JP6340966B2 - Method for determining soil depth and planar source strength of radiation sources in radioactive material contaminated areas - Google Patents
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本発明は、放射性物質によって汚染された区域における放射線源の土壌深さ及び所定面積当たりの面状線源強度を求める方法、更に詳しくは、放射性物質による汚染が均一と見做せる平坦な区域における放射線源の土壌深さ及び所定面積当たりの面状線源強度を求める方法に関する。 The present invention provides a method for determining the soil depth of a radiation source and the intensity of a planar radiation source per predetermined area in an area contaminated with radioactive material, and more particularly, in a flat area where contamination by radioactive material can be considered uniform. The present invention relates to a method for determining a soil depth of a radiation source and a planar radiation source intensity per predetermined area.
放射性物質によって汚染された区域を適宜に除染するためには、当該区域の環境放射線量を認識し、かかる環境放射線量に基いて除染作業計画を立案することが重要である。下記特許文献１には、当該区域を格子状の多数の所定面積領域に分割し、かかる多数の所定面積領域の各々において測定した線量に変換係数を乗じて所定面積当たりの面状線源強度に変換し、次いで線源強度を反映した距離と線量の相関を指数関数で示す近似式によって環境放射線量を求め、更に各所定面積領域の線量を総和して当該区域の環境放射線量を求めることが開示されている。 In order to appropriately decontaminate an area contaminated with radioactive material, it is important to recognize the environmental radiation dose in the area and to develop a decontamination work plan based on the environmental radiation dose. In the following Patent Document 1, the area is divided into a large number of lattice-shaped predetermined area regions, and the dose measured in each of the large number of predetermined area regions is multiplied by a conversion coefficient to obtain a planar radiation source intensity per predetermined area. The ambient radiation dose is calculated by an approximate expression that expresses the correlation between the distance and dose reflecting the source intensity by an exponential function after conversion, and the dose of each predetermined area is summed to obtain the ambient radiation dose in the area. It is disclosed.
而して、上記特許文献１に開示されている方法によれば、土壌自体における相当程度の高低変動及び建造物の存在等に起因して、汚染された区域における所定面積当たりの面状線源強度が不均一であり面状放射線源強度に相当程度の変動が存在する場合にも、個々の領域における面状放射線源強度を求め、これに基いて放射性物質によって汚染された区域の環境放射線量マップを作成することができる。しかしながら、上記特許文献１に開示されている方法も、未だ充分に満足し得るものではなく、次のとおりの問題が存在する。第一に、放射線源は地表面上ではなく地表面から幾分土壌中に浸透しており、従って地表から所定高さの点即ち所定地上高さの点における環境放射線量に対する関する放射線源の影響を算出する場合には、土壌中における減衰率と空気層における減衰率が異なる故に、放射線源の土壌深さを求めることが重要であるが、上記特許文献１に開示されている方法においては放射線源の土壌中への浸透について考慮されていない。第二に、特に除染すべき区域が比較的小さい場合に、得られる環境放射線源が実測することによって確認され得る実際の値から相当異なる傾向がある。 Thus, according to the method disclosed in Patent Document 1, a planar radiation source per predetermined area in a contaminated area due to considerable height fluctuations in the soil itself and the presence of buildings, etc. Even if the intensity is non-uniform and there is a considerable variation in the intensity of the planar radiation source, the intensity of the planar radiation source in each region is determined, and based on this, the environmental radiation dose in the area contaminated by the radioactive material is obtained. A map can be created. However, the method disclosed in Patent Document 1 is still not fully satisfactory, and has the following problems. First, the radiation source is penetrating into the soil somewhat from the ground surface rather than on the ground surface, so the influence of the radiation source on the environmental radiation dose at a given height point from the ground surface, ie a given ground height point. Is calculated, it is important to determine the soil depth of the radiation source because the attenuation rate in the soil is different from the attenuation rate in the air layer. However, in the method disclosed in Patent Document 1, radiation is used. No consideration is given to the penetration of the source into the soil. Second, especially when the area to be decontaminated is relatively small, the resulting environmental radiation source tends to differ considerably from the actual values that can be confirmed by actual measurements.
一方、本発明者の調査によれば、除染すべき区域には農地、運動場或いは公園等の平坦な区域が少なくなく、これらの平坦な区域においては放射性物質による汚染、特に原子力発電所の事故に起因する汚染、は均一と見做しても除染上全く問題がないことが判明した。 On the other hand, according to the investigation by the present inventor, there are not a few flat areas such as farmland, playground or park in the areas to be decontaminated. In these flat areas, contamination by radioactive materials, especially accidents at nuclear power plants. It has been found that there is no problem in decontamination even if the contamination due to is regarded as uniform.
本発明は上記のとおりの事実に鑑みてなされたものであり、その第一の技術的課題は、放射性物質による汚染が均一と見做すことができる平坦な区域に限定されるものではあるが、放射線源の土壌深さを充分適切に求める方法を提供することである。 The present invention has been made in view of the facts as described above, and the first technical problem thereof is limited to a flat area in which contamination by radioactive material can be regarded as uniform. It is to provide a method for determining the soil depth of a radiation source adequately and appropriately.
本発明の第二の技術的課題は、放射性物質による汚染が均一と見做すことができる平坦な区域に限定されるものではあるが、除染すべき区域が比較的小さい場合においても、環境放射線量を充分適切に求めることを可能にする、所定面積当たりの面状線源強度を求める方法を提供することである。 The second technical problem of the present invention is limited to a flat area where the contamination by radioactive material can be considered to be uniform. However, even if the area to be decontaminated is relatively small, It is an object of the present invention to provide a method for determining the intensity of a planar radiation source per predetermined area that makes it possible to determine the radiation dose sufficiently adequately.
本発明の第一の局面によれば、上記第一の技術的課題を解決する方法として、放射性物質による汚染が均一と見做すことができる平坦な区域における、放射線源の土壌深さｔを求める方法にして、
地表面投影位置が同一で、地上高さが第一の高さｈ１及び第二の高さｈ２である２個の評価点Ｐ１及びＰ２において環境放射線量Ｉ＊ｈ１及びＩ＊ｈ２を実測すること、
実測した環境放射線量Ｉ＊ｈ１及びＩ＊ｈ２の比γ＊＝Ｉ＊ｈ１／Ｉ＊ｈ２を求めること、
放射線源の仮定土壌深さｔ０及び所定面積当たりの仮定面状線源強度Ｓ０を仮定すること、
仮定土壌深さｔ０及び仮定面状線源強度Ｓ０に基いて、距離と線量との相関を指数関数で近似して評価点Ｐ１及びＰ２の環境放射線量Ｉ１ｈ１及びＩ１ｈ２を算出し、かかる環境放射線量Ｉ１ｈ１及びＩ１ｈ２の比γ１＝Ｉ１ｈ１／Ｉ１ｈ２を算出すること、仮定土壌深さｔｎを繰り返し変化せしめて環境放射線量Ｉｎｈ１及びＩｎｈ２を算出し、かかる環境放射線量Ｉｎｈ１及びＩｎｈ２の比γｎ＝Ｉｎｈ１／Ｉｎｈ２を算出することを含むニュートン法によって、放射線源の土壌深さｔを算出すること、
からなることを特徴とする方法が提供される。
According to the first aspect of the present invention, as a method for solving the first technical problem, the soil depth t of the radiation source in the flat area where the contamination by the radioactive material can be regarded as uniform is obtained. In the way you ask
Measure environmental radiation doses I * h1 and I * h2 at two evaluation points P1 and P2 having the same ground surface projection position and a ground height of the first height h1 and the second height h2. ,
Determining the ratio γ * = I * h1 / I * h2 of the measured environmental radiation doses I * h1 and I * h2,
Assuming an assumed soil depth t 0 of the radiation source and an assumed planar source intensity S 0 per predetermined area;
Based on the assumed soil depth t 0 and the assumed planar source intensity S 0 , the environmental radiation doses I 1 h1 and I 1 h2 at the evaluation points P1 and P2 are calculated by approximating the correlation between the distance and the dose with an exponential function. Then, the ratio of the environmental radiation doses I 1 h1 and I 1 h2 γ 1 = I 1 h1 / I 1 h2 is calculated, the assumed soil depth t n is repeatedly changed, and the environmental radiation doses I n h1 and I n calculating h2 and calculating the soil depth t of the radiation source by Newton's method including calculating the ratio γ n = I n h1 / I n h2 of such environmental radiation doses I n h1 and I n h2,
A method is provided that comprises:
また、本発明の第二の局面によれば、上記第二の技術的課題を達成する方法として、放射性物質による汚染が均一と見做すことができる平坦な区域における、所定面積当たりの面状線源強度Ｓを求める方法にして、
複数個の所定面積領域の各々における所定地上高さｈにおける環境放射線量Ｉ＊を測定すること、
該所定面積領域の仮定面状線源強度Ｓ０を仮定すること、
該仮定面状線源強度Ｓ０に基いて、距離と線量との相関を指数関数で近似して該所定面積領域の各々における該所定地上高さｈにおける環境放射線量Ｉ１ｈを算出し、該所定面積領域の環境放射線量Ｉ１ｈの総和を算出すること、仮定面状線源強度Ｓｎを繰り返し変化せしめて該所定面積領域の各々における該所定地上高さｈにおける環境放射線量Ｉｎｈを算出し、該所定面積領域の環境放射線量Ｉｎｈの総和を算出することを含むニュートン法によって、所定面積当たりの面状線源強度Ｓを求めること、
からなることを特徴とする方法が提供される。
Further, according to the second aspect of the present invention, as a method for achieving the second technical problem, a planar shape per predetermined area in a flat area where contamination by radioactive material can be regarded as uniform. As a method for obtaining the source strength S,
Measuring an environmental radiation dose I * at a predetermined ground height h in each of a plurality of predetermined area regions;
Assuming an assumed planar source intensity S 0 of the predetermined area region;
Based on the assumed planar source intensity S 0 , the correlation between distance and dose is approximated by an exponential function to calculate the environmental radiation dose I 1 h at the predetermined ground height h in each of the predetermined area regions, calculating the sum of the environmental radiation amount I 1 h of the predetermined area region, assuming planar ray source intensity S environmental radiation amount in the predetermined ground height h n repeatedly changes made to the in each the predetermined area region I n calculating a planar radiation source intensity S per predetermined area by a Newton method including calculating h and calculating a sum of environmental radiation doses I n h in the predetermined area region;
A method is provided that comprises:
本発明の第一の局面における発明によれば、放射線源の土壌深さを充分適切に求めることができる。また、本発明の第二の局面における発明によれば、除染すべき区域が比較的小さい場合でも、所定面積当たりの面状線源強度を充分適切に求めることができ、従って求めた面状線源強度に基いて充分適切に環境放射線量を求めることができる。 According to the invention in the first aspect of the present invention, the soil depth of the radiation source can be determined sufficiently appropriately. Further, according to the invention of the second aspect of the present invention, even when the area to be decontaminated is relatively small, the surface radiation source intensity per predetermined area can be determined sufficiently appropriately, and thus the determined surface state. The environmental radiation dose can be determined sufficiently adequately based on the radiation source intensity.
図１には、セシウムの如き放射性物質による汚染が均一と見做せる比較的小さい平坦な区域２が図示されている。そして、かかる区域２が格子状に区画された複数個（図示の場合は９個）の所定面積、例えば１ｍ２、の領域に分割されている。 FIG. 1 illustrates a relatively small flat area 2 that can be considered uniform with radioactive material such as cesium. The area 2 is divided into a plurality of (9 in the illustrated example) predetermined areas, for example, 1 m 2 , which are partitioned in a grid pattern.
放射線源の土壌深さの算出
放射線源の土壌深さを求めるために、本発明の方法においては、地表面投影位置が同一の地点、例えば区域２の中央の領域（ｉ，ｊ）の中心地点、において第一の高さｈ１（例えば地表面から１ｃｍの高さ）及び第二の高さｈ２（例えば地表面から１ｍの高さ）である第一の特定評価点Ｐ１及び第二の特定評価点Ｐ２における環境放射線量Ｉ＊ｈ１及びＩ＊ｈ２を実測する。次いで、実測した環境放射線量Ｉ＊ｈ１及びＩ＊ｈ２の比γ＊＝Ｉ＊ｈ１／Ｉ＊ｈ２を求める。
Calculation of the soil depth of the radiation source In order to determine the soil depth of the radiation source, in the method of the present invention, the ground surface projection position is the same point, for example, the central point of the central region (i, j) of the area 2 , The first specific evaluation point P1 and the second specific evaluation that are the first height h1 (for example, a height of 1 cm from the ground surface) and the second height h2 (for example, a height of 1 m from the ground surface). The environmental radiation doses I * h1 and I * h2 at the point P2 are measured. Next, a ratio γ * = I * h1 / I * h2 of the measured environmental radiation doses I * h1 and I * h2 is obtained.
次に、放射線源Ｒの仮定土壌深さｔ０及び所定面積当たりの仮定面状線源強度Ｓ０を適宜に仮定する。そして、かかる仮定土壌深さｔ０及び仮定面状線源強度Ｓ０に基いて、距離と線量との相関を指数関数で近似して、９個の領域の各々から上記第一の特定評価点Ｐ１及び上記第二の特定評価点Ｐ２に及ぼされる放射線量を算出し、これらの放射線量を総和して第一の特定評価点Ｐ１及び第二の特定評価点Ｐ２において環境放射線量Ｉ１ｈ１及びＩ１ｈ２を算出する。例えば、各領域から第一の特定評価点Ｐ１に及ぼされる放射線量は、下記式１によって算出することができる。
∂In／∂x∂y＝S０／４πL２・{B1・exp（−μ１L１）｝・｛B２・exp（−μ２Ｌ２）｝
．．．式１
図１と共に図２を参照して説明を続けると、上記式１において、
Ｌ１は線源から特定評価点までの距離Ｌ中の土壌内長さ、
Ｌ２は線源から特定評価点までの距離Ｌ中の空気層内長さ、
Ｌ＝Ｌ１＋Ｌ２
μ１は土壌通過における線減弱定数
(土壌の密度が１．６ｇ／ｍ３の場合、μ１＝１２．３１／ｍ)
μ２は空気層通過における線減弱定数、
（μ２＝０．００９９８１／ｍ）
B1は土壌通過ビルドアップ係数（散乱による補正係数）で、B1＝１＋μ１L１
B2は空気層通過ビルドアップ係数(散乱による補正係数)で、B2＝１＋μ２Ｌ２
である。
Next, an assumed soil depth t 0 of the radiation source R and an assumed planar source intensity S 0 per predetermined area are appropriately assumed. Then, based on the assumed soil depth t 0 and the assumed planar source intensity S 0 , the distance between the dose and the dose is approximated by an exponential function, and the first specific evaluation point is obtained from each of the nine regions. The radiation dose exerted on P1 and the second specific evaluation point P2 is calculated, and these radiation doses are summed, and the environmental radiation dose I 1 h1 and the first specific evaluation point P1 and the second specific evaluation point P2 I 1 h2 is calculated. For example, the radiation dose exerted from each region to the first specific evaluation point P1 can be calculated by the following equation 1.
∂In / ∂x∂y = S 0 / 4πL 2 · {B 1 · exp (−μ 1 L 1 )} · {B 2 · exp (−μ 2 L 2 )}
. . . Formula 1
The description will be continued with reference to FIG. 2 together with FIG.
L 1 is the length in the soil during the distance L from the source to the specific evaluation point,
L 2 is the length in the air layer during the distance L from the radiation source to the specific evaluation point,
L = L 1 + L 2
μ 1 is the linear attenuation constant in soil passage
(When the soil density is 1.6 g / m 3 , μ 1 = 12.31 / m)
μ 2 is the linear attenuation constant when passing through the air layer,
(Μ 2 = 0.009981 / m)
B 1 is the soil build-up coefficient (correction coefficient due to scattering), B 1 = 1 + μ 1 L 1
B 2 is an air layer passage build-up coefficient (correction coefficient due to scattering), and B 2 = 1 + μ 2 L 2
It is.
次いで、上記環境放射線量Ｉ１ｈ１及びＩ１ｈ２の比γ１＝Ｉ１ｈ１／Ｉ１ｈ２を算出する。そして、ニュートン法（反復法）によって放射線源Ｒの土壌深さｔを求める。更に詳述すると、仮定土壌深さｔｎを微細に変化せしめて環境放射線量Ｉｎｈ１及びＩｎｈ２の比γｎ＝Ｉｎｈ１／Ｉｎｈ２を繰り返し算出し、Δγｎ≦γｍａｘに到達したときのｔｎを放射線源Ｒの土壌深さｔとする。ここで、Δγｎ＝γｎ−γ＊であり、γｍａｘは例えば０．００１に設定することができる。ｔｎの変動は式ｔｎ＝ｔｎ−１＋α（γｎ−１−γ０）、αは緩和係数で例えば０．０１に設定することができる、に基いて設定することができる。 Then calculates the ratio γ 1 = I 1 h1 / I 1 h2 of the environmental radiation amount I 1 h1 and I 1 h2. And the soil depth t of the radiation source R is calculated | required by the Newton method (iteration method). More specifically, the assumed soil depth t n is finely changed to repeatedly calculate the ratio γ n = I n h1 / I n h2 of the environmental radiation doses I n h1 and I n h2 so that Δγ n ≦ γ max Let tn when it arrives be the soil depth t of the radiation source R. Here, Δγ n = γ n −γ * , and γ max can be set to 0.001, for example. variation of t n can be set based on, it is possible to set the equation t n = t n-1 + α (γ n-1 -γ 0), α is a relaxation factor for example 0.01.
面状線源強度の算出
所定面積当たりの面状線源強度Ｓを求めるために、本発明の方法においては、上述した９個の所定面積領域の各々において所定地上高さ、例えば地表面から１ｍの高さ、の特定評価点Ｐにおける環境放射線量Ｉ＊を実測する。領域における特定評価点Ｐの地表面投影位置は、各領域の中心でよい。
Calculation of planar source intensity In order to obtain the planar source intensity S per predetermined area, in the method of the present invention, each of the nine predetermined area regions described above has a predetermined ground height, for example, 1 m from the ground surface. The environmental radiation dose I * at the specific evaluation point P of the height of is measured. The ground surface projection position of the specific evaluation point P in the area may be the center of each area.
次に、領域の仮定面状線源強度Ｓ０を適宜に仮定する。そして、仮定面状線源強度Ｓ０に基いて、距離と線量との相関を指数関数で近似して領域の各々の特定評価点Ｐにおける環境放射線量Ｉ１ｈを算出し、全ての領域の特定評価点Ｐにおける環境放射線量Ｉ１ｈを総和する。そして、ニュートン法（反復法）によって所定面積当たりの面状線源強度Ｓを求める。更に詳述すると、仮定面状線源強度Ｓｎを微細に変化せしめて領域の各々の特定評価点Ｐにおける環境放射線量Ｉｎｈを算出し、全ての領域の特定評価点Ｐにおける環境放射線量Ｉｎｈを総和する。仮定面状線源強度の変化は、式Ｓｎ＝Ｓｎ−１＋α×Δｓｎ−１、αは緩和係数で例えば０．０１に設定することができる、に基いて設定することができる。収束判定は、例えば、
（１）全ての領域におけるΔＩｎ≦ΔＩｍａｘ
（２）ΣΔＩｎ≦ΣΔＩｍａｘ
（３）ΔＳｎ≦ΔＳｍａｘ
（４）ΣΔＳｎ≦ΣΔＳｍａｘ
のいずれかが満足されるか否かによって遂行することができる。ここで、
ΔＩｎ（ｉ，ｊ）＝Ｉｎ（ｉ，ｊ）−Ｉ＊（ｉ，ｊ）
ΔＳｎ（ｉ、ｊ）＝ΔＩｎ（ｉ、ｊ）×ｐ（ｉ，ｊ）×ｑ（ｉ，ｊ）
であり、ｐ（ｉ，ｊ）は領域（ｉ、ｊ）における環境放射線量Ｉ０における自己寄与率、即ち領域（ｉ，ｊ）自体の面状線源が環境放射線量Ｉ０に及ぼす線量ｉの比率、ｐ（ｉ，ｊ）＝ｉ（ｉ、ｊ）／Ｉ０（ｉ，ｊ）、であり、ｑ（ｉ，ｊ）は面状線源強度Ｓ０とＩ０（ｉ，ｊ）との比率、ｑ（ｉ，ｊ）＝Ｓ０／Ｉ０（ｉ、ｊ）である。ΔＩｍａｘ、ΣΔＩｍａｘ、ΔＳｍａｘ及びΣΔＳｍａｘは適宜に設定することができる。
Next, the assumed planar source intensity S 0 of the region is assumed as appropriate. Based on the assumed planar source intensity S 0 , the correlation between the distance and the dose is approximated by an exponential function to calculate the environmental radiation dose I 1 h at each specific evaluation point P in the region, Sum the environmental radiation dose I 1 h at the specific evaluation point P. Then, the planar source intensity S per predetermined area is obtained by the Newton method (iterative method). Further More specifically, to calculate the environmental radiation dose I n h at a particular evaluation point P of each region finely contain altered assumptions planar ray source strength S n, environmental radiation dose at a particular evaluation point P in all areas Sum the I n h. The change in the assumed planar source intensity can be set based on the formula S n = S n−1 + α × Δs n−1 , α being a relaxation coefficient, for example, 0.01. Convergence judgment is, for example,
(1) ΔI n ≦ ΔI max in all regions
(2) ΣΔI n ≦ ΣΔI max
(3) ΔS n ≦ ΔS max
(4) ΣΔS n ≦ ΣΔS max
This can be accomplished depending on whether one of the above is satisfied. here,
ΔI n (i, j) = I n (i, j) −I * (i, j)
ΔS n (i, j) = ΔI n (i, j) × p (i, j) × q (i, j)
P (i, j) is the self-contribution ratio in the environmental radiation dose I 0 in the region (i, j), that is, the dose i that the planar radiation source in the region (i, j) itself exerts on the environmental radiation dose I 0. P (i, j) = i (i, j) / I 0 (i, j), where q (i, j) is the planar source intensity S 0 and I 0 (i, j) Q (i, j) = S 0 / I 0 (i, j). ΔI max , ΣΔI max , ΔS max and ΣΔS max can be set as appropriate.
上述したとおりにして所定面積当たりの面状線源強度Ｓを求めると、かかる面状線源強度Ｓに基いて、区域２における土表面から所定高さ（例えば１ｍの高さ）における環境放射線量マップ(分布マップ)を作成し、かかるマップに基いて所要の除染作業を効率的に遂行することがでる。 When the planar radiation source intensity S per predetermined area is obtained as described above, the environmental radiation dose at a predetermined height (for example, a height of 1 m) from the soil surface in the area 2 based on the planar radiation source intensity S. A map (distribution map) can be created, and required decontamination work can be efficiently performed based on the map.
２：放射性物質による汚染が均一と見做せる区域
Ｐ、Ｐ１及びＰ２：特定評価点
Ｒ：放射線源
2: Area where contamination by radioactive material can be considered uniform P, P1, and P2: Specific evaluation points R: Radiation source
Claims (2)
地表面投影位置が同一で、地上高さが第一の高さｈ１及び第二の高さｈ２である２個の評価点Ｐ１及びＰ２において環境放射線量Ｉ＊ｈ１及びＩ＊ｈ２を実測すること、
実測した環境放射線量Ｉ＊ｈ１及びＩ＊ｈ２の比γ＊＝Ｉ＊ｈ１／Ｉ＊ｈ２を求めること、
放射線源の仮定土壌深さｔ０及び所定面積当たりの仮定面状線源強度Ｓ０を仮定すること、
仮定土壌深さｔ０及び仮定面状線源強度Ｓ０に基いて、距離と線量との相関を指数関数で近似して評価点Ｐ１及びＰ２の環境放射線量Ｉ１ｈ１及びＩ１ｈ２を算出し、かかる環境放射線量Ｉ１ｈ１及びＩ１ｈ２の比γ１＝Ｉ１ｈ１／Ｉ１ｈ２を算出すること、仮定土壌深さｔｎを繰り返し変化せしめて環境放射線量Ｉｎｈ１及びＩｎｈ２を算出し、かかる環境放射線量Ｉｎｈ１及びＩｎｈ２の比γｎ＝Ｉｎｈ１／Ｉｎｈ２を算出することを含むニュートン法によって、放射線源の土壌深さｔを算出すること、
からなることを特徴とする方法。 In a flat area where contamination by radioactive material can be considered uniform, the soil depth t of the radiation source is determined,
Measure environmental radiation doses I * h1 and I * h2 at two evaluation points P1 and P2 having the same ground surface projection position and a ground height of the first height h1 and the second height h2. ,
Determining the ratio γ * = I * h1 / I * h2 of the measured environmental radiation doses I * h1 and I * h2,
Assuming an assumed soil depth t 0 of the radiation source and an assumed planar source intensity S 0 per predetermined area;
Based on the assumed soil depth t 0 and the assumed planar source intensity S 0 , the environmental radiation doses I 1 h1 and I 1 h2 at the evaluation points P1 and P2 are calculated by approximating the correlation between the distance and the dose with an exponential function. Then, the ratio of the environmental radiation doses I 1 h1 and I 1 h2 γ 1 = I 1 h1 / I 1 h2 is calculated, the assumed soil depth t n is repeatedly changed, and the environmental radiation doses I n h1 and I n calculating h2 and calculating the soil depth t of the radiation source by Newton's method including calculating the ratio γ n = I n h1 / I n h2 of such environmental radiation doses I n h1 and I n h2,
A method characterized by comprising:
複数個の所定面積領域の各々における所定地上高さｈにおける環境放射線量Ｉ＊を測定すること、
該所定面積領域の仮定面状線源強度Ｓ０を仮定すること、
該仮定面状線源強度Ｓ０に基いて、距離と線量との相関を指数関数で近似して該所定面積領域の各々における該所定地上高さｈにおける環境放射線量Ｉ１ｈを算出し、該所定面積領域の環境放射線量Ｉ１ｈの総和を算出すること、仮定面状線源強度Ｓｎを繰り返し変化せしめて該所定面積領域の各々における該所定地上高さｈにおける環境放射線量Ｉｎｈを算出し、該所定面積領域の環境放射線量Ｉｎｈの総和を算出することを含むニュートン法によって、所定面積当たりの面状線源強度Ｓを求めること、
からなることを特徴とする方法。 In a flat area where contamination by radioactive material can be regarded as uniform, a method for obtaining the planar source intensity S per predetermined area,
Measuring an environmental radiation dose I * at a predetermined ground height h in each of a plurality of predetermined area regions;
Assuming an assumed planar source intensity S 0 of the predetermined area region;
Based on the assumed planar source intensity S 0 , the correlation between distance and dose is approximated by an exponential function to calculate the environmental radiation dose I 1 h at the predetermined ground height h in each of the predetermined area regions, calculating the sum of the environmental radiation amount I 1 h of the predetermined area region, assuming planar ray source intensity S environmental radiation amount in the predetermined ground height h n repeatedly changes made to the in each the predetermined area region I n calculating a planar radiation source intensity S per predetermined area by a Newton method including calculating h and calculating a sum of environmental radiation doses I n h in the predetermined area region;
A method characterized by comprising:
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