April, 2012
Summarized Version of the “Results of the Research on
Distribution of Radioactive Substances Discharged by the
Accident at TEPCO’s Fukushima Dai-ichi NPP”
Emergency Operation Center, Ministry of Education, Culture, Sports, Science and Technology
Agriculture, Forestry and Fisheries Research Council, Ministry of Agriculture, Forestry and Fisheries
1. REPORT OF DISTRIBUTION MAPS OF RADIATION DOSES, ETC. (PART 1)··································1
2. REPORT ON THE RESEARCH RELATING TO DISTRIBUTION MAPS OF RADIATION DOSES,
ETC. (PART 2) ·······································································································································24
3. REPORT ON THE RESEARCH RELATING TO RADIATION CONCENTRATION DISTRIBUTION
MAPS FOR FARMLAND SOIL (PART 3) ····························································································43
1. Report of Distribution Maps of Radiation Doses, etc. (Part 1)
1.1 Purpose of distribution maps of radiation doses, etc.
This monitoring survey comprised a part of the project under the 2011 Strategic Funds for the Promotion
of Science and Technology, entitled “Establishment of the Base for Taking Measures for Environmental
Impact of Radioactive Substances,” and for the purpose of ascertaining effects of radioactive substances
discharged by the accident at the Fukushima Dai-ichi NPP, it was determined to prepare “distribution
maps of ambient dose rates,” which compile measurement results of ambient dose rates at a height of 1m
above the ground surface, and “soil deposition density maps,” which compile distributions of deposition
densities by radioactive nuclides deposited on soil.*
The monitoring survey was conducted as consigned by MEXT, under the initiative of the Japan Atomic
Energy Agency, with cooperation of various universities and research institutes. Each of the surveys was
carried out after the Advisory Board of Distribution Map of Radiation Dose, etc. established within
MEXT had verified their validity.
* They are called “soil deposition density maps” for descriptive purposes to clarify their features,
i.e., indicating distributions of radiation levels remaining close to the soil surface per unit area.
1.2 Survey period
This monitoring survey aimed to detect I-131, which is one of the important nuclides for assessing
exposure immediately after the accident but is expected to become difficult to be detected due to its short
half-life period, and to ascertain initial conditions of radioactive substances before flowing out from the
soil surface due to rainfall during the rainy season. Therefore, the measurement of ambient dose rates and
soil sampling were conducted in a short period from June 6 to July 8, 2011.
1.3 Targeted areas
Based on the results of airborne monitoring and other environmental monitoring, the areas within 80km
from the Fukushima Dai-ichi NPP were divided into 2km×2km grids, whereas the areas between 80km
and 100km and areas of Fukushima prefecture out of that scope were divided into 10km×10km grids.
Ambient dose rates were measured at a height of 1m above the ground surface at one location each in
these divided grids (nearly 2,200 locations in total), and soil samples were collected at five points in
principle at each location.
1.4 Organizations offering cooperation
(i) Measurement of ambient dose rates and soil sampling (440 persons in total from 107 organizations)
Researchers from Osaka University, Kyoto University, University of Tsukuba, the University of
Tokyo, the Japan Atomic Energy Agency, and the Japan Chemical Analysis Center, and members
of the local support team of the Federation of Electric Power Companies of Japan, etc.
(ii) Nuclide analysis of soil samples (291 persons in total from 21 organizations)
Researchers from the Japan Chemical Analysis Center, and the University of Tokyo, etc.
* Analysis of alpha-emitting nuclides and beta-emitting nuclides was conducted solely by the Japan
Chemical Analysis Center.
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1.5 Results and considerations
(1) Measurement results of ambient dose rates and considerations
At locations where soil samples were collected within the 100-km range from the Fukushima Dai-ichi
NPP and within Fukushima prefecture out of that scope (around 2,200 locations), ambient dose rates at a
height of 1m above the ground surface were measured by using calibrated NaI (Tl) scintillators and
ionization chamber type survey meters, and a distribution map of ambient dose rates (see Fig. 1) showing
the distribution of ambient dose rates 1m above the ground surface at each of the soil sampling points
were prepared, based on the obtained data and the latitude/longitude information from GPS (hereinafter
referred to as the “GPS information”).
Furthermore, in order to ascertain the distribution of radioactive substances around roads in detail, a
vehicle-borne survey*1 was also conducted by using the KURAMA system mainly at national roads and
prefectural roads in the targeted areas, and a vehicle-borne survey map (see Fig. 2) showing the
distribution of ambient dose rates 1m above the ground surface along roads was prepared, based on the
results of continuous measurement and the GPS information.
* A vehicle-borne survey is a technique in which radiation detectors are installed in a vehicle, and
gamma rays from radioactive substances accumulated on the ground are measured quickly and in
detail, in order to continuously measure air does rates around roads. In this monitoring survey, the
KURAMA system, which was originally developed by Kyoto University, was used with the
cooperation of Fukushima prefecture
Measurement of ambient dose rates at soil sampling points was carried out by carefully choosing places
with a certain space free from disturbance, and the distribution of ambient dose rates reflecting the
deposition of radioactive substances as of June to July was successfully ascertained widely and in detail.
The vehicle-borne survey also clarified ambient dose rates in people’s living environment as of June
widely and in detail.
These results are expected to be utilized as precious initial data for assessing exposure levels and
following up changes in deposition of radioactive substances over time in the future.
The results of subsequent airborne monitoring revealed that there were areas outside the areas covered by
this monitoring survey where a considerable amount of radioactive cesium seemed to have been
deposited. Therefore, it is necessary to conduct a detailed monitoring survey also covering these areas.
(Starting from December 2011, a vehicle-borne survey was conducted by expanding the targeted areas
from Iwate prefecture to Yamanashi prefecture, and distribution maps of ambient dose rates are now
being prepared.)
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Fig. 1 Distribution Map of Ambient dose rates
(Based on measurement results at soil sampling points)
Fig. 2 Distribution Map of Ambient dose rates
(Based on continuous measurement results through vehicle-borne survey)
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(2) Results of soil deposition density maps and considerations
1) Results of maps of gamma-emitting nuclide deposition density in soil and considerations
With regard to around 11,000 soil samples, deposited amounts (radiation levels per unit area) of five
gamma-emitting nuclides (Cs-134, Cs-137, I-131, Te-129m, and Ag-110m) were measured by using
germanium semiconductor detectors, and maps were prepared based on those amounts and the GPS
information (see Fig. 3 for Cs-134, Fig. 4 for Cs-137, Fig. 5 for I-131, Fig. 6 for Te-129m, and Fig. 7 for
Ag-110m).
In order to reduce influences of dispersion in radiation levels obtained at each monitoring point, the
arithmetic average calculated among up to five samples collected at each point (within a three-meter
square area) was used as the amount of radionuclides deposited at each point when preparing maps.
At all monitoring points, statistically significant data were obtained with regard to radioactive cesium but
not for some other nuclides. Accordingly, regarding points where it was judged under certain criteria that
radionuclides were detected, the most probable radiation levels were calculated and indicated on maps.
All the soil deposition density maps were based on the measurement results of soil samples that were
collected at carefully chosen places with a certain space free from disturbance, and the distribution of
radioactive substances as of June to July could be confirmed widely and in detail.
These results are expected to be utilized as precious initial data for assessing exposure levels and
following up changes in deposition of radioactive substances over time in the future, and at the same
time they are expected to be utilized in examining radioactive plumes initially discharged from the NPP
and figuring out their route to be deposited on the ground surface.
The measurement results of I-131 are important fundamental data for assessing radiation effects
immediately after the accident, but due to its short half-life period (eight days), significant measurement
results were not obtained at many points. Therefore, in the future, it is necessary to obtain deposition
density levels of I-129, which was discharged together with I-131 but has a much longer half-life period
(15.7 million years), and to clarify the correlation between deposition density levels of I-131 and I-129,
thereby elaborating the map for I-131. (I-129 has been quantified since December 2011 mainly with
regard to soil samples collected through this monitoring survey.)
(i) Considerations on the maps of radioactive cesium deposition density in soil
Confirming ratios of the standard deviation to the average deposition density among five samples
collected at the same point (coefficients of variation), the average was 36% and some of the coefficients
exceed 100%, as shown in Fig. 8. Deposition amounts of radioactive cesium thus vary significantly even
among samples collected at the same point.
The causes therefor may include differences in soil characteristics and differences in how radioactive
substances fell at each point or how they were deposited depending on the existence of organic
substances in soil.
As a result of comparing the total deposition amounts of Cs-134 and Cs-137 and ambient dose rates at
soil sampling points, it was confirmed that they have a certain correlation with each other (see Fig. 9). It
became clear that it will be possible in the future to estimate deposition amounts of Cs-134 and Cs-137
based on the measurement results of ambient dose rates by calculating deposition density ratios of
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Cs-134 and Cs-137, and accurately assessing the movement of radionuclides into soil.
(ii) Considerations on the map of I-131 deposition density in soil
In order to ascertain the deposition on the soil surface of I-131 discharged by the accident at the
Fukushima Dai-ichi NPP, the ratios of the deposition of I-131 to that of Cs-137 were checked by location.
As shown in Fig. 10, deposition amounts of I-131 at monitoring points located to the south of the NPP
were not large compared to those at monitoring points located to the north of the NPP, but in the southern
coastal areas, I-131 was confirmed to be deposited on the ground surface at different ratios from those
observed at monitoring points in the northern areas and the southern inland areas. The reasons may be as
follows.
࣭The ratios of I-131 to Cs-137 contained in radioactive plumes and their chemical forms varied due to a
difference in when each radioactive plume was released.
࣭Weather conditions were not the same when I-131 and Cs-137 were deposited on the ground surface.
(iii) Considerations on the maps of Te-129m and Ag-100m deposition density in soil
In order to ascertain the deposition on the soil surface of Te-129m and Ag-100m discharged by the
accident at the Fukushima Dai-ichi NPP, the ratios of their deposition to that of Cs-137 were checked by
location.
Although the deposition of Cs-137 was not larger in the southern areas than in the northern areas from
the NPP, Te-129m was confirmed to be deposited on the ground surface in the southern coastal areas at
different ratios from those observed at monitoring points in the northern areas and the southern inland
areas, as seen in Fig. 11. At some of the inland parts in the southern coastal areas, the ratios of deposition
amounts of Te-129m to those of Cs-137 were considerably high.
Regarding Ag-110m, no clear correlation was found with the deposition amounts of Cs-137. However,
relatively higher ratios of deposition amounts of Ag-110m to those of Cs-137 were confirmed along the
coast in the northern and southern areas, compared with the surrounding areas.
The reasons may be as follows.
࣭The ratios of Te-129m and Ag-110m to Cs-137 contained in formed radioactive plumes and their
physical and chemical forms varied due to a difference in when each radioactive substance was
released from the NPP.
࣭Weather conditions were not the same when multiple radioactive plumes with different compositions
of Te-129m, Ag-110m, and Cs-137 moved away.
㻡
Fig. 3 Map of Cs-134 Deposition density in Soil
(Converted to radiation levels as of June 14, 2011)
Fig. 4 Map of Cs-137 Deposition density in Soil
(Converted to radiation levels as of June 14, 2011)
㻢
Fig. 5 Map of I-131 Deposition density in Soil
(Converted to radiation levels as of June 14, 2011)
Fig. 6 Map of Te-129m Deposition density in Soil
(Converted to radiation levels as of June 14, 2011)
㻣
Fig. 7 Map of Ag-100m Deposition density in Soil
(Converted to radiation levels as of June 14, 2011)
Frequency
Averageofvariationcoefficientis36%.
Variationcoefficient
Fig. 8 Frequency of variation coefficients in activity if radioactive cesium between 5 soil samples at
the same location (Variation coefficient is the ratio of standard deviation to the averaged activities for
5 soil samples).
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Nuclideconcentration
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Ambientdoseequivalentrateinair䠄䃛Sv/h䠅
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Fig. 9 Correlation between ambient dose equivalent rate in air, H*(10) and activity of radioactive
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2)
DepositedactivityofCs137䠄Bq/m
ἍἉỸἲᵏᵑᵕආბ᣽
Northfromthesite
(a)Northfromthesite
AverageofratioofI131toCs137:
ἺỸእᵏᵑᵏආბ᣽ᵍἍἉỸἲᵏᵑᵕආბ᣽
0.059
ỉ࠯‫͌ר‬ᾊ
ᵎᵌᵎᵎᵓᵗ
2)
ἍἉỸἲᵏᵑᵕආბ᣽
DepositedactivityofCs137䠄Bq/m
ἺỸእᵏᵑᵏආბ᣽
2)
DepositedactivityofI131(Bq/m
(b)Southfromthesitecoastalarea
(farmorethan34kmtothewestfrom
thesite)
Southfromthesiteinlandarea
Southfrom
Ҥ૾ϋᨕᢿ
thesiteinlandarea
AverageofratioofI131toCs137:
ἺỸእᵏᵑᵏආბ᣽ᵍἍἉỸἲᵏᵑᵕආბ᣽
0.0082
ỉ࠯‫͌ר‬ᾊ
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2)
DepositedactivityofCs137䠄Bq/m
ἍἉỸἲᵏᵑᵕආბ᣽
2)
ἺỸእᵏᵑᵏආბ᣽
DepositedactivityofI131(Bq/m
Southfromthesitecoastalarea
Southfrom
Ҥ૾ඝެᢿ
thesitecoastalarea
(c) Southfromthesitecoastalarea
(within34kmtothewestfromthesite)
ἺỸእᵏᵑᵏආბ᣽ᵍἍἉỸἲᵏᵑᵕආბ᣽
AverageofratioofI131toCs137:
ỉ࠯‫͌ר‬ᾊ ᵎᵌᵎᵐᵒᵒ
0.00244
2)
DepositedactivityofI131(Bq/m
ἺỸእᵏᵑᵏආბ᣽
Fig. 10 Relation of deposited activity between Cs-137 and I-131 (on June 14, 2011).
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㻭㼢㼑㼞㼍㼓㼑㻌㼛㼒㻌㼞㼍㼠㼕㼛㻌㼛㼒㻌㼀㼑㻙㻝㻞㻥㼙㻌㼠㼛㻌㻯㼟㻙㻝㻟㻣㻦㻌
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Fig. 11 Relation of deposited activity between Cs-137 and Te-129m (No. 1)
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(d)Southfromthesite
inlandarea South from
the site
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inlandarea 㻭㼢㼑㼞㼍㼓㼑㻌㼛㼒㻌㼞㼍㼠㼕㼛㻌㼛㼒㻌㼀㼑㻙㻝㻞㻥㼙㻌㼠㼛㻌㻯㼟㻙㻝㻟㻣㻦㻌
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(e) Area with the high ratio of
Te129m at south from the site
coastal area (within the blue
coloredline)
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thesitecoastalarea
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㻰㼑㼜㼛㼟㼕㼠㼑㼐㻌㼍㼏㼠㼕㼢㼕㼠㼥㻌㼛㼒㻌㼀㼑㻙㻝㻞㻥㼙㻔㻮㼝㻛㼙㻞㻕㻌
Fig. 11 Relation of deposited activity between Cs-137 and Te-129m (No. 2)
2) Maps of alpha-emitting nuclide and beta-emitting nuclide deposition density in soil
With regard to soil samples collected at 100 locations (one sample each) out of around 2,200 monitoring
points within the 100-km range from the Fukushima Dai-ichi NPP and within Fukushima prefecture out
of that scope, radiochemical analysis was conducted for Pu-238 and Pu-239+240 (alpha-emitting
nuclides) and Sr-89 and Sr-90 (beta-emitting nuclides) to obtain their deposition amounts. Based on the
obtained data and the GPS information, soil deposition density maps for Pu-238 and Pu-239+240 and for
Sr-89 and Sr-90 were prepared (see Fig. 12 and Fig. 13).
Pretreatment of alpha-emitting nuclides and beta-emitting nuclides for nuclide analysis takes time
compared with that for gamma-emitting nuclides. Therefore, MEXT selected points for nuclide analysis
in the following manner.
(i) Selecting one point each in the municipalities located within 80km from the Fukushima Dai-ichi
NPP (59 municipalities), while taking into consideration population distribution and ambient dose
rates for each municipality
(ii) Selecting 49 points within the restricted areas, evenly in all directions from the Fukushima
Dai-ichi NPP
㻝㻞
Nuclide analysis was conducted in line with the MEXT’s Radiation Measurement Method Series,
“Analysis Method of Plutonium (revised in 1990)” and “Analysis Method of Radioactive Strontium
(revised in 2003).”
Although monitoring points were limited, this monitoring survey showed the distribution of Pu-238,
Pu-239+240, Sr-89, and Sr-90 within the 80km range from the Fukushima Dai-ichi NPP. However, in
order to ascertain their distribution trends more accurately, it is necessary to conduct an additional survey
covering areas other than those 100 points. (An additional survey on Pu-238, Pu-239+240, Sr-89, and
Sr-90 has been underway since December 2011 with regard to soil samples collected through this
monitoring survey. From the perspective of further elaborating the soil deposition density map for
Pu-238 and Pu-239+240, Pu-241 was newly added as a survey target.)
(i) Results of the map of deposition density of Pu-238 and Pu-239+240 in soil, and considerations
In the northwestern areas from the Fukushima Dai-ichi NPP, Pu-238 and Pu-239+240 were both detected
at five points and only Pu-238 was detected at one point.
Detected Pu-238 and Pu-239+240 are considered to have been deposited newly after the accident at the
Fukushima Dai-ichi NPP on the following grounds.
࣭As seen in Fig. 14, the ratio of deposition amounts of Pu-238 (half-life: 87.7 years) against those of
Pu-239+240 (Pu-239 half-life: 2.41×104 years; Pu-240 half-life: 6,564 years) that were monitored in a
nation-wide survey from FY1999 to FY2008 was around 0.026 (national average). However, the
ratios were around 0.33 to 2.2 at five points where Pu-238 and Pu-239+240 were both detected in this
monitoring survey. These ratios are higher than those prior to the accident.
࣭At one point where only Pu- 238 was detected, the deposition amount of Pu-238 was larger than the
detection limit for Pu-239+240 (around 0.5 Bq/m2).
Deposition amounts of Pu-238 and Pu-239+240 confirmed in this monitoring survey all fell within the
range of measured values of Pu-238 and Pu-239+240 that were monitored nationwide prior to the
occurrence of the accident (range of the influence of past nuclear tests in the atmosphere).
(ii) Results of the map of deposition density of Sr-89 and Sr-90 in soil and considerations
High levels of Sr-89 and Sr-90 were confirmed to the northwest of the Fukushima Dai-ichi NPP, and
Sr-89 and Sr-90 were also detected at Nakadori in Fukushima prefecture and to the south of the NPP.
As the half-life period of Sr-89 is 50.53 days (the half-life period of Sr-90 is 28.8 years), Sr-89 detected
in this monitoring survey is considered to be newly deposited due to the latest accident.
The detected levels of Sr-90 at measurement points where only Sr-90 was detected in this monitoring
survey fall within the scope of the values of Sr-90 observed nationwide prior to the occurrence of the
accident (2.3 to 950Bq/m2).
With regard to soil samples from which Sr-89 was detected, it was confirmed that calculated ratios of
deposition amounts of Sr-89 to Cs-137 vary significantly from 5.6×10-4 to 1.9×10-1 (average: 9.8×10-3).
These results show that distribution of radioactive strontium and that of radioactive cesium differ widely.
(Reference) Ratios of deposition amounts of Sr-90 to Cs-137
Ratios of deposition amounts of Sr-90 to Cs-137 in soil samples from which Sr-90 was detected:
1.6×10-4 to 5.8×10-2 (average: 2.6×10-3)
㻝㻟
:WherePu238andPu239+240areconsideredtohavebeennewlydepositedduetotheaccidentat
theFukushimaDaiichi NPP
:WhereSr89andSr90areconsideredtohavebeennewlydepositedduetotheaccidentattheFukushimaDaiichi NPP
Fig. 12 Map of Pu-138 and Pu-239+240
Concentration in Soil
(Converted to radiation levels as of June 14, 2011)
Fig. 13 Map of Sr-89 and Sr-90
Concentration in Soil
(Converted to radiation levels as of June 14, 2011)
㻥
㻤
㻼㼡㻙㻞㻟㻤㻌㻮㼝㻛㼙㻞
㻣
㼥㻌㻩㻌㻜㻚㻜㻞㻢㻝㻌㼤㻌㻗㻌㻜㻚㻝㻞㻥㻟
㻾㻞 㻌㻩㻌㻜㻚㻣㻤㻟㻜
㻢
㻡
㻠
㻟
㻞
㻝
㻜
㻜
㻡㻜
㻝㻜㻜
㻝㻡㻜
㻞㻜㻜
㻞㻡㻜
㻼㼡㻙㻞㻟㻥㻗㻞㻠㻜㻌㻮㼝㻛㼙㻞
Fig. 14 Results of Environmental Radioactivity Level Survey between FY1999 and FY2009 (Relation
between Deposition Amounts of Pu-238 and Pu-239+240)
(Comparing measurement results of 252 soil samples out of 1,054 soil samples collected between
FY1999 and FY2009, from which Pu-238 and Pu-239+240 were detected)
(3) Estimated effective doses over 50 years for each radionuclide by using IAEA-TECDOC-1162
㻝㻠
conversion factors
In order to ascertain the effects of exposure to each radionuclide detected in this monitoring survey, we
calculated possible external exposure and committed effective doses due to resuspension under the
assumption that a person stays on the ground surface with radionuclides deposited for 50 years since
June 14, 2011 (hereinafter referred to as the “estimated effective doses over 50 years”) by using
conversion factors defined in the method of exposure assessment in an emergency as proposed by IAEA
(IAEA-TECDOC-1162).
Table 1 shows estimated effective doses over 50 years under the assumption that a person stays where
the maximum amount of each radionuclide was detected for 50 years. As the amounts of radioactive
cesium discharged and deposited due to the accident at the Fukushima Dai-ichi NPP were much larger
than those of other nuclides, compared with estimated effective doses over 50 years for Cs-134 and
Cs-137, those for other nuclides were very small.
Therefore, it will be appropriate to focus on deposition amounts of Cs-134 and Cs-137 when assessing
exposure levels and taking decontamination measures in the future.
(Table 1: Estimated Effective Dose over 50 Years at Points where the Maximum Amount of Each
Type of Radionuclides was Detected)
Radionuclide
Half-life period
Cs-134
Cs-137
I-131
Sr-89
Sr-90
Pu-238
Pu-239+240
Ag-110m
Te-129m
2.065 years
30.167 years
8.02 days
50.53 days
28.79 years
87.7 years
2.411×104 years
249.95 days
33.6 days
Maximum
deposition
density level*1
(Bq/m2)
1.4×107
1.5×107
5.5×104
2.2×104
5.7×103
4.0
15.0
8.3×104
2.7×106
Estimated effective dose over 50 years
Conversion factor
(mSv/kBq/m2)
Obtained results (mSv)
5.1×10-3
1.3×10-1
2.7×10-4
2.8×10-5
2.1×10-2
6.6
8.5
3.9×10-2
2.2×10-4
71
2000 (2.0Sv)
0.015
0.00061 (0.61Sv)
0.12
0.027
0.12
3.2
0.6
*1: Converted to radiation levels as of June 14, 2011
(4) Ambient dose rates by gamma-emitting nuclides as of June 14, 2011, and their contributions to
estimated effective doses over 50 years since June 14, 2011
Selecting 43 measurement points out of those targeted in this monitoring survey, where measured
ambient dose rates fell between 0.1 and 5Sv/h and were relatively close to values assessed based on
deposition amounts of respective radionuclides, we examined the contribution of each gamma-emitting
nuclide to ambient dose rates as of June 14, 2011, by using conversion factors defined in the method of
exposure assessment in an emergency as proposed by IAEA (IAEA-TECDOC-1162). As a result, it was
confirmed that contributions to ambient dose rates as of June 14, 2011, were around 70% for Cs-134 and
around 30% for Cs-137. I-131, Te-129m and Ag-110m combined contributed by only 1% or less.
Furthermore, when examining their contributions to estimated effective doses over 50 years, Cs-137 and
㻝㻡
Cs-134 accounted for nearly 96% and nearly 4%, respectively, and the others accounted for 1% or less of
the total.
(5) Comparison with effects of radioactive substances due to the Chernobyl accident
1) Considerations on the amount of radioactive substances discharged into the air due to the accident
at the Fukushima Dai-ichi NPP
In order to make comparison between the scope of effects of the accident at the Fukushima Dai-ichi NPP
and that of the accident at the Chernobyl NPP (hereinafter referred to as the “Chernobyl accident”), we
compared the amounts of I-131 and Cs-137 discharged into the air due to the Chernobyl accident with
the estimated amounts of I-131 and Cs-137 discharged due to the accident at the Fukushima Dai-ichi
NPP, which were released by the Nuclear Safety Commission of Japan, and the Nuclear and Industrial
Safety Agency.
As shown in Table 2 below, compared with the amounts discharged due to the Chernobyl accident, the
estimated amounts of I-131 and Cs-137 discharged due to the accident at the Fukushima Dai-ichi NPP
are considered to be around one-eleventh or one-fourteenth for I-131, and around one-sixth or one-eighth
for Cs-137.
(Table 2: Amounts of I-131 and Cs-137 Discharged into the Air due to the Accident at the Fukushima
Dai-ichi NPP and the Chernobyl Accident)
Amounts discharged
Estimated amounts discharged due to the accident at the
due to the Chernobyl
Fukushima Dai-ichi NPP (Bq)
Radionuclide
accident (Bq)
Nuclear Safety Commission
Nuclear and Industrial
*1
*2
of Japan
Safety Agency
17
I-131
1.6×10
1.3×1017
1.8×1018
Cs-137
1.5×1016
1.1×1016
8.5×1016
*1 “Regarding the Evaluation of the Conditions on Reactor Cores of Units 1, 2 and 3 related to the
Accident at Fukushima Dai-ichi Nuclear Power Station, Tokyo Electric Power Co. Inc.” (June 6,
2011 (partially corrected on October 20, 2011))
*2 Released by the Nuclear Safety Commission of Japan (August 24, 2011)
2) Considerations on radiation levels of radioactive substances deposited on soil
The report on the Chernobyl accident prepared by the IAEA and UNSCEAR contains soil contamination
maps which show deposition amounts of respective radionuclides as of three years and eight months
after the accident by dividing all areas in Europe around the NPP and three countries in the former Soviet
Union (the Russian Federation, Republic of Belarus, and Ukraine) according to deposition amounts.
Therefore, we compared the disclosed maps of soil contamination due to the Chernobyl accident and the
soil contamination maps prepared in this monitoring survey.
(i) Considerations on the comparison of the deposition of Cs-137
As shown in Fig. 15 (a), the areas where deposition amounts of Cs-137 exceeded 1,480kBq/m2 (parts
indicated in red) can be observed not only within a 30km range but also in areas around 250km from the
Chernobyl NPP.
㻝㻢
On the other hand, the same radiation levels have been confirmed at 34 points around the Fukushima
Dai-ichi NPP in this monitoring survey, and the farthest point was observed around 32.5km from the
NPP in Namie town.
As shown in Fig. 15 (b), in the case of the Chernobyl accident, the areas where deposition amounts of
Cs-137 exceeded 40kBq/m2 (parts indicated in dark orange) are also seen in Norway, around 1,700km
from the Chernobyl NPP.
When examining the distribution of the same radiation levels in the case of the accident at the Fukushima
Dai-ichi NPP, while referring to the results of airborne monitoring covering all areas in East Japan
(converted to radiation levels as of November 5, 2011) (see Fig. 16), the areas where deposition amounts
of Cs-137 exceeded 30kBq/m2 (a level even lower than 40kBq/m2) (parts indicated in gray) are only
confirmed within an approximately 250km range from the NPP.
Given these facts, radiation levels of Cs-137 near the Fukushima Dai-ichi NPP cannot be judged to be
low compared with those in the case of the Chernobyl NPP, but it was confirmed that the scope of effects
of radiation discharged into the environment due to the Chernobyl accident was one decimal place larger
than the effects caused by the accident at the Fukushima Dai-ichi NPP.
(ii) Considerations on the comparison of the deposition of Sr-90 and Pu-239+240
The maximum deposition amount of Sr-90 (5.7kBq/m2) was detected in this monitoring survey at the
point 4.9km from the Fukushima Dai-ichi NPP and the point near the NPP. The maximum deposition
amount of Pu-239+240 (15Bq/m2) was detected at the point 18km from the NPP.
On the other hand, in the case of the Chernobyl accident, as shown in Fig. 17 (a) and (b), the areas where
deposition amounts of Sr-90 exceeded 111kBq/m2 and the areas where deposition amounts of
Pu-239+240 exceeded 3.7kBq/m2 are also found around the border of 30km from the NPP.
Given these facts, the scope of effects of Sr-90 and Pu-239+240 due to the accident at the Fukushima
Dai-ichi NPP is confirmed to be rather limited compared to the case of the Chernobyl accident.
㻝㻣
(a) Deposition of Cs-137 in the Russian Federation, Republic of Belarus, and Ukraine after the
Chernobyl Accident (Converted as of December 1989)
(b) Deposition of Cs-137 All over Europe after the Chernobyl Accident
(Converted as of December 1989)
Fig. 15 Maps of Radioactive Cesium Deposition density in Soil after the Chernobyl Accident
Prepared by IAEA
(Soil deposition density maps of 3 years and 8 months after the accident)
[ATLAS of cesium deposition on Europe after the Chernobyl accident. EUR 16733]
㻝㻤
Fig. 16 Results of Airborne Monitoring Covering All Areas in East Japan (Deposition density of
Cs-137 deposited on the ground surface)
(Converted to radiation levels as of November 5, 2011)
(Around 8 months from the accident)
㻝㻥
30km
30km
Kiev
Kiev
(a) Deposition of Sr-90 around the
Chernobyl NPP
(b) Deposition of Pu-239+240 around
the Chernobyl NPP
Fig. 17 Maps of Radionuclides (Sr-90 and Pu-239+240) Deposition density in Soil after the Chernobyl
Accident Prepared by IAEA
(Soil deposition density maps of 3 years and 8 months after the accident)
[The International Chernobyl Project. Assessment of radiological consequences and evaluation of protective measures. Technical Report.
IAEA, Vienna (1991).]
(6) Possible effects into the future
In preparing maps, as of the base date (June 14, 2011), on which radiation levels were converted while
considering physical attenuation, ratios of deposited Cs-134 and Cs-137 were almost the same.
As of this point in time, it was confirmed that Cs-134 and Cs-137 contributed by around 70% and 30%,
respectively, to the overall ambient dose rates.
Therefore, focusing on physical attenuation of Cs-134 and Cs-137 in the future, we calculated possible
future effects of radioactive substances based on their half-life periods and conversion factors to ambient
dose rates (ambient dose equivalent rates) defined in the IAEA-TECDOC-1162.
Assuming that deposition amounts of Cs-134 and Cs-137 were the same as of June 14, 2011, trends of
attenuation of deposition amounts (deposition density in soil) of radioactive cesium and ambient dose
rates are slightly different as shown in Fig. 18. Therefore, it will take three or four years for ambient dose
rates and around six years for deposition amounts (deposition density in soil) of radioactive cesium to
reduce by half from the levels of mid-June 2011.
Trends shown in Fig. 18 do not include changes in deposition of radioactive substances caused by natural
phenomena such as rainfall and wind, and decontamination. Decreases in ambient dose rates due to
decontamination can be confirmed through monitoring surveys, etc. at the relevant points, but the
㻞㻜
movement of radioactive substances due to natural phenomena need to be figured out in the future
through on-site survey activities in the areas affected by the accident at the Fukushima Dai-ichi NPP.
㻢 ᭶to㻝the
㻠 ᪥ value
᫬ Ⅼ 䛾onᩘJune
್ 䛻 14,
ᑐ 䛩
䜛 ẚ
Ratio
2011
㻝
㻜 㻚㻝
㻯 㼟㻙㻝 㻟㻠䛾 ᅵ ተ ⃰ ᗘ
䕔㻌 㻰㼑㼜㼛㼟㼕㼠㼑㼐㻌㼍㼏㼠㼕㼢㼕㼠㼥㻌㼕㼚㻌㼟㼛㼕㼘㻌㼛㼒㻌㻯㼟㻙㻝㻟㻠㻌
㻯 㼟㻙㻝 㻟㻣䛾 ᅵ ተ ⃰ ᗘ
䕔 㻰㼑㼜㼛㼟㼕㼠㼑㼐㻌㼍㼏㼠㼕㼢㼕㼠㼥㻌㼕㼚㻌㼟㼛㼕㼘㻌㼛㼒㻌㻯㼟㻙㻝㻟㻣㻌
㻖
䕔 㻰㼑㼜㼛㼟㼕㼠㼑㼐㻌㼍㼏㼠㼕㼢㼕㼠㼥㻌㼕㼚㻌㼟㼛㼕㼘㻌㼛㼒㻌㼞㼍㼐㼕㼛㼍㼏㼠㼕㼢㼑㻌㼏㼑㼟㼕㼡㼙㻌
ᨺ ᑕ ᛶ 䝉䝅 䜴 䝮 䛾 ᅵ ተ ⃰ ᗘ 䚷
䕔 㻭㼙㼎㼕㼑㼚㼠㻌㼐㼛㼟㼑㻌㼑㼝㼡㼕㼢㼍㼘㼑㼚㼠㻌㼞㼍㼠㼑㻌㼕㼚㻌㼍㼕㼞㻌㼒㼞㼛㼙㻌㼞㼍㼐㼕㼛㼍㼏㼠㼕㼢㼑㻌㼏㼑㼟㼕㼡㼙㻌
ᨺ ᑕ ᛶ 䝉䝅 䜴 䝮 䛻 䜘 䜛 ✵ 㛫 ⥺ 㔞 ⋡
㻜
㻝 㻌㻤 㻌㻞㻡㻡㻌 㻌
㻟㻌 㻌㻢㻝㻡㻜㻜 㻌 㻌
㻡㻌 㻌㻠㻝㻣㻡㻡 㻌 㻌
㻣㻌 㻌㻟㻞㻜 㻜㻜 㻌 㻌
㻥㻌 㻝㻌 㻞㻞 㻡㻡 㻌 㻌 㻝㻌 㻜㻌 㻟㻥 㻡㻜 㻜㻌 㻌
⤒ 㐣 ᖺ ᩘ 䠄 㻝 ᖺ 䜢 㻟 㻢 㻡 ᪥ 䛸GD\V㸧
䛧䛶 ィ ⟬ 䠅
㸦(ODSVHG\HDUV\HDU
Fig. 18 Forecast of Deposition Amounts of Radioactive Cesium and Ambient dose rates
(Assuming that deposition density levels of Cs-134 and Cs-137 as of the conversion date (June 14,
2011) were the same)
(7) Opening of a website to enlarge distribution maps of radiation doses, etc.
For the purpose of enabling people to ascertain the effects of radioactive substances discharged from the
Fukushima Dai-ichi NPP in more detail, MEXT prepared the “Website to Enlarge Distribution Maps of
Radiation Doses, etc.,” where users can freely enlarge distribution maps of radiation doses, etc.
(distribution maps of ambient dose rates and soil deposition density maps of radioactive cesium, etc.) and
other maps showing the results of various monitoring surveys that MEXT has conducted so far
(distribution of ambient dose rates and radiation deposition density) (see Fig. 19).
This website was made available on October 18, 2011 (http://ramap.jaea.go.jp/map/).
In ten days, over 300,000 people accessed this website, and requests exceeding 110 million cases were
made to the server, but the website worked without any trouble.
When new measurement results are obtained, MEXT will update maps on this website, and if new types
of maps are prepared, they will also be made available on this website as necessary.
㻞㻝
Fig. 19 Website to Enlarge Distribution Maps of Radiation Doses, etc. (Front page)
(8) Release of database on radiation doses, etc.
There has been no database that compiles the measurement results for preparing distribution maps of
radiation doses, etc. or the results of the measurement of ambient dose rates that MEXT, Fukushima
prefecture, and other related entities have carried out since immediately after the occurrence of the
accident at the Fukushima Dai-ichi NPP and that can be utilized for the examination of the accident.
Therefore, MEXT developed the “Database on Radiation Doses, etc.” that can be managed and operated
with high security, by compiling these past measurement results and by adding assorted information,
such as the measurement methods, analysis methods, and measurement accuracy, with the aim of
enabling administrative officials and general people including residents in related municipalities to
confirm them easily and for researchers worldwide to utilize them for the examination of the accident at
the Fukushima Dai-ichi NPP (see Fig. 20).
This website is scheduled to be made available in mid-March 2012.
In addition to the measurement data already registered in this database, any new data that are found
reliable will be registered and released sequentially after confirming the content of assorted information
of measurement data.
㻞㻞
Fig. 20 Database on Radiation Doses, etc. (Sample of indicating data)
㻞㻟
2. Report on the Research relating to Distribution Maps of Radiation Doses, etc. (Part 2)
2.1 Purpose of the research relating to distribution maps of radiation doses, etc.
Part 1 explains that MEXT carried out measurement of ambient dose rates in the 100km range from the
Fukushima Dai-ichi NPP and in Fukushima prefecture out of this scope, at one point each in 2×2km
grids within 80km from the NPP and in 10×10km grids in the other areas, and prepared distribution maps
of ambient dose rates, and that MEXT collected soil samples at the same time at five points in each of
said locations, conducted nuclide analysis thereof, and prepared soil deposition density maps based on
radiation doses per unit area.
However, the distribution of radionuclides in soil is considered to differ even within a 2×2km grid,
depending on the quality of the soil and other various factors.
Furthermore, the experience of the Chernobyl accident has revealed that radionuclides once deposited on
soil or in the forests, etc. infiltrate soil and move in various manners in the environment in accordance
with the movement of water and wind.
Therefore, in order to examine the movement of radioactive substances discharged due to the accident at
the Fukushima Dai-ichi NPP, MEXT conducted research surveys on the following individual themes of
great importance as research relating to distribution maps of radiation doses, etc.
MEXT compiled Part 2 of the report by editing the research results by researchers specialized in
respective themes and having the members of the Advisory Board of Distribution Map of Radiation Dose,
etc. verify the validity thereof.
(i) Confirmation of the Distribution of Radioactive Substances within a Narrow Area of Soil, and
Examination of Factors Thereof [Haruyasu NAGAI (Japan Atomic Energy Agency), et al.]
(ii) Confirmation of the Depth distribution of Radioactive Substances in Soil, and Examination of Factors
for the Distribution
[Survey Using Geoslicers to Confirm the Depth distribution of Radioactive Substances in Soil:
Kazuhiro AOKI (Japan Atomic Energy Agency), et al.]
[Survey Using Iron Pipes to Confirm the Depth distribution of Radioactive Substances in Soil: Isao
TANIHATA (Osaka University), et al.]
(iii) Confirmation of Trends in Deposition density Levels of Radioactive Substances in Rivers (River
Water, Riverbed sediment, and Suspended Sediment) and Well Water [Yoshihiro IKEUCHI (Japan
Chemical Analysis Center)]
(iv) Confirmation of Comprehensive Movement of Radioactive Substances in the Model Area [Yuichi
ONDA (Tsukuba University), et al.]
2.2 Details of the surveys (Survey content, survey results, and considerations)
(1) Investigation on local distribution of radioactive substances and examination of controlling
factors
1) Outline of the survey
In order to confirm the meaning of the measurement results obtained in 2×2km grids, which were
targeted in preparing soil deposition density maps as explained in Part 1, soil samples were collected in
㻞㻠
parts with different ecosystems within those 2×2km grids, and analysis thereof was conducted to
ascertain uneven deposition of radioactive substances on the ground surface. Furthermore, physical and
chemical features of soil that may affect such uneven deposition were examined and a correlation
between those features and deposition of radioactive substances was sought.
2) Survey period
Samples were collected from June 18 to June 20 (before the rainy season), from July 19 to July 20, and
from August 1 to August 2 (after the rainy season), 2011. Nuclide analysis was conducted thereafter.
3) Targeted areas
Within the 2×2km grid in the southwest part of Fukushima city, located at around 73km from the
Fukushima Dai-ichi NPP
As measurement points, selecting six points in agricultural land (three points in upland fields, one point
in a paddy field, and two points in orchards), four points in grass fields (three points in meadows, and
one point in a lawn), and five points in the forests (three points on broad-leaved forests and two points on
needle-leaved forests)
4) Survey results and considerations
As shown in Fig. 21, the total deposition amounts of radioactive cesium on soil were at the same level
within the 2×2km grid, irrespective of land use.
As shown in Fig. 22, radioactive cesium was detected mostly up to a depth of 5cm into the soil including
vegetation and the litter layer, except in disturbed agricultural land soil.
Regarding radioactive cesium inventory in mineral soil (excluding vegetation and the litter layer) from
the targeted 2×2km grid, the relation between how easily radioactive cesium is concentrated in the
surface layer (0 to 1cm) (retention rate) and soil features was examined and the following were
ascertained as shown in Fig. 23:
࣭
Radioactive cesium is apt to filter deeper into the soil, when its abundance in mineral soil to the
total inventory including aboveground is smaller, and the percentage of its deposition on vegetation
and the litter layer is larger.
࣭
Radioactive cesium is also apt to filter deeper into the soil when the surface layer contains a
larger amount of carbon (originates from plant organic substances).
࣭
On the other hand, radioactive cesium is apt to remain in the surface layer when the surface layer
contains a larger amount of clay.
It was thus confirmed that there is a certain relation between soil features and how easily radioactive
cesium is deposited in the surface layer (0 to 1cm).
Investigating the depth distribution of radioactive cesium in soil for each ecosystem, while giving due
consideration to soil features, will be effective for reviewing efficient decontamination policies and
estimating possible future changes in contamination.
㻞㻡
Grassland 4
Grassland 3
Grassland 2
Grassland 1
Grassland
Fig. 21 Cs-137 inventory in vegetation, litter, and top 0-20 cm mineral soil. Locations with * notation
indicate that soils were disturbed by tilling after the accident.
Fig. 22 Cumulative inventory of Cs-137 at the first sampling (before rainy season) as a percentage of
the total inventory. Depth = 0 cm means aboveground vegetation or litter. Locations with * notation
indicate that soils were disturbed by tilling after the accident.㻌
Fig. 23 Correlations between Cs-137 retention rate and influential factors. The Cs-137 retention rate
was defined as a ratio of Cs-137 inventory in the topmost 0-1 cm layer to the total Cs-137 inventory
in and below the layer.
㻞㻢
(2) Confirmation of the depth distribution of radioactive substances in soil, and examination of
factors for the distribution
[Survey using Geoslicers to confirm the depth distribution of radioactive substances in soil]
1) Outline of the survey
In order to examine the depth distribution of radioactive substances in soil as of June 2011, a survey was
conducted by using Geoslicers (see Fig. 24) as tools to collect soil samples. Furthermore, based on data
such as half-life periods of radioactive substances and soil quality, the characteristics of radioactive
substances in soil (diffusion coefficients (apparent diffusion coefficients) and dispersion coefficients
(apparent dispersion coefficients)) were confirmed.
2) Survey period
An on-site survey, etc. was conducted from June 7 to June 19, 2011.
3) Targeted areas
As major survey targets, selecting areas where high deposition amounts of radioactive cesium and
relatively high ambient dose rates are detected, and where I-131 is considered to be remaining even
taking into account its physical attenuation (Namie town (excluding the 20km-range from the NPP) and
Kawamata town, etc.)
4) Survey results and considerations
Examination of the depth distribution of radioactive cesium, Te-129m, and Ag-100m in soil revealed, as
shown in Fig. 25, that in soil samples that have been clearly found free from any influences of
contamination, almost all radioactive substances remain within a depth of 5cm from the surface layer.
Although there remain some uncertainties due to contamination, it was confirmed that at all locations
that are supposed to have been used as farmland, almost all radioactive substances existed within a depth
of 14cm, as shown in Fig. 25.
Despite a large difference in the measurement of cation(cesium) and anion (iodine) in the sorption
distribution coefficients which are indicative of the radionuclide retention capacity of soil near the
surface, there was no obvious difference in the apparent diffusion coefficient which show the mobility by
concentration gradient. This observation indicates that the infiltration of radionuclides in the soil near the
surface is due mainly to rainwater seeping through the surface and having a dispersing effect.
According to the measurement results of radiation deposition density in soil samples collected by using
Geoslicers and the results of the depth distribution of radioactive substances calculated based on
diffusion coefficients obtained through this survey, it is estimated that as of three months after the
accident, radioactive substances were deposited up to a depth of around 15cm at most both in soil in the
surface layer and in soil at locations that are supposed to have been used as farmland.
㻞㻣
(a) Soil Sampling by wide-sized Geoslicer
(1.1m (Width)×1.2m (Depth)×10cm(Thickness)
(b) Soil Sampling by handheld Geoslicer
(10cm (Width)×1.0m (Depth)×2cm(Thickness)
Fig. 24 Survey of the Depth distribution of Radioactive Substances in Soil by Using Geoslicers
㻌 㻌 㻥㻝㻑㻌㼡㼜㻌㼠㼛㻌㻞㼏㼙㻌㼐㼑㼜㼠㼔㻌
㻌 㻌 㻥㻥㻑㻌㼡㼜㻌㼠㼛㻌㻠㼏㼙㻌㼐㼑㼜㼠㼔㻌
㻌 㻌 㻝㻜㻜㻑㻌㼡㼜㻌㼠㼛㻌㻢㼏㼙㻌㼐㼑㼜㼠㼔㻌
㻹㼍㼠㼟㼡㼗㼕㼥㼍㼙㼍㻌㼀㼟㼡㼟㼔㼕㼙㼍㻘㻌 㻌
㻺㼍㼙㼕㼑㻙㼙㼍㼏㼔㼕㻌 㻌
㻹㼍㼠㼟㼡㼗㼕㼥㼍㼙㼍㻌㼀㼟㼡㼟㼔㼕㼙㼍㻘
㻺㼍㼙㼕㼑㻙㼙㼍㼏㼔㼕㻌 㻌
㻿㼍㼙㼜㼘㼕㼚㼓㻌㼐㼍㼠㼑䠖㻞㻜㻝㻞㻛㻢㻛㻝㻟㻛㻝㻝㻦㻝㻡㻌
㻯㼟㻙㻝㻟㻠㻌㻵㼚㼢㼑㼚㼠㼛㼞㼥㻌㻠㻚㻠㻥㻡㻱㻢㻌㻮㼝㻛㼙㻞㻌
㻯㼟㻙㻝㻟㻣㻌㻵㼚㼢㼑㼚㼠㼛㼞㼥㻌㻠㻚㻥㻠㻜㻱㻢㻌㻮㼝㻛㼙㻞㻌
㻿㼍㼙㼜㼘㼕㼚㼓㻌㼐㼍㼠㼑䠖㻴㻞㻟㻛㻢㻛㻝㻟㻛㻝㻝㻦㻝㻡㻌
㼀㼑㻙㻝㻞㻥㼙㻌㻵㼚㼢㼑㼚㼠㼛㼞㼥㻌㻤㻚㻤㻝㻝㻱㻡㻮㼝㻛㼙㻞㻌
㻯㼑㼟㼕㼡㼙㻌㻝㻟㻠㻌㼍㼚㼐㻌㻝㻟㻣㻌㼛㼒㻌㻴㻳㻿㻙㻝㻜㻌 㻌
㼟㼍㼙㼜㼘㼑㼟㻌㼣㼕㼠㼔㼛㼡㼠㻌㼏㼛㼚㼠㼍㼙㼕㼚㼍㼠㼕㼛㼚㻌 㻌
㻌 㻌 㻌 㻌 㻔㼚㼛㼚㻙㼒㼍㼞㼙㼘㼍㼚㼐㻌㼟㼡㼞㼒㼍㼏㼑㻕㻌 㻌
㼀㼑㼘㼘㼡㼞㼕㼡㼙㻌㼛㼒㻌㻴㻳㻿㻙㻝㻜㻌㼟㼍㼙㼜㼘㼑㼟㻌
㼣㼕㼠㼔㼛㼡㼠㻌㼏㼛㼚㼠㼍㼙㼕㼚㼍㼠㼕㼛㼚㻌
㻌 㻌 㻔㼚㼛㼚㻙㼒㼍㼞㼙㼘㼍㼚㼐㻌㼟㼡㼞㼒㼍㼏㼑㻕㻌 㻌
Fig. 25(a) Results of handheld Geoslicer 10 for depth distribution of radionuclides in soil
㻞㻤
㻢㻤㻑㻌㼡㼜㻌㼠㼛㻌㻞㼏㼙㻌㼐㼑㼜㼠㼔㻌
㻣㻠㻑㻔㼀㼑㻙㻝㻞㻥㼙㻕㻛㻣㻜㻑㻔㻭㼓㻙㻝㻝㻜㼙㻕㼡㼜㻌㼠㼛㻌㻞㼏㼙㻌㼐㼑㼜㼠㼔㻌
㻤㻡㻑㻔㼀㼑㻙㻝㻞㻥㼙㻕㻛㻤㻞㻑㻔㻭㼓㻙㻝㻝㻜㼙㻕㼡㼜㻌㼠㼛㻌㻠㼏㼙㻌 㻌
㻥㻡㻑㻔㼀㼑㻙㻝㻞㻥㼙㻕㻛㻥㻠㻑㻔㻭㼓㻙㻝㻝㻜㼙㻕㼡㼜㻌㼠㼛㻌㻢㼏㼙㻌
㻝㻜㻜㻑㻔㼀㼑㻙㻝㻞㻥㼙㻕㻛㻥㻢㻑㻔㻭㼓㻙㻝㻝㻜㼙㻕㼡㼜㻌㼠㼛㻌㻝㻠㼏㼙㻌
㻝㻜㻜㻑㻔㻭㼓㻙㻝㻝㻜㼙㻕㼡㼜㻌㼠㼛㻌㻝㻤㼏㼙㻌
㻣㻤㻑㻌㼡㼜㻌㼠㼛㻌㻠㼏㼙㻌㼐㼑㼜㼠㼔㻌
㻤㻡㻑㻌㼡㼜㻌㼠㼛㻌㻢㼏㼙㻌㼐㼑㼜㼠㼔㻌
㻥㻤㻑㻌㼡㼜㻌㼠㼛㻌㻟㻜㼏㼙㻌㼐㼑㼜㼠㼔㻌
㻷㼡㼚㼡㼓㼕㼐㼍㼕㼞㼍㻌㻭㼗㼛㼓㼕㻘㻌㻺㼍㼙㼕㼑㻙㼙㼍㼏㼔㼕㻌
㻝㻜㻜㻑㻌㼡㼜㻌㼠㼛㻌㻡㻜㼏㼙㻌㼐㼑㼜㼠㼔㻌
㻹㼕㼦㼡㼦㼍㼗㼍㼕㻌㼀㼟㼡㼟㼔㼕㼙㼍㻘㻌㻺㼍㼙㼕㼑㻙㼙㼍㼏㼔㼕㻌
6DPSOLQJGDWH㸸+
7HP,QYHQWRU\(%TP
$JP,QYHQWRU\(%TP
㻿㼍㼙㼜㼘㼕㼚㼓㻌㼐㼍㼠㼑䠖㻴㻞㻟㻛㻢㻛㻝㻡㻛㻝㻟㻦㻟㻜㻌
㻯㼟㻙㻝㻟㻠㻌㻵㼚㼢㼑㼚㼠㼛㼞㼥㻌㻢㻚㻠㻜㻣㻱㻡㻮㼝㻛㼙㻞㻌
㻯㼟㻙㻝㻟㻣㻌㻵㼚㼢㼑㼚㼠㼛㼞㼥㻌㻣㻚㻜㻢㻤㻱㻡㻮㼝㻛㼙㻞㻌
㻯㼑㼟㼕㼡㼙㻌 㻝㻟㻠㻌 㼍㼚㼐㻌 㻝㻟㻣㻌 㼛㼒㻌 㻴㻳㻿㻙㻝㻥㻌
㼟㼍㼙㼜㼘㼑㼟㻌㼣㼕㼠㼔㻌㼏㼛㼚㼠㼍㼙㼕㼚㼍㼠㼕㼛㼚㻌 㻌 㻔㼒㼛㼞㼙㼑㼞㻌
㼒㼍㼞㼙㼘㼍㼚㼐㻕㻌 㻌
㼀㼑㼘㼘㼡㼞㼕㼡㼙㻌 㼍㼚㼐㻌 㼟㼕㼘㼢㼑㼞㻌 㼛㼒㻌 㻴㻳㻿㻙㻝㻢㻌
㼟㼍㼙㼜㼘㼑㼟㻌 㼣㼕㼠㼔㻌 㼏㼛㼚㼠㼍㼙㼕㼚㼍㼠㼕㼛㼚㻌 㻔㼒㼛㼞㼙㼑㼞㻌
㼒㼍㼞㼙㼘㼍㼚㼐㻕㻌 㻌
Fig. 25(b) Results of handheld Geoslicer 16 and 19 for depth distribution of radionuclides in soil
㻞㻥
[Survey using iron pipes to confirm the depth distribution of radioactive substances in soil]
1) Outline of the survey
In order to examine the depth distribution of radioactive substances in soil as of June 2011, soil core
samples were collected by using iron pipes as tools to collect soil samples (see Fig. 26). Then, counting
rates of radioactive cesium contained in each sample were measured by using a germanium
semiconductor detector, and the depth distribution of radioactive cesium in soil was examined based
thereon.
2) Survey period
Soil core samples were collected by using iron pipes in June 2011, and then nuclide analysis was
conducted.
3) Targeted areas
Out of the locations where soil samples were collected for preparing soil deposition density maps as
explained in Part 1 (around 2,200 locations), around 300 locations were selected as targets where soil
was soft and contained a smaller number of stones.
4) Survey results and considerations
Out of around 300 samples collected up to a depth of 30cm in this survey, examination was conducted
with regard to 77 samples for which counting rates of radioactive cesium were relatively large and
measurable. As a result, as shown in Fig. 27, counting rates of radioactive cesium decreased
exponentially for deeper parts of all samples. It was confirmed that counting rates of radioactive cesium
decrease to one-tenth at 5cm or deeper from the ground surface (see Fig. 28 for a list of depths at which
counting rates of radioactive cesium decrease to one-tenth (L1/10)).
The depth distribution of Cs-134 and Cs-137 in soil showed almost the same trends without any
significant differences.
㻼㼔㼛㼠㼛䐟㻌
㻼㼔㼛㼠㼛䐠
㻼㼔㼛㼠㼛䐡
㻼㼔㼛㼠㼛䐢㻌
㻼㼔㼛㼠㼛䐣
Fig. 26 Method of Collecting Soil Core Samples by Using Iron Pipes
㻟㻜
1.0
ᶿ -rays were measured
㻮 㻮
134Cs counts/s [1/s]
㻮
sliding the core
sample in5 mmsteps.
㻮
e
lpel
sapm
em
a
r
s
o
Lead collimator
ec
mr
co
30c
m
c
30
㻮
㻮
㻮
Ge
Detector
㻮
㻮
㻮
0.1
L1/10
soil surface
㻮
Intensity
decays to 1/10
㻮
Fig. 27.
An example of the depth
distribution of Ț -rays from Cs-137.
Measured Ț-ray counts per second are
shown by solid squares with error bars.
The black solid line shows the fitted
exponential shape of the distribution.
The data beyond 30 mm distance were
used for the fitting. The 1/10 attenuation
depth (L1/10) is also indicated in the
figure. The inset show the method of the
measurement. Ț -rays were collimated
by a set of 5cm thick lead blocks. The
position resolution was 5 mm in
full-width-at half maximum (FWHM).
0.01
0
40 60 80 100 120
Distance from Length
the edge[mm]
of iron pipe [mm]
ID
NS
EW
82 N
16
66 N
18
62 N
32
60 N
12
56 N
42
52 N
30
52 N
40
46 N
30
46 N
36
46 N
42
44 N
44
40 N
56
38 N
36
38 N
48
36 N
40
34 N
10
34 N
18
34 N
24
34 N
28
34 N
34
34 N
38
34 N
48
32 N
30
32 N
42
32 N
44
30 N
20
30 N
48
28 N
24
28 N
26
28 N
46
26 N
26
26 N
30
26 N
38
24 N
12
24 N
18
24 N
56
22 N
44
20 N
10
20 N
24
20 N
32
20 N
40
16 N
18
16 N
40
14 N
20
14 N
42
14 N
46
14 N
50
10 N
24
8N
20
8N
58
6N
20
6N
50
6N
56
20
㻭㼠㼠㼑㼚㼡㼍㼠㼕㼛㼚
㼐㼑㼜㼠㼔 (L1/10) 㻿㼍㼙㼜㼘㼑㼐㻌㼜㼘㼍㼏㼑
㼏㼕㼠㼥㻘㼠㼛㼣㼚㻘㼢㼕㼘㼘㼍㼓㼑
[mm]
17 㻵㼣㼍㼚㼡㼙㼍㻌㼏㻚
23 㻷㼍㼗㼡㼐㼍㻌㼏㻚
39 㻿㼔㼕㼞㼍㼕㼟㼔㼕㻌㼏㻚
29 㼅㼍㼙㼍㼙㼛㼠㼛㻌㼠㻚
48 㻷㼡㼚㼕㼙㼕㻌㼠㻚
33 㻰㼍㼠㼑㻌㼏㻚
48 㻷㼡㼣㼍㼛㼞㼕㻌㼠㻚
30 㻰㼍㼠㼑㻌㼏㻚
59 㻰㼍㼠㼑㻌㼏㻚
32 㻰㼍㼠㼑㻌㼏㻚
26 㻲㼡㼗㼡㼟㼔㼕㼙㼍㻌㼏㻚
37 㻲㼡㼗㼡㼟㼔㼕㼙㼍㻌㼏㻚
30 㻰㼍㼠㼑㻌㼏㻚
34 㻲㼡㼗㼡㼟㼔㼕㼙㼍㻌㼏㻚
33 㻲㼡㼗㼡㼟㼔㼕㼙㼍㻌㼏㻚
30 㻹㼕㼚㼍㼙㼕㻙㻿㼛㼙㼍㻌㼏㻚
27 㻵㼕㼐㼍㼠㼑㻌㼢㻚
28 㻵㼕㼐㼍㼠㼑㻌㼢㻚
36 㻵㼕㼐㼍㼠㼑㻌㼢㻚
20 㻰㼍㼠㼑㻌㼏㻚
33 㻷㼍㼣㼍㼙㼍㼠㼍㻌㼠㻚
24 㻲㼡㼗㼡㼟㼔㼕㼙㼍㻌㼏㻚
24 㻵㼕㼐㼍㼠㼑㻌㼢㻚
25 㻲㼡㼗㼡㼟㼔㼕㼙㼍㻌㼏㻚
29 㻲㼡㼗㼡㼟㼔㼕㼙㼍㻌㼏㻚
30 㻵㼕㼐㼍㼠㼑㻌㼢㻚
39 㻲㼡㼗㼡㼟㼔㼕㼙㼍㻌㼏㻚
23 㻵㼕㼐㼍㼠㼑㻌㼢㻚
18 㻵㼕㼐㼍㼠㼑㻌㼢㻚
20 㻲㼡㼗㼡㼟㼔㼕㼙㼍㻌㼏㻚
37 㻵㼕㼐㼍㼠㼑㻌㼢㻚
28 㻷㼍㼣㼍㼙㼍㼠㼍㻌㼠㻚
28 㻷㼍㼣㼍㼙㼍㼠㼍㻌㼠㻚
38 㻹㼕㼚㼍㼙㼕㻙㻿㼛㼙㼍㻌㼏㻚
34 㻵㼕㼐㼍㼠㼑㻌㼢㻚
38 㻺㼕㼔㼛㼚㼙㼍㼠㼟㼡㻌㼏㻚
31 㻺㼕㼔㼛㼚㼙㼍㼠㼟㼡㻌㼏㻚
36 㻹㼕㼚㼍㼙㼕㻙㻿㼛㼙㼍㻌㼏㻚
40 㻺㼍㼙㼕㼑㻌㼠㻚
72 㻷㼍㼣㼍㼙㼍㼠㼍㻌㼠㻚
41 㻺㼕㼔㼛㼚㼙㼍㼠㼟㼡㻌㼏㻚
45 㻺㼍㼙㼕㼑㻌㼠㻚
24 㻺㼕㼔㼛㼚㼙㼍㼠㼟㼡㻌㼏㻚
28 㻺㼍㼙㼕㼑㻌㼠㻚
35 㻺㼕㼔㼛㼚㼙㼍㼠㼟㼡㻌㼏㻚
30 㻺㼕㼔㼛㼚㼙㼍㼠㼟㼡㻌㼏㻚
30 㻻㼠㼍㼙㼍㻌㼢㻚
22 㻷㼍㼠㼟㼡㼞㼍㼛㻌㼢㻚
31 㻷㼍㼠㼟㼡㼞㼍㼛㻌㼢㻚
35 㻷㼛㼞㼕㼥㼍㼙㼍䚷䠿䠊
27 㻷㼍㼠㼟㼡㼞㼍㼛㻌㼢㻚
33 㻷㼛㼞㼕㼥㼍㼙㼍䚷䠿䠊
44 㻹㼛㼠㼛㼙㼕㼥㼍㻌㼏㻚
㼀㼔㼑㻌㼚㼛㼞㼠㼔㻌㼘㼍㼠㼕㼠㼡㼐㼑
㼐㼑㼓㻚 㼐㼑㼓㻚
38
6
37
58
37
56
37
55
37
53
37
51
37
51
37
48
37
48
37
48
37
47
37
45
37
44
37
44
37
43
37
42
37
42
37
42
37
42
37
42
37
42
37
42
37
41
37
41
37
41
37
40
37
40
37
39
37
39
37
39
37
37
37
38
37
38
37
37
37
37
37
37
37
36
37
35
37
35
37
35
37
35
37
33
37
33
37
32
37
32
37
32
37
32
37
30
37
29
37
29
37
28
37
28
37
28
㼐㼑㼓㻚
24.80
8.00
59.94
7.00
19.53
21.00
40.60
36.80
10.40
52.00
52.70
18.90
48.00
50.50
36.10
37.00
15.80
25.20
56.50
57.50
9.40
20.40
4.20
4.40
25.70
52.40
39.83
51.20
50.50
31.40
58.98
57.00
53.10
43.20
31.40
30.50
40.90
43.40
48.50
27.30
39.94
37.90
40.31
15.95
32.70
57.00
23.80
16.90
37.50
9.50
54.90
32.20
54.50
decimal
38.106889
37.968889
37.949982
37.918611
37.888759
37.855833
37.861278
37.810222
37.802889
37.814444
37.797972
37.755250
37.746667
37.747361
37.726694
37.710278
37.704389
37.707000
37.715694
37.715972
37.702611
37.705667
37.684500
37.684556
37.690472
37.681222
37.677731
37.664222
37.664028
37.658722
37.633050
37.649167
37.648083
37.628667
37.625389
37.625139
37.611361
37.595389
37.596806
37.590917
37.594429
37.560528
37.561196
37.537765
37.542417
37.549167
37.539944
37.504694
37.493750
37.485972
37.481917
37.475611
37.481806
㼀㼔㼑㻌㼑㼍㼟㼠㻌㼘㼛㼚㼓㼕㼠㼡㼐㼑
㼐㼑㼓㻚
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
㼐㼑㼓㻚
50
48
38
53
31
39
32
39
35
30
29
19
35
26
32
55
48
44
41
36
33
26
39
30
29
46
26
43
43
27
43
39
34
53
48
20
29
54
44
38
32
49
31
46
30
28
24
44
47
18
46
25
19
㼐㼑㼓㻚
40.60
17.00
26.89
35.50
26.97
58.00
10.80
4.40
16.40
59.00
16.10
47.10
52.00
20.60
7.40
14.30
20.70
28.10
41.00
13.00
43.80
42.70
33.60
58.50
16.80
48.70
40.43
58.10
15.70
31.40
15.13
26.00
4.50
53.70
37.90
39.90
15.10
31.60
17.60
33.30
27.64
25.70
50.41
48.84
19.00
7.10
23.20
33.50
16.50
18.40
40.30
11.40
51.70
decimal
140.844611
140.804722
140.640802
140.893194
140.524159
140.666111
140.536333
140.651222
140.587889
140.516389
140.487806
140.329750
140.597778
140.439056
140.535389
140.920639
140.805750
140.741139
140.694722
140.603611
140.562167
140.445194
140.659333
140.516250
140.488000
140.780194
140.444565
140.732806
140.721028
140.458722
140.720871
140.657222
140.567917
140.898250
140.810528
140.344417
140.487528
140.908778
140.738222
140.642583
140.541012
140.823806
140.530669
140.780232
140.505278
140.468639
140.406444
140.742639
140.787917
140.305111
140.777861
140.419833
140.331028
㻟㻝
㻾㼍㼐㼕㼍㼠㼕㼛㼚㻌㼐㼛㼟㼑
㼍㼠㻌㻝㼙㻌㼔㼕㼓㼔
㻔䃛㻿㼢㻛㼔㻕
0.14
0.49
0.62
0.25
1.22
0.60
1.40
0.50
1.45
1.10
0.85
0.36
1.40
0.88
1.71
1.15
3.42
5.70
5.92
1.40
1.00
1.26
1.60
1.30
1.35
6.10
1.10
4.71
7.00
0.87
8.70
1.50
1.08
4.38
14.42
0.60
1.70
3.27
10.71
1.22
2.11
41.86
2.86
8.10
2.30
2.30
2.04
1.95
1.76
0.36
2.67
1.32
0.63
Fig. 28. Results of present depth analysis
of Cs radioactivity. The 1/10 attenuation
depths (L1/10), the distance where
intensity of Ț-rays decreases to 1/10, are
listed together with information of the
sampling locations.
(3) Confirmation of trends in concentration levels of radioactive substances in rivers (river water,
riverbed sediment, and suspended sediment) and well water
1) Outline of the survey
In order to confirm the movement of radioactive substances discharged from the Fukushima Dai-ichi
NPP into rivers and wells, changes in concentrations of radioactive substances before and after the rainy
season were surveyed, targeting rivers (river water, riverbed sediment, and suspended sediment) and
wells (well water) in Fukushima prefecture.
࣭River water: measurement of the concentration of radioactive cesium, I-131, Pu-238, Pu-239+240,
Sr-89, and Sr-90
࣭Riverbed sediment: measurement of the concentration of radioactive cesium and I-131
࣭Suspended sediment: measurement of the concentration of radioactive cesium and I-131
࣭Well water: measurement of the concentration of radioactive cesium, I-131, Sr-89, and Sr-90
2) Survey period
Samples of river water, riverbed sediment, and well water were collected twice from late June to early
August (samples of suspended sediment were collected late August and late September).
3) Targeted areas
Within Fukushima prefecture, selecting 50 points for collecting samples for rivers (river water, riverbed
sediment, and suspended sediment), and 51 points for collecting samples of well water (see Fig. 29 for
details)
Measurement points were selected from among points where deposition amounts of radioactive cesium
are relatively large.
4) Survey results and considerations
In this survey, radioactive cesium and radioactive strontium were detected from samples for rivers (river
water, riverbed sediment, and suspended sediment), and Te-129m and Ag-110m were also detected from
a small number of samples. Furthermore, radioactive cesium and Sr-90 were detected from some of the
samples of well water. I-131, Pu-238, and Pu-239+240 were not detected from any of the samples.
As shown in Fig. 30, no trends common to sampling places were confirmed with regard to concentration
levels of radioactive cesium and radioactive strontium contained in samples for rivers (river water,
riverbed sediment, and suspended sediment) before and after the rainy season. The period of this survey
was rather short. In order to confirm changes in concentration levels of radioactive substances in samples
for rivers (river water, riverbed sediment, and suspended sediment) in more detail, it is necessary to
continue a long-term survey.
The maximum concentration levels in samples of river water and well water were 1.9Bq/kg for Cs-134
and 2.0Bq/kg for Cs-137, which were far lower than the Provisional Regulation Values relating to Limits
on Food and Drink Ingestion (200Bq/kg).
The concentration of Sr-90 in samples of well water detected in this survey (1.4×10-3 Bq/kg) falls within
the concentration levels of Sr-90 in tap water, etc. detected nationwide prior to the accident (the detection
㻟㻞
limit to 2.3×10-3 Bq/kg (average: 1.0×10-3 Bq/kg: results of the FY2009 survey)). As Sr-89 was not
detected in samples of well water in this survey, influences of the accident at the Fukushima Dai-ichi
NPP could not be confirmed with regard to well water.
The possible internal exposure dose when a person continues to drink river water for one year was
calculated by using the adults’ water intake used in ICRP Publication 23 (2.65 liters per day) and the
effective dose coefficients (mSv/Bq) defined in the Act on the Regulation of Nuclear Source Material,
Nuclear Fuel Material and Reactors. As a result, it was confirmed that compared with the internal
exposure dose when a person continues to drink, for a period of one year, river water from which
radioactive cesium was detected at the largest concentration level, internal exposure dose caused by
radioactive strontium is extremely low, at around 1% of the former.
It became clear that there is certain proportional relationship between concentration levels of radioactive
cesium contained in river water, riverbed sediment, and suspended sediment and deposition amounts of
radioactive cesium in upstream regions of sampling points (see Fig. 31). Given these, it was confirmed
that concentration levels of radioactive cesium contained in river water, riverbed sediment, and
suspended sediment at any sampling point may be estimated by obtaining the average concentration of
radioactive cesium deposited in the upstream region.
Furthermore, it was also confirmed that at different points with various particle size characteristics of
soil particles, it is possible to estimate concentration levels of radioactive cesium in river water, based on
measurement results of radioactive cesium contained in riverbed sediment, by way of particle size
corrections of riverbed sediment particles (see Fig. 32).
Fig. 29 Points to Collect Samples for Rivers and
Well Water Samples
Fig. 30 Changes in Concentration Levels of
Radioactive Substances in Samples for
Rivers (Example of Cs-137)
㻟㻟
st
1 RiverWater(Cs137)(Bq/L)
Cs137deposition in the catchment soils based on
thesoilinvestigation 䠄Cs137䠅䠄Bq/m 䠅
nd
2 RiverWater(Cs137)(Bq/L)
2
When the concentration (average) of Cs-137 in
soil at the upstream region of a sampling point is
large, the measured concentration of Cs-137 in
river water is also large.
Cs137deposition in the catchment soils based on
thesoilinvestigation 䠄Cs137䠅䠄Bq/m 䠅
2
Fig. 31 The relationship between radiocesium concentration (Bq/m2) in the river and the radiocesium
deposition (Bq/m2) (mean value) in soil
at
the upstream of river water sampling site. (case of
Correction
Cs137Concentration(RiverWater)Bq/L
Cs137Concentration
Cs137Concentration
(Sediment䞉RawData)Bq/kg
Particle Size
(Sediment䞉ParticleSizeCorrection)Bq/kg
Cs-137)
Cs137Concentration(RiverWater)Bq/L
Fig. 32 The relationship between radiocesium concentration (Bq/L) in the river and radiocesium
deposition (Bq/kg) in sediment (case of Cs-137)
㻟㻠
(4) Confirmation of comprehensive movement of radioactive substances in the model area
1) Outline of the survey
The experience of the Chernobyl accident, etc. has revealed that radioactive substances accumulated on
the ground surface later move in accordance with natural environments of soil and rivers.
Therefore, in order to forecast future changes in accumulated amounts of radioactive substances, a model
area was chosen and a comprehensive survey was conducted with regard to the movement of radioactive
substances in the forests, soil, underground water, and river water, as well as on their movement after
being blown upward from trees and soil (see Fig. 33).
2) Survey period
The installment of measurement equipment was commenced on June 6, and an on-site survey was
conducted up to August 31.
3) Targeted area (see Fig. 34)
Considering that the survey results will be later utilized as significant basic data for promoting residents’
return home, the Yamakiya district, Kawamata town, Date county was chosen as the targeted area. The
district is located in the upstream region of the Kuchibutogawa River in the Abukuma River system,
which is in the planned evacuation areas and where deposition amounts of radioactive substances are
relatively large.
As survey points for rivers, in addition to the Kuchibutogawa River, which is the outlet of water and dirt
from the Yamakiya district, the main stream of the Abukuma River downstream of Kuchibutogawa River
were selected.
As survey points for lakes and reservoirs, in addition to a reservoir in the main stream of the Abukuma
River, reservoirs in Nihonmatsu city, where deposition amounts of radioactive substances have been
confirmed to be relatively large, were also included.
4) Survey results and considerations
This survey mainly targeted the Yamakiya district, Kawamata town, Date county, Fukushima prefecture,
and monitoring was conducted with regard to how radioactive substances had moved in natural
environments, such as soil, underground water, and river water, and how they had been blown upward
from trees and soil, in a short period of time after the accident at the Fukushima Dai-ichi NPP. The
survey results fell short of confirming comprehensive movement of radioactive substances, but have
revealed their initial movement in respective natural environments to a certain degree (see Fig. 35)
The survey results showed that the movement of radioactive cesium into soil water, torrent water, and
underground water had still been small.
At all surveyed reservoirs, when examining the depth distribution of radioactive cesium in the bottom
mud, it was confirmed that concentration levels of radioactive cesium were the largest in the surface
layer and declined sharply as becoming deeper from the mud surface.
On the other hand, at the dam reservoir (Horai Dam), high-level radioactive cesium was detected even in
the lower layer of the bottom mud at around 20cm from the mud surface, which was the deepest
㻟㻡
monitoring point in this survey. This suggests the possibility that soil particles with radioactive cesium
flowing in from rivers had been deposited in large quantity, or that the bottom mud had been blended and
mixed considerably.
Transport of radioactive cesium in rivers (excluding transport due to sand that runs along the river
bottom (bed load)) was also examined and a comparison between the concentration levels of radioactive
cesium in water and in suspended sediment revealed that in all monitoring points, over 90% of
radioactive cesium was flowing down in the form of suspended sediment.
Small-size sand particles constituting suspended sediment are considered to have originated from soil
erosion flowing into rivers in the form of minute soil particles. Therefore, the outflow of radioactive
cesium due to soil erosion from different districts used for various purposes was also checked, and it was
ascertained that the outflow was small at monitoring points covered with rich vegetation. On the other
hand, it was suggested that in young Japanese cedar forests, where understory vegetation is not so rich
but the soil is covered with litter, the outflow of soil due to rainfall is prevented and consequently the
outflow of radioactive cesium is small.
As a result of examining the distribution of radioactive cesium by building towers in Japanese cedar
forests and broad-leaved forests, it was found that a large amount of radioactive cesium was deposited on
tree crowns in needle-leaved forests. Radioactive cesium deposited on leaves and trunks is considered to
have been moving gradually to the forest floor, being washed down by rainwater that falls down from
tree crowns. As concentration levels of radioactive cesium contained in rainwater falling within the
forests were higher than those in rainwater flowing down on tree trunks, increases in radioactive cesium
on the ground surface in the forests are considered to have been largely caused by the movement of
radioactive cesium deposited on tree leaves that was washed down by rainfall.
Looking at the scattering (resuspension) of radioactive substances from soil and the forests, a correlation
was found between concentration levels of radioactive cesium in atmospheric suspended dust and
deposition amounts of radioactive cesium on the soil surface, which means that radioactive cesium
deposited on the soil surface scatters in the air.
On the other hand, in young Japanese cedar forests and forests of various broad-leaved trees, deposition
amounts of radioactive cesium in soil were almost the same as those in districts used for other purposes,
but concentration levels of radioactive cesium in atmospheric suspended dust tend to be higher. This
implies that the scattering of radioactive cesium from tree crowns has a different mechanism from that
for the scattering from the soil.
In addition, in paddy fields, concentration levels of scattering radioactive cesium are lower compared
with neighboring areas, which suggests that the scattering is prevented by soil moisture.
㻟㻢
Fig. 33 Outline of This Survey
Fig. 34 Points for Survey of Comprehensive Movement of Radioactive Substances
㻟㻣
Fig. 35 Existence and Movement of Radioactive Substances in the Targeted Area
(Example of Radioactive Cesium)
㻟㻤
(5) Summary of respective research surveys (Results of the surveys on movement of radioactive
substances in various natural environments, and considerations thereon)
Through the overall research relating to distribution maps of radiation doses, etc., measurement results
on the movement of radioactive substances in various natural environments have been obtained and
some of the research surveys confirmed the same facts. Therefore, we compiled the summary of each of
the survey contents.
1) In-depth distribution of radioactive cesium in soil
It was confirmed that radioactive cesium exists within a depth of almost 5cm from the surface layer of
soil used for various purposes (upland fields, forests (Japanese cedar forests and forests of various
broad-leaved trees), paddy fields, and grass fields) at all locations surveyed, within the 100km-range
from the Fukushima Dai-ichi NPP, during the survey period from June to August.
However, the depth distribution differs depending on land use, as shown below.
(i) Forests
In all forest soil samples, around 80% of the detected radioactive cesium was deposited within a depth of
2cm from the surface layer.
In all forests surveyed, over 50% of the radioactive cesium detected at the ground surface was deposited
in the litter layer (layer of fallen leaves) (in the forest of various broad-leaved trees in the Yamakiya
district, 90% was deposited in the litter layer).
(ii) Upland fields (Cultivated and uncultivated)
In uncultivated upland fields, most of the detected radioactive cesium was deposited within a depth of
5cm from the surface layer.
In some upland fields covered with rich vegetation, a significant amount of radioactive cesium was
deposited on the vegetation, but in upland fields not covered with rich vegetation, most of the detected
radioactive cesium was deposited on soil. In upland fields cultivated after the accident, concentration
levels of radioactive cesium were high up to a depth of 5cm from the surface layer.
(iii) Grass fields
In the grass field that continued to be disturbed due to grazing, etc. even after the occurrence of the
accident (Mizusakai rangeland, Kawamata town), radioactive cesium was detected at a depth of 5cm or
deeper from the surface layer, but in most grass fields, radioactive cesium mostly existed within a depth
of 5cm from the surface layer.
In grass fields covered with rich vegetation, a significant amount of radioactive cesium was deposited on
the vegetation, but in most grass fields, only around 20 to 30% of the detected radioactive cesium was
deposited on the vegetation. In some rangelands, a high level of radioactive cesium was detected up to a
depth of around 4cm from the surface layer due to disturbance of the surface soil caused by grazing
livestock.
㻟㻥
(ii) Paddy fields (Cultivated and uncultivated)
In paddy fields left uncultivated after the accident, most of the detected radioactive cesium was deposited
at a depth of 0.5 to 1.0cm from the surface layer, but in paddy fields cultivated after the accident,
radioactive cesium was detected especially deep in soil.
In soil cultivated after the accident, high level radioactive cesium was detected up to a depth of around
5cm from the surface layer.
2) Radionuclides contained in rivers
Concentration levels of radioactive cesium contained in river water, riverbed sediment, and suspended
sediment in Fukushima prefecture during the survey period from late June to mid-October showed no
clear trends common to sampling points, although some increases or decreases were observed before and
after the rainy season. I-131 was not detected at any of the monitoring points.
Regarding the transport of radioactive cesium from river streams to outlets, the amounts transported by
suspended sediment are much larger than those transported by river water, while their ratios to the total
amounts transported vary by monitoring points.
The calculated estimate of transported amounts of Cs-137 that flew down near the outlet from mid-July
to mid-August was around 7.4×1011Bq in 20 days, which was around 1/20000 or 1/15000 of the
estimates of discharged Cs-137 made by the Nuclear and Industrial Safety Agency or the Nuclear Safety
Commission of Japan (1.5×1016Bq or 1.1×1016Bq).
During this survey period, at some survey points for rivers in Fukushima prefecture, radioactive
strontium was detected, although in an extremely small quantity compared with radioactive cesium, and
it was confirmed that radioactive strontium had moved into river water.
For river water samples from which radioactive strontium was detected, analysis was conducted also
with regard to Pu-238 and Pu-239+240, but the results were all below the detection limits.
3) Movement of radionuclides through soil water, underground water (well water), torrent water, and
spring water
Mainly targeting the Yamakiya district, Kawamata town, Date county, Fukushima prefecture,
measurement was carried out with regard to concentration levels of radioactive cesium contained in soil
water, underground water (well water), torrent water, and spring water, during the period from early July
to mid-August. Most of the results were below the detection limits, and the movement of radioactive
cesium in these hydrologic circulation processes could not be ascertained during this period.
The results of the measurement with regard to well water samples collected in 50 locations in Fukushima
prefecture were the same.
The targeted area is limited to the Yamakiya district, Kawamata town, Date county, Fukushima
prefecture, but the following results were confirmed with regard to the distribution of radioactive cesium in
the forests, the movement of radioactive substances due to soil erosion, the movement of radioactive
cesium with suspended sediment from paddy fields to rivers, the distribution of radioactive cesium in lakes
and reservoirs, and the scattering of radioactive substances from natural environments such as the forests
㻠㻜
and soil.
4) Distribution and movement of radioactive cesium in the forests
The amounts of radioactive cesium accumulated in soil in the forests are considered to be increasing
gradually as fallen leaves are piled up and radioactive cesium attached to leaves moves to the ground
surface in the forests due to rainfall.
It was implied that in forests of various broad-leaved trees, radioactive cesium deposited on the surface
layer (the litter layer in particular) has started to infiltrate deeper into soil due to the infiltration of
rainwater and decomposition of organic matter.
In forests of various broad-leaved trees, deposition amounts of radioactive cesium are large in the litter
layer of fallen leaves. Therefore, in order to reduce ambient dose rates within the forests at present, it is
deemed to be effective to remove the litter layer piled on the ground surface, while taking into
consideration the effects on the ecosystem.
In Japanese cedar forests, concentration levels of radioactive cesium attached to growing leaves and dead
leaves are high. Therefore, it is deemed to be effective to remove growing leaves and dead leaves. In
aged Japanese cedar forests, amounts of radioactive cesium deposited on the ground surface are larger
than in young Japanese cedar forests or forests of various broad-leaved trees, and therefore the removal
of the litter layer will also be effective.
5) Movement of radioactive substances due to soil erosion
At locations covered with rich vegetation, the vegetation prevents the outflow of soil and the movement
of radioactive substances, and the outflow of radionuclides was confirmed to be small.
In the meantime, in young Japanese cedar forests, understory vegetation is not so rich but the soil is
covered with litter, which seems to prevent both soil flowing out due to rainwater and the movement of
radioactive substances.
The amounts of radioactive substances moved due to soil erosion during the survey period (one and a half
months) were less than around 0.3% at the largest of the total amounts of radioactive cesium detected at
each monitoring point.
6) Distribution of radioactive cesium in lakes and reservoirs
Concentration levels of radioactive cesium contained in the bottom mud of reservoirs were higher in the
surface layer and declined sharply as becoming deeper from the mud surface. The amounts of radioactive
cesium deposited in reservoirs were almost at the same level as those measured in nearby soil.
On the other hand, at the dam reservoir (Horai Dam), high level radioactive cesium was detected even in
the lower layer of the bottom mud at around 20cm from the mud surface, in the amount of around ten
times larger (3MBq/m2 or larger) than the amounts measured at the other reservoirs (200 to 400kBq/m2
except for some reservoirs). This may be because soil particles with radioactive cesium flowed in from
rivers and have been deposited in large quantity, or there has been continuous inflow from rivers and the
bottom mud has been stirred considerably.
㻠㻝
7) Scattering of radioactive substances from natural environments such as soil and the forests
Examining the scattering (resuspension) of radioactive substances from soil and the forests, a certain
correlation was found between concentration levels of radioactive cesium in atmospheric suspended dust
and deposition amounts of radioactive cesium on the soil surface. Consequently, it was confirmed that
radioactive cesium deposited on the soil surface has been scattering in the air.
In the meantime, in young Japanese cedar forests and forests of various broad-leaved trees, concentration
levels of radioactive cesium in atmospheric suspended dust tended to be higher than in districts used for
other purposes, although deposition amounts of radioactive cesium in soil were almost the same.
(Conclusion)
Through this survey, it was confirmed that the distribution of radionuclides differs among soil at locations
used for various purposes or in needle-leaved forests and broad-leaved forests. Furthermore, extremely
significant results could be obtained with regard to the movement of radionuclides due to soil erosion,
the movement of radioactive substances from soil and the forests, etc., and the movement of radioactive
substances through hydrologic circulation processes of rivers and lakes, soil water, and underground
water, etc., for the period before and after the rainy season at an early stage after the occurrence of the
accident. It is expected that the knowledge found through this survey will be fully utilized for
decontamination work and future monitoring surveys.
On the other hand, this survey only covered limited areas for a limited period of time from June to around
September 2011, and it is necessary to expand the survey scope, elaborate survey methods, and further
increase survey items in order to generalize the overall movement of radioactive substances and resolve
problems newly recognized in the process of this survey.
Therefore, in the future, it is necessary to conduct a survey on the depth distribution of radioactive
substances on an ongoing basis, while eliminating the influence of contamination that was raised as a
problem in this survey, and to continuously monitor concentration levels of radioactive substances in
river water and well water and the comprehensive movement of radioactive substances, thereby
obtaining measurement results concerning the behavior of radioactive substances. (Since December 2011,
an additional survey has been conducted, taking into consideration problems found in this survey.)
When ascertaining the movement of radioactive substances, changes in the deposition of radioactive
substances due to decontamination work and the movement of radionuclides due to human activities
cannot be ignored. Therefore, future surveys also need to cover the movement of radionuclides in
people’s living areas. (In the survey being conducted since December 2011, the movement of
radionuclides in people’s living areas has been monitored additionally.)
㻠㻞
3. Report on the Research relating to Radiation Concentration Distribution Maps for Farmland Soil
(Part 3)
3.1 Outline of the research relating to radiation concentration distribution maps for farmland soil
This survey was conducted as a part of the project under the 2011 Strategic Funds for the Promotion of
Science and Technology, entitled “Establishment of the Base for Taking Measures for Environmental
Impact of Radioactive Substances,” aiming to clarify the effects on farmland soil of radioactive
substances discharged due to the accident at the Fukushima Dai-ichi NPP and to ascertain their
distribution over the areas. In this survey, concentration levels of radioactive cesium* in farmland soil
were measured in Miyagi, Fukushima, Tochigi, Gunma, Ibaraki, and Chiba prefectures, and a radiation
concentration distribution map for farmland soil was prepared by compiling the measurement results.
Furthermore, a map indicating estimated concentration levels of radioactive substances in farmland soil
in Fukushima prefecture was also prepared based on the correlation with ambient dose rates.
The depth distribution of radioactive cesium in farmland soil was also investigated. This project was
consigned by the Ministry of Agriculture, Forestry and Fisheries and was conducted with the cooperation
of the National Institute for Agro-Environmental Sciences, universities, and related parties of respective
prefectures. Each survey was carried out after the members of the Advisory Board of Distribution Map of
Radiation Dose, etc. verified the validity thereof.
* In this report, Cs-134 and Cs-137 are collectively indicated as radioactive cesium.
3.2 Researchers
(1) Ascertaining of the wide-area distribution of radioactive cesium concentration in farmland soil,
and the estimation map
Yusuke TAKATA, Kazunori KOHYAMA, Hiroshi OBARA, Yuji MAEJIMA, Shuntaro HIRADATE,
Nobuharu KIHOU, and Ichiro TANIYAMA (National Institute for Agro-Environmental Sciences);
Hideki WASHIO (Miyagi
Prefectural Furukawa Agricultural Experiment Station); Takashi SAITO
(Fukushima Agricultural Technology Center); Masaharu IKEBA (Ibaraki Agriculture Institute);
Satoshi SUZUKI (Tochigi Prefectural Agricultural Experiment Station); Tadashi SHOJI (Gunma
Agricultural Technology Center); and Kenji SAITO (Chiba Prefectural Agriculture and Forestry
Research Center)
(2) Depth distribution and dynamic state of radioactive cesium in farmland soil
Yasuyuki MURAMATSU (Gakushuin University)
3.3 Survey period and targeted areas
(1) Ascertaining of the wide-area distribution of radioactive cesium concentration in farmland soil,
and the estimation map
The survey was conducted at 51 points in Miyagi prefecture from July 15 to July 22, at 201 points in
Fukushima prefecture from May 23 to August 5, at 44 points in Ibaraki prefecture from July 1 to July 15,
at 34 points in Tochigi prefecture from June 20 to June 24, at five points in Gunma prefecture on July 29,
and at 20 points in Chiba prefecture from July 1 to July 13, 2011.
Previously, a survey was conducted at 14 points in Miyagi prefecture on April 1, at 134 points on April 1
㻠㻟
and at 26 points on April 15 in Fukushima prefecture, at 18 points in Ibaraki prefecture from April 1 to
April 5, at 14 points in Tochigi prefecture from March 31 to April 1, at eight points in Gunma prefecture
on April 2, and at 10 points in Chiba prefecture on April 2, 2011. In preparing the concentration
distribution map, these results previously obtained were also used. The total number of survey points is
579. The radiation concentration distribution map for farmland soil was prepared by plotting radiation
concentration levels as of the base date (June 14, 2011) on a map.
(2) Depth distribution and dynamic state of radioactive cesium in farmland soil
The survey was conducted in paddy fields, upland fields, an orchard, and a forest within the Fukushima
Agricultural Technology Center from April 23 to September 9, at an orchard within the Fruit Tree
Research Centre of the Fukushima Agricultural Technology Center from June 1 to June 22, and in paddy
fields in the Obama district in Nihonmatsu city on September 19 and October 2, 2011.
3.4 Survey results and considerations
(1) Ascertaining of the wide-area distribution of radioactive cesium concentration in farmland soil,
and the estimation map
(i) Distribution of radioactive cesium concentration in soil in farmland
Fig. 36 shows the distribution of radioactive cesium concentration in farmland soil based on the results of
the current survey.
By prefecture, concentration levels of radioactive cesium in soil were from 24 to 2,214Bq/kg-dry soil in
Miyagi prefecture, from below the detection limits to 30,231Bq/kg-dry soil in Fukushima prefecture,
from below the detection limits to 648Bq/kg-dry soil in Ibaraki prefecture, from below the detection
limits to 4,097Bq/kg-dry soil in Tochigi prefecture, from 55 to 688Bq/kg-dry soil in Gunma prefecture,
and from 19 to 800Bq/kg-dry soil in Chiba prefecture. In this report, with regard to the total
concentration of Cs-134 and Cs-137, when either of the measurement results was below the detection
limit, the detected value is indicated as the total, and when both of the measurement results were below
the detection limits, the total is indicated to be “Not detectable.”
Measured concentration levels of radioactive cesium in farmland soil were high in the Hamadori district
and the Nakadori district in Fukushima prefecture, and their spatial distribution showed a similar trend as
the results of the ground-based monitoring of ambient dose rates and the airborne monitoring being
conducted by MEXT. Points where high level radioactive cesium over 10,000Bq/kg-dry soil was
detected were found, in particular, in the restricted areas and planned evacuation areas to the northwest
from the Fukushima Dai-ichi NPP.
(ii) Relation between concentration levels of radioactive cesium in soil and ambient dose rates
Fig. 37 shows the relation between concentration levels of radioactive cesium in soil and ambient dose
rates at a height of 1m measured at the time of the survey of farmland soil.
A positive correlation was confirmed between concentration levels of radioactive cesium in soil and
ambient dose rates (R2=0.82, the number of samples: 325), and it became clear that if concentration
levels of radioactive cesium in soil increase, ambient dose rates also increase.
㻠㻠
Comparing the points in farmland cultivated after the accident at the Fukushima Dai-ichi NPP and points
in uncultivated land for examining this relation in more detail, ambient dose rates were lower in
cultivated land than in uncultivated land, although concentration levels of radioactive cesium in soil were
at the same level. This is considered to be mainly due to the difference in the depth distribution of
radioactive cesium in cultivated soil and uncultivated soil, which had changed the relation between
ambient dose rates and radiation concentration levels in soil. Furthermore, as the bulk density varies by
soil quality, ambient dose rates seemed to be lower for the Andosol soil group than the other soil group,
even when concentration levels of radioactive cesium in soil were at the same level.
In orchards, ambient dose rates tended to be higher than in land in other categories, even when
concentration levels of radioactive cesium in soil were at the same level. Such higher ambient dose rates
in orchards than in land in other categories are considered to be due to indirect influences of radioactive
cesium deposited on tree crowns, etc. and the fact that soil in orchards is not cultivated.
(iii) Map indicating estimated concentration levels of radioactive cesium in farmland soil
Based on data for ambient dose rates and by using the regression formula found in (ii) above, a map
indicating estimated concentration levels of radioactive cesium in farmland soil covering all targeted
areas was prepared (see Fig. 38).
As a result, concentration levels of radioactive cesium in farmland soil were the highest in the Hamadori
district in Fukushima prefecture, where the Fukushima Dai-ichi NPP is located, followed by the
Nakadori district, and the Aizu district. In particular, concentration levels of radioactive cesium in
farmland soil were high in the restricted areas and planned evacuation areas.
When estimating the hectarage by concentration levels of radioactive cesium in farmland soil in
Fukushima prefecture, farmland where estimated concentration levels of radioactive cesium in soil
exceed 5,000Bq/kg-dry soil was 8,300 hectares in total, accounting for around 6% of the prefectural total
hectarage of paddy fields and upland fields.
(2) Depth distribution and dynamic state of radioactive cesium in farmland soil
In uncultivated paddy fields, concentration levels of radioactive cesium were high at the surface layer,
and most of the detected radioactive cesium existed within 0 to 4cm from the surface. Concentration
levels and the depth distribution varied by nearly ten times depending on sampling points. This may be
because at the time of being contaminated, there was no water lying on paddy fields, and radioactive
cesium was deposited in hollows where water was apt to gather.
In uncultivated upland fields, most of the detected radioactive cesium existed within 0 to 4cm from the
surface, as in the case of paddy fields. Disparity in concentration levels and the depth distribution among
sampling points was not as significant as seen in paddy fields. This may be because, unlike in paddy
fields, water did not stay long on upland fields.
Also at orchards and the forest, most of the detected radioactive cesium existed in the surface layer and in
particular in the surface litter layer in the forest.
In cultivated paddy fields in Nihonmatsu city in Fukushima prefecture, the depth distribution of
radioactive cesium was uneven, although the soil had been cultivated, and especially high concentration
㻠㻡
levels were observed in the surface layer within a depth of 0 to 2.5cm. Concentration levels of
radioactive cesium tended to be lower as becoming deeper. This is considered to be because soil of the
targeted area contained a larger percentage of sand, and after being cultivated, the part of heavy sand
(with lower concentration levels) sank earlier, leaving light and minute sand particles containing
radioactive cesium of higher concentration levels remaining at the upper layer.
㻠㻢
㻭㼓㼞㼕㼏㼡㼘㼠㼡㼞㼍㼘㻌㼒㼕㼑㼘㼐㻌
㻾㼍㼐㼕㼛㼍㼏㼠㼕㼢㼑㻌 㻯㼟㻌 㼏㼛㼚㼏㼑㼚㼠㼞㼍㼠㼕㼛㼚㻌
㻔㻮㼝㻛㼗㼓㻕㻌
㻌
Fig. 36 Measured spatial distribution of radioactive Cesium (Cs) concentration in agricultural soil
㻠㻣
1m㧗䛥䛾✵㛫⥺㔞⋡䠄Sv/h䠅
Ambient
dose rate at 1m height (ȣSv/h)
1m㧗䛥䛾✵㛫⥺㔞⋡䠄Sv/h䠅
Ambient dose rate at 1m height (ȣSv/h)
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
0
1000
2000
3000
4000
5000
6000
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00
0
1m㧗䛥䛾✵㛫⥺㔞⋡䠄Sv/h䠅
Ambient dose
rate at 1m height (ȣSv/h)
1m㧗䛥䛾✵㛫⥺㔞⋡䠄Sv/h䠅
Ambient dose rate at 1m height (ȣSv/h)
Ambient1m㧗䛥䛾✵㛫⥺㔞⋡䠄Sv/h䠅
dose rate at 1m height (ȣSv/h)
12.00
10.00
8.00
6.00
4.00
2.00
0.00
0
10000
20000
30000
2000
4000
6000
8000
10000
Radioactive
Cs conc. in soil (Bq/kg)
ᅵተ୰䛾ᨺᑕᛶ䝉䝅䜴䝮⃰ᗘ
(2) Cultivated 䠄Bq/kg஝ᅵ䠅
paddy and upland field
㠀㯮䝪䜽ᅵ䠅
(2)⏣䞉ᬑ㏻⏿⏝䠄
(Non-Andosols)
Radioactive
Cs conc. in soil (Bq/kg)
ᅵተ୰䛾ᨺᑕᛶ䝉䝅䜴䝮⃰ᗘ
䠄Bq/kg஝ᅵ䠅
(1) Cultivated
paddy and upland field
䠄㯮䝪䜽ᅵ䠅
(1)⏣䞉ᬑ㏻⏿⏝
(Andosols)
40000
ᅵተ୰䛾ᨺᑕᛶ䝉䝅䜴䝮⃰ᗘ
Radioactive
Cs conc. in soil (Bq/kg)
䠄Bq/kg஝ᅵ䠅
(3) Uncultivated
paddy and upland field
(Andosols)
(3)ᮍ⪔㉳_⏣䞉ᬑ㏻⏿⏝䠄㯮䝪䜽ᅵ䠅
1.40
1.20
1.00
0.80
0.60
0.40
0.20
0.00
0
1000
2000
3000
4000
5000
6000
ᅵተ୰䛾ᨺᑕᛶ䝉䝅䜴䝮⃰ᗘ
Radioactive
Cs conc. in soil (Bq/kg)
䠄Bq/kg஝ᅵ䠅
(4) Uncultivated
paddy and upland field
(Non-Andosols)
(4)ᮍ⪔㉳_⏣䞉ᬑ㏻⏿⏝䠄㠀㯮䝪䜽ᅵ䠅
2.50
2.00
1.50
1.00
0.50
0.00
0
1000
2000
3000
4000
ᅵተ୰䛾ᨺᑕᛶ䝉䝅䜴䝮⃰ᗘ
Radioactive
Cs conc. in soil (Bq/kg)
䠄Bq/kg஝ᅵ䠅
(5) Orchard
(5)ᶞᅬᆅ⏝
Fig. 37 The correlations between radioactive Cs concentration and ambient dose rate in different
soil and land use units
㻠㻤
5DGLRDFWLYH&VFRQFHQWUDWLRQLQ
DJULFXOWXUDOVRLO%TNJ
(VWLPDWHG0HDVXUHG
Fig. 38 Measured and estimated spatial distribution of radioactive Cesium (Cs) concentration in
agricultural soil
㻠㻥