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Journal of Environmental Radioactivity 113 (2012) 37e44

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Journal of Environmental Radioactivity

journal homepage: www.elsevier .com/locate/ jenvrad

Isotopic ratio and vertical distribution of radionuclides in soil affected by theaccident of Fukushima Dai-ichi nuclear power plants

Takeshi Fujiwara a,*, Takumi Saito b, Yusa Muroya a, Hiroyuki Sawahata a, Yuji Yamashita c,Shinya Nagasaki d, Koji Okamoto a, Hiroyuki Takahashi b, Mitsuru Uesaka a, Yosuke Katsumura a,Satoru Tanaka b

aNuclear Professional School, School of Engineering, The University of Tokyo, 2-22 Shirakatashirane, Tokai-mura, Naka-gun, Ibaraki 319-1188, JapanbDepartment of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, JapancDivision of Environment and Radiation Sciences, Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency, Shirakatashirane 2-4, Tokai-mura,Ibaraki 319-1195, JapandDepartment of Engineering Physics, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L8, Canada

a r t i c l e i n f o

Article history:Received 4 November 2011Received in revised form23 March 2012Accepted 17 April 2012Available online xxx

Keywords:131I134Cs137CsFukushimaFalloutSoil

* Corresponding author. Tel.: þ81 29 287 8495; faxE-mail address: fujiwara@n.t.u-tokyo.ac.jp (T. Fujiw

0265-931X/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.jenvrad.2012.04.007

a b s t r a c t

The results of g analyses of soil samples obtained from 50 locations in Fukushima prefecture on April 20,2011, revealed thepresence of a spectrumof radionuclides resulted fromthe accident of the FukushimaDai-ichi nuclear power plant (FDNPP). The sum g radioactivity concentration ranged in more than 3 orders ofmagnitude, depending on the sampling locations. The contamination of soils in the northwest of the FDNPPwas considerable. The 131I/137Cs activity ratios of the soil samples plotted as a function of the distance fromthe F1 NPPs exhibited three distinctive patterns. Such patterns would reflect not only the differentdeposition behaviors of these radionuclides, but also on the conditions of associated release events such astemperature and compositions and physicochemical forms of released radionuclides. The 136Cs/137Csactivity ratio, on the other hand, was considered to only reflect the difference in isotopic compositions ofsource materials. Two locations close to the NPP in the northwest direction were found to be depleted inshort-lived 136Cs. This likely suggested the presence of distinct sources with different 136Cs/137Cs isotopicratios, although their detailswere unknownat present. Verticalg activity profiles of 131I and 137Cswere alsoinvestigated, using 20e30 cm soil cores in several locations. About 70% or more of the radionuclides werepresent in the uppermost 2-cm regions. It was found that the profiles of 131I/137Cs activity ratios showedmaxima in the 2e4 cm regions, suggesting slightly larger migration of the former nuclide.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

The great east Japan earthquake of an intensity of 9.0 on theRichter scale hit the northeastern area (Touhoku) of Japan at 2:46pm onMarch 11, 2011. Soon after the earthquake, massive tsunamisattacked the costal region and caused devastating damages onbuildings and utilities and cost many lives.

Eleven nuclear power plants (NPPs)were in service at themomentof the earthquake in the disaster region. All NPPs shut down auto-matically and started cooling their reactors. Fukushima Dai-ichi (FD)NPP operated by Tokyo Electric Power Company (TEPCO) consisted ofsix boiling water reactor units (BWRs) with 13 emergency powergenerators in total. Three units of the FDNPP were not in service forregularmaintenance. TheFDNPPwerefloodedby the tsunamis,and12out of the 13 generators sank under sea water, leading to the loss of

: þ81 29 287 8488.ara).

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cooling functions for the acting BWRs (Units 1, 2, 3) (Japan AtomicIndustrial Forum, 2011). The overheated reactors caused an increaseof the pressure of the reactor vessels. In order to depressurize thevessels, TEPCO performed venting on March 12 for Unit 1, March 13and 15 for Unit 2, and March 12, 13 and 14 for Unit 3 (Fig. 1), with theapproval of theNuclear Industrial Security Agency (NISA), a regulatorybody in Japan (Japan Atomic Industrial Forum, 2011).Meanwhile, theymade tremendous efforts to cool down not only the overheatedreactors but spent fuels in the spent-fuel pools of Units 1, 2, 3 and 4,which turned out to be overheated as well, by injecting sea or freshwater by fire-extinguishing vehicles at first, then through fire-extinguisher lines as well as normal water-feed lines (Japan AtomicIndustrial Forum, 2011). During these efforts, hydrogen explosionoccurred on March 12 in Unit 1 and March 14 in Unit 3 (Fig. 1) due toreaction between water vapors and heated fuel cladding materials(Japan Atomic Industrial Forum, 2011). Unidentified explosion alsooccurred inUnit 2 onMarch15,whichwas supposedlyassociatedwithdamagesof its suppressionpool (JapanAtomic Industrial Forum,2011).

a

b

Fig. 1. Maps of the Japan islands and the region around the Fukushima Prefecture (shaded) (a) and chronological record of events in the Units 1, 2, 3 and 4 of the FDNPP togetherwith the records of air dose rates at Minamisouma City, Fukushima City and Tokai Village (b).

T. Fujiwara et al. / Journal of Environmental Radioactivity 113 (2012) 37e4438

Tremendous amounts of radionuclides have been released fromthe FDNPP to environments (METI (Ministry of Economy, Trade andIndustry, Japan), 2011a; Chino et al., 2011). Some of them werereleased on purpose during venting to atmosphere and disposal oflow-level contaminated water used the reactor cooling to sea andothers by accident through the explosions to atmosphere andleakage of highly contaminated water in trenches to sea. Totalamount of radionuclides released to atmosphere is estimated to bemore than 370,000 TBq (METI, 2011a; Chino et al., 2011), based onwhich the Japanese Government assessed the significance of thisaccident as level 7 on the international nuclear accident scale,which is same as the one for the Chernobyl accident, although theamount of the atmospheric release from the FDNPP is likely onetenth of that in the Chernobyl accident (METI, 2011a).

Atmospheric release of radionuclides, mostly volatile nuclidessuch as I and Cs, caused widespread contamination of cities, agri-cultural lands and forests of east Japan. Monitoring post (MP)located at different places recorded elevated air dose rates causedby such releases, as exemplified in Fig.1. Soon after the first venting,MPs close to the FDNPPmeasured sudden increases of air dose rate.An example is the MP located in Minamisouma City at about 25 kmnorth northwest of the FDNPP (Fig. 1) (Fukushima Prefecture, 2011;METI, 2011b). Later, MPs away from the NPPs reported similarincreases, including the one at the research reactor “Yayoi” site ofthe University of Tokyo in Tokai, Ibaraki Prefecture, which is locatedabout 100 km south southwest of the FDNPP, and the one inFukushima City, 60 km northwest of the FDNPP. Increased radiationlevel and contamination of environments by radionuclides havethreatened ordinary lives of many Japanese people in differentaspects. Inhabitants within 20 km radius from the FDNPP as well asthose living in highly contaminated areas outside this perimeterhave forcedly evacuated. Contamination of agricultural, animal andmarine products is posing serious economical problems for theirproducers and emotional impacts on their consumers.

The accident in the FDNPP is still ongoing. The TEPCO estimatedthat 6e9months were necessary to bring the overheated reactors tocold shutdown (Tokyo Electric Power Company, 2011) and thegovernment declared it in the middle of December 2011 (NuclearEmergency Response Headquarters, 2011). It will take many years

to de-contaminate the FDNPPsite anddispose avariety of radioactivewastes from the decontamination and decommission. It is nowhighly demanded to objectively understand the range and mecha-nismsof the environmental contaminationby radionuclides fromtheaccident for environmental restoration activities, possible adjust-ment of the evacuation zone, estimation of long-term committeddose for public, and discussion of future crisis management of NPPs.

Contamination of various environments has been a major topic ofresearch in environmental radiochemistry through investigations oncontaminated sites of nuclear-related facilities (e.g., Kersting et al.,1999; Zachara et al., 2002; IAEA, 2006; Novikov et al., 2006). Large-scale release of radionuclides in the Chernobyl accident is of partic-ular interest, from which atmospheric transport and deposition ofradionuclides,mainly volatilefission-products suchas long-lived 137Cs(T1/2 ¼ 30.10 a) and to lesser extent short-lived 131I (T1/2 ¼ 8.04 d) areknown (e.g. see IAEA, 2006 and references therein). Migration of suchradionuclides in soils has been also studied in northern and easternEurope (IAEA, 2006; Arapis et al., 1997). In response to the FDNPPaccident, the Ministry of Education, Culture, Sports, Science andTechnology (MEXT), Japan, constructed the detailed maps of radio-active cesiumand iodinewith thehelpof nation-wideuniversities andresearch institutes in June 2011, which covered more than 2000locations within about 100 km from the FDNPP (MEXT, 2011a, b).

Regardless of a number ofwell-documented reports on this topic,immediate pictures of environmental contamination by radionu-clides after release as well as the behavior of radionuclides in Japa-nese soils (Tsukada et al., 2008),which are ratherdifferent fromthosein Europe, are still limited. In this report, we present the results of g-ray analyses of soil samples obtained from50 locations in FukushimaPrefecture on April 20, 2011. The particular focus is the behaviors ofshort-lived radionuclides such as 131I and 136Cs, which would behardlydetected in later samplingcampaigns, in comparisonwith thatof long-lived 137Cs. The comparison allowed us to discuss the varia-tions of the deposition behaviors and source materials of the radio-nuclides. Vertical profiles of 131I and 137Cs are also provided, using20e30 cm soil cores in several locations. It will be shown that thereported data is valuable to grasp the initial condition of thecontamination, which can serve as a starting point for the evaluationof future radionuclide migration as well as planning and application

T. Fujiwara et al. / Journal of Environmental Radioactivity 113 (2012) 37e44 39

of soil decontamination, and to assess the atmospheric releasemechanism in the accident of the FDNPP, which could be used torestore the details of release events during the accident.

2. Materials and methods

Soil samples were collected on April 20th, 2011 at 50 locations inthe eastern area of Fukushima Prefecture, using house-made soilsamplers (5 cm f � 5 cm length). The detailed locations and the airdose rates measured at 1 m and 15 cm above the ground are tabu-lated in Table A.1. The eastern part of Fukushima Prefecture consistsof costal areas, where many cities and industrial plants includingFDNPP are located, and mountainous lands covered by forests,where small towns and villages are located. The choices of thesampling locations were made from the following considerations:(i) wide coverage of the east Fukushima, (ii) undisturbed soils afterthe accident and (iii) different land uses: brown forest soils, soils ofthe fields of rice and other plants and urban soils (mostly con-structed soils). All of these soil types are common in the areainvestigated. Only one sample was taken at each sampling location.Althoughwe cannot clarify how representative each sample is in itssampling location, the clear trends observed in the results of thecurrent study could indicate that possible variations of the radio-nuclide concentrations in a certain location are small at least enoughto assure the outcomes. At several locations, soil cores of 20e30 cmin length were taken for the depth profiles of radionuclides, usinga soil sampler (5 cm f � 30 cm length, HS-30, Fujiwara ScientificCompany). The soil cores were sliced by 2e5 cm sections. Theobtained depth profile must be seen with caution, as sampling ofa soil core in this way tends to compress the soil column. Indepen-dent tests revealed maximum 30% compression with the averagecompression of 7%. Ambient g-ray radiation level was measured ateach sampling location, while collecting the samples, using a g-raysurvey meter (TCS-171B, HITACHI-ALOKA), which comprised NaIdetector with a reading range of 0e1 mSv/h. The survey meter wascalibrated at regular intervals using standard 137Cs source. All thereadings were taken at 1 m and 15 cm above the ground level.

All soil samples were homogenized and placed into plasticcontainers (5 cm f � 5 cm length, U8, AS ONE corporation), thenmeasured with a high-energy resolution high-purity germanium(HPGe) g-ray spectrometer system consisting of a p-type intrinsicgermanium coaxial detector (GEM10P4-PLUS, ORTEC) mountedvertically and coupled to a multichannel analyzer with 4 k channels(MCA7600, SEIKO EG&G). The detector was placed inside a massivelead shield to reduce the background signals. Also, 5-mm thickcopper shields were installed around the sample to shield charac-teristic x-ray of lead. Detector was calibrated using a multi-nuclidestandard reference material fixed in epoxy resin (Eckert & ZieglerIsotope Product). The differences in the self-absorption coefficientsbetween the samples in soil matrices and that of the referencematerial in epoxymatrix turned out to be 3e5%, depending on g-rayenergies of radionuclides, and were considered in the calculation ofthe radioactivity in Bq from the measured counts. The energyresolution of 0.76 keV at 662 keV was achieved with the system.Each sample was kept on top of the HPGe detector and counted for1800 s. The activity of 131I was evaluated from the g-ray at365 keV, while 604 keV g-ray line was used to determine 134Cswith the correction of the coincident sum effect by the energydependence of the P/T (peak-to-total) ratio of the detector. 137Cs,129mTe and 136Cs were determined using 662 keV, 697 keV and818 keV peaks, respectively. The activity of each radionuclide wasdetermined using the total net counts under the selectedphotopeak after subtracting appropriate background counts andapplying appropriate correction factors for the detector efficiency,the relative intensity of the selected peaks, the difference in the

self-absorption between the soil and standard samples and thesample weight. The measured radioactivity was corrected for thedecay with respect to the sampling date, April 20th.

It is noteworthy to mention that three g-ray peaks at 106, 228and 278 keV could be assigned as the characteristic g-ray radiationof 239Np (T1/2 ¼ 2.36 d), which could be in secular equilibriumwithits parent nuclide, 243Am (T1/2 ¼ 7.38 � 103 a) having 75 keV g-rayemission (Lide, 2005). Although all four peaks were measured forsome of the soil samples, the presence of 239Np and 243Am wererejected because the first three peaks were disappeared after threemonths and the last one after removing the lead shield. Themeasured four peaks are now assigned to short-lived 129mTe, 132Teand 129Te as well as a characteristic X-ray from lead, which couldnot be completely removed by the copper shields, respectively.

3. Results and discussion

3.1. Contamination maps of g-ray emitting radionuclides close tothe Fukushima Dai-ichi NPP

Fig. 2(a) shows a map of the sum of the inventories of g-rayemitting radionuclides, 131I, 134Cs, 137Cs, 129Te and 129mTe, in the soilsamples (5 cm f � 5 cm height) collected in the east part ofFukushima Prefecture. These nuclides are major contributors to g

radioactivity fromthe soil samples. Individual inventorymapsof 131I,137Cs and 129Te are given in Fig. A.2 and the entire data are shown inTable A.1 with the locations, soil types and air dose rates of thecorresponding sampling points. Minor radionuclide such as 136Cs isfound in some samples (Table A.1) and its inventory map is pre-sented in Fig. A.2. Note that 129Te (T1/2 ¼ 1.16 h) was in transientequilibriumwith 129mTe (T1/2 ¼ 33.60 d) and that the mean activityratio of these radionuclides was 0.71, which was close to the theo-retical value, 0.63 (Lide, 2005), considering the associated uncer-tainties (Fig. A.3). The inventory of g-ray emitting radionuclideranges in more than 3 orders of magnitude, depending on thesampling locations. From Fig. 2(a), it is seen that the contaminationof soils in thenorthwest of the FDNPPare considerable,which agreeswith the results of the airplane g-ray monitoring performed by theMEXT and the US Department of Energy (MEXT, 2011c). It is note-worthy tomention that theMP in Fukushima Citywas located in thesame direction from the NPPs, which showed a sudden increase ofthe air dose rate in themidnight ofMarch 15 (Fig.1), followed by thegradual decrease. It is likely that this increase was caused by singlerelease event from one of the damaged reactors and that the sameevent caused the aforementioned relatively high contamination ofthe northwest region by the g-emitting radionuclides.

Fig. 2(b) and (c) exhibit the 131I/137Cs and 136Cs/137Cs activityratios of the soil samples plotted as a function of the distance fromthe FDNPP. The different colors correspond to the directions of thesampling points from the FDNPP. The 131I/137Cs ratio reflectsconditions of associated release events such as temperature andcompositions of damaged fuels and physicochemical forms ofreleased radionuclides (IAEA, 2006). The ratio can also depends onthe distance from source due to the different deposition behaviorsof these radionuclides, but noton thedifference in theirmigration insoil, because at present these nuclides are contained in 5 cm depthfrom ground as discussed below. The 131I/137Cs ratios show threedistinctive patterns. The first group, which locates in the south andto some extent southwest of the FDNPP, is characterized with anincreasing pattern of the activity ratiowith the distance. The secondgroup includes the locations close to the NPPs in the northwestdirection, where the contaminated soils are relatively rich in 131I.The rest could be the third group, which exhibits nearly constant131I/137Cs ratio not depending on the distance from the NPPs anddistributes from the northwest to southwest directions. These

a

b

c

Fig. 2. Mapof the east of part of FukushimaPrefecturewith bubble plots of the sumof the inventories ofg-rayemitting radionuclides (at dateApril 20th, 2011),131I, 134Cs,137Cs,129Te and129mTe, in Bq/m2 (a) and 131I/137Cs (b) and 136Cs/137Cs (c) activity ratios as a function of the distance from the FDNPP. Different colors in the plots correspond to the direction from theFDNPP and vertical lines to the associated errors. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

T. Fujiwara et al. / Journal of Environmental Radioactivity 113 (2012) 37e4440

observations agreewith the results of the detailed surveyconductedby the MEXT (MEXT, 2011b). The constancy of the ratio in thenorthwest directions from the FDNPP at relatively large distances,where the contamination most likely resulted from single event onMarch 15 as shown in the record of the dose rate at Fukushima Cityin Fig. 1(b), may suggest that the deposition behaviors of thesenuclides were similar. Possible exceptions are the locations close tothe FDNPP, where various events would have contributed.

The 136Cs/137Cs activity ratio, on the other hand, is considered toonly reflect the difference in isotopic compositions of source mate-rials. To be more specific, this ratio could be a good indicator ofelapsed time after fission reactions stop, as short-lived 136Cs (T1/2¼12.97 d) decaysmore rapidly than long-lived 137Cs (T1/2¼ 30.10 a).Most of the locations show almost constant 136Cs/137Cs activity ratio(0.02e0.03) regardless of the distance and direction from the NPPs.Only two locations close to the NPPs in the northwest direction showsignificantly low ratios (w0.02), suggesting the presence of differentsource materials, although their details are still unknown.

3.2. Depth profiles of 137Cs and 131I

Vertical profiles of 131I and 137Cs concentration shown in Fig. 3indicate infiltration/migration of these nuclides in soil columnsby the time of the sampling (April 20), presumably depending onsoil types and different use of the lands. Two sample locationsindexed with S7 and S13 exhibit infiltration up to 5 cm in the soilcolumns, although about 70% of these radionuclides are present inthe uppermost 2-cm layers. Meanwhile, at one sample location(S15) these radionuclides are predominantly confined in theupmost 2-cm layer (86% for 131I and 93% for 137Cs). At all threesample locations the profiles of 131I/137Cs activity ratios showincreases from the 0e2 to 2e4 cm layers within uncertainties.

The depth profiles of 137Cs and 131I in the three locations aroundthe FDNPP in Fig. 3 were quantitatively analyzed using a simple butintuitive exponential model (Beck, 1966):

cðxÞ ¼ c0exp��x

.h�

(1)

where c(x) is the concentration of a radionuclide in Bq/Kg at thedepth, x, and h is a characteristic width of the depth profile of the

nuclide. The optimized values of h of 137Cs and 131I for S3, 15 and 17are tabulated in Table 1 together with the values obtained by Katoet al. for a soil of a home garden in Kawamata Townwhich is located40 km northwest from the FDNPP (Kato et al., 2011). The charac-teristicwidths of the depth profiles are larger for 131I than 137Cs in allthree locations, meaning larger migration of 131I downward in thesoil columns. At maximum 131I migrates 1.7 times larger than 137Cs.These observations are in accordance with the result of Kato et al.(Katoet al., 2011).Among the three locations investigated, S7 (brownforest soil) exhibits the largest migration of the both nuclides andS17 from a vegetable field the smallest migration. Kato et al. inves-tigated the width of depth profiles of 137Cs in various soils on thebasis of their claycontents and suggested that the penetration depthof 137Cs increased with the clay content of a soil. Thus, the observedvariations of the radionuclides in our samples could be explained bythe clay contents in the samples. The contents of organic matterswould also affect the mobility of 137Cs especially immediately aftercontamination (Kruyts and Delvaux, 2002). Natural organic mate-rials are also known to regulate the chemical speciation of iodine insoil/water systems and therefore could affect the mobility of 131I insoils (Shimamoto et al., 2011). Further investigation of the depthprofiles of the radionuclides in a number of different soils togetherwith physicochemical and mineralogical analyses of soils arenecessary to understand key factors affecting their migration.

Compared with previous researches on 137Cs migration in soilcolumns in northern and eastern parts of Europe affected by theChernobyl accident in 1986, where vertical infiltration velocitieswereestimated to be less than 1 cm/year (Arapis et al., 1997), 137Cs move-ment observed in this study is relatively large. This couldmean that atthe initial stage of soil contamination 137Cs could exist in relativelymobile forms, for instance, by binding to exchangeable sites of clayminerals or to (dissolved) organic materials, andmove downward byprecipitation. Larger precipitation amounts in Japan than those ofnorthern and eastern Europe or differences in soil types and land usesmay further contribute to the observed difference of 137Cs migration.As time being, this relatively mobile faction will shift to more inertfactions by, for instance, binding to frayed edges of clay mineral andthen the migration will be significantly retarded (Comans andHockley, 1992). Periodical monitoring of vertical activity profile of

d

a

c

b

Fig. 3. Vertical profiles of 137Cs and I31I concentration and their ratio (aec) in soil samples obtained at several locations close to the FDNPP (d). Gray hatches for the g activity andactivity ratio profiles indicate the associated uncertainties resulting from counting statistics and peak fitting errors.

Table 1Characteristic width of the depth profiles of 137Cs and 131I in the contaminated soilsaround the FDNPP.

Sample ID/ reference Sampling date Characteristic width (cm)

137Cs 131I

S7 20 Apr 1.4 1.7S13 20 Apr 1.1 1.9S15 20 Apr 0.5 0.8Kato et al. (Kato et al., 2011) 28 Apr 0.8 1.2

T. Fujiwara et al. / Journal of Environmental Radioactivity 113 (2012) 37e44 41

137Cs as well as detailed studies on fixation and migration mecha-nisms of 137Cs in soils are required especially for soil types unique toJapan such as soil of rice fields and andosols with high contents oforganic materials and clay minerals derived from volcanic ashes.

4. Conclusion

Various g-ray emitting radionuclides resulted from the accidentfrom the FDNPPwere detected in the soil samples from50 locationsin Fukushima Prefecture on April 20, 2011. The inventories of g-emitting radionuclides ranged in more than 3 orders of magnitude,

and the contamination of soils in the northwest of the FDNPP wasconsiderable. The 131I/137Cs and 136Cs/137Cs activity ratios of the soilsamples plotted as a function of the distance from the FDNPPexhibited distinctive patterns. Such patterns would reflect thedifferences in the deposition behaviors and the release mecha-nisms of these radionuclides as well as the different isotopiccompositions of source materials. The 131I/137Cs ratios in the southand to some extent southwest of the NPPs exhibited an increasingpattern with the distance. On the other hand, the constant ratioobserved in the northwest direction, where the contamination wasmost likely caused by single event, indicated the similar depositionbehaviors of these nuclides at relatively large distances from theFDNPP. Exceptionally low 136Cs/137Cs ratios observed close to theFDNPP suggested the rather different sources for those locations.Vertical profiles of 131I and 137Cs concentration showed that about70% or more of the radionuclides were present in the uppermost 2-cm layers with 131I migrating deeper downward in the soil columns.

Appendix A

An example of the g-ray spectra of the soil samples is given inFig. A.1 (sample ID: 27). Individual inventory maps of 131I, 137Cs and

Fig. A. 1. Gamma-ray spectrum of a soil sample (sample ID: 27).

a b

c d

Fig. A. 2. Map of the east of part of Fukushima prefecture with bubble plots of the inventories in Bq/m2 of 131I (a), 137Cs (b), 129Te (c) and 136Cs (d).

T. Fujiwara et al. / Journal of Environmental Radioactivity 113 (2012) 37e4442

Fig A. 3. Activity ratios of 129Te and 129mTe as a function of the distance from the FDNPP. Different colors in the plots correspond to the direction from the NPPs and vertical lines tothe associated errors. The dashed line corresponds to the theoretical ratio assuming secular equilibrium between the nuclides.

T. Fujiwara et al. / Journal of Environmental Radioactivity 113 (2012) 37e44 43

129Te are given in Fig. A.2 and the entire data are shown in Table A.1with the locations, soil types and air dose rates of the correspondingsampling points. Minor radionuclide such as 136Cs is found in somesamples (Table A.1) and its inventory map is presented in Fig. A.2.

Table A.1. Locations, soil types, air dose rates and g activity inventories of selected radion

SampleID

Location Soiltypea

Air dose rate (mSv/h) Activity inventory (k

Latitude Longitude 1 Mb 15 cmb 131I 134C

S1 37�09047" 140�51013" B 0.28 0.33 35.9 (1.4)S2 37�11049" 140�51005" B 1.03 0.93 10.9 (0.8)S3 37�20014" 140�48031" O 0.43 0.47 36.2 (1.4)S4 37�27027" 140�42013" B 1.60 1.65 40.9 (1.5)S5 37�30044" 140�34036" B 1.60 1.65 43.5 (1.7) 1S6 37�33031" 140�39053" B 0.95 1.00 58.4 (1.8)S7 37�33018" 140�44017" B 7.55 8.90 211.6 (3.5) 4S8 37�37004" 140�44041" B 17.70 20.50 606.8 (6.1) 17S9 37�44025" 140�36037" B 1.60 1.65 42.6 (1.5)S10 37�46010" 140�44040" B 1.65 2.50 55.6 (1.7)S11 37�47015" 140�55058" O 0.68 0.75 33.7 (1.4)S12 37�42023" 140�59048" F 0.55 0.65 40.5 (1.5)S13 37�36035" 141�00035" F 0.50 0.80 27.7 (1.3)S14 37�29038" 141�00000" O 0.67 0.97 80.8 (2.1)S15 37�30007" 140�56047" V 7.50 9.80 496.0 (5.6) 15S16 37�32026" 140�51044" V N.R. N.R. 1603.8 (10.4) 45S17 37�36006" 140�40025" B 3.15 4.15 165.9 (3.2) 4S18 37�39029" 140�28036" O 1.45 2.00 125.9 (2.7) 2S19 37�41028" 140�27050" O 1.00 1.30 8.0 (0.7)S20 37�34030" 140�25047" O 2.00 2.90 51.9 (1.8) 1S21 37�04010" 140�50009" R 0.26 0.27 53.1 (1.7)S22 37�08052" 140�40023" R 0.32 0.36 41.1 (1.5)S23 37�14043" 140�33047" R 0.23 0.25 17.9 (1.0)S24 37�17003" 140�36056" R 0.21 0.22 12.3 (0.8)S25 37�28014" 140�34020" R 0.49 0.57 31.0 (1.3)S26 37�36005" 140�34043" R 0.92 1.04 78.1 (2.2) 1S27 37�41030" 140�36036" R 1.23 1.15 83.1 (2.2) 1S28 37�41031" 140�40042" R 2.65 2.95 384.8 (4.9) 9S29 37�41004" 140�46042" R 3.74 3.80 132.7 (2.9) 4S30 37�39058" 140�52010" R 3.54 4.05 137.5 (3.2) 8S31 37�3705" 140�52021" R 5.15 6.10 217.2 (3.8) 8S32 37�1206" 140�59022" R 19.70 23.40 653.1 (6.3) 16S33 37�27021" 141�00007" R 3.33 3.74 293.2 (4.0) 2S34 37�2702" 141�00034" R 18.00 18.00 452.7 (4.9) 2S35 37�27022" 141�01008" R 42.70 51.40 2202.6 (11.7) 51S36 37�26025" 141�00005" R 3.44 4.21 552.6 (5.6) 6S37 37�25052" 140�59027" R 66.00 77.10 4799.4 (17.7) 93S38 37�25052" 140�59011" R 15.90 19.20 1269.7 (8.6) 22S39 37�24026" 140�52026" R 3.32 3.99 269.0 (3.9) 2S40 37�25053" 140�48025" R 0.85 0.97 61.6 (1.9) 1S41 37�30008" 140�45052" R 1.84 2.06 110.3 (2.5) 2S42 37�23001" 140�43025" R 0.68 0.78 16.9 (1.0)S43 37�16013" 140�45052" R 1.74 1.94 101.0 (2.6) 3S44 37�20009" 140�50043" R 0.88 1.09 59.4 (1.8) 1

Note that 129Te (T1/2 ¼ 1.16 h) was in transient equilibrium with129mTe (T1/2 ¼ 33.60 d) and that the mean activity ratio of theseradionuclideswas0.71,whichwas close to the theoretical value, 0.63(Lide, 2005), considering the associated uncertainties (Fig. A.3).

uclides (131I, 134Cs, 137Cs, 136Cs, 129mTe, and 129Te) of the soil samples.

Bq/m2)c

s 137Cs 136Cs 129mTe 129Te

22.2 (1.5) 21.7 (1.3) N.D. N.D. 69.6 (7.5)29.2 (1.8) 31.1 (1.6) 0.7 (0.3) N.D. N.D.29.5 (1.8) 30.6 (1.6) N.D. 19.8 (8.8) 17.6 (5.6)76.6 (2.9) 76.4 (2.6) 1.4 (0.4) 61.8 (13.6) 21.6 (8.0)24.0 (3.7) 126.8 (3.3) 3.3 (0.5) N.D. N.D.97.9 (3.2) 99.3 (2.9) N.D. N.D. 51.5 (8.7)17.9 (6.7) 427.3 (6.0) 9.7 (1.0) 282.3 (31.1) 204.9 (19.1)29.7 (13.6) 1759.2 (12.1) 38.7 (2.1) 951.1 (60.9) 648.0 (37.1)35.4 (2.0) 37.1 (1.7) N.D. N.D. N.D.69.9 (2.7) 73.8 (2.5) 2.4 (0.5) N.D. N.D.69.3 (2.7) 70.9 (2.4) 1.7 (0.4) N.D. N.D.85.8 (3.0) 86.6 (2.7) N.D. N.D. N.D.43.0 (2.1) 41.0 (1.9) N.D. N.D. N.D.82.3 (3.0) 86.5 (2.7) N.D. N.D. N.D.53.7 (12.9) 1697.4 (11.9) 35.6 (2.0) 1176.5 (65.8) 925.8 (44.8)46.9 (22.2) 4641.9 (19.8) 115.6 (3.6) 2293.6 (108.4) 1672.8 (71.5)60.7 (7.0) 483.5 (6.3) 10.6 (1.1) 330.4 (34.8) 183.9 (18.5)23.7 (4.9) 226.7 (4.3) 6.7 (0.8) 163.6 (24.5) 110.0 (14.3)36.3 (2.0) 34.5 (1.7) N.D. N.D. N.D.77.8 (4.3) 180.4 (3.8) 4.4 (0.7) 63.6 (17.1) 71.5 (10.9)22.3 (1.5) 20.9 (1.3) N.D. N.D. 63.1 (8.1)70.2 (2.8) 72.5 (2.5) N.D. N.D. N.D.35.1 (1.9) 34.1 (1.7) N.D. N.D. N.D.22.1 (1.5) 22.6 (1.4) N.D. N.D. N.D.61.7 (2.5) 53.9 (2.1) N.D. N.D. N.D.60.1 (4.1) 158.7 (3.6) N.D. N.D. N.D.15.0 (3.5) 117.8 (3.1) N.D. N.D. N.D.59.8 (10.1) 989.0 (9.1) 24.0 (1.6) 510.1 (45.0) 404.0 (29.6)77.4 (7.1) 483.9 (6.3) 11.4 (1.1) 201.1 (29.0) 134.0 (19.3)00.0 (9.2) 792.8 (8.1) N.D. 367.1 (39.4) 226.7 (24.6)99.5 (9.8) 920.2 (8.8) 19.0 (1.5) 483.0 (46.2) 339.8 (30.5)77.1 (13.4) 1924.8 (12.7) 5.7 (1.3) 1529.9 (76.5) 1170.1 (48.6)16.6 (4.8) 234.1 (4.4) N.D. N.D. 122.0 (14.4)59.4 (5.3) 293.9 (4.9) N.D. 189.4 (26.5) 110.5 (15.3)30.2 (23.6) 5809.1 (22.1) 10.2 (1.9) 4301.7 (128.4) 3024.3 (76.1)20.9 (8.1) 645.1 (7.3) 13.3 (1.2) N.D. 149.7 (22.2)13.6 (32.0) 9692.2 (29.1) 229.4 (5.4) 5298.9 (155.2) 3862.5 (95.9)59.9 (15.6) 2315.4 (13.9) 50.4 (2.4) 1263.7 (69.1) 1019.9 (49.1)33.7 (5.0) 238.7 (4.4) 5.4 (0.7) N.D. 131.2 (14.4)05.4 (3.4) 105.1 (2.9) N.D. N.D. 40.6 (8.7)54.7 (5.2) 259.7 (4.6) N.D. N.D. 62.2 (12.0)34.6 (1.9) 35.9 (1.7) N.D. N.D. N.D.11.6 (5.7) 327.0 (5.2) 8.4 (0.9) N.D. 94.6 (15.0)01.2 (3.3) 101.8 (2.9) N.D. N.D. 34.1 (8.2)

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SampleID

Location Soiltypea

Air dose rate (mSv/h) Activity inventory (kBq/m2)c

Latitude Longitude 1 Mb 15 cmb 131I 134Cs 137Cs 136Cs 129mTe 129Te

S45 37�21008" 140�53049" R 1.81 2.20 88.0 (2.3) 243.4 (5.1) 251.9 (4.6) N.D. 93.3 (20.3) 58.4 (12.5)S46 37�24030" 141�00017" R 34.10 44.50 1213.3 (9.1) 3623.6 (19.7) 3750.7 (17.7) 93.1 (3.2) 1497.6 (92.1) 1050.8 (58.0)S47 37�24040" 140�59049" R 109.00 119.00 5701.5 (19.0) 11136.9 (35.3) 11671.3 (32.1) 264.9 (5.9) 5500.2 (180.6) 4213.3 (103.4)S48 37�22018" 141�00027" R 16.10 16.90 1072.9 (8.0) 1488.4 (12.6) 1539.6 (11.3) 33.3 (1.9) 865.3 (56.2) 687.8 (38.1)S49 37�12024" 141�00027 R 2.22 2.56 148.5 (2.9) 137.9 (3.8) 143.0 (3.4) 2.8 (0.6) 105.4 (18.9) 76.9 (11.7)S50 37�12024" 140�59040" R 0.74 0.80 47.6 (1.6) 26.1 (1.7) 24.2 (1.4) N.D. 24.2 (10.0) 16.1 (5.9)

N.R. Not recorded.N.D. Not detected.

a Brown forest soil (B), fulvisol (F), andisol (A), rice field (R), vegetable fields (V), others, mostly urban areas (O).b Above the ground.c Numbers in parentheses indicate errors associated with counting statistics and peak fitting errors.

T. Fujiwara et al. / Journal of Environmental Radioactivity 113 (2012) 37e4444

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