1.0〜2.0cm3であることがより好ましい。 Further, the size of the radiation receiving element 11 is not particularly limited, and can be appropriately changed according to the size of the radiation detecting probe 10. However, to achieve high detection accuracy, from the viewpoint of enabling to grasp more accurate radioactivity distribution that the size of the radiation receiving element 11 is 0.5 cm 3 or more preferably 1.0～2.0Cm 3 Is more preferable.
前記放射線検出プローブ１０の本体は、図３に示すように、土壌１００に挿入しやすいような形状を有している。形状については特に限定されず、円筒状、多角柱状等とすることができるものの、土壌１００への挿入しやすさ等から考慮すると、図３に示すように、円筒状で先端がテーパーになった針のような形状であることが好ましい。
また、前記放射線検出プローブ１０の本体を構成する材料は、土壌１００に挿入するため一定の強度を有しており、内部の前記放射線受光素子１１が放射線を検出できるように放射線を完全には遮断しない材料を用いることが好ましい。具体的には、鉄、ステンレス、チタン、アルミニウム及びそれらの合金等から構成されることが好ましい。
As shown in FIG. 3, the main body of the radiation detection probe 10 has a shape that can be easily inserted into the soil 100. The shape is not particularly limited, and it can be cylindrical, polygonal columnar, etc. However, considering the ease of insertion into the soil 100, etc., as shown in FIG. 3, the shape is cylindrical and the tip is tapered. It is preferably shaped like a needle.
Further, the material constituting the main body of the radiation detection probe 10 has a certain strength because it is inserted into the soil 100, and completely blocks the radiation so that the radiation receiving element 11 inside can detect the radiation. It is preferable to use a material that does not. Specifically, it is preferably composed of iron, stainless steel, titanium, aluminum and alloys thereof.
また、図３に示すように、前記放射線検出プローブ１０の長さＬは、挿入する深さに応じて適宜選択することができるが、広い範囲での放射能分布を把握できる点からは、10cm以上であることが好ましく、50cm以上であることがより好ましい。なお、前記放射線検出プローブ１０の長さＬとは、前記放射線検出プローブ１０の露出した部分の長さであり、プローブの後述するガイドロット１２に覆われた部分については長さに含めていない。
さらに、前記放射線検出プローブ１０の外径Ｋについても特に限定はされないが、土壌１００への挿入のし易さと、プローブの強度とのバランスを考慮すると、10〜50mmであることが好ましく、20〜30mmであることがより好ましい。
Further, as shown in FIG. 3, the length L of the radiation detection probe 10 can be appropriately selected according to the insertion depth, but 10 from the viewpoint that the radioactivity distribution in a wide range can be grasped. it is preferably cm or more, and more preferably 50cm or more. The length L of the radiation detection probe 10 is the length of the exposed portion of the radiation detection probe 10, and the portion of the probe covered with the guide lot 12 described later is not included in the length.
Further, the outer diameter K of the radiation detection probe 10 is not particularly limited, but is preferably 10 to 50 mm, preferably 20 to 50 mm, in consideration of the balance between the ease of insertion into the soil 100 and the strength of the probe. More preferably, it is 30 mm.
また、前記放射線検出プローブ１０は、図３に示すように、外周位置に、ガイドロット１２をさらに備えることが好ましい。ガイドロット１２を備えることで、前記放射線検出プローブ１０の保護を図り、硬い土壌であっても、前記放射線検出プローブ１０を挿入することが容易になり、プローブ１０の損傷を防ぐことができる。
ここで、前記ガイドロットは、高い強度と軽量性を実現する点から、チタン、ポリ塩化ビニル、アクリル、アルミニウム合金等から構成されることが好ましい。
Further, as shown in FIG. 3, the radiation detection probe 10 preferably further includes a guide lot 12 at the outer peripheral position. By providing the guide lot 12, the radiation detection probe 10 can be protected, the radiation detection probe 10 can be easily inserted even in hard soil, and damage to the probe 10 can be prevented.
Here, the guide lot is preferably made of titanium, polyvinyl chloride, acrylic, an aluminum alloy or the like from the viewpoint of achieving high strength and light weight.
さらに、前記放射線検出プローブ１０は、特に限定はされないが、水位を把握するための水位計（図示せず）、放射線検出プローブ１０をつなぐケーブル１５を固定するためのケーブル固定部１３、前記ガイドロット１２とともに強度向上に寄与するロットレジューサ１４をさらに有することができる。 Further, the radiation detection probe 10 is not particularly limited, but is a water level gauge (not shown) for grasping the water level, a cable fixing portion 13 for fixing the cable 15 connecting the radiation detection probe 10, and the guide lot. Along with 12, a lot reducer 14 that contributes to strength improvement can be further provided.
（解析部）
本発明の放射能測定装置は、図１に示すように、解析部２０を備える。該解析部２０は、図２（ｃ）に示すように、前記放射線受光素子１１毎に取得したカウント数（図２（ｂ））から不要なカウント数を除いた最尤カウント数を算出することによって、前記土壌１００の深さに応じた放射能を導出する。
なお、前記解析部２０は、上述した放射線検出プローブ１０と、ケーブルを介して、直接又は接続装置５０（図１）を経て接続されている。
(Analysis department)
As shown in FIG. 1, the radioactivity measuring device of the present invention includes an analysis unit 20. As shown in FIG. 2C, the analysis unit 20 calculates the maximum likelihood count number obtained by subtracting the unnecessary count number from the count number (FIG. 2B) acquired for each radiation receiving element 11. To derive the radioactivity according to the depth of the soil 100.
The analysis unit 20 is connected to the radiation detection probe 10 described above directly or via a connecting device 50 (FIG. 1) via a cable.
ここで、前記放射線受光素子１１毎に取得したカウント数おける不要なカウント数とは、正確な放射能分布を把握する上で不要なカウント数のことであり、具体的には、前記各放射線受光素子１１が取得するべき深さ位置とは異なる深さ位置にある放射性物質の放射線から取得した過剰なカウント数のことである。これらのカウント数を加味すると、深さ位置ごとに通常の放射能よりも多くの放射能があると検出され、得られたカウント数の分布は鈍ったデータとなる結果、正確な放射能分布を得ることができない。 Here, the unnecessary count number in the count number acquired for each radiation receiving element 11 is a count number unnecessary for grasping an accurate radioactivity distribution, and specifically, each radiation receiving element. It is an excessive count number acquired from the radiation of a radioactive substance at a depth position different from the depth position to be acquired by the element 11. When these counts are taken into consideration, it is detected that there is more radioactivity than normal radioactivity at each depth position, and the distribution of the obtained counts becomes blunt data, resulting in an accurate radioactivity distribution. I can't get it.
そして、前記不要なカウント数を除き、最尤カウント数を算出するための手法としては、逆解析を行うことが好ましい。これによって、前記不要なカウント数を確実に除くことができ、高精度に最尤カウント数を得ることができるためである。
前記逆解析の方法とは、前記不要なカウント数を除くことができれば特に限定はされないが、例えば、前記放射線受光素子１１からの距離に応じた放射線の減衰率を元に数値解析を行い、所定の値を前記放射線受光素子１１毎に取得したカウント数から除く計算（逆解析）である。なお、放射線受光素子１１毎に取得したカウント数については、土壌の種類や、土壌の深さ、温度、検出した放射能等に基づいて、計算によって算出される。
Then, as a method for calculating the maximum likelihood count number by removing the unnecessary count number, it is preferable to perform an inverse analysis. This is because the unnecessary count number can be reliably removed and the maximum likelihood count number can be obtained with high accuracy.
The method of the inverse analysis is not particularly limited as long as the unnecessary count number can be removed, but for example, a numerical analysis is performed based on the radiation attenuation rate according to the distance from the radiation receiving element 11, and a predetermined method is performed. Is a calculation (inverse analysis) in which the value of is excluded from the count number acquired for each radiation receiving element 11. The count number acquired for each radiation receiving element 11 is calculated by calculation based on the type of soil, the depth of soil, the temperature, the detected radioactivity, and the like.
また、上述の算出された最尤カウント数から前記土壌における放射能分布（図２（ｃ））を導出する方法については、特に限定されず、公知の方法を用いて導出することができる。例えば、ガンマ線のエネルギースペクトルから特定の放射性物質の放射能を求める方法や、予め求めたカウント数と放射能の関係式を使った変換（キャリブレーション）によって算出することができる。 Further, the method for deriving the radioactivity distribution (FIG. 2C) in the soil from the calculated maximum likelihood count number is not particularly limited, and a known method can be used for deriving the radioactivity distribution. For example, it can be calculated by a method of obtaining the radioactivity of a specific radioactive substance from the energy spectrum of gamma rays, or a conversion (calibration) using a relational expression between the count number and the radioactivity obtained in advance.
なお、前記解析部に用いられる機器としては特に限定はされず、通常の電子計算機に特定のソフトを組み込むことで、解析部として用いることが可能である。 The device used for the analysis unit is not particularly limited, and can be used as an analysis unit by incorporating specific software into a normal computer.
（キャリブレーション手段）
また、本発明の放射能測定装置は、既知の汚染濃度の土壌から汚染成分ごとの換算係数を算出し、前記導出された放射能分布に該換算係数を適用することで、前記導出された放射能分布を汎用的なデータへと変更する、キャリブレーション手段をさらに備えることが好ましい。前記キャリブレーション手段によるキャリブレーションが行われることによって、本発明の放射能測定装置によって得た最尤カウント数基づく放射能分布を、従来の放射線測定装置によって測定され、使用されているデータと同様に扱うことができ、測定結果の利用範囲を広げることができる。
(Calibration means)
Further, the radioactivity measuring apparatus of the present invention calculates the conversion coefficient for each contaminated component from the soil having a known contamination concentration, and applies the conversion coefficient to the derived radioactivity distribution to obtain the derived radiation. It is preferable to further provide a calibration means for changing the function distribution into general-purpose data. By performing the calibration by the calibration means, the radioactivity distribution based on the most probable count number obtained by the radioactivity measuring device of the present invention is measured by the conventional radioactivity measuring device and is the same as the data used. It can be handled and the range of use of measurement results can be expanded.
前記キャリブレーション手段によるキャリブレーションは、本発明の測定装置によって導出された放射線濃度分布を汎用的なデータへと変更することができるものであれば特に限定はされない。例えば、図７（ａ）に示すように、放射能測定用容器６０に、既知の放射能濃度（汎用的な放射能濃度のデータが用いられている）の土を複数充填した後、図７（ａ）に示すように、本発明の放射線検出プローブ１０によって容器中の土壌の放射能濃度（ここでは、セシウム137のカウント数の分布）を測定し、本発明の放射能測定装置によって得られるセシウム137のカウント数（図８（ａ））と、既知の汎用的なセシウム137濃度データ（放射能量（kBq/kg））との関係（図８（ｂ））から汚染成分（ここではセシウム137）の換算式を導出する方法が挙げられる。本発明の放射能測定装置によって得られる放射線濃度（カウント数）を、汎用的なデータ（放射能量）に変換するための換算式（図８（ｂ）では、ｙ＝0.56ｘ−0.60（R2＝0.97）のことである。）を、発明の放射能測定装置によって測定した放射線濃度分布に適用することによって、汎用的な放射能濃度分布データとして扱うことが可能となり、従来の測定装置による結果との比較等も可能になる。 The calibration by the calibration means is not particularly limited as long as the radiation concentration distribution derived by the measuring device of the present invention can be changed into general-purpose data. For example, as shown in FIG. 7A, after the radioactivity measuring container 60 is filled with a plurality of soils having a known radioactivity concentration (general-purpose radioactivity concentration data is used), FIG. As shown in (a), the radioactivity concentration of the soil in the container (here, the distribution of the count number of cesium-137) is measured by the radiation detection probe 10 of the present invention, and is obtained by the radioactivity measuring apparatus of the present invention. From the relationship between the count number of cesium-137 (Fig. 8 (a)) and the known general-purpose cesium-137 concentration data (radioactivity amount (kBq / kg)) (Fig. 8 (b)), the contaminating component (here, cesium-137). ) Is derived from the conversion formula. In the conversion formula for converting the radiation concentration (count number) obtained by the radioactivity measuring device of the present invention into general-purpose data (radioactivity amount) (in FIG. 8B, y = 0.56x-0.60 (R 2). By applying = 0.97)) to the radiation concentration distribution measured by the radioactivity measuring device of the present invention, it becomes possible to handle it as general-purpose radioactivity concentration distribution data, and the result of the conventional measuring device. It is also possible to compare with.
なお、前記放射能測定用容器６０は、図７（ａ）に示すように、円筒状の複数の容器６０ａ〜６０ｎから構成することができる。複数の容器６０ａ〜６０ｎ中に充填される土は、同じものでも良いし、異なるものであってもよい。また、前記容器６０ｎについては、中に土を充填できるものであれば特に限定はされない。例えば、図７（ｂ）に示すように、側面に充填孔６１及び放射線検出プローブ用孔６２を設けられたものが挙げられる。 As shown in FIG. 7A, the radioactivity measurement container 60 can be composed of a plurality of cylindrical containers 60a to 60n. The soil filled in the plurality of containers 60a to 60n may be the same or different. Further, the container 60n is not particularly limited as long as it can be filled with soil. For example, as shown in FIG. 7B, a filling hole 61 and a radiation detection probe hole 62 are provided on the side surface.
（その他）
本発明の放射能測定装置は、上述した放射線検出プローブ１０及び解析部２０以外にも、例えば図１に示すように、水位計測部３０や、電源４０を備えることができる。
前記水位計測部３０は、前記放射線検出プローブ１０を挿入する地盤の水位を測定するための機器であり、ため池の底質中の放射能分布を把握する場合等に有用である。前記水位計測部３０は、例えば図４に示すように、前記放射線検出プローブ１０を、前記水位計測部３０の中心に通した状態で、土壌へと挿入する形で用いられる。
(Other)
In addition to the radiation detection probe 10 and the analysis unit 20 described above, the radioactivity measuring device of the present invention may include a water level measuring unit 30 and a power supply 40, for example, as shown in FIG.
The water level measuring unit 30 is a device for measuring the water level of the ground into which the radiation detection probe 10 is inserted, and is useful when grasping the radioactivity distribution in the bottom sediment of the reservoir. As shown in FIG. 4, for example, the water level measuring unit 30 is used in such a form that the radiation detection probe 10 is inserted into the soil in a state of being passed through the center of the water level measuring unit 30.
例えば、ため池等の水底における土壌の放射能濃度分布を取得する場合には、前記放射線検出プローブ１０をため池及び土壌の深さ方向へ進め、停止した時点の水深を前記水位計測部３０により測定する。具体的には、前記水位計測部を水底まで沈めて水底の水深ａを測定する。その後、水位計測部３０を引き上げ止まるところで引き上げ時の水深ｂを測定する。そして、放射線検出プローブ１０の長さは決まっているため、土壌への前記放射線検出プローブ１０の挿入量は、前記放射線検出プローブ１０の長さ−（水底の水深ａ−引き上げ時の水深ｂ）から算出できる。 For example, when acquiring the radioactivity concentration distribution of soil on the bottom of a pond or the like, the radiation detection probe 10 is advanced in the depth direction of the pond and soil, and the water depth at the time of stopping is measured by the water level measuring unit 30. .. Specifically, the water level measuring unit is submerged to the bottom of the water to measure the water depth a of the bottom of the water. After that, the water depth b at the time of pulling up is measured at the point where the water level measuring unit 30 is pulled up and stopped. Since the length of the radiation detection probe 10 is fixed, the amount of the radiation detection probe 10 inserted into the soil is derived from the length of the radiation detection probe 10- (water depth a at the bottom of the water-water depth b at the time of raising). Can be calculated.
さらに、本発明の放射能測定装置は、水位計測部３０や、電源４０の他にも、必要に応じて、接続装置５０や、その他必要な機器を適宜備えることができる。 Further, the radioactivity measuring device of the present invention may be appropriately provided with a connecting device 50 and other necessary devices in addition to the water level measuring unit 30 and the power supply 40, if necessary.
＜放射能測定方法＞
次に、本発明による放射能測定方法について説明する。
本発明の放射能測定方法は、図２（ａ）〜（ｃ）に示すように、長手方向に複数の放射線受光素子１１を有する放射線検出プローブ１０を土壌１００に挿入し、前記複数の放射線受光素子１１が、それぞれカウント数を取得し、前記放射線受光素子１１毎に取得したカウント数から不要なカウント数を除いた最尤カウント数を算出し、該最尤カウント数から、前記土壌１００の深さに応じた放射能を導出することを特徴とする。
<Radioactivity measurement method>
Next, the radioactivity measuring method according to the present invention will be described.
In the radioactivity measuring method of the present invention, as shown in FIGS. 2A to 2C, a radiation detection probe 10 having a plurality of radiation receiving elements 11 in the longitudinal direction is inserted into the soil 100, and the plurality of radiation receiving elements are received. Each element 11 acquires the count number, calculates the most probable count number obtained by subtracting the unnecessary count number from the count number acquired for each radiation receiving element 11, and from the most probable count number, the depth of the soil 100. It is characterized by deriving the corresponding radioactivity.
上記構成を具備することで、前記複数の放射線受光素子１１が、土壌１００で、それぞれ放射線のカウント数を取得することによって、複雑な設備や時間をかけることなく、土壌における深さ方向に沿った放射能の大まかな分布を取得でき、さらに、図２（ｃ）に示すように、放射線受光素子ごとに取得したカウント数（図２（ｂ））から不要なカウント数を除く処理を行うことによって、土壌１００の放射能分布を正確に予測することが可能となる。 By providing the above configuration, the plurality of radiation receiving elements 11 acquire the count number of radiation in the soil 100, respectively, so as to follow the depth direction in the soil without spending complicated equipment and time. A rough distribution of radioactivity can be obtained, and as shown in FIG. 2C, by performing a process of removing unnecessary counts from the number of counts acquired for each radiation receiving element (FIG. 2B). , It becomes possible to accurately predict the radioactivity distribution of soil 100.
本発明の放射能測定方法のその他の条件については、上述した本発明の放射能測定装置の中で記載された内容と同様である。 Other conditions of the radioactivity measuring method of the present invention are the same as those described in the above-mentioned radioactivity measuring device of the present invention.
以下に、実施例を挙げて本発明をさらに詳しく説明するが、本発明は下記の実施例に何ら限定されるものではない。 Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.
（実施例）
図１に示すように、放射線検出プローブ１０と、解析部２０とを備える放射能測定装置を作製した。
なお、放射線検出プローブ１０については、図３に示すように、ガイドロット１２、ケーブル固定部１３、ロットレジューサ１４を備えるものであり、プローブの長さが50cm、外径が24mmである。また、放射線受光素子１１はCsI(Tl)からなり、サイズが10mm×10mm×10mmで、前記前記放射線検出プローブ１０の内部に設けられ、配設間隔が前記プローブ１０の長手方向に25mmであった。
また、解析部２０については、市販のノートパソコンに、前記各放射線受光素子１１が取得するべき深さ位置とは異なる深さ位置にある放射性物質に起因したカウント数を取り除くための逆解析プログラムを組み込んだものである。
(Example)
As shown in FIG. 1, a radioactivity measuring device including a radiation detection probe 10 and an analysis unit 20 was produced.
As shown in FIG. 3, the radiation detection probe 10 includes a guide lot 12, a cable fixing portion 13, and a lot reducer 14, and has a probe length of 50 cm and an outer diameter of 24 mm. Further, the radiation receiving element 11 was made of CsI (Tl), had a size of 10 mm × 10 mm × 10 mm, was provided inside the radiation detection probe 10, and had an arrangement interval of 25 mm in the longitudinal direction of the probe 10. ..
Further, regarding the analysis unit 20, a commercially available notebook computer is provided with an inverse analysis program for removing the count number caused by the radioactive substance at a depth position different from the depth position to be acquired by each radiation receiving element 11. It is a built-in one.
（評価）
（１）土壌におけるセシウム137の深さ方向放射能分布
図５に示すように、福島県飯舘村のため池において（図５（ａ））、実施例で作製した放射能測定装置を用いて、ため池底部の土壌におけるセシウム137の深さ方向濃度分布を得た（図５（ｂ）に実測値及び計算（逆解析）結果を示し、計算結果を整理したものを図５（ｃ）に「実施例」として示す。）。
また、実際の放射能分布を把握するため、ため池底部の土壌について、5cmの深さ毎に土壌を抜き出し、セシウム137の濃度を測定し、深さ方向濃度分布を導出した（図５（ｄ）に「実測」として示す。）。
実施例の放射能測定装置によって算出された放射能分布（図５（ｃ））と、実測に基づいて算出した放射能分布（図５（ｄ））とを比較した結果、同じような分布状態が得られている（棒グラフの形状が近似している）ことがわかった。
(Evaluation)
(1) Depth-direction radioactivity distribution of cesium-137 in soil As shown in Fig. 5, in a pond in Iitate Village, Fukushima Prefecture (Fig. 5 (a)), a pond using the radioactivity measuring device prepared in the example. The distribution of the concentration of cesium-137 in the bottom soil in the depth direction was obtained (Fig. 5 (b) shows the measured value and the calculation (reverse analysis) result, and the calculation results are arranged in Fig. 5 (c). It is shown as.).
In addition, in order to grasp the actual radioactivity distribution, the soil at the bottom of the pond was extracted at every 5 cm depth, the concentration of cesium-137 was measured, and the concentration distribution in the depth direction was derived (Fig. 5 (d)). Shown as "actual measurement").
As a result of comparing the radioactivity distribution calculated by the radioactivity measuring device of the example (FIG. 5 (c)) and the radioactivity distribution calculated based on the actual measurement (FIG. 5 (d)), the distribution state is similar. Was obtained (the shape of the bar graph is similar).
（２）実施例の放射能測定装置によって算出された放射能と実測した放射能との対比
次に、放射能に汚染された複数のため池底部について、実施例の放射能測定装置によって算出された放射能分布と実測したものとの比較を行った。
具体的には、実施例で作製した放射能測定装置を用いて、ため池底部の土壌におけるセシウム137の深さ方向濃度分布を得た後、プローブを挿入した場所から土壌を抜き出し、5cmの深さ毎に切り分けてサンプルを測定し、各サンプルからゲルマニウム測定器を用いてセシウム137の濃度を測定した。比較結果を図６に示す。
図６における○プロットは、１つの測定箇所における放射能測定装置の算出値と実測値との関係を示したものであり、４ヶ所のため池で計２２箇所について比較を行ったものである。
図６から、実施例の放射能測定装置により得られたセシウム137の深さ方向濃度分布と、実測したセシウム137の深さ方向濃度分布とは、相関関係（近似線：R2=0.8066）を示すことがわかった。その結果、本発明の構成を備える放射能測定装置は、実測値との相関関係を反映することで、正確に、土壌の放射能分布を把握できることがわかった。
また、実施例の放射能測定装置を用いてセシウム137の深さ方向濃度分布を導出するのに要した時間は、実測の場合に比べて大幅に削減できた。その結果、短時間で土壌中の放射能分布を把握できることがわかった。
(2) Comparison between the radioactivity calculated by the radioactivity measuring device of the example and the measured radioactivity Next, the bottom of the pond contaminated with radioactivity was calculated by the radioactivity measuring device of the example. The radioactivity distribution was compared with the measured one.
Specifically, after obtaining the concentration distribution of cesium-137 in the soil at the bottom of the pond in the depth direction using the radioactivity measuring device prepared in the example, the soil was extracted from the place where the probe was inserted, and the depth was 5 cm. The samples were cut into pieces and the samples were measured, and the concentration of cesium-137 was measured from each sample using a germanium measuring device. The comparison result is shown in FIG.
The ○ plot in FIG. 6 shows the relationship between the calculated value and the measured value of the radioactivity measuring device at one measurement point, and compares a total of 22 points with four ponds.
From FIG. 6, the correlation (approximate line: R 2 = 0.8066) between the depth concentration distribution of cesium-137 obtained by the radioactivity measuring device of the example and the actually measured depth concentration distribution of cesium-137. It turned out to show. As a result, it was found that the radioactivity measuring device having the configuration of the present invention can accurately grasp the radioactivity distribution of soil by reflecting the correlation with the measured value.
In addition, the time required to derive the concentration distribution of cesium-137 in the depth direction using the radioactivity measuring device of the example could be significantly reduced as compared with the case of actual measurement. As a result, it was found that the radioactivity distribution in the soil can be grasped in a short time.
本発明によれば、複雑な設備を用いることなく、短時間且つ正確に、土壌中の放射能分布を把握できる放射能測定装置及び放射能測定方法を提供することが可能となる。 According to the present invention, it is possible to provide a radioactivity measuring device and a radioactivity measuring method capable of grasping the radioactivity distribution in soil in a short time and accurately without using complicated equipment.
１０ 放射線検出プローブ
１１ 放射線受光素子
１２ ガイドロット
１３ ケーブル固定部
１４ ロットレジューサ
１５ ケーブル
２０ 解析部
３０ 水位計測部
４０ 電源
５０ 接続装置
６０ 放射能測定用容器
６０ｎ 容器
６１ 充填孔
６２ 放射線検出プローブ用孔
10 Radiation detection probe 11 Radiation light receiving element 12 Guide lot 13 Cable fixing part 14 Lot reducer 15 Cable 20 Analysis unit 30 Water level measurement unit 40 Power supply 50 Connection device 60 Radioactivity measurement container 60n Container 61 Filling hole 62 Radiation detection probe hole
Claims (9)
前記放射線検出プローブが土壌に挿入された際、前記複数の放射線受光素子が、それぞれ放射線のカウント数を取得し、前記解析部が、前記放射線受光素子毎に取得したカウント数から不要なカウント数を除いた最尤カウント数を算出し、該最尤カウント数から前記土壌における放射能分布を、前記放射能検出プローブ及び前記水位計測部を引き揚げることなく導出することを特徴とする、放射能測定装置。 A radiation detection probe having a plurality of radiation receiving elements in the longitudinal direction, an analysis unit that performs analysis based on the count number of radiation detected for each radiation receiving element, and a water level of the ground into which the radiation detection probe is inserted are measured. Equipped with a water level measurement unit
When the radiation detection probe is inserted into the soil, the plurality of radiation receiving elements each acquire a radiation count number, and the analysis unit obtains an unnecessary count number from the count number acquired for each radiation receiving element. A radioactivity measuring apparatus characterized by calculating the excluded most probable count number and deriving the radioactivity distribution in the soil from the most probable count number without pulling up the radioactivity detection probe and the water level measuring unit. ..
By calculating a conversion formula for each contaminated component from soil with a known pollution concentration and applying the conversion formula to the derived radioactivity distribution, the derived radioactivity distribution is changed to general-purpose data. The radioactivity measuring method according to claim 8, wherein the radioactivity is measured.
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