Kyoto University
Research Reactor Institute
Institute of Environmental Radioactivity
at Fukushima University

International Symposium onRadiological Issues for
Fukushima's
Revitalized Future
Kyoto University
Research Reactor Institute
KUR Research Program for Scientific
Basis of Nuclear Safety

Proceedings

Proceeding of the International Symposium onRadiological Issues for Fukushima's Revitalized Future
Paruse Iizaka, Fukushima City, Japan, May 30–31(Sat.–Sun.), 2015
Edited by

Tomoyuki Takahashi
Hajimu Yamana
Hirofumi Tsukada
Nobuhiro Sato
Maki Nakatani

KUR Research Program for Scientific Basis of Nuclear SafetyⅰISBN-978-4-9906815-3-1 (Book) C3053
ISBN-978-4-9906815-4-8 (CD) C3853
ISBN-978-4-9906815-5-5 (from Web) C3853¥ 0E© KUR Research Program for Scientific Basis of Nuclear Safety
Office of KUR Research Program for Scientific Basis of Nuclear Safety
Kyoto University Research Reactor Institute2 Asashiro-nishi Kumatori-cho Sennan-gun Osaka 590-0494, JAPANE-mail: anzenkiban@rri.kyoto-u.ac.jp
Tel : +81-72-451-2432
Fax: +81-72-451-2639

ⅱ

Proceedings of the International Symposium onRadiological Issues for Fukushima's Revitalized Future
Paruse Iizaka, Fukushima City, Japan, May 30-31 (Sat.-Sun.), 2015

Host Organization

Kyoto University Research Reactor InstituteSupport Organizations

Institute of Environmental Radioactivity at Fukushima University
Fukushima Prefectural Government
Fukushima Prefectural Board of Education
Fukushima City Government
Atomic Energy Society of JapanThe Japan Society of Nuclear and Radiochemical Sciences
The Japan Radiation Research Society
The Japan Health Physics Society

Cooperative Organizations

Iizaka Onsen Tourist Association
Iizaka Onsen Ryokan Cooperative Association
Fukushima City Kanko-Bussan (Tourism and Local Products) Association
THE FUKUSHIMA MINYU SHIMBUN
Fukushima-Minpo Co. Ltd.

ⅲ

Organizing Committee
Chairperson
Vice Chairperson
Vice Chairperson

Yuji Kawabata
Takayuki Takahashi
Sentaro Takahashi
Jiro Inaba
Shigeo Uchida
Itsumasa Urabe
Kimiaki Saito
Kazuo Sakai
Ken Nakajima
Noriyuki Momoshima
Hiromi Yamazawa
Hajimu Yamana
Minoru Yoneda

Program Committee
Chairperson
Vice Chairperson

Tomoyuki Takahashi
Hirofumi Tsukada
Takeshi Iimoto
Masahiro Osako
Nobuyuki Sugiura
Takatoshi Hattori
Nobuhiko Ban
Satoshi Fukutani
Hirokuni Yamanishi
Hiroshi Yashima
Sumi Yokoyama
Satoshi Yoshida

Conference Secretariat
Chairperson
Vice Chairperson

Nobuhiro Sato
Maki Nakatani
Takumi Kubota
Yuji Shibahara
Hidehito Nakamuraⅳ

Preface
The nuclear accident at the TEPCO’s Fukushima Daiichi Nuclear Power Plants in March
2011, which followed an earthquake and a tsunami, brought serious impacts on society. This
accident inevitably emphasized the necessity of establishing new and comprehensive scientificresearch for promoting nuclear safety. Facing this situation, the Kyoto University Research Reactor
Institute (KURRI) developed a new research program called the “KUR Research Program for
Scientific Basis of Nuclear Safety” from 2012. In this program, it is planned to hold an annual series
of international symposia along with identified research activities for promoting nuclear safety.
The title of the symposium of the first year was “Environmental monitoring and dose
estimation of residents after the accident of TEPCO's Fukushima Daiichi Nuclear Power Stations”.
We tried to collect a wide range of those data to obtain an accurate estimation of the radiation dose.
The purpose of the second year of the symposium was “Nuclear Back-end Issues and theRole of Nuclear Transmutation Technology”. As you are aware, the issues of the nuclear back-end
is not limited to the technical or technological issues. But we are faced with the social difficulty ofdisposal after the accidents and the issues of the back-end is quite important. In this symposium, we
had a lot of participants from abroad. We discussed about the current situation and the future
prospective.
The third symposium with the little “Earth quake, Tsunami and Nuclear Risks After theaccident of TEPCO‘s Fukushima Daiichi Nuclear Power Stations”. Today in Japan, the safetyassessment of nuclear power plants ongoing regarding the earthquake and tsunami and massive
natural disasters.
Finally, the fourth symposium titled “Radiological Issues for Fukushima’s Revitalized
Future” was held with approximately 14 invited lectures and 80 scientific papers. Residents andSpecialists gathered and talked with many issues to revitalize the future of Fukushima though
presentations, science café, and panel discussions, with 668 participants in total. Almost all thepresentations have been written as original scientific papers, peer reviewed by specialists of therelevant research fields, and included in the proceedings booklet. On behalf of all the participants ofthe symposium, I sincerely hope that this symposium and its proceedings will contribute to the fasterrecovery of people who have encountered damages from the accident and will promote further
progress in the research on nuclear safety and the recovery of Fukushima.

Yuji Kawabata
Director, Kyoto University Research Reactor Institute
Chair of the organizing committeeⅴ

Contents
Part 1 Decontamination/radioactive waste
Identify the place and the execution of the decontamination. Whole process fromclassification ~ transportation till disposal.
1 Cesium decontamination using a microbubble-treated aqueous solution of sodium metasilicate
Yoshikatsu UEDA, Yomei TOKUDA, Hiroshi GOTO

1

Decontamination system of radiocesium contaminated water
Kahori YOKOTA, Shio ARAI, Hideki OGAWA, Ritsuko NAKAMURA, Hirohisa YOSHIDA

6

2

3 Application of mass spectrometry for analysis of cesium and strontium in environmental samples
obtained in Fukushima prefecture
Yuji SHIBAHARA, Takumi KUBOTA, Satoshi FUKUTANI, Toshiyuki FUJII, Koichi TAKAMIYA,
Tomoko OHTA, Tomoyuki SHIBATA, Masako YOSHIKAWA, Mitsuyuki KONNO, Satoshi MIZUNO,
Hajimu YAMANA

11

4 Safe decontamination system for combustion of forestry wastes
Hirohisa YOSHIDA, Hideki OGAWA, Kahori YOKOTA, Shigemitsu IGAI, Shio ARAI,
Ritsuko NAKAMURA

14

Part 2 Environmental radiation/external exposure
Prospects for the future, reduction, measurement estimation of the external exposure,and so on.
1 Integrating nuclide specific and dose rate based methods for airborne and ground based gamma
spectrometry.
David SANDERSON, Yukihisa SANADA, Alan CRESSWELL, Sheng XU, Simon MURPHY, Chika
NAKANISHI., Tsutomu YAMADA

18

2 Bacterial microflora characteristics of plant samples from contaminated by radionuclides
Chernobyl area
Pavlina ZELENA, Julia SHEVCHENKO, Valentina BEREZHNA, Julia SHYLINA, Mykola
GUSCHA, Olha MOLOZHAVA

24

3 Fields of View for Environmental Radioactivity
Alex MALINS, Masahiko OKUMURA, Masahiko MACHIDA, Hiroshi TAKEMIYA, Kimiaki SAITO

28

4 Study on applicability of CdZnTe semiconductor detector to in situ environmental radioactivity
measurement in high dose rate areas
Munehiko KOWATARI, Takumi KUBOTA, Yuji SHIBAHARA, Toshiyuki FUJII, Koichi TAKAMIYA,
Satoru MIZUNO, Hajimu YAMANA

35

5 Prediction of ambient dose equivalent rates for the next 30 years after the accident
Sakae KINASE, Tomoyuki TAKAHASHI, Satoshi SATO, Hideaki YAMAMOTO, Kimiaki SAITO

40

ⅵ

Part 3 Environmental radioactivity/internal exposure
Farm/marine products, food, food ingestion, resorption control, and so on.
1 Effect of nitrogen and potassium fertilization on radiocesium absorption in soybean
Naoto NIHEI, Atsushi HIROSE, Keitaro TANOI, Tomoko M. NAKANISHI

44

2 Biological effect of soil sterilization on the Cesium-137-transfer to plants
Tadatoshi KINOUCHI, Yuki HATTORI, Keiko FUJIWARA, Tomoyuki TAKAHASHI,
Satoshi FUKUTANI, Sentaro TAKAHASHI

48

3 Radioactivity levels of vegetables, rice, fruits and drinking water in Minami-Souma City
Kiyoshi SHIZUMA, Yushi SAKURAI

51

4 The amount of 137Cs deposition and transfer ratio of 137Cs to wild edible-wild-plants after
the accident at TEPCO's Fukushima Daiichi Nuclear Power Station
Yoshiyuki KIYONO, Akio AKAMA

57

5 Examination of Iodine-131 Concentrations in Food and Drink in the Early Phase after the Accident
Masaki KAWAI, Nobuaki YOSHIZAWA, Sachiko HIRAKAWA, Kana MURAKAMI,
Mari TAKIZAWA, Osamu SATO, Shunji TAKAGI, Hirokazu MIYATAKE, Tomoyuki TAKAHASHI,Gen SUZUKI

62

6 The distributions of radiocesium in seawaters and sediments collected off the Niida River estuary,
Fukushima Prefecture
Miho FUKUDA, Shinnosuke YAMAZAKI, Tatsuo AONO, Satoshi YOSHIDA, Takashi ISHIMARU,
Jota KANDA

66

7 Review of the gastrointestinal absorption rates of cesium in human and animals from food products
and soil particles
Kayoko IWATA, Hiroshi YASHIMA, Yuko KINASHI, Tomoyuki TAKAHASHI,
Sentaro TAKAHASHI

70

8 Transfer of radioactive cesium to earthworms after the Fukushima Daiichi nuclear power plant
accident
Sota TANAKA, Tomoyuki TAKAHASHI, Keiko FUJIWARA, Sentaro TAKAHASHI

74

Part 4 Others
1 Case Study of Radiation Education in Compulsory Education for Fukushima's Revitalized Future
Hiroko MIYUKI
2 Derivation of apparent diffusion coefficient (Da) and distribution coefficient (KD) from evolution of
depth distribution of radiocaesium in soil contaminated by the Fukushima NPP accident

Haruo SATO

ⅶ

78

85

Part 1
Decontamination/radioactive waste

Cesium decontamination using a microbubbletreated aqueous solution of sodium metasilicate
Yoshikatsu Ueda*1), Yomei Tokuda2), Hiroshi Goto3)
1) Research Institute for Sustainable Humanosphere, Kyoto University, Gkasho, Uji, Kyoto, Japan, 611-0011
2) Institute for Chemical Research, Kyoto University, Gkasho, Uji, Kyoto, Japan, 611-0011
3) Kureha Trading Co. Ltd., 1-2-10, Horidome-sho, Nihonbashi, Chuo-ku, Tokyo, 103-0012*yueda@rish.kyoto-u.ac.jp

The remediation of materials contaminated with radioactive materials, such as 137Cs, is important. Here,
we report the effectiveness of an aqueous Sodium Metasilicate prepared via a microbubble Crushingprocess (SMC) for the removal of radioactive 137Cs from granule conglomerates and nonwoven cloth. A
137
Cs removal ratio of 78% was achieved for the nonwoven cloth sample, and multiple washings at low
SMC concentrations were effective. In addition, the volume of the waste solution could be reduced byneutralizing the SMC and using gelation to remove the radioactive material. The decontaminationachieved using this process was more efficient than that with sodium hydroxide, even for granuleconglomerates.
Keywords: Microbubble, Sodium metasilicate, 137Cs

1. Introduction
The accident at the Fukushima Dai-ichi nuclear
power plant in 2011 following the Great East Japan
Earthquake resulted in the dispersal of radioactive Cs
into the environment and the contamination of an
extensive area of soil. Various decontamination
methods have been developed and applied in
Fukushima Prefecture1-5), but the optimal methods forthe remediation of materials under specificcontamination conditions still need to be developed.
Radioactive Cs adsorbs on soil particles through ion
exchange with potassium6,7). Our research focused onusing aqueous sodium metasilicate as a novel detergent
and possible decontamination agent. We examined themechanism and principle underlying the change in thechemical reaction characteristics of aqueous sodium
metasilicate after microbubble and ultrasonic treatments.
Secause aqueous sodium metasilicate is not a surfactant,it has a low environmental load and does not exhibit
foaming characteristics. It can be used with hard, soft,and sea waters, and its cleaning activity make it a“peeling detergent”, which differentiates it from

Figure 1 Photographs of aqueous sodium metasilicate
irradiated by a green laser (Wavelength:532nm) after
storage for one-half year. The metasilicate wasdissolved in water (a) without crushing, and (b) withcrushing. The black object in the lower right corner isthe green laser. 1)

dissolving detergents, such as organic solvents. As apeeling detergent, aqueous sodium metasilicate issuitable for foaming, jet streaming, high pressure–ultrasonic wave, and spray cleaning. A microbubble
crushing process8,9) can also be used to suppress
precipitation during long-term storage10) (see Figure 1).
Coprecipitation can be used to decrease the volume1

of the waste solution produced because sodium
metasilicate forms a gel that traps Cs when neutralizedwith acid11). Coprecipitation followed by gel formation
can be used to separate the 137Cs gel from the soil,
yielding a decontaminated waste product.

wt%). To determine the effects of multiple washings,
samples were tested after 6 h of immersion before thesecond and third washes. After these immersion tests,
the samples were dried at 40 °C for 40 h until they were
free of moisture 3).
To reduce the volume of waste solution, hydrochloric
acid (HCl) was added to neutralize the detergent
solutions after washing, which resulted in gelation. The
gel and clear supernatant were then separated byfiltration, and the radiation intensity (counts per second,cps) of the gel and supernatant was measured. We
attempted to remove 137Cs from the SMC solutions byneutralization. We prepared three samples of 10- and100-wt% SMC solutions and then neutralized andfiltered them. Subsequently, we measured the radiation
intensity and compared the results of the two
remediation methods.

2. Experimental(a) Cleaning method

Depending on the individual diameters andbuoyancies, microbubbles may only remain in water forseveral minutes. However, they can persist in an
aqueous environment for longer times if an ultrasonictreatment is used to reduce their size 12). The ultrasonic
pretreatment of aqueous sodium metasilicate to form
SMC (Sodium Metasilicate prepared via a
microbubble Crushing process) and to reduce thebubble size does not decrease the eduction rate of
aqueous sodium metasilicate and offers the possibilityof sustained cleansing. In this experiment, we conducteda cleaning test in a standing solution so that we could
focus on the chemical cleansing effects resulting fromthe synergy between aqueous sodium metasilicate andmicrobubbles rather than on the physical cleansing
effects 1,2).
Granule conglomerates and nonwoven cloths werethe materials to be cleaned. The ~150-g granuleconglomerate samples were collected from soil in a hot
spot (∼500,000 Bq/kg) at the Fukushima Agricultural
Technology Centre. These pieces of nonwoven
polypropylene cloth were used in agricultural work at
farms exposed to the fallout from the nuclear accident inFukushima Prefecture. The cloths had an average
weight of 2.65 g, and the average amount of 137Cs they
contained exhibited approximately 1633 Bq/sample(616,226 Bq/kg) of radioactivity.
The granule conglomerate and nonwoven cloth
samples were immersed in 100 mL of solutions
containing a range of SMC concentrations for 20 h.
Twelve granule conglomerate samples were prepared.
These samples were divided into four groups of threesamples each. One group was washed in sodiumhydroxide, one was washed in normal sodium
metasilicate, and the remaining two were washed in
SMC solutions (10 and 100 wt%). The 28 cloth samples
were divided into four groups of seven samples each.
One group was washed in water, while the other threegroups were washed in SMC solutions (1, 10, and 100(b) Radiation measurement

The background radiation intensity of the nonwoven
cloth specimens was measured using the germanium
semiconductor detector at the Radioisotope ResearchCenter at Kyoto University. The main unit of thedetector is made of high purity germanium (GMX18200-S; EG&G Ortec), with a 102-cm3 germanium
crystal and a relative efficiency of 22.3% (efficiency
ratio of a 3" × 3" NaI (TI) (76 × 76 mm) crystal relative
to that of the 137Cs 662 keV gamma ray). The entrance
window is a 0.5-mm-thick beryllium plate, whichallows the detection of X-rays with energies of at least 3
keV, as well as high energy gamma rays. The energy
resolution was 0.54 keV for 55Fe 5.9-keV (Mn Kα) Xrays and 1.8 keV for 60Co 1.33 MeV gamma rays. A
special container (100 mL) was used to analyze thenonwoven cloth specimens. The removal ratio wasdefined as the ratio of the radiation intensities from thesample before and after immersion, as shown in thefollowing equation.
Removal ratio [%] =3. Results

𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 [𝑐𝑐𝑐𝑐𝑐𝑐]
× 100
𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵𝐵 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 [𝑐𝑐𝑐𝑐𝑐𝑐](a) Washing the granule conglomerate

The removal ratios of 137Cs from the granuleconglomerate using SMC (10 and 100 wt%), sodiumhydroxide, and aqueous sodium hydroxide (Figure 2)
show that, while the decontamination efficiency of2Removal ratio [%]break down organic materials via saponification due toits alkaline nature. We anticipate that we will be able toincrease the efficiency of this detergent using
microbubbles and ultrasonic treatments. Organic
components, such as sebum and oil, which arecontaminated with 137Cs are likely to be eluted from thenonwoven cloth because of the alkalinity of SMC. The
data in Table I also show that even when 1-wt% SMC isused, the removal ratio is 60% of that obtained with
100-wt% SMC after the first washing. This result
demonstrates that a low concentration of detergent canbe used for remediation.
In the case of multiple washings, the backgroundradiation intensity decreased considerably after the third
washing when a highly concentrated (10- or 100-wt%)
SMC solution was used. Therefore, a 1-wt% SMC
solution was used for further analyses. The removal
ratios after each wash with the 1-wt% solution, which
are listed in Table I, were 64% for the second wash and
71% for the third wash, indicating that even at aconcentration of 1 wt%, significant decontamination of
nonwoven cloth materials can be achieved after multiple
washings. Although only a slight decrease in theremoval ratios occurred compared with higher wt%
SMC solutions, we believe that using 1-wt% SMC is aneffective washing method, even for higher levels ofcontaminants because the need for further
decontamination of materials in the Fukushima
Prefecture still exists.

Figure 2 Average removal ratios of 137Cs from the granuleconglomerate samples using 10- and 100-wt% SMC, NaOH,
and sodium metasilicate.1)

SMC was low, it was still more than 10 times higher
than that obtained using sodium hydroxide at the same
pH. Furthermore, the higher efficiency of SMC
compared with sodium metasilicate without the
microbubble treatment confirms the effectiveness of
SMC. One characteristic of SMC is that theconcentration of dissolved oxygen does not increase
after aeration. Hence, a large number of adsorption pits
(sites) are likely present, similar to zeolites. Thus, the Csions present in water will be incorporated into thesilicate. The dissolution of the granule conglomerate by
the alkaline solutions also contributed to increasing thedecontamination efficiency.

(b) Washing the nonwoven cloth

The cleaning performance of SMC at various
concentrations is presented in Table I, which lists theaverage removal ratios for multiple washings with SMC
concentrations of 1, 10, and 100 wt% compared withpure water 2).
As expected, almost no 137Cs was removed bywashing with pure water, but significant
decontamination occurred as soon as SMC wasintroduced. Because the nonwoven cloth samples werepreviously used in agricultural fields, they also
contained traces of fertilizers and other organic
materials. As mentioned previously, sodium
metasilicate detergent is used for washing because it can(c) Remediation of 137Cs by neutralizing SMC

Methods to reduce the waste solution volume
obtained after using SMC were also investigated. We
prepared three samples each of 10- and 100-wt% SMC
waste solutions. The solutions were neutralized with
HCl, and the gels were separated from the filteredsolution. By measuring the radiation intensity and thennormalizing the readings, we were able to compare thegels and filtered solutions (Figure 3). 137Cs was captured
in the gel after coprecipitation 1,2). Hence, each tested
concentration of SMC can effectively capture Cs.

Table 1 137Cs removal ratios of using purified water and SMC for the nonwoven cloth samples
Washing

Pure water

1-wt% SMC

10-wt% SMC

100-wt% SMC

First

0

44.5

59.5

77.5

Second

34.5

27.5

51.4

Third

20.6

-

*Pure water was used for the first washing, whereas 10- and 100-wt% SMCs were used for the second washing.

3

100
90
80
70
60

Removal ratio [%]

50
40
30
20
10
0
10wt% SMC

10wt% SMC

10wt% SMC

100wt% SMC

100wt% SMC

100wt% SMC

filtrated water

filtration

Figure 3 Remediation of 137Cs by neutralizing SMC (10 wt% and 100 wt%).1)

However, the 100-wt% SMC solution exhibited a
behavior opposite that of the other solutions. This isbecause sodium metasilicate can leave its captured ionsin water. Substantial additional experimentation isneeded to determine the optimum conditions for
capturing Cs in SMC gels. We are currently
experimenting with using alcohol to neutralize the SMC
and remove 137Cs from waste solutions.

Acknowledgments

This work was financially supported by Kyoto
University, The Japan Association of National
Universities, Japan Association for Chemical
Innovation (JACI), ITOCHU Foundation, and theCollaborative Research Program of Institute for
Chemical Research, Kyoto University (No. 2013- 63).
We thank N. Nihei, S. Fujimura, T. Kobayashi, Y. Ono,
M. Tosaki, and T. Minami for helpful discussions andexperimental preparation. We appreciate the SMC
samples (JPAL) provided by Kureha Trading Co. Ltd.
The synchrotron radiation experiments were performedat the BL14B2 beamline of the SPring-8 facility withthe approval of the Japan Synchrotron Radiation
Research Institute (JASRI) (Proposal No. 2015A1662).

4. Conclusions

We have examined the cleaning performance of
SMC by comparing the radioactivity of waste solutions
before and after washing contaminated granuleconglomerates and nonwoven cloth samples. A study ofthe changes in the chemical characteristics of SMC wasalso undertaken. 137Cs particulates attached to a
nonwoven cloth sample were removed effectively by
SMC cleaning. After cleaning, the remaining dissolved
aqueous sodium metasilicate from the SMC had a better
treatment capacity (after neutralization) than standard
aqueous solutions. Thus, the use of SMC should
contribute significantly to the decontamination work
currently being undertaken in urban and rural areas
where decontamination cannot be performed by using
water alone. We are currently attempting to measure thechemical structure of SMC using SPring-8. We willreport the results of this new study in the near future.

References
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2)
3)

4

Y. Ueda, Y. Tokuda, H. Goro, Radiological
Issues for Fukushima’s Revitalized Future,
Fukushima, Springer, in print.

Y. Ueda, Y. Tokuda, H. Goto, T. Kobayashi, and
Y. Ono, ECS Trans., 58(19), 35 (2014).
Y. Ueda, Y. Tokuda, H. Goto, T. Kobayashi, and
Y. Ono, J. Soc. Remed. Radioact. Contam.
Environ., 1, 191 ( 2013).

4) Y. Ueda, Y. Tokuda, S. Fujimura, N. Nihei,
and T. Oka, ECS Trans., 50(22), 1, (2013).
5) Y. Ueda, Y. Tokuda, S. Fujimura, N. Nihei,
and T. Oka, Water Sci. Technol., 67, 996(2013).
6) I. Raskin and B. D. Ensley, Editors,
Phytoremediation of Toxic Metals: Using
Plants to Clean Up the Environment, John
Wiley & Sons, New York (2000).
7) N. Willey, Editor, Phytoremediation: Methods
and Reviews, Humana Press, Totowa (2007).
8) A. Agarwal, W. J. Ng, and Y. Liu,
Chemosphere, 84, 1175 (2011).
9) E. Stride, Philos. Trans. R. Soc. A, 366, 2103
(2008).
10) J. Suwabe, Japanese Patent (Kokai), 20101451 (2010).
11) R. C. Merrill and R. W. Spencer, J. Phys.
Colloid Chem., 54, 806 (1950).
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Ohnari, S. Himuro, and H. Shakutsui, J. Phys.
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5Decontamination system of radiocesium
contaminated water.
Kahori YOKOTA 1) , Shio ARAI1) , Hideki OGAWA 1, 2) ,Ritsuko NAKAMURA 1) * , Hirohisa YOSHIDA 1)
1) Graduate School of Environmental Science, Tokyo Metropolitan University, 1-1, Minami-Osawa, Hachiouji, Tokyo
192-0397 JAPAN
2) Fukushima Forestry Reactor Center, 1, Nishisimasaka, Asaka-machi, Koriyama, Fukushima 963-0112 JAPAN* ritsuk_n@tmu.ac.jp
The high performance filter absorbed radiocesium ( 134 Cs and 137 Cs) selectively and efficiently
form low contaminated water was developed. Two types of filter with the hydrophobic and thehydrophilic surface wool fibers were used as the support substrate for Prussian Blue (PB). Two
PB supported wool fibers (hydrophobic, PB-O and hydrophilic, PB-T) were used for theabsorption filter for 134 Cs and 137 Cs. Three types of contaminated water (the combustion gas
washed water: 600 L, 2 Bq/L, pH6, the woody sludge contained water: 700 L, 1.3 Bq/L, pH7 andthe combustion ash extracted water: 1 L, 120 Bq/L, pH10) were used for the absorption
experiments by PB-O and PB-T filters. The efficient absorption of 134 Cs and 137 Cs in thecontaminated water was proceeded to decrease below 0.2 Bq/L by the filtration with 2 hrs and2 min for large and small volume water, respectively. The decreased 134 Cs and 137 Cs in thecontaminated water were absorbed in PB-O and PB-T filters. PB supported wool filters acted
as the high performance filter for 134 Cs and 137 Cs in various conditioned water with different
pH and dispersed materials.
Key Words: Water soluble radiocesium, Wool fiber filter dyed with Prussian Blue,
Decontamination of water,
polypropylene containers collected in each towns and1. Introduction

villages. The reduction of volume of radioactive waste by
Four years has passed after the Fukushima Daiichi

the combustion is planned. Thermal and biological

Nuclear Power Plant (FDNP) accident, radioactive cesium,

degradation of organic wastes induce the water soluble

radiocesium (134

Cs and137Cs), major components ofform of 134Cs and 137Cs. The absorption system for ionicreleased radionuclear, are still observed widely in East

134

Japan, including Tokyo [1]. The most of 134Cs and 137Cs

decontaminated environment.

Cs and 137Cs is required to proceed the recovery ofPrussian Blue (PB) has high ability of cesium absorber.

absorbed in clay materials on the ground and barks of
Cs

Various types of 134Cs and 137Cs absorber based on PB

from soils to plants though plant root, bark and leaves was

supported on substrate have developed after FDNP

caused by ionic form oftrees in the forest [2]. The transportation of134

Cs and137

Cs. The leak ofaccident, however the acceptable absorber was few [4-6].

contaminated water induced by mainly rainfall occurred

We have developed PB dyed wool fibers, the synthesis offrequently in FDNP. The half of

Cs in thePB was carried out in the high energy surface layer on

contaminated water in FDNP was water soluble form [3],wool fibers [8, 9]. The obtained PB crystal with 10 – 20

which influenced easily the biological system including

nm crystallite size dispersed on wool fiber surface. In thisfishes and plants. The decontamination proceeded instudy, the 134Cs and 137Cs absorption ability of two types

Fukushima was mainly the removal of soil and plants,of PB dyed wool fibers were investigated by thethese radioactive waste packed in rubber coateddemonstration tests for the contaminated swage water.

134

Cs and134

137

Cs and137

6

attributed of each water tank. 5 g of PB-O or PB-T fibers

2. Experimental

putting in poly(ethyleneterephthalate) small mesh bag
were setting on PB-T or PB-O filters as necessary to(1) Samples
The synthesis of Prussian Blue (PB) was carried out

evaluate the time dependence of absorption behaviors.

two step reactions in the high energy surface layer (about
100 nm thickness) of wool fibers. Two types of wool
fibers with hydrophilic and hydrophobic surface were
immersed in the aqueous solution of ferrocyanide(Na4[Fe(CN)6]･10H2O) under the acidic condition (pH3.5) for 5 hrs at 30 oC [10]. After wiped off the excess
ferrocyanide solution on fiber surface, the ferrocyanide
doped wool fibers immersed in aqueous solution offerrous sulfate and ammonium sulfate and heated up to
70 oC.
The PB crystallite size obtained by this method,
evaluated by the Scherrer's equation using a wide angle
X-ray diffraction profile, was 10 – 20 nm corresponding
to the surface hydrophilicity.

PB dyed fibers were

Fig.1 Out view of water contamination system madeof two water tanks (black tanks) and control system.

washed by fresh water repeatedly, then dried at room
temperature. Two types of PB supported wool fibers,hydrophilic: PB-O and hydrophilic: PB-T, were obtained.
The color fastness tests were performed by the method

To water pomp

according to JIS L 0844, JIS L 0849, the grade 4 and 5
for the washing fastness and the rubbing fastness,

Shower headrespectively. These dates indicated that PB supported
wool fibers had the same color fastness of textiles on the

PB supported wool filtersmarket. The extraction test of cyanogen from PB

Bag filter and mesh cage

supported wool fibers was performed by the method
according to JIS K 0102, the extraction amount of
cyanogen was 0.1～0.2 mg/L, which was lower than theregulation value of the Water Pollution Prevention Act

Stainless water tank

(1 mg/L) and Fukushima Prefecture regulation low of theFig.2 Schematic view of filtration system

Water Pollution (0.5 mg/L). These results indicated that
PB scarcely seceded from wool fibers.

One water tank (the front side in Fig.1) was used for the
first step filtration to eliminate the suspended subjects(2) Water decontamination system
The developed water decontamination system was(wood powders, suspended soils and oily emulsions etc.)
in contaminated water by rough bag filters. The othershown in Fig. 1 (outside) and Fig 2 (schematic drawing ofwater tank used to decontaminate 134Cs and 137Cs from theabsorption filter system). The system consisted of two

contaminated water after the first step filtration. The inner

water tanks made of stainless steel (volume: 1,100 L,pressure and flow rate in each laying pipes and the water

diameter: 1 m, height: 1.5 m), two water pumps and thelevel in tanks were electrically monitored and the water

control system as shown in Fig. 1. In the stainless steel

flow systems were controlled.

water tank, the stainless steel mesh cages (diameter: 300

The contaminated water in water tank was pumped up

mm, height: 500 mm) were set on the frame, the water bag

by water pomp (Koshin Co. Ltd., Ponster PSK-532190)

filter made of polyamid (mesh size: 2 µm, size: 250 mmφx 400 mm) contained PB-O and PB-T filters (800 – 900

and poured on PB supported wool filters homogeneously
throughg) was put in each stainless mesh cage as shown in Fig. 2.

showerhead

decontamination of

One water pomp and four stainless steel mesh cages were

7

134

as

shown

Cs and137

inFig.2.

The

Cs in water wasperformed by the circulated flow for the fixed period

Alumina oxide and the suspended small woody powder

through PB supported filter.

was filtered by the first filtration, and the sludge treatedwater (700 L, 1.3 Bq/L, pH7) was decontaminated by the(3) Demonstration tests
The demonstration tests for decontamination of watersecond filtration using 800 g of PB-O filter for 2 hrs. The

were performed using three types of decontaminatedfiltration, 134Cs and 137Cs concentration decreased below

water, such as the sludge treated water (700 L, 1.3 Bq/L,

0.2 Bq/L, and the decreased 134Cs and 137Cs absorbed onpH7), the combustion gas washed water (600 L, 2 Bq/L,

PB-O filter.

decontamination result was shown in Fig.3. After 2 hrs

pH6) and the combustion ash extracted water (1 L, 120
Bq/L, pH10).
Radioactivity of samples were measured by theRadioactivity / Bq

Germanium semiconductor detector (SEG-EMS: SEIKO
EG&G Inc., Japan) with 100 ml of U8 container at
10,000 - 40,000 sec of accumulation time to obtain 1 - 2
Bq/kg of the lower limit for the solid samples and with
2 L of marinelli vessel at 10,000 sec to obtain 0.2 Bq/Lof the lower limit for the liquid samples. The radiation
decay was compensated at March 1, 2012.
3. Results

1000
900
800
700
600
500
400
300
200
100
0

Water
contamination

Filtercontamination

N.D

BeforeAfter

PB filter

Fig.3 Decontamination results of sludge treatedwater (700 L, 1.3 Bq/L, pH7) for 2 hrs filtration.

(1) Sludge treated water (pH7)
About 50 % of bed-logs used for mushroom(2) Combustion gas washed water (pH6)
The decontamination tests of forest wastes (Pinecultivation in Japan was supplied from Fukushima
prefecture before FDNP accident. The inoculated bed-

needles: 10,000 - 30,000 Bq/kg, Cedar bark: 10,000 –logs putting in forest before the accident was

15,000 Bq/kg collected in Forestry Research Center incontaminated heterogeneously on upper side surface ofApril 2011) were carried out at Fukushima Forestry

bed-logs, the harvested mushrooms contained higher

Research Center in February and March 2012. The

amount of 134Cs and 137Cs than the regulation value (100combustion gas of forestry wastes contained carbonic

Bq/kg). The bark and fallen leaves of broad leaved

acid, the gas washed water showed slight acidity. The

deciduous trees in November 2011 contained highcombustion gas was washed by water jet, theamount of 134Cs and 137Cs. Although the 134Cs and 137Cs

contaminated water contained oily suspended carbon

concentration of fallen leaves in November 2012

particles.

decreased, the contamination of bark was in the higher

After dipping up the suspended carbon particles fromlevel. The decontamination of bark is necessary to use

the combustion gas washed water, the contaminatedbroad leaved deciduous trees, such as Konara andwater (600 L, 2 Bq/L, pH6) was filtrated by 800 g of PB-

Mizunara for the mushroom cultivation.

O (R) filter for 2 hrs. The decontamination results wereWe participated the decontamination trials for roadshown in Fig.4. After the filtration, the 134Cs and 137Cs

and rubbles [11, 12] by the wet blasting in 2012. The wet

concentration in water decreased below 0.2 Bq/L. The

blasting is the method to polish metal surface by the highamount of 134Cs and 137Cs in PB-O filter was slightly

pressure water jet containing grinding preparations suchsmaller than the decontaminated amount of 134Cs andas alumina oxide particles. August 2012, we applied the137

wet blasting to eliminate 134Cs and 137Cs form barks of

Cs. During this experiment, 5 g of PB-O and PB-T

filters were put on 800 g of PB-O (R) filter to evaluate thebroad leaved deciduous trees, and obtained successive

absorption ability of each filter. The decontamination

results [13]. 80 % of 134Cs and 137Cs in bark was

ability of PB-T filter was three times higher than PB-O

eliminated by polishing 2 mm thickness of bark surface.

filter, due to the larger contact surface area of hydrophilic

The sludge treated water containing alumina oxide

PB-T filter.

particles was also decontaminated by PB-O filter system.

8

Radioactivity / Bq

12000

decontamination ability than hydrophilic PB-O. Under
11082

the same filtration condition, the decontamination ratio

10173

10000

of PB-O and PB-T were 30 % and 90 %, respectively.

8000

Not only the hydrophilicity of wool fiber surface but also

6000

the PB crystallite size and its distribution on fiber

4000

surfaces affected the decontamination ability of PB

2000

N.D

0

137

36

supported wool filters.
4. Conclusions
Three types of contaminated water (below 120 Bq/L)

Fig.4 Decontamination results of combustion gas

with different hydrogen ion concentration (pH) andwashed water (600 L, 2 Bq/L, pH6) for 2 hrs

various suspended substances were decontaminated byfiltration.

two

As mentioned above, the mass balance of 134Cs and
137

of

PB

supportedwool

filters.

The

below 0.2 Bq/L by simple filtration. The decreased 134Cs

Cs collided before and after the filtration. The oily

and 137Cs was trapped on PB-O and PB-T filters. Thissuspended carbon adhered on the surface of PB-O (R)radiocesium absorption filter will contribute to thefilter and bag filter. The suspended carbon dipped up fromdecontaminate activity in Fukushima prefecture.

the contaminated water contained 313,650 Bq/kg-DW of
134

types

decontamination proceeded selectively and efficiently

Cs and 137Cs. The difference 134Cs and 137Cs amount

before and after the filtration was caused by the oily

References
1) H. Yoshida, “Pollution analysis of soil and plants bynuclear power plant accident”, chemicalengineering, 250 (2012)2) H. Ogawa, etc., “The early stage pollution ofJapanesecedar(Cryptomeria
japonica)byradioactive nuclear from the accident of Tokyo
Electric Power Company Fukushima Dai-ichi
nuclear power plant” report of research in Fukushima
Prefecture3) Website of the TEPCO, “Survey on K drainage andfuturemeasures”(http://www.tepco.co.jp/nu/fukushimanp/handouts/2015/images/handouts_150325_04j.pdf, accessed 28 July. 2015)4) K. Saito, “Applications of adsorptive fibers fortreatment of water contaminated with radioactive
substances of Fukushima Daiichi Nuclear Power
Plant, prepared by radiation-induced graftpolymerization”, The Society of Fiber Science andTechnology Japan, June 10-12, 2D08
5) D. Parajulu, A. Kitajima, etc., “Prussian Blue
Nanoparticles for the Enrichment of Radioactive
Cesium in Solutions”, WM2013 Conference,
February 24-28, 2013, Phoenix, Arizona USA,
13275
6) K. Minami, T. Kawamoto, etc., “Processing
methods and system of the radioactive substance”,
unexamined patent application 2014-0666477) T. Shiono, K. Fukunishi, etc., “Radiocesium
adsorption resistant fabric”, unexamined patentapplication 2013-61220
8) Patent application 2014-0023
9) K. Yokota, etc., “Prussian blue dyed wool and its

suspended carbon adhered on bag filter.
(3) Combustion ash extracted water (pH10)
The combustion ash from forestry wastes consisted ofsolid solution with calcium oxide containing various
elements such as boron, silica, copper, magnesium andphosphor. 10 g of combustion ash was suspended andstirred in water to extract 134Cs and 137Cs overnight. The
combustion ash extracted water (1 L, 120 Bq/L, pH10)
was decontaminated by 5 g of PB-O and PB-T filters for
2 mins filtration. The decontamination results were shownin Fig. 5.
As described in the decontamination of combustion
gas washed water, hydrophilic PB-T showed better
140
Radioactivity / Bq

120
100
80

Water
contamination

Water
contamination

60

Filtercontamination

40
20
0

Before

After

PB-O

PB filter

BeforeAfter

PB filter

PB-T

Fig.4 Decontamination results of combustion ash
extracted water (1 L, 118 - 124 Bq/L, pH10) for 2
mins filtration.

9

abilityforradiocesium”,
decontamination
International Symposium on Fiber Science andTechnology 2014, September 28 to October 1, PG301
10) Office for Administrative Support for Affected
People by Nuclear Disaster, “2011 fiscal year,
summary of result, Decontamination technology
demonstration
test
buisiness”,(http://josen.env.go.jp/material/link/pdf/20120501_
02.pdf, accessed 28 July. 2015)11) S. Matsubara, etc., “Demonstration of wet blasting
decontamination technology”, Decommissioning
technical report Environmental recovery technology
development Special issue, 12 (2013)12) K. Suzuki, etc., “Decontamination of Shiitake logs
by wet blast”, The 63th Annual Meeting of the Japan
Wood Research Society, Morioka, 27-29 March
2013, p82,

10

Application of mass spectrometry for analysis of cesium
and strontium in environmental samples obtained in
Fukushima prefecture
Yuji SHIBAHARA*1, Takumi KUBOTA1, Satoshi FUKUTANI1, Toshiyuki FUJII1,
Koichi TAKAMIYA1, Tomoko OHTA2, Tomoyuki SHIBATA3, Masako YOSHIKAWA3,
Mitsuyuki KONNO4, Satoshi MIZUNO4, Hajimu YAMANA1
1 Kyoto University Research Reactor Institute2 Hokkaido University
3 Kyoto University Institute for Geothermal Sciences
4 Nuclear Power Safety Division, Fukushima Prefectural Government* y-shibahara@rri.kyoto-u.ac.jp
For the assessment of Fukushima Dai-ichi Nuclear Power Plant accident, the applicability of the thermal
ionization mass spectrometry (TIMS) which is a type of mass spectrometry was studied. This study was
focused on the analysis of the isotopic ratios of cesium and strontium, among the fission products, nuclear
fuels and materials released on this accident. The amount of radionuclide per unit weight of theenvironmental samples would be infinitesimal, because of the wide distribution of radionuclide inenvironment released on the accident. For the study of the recovery/analysis method of cesium and strontium,
at first, the radioactive cesium and strontium were generated by the irradiation of natural uranium at Kyoto
University Research Reactor (KUR). After this study, the applicability of this method to the environmental
samples obtained in Fukushima prefecture was verified.
Keywords: accident of Fukushima Dai-ichi Nuclear Power Plant, strontium cesium chromatography, mass
spectrometry, isotopic ratio
The purpose of the present study is to study theapplicability of the mass spectrometry for the analysis of
the radionuclides released at the accident of FDNPP. For
the study of the recovery/analysis methods of Cs and Sr,
at first, the radioactive Cs and Sr were generated by theirradiation of natural uranium at KUR. After this study,
the applicability of these methods to the environmental
samples obtained in Fukushima Prefecture was verified.

1. Introduction
For the evaluation of the external and internal
exposures and to analyze the source of radioactive
nuclides released at the accident of Fukushima Dai-ichi
Nuclear Power Plant (FDNPP), our group has analyzed
Cs, Sr, U and Pu by the measurement of the isotopic ratio.
In general, the γ-ray measurement have been used forthe analysis of radioactive Cs of 134Cs (T1/2 = 2.06 y) and137
Cs (T1/2 = 30.2 y). In addition to 134Cs and 137Cs, 135Cs(T1/2 = 2.3×106 y) is also generated during the operationof reactor. This suggests that the analysis of three isotopesof 134Cs, 135Cs and 137Cs would bring the useful
information for the more detail analysis of radioactive Cs
such as the source of Cs1). Because of the half-life of
135
Cs, however, the analysis of 135Cs is difficult by theradiation measurement. Though the β-ray measurement
have been generally used for the analysis of 90Sr (T1/2 =28.9 y), this method also has the issues such as thedemand of long time measurement and the low energy
resolution.
The mass spectrometry provides the isotopic
compositions of elements, and has been used for the
analysis of radioactive nuclides and actinides having thelong half-life and showing the α/β-emitter property.
However, there is little report relevant to the analysis of
the accident of FDNPP by the mass spectrometry.

2. Experimental(1) Irradiation of natural U at KUR
After irradiation for 3 hours at the Kyoto University
Research Reactor with the neutron flux 5.5×1012 n/s cm2(2 days later), 10 mg of natural U was dissolved in conc.
HNO3 and evaporated to dryness. From the calculation
with ORIGEN-II code 2), the amounts of the major
radionuclide of Cs and Sr were estimated as 7.4×10-11 g(137Cs) and 4.5×10-11 g (90Sr), respectively. The residue
was dissolved in 8M HNO3/0.3 % H2O2 for the separationof the TRU elements such as U and Pu by the extraction
chromatography with UTEVATM-resin3).
After the extraction of U and Pu, Sr was recovered byusing SR-resin5). And then, Cs was recovered by using
ammonium phosphomolybdate (AMP)1) respectively. The
solutions containing the recovered Cs and Sr were
evaporated and dissolved in 1 M HNO3 for the preparationof the sample solution for mass spectrometry (20 μL for11

environmental samples obtained in Fukushima
prefecture
The plant samples (moss, bark, grass etc) were obtained
from the four sampling points in Fukushima prefecture(Fig,1) at Nov. 2012 and May 2013.
About 2.5 g of samples which were washed with purewater and dried was incinerated with a ring furnace at 873
K, and dissolved in 20 mL of concentrated HNO3 at 403
K and evaporated to dryness. After the dissolving of theresidue in 20 mL of 8 M HNO3, Cs and Sr were recoveredby the same manner above mentioned. Before the analysis
of Cs isotope composition, the activity of radioactive Cs
was measured by γ-ray measurement. For the analysis ofSr, the determination of 88Sr by ICP-QMS and that of 90Srby the Cherenkov counting5) was carried out. For the mass
spectrometry of Cs and Sr, 5000 Bq/mL for 137Cs in 1 M
HNO3 and 50 ppm of 88Sr in 1 M HNO3 were prepared.
As above mentioned, the mass spectra of radioactive Cs
and Sr were obtained with a SEM, while that of stable Csand Sr were obtained with Faraday cup detector, since theamounts of stable nuclide were much larger than those ofradionuclide.

0.25μSv/h

2.5μSv/h

0.6μSv/h

6.0μSv/h

ITT

12μSv/h

FTB35

FTB
1F
OKM

Fig. 1 Sampling area and air radiation dose rate.
Air radiation rose rate was made using published datafrom MEXT 4)．
Cs, and 10 μL for Sr, respectively).
Isotopic compositions of Cs and Sr were measured witha TIMS (Triton-T1, Thermo Fisher Scientific). A 1 μL
aliquot of each solution was loaded onto a rhenium
filament with a TaO activator. The mass spectra ofradioactive Cs and Sr were obtained with a secondary
electron multiplier detector (SEM) because of the small
total amounts of radionuclide loaded onto the filament (ca.
3.7×10-12 g for 137Cs, and ca. 4.5×10-12 g for 90Sr,
respectively). For Sr, the standard reference material,
SRM987, was also used for the analysis of stable Sr.
(2)Analysis

of

Cs

and

Sr

recovered

3. Results and Discussion(1) Analysis of Cs and Sr from irradiated U
Mass spectra of Cs and Sr recovered from irradiated U
are shown in Fig. 2.
The mass spectrum of Cs (Fig.2(a)) shows three peaksof 135Cs, 136Cs(T1/2 = 13.2 d) and 137Cs: 134Cs was notobserved since the generated amount in this irradiation
condition was very low. According to the amountestimated with ORIGEN-II code as above mentioned andthe loading amount onto the filament, ca. 3.7×10-12 g of137
Cs would be used for the observation of this mass
spectrum: the isotopic ratio of 135Cs/137Cs was obtained as
0.9103±0.0008 (±2σ).
The mass spectra of Sr (Fig.2(b)) shows three peaks of89
Sr (T1/2=50.5d), 90Sr and 91Sr (T1/2= 9.5h) in the case of
the measurement of 2.6 days later. The peak of eachisotope was declined with the time, the intensity of 91Sr
and 89Sr became lower than the detection limit at themeasurement of 31 and 574 days later. Same as theanalysis of Cs, ca. 4.5×10-12 g of 90Sr was used for theobservation of these mass spectra: 89Sr/90Sr =0.7949±0.0003 (±2σ) was obtained at the measurement of
2.6 days later.
In both case of Cs and Sr, the loading amount of the
major nuclide of several pico-gram brought the enoughpeak intensity. The minor nuclides of 136Cs and 91Sr in
Fig.2(a) and (b) were estimated at 5.5×10-14 g and
4.0×10-14 g, meaning that several femto-gram would be
detectable.

fromIntensity (arb)

(a)

x10

x10
134

135

136

137

138

Atomic mass [u]Intensity (arb)x10
2.6 days laterx100

30.6 days later(b)84(2) Analysis of Cs and Sr from environmental
sampleIn the analysis of Cs recovered from environmental
sample obtained in four sampling area as shown in Fig. 1,
the peak of 134Cs, which was not observed in the analysis
of Cs recovered from irradiated U (Fig.2(a)), wasobserved1, 6)(Table 1). The activity ratios calculated fromthe isotopic ratio of 134Cs/137Cs were ranged from 1.000 to

573.9 days later
85

86

87

88

89

90

91

Atomic mass [u]Fig. 2 Mass spectra of Cs and Sr6). (a)Cs, (b)Sr.
Mass spectra of stable Sr were obtained frommeasurement of SRM987.

121.055(corrected on 11 Mar 2011). This means that theorigin of 134Cs and 137Cs observed in this study is theaccident of FDNPP, since this range shows the agreementwith the estimation results of the generated amount in
FDNPP with ORIGEN-II code7). The isotopic ratio of135
Cs/137Cs, on the other hand, was ranged from 0.359 to
0.367 (corrected on 11 Mar 2011). This range also shows
the agreement with the estimation results with
ORIGEN-II code, and is lower than that of global fallout(~0.5 for Chernobyl accident, and ~2.7 for nuclear
weapon testing3), corrected to Mar. 11, 2011), meaningthat the isotopic ratio of 135Cs/137Cs will also be useful forthe analysis of Cs: especially, this isotopic ratio would be
useful in the case that the amount of 134Cs is underdetection limit (such as after the disappearance of 134Cs
and/or very low activity of Cs).

2) Shibahara Y., Kubota T., Fujii T., Fukutani S., Ohta T.,
Takamiya K., Okumura R., Mizuno S., Yamana H.
(2015) J. Radioanal. Nucl. Chem., 303: 1421-1424.
3) Ludwig S. B., Renier J. P. Standard- and ExtendedBurnup PWR and BWR Reactor Models for the
ORIGEN2 Computer Code: Oak Ridge National
Laboratory; 1989, ORNL/TM-11018.
4) http://www.mext.go.jp/b_menu/shingi/chousa/
gijyutu/017/shiryo/__icsFiles/afieldfile/2011/09/02/131
0688_1.pdf (accessed on Dec. 16, 2013).
5) Kubota T., Shibahara Y., Fujii T., Fukutani S., Ohta T.,
Takamiya K., Okumura R., Mizuno S., Yamana H.
(2015) J. Radioanal. Nucl. Chem. 303: 39-46.
6) Shibahara Y., Kubota T., Fukutani S., Fujii T.,
Takamiya K., Ohta T., Shibata T., Yoshiwaka M.,
Konno M., Mizuno S., Yamana H., Application of mass
spectrometry for analysis of cesium and strontium inenvironmental samples obtained in Fukushima
prefecture-Analysis of Cesium Isotope Compositions inEnvironmental Samples by Thermal Ionization Mass
Spectrometry-2, Radiological Issues for Fukushima's
Revitalized Future, Springer, in press.
7) Nishihara K., Iwamoto H., Suyama K. (2012) JAEAData/Code 2012-018 [in Japanese]

Table 1 Results of isotopic analysis of Cs
134
135
Sample ID
Cs/137Cs**
Cs/137Cs***
OKM01*
1.040(3)0.3669(2)OKM02
1.037(3)0.3655(3)FTB*
1.020(7)0.3663(5)FTBR35*1.000(12)0.3586(8)ITT*1.055(5)0.3662(6)*: Data were reproduced from ref 1)**: Activity ratio (corrected on 11 Mar 2011)***: Atomic ratio (corrected on 11 Mar 2011)
In the analysis of Sr recovered from environmental
sample, the variation of the isotopic ratio of 87Sr/86Sr wasobserved, while 90Sr was under detection limit6). If thisvariation of the isotopic ratio of 87Sr/86Sr was brought by
the accident of FDNPP, several 10 MBq/g of 90Sr must be
contained in these samples. Our Cherenkov counting,however, showed that the amount of 90Sr was less than
1Bq/g4), suggesting that this might be caused by theisotopic fractionations in the biological processes alongwith the contamination of sample by the soil6).
4. Conclusions
For the study of the applicability of the mass
spectrometry of Cs and Sr released at the accident of
FDNPP, Cs and Sr were recovered from the natural U
irradiated at KUR. The recovery/analysis method
discussed in this study showed that the several 10-14 g of
nuclide would be detectable.
By the same method, Cs and Sr were recovered fromthe plant samples obtained from Fukushima prefecture.
Radioactive Sr was under the detection limit, while
radioactive Cs from FDNPP was detected. Since 135Cs
was also detected by TIMS, by using the activity ratio of134
Cs/137Cs and the isotopic ratio of 135Cs/137Cs, the sourceof radioactive Cs would be evaluated apart from that ofglobal fallout after 134Cs became below the detection
limit.
References
1) Shibahara Y., Kubota T., Fujii T., Fukutani S., Ohta T.,
Takamiya K., Okumura R., Mizuno S., Yamana H.
(2014) J. Nucl. Sci. Technol. 51: 575-579.

13

Safe decontamination system for combustionof forestry wastes
Hirohisa YOSHIDA 1) * , Hideki OGAWA 1), 2) , Kahori YOKOTA 1) ,Shigemitsu IGAI1) , Shio ARAI1) , Ritsuko NAKAMURA 1)
1) Graduate School of Environmental Science, Tokyo Metropolitan University, 1-1, Minami-Osawa, Hachiouji, Tokyo
192-0397 JAPAN
2) Fukushima Forestry Reactor Center, 1, Nishisimasaka, Asaka-machi, Koriyama, Fukushima 963-0112 JAPAN* yoshida-hirohisa@tmu.ac.jp
Thermal decomposition behavior of forestry wasters, cedar bark, leaves, wood and pain leaves
were observe by TG/DTA-FTIR method. The mass balance including radioactive cesium(radiocesium hereafter) during the combustion of forestry wastes was evaluated by thelaboratory scale combustion test. About 30 – 35 % of radiocesium in cedar bark transferred in
combustion gas at the combustion above 500 o C. By washing the combustion gas with water,
98 % of radiocesium vaporized during the combustion was retrieved. A pilot scaledecontamination system for the combustion of forestry wastes was developed and was tested.
The decontamination system consisted of three parts, a combustion gas washing system, acombustion ash enclosing system and a contaminated water filtration system. Using our system,
95 % of radiocesium was retrieved.
Key Words: Forestry wastes, Combustion, Smoke extraction, Radiocesium,
forestry waste by the periodic thinning each year,

1. Introduction

necessitating a proper method for the volume reduction of
the waste.

Before the Fukushima Daiichi Nuclear Power Plant(FDNP) accident, the biomass power generation has been

Most of lumbermill has a small incinerator to burn theone of the most effective utilization of forestry wastes,

forestry wastes such as bark and wood chips. However,such as thinned wood, bark, leaves and twinges. Twothese incinerators have not been used after the FDNP

major economic activities in Fukushima prefecture, i.e.,

accident, since the emission constraint act prohibits small

agriculture and forestry work, have been damaged

incinerators equipped with poor emission gas treatment

seriously by the FDNP accident. Four years after thefacilities to burn the forestry waste contaminated with

FDNP accident, agriculture in Fukushima has come backradiocesium.

the level close to that before the accident, but the forestry

We have designed a decontamination system forwork is still in a confused situation 1-4). Fukushimacombustion of forestry waste using small incinerators 5).

prefecture started the forest maintenance by the periodic

In this study, the outline of the combustion gas washingthinning on 2013. The regular periodic thinning lumberedsystem, the combustion results in the laboratory and the

10 % of standing trees in the forest. For 1000 ha of forest,

pilot scale tests were discussed.

about 150,000 m3 of standing tree is lumbered, and 30,000
m3 of leaves and twigs are left in the forest, and 15,000 m3

2. Experimentsof barks are reeved at lumbermills. Before the FDNP
accident, barks and leaves have been reused for
agriculture as a compost. After the FDNP accident, such(1) Samples
Samples used in this study were radiocesium

reusedifficult.

contaminated Japanese cedar bark, cedar leaves, cedar

Nevertheless, 3.4 x 10 m of barks has been produced as

sapwood, cedar heartwood and pine needles collected atofforestry

wastes9hasbecome3

14

Fukushima Forestry Research Center in autumn 2011.
Mass loss / %After drying at 60 oC for three days, samples were
subjected to combustion. The water content of samples
evaluated by the 60 C drying was 28.6, 56.8, 61.8, 54.3
oand 10% for Cedar bark, Cedar leaves, Cedar sapwood,600

wet mass.
(2) Measurements
Radioactivity of solid samples in 100 ml of U8

DTA

400

container, and water suspended samples in 2 L ofmarinelli vessel were measured by a germanium
semiconductor detector (SEG-EMS: SEIKO EG&G Inc.,

200

0Japan) at 10,000 - 40,000 sec of accumulation time toobtain 1 - 2 Bq/kg of the detection limit for solid samples

Tem / oC

heartwood and pine needle, respectively, based on the

800

5

10

15

20

Time / s25

Fig. 1 TG/DTA results of cedar bark under air (blue)

and at 10,000 sec to obtain 0.2 Bq/L of the detection

and dry N2 atmosphere (red) conditions at 20 K/min

limit for liquid samples. The radioactive decay wascompensated at March 1, 2012.
Thermogravimetry measurements of forestry wastes

3. Results and Discussions(Japanese cedar sapwood chip, cedar bark, cedar leaves
and pine needles) were carried out by TG/DTA 7200

(1) Laboratory scale tests
TG/DTA results of Cedar bark under air (perfect(Hitachi High-Tech Science Co., Japan) under air andnitrogen gas flow. About 3 mg of samples were heatedcombustion condition) and nitrogen gas (imperfectat 20 K/min from room temperature to 900 oC. The

combustion condition) atmospheres are shown in Fig.1.

exhaust gas analysis was carried out by Fourier

The mass loss occurred in three temperature ranges, below

transform Infrared spectroscopy, FTIR (JASCO FTIR-

200 oC, 200 – 400 oC and above 400 oC for both conditions.

650, MCT detector) connected with TG/DTA, IR

These mass decreases were caused by water evaporation,

spectrum of exhaust gas was collected each 4 oC.

thermal decomposition of cellulose, hemicellulose andMorphological observation and elemental analysis ofthermal decomposition of lignin, respectively by the

combustion ash were carried out by a transition electron

exhaust gas analysis. Under air condition, the exothermic

microscope (JEOL JEM-3200 FS) equipped with theenergy dispersed elemental analyzer.

peaks were observed as two steps corresponding to(3) Combustion tests
Laboratory scale combustion tests of radiocesium

hemicellulose in 200 – 400 C and that of lignin above 400

thermalbehaviorsofcellulose

and

o

o

contaminated Japanese cedar bark (10g, 20,000 Bq/kg)

C from the exhaust gas analysis. The exothermic heatobtained by thermal decomposition of woody samples

were carried out using the combustion instrument madewere evaluated by the exothermic enthalpy and the massof glass. The combustion gas were washed by 2 L ofloss. Thermal decomposition enthalpy were 12.2 kJ/g fortrapped water. Pilot scale tests of forest waste were

Cedar bark, 11.6 kJ/g for Cedar sapwood, 10.6 kJ/g for

carried out at Fukushima Forestry Research Center inCedar leaves and6.9 kJ/g for pine needles under the

March 2012. Two time demonstration tests using 2.3 kg

perfect combustion condition. The residues at 890 oC

of pine needles, 3.6 kg of Japanese cedar bark and 0.4 kg

under the perfect and imperfect combustion conditionsof cedar sapwood were carried out by the combustion

were 1.7 and 29 %, respectively.

system described later.
Table 1degradation

Mass loss and radiocesium loss in the laboratory scale combustion tests

Combustion temperature (oC)

300

350

400

450

500

800

900

Mass loss (%)

54

65

85

86

87

98

99

134

Cs loss (%)

2

13

27

22

34

35

36

137

Cs loss (%)

1

15

24

30

31

32

31

15

The mass loss and radiocesium loss under the perfectmouth connecter at the upper side of the scrubber

combustion condition at 300 – 900 oC were shown inconnected to the ash enclosure system and the filtration

wasTable 1. Mass loss showed a good agreement withsystem for contaminated water.

TG/DTA result under air flow condition, which indicatedthe laboratory scale combustion test was done under theperfect combustion condition. The radiocesium loss was(3) Demonstration combustion test
Two combustion tests were carried out using the pilot

increased linearly with the combustion temperature below

system for combustion of forestry waste. The first test

450 C, and was approximately 30 – 35 % above 500 C.

used 2.3 kg of pine needles and 1 kg of cedar bark for 40oo

The radiocesium in combustion gas were washed andmins combustion, whereas the second test used 2.5 kg ofcollected by water, and the amount of radiocesiumbark and 0.4 kg of sapwood for 50 mins combustion. After

retrieved was 98 % of the initial mass.

the two combustion tests, water temperature in the watertank changed from 5 to 45 oC, and about 5 L of water was(2) Decontamination system
The pilot scale combustion system equipped with thelost by evaporation, which indicated that the heat of thedecontamination of forestry waste was designed based on

is useable to dry the forestry wastes before the combustion.

combustion gas was 2.9 kWh. The heat of combustion gas

the result obtained by the laboratory scale combustion test.

Theradiocesium

and

mass

balancesoftwoThe decontamination system for combustion of forestry

demonstration combustion tests were shown in Fig.3. The

waste consisted of three parts, the combustion gas

radiocesium in combustion gas and in soot absorbed

washing system, the combustion ash collecting system

inside of flue and furnace were extracted by water, theand the filtration system for the contaminated washedmass of these radiocesium were shown in L instead of kg.

water. The out view of combustion gas washing system

The combustion ash obtained by two combustion tests

was shown in Fig.2. The design of this system was based

was 2.25 % of starting materials, which corresponded toon 800 – 900 oC of combustion temperature and 100 kWh

the perfect combustion at 750 oC. The condense ratio ofof combustion heat. Water used for washing theradiocesium by the combustion was 27.6 times against the

combustion gas 550 L without cooling equipment. About

initial concentration by the evaluation based on mass and

40 kg of Cedar bark can be combusted per 1 hour using

radiocesium changes during the combustion.

this system. The combustion gas washing system shownin Fig.2 consisted of the furnace (A) connected with the

Combustion gas

smoke extraction apparatus by jet stream of water (C)38 %through the smoke tube (B), water supplied from thewater tank (D) by pump (E). The picture in Fig.2

Pine needle

indicates the scrubber where the combustion gas was

50,600 Bq / 2.3 kg

washed by jet stream of high pressure water. The three

Cedar bark

Gaseous state
27,250 Bq / 545 L
Solid state (soot)

48,300 Bq / 3.5 kg

435 Bq / 0.0015 kg

Cedar sapwood

6,000 Bq / 100 L

20 Bq / 0.4 kg
62 %

B

Ash
61,600 Bq / 0.14 kg

Fig.3 Radiocesium mass balance during combustionE

tests.
D

The radiocesium in ash was 62 % of the initial amountAof radiosecium in the wastes, 38 % of radiocesium wasCtransferred to the combustion gas in a gaseous state. With

Fig.2 Out view of combustion gas wash system

the increase of combustion temperature, the amount ofgaseous radiocesium was increased. Comparing to the16laboratory scale test, the highest combustion temperature

gas with water. A 95 % of radiocesium was collectedduring the demonstration test was estimated to be abovesafely by the decontamination system developed.

900 C.
oUsing the decontamination system, 95 % of the initial

References

amount of radiocesium in the forestry wastes (98,920 Bq)

1) T.

Nakanishi,

K.

Tanoi

(eds)

Agricultural

was retrieved as the combustion gas washing water

Implications of the Fukushima Nuclear Accident,(22,685 Bq) and the ash (61,600 Bq). The difference

Springer Tokyo (2013).

between the initial and the retrieved amounts remained in2) H.

Yoshida,“Contamination

analysisofthe furnace and the flue. The maintenances andradionuclide in soils and plants caused bymonitoring of facilities in the volume reduction factory

Fukushima

were necessary to keep the facilities in good working

Chemical Engineering, No.6, 250 – 257 (2012)order and to guarantee the safety.

3)

Nuclear

Power

Plant

accident”,

Y. Kikawada, M. Hirose, A. Tsukamoto, K. Nakamachi, T.

The gas washing water containing radiocesium (50Oi, T. Honda, H. Takahashi, K. Hirose, “Mobility of

Bq/L) was decontaminated to below 0.2 Bq/L by theradioactive cesium in soil originated from the Fukushima

filtration using a Prussian Blue supported wool filter for 2

Daiichi nuclear disaster; application of extraction

hours .

experiments”,

6)(4) Combustion ash treatment

J.

Radioanalytical&

NuclearChem., 304(1), 27-31 (2015).
4) T. Yoshihara, H. Matsumura, S. Hashida, T.

The combustion ash was subjected to the powder X-ray
electron

Nagaoka, “Radiocesium contaminations of 20 wood

microscopic (TEM) observation equipped with energy

species and the corresponding gamma-ray dose rates

dispersion X-ray spectrometer analysis (EDX). The mainaround the canopies at 5 months after the Fukushima

component of ash was crystalline oxide containing

nuclear power plant accident”, J. Env. Radioactivity,

various elements. EDX results suggested the presence of115, 60-68 (2013).

diffraction

analysisandthetransition

5) Tokyoboron (0.187 keV, BKα), magnesium (1.25 keV, MgKα),Metropolitan

University,“Closedsilica (1.74 keV, SiKα), phosphor (2.01 keV, PKα),

combustion gas treated system”, Japanese patent

manganese (5.89 keV, MnKα), iron (6.38 keV, FeKα),2013-224831

copper (8.0 keV, CuKα), zinc (8.63 keV, ZnKα) and6) K. Yokota, etc., “Prussian blue dyed wool and its

strontium (14.1 keV, SrKα) addition to calcium (3.69

decontamination

keV, CaKα),. Mg, P, Mn, Zn and Ca were the baseelement of plants, and B, Si, Fe, Cu and Sr came fromInternational Symposium on Fiber Science andthe soil contamination of plants.

01

for

radiocesium”,

Technology 2014, September 28 to October 1, PG3.

TEM observation suggested that the ash had a needle likestructure with 10 – 20 µm length and 0.5 – 1 µm width,
which had the possibility of affecting the human healththrough the mechanisms similar to the exposure toasbestos. The combustion ash contained high amount ofradiocesium (440,000 Bq/kg), andability

was collected

automatically by vacuum suction and was packed in aplastic bag to reduce the risk of workers health.
3. Conclusions
The laboratory scale combustion tests of forestry
wastes were carried out, and the combustion heatefficiency was determined. The radiocesium massbalance during the combustion test was evaluated. A
98 % of radiocesium vaporized during the combustion
was successively collected by washing the combustion

17

Part 2
Environmental radiation/external exposureIntegrating nuclide specific and dose rate
based methods for airborne and ground based
gamma spectrometry.
David SANDERSON 1)* , Yukihisa SANADA 2) , Alan CRESSWELL1,3) ,Sheng XU 1) , Simon MURPHY 1) , Chika NAKANISHI 2) , Tsutomu YAMADA 2)
1) Scottish Universities Environmental Research Centre (SUERC), East Kilbride, SCOTLAND.
2) Japan Atomic Energy Agency (JAEA), 1, Kanayagawa, Fukushima-shi, Fukushima, JAPAN.
3) Institute of Environmental Radioactivity (IER), Fukushima University, 1 Kanayagawa, Fukushima-shi, Fukushima JAPAN*David.Sanderson@glasgow.ac.uk
Results of joint airborne survey work conducted by SUERC and JAEA are presented, for areas tothe north and south of Fukushima Dai ichi using four different airborne survey systems, crosscalibrated at reference sites in Scotland and near Namie. Airborne measurements were made ata series of different survey heights using three high volume NaI based spectrometers, and for the
first time using a high resolution system based on the Ortec IDM HPGe spectrometer. The JAEA
data sets were analysed using the same methods applied to national scale mapping in Japan since
the accident. The SUERC data sets were analysed using nuclide specific approaches validated in
the European ECCOMAGS project. The data presented on a digital terrain model show marked
correspondence with landscape features, which both suggest the initial deposition processes, andindicate trajectories for future re-deposition by natural processes. All data sets are traceable toeach other, and to the ground based calibration site s. Nuclide specific inventories have been
defined, which can serve as a future reference to evaluate environ mental change.
Key Words: Airborne monitoring, Manned helicopter, Accident of Fukushima Daiichi NPS
1. Introduction: A multiscale problem

conjunction with methods based on dose rate apportionment.

As recovery progresses more quantitative means to accountneeded. This is a significant multi-scale problem.

2. Joint airborne surveys in November 2014
Airborne surveys were conducted in November 2014

Contamination ranges from national and regional (100-1000

with UK and Japanese systems. The survey areas arekm), through local (1-10 km), and site specific (1-100m)

shown in Figure 1. Areas 1 and 5 are mountainous andspatial scales. Yet the physical, chemical and biologicalforested and were surveyed at nominal heights of 150m

behaviour of radionuclides is influenced by speciation and(500 feet) , 300m (1000 feet) and 450 m (1500 feet).

for radionuclide inventories in complex environments areprocesses

determinedat

sub-microscopic

scales.

Comprehensive knowledge on all scales is needed to predict
future behavior, and enhance the knowledge base for amanaged recovery. Moreover, since 2011, measurements
have been conducted by different institutions using diverse
methods. It is important to integrate and cross validate data
and methods to enhance confidence in the outcomes.
Here we present recent collaborative work between SUERC
and JAEA(1) which aimed to (a) establish traceable ground to
air comparisons for airborne gamma spectrometry (AGS)
Figure 1: Map of survey areas for November 2014 joint
airborne survey. Image: Landsat ©Google 2015

in Japan, and (b) assess nuclide specific AGS methods in18

approaches validated in the European ECCOMAGSECCOMAGS Exercise : Calibration Sites
Dumfries

project(2,3). For the NaI(Tl) data nuclide specific energy

Dumfries and Galloway Region

regions were integrated, and standard approaches applied
Stranraer

CastleKennedy

based on background subtraction, matrix stripping (using

Wigtown
Merse

matrices derived from measured and simulated spectra for

Inch Farmeach radionuclide or series to deconvolve interferences),
altitude standardization and conversion to nuclide specificactivities for 137Cs and 134Cs (in kBq m-2) and naturally

Solway Firthoccurring nuclides 40K, 214Bi, 208Tl (in Bq kg-1). High
0

10

20km

resolution data were calibrated using specific gamma raylines.

Figure 2: Location of calibration sites in SW Scotland.
JAEA has conducted airborne surveys using manned aircraft

For areas 1 and 5 each survey comprised 180 line km,

since 2011(4,5) contributing extensively to the MEXT

and took 80-100 minutes of flight time.

programme of national surveys. Dose rate mapping methods
have been adopted in Japan using the “non-natural” dose rate

SUERC deployed two NaI(Tl) spectrometers, of 16 litre (theapproach, with apportionment to 137Cs and 134Cs activity“Rack” system) and 4 litre (the “Black Box” system) volume,

estimates based on conversion between dose rate and activity

plus a system developed with the Ortec IDM-200V self-

per unit area using coefficients from ICRU53(6), andcooled hyperpure Ge spectrometer (the “IDM” system), andknowledge of mean isotope ratios.

tested for the first time in the air during this project. Thesesystems were extensively tested in the UK prior to shipping

3.1 Ground to air calibration at reference sites

to Japan; the rack and black box systems being flight

Scotland (UK)calibrated at the ECCOMAGS sites in SW Scotland. In Japan

Reference sites provide traceability between soil samples,

the SUERC spectrometers were bench tested in JAEA’s

in-situ, backpack, and airborne gamma measurements. The

laboratory at Fukushima University, and then installed in a

SUERC spectrometers were flight tested at the ECCOMAGSBell 412 helicopter operated by Aero Asahi, and used forintercomparison sites in SW Scotland(2,3) (Figure 2). Table 1

national mapping in Japan. JAEA also conductedshows the airborne and ground based data on these sites, andmeasurements using Radiation Solutions 12 litre NaI(Tl)establishes international traceability to the work. For 137Cs aspectrometers. The systems were powered independently

mean mass depth of 8.5 g cm-2 which matches the reference

from the aircraft, and combination of GPS data and a digital

depths for Inch Farm (IF) and Castle Kennedy(CK), where

elevation model used for ground clearance estimation.

radiocaesium was deposited by atmospheric processes,
reasonably well. At Wigton Merse the activity was deposited

3. Data analysis approaches
SUERC data sets were analysed using nuclide specific

Table 1: Results for the ECCOMAGS calibration sites measured in September 2014, together with reference values updated to
2014.
.Site

WG
IF
CK

137

Value

Cs
40

214

208

Dose rate µGy h-1(8.5)

333 ± 5

18.6 ± 0.9

5.8 ± 0.1

0.053 ± 0.001

170 ± 1026383 ± 1313.4 ± 0.4

7.5 ± 0.3

Measured

14.6 ± 0.58.5

358 ± 524.4 ± 1.1

7.8 ± 0.1

0.039 ± 0.001

Reference

16.9 ± 0.88.5376 ± 1423.8 ± 1.9

9.9 ± 0.6

0.054 ± 0.003

Measured

4.3 ± 0.2

8.5

207 ± 411.3 ± 0.7

4.2 ± 0.1

0.023 ± 0.001

Reference

4.8 ± 0.2

12.8

270 ± 1314.4 ± 0.7

6.5 ± 0.5

0.033 ± 0.005

Activity

Mass depth

kBq m-2

g cm-2

Measured(56 ± 1)

Reference

K Bq kg-1

19

Bi Bq kg-1

Tl Bq kg-1

by tidal inundation of sediments contaminated by past marine137

discharges from the Sellafield reprocessing site. It shows a.
pronounced subsurface maximum with mean mass depth of

500

100

200

307 ± 38 (n=74)1000

354 ± 11 (n=66)

and the higher activity levels in the SE quadrant, which had notundergone active remediation at time of survey

385 ± 5 (n=70)

Cs altitude corrected cps

November 2014. Note the lower activity levels along roads,

1500

372 ± 3 (n=65)

Rack System (Summed Array)

Figure 3: Backpack survey of the Namie calibration site,

0
-500
-1000
0

300

400

500

Height (m)26 g cm-2 (2014 value) resulting in a significantly different

Figure 4: Mean spectra (top) and altitude corrected countCs calibration factor, as previously observed2.

rates (below) recorded at different heights above the Namiecalibration site, using the SUERC rack system.

Fukushima (Japan)
A reference site was sampled near Namie in November 2014

Full results for all survey areas are given in Sanderson et.al.

ahead of the airborne work. 31 soil cores were collected on an2015(1). Here we illustrate some of the data from area 5 (SWexpanding hexagonal pattern designed to accommodateof FDNPP). Average spectra for the three SUERC systems

spatial heterogeneity(7). They were subdivided into depth

for the 500ft survey of this area are shown in Figure 5. These

intervals, dried and prepared for later laboratory analysis byshow the difference in relative efficiency between thehigh resolution gamma spectrometry. Backpack mapping
1-100m scale, also showing the effects of ongoing
remediation, and self-cleaning of road surfaces. Dose rates
were measured at ground level by JAEA. Table 2 shows theagreement between sample based and airborne results fromthe site, establishing nuclide specific traceability between
ground sampling and airborne observations for the first timein Japan.
4. Results
Figure 4 shows spectra and altitude corrected count rate datafor 137Cs at different heights above the Namie calibration site
for the 16 litre (rack) system. As expected (eg the half depth
for 662 keV radiation in air is ~72 m) the spectra show
marked reductions peak intensities and relative increase in
scatteredcomponents

withincreasingheight.

Altitudecorrected peak count rates show increasing
dispersion with height, reflecting these features, confirmingthat measurement precision for nuclide specific mapping is
Figure 5: Average spectra recorded with the threestrongly dependent on ground clearance.

SUERC systems for the 500ft survey of Area 5.

20

Table 2: Results of measurements on the Namie reference site at different ground clearances. For 137Cs and 134 Cs a mean mass
depth of 3 g cm-2 was applied..
137

Cs kBq m-2

134

40

214

208

Dose rate µGy h-1

500ft

73.3 ± 0.7

19.3 ± 0.5

258 ± 622.3 ± 2.0

7.0 ± 0.2

0.185 ± 0.001

750ft

75.8 ± 1.0

18.7 ± 0.6

243 ± 1024.8 ± 2.9

6.5 ± 0.3

0.186 ± 0.001

1000ft69.8 ± 2.2

19.6 ± 1.0

268 ± 1220.6 ± 4.7

6.6 ± 0.4

0.182 ± 0.001

1500ft60.5 ± 7.5

21.5 ± 2.2

278 ± 26

18.6 ± 11.7

8.1 ± 0.6

0.193 ± 0.002

500ft

74.9 ± 1.5

16.5 ± 0.7

219 ± 1423.4 ± 2.2

6.5 ± 0.5

0.182 ± 0.003

750ft

80.3 ± 1.7

16.6 ± 1.0

235 ± 15

20.6 ± 3.8

6.5 ± 0.8

0.189 ± 0.002

1000ft66.2 ± 3.1

17.5 ± 1.7

198 ± 20

25.6 ± 5.1

5.6 ± 1.1

0.176 ± 0.002

1500ft60.9 ± 9.2

11.4 ± 3.3

220 ± 4447.2 ± 8.4

3.1 ± 2.2

0.176 ± 0.004

500ft

61.5 ±5.1

20.1 ±1.7---0.183 ± 0.015

66.6 ± 6.2

17.3 ± 1.6

298 ± 722.7 ± 0.8

10.0 ± 0.2

0.182 ± 0.009

SystemRack

Black box

JAEA (σ=3)
Reference

Cs kBq m-2

K Bq kg-1

Bi Bq kg-1

Tl Bq kg-1

HPGe detector allowing the quantification of line specific5. Discussion
Collaborative work between JAEA and SUERC has

count rates without the use of a stripping algorithm. The use

established traceability between airborne and ground based

systems, and also the much higher spectral resolution of the

137

134

Cs in the HPGe

measurements through measurements at calibration sites inspectra allows for quantification of isotope ratio and mass

SW Scotland developed for an international intercomparisonof the different discrete peaks for

Cs and137

Cs estimates for the

exercise and the development of a calibration site near Namie.

SUERC rack and JAEA 12 litre system, showing similar

Reference values have been defined from laboratory

deposition patterns, and inventories in TBq (Table 3).

measurement of samples, and a backpack survey used todepth. Figure 6 compares dose rate andevaluate spatial variability. This has highlighted the
Figure 7 compares high volume (16 litre) with low volume (4self-cleaning of road surfaces, and the effect of ongoing site

litre) NaI systems with the Ge based IDM spectrometer in

remediation

Area 5. Positions and activity concentrations correspond well,comparisons have been made between airborne measurementswith 150 m (500 feet) ground clearance, and the data confirm

with spectrometry systems utilizing spectral analysis methods

the first use of IDM systems for airborne mapping.

to directly quantify radionuclide activity concentrations, andwithinadynamic

environment.

Initialwith dose rate apportionment methods. These approaches
The data, on digital terrain models (Figure 8), identify wet

reproduce the general features of the common survey areas,and dry deposition areas, and suggest future movement ofand inventories, however nuclide specific approaches haveactivity within valley catchments

advantages in providing independent means of registering

Table 3: Inventories of 134Cs and 137Cs in each of the two survey areas determined from the different NaI(Tl)systems at three different ground clearances.

Area 1

Area 5

Rack Inventory (TBq)

Black Box Inventory (TBq)

JAEA Inventory (TBq)

137

137

137

Cs

134

Cs

Cs

134

Cs

Cs

134

Cs

500ft

43.79 ± 0.03

14.74 ± 0.01

40.45 ± 0.03

12.39 ± 0.02

29.8

9.65

1000ft41.13 ± 0.07

11.37 ± 0.02

30.67 ± 0.08

8.81 ± 0.03

32.6

10.5

1500ft39.98 ± 0.25

10.99 ± 0.06

27.67 ± 0.26

7.24 ± 0.09

26.3

8.52

500ft

39.77 ± 0.02

13.23 ± 0.01

39.74 ± 0.03

12.53 ± 0.01

30.4

9.84

1000ft40.03 ± 0.05

11.33 ± 0.02

37.77 ± 0.05

5.67 ± 0.02

27.8

8.99

1500ft44.72 ± 0.17

12.67 ± 0.05

30.83 ± 0.19

8.13 ± 0.07

25.9

8.37

21

and 137Cs estimates for the SUERC rack and JAEA 12 litre
system, showing similar deposition patterns, and inventories in
TBq. エリア5におけるSUERCとJAEAの測定結果は、線量率及び分布のパターンにおいて同じ傾向を示した。
SUERC (150m)

SUERC (300m)

JAEA (300m)
μSv h-1

137Cs

Bq m-2

Figure 6: Dose rate and 137Cs distribution in area 5 measured with the SUERC rack system at 150m and 300m ground clearance,
and with the JAEA system at 300m
there is scope for further application of these approaches toisotopic variations, and placing the radiocaesium and naturally

visualization of the activity distributions and movements

occurring nuclides in context. There is scope for further

within complex and dynamic environments in Fukushima. The

analysis of the potential for applying nuclide specific methods

work was successful in establishing the ability of UK andto the JAEA data sets and to earlier national surveys to build

Japan teams to produce high quality airborne data sets using

4D models for the nuclide migration in these upland areas. The

diverse systems. It also verified, for the first time, the potential

Comparing high volume (16 litre) withlow volume (4 litre) NaI
of new IDM technology for AGS
use of landscape 3D drapes with the lowest altitude data setssystems
the Gebased features,
IDM spectrometer in Area 5. Positions
show
remarkable withcorrespondence
to landscapeAcknowledgements
includingsignals
in valley bottoms in areacorrespond
1, andand enhanced
activity
concentrations
well, with 150 m (500 feet)
The work was supported by JAEA and SUERC under atopographically significant positioning of activities in area 5
ground clearance, and the data confirm the first use of IDM systems
bilateral research agreement. Support is also acknowledgedwhich are suggestive both of the depositional processes andfortrajectories
airborne
likelyfor longmapping.
term migration of activity. Again.

16 l Rack

4 l Black Box

Ge IDM system

Figure 7: Comparison between the three SUERC systems at 150m for area 5.

150m高さから測定したSUERCの3種類の検出器の測定結果は、概ね同様の傾向を示した。IDMを航空機に搭載して測定したのは世界22で初めてである。

View from NNE

Area 1

Area 1, nominal 500ft survey

View from S

Area 5
Area 5, nominal 500ft survey

Figure 8: 137Cs activity distribution on 3D landscape models for area 1 (top) showing increased concentration in river valley
floors, and area 5 (bottom) showing deposition on mountains. Image: Landsat ©Google 2015
from the GB Sasakawa Foundation, the University of5) Sanada, Y., Nishizawa, Y., Urabe, Y., Yamada, T.

Glasgow, and the UK FCO Prosperity Fund for visits to

Ishida, M., Sato, Y., Hirayama H., Takamura, Y.,

Fukushima, to the Institute for Environmental Radioactivity

Nishihara, K., Imura, M., Tsuchida, K., Ishibashi, S.,

Fukushima University for support with sample preparation,

M., Yuuki, Y. and Torii, T., “Radiation monitoring

to Aero-Asahi and PDG helicopters for aircraft operations,using manned helicopter around the Fukushima dai-ichi

and to Seiko-EG&G for provision of the IDM system innuclear power plant in the fiscal 2013”(Contract

Japan.

Research),

1) Sanderson D.C.W., Cresswell A. J., Xu S., Murphy S.,
Sanada Y., Nakanishi C., Yamada T. “Joint SUERC/

0-913394-52-1.

2) Sanderson D. C. W., Cresswell A. J., Lang J. J. (Eds). “AnInternational Comparison of Airborne and Ground

Environ. Radioact. 33, 213-235.

Based Gamma Ray Spectrometry.” University ofGlasgow, UK (2003), ISBN: 0-85261-783-6.
3) Sanderson D.C.W., Cresswell A.J., Scott E.M., Lang J.J.
(2004). Demonstrating the European Capability for
Airborne Gamma Spectrometry: Results from theRadiation(in7) Tyler A.N., Sanderson D.C.W., Scott E.M., Allyson J.D.
(1996). Accounting for spatial variability and fields ofview in environmental gamma ray spectrometry. J.

2014.” SUERC/JAEA report (2015).

Exercise.

2014

environment.” ICRU Report No. 53 (1994). ISBN

Japan:

SUERC Instrumental Measurements in November

ECCOMAGS

2014-014,

Japanese).
6) International Commission on Radiation Units andMeasurements. “Gamma-ray spectrometry in the

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Bacterial microflora characteristics of plant samples
from contaminated by radionuclides Chernobyl area
Pavlina ZELENA 1) , Julia SHEVCHENKO 1)* , Valentina BEREZHNA 2) , JuliaSHYLINA 2) , Mykola GUSCHA 2) , Olha MOLOZHAVA 1) ,1) ESC Institute of Biology, Taras Shevchenko National University of Kiev, 64/13, Volodymyrska Street, Kyiv 01601
Ukraine2) Institute of Cell Biology and Genetic Engineering NASU, 148, Zabolotnogo Street, Kyiv -143, 03680, Ukraine* julia.i.shevchenko@gmail.com
Two serious nuclear accidents during the last quarter century (Chernobyl, 1986 and Fukushima,2011) contaminated large agricultural areas with radioactivity. In radioactive areas allcomponents of ecosystems, including microorganisms, exposed to ionizing radiation. The
aim of this study was isolation and identification of dominant bacteria from plant samples,
which were collected from the area of radioactive contamination and to compare it withbacteria isolated from plant collected in a non-radioactive area by their qualitative
composition, physiological, biochemical and pathogenic characteristics. Bacteria wereisolated from plant samples grown in a radioactive field located 5 km from the Chernobyl
Nuclear Power Plant (CNPP). Physiological, biochemical and pathogenic properties werecharacterized from nine pure bacterial isolates. The common features of bacteria fromradionuclide contaminated plant samples were increased synthesis of mucus and capsulecreation. It was found that all selected isolates produce catalase, therefore, bacteria wereresistant to oxidative stress. The increased pathogenicity of most bacteria isolated from theplant grown in radioactive Chernobyl area compare to the isolates from the plant without
radioactive contamination was established from the phytopathogenic tests. Consequently,
bacterial isolates from the plants grown in the radioactive environment tends to dominate
enterobacteria similar to agents of opportunistic infections.
Key Words: Plant microflora, Chernobyl area, Pathogenicity

body's stress levels [3]. On the other hand, in case ofirradiation, stress factor affects the microflora
directly and changes its properties.
Thus far, previous studies have demonstrated thatthe effect of chronic exposure of low intensity
radiation leads to a change in plant resistance andaggressiveness of pathogenic fungi. In particular,
the reduction of plant resistance to biotic stress wasrecorded in plants grown in clean soil from seeds
formed in conditions of radioactive contamination,and plants grown from clean seed in the
30-kilometer zone of the Chernobyl Nuclear Power
Plant (CNPP) [4]. Concerning phytopathogenic
bacteria such data are not available.
The aim of this study was isolation andidentification of dominant forms of bacteria fromplant samples, which were collected from the area ofradioactive contamination, and comparing withbacteria isolated from plant collected in a
non-radioactive
area
by
their
qualitative
composition, physiological, biochemical andpathogenic characteristics.

Introduction
Comparedwithmacroorganisms,
microorganisms demonstrate higher resistance toirradiation. There is a possibility that doses harmful
for macroorganisms lead to stimulation of
microorganisms’ activity. As a result, it willprobably change the host-pathogen relationships.
In case of chronic irradiation, such changes of
microflora are considered as a sensitive indicator of
host' immunoreactivity modification. There are
increases of biochemical activity, pathogenicity andresistance to adverse environmental factors in theirradiated organism’ microflora [1]. The growth of
the immunosuppressive properties takes place inopportunistic microorganisms by dramatic rise ofculture concentration and pathogen aggressiveness[2]. In the irradiated organism, saprophytes arecapable of changing their properties by increasing
biochemical activity, potential pathogenicity andantibiotic resistance.
It is known that the microbiota responds to thephysiological state of the host, in particular, at the24determine if bacteria metabolize glucose byfermentation or aerobic respiration (oxidatively) [7].
It was found that k/15m, k/15b, k2j/2, k3j2/13
isolates are nonfermenting bacteria that metabolize
glucose via oxidative metabolism (O). Facultative
anaerobic metabolism (F) was typical for k2pr/1,
k3j1/6, k3j3/11, k3pr1/9, k3j3/12 isolates (Table 1).
MRVP-test (methyl red and Voges-Proskauer
tests) exploits for formic acid fermentation typedetermination. It has been demonstrated that bacteriaof the genera Escherichia, Salmonella, Shigellaexhibit mixed formic acid fermentation type andferment sugars to lactic, acetic, succinic & formic
acids, ethanol and CO 2 . Whereas bacteria of thegenera Enterobacter, Serratia, Erwinia produce lessacid, but more CO 2 , ethanol, acetone and2,3-butanediol by butanol-formic acid fermentation
type. The mixed type of formic acid fermentation was
detected in isolate k3j1/6 and butanol type offermentation was typical for k/15m, k/15b, k2pr/1,
k2j/2, k3j1/6, k3j3/11, k3pr1/9, k3j3/12 isolates(Table 1).
Oxidase-test. It has been demonstrated that
C-oxidase positive reaction inherent in bacteria
Alcaligenes spp., Campilobacter spp., Bordetella
pertusis,
Brucellaspp.,
Moraxella
spp.,
Pseudomonas spp., etc. On the other hand, oxidase
negative bacteria are Acinetobacter spp., Francisellatularensis,
Flavimonas
oryzihabitans,
Stenotrophomonas maltophilla, representatives of thefamily Enterobacteriaceae, etc. [7]. Among theisolated bacteria the cytochrome oxidase was present
in isolates k/15m and k3j2/13 (Table 1).
NO 2 -test. Anaerobic bacteria use nitrate NO 2 as aterminal acceptor of electrons for anaerobic
respiration. Among obtained bacteria, isolates
k2pr/1, k3j1/6, k3j3/11, k3pr1/9, k3j3/12 arecapable for nitrate respiration (Table 1).
Catalase-test. A number of studies proved thatmicroorganisms that exist in presence of molecularoxygen express superoxide dismutase, peroxidaseand catalase. It was found that bacterial isolates
produce catalase and exhibit resistance to oxidative
stress (Table 1).
Bacterial isolates k2j/2 and k3j3/12 showed
positive reaction with Ellman's reagent, which
specifically reacts with free SH-groups. By this test
the intracellular concentration of low molecularweight thiols (glutathione, etc.), which involved indetoxification reactions of aldehydes was determined.
It is believed that glutathione plays an important rolein cell protection from oxidative stress, caused by the
influence of reactive oxygen species.
Pathogenicity tests. Taken together, these results
suggest that the majority of bacterial isolates fromplant samples collected in the territory ofradionuclide contamination exceeded the level ofpathogenicity of bacteria isolated from plant samples
collected in a non-radioactive area.
Bacterial isolates k2pr/1 and k2j/2, extracted

Materials and methods
Bacterial isolates were selected from plant
samples collected on the radioactive field located 5km from the CNPP, near the village Chystogalivka(20650±1050 Bq/kg for 137Cs and 5180±550 Bq/kg
for 90Sr) and in a control field established directly
in a non-radioactive area in the town of Chernobyl(1414±71 Bq/kg for 137Cs and 550±55 Bq/kg for
90Sr).
For bacteria isolation a small amount of driedplant material was homogenized in a mortar withsterile distilled water and applied on a surface ofpotato agar medium. A selection of pure cultures
was performed according to the recommendations ofBergey's Manual [5]. Cytological examination of theobtained cultures was performed by Gram's method[6].
Biochemical studies of isolated bacteria were
performed according to standard techniques [7] bydifferential tests (OF-test, MRVP-test, oxidase-test,
catalase-test, NO 2 -test) and by microbial analyzer
VITEC 2 compact (bioMérieux Inc., France).
The pathogenic properties of bacterial isolates
were confirmed by using various plant test-systems:
Arabidopsis thaliana, seedlings of maize and flax
seeds.
Adult plants of A. thaliana ecotype Columbia(Сol-0 wt - wild type) were infected with bacterial
suspension (48-hour culture, 109 cells/mL) by
inoculation with a syringe [8]. Damaged leaves withvarious symptoms were accounted after three days.
The degree of lesion was calculated by the point
system (Fig. 1).
The corn seedlings MOC 182CV (hybrid
culture) were infected with bacterial suspensions (ina final concentration 1.107 cells/mL) in water.
Determination of growth parameters took place after
three and nine days of incubation; examination of
dry weight of roots and stems at nine day of
incubation.
The bulked flax seeds (1.5 g) were infected withbacterial suspension (0.5 units of Macfarland). Theenergy of seeds germination was calculated after
three days of growth.
Statistical analysis of the results was performedby the software package Microsoft Office Excel.
Results and Discussion
All of the nine characterized bacterial isolates
were gram-negative, rod-shaped and contained
capsule. Highly developed capsules were found in thebacteria isolated from the area of radioactive
contamination. The most interesting finding was thatbacterial isolates, collected in the territory
contaminated with radionuclides demonstrated a highbiochemical activity and broad range of biochemical
characteristics.
OF-test. The oxidative-fermentative test is used to25

from the flax seeds, demonstrated the highest
virulence and aggressiveness at all plant test-systems(flax, corn, Arabidopsis) (Fig. 1).
Bacterial isolates identification results. Most
bacteria which were isolated from the area withradioactive
contamination
demonstrated
characteristics of opportunistic microorganisms. The
bacterial isolates from the flax seeds, which weregrown in the absence of radioactive contamination,
were identified as Pseudomonas fluorescens (k/15m)
and gram-variable Bacillus spp. (k/15b). Isolated
bacteria Bacillus spp. formed a well-developed
capsule and was found in the samples from the zoneof radioactive contamination as well. SelectedisolatesofP. fluorescensbybiochemical
characteristics were similar to Pseudomonas
aeruginosa, but instead of pyocyanin synthesis,
bacteria were producing green fluorescent pigment
and did not grow at 42°C
The bacteria isolated from the flax seeds collectedin the zone of radioactive contamination, wereidentified as Enterobacter spp. (k2pr/1) &Cupriavidus pauculus (k2j/2) and obtained a highlevel of pathogenicity. The genus Enterobacter refers
to opportunistic bacteria which cause nosocomial
angiogenic infections and infections of therespiratory and urinary tracts. Cupriavidus pauculus(Ralstonia solanacearum) is phytopathogenic
bacteria, the causative agent of withering amongcrops and ornamental plants, altogether affects up to
200 plant species. In particular, it causes one of themost dangerous diseases of potato - brown rot. This
bacterium is a quarantine organism in Ukraine, which
included in the first list “The List of pests, plantdiseases and weeds that are of quarantine significancein Ukraine". It is also included in the A2 list ofquarantine organisms of EPPO (European andMediterranean Plant Protection Organization).
From the evening-primrose inflorescences wereisolated Pantoea sp. (k3j1/6), Pantoea agglomerans(k3j3/11, k3pr1/9, k3j3/12) and Acinetobacterbaumannii (k3j2/13). It is known that Pantoea
bacteria are isolated from various environments (soil,
water, plants and seeds, animals, insects) and causes
opportunistic infections in humans (wound infection,
respiratory tract and conjunctiva inflammation, etc.)[9].
Acinetobacter baumannii, is one of the causative
agents of nosocomial infection (causing 2-10% ofGram-negative infections in Europe and the US and
1% of all nosocomial infection), well adapted to thehospital environment and has high resistance to themost antimicrobial and antiseptic drugs [10]Overall, these results confirm our earlier
assumption that one of the negative consequences ofthe stressful impacts on ecosystems is accumulationin environment highly-developed microorganisms
with increased aggressiveness [11]. In addition,

opportunistic pathogens similar to saprophytes andhighly specialized pathogens possess a high adaptive
capacity,
betterresistanttounfavorable
environmental factors (biofilm formation, highbiochemical activity, resistance to oxidative
damages) and capable of finding new hosts. All thisallows for the description of the situation in
Chernobyl area as “unfavorable”. Therefore, theterritories with radioactive contamination, including
the Fukushima region, require opportunistic
microorganisms monitoring and preventing its further
spreading.
References
1) Vasilenko I., Vasilenko O. “Biological effects ofnuclear fission products”, BIONOM. 384p.
(2011) (in Russian).
2) Lukyanova E., Antypkin Y., Chernyshov V.,
Vykhovanets E. “Ionizing radiation and theimmune system in children”, Expert. 210p.
(2003) (in Russian).
3) Oleskin A., Botvinko A., Cevkelova I. “Colonialorganization and intercellular communication in
microorganisms”, Microbiology 69(3), pp309-327 (2000) (in Russian).
4) Grodzinsky D., Huscha M., Dmitriev A. et al.,“Radiobiological effects of chronic irradiationof plants in the areas affected by the Chernobyl
disaster”, Nauc. dumka. 376p. (2008) (inUkrainian).
5) Holt J., Krieg N., Sneath P., Steil J. “Bergey's
Manual of Systematic Bacteriology”, Mir. 432p.
(1997) (in Russian).
6) Radchenko O., Stepura L., Dombrovskaja I et al.
“Workshop
on
GeneralMicrobiology”,
Phitocentr (2011) (in Ukrainian).
7) Radchenko O. “The physiological andbiochemical properties of microorganisms andmethods of their determination”, Kiev. 212p
(2012) (in Ukrainian).
8) Klement Z., Rudolf K., Sands D. “Methods in
phytobacteriology”, Budapest: Acad. sci. 568 p.
(1990).
9) Medrano E., Bell A. “Role of Pantoea
agglomerans in opportunistic bacterial seed andboll rot of cotton (Gossypium hirsutum) grownin the field”, J. Appl .Microbiol. 102(1), pp
134-143 (2007).
10) Horbych J., Karpov I, Krechikova O. “Infections
caused by Acinetobacter baumannii: risk factors,
diagnosis, treatment, prevention approaches”,
Medicinskie novosti. 5, pp 31-39 (2011) (inRussian).
11) Shilina J., Huscha M., Dmitriev A. “The problem
of modification of the pathogenicity of
microorganisms in anthropogenically modified
ecosystems”, Agroecological journal. 2, pp
62-66(2006)(inUkrainian).

26

Table 1. Biochemical characteristics of isolated bacteria: P. fluorescens (k/15m), Bacillus spp. (k/15b), Enterobacter spp. (k2pr/1),
C. pauculus (k2j/2), Pantoea spp. (k3j/6, k3j3/11, k3pr1/9, k3j3/12), A. baumannii (k3j2/13).
Isolated bacteria
Biochemical characteristics
k/15m k/15b k2pr/1
k2j/2
k3j1/6
k3j3/11OF-test, glucose
O
O
F
O
F
F
MR-test+VP-test+++++Cytochrome oxidase+
Nitrate reductase+++
Catalase
+
+
+
+
+
+
Ellman test+
L-Arabitol
Cellobiose+
H2S formation
D-Glucose
+
+
+
+
+
+
Beta-glucosidase++
D-Maltose++++
D-Mannitol++++
D-Mannose++++
Beta-xylosidase+
Lipase+Palatinose+
D-Sorbitol++
Saccharose/sucrose++++
D-Tagatose+
D-Trehalose++++
Citrate (sodium)
+
+
+
+
+
Malonate+++++
5-Keto- D-gluconate
L-Lactate-alkalinization
+
+
+
+
+
+
Alfa-glucosidase+
Succinate-alkalinization++++
Alfa-galactosidase++
Ornithine-decarboxylase+
Decarboxylase-base
L-Histidine-assimilation++
Beta-glucuronidase
Glu-Gly-Arg-arylamidase-

k3pr1/9
F
+
+
+
+
+
+
+
+
+
+
+
+
+
-

k3j2/13
O
+
+
+
+
+
+
+
+
+
+
-

k3j3/12
F
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
-

Fig. 1. A. thaliana lesion on 3d day after isolates inoculation, which were collected from plant material in zone of radioactive
contamination and in radionuclide-free area27

Fields of View for Environmental
Radioactivity
Alex MALINS 1)* , Masahiko OKUMURA 1) , Masahiko MACHIDA 1) ,Hiroshi TAKEMIYA 1) , Kimiaki SAITO 2)
1) Center for Computational Science & e-Systems, JAEA, 178-4-4 Wakashiba, Kashiwa, Chiba 277-0871 JAPAN
2) Fukushima Environmental Safety Center, JAEA, 2-2-2 Uchisaiwai-cho, Chiyoda, Tokyo 100-8577 JAPAN* malins.alex@jaea.go.jp
The gamma component of air radiation dose rates is a function of the amount and spread ofradioactive nuclides in the environment. These radionuclides can be natural or anthropogenic
in origin. The field of view describes the area of radionuclides on, or below, the ground that is
responsible for determining the air dose rate, and hence correspondingly the external radiation
exposure. This work describes Monte Carlo radiation transport calculations for the field of view
under a variety of situations. Presented first are results for natural 40 K and thorium and uranium
series radionuclides distributed homogeneously within the ground. Results are then describedfor atmospheric radioactive caesium fallout, such as from the Fukushima Daiichi Nuclear Power
Plant accident. Various stages of fallout evolution are considered through the depth distributionof 134 Cs and 137 Cs in soil. The fields of view for the natural radionuclides and radiocaesium are
different. This can affect the responses of radiation monitors to these nuclides if the detector ispartially shielded from the ground within its field of view. The field of view also sets the
maximum reduction in air dose rates that can be achieved through local decontamination or
remediation measures. This maximum efficiency can be determined quickly from the data
presented here for the air dose rate versus the spatial extent of radioactive source on the ground.
Key Words: field of view, air dose rate, environmental radioactivity
wide area of land can contribute to the air dose rate.
The field of view describes the size of the region
containing radioactivity whose radiation contributes
significantly to the dose rate at a detection point. The fieldof view of environmental radionuclides, present on or
below the ground, can thus be defined as the volume ofearth from which a specified fraction of the total gamma
radiation intensity contributing to an air dose rate
originates from 3). Previous authors have characterized thefield of view for 1 m air dose rates from natural andanthropogenic radionuclides distributed within soils.
Techniques employed have included first principles
calculations for photon fluxes 3) 4) and Monte Carlosimulations of dose rates 5) from increasing area sourceson the ground. Others have characterized the angulardependence and the field of view of the air kerma 6) 7) 8).
This paper presents Monte Carlo calculations for thefield of view for ambient dose equivalent rates fromnatural radionuclides distributed uniformly in the ground,and radioactive 134Cs and 137Cs fallout distributed

1. Introduction
Humans are exposed to external gamma radiation fromcosmic sources and from radioactivity in the environment
on earth. Environmental gamma radiation sources can benatural or man-made in origin. Examples of the former
include 40K, and thorium and uranium series radionuclides
within the ground, and the latter include fallout fromatomic weapons testing and civil nuclear accidents. The
level of gamma radiation at a particular location can bequantified by measuring an external radiation dose rate.
The radiation protection quantity ambient dose equivalent
rate is commonly used for this purpose 1).
Gamma rays can travel hundreds of metres in air
without undergoing interactions. The U. S. National
Institute of Standards and Technology (NIST) lists a massattenuation coefficient ( / ) for 1.0 MeV photons in dry
air of 0.06358 cm2/g 2). For air with density 0.0012 g/cm3,
this equates to a mean free path of 131 m between
interactions. Therefore, gamma rays originating from a28

exponentially with depth. Two applications of the fieldsof view results are presented within: i) for interpreting
differences between KURAMA survey results taken incars and buses, and ii) for undertaking quick calculations
for the effectiveness of land remediation methods.
2. Methods
All calculations were undertaken with the Monte Carloradiation transport code PHITS 9). The simulations
modelled the infinite half-space geometry 10). Thisgeometry consists of a plane which separates a lower
region of soil (density
1.6 g/cm3) and an upper
region consisting of air (0.0012 g/cm3). The
elemental compositions of the soil and air materials
followed ref. 11).
Table 1. Radiation sources and their distributions
within soil simulated in this work.
SourceDepth distrib.

Emission dataK
232
Th series
235
U series
238
U series
134
Cs
137
Cs

Uniform
Uniform
Uniform
Uniform
Exponential
Exponential

ICRP 107 12)
ICRP 107 12)
ICRP 107 12)
ICRP 107 12)
NuDat2 13)
NuDat2 13)40

The natural potassium radioisotope 40K, the isotopes inthree thorium and uranium radionuclide decay chains, andtwo radiocaesium isotopes common in nuclear accident
fallout were considered as terrestrial gamma radiation
sources. The source types, their depth distributions within
the ground, and the references used for their x-ray and

Figure 1. Photon emission spectra per decay for thedifferent source types. For sources that are a decay
chain, the spectra include decay photons fromdaughter nuclides assumed to be in secularequilibrium and the intensity values shown are
applicable per decay of the head isotope in the chain.

gamma radiation emission data are listed in Table 1.
The photon energy spectra inputted into the simulations
for each of the source types are shown in Fig. 1. All
photons with energy greater than 10 keV and emission
probability greater than 0.1%, according to the references

d ′,
where

[cm] is the depth below the ground surface.

For computational efficiency, the radiation source
volume was scaled to a line within the soil at the centre of
the simulation space, and the Monte Carlo tally regions tocircular planes at fixed height above the ground and withvarying radii 14). This set-up enabled fast calculation of afield of view in terms of contributions from increasingradii cylindrical volumes of soil centred beneath the air
dose rate location. Fig. 2 shows the real geometry
achieved by this simulation method. The tally response
function calculated was the ambient dose equivalent rate,∗
10 [µSv/h] 1).
Two limitations of simulating the infinite half-space

listed in Table 1, were included in the spectra. Photons
were emitted isotropically from the source radionuclides.
The natural radionuclides were modelled with constantactivity per unit soil mass at all depths. Caesium wasmodelled as exponentially distributed with soil depth,/ ,(1)[Bq/kg] is the activity per unit soil mass at
, exp

where

(2)

mass depth [g/cm2],, [Bq/kg] is the activity perunit mass at the ground surface, and[g/cm2] is therelaxation mass per unit area that quantifies the depth of
fallout penetration into the ground. The mass depth is

29

Air

Dose Rate Point
h [m]
r [m]

Soil

∗
Figure 2. The field of view for
10 wascalculated in terms of the contribution from the decayof radionuclides within increasing radii volumes ofground beneath the dose rate point.

Figure 3. Comparing the field of view from naturalradionuclides, 134Cs and 137Cs.
The length scale of the field of view is of comparable
order of magnitude for all the nuclides. Around 60-80%
of the radiation contributing to ∗ 10 originates fromwithin 10 m around the dose rate point. Slowly increasing
tails on the graphs mean that it takes 100 m for ∗ 10
to reach 90% of its infinite limit. Radiation contributing
to the final 10% of ∗ 10 originates more than 100 mfrom the dose rate location.
To compare the fields of view of the naturalradionuclides with radiocaesium, we consider the source
radius contributing to 60% of ∗ 10 . The field of viewis narrower for 40K, the 232Th series and the 238U series( ≃ 4 m) than for radiocaesium (8 m). This is aconsequence of the different distributions of theradionuclides within the ground, and because higher
energy decay photons (Fig. 1) make the dominant
contribution to ∗ 10 for 40K, the 232Th series and the238
U series than for 134Cs and 137Cs. The field of view for
60% of ∗ 10 is wider for the 235U series (5.5 m)
than for the other natural nuclides. This is because of thelower energy decay photons emitted by the 235U series(typically <500 keV} – Fig. 1). It should be noted that in
the environment, the 235U series makes a minimal
contribution to the total ambient dose equivalent rate fromnatural terrestrial sources 15). This is because of its low
abundance in natural uranium (≃0.7% by mass).
The field of view for the air dose rate from natural
terrestrial sources is unlikely to change significantly
depending on the relative concentrations of 40K, the 232Th
series and the 238U series radioisotopes in the ground. Thisis because the fields of view for each of these threecomponents are similar (black, red and blue lines ingeometry are as follows. First, as the model assumes
perfectly flat land it does not account for the radiation
shielding provided by any topographic features on theland, such as slopes and mountains, or shielding byvegetation and buildings. The effect of shielding is todecrease the field of view, so the results presented here
can be considered as upper bounds for field of view insettings where shielding features are present.
The second limitation is that the model assumes aperfectly uniform distribution of the radionuclides acrossthe land surface. This approximation may be overly
simplistic if geological or soil conditions lead to different
concentrations of natural radionuclides across an area. Or
for anthropogenic radionuclides, atmospheric fallout andsubsequent radionuclide absorption and redistribution
may be quite heterogeneous, again depending on local
conditions. These source distribution effects can widen or
narrow the air dose rate field of view depending on a caseby-case basis. The reader should be aware thatheterogeneous source distributions may be important insetting the field of view at some locations.
3. Results
The field of view from natural radionuclides distributed
homogeneously within the ground and for 134Cs and 137Cs
exponentially distributed with depth (1.0 g/cm2) are
shown in Fig. 3. The graph shows the fraction of ∗ 10
at 1 m above the ground attributable to each of the sources
within a radius [m] cylindrical volume of soil below thedose rate point. The data are plotted relative to the ambient
dose equivalent rate from a 1000 m radius volume, which
is a sufficiently large range for ∗ 10 to reach its
asymptotic limit to three significant figures.

Fig. 3).

30

Figure 4. The field of view from 134Cs and 137Cs withvarying

Figure 5. The field of view from 134Cs and 137Cs atvarious heights above the ground.

.

Fig. 4 shows the effect of fallout penetration into thesoil on the field of view from 134Cs and 137Cs. The
relaxation mass per unit area is shown for the range 0.120.0 g/cm2.
is typically between 0.1-3.0 g/cm2 in thefirst year after fallout deposition, increasing to 1.07.0 g/cm2 after several years, and then in the range 2.020.0 g/cm2 for fallout deposited greater than 10 years
previously 9). When considering the source radiuscontributing to 60% of ∗ 10 , the field of view narrows
as fallout radiocaesium weathers deeper into the ground( decreases from 13.5 m to 4.5 m whenincreases
2
between 0.1-20.0 g/cm , Fig. 4).
The effect of elevation above the ground on field ofview for ∗ 10 from 134Cs and 137Cs is shown in Fig. 5.
Elevating the dose rate point changes the relative distance
between different areas of the ground and the dose rate
point, and leads to more shielding of the radiation by air.
The field of view always widens with increasing height ofthe dose rate point. It is narrow when the dose rate point
is located close to the ground (less than 1 m for 60% of∗
10 when0.01 m). It extends to over 100 m forthe highest elevations studied (100 m).
In all cases the tail of the distributions mean that 134Cs
and 137Cs at large distances makes a significant
contribution to the dose rate. Fallout more than 100 mfrom the dose rate point needs to be considered for∗
10 to reach its asymptotic limit at all dose rate
elevations above the ground.
Figs. 3-5 show that the fields of view from 134Cs and137
Cs are almost identical. This is because the dominantphotons contributing to ∗ 10 emitted by both isotopes
have similar energies (600-800 keV – Fig. 1).

4. Example Applications
4.1 Interpreting KURAMA Car and Bus Survey Data
KURAMA and KURAMA-II are vehicle-borne
radiation survey systems deployed on cars and buses
within Fukushima Prefecture and across Japan to measure
air dose rates 16) 17) 18) 19). They consist of a NaI/CsI
scintillator to detect gamma rays, a GPS unit to determine
measurement locations, a control computer, and a 3G
network connection to transmit results.
In cars, the devices are mounted either above the rearright-side door or behind the headrest of the rear seat 16) 17).
In public buses, the systems are placed above the engine
bay at the rear of the bus 19). These geometries mean thatthe systems respond differently to radiation from 134Cs
and 137Cs fallout, and to radiation from naturalradionuclides when operated in different types of vehicle.
The difference is due to differences in the fields of view
between the anthropogenic and the natural radionuclides,
and the fact that the bus engine acts as a shield. The effectis depicted in Fig. 6(a). The narrower field of view fromnatural radionuclides than from 134Cs and 137Cs means thata greater portion of the field of view from naturalradionuclides is shielded by the bus engine.
The effect bears out as a different response of the
KURAMA systems when mounted in cars and buses
between low dose rate areas, where radiation from natural
terrestrial radionuclides dominates ( ≈ 0.05 µSv/h), andhigh dose rate areas (>0.25 µSv/h) with large amounts of134
Cs and 137Cs fallout. The graph in Fig. 6(b) shows how
the ratio of the air dose rate within a car to the dose rate
above a bus engine bay depends on the level of 134Cs and137
Cs fallout in the environment. The data in Fig. 6(b)

31

(a)

KURAMAdetector

134Cs & 137Cs

Bus
engine

40K

232Th
238U

Figure 7. Using the field of view to evaluate theeffectiveness of remediation for reducing

∗

10 .

deeper into the ground. This is because the field of viewof radiocaesium narrows with deeper migration (Fig. 4)
and becomes more comparable to the field of view fromnatural radionuclides. The shielding effect of the bus
engine is therefore less important.
4.2 The Effectiveness of Land Remediation
Field of view graphs like Figs. 3-5 can be used toquickly evaluate the effectiveness of land remediation for
reducing air dose rates. Fig. 7 demonstrates the technique.
The field of view results show that 68% of the ambient
dose equivalent rate attributable to the radiocaesium
fallout comes from 134Cs and 137Cs within a 10 m areaaround the dose rate point. If the land within this area wereremediated perfectly, so that no 134Cs and 137Cs remained∗
afterwards, the component of
10 attributable toradiocaesium would decrease by 68%
It is also possible to account for the effectiveness of theremediation through the decontamination factor (DF). DF
is defined as the ratio of the caesium radioactivity in theland before and after remediation. DF values vary
between different remediation methods. For DF 20 ,5% of the radioactivity will remain in the land after
remediation, and hence the reduction in the 134Cs and137
Cs component of ∗ 10 would be 68% ∙ 100%

Figure 6. (a) The bus engine shields a greater portionof the field of view of natural radionuclides than for134
Cs and 137Cs. Shaded red and yellow volumes
illustrate natural and 134/137Cs radionuclides inrespective fields of view. (b) Ratio of ∗ 10 at the
KURAMA position within a car to within a buses, asa function of environmental radiocaesium levels.
Inset text on graph lists outdoor ∗ 10 values.
134
Cs/137Cs activity ratio is 0.57, applicable on
January 01, 2013.
were generated by PHITS simulations of car and bus
geometries placed within the half-space geometry.
In the low dose rate regime, the ratio is high as the dose
rate in the bus is lowered by the shielding of gamma raysfrom natural radionuclides by the bus engine. However, athigh dose rates radiocaesium is dominant, and its wider
field of view means that the shielding by the bus engine isless important. Thus, the ratio of the air dose rate in the
car and the bus is smaller. This effect is also seen in real
data from KURAMA operation on vehicles in Fukushima.
The ratio of the dose rates in the car and bus becomesless sensitive to the fallout levels as caesium migrates

5%64.6%.
The field of view graphs thus allow quick calculations
for the order of magnitude of reduction in a dose rate thatcan be achieved by remediation. More accurate
calculations for the effectiveness of remediation can beobtained using a specialist tool to model the land type,
topography and local area of the remediation target. An
example of such a tool is the calculation system for the32

(1996).
5) Y. Iwamoto et al. "Study on Soil Decontamination
and Dose Rate Reduction Effect", JAEA-Technology
2011-026 (2011).
6) K. Saito. “External Doses due to Terrestrial Gamma
Rays on the Snow Cover”, Radiat. Prot. Dosim.

estimation of decontamination effects (CDE) 20).
5. Conclusions
PHITS simulations were used to characterize the fieldof view from natural terrestrial radionuclides andanthropogenic cesium fallout in the environment. 134Cs
and 137Cs fallout has a wider field of view than the naturalradionuclides (excluding 235U series) due to different
source positions and characteristic gamma ray energies.
The field of view from 134Cs and 137Cs fallout narrows as
the radiocaesium migrates deeper into the ground. The
134
Cs and 137Cs field of view widens with height of the air
dose rate location above the ground.
The differences in the field of view between naturalradionuclides and of 134Cs and 137Cs can explain different
KURAMA detector responses between low dose rate andhigh dose rate areas when operated above a bus engine
bay. Field of view graphs can be used to make quick
calculations for the reduction in air dose rates before andafter land remediation.

35(1), 31 (1991).
7) K. Saito and P. Jacob. "Gamma Ray Fields in the Air
Due to Sources in the Ground", Radiat. Prot. Dosim.
58(1), 29 (1995).
8) K. Saito and P. Jacob. "Fundamental Data on
Environmental Gamma-Ray Fields in the Air due toSources in the Ground", JAERI-Data/Code 98-001(1998).
9) T. Sato et al. "Particle and Heavy Ion Transport code
System, PHITS, version 2.52", J. Nucl. Sci. Technol.
50(9), 913 (2013).
10) ICRU Publ. 53. "Gamma-Ray Spectrometry in theEnvironment" (1994).
11) K. F. Eckerman
and J. C. Ryman. "External
Exposure to Radionuclides in Air, Water, and Soil",
EPA-402-R-93-081 Federal Guidance Report No. 12,
U. S. Environmental Protection Agency (1993).
(http://www.epa.gov/radiation/docs/federal/402-r93-081.pdf, accessed 26 May 2015)12) ICRP Publ. 107. "Nuclear Decay Data for DosimetricAcknowledgements
We acknowledge fruitful discussions with M. Tanigaki,
D. C. W. Sanderson and JAEA colleagues. Calculations
were performed on JAEA's BX900 supercomputer.

Calculations", Ann. ICRP 38(3), 1 (2008).
13) NuDat2. "Software to search and plot nuclear
structure and decay data interactively. Employs datafrom the Evaluated Nuclear Structure Data File
(ENSDF)".
(http://www.nndc.bnl.gov/nudat2/,
accessed 13 May 2014)
14) Y. Namito et al. "Transformation of a system
consisting of plane isotropic source and unit spheredetector into a system consisting of point isotropic
source and plane detector in Monte Carlo radiation

References
1) ICRP Publ. 74. "Conversion Coefficients for use inRadiological Protection against External Radiation",Ann. ICRP 26(3-4), 1 (1996).
2) J. H. Hubbell and S. M. Seltzer. "Tables of X-Ray
Mass Attenuation Coefficients and Mass EnergyAbsorption Coefficients from 1 keV to 20 MeV for
Elements Z = 1 to 92 and 48 Additional Substancesof Dosimetric Interest", NISTIR 5632 (2004).
(http://www.nist.gov/pml/data/xraycoef/, accessed
26 May 2015)3) J. D. Allyson. "Environmental γ-ray Spectrometry:
Simulation of Absolute Calibration of In-Situ andAirborne
Spectrometersfor
NaturalandAnthropogenic
Sources",
Ph.D. thesis,
The
UniversityofGlasgow(1994).
(http://theses.gla.ac.uk/2028/1/1994allysonphd.pdf,
accessed 26 May 2015)4) A. N. Tyler et al. "Accounting for spatial variability
and fields of view in environmental gamma ray
spectroscopy",

J. Environ. Radioactiv. 33,

transport calculation", J. Nucl. Sci. Technol. 49(2),167 (2012).
15) UNSCEAR. "Sources, Effects and Risks of Ionizing
Radiation, 2000 Report, Volume I" (2000).
(http://www.unscear.org/unscear/en/publications/20
00_1.html, accessed 26 May 2015)16) M. Tanigaki et al. "Development of a car-borne
survey system, KURAMA", Nucl. Instrum. Methods
Phys. Res. Sect. A 726, 162 (2013).
17) M. Andoh et al. "Measurement of air dose rates overa wide area around the Fukushima Dai-ichi Nuclear
Power Plant through a series of car-borne surveys", J.

213

33

Environ. Radioactiv. 139, 266 (2014).
18) S. Tsuda et al. "Characteristics and verification of a
car-borne survey system for dose rates in air:
KURAMA-II", J. Environ. Radioactiv. 139, 260(2014).
19) M. Tanigaki et al. "Development of KURAMA-II and
its operation in Fukushima", Nucl. Instrum. Methods
Phys. Res. Sect. A 781, 57 (2015).
20) D. Satoh et al. "Development of a calculation system
for the estimation of decontamination effects", J.
Nucl. Sci. Technol. 51(5), 656 (2014).

34

Study on applicability of CdZnTe semiconductor
detector to in situ environmental radioactivity
measurement in high dose rate areas
Munehiko KOWATARI 1)* , Takumi KUBOTA 2) , Yuji SHIBAHARA 2) ,Toshiyuki FUJII2) , Koichi TAKAMIYA 2) , Satoru MIZUNO 3) , Hajimu
YAMANA 2)
1) Department of Radiation Protection, Nuclear Science Research Institute, Japan Atomic Energy Agency, 2-4
Shirakata, Tokai, Naka, Ibaraki 319-1195, JAPAN2) Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494, JAPAN
3) Nuclear Power Safety Division, Fukushima Prefectural Government, Fukushima, Fukushima 960-8670, JAPAN*kowatari.munehiko@jaea.go.jp

There have still been difficulties for decontamination and remediation works in Fukushima regions. This
article describes a series of investigation on characteristics of a small and light detector, CdZnTe
semiconductor detector to apply for in situ environmental radioactivity measurement. Less sensitivity to
gamma rays with greater than 1 MeV and low resolution of peak identification of pulse height spectra for
the CZT detector turned out to be advantageous when measuring spectrometry in regions where higher dose
equivalent rates are observed. A series of performance tests indicates that the CZT detector is the promising
candidate for verification of the effect of decontamination even in regions whose dose equivalent rates
exceed more than 40 micro Sv h-1.
Key Words:CdZnTe detector, in situ gamma ray environmental measurement, 137Cs, 134Cs,dose rate,

1. Introduction

environmental radioactivity measurement in deeply contaminated

Verification of the effect should be properly implemented after

Sv h-1 have been observed. Decontaminating radioactive materials as

decontamination works. Decrease of dose equivalent rates may not be

quick as possible is imperative for remediation and revival in thesealways proof as a successful decontamination in the areas. This isareas. There has been still difficulty in decontamination due to highbecause dosimeters could not distinguish the energy and the direction

dose equivalent rate in the atmosphere. Comparing Ge detectorsof gamma rays coming from the environment. For determining surface

generally used for in situ environmental radioactivity measurement, thedeposition densities on soil, an in situ environmental radioactivity

CZT detector has less sensitivity to gamma rays and low resolution of

measurement using gamma ray spectrometers like Ge semiconductor

pulse height spectrum. It is expected, however, that less sensitivity todetector is a quite powerful method

region where high dose equivalent rate with more than few tenth micro, besides radioactivity

gamma rays enhance the upper limit of dose equivalent rate available.

measurement in laboratory with sampling. The in situ environmental

In addition, the CZT detector is a USB-powered, small, light and easy-

radioactivity measurement also is a promising method to verify theto-use detector assembly. The measurement operation is limited in

effect of decontamination, because the method allows us to directly

high dose equivalent rate areas due to the limitation of exposure to

identify surface deposition densities of radioactive materials left on theworkers. The characteristic of the CZT detector allows to shorten

surface of interest, obtaining and interpreting pulse height spectra.

residence time in the region.

However, high dose equivalent rate due to gamma rays emitted from

A series of experiments and Monte Carlo calculations wasradioactive materials as contaminants largely affects proper

performed to evaluate specific features of the CZT detector for in situ

spectrometry using highly sensitive Ge detectors.

environmental radioactivity measurement. A peak efficiency curve

The authors investigated the applicability of a newly developed

was evaluated to convert peak areas obtained in pulse height spectra

CdZnTe semiconductor detector (CZT detector) to in situ

into surface deposition density on soil for radioactive materials of1), 2)

35

interest. Angular dependences of peak efficiency to incident gamma

anthropogenic radioactive materials like 134Cs and 137Cs in affectedrays with various energies were also evaluated for accurate

areas. Using the CZT for gamma ray spectrometry in the environment

determination of surface deposition density. In this study, special

will exclude background components inherently due to its low

attention was paid tosensitivity to gamma rays with energies greater than 1 MeV.

Cs and134

Cs. This is because these137

contaminants have been still predominant in the areas and largely

Energy dependence of peak efficiency and angular dependence ofcontributes to dose equivalent rate in the environment. Air kerma rates

peak efficiency must be evaluated in order to determine surface

from obtained pulse height spectra were estimated as well. It would be

deposition density on soil. Peak efficiency for incident gamma ray,more informative and helpful if surface deposition density on soil andN0/φ (cps (cm-2 s-1)-1), is obtained by dividing peak area of interest by

air kerma rate at the measurement point were to be obtained at the same

gamma ray fluence rate at the measurement point. Checking

time from the same spectrum. This must enhance the characteristics ofradioactive sources, such as 152Eu, 60Co and 137Cs was used for

the CZT detector for rapid and easy in situ environmental radioactivity

measurement of peak areas and simulations were performed using themeasurement and long term monitoring in deeply contaminated areas.

Monte Carlo code the EGS 4. The angular dependence of a net peakarea was also measured by the same checking sources and calculatedusing the MCNP-4C Monte Carlo calculation code. The same

2. Materials and Methods

geometry for the CZT detector was used in both EGS 4 and MCNP4C code. Almost identical relative peak efficiencies with 0 degree were

(1) CdZnTe semiconductor detector

obtained from both Monte Carlo calculation codes, applying the same
geometry.

A promising candidate CdZnTe semiconductor detector (CZT
detector) was selected for a detector used in situ radioactivity
measurement in high dose equivalent rate areas. Figure 1 shows the(2) Estimation of air kerma rate from pulse heightspectrumappearance of the CZT detector used in the study. The dimension of
the CdZnTe semiconductor is 10 × 10 × 10 mm3. All electronics
including ADC and amplifiers are assembled in the aluminum-madeGamma ray spectrometry in the environment allows us to provide

chassis depicted in the Figure 1. The CZT detector has a thin entrance

useful information, by interpreting obtained spectra. Besides

window in front of the CdZnTe semiconductor and electronics forcalculation of identified peak areas for determination of surface

signal processing and DC supply is installed behind the semiconductor.

deposition density on soil, air kerma rates at measurement points can

Between the semiconductor and the electronics, an aluminum-madebe estimated from the same spectra. Evaluating dose rate in thepartition plate was set inside the chassis.

atmosphere using the same pulse height spectra would enhance

The CZT detector has an excellent sensitivity to gamma / X rays withinformation on measurement points, help shorten staying time inenergies below 100 keV, and usually used for diagnostic purposes inhigher-dose rate areas and facilitate a long term monitoring of heavily
contaminated areas.
In this study, by using the same spectra obtained by the CZT detector,
air kerma rates at measurement point were estimated by the G(E)function method3), besides estimation of air kerma rates by measured
surface contamination densities on soil. The G(E) function method
enables us to directly determine air kerma rates from the accumulated
pulse height spectra, by applying the operator defined “G(E) function”
to obtained pulse height spectra. The method is also taken advantage
of direct determination of air kerma rates which the effect of scattered

Figure 1 appearance of the CZT detector (Kromek GR1TM )gamma ray components is included. The G(E) function for the CZT
detector was derived from the calculated responses matrix of the CZTthe medical fields. However, the CZT detector does not have enoughdetector to mono-energetic gamma rays ranging from 50 keV to 3

sensitivity to gamma rays with energies higher than 1 MeV which is

MeV as well. The EGS4 was also used for the calculation. For

asked to monitor in the guidelines regarding environmental

estimating air kerma, the fluence-to-air-kerma conversion coefficientmeasurement provided by the authorities. In the environment, there are

was taken from ICRP 74 4). Applying derived G(E) function to pulse

potentially gamma ray emitters whose gamma ray energies exceed 1

height spectrum of the CZT detector obtained in the 137Cs calibration

MeV, such as 40K (1460 keV), 208Tl (2605 keV) and so on. Gamma

field in the Facility of Radiation Standards in Japan Atomic Energy

rays from these natural radionuclides interfere identification of

Agency (JAEA), ambient dose equivalent rate in the 137Cs calibration

36

field was estimated and compared with reference value. The ambient
dose equivalent rate obtained from the CZT detector was estimated to
be 57.5 μSv h-1 and was in quite good agreement with reference value,
56.3 μSv h-1. For comparison, a preliminary field test was also
conducted in open field in JAEA where little radioactive contaminants
were left. The ambient dose equivalent rate was estimated to be 0.12
μSv h-1, from a measured spectrum obtained by the CZT detector.
Comparing with the result obtained by the conventional NaI(Tl)scintillation survey-meter (0.1 μSv h-1), estimated ambient dose
equivalent rate seems consistent.
Figure 3 angular dependence of relative net peak area togamma ray with various energies

Figure 2 measured and calculated energy dependence of peakefficiency of the CZT detector
Figure 4 comparison of pulse height spectra obtained by the
CZT detector and the Ge detector measured in JAEA, Tokai

3. Results and discussion(1) Characteristics of CZT detector for in situ

angle for higher energy gamma rays greater than 365 keV. Measured

environmental measurement

results were also found to be within 20% of those obtained at 90 degree.

Figure 2 shows measured and calculated peak areas per unit gamma(2) Field test of in situ environmental radioactivity
measurement using a CZT detector

ray fluence as a function of gamma ray energy. In the energy region
around 100 keV, a calculated peak efficiency reaches up to almost 0.9.
On the other hand, quite low efficiencies with energies greater thanFigure 4 shows the comparison of pulse height spectra obtained by1500 keV were obtained. Value for gamma ray with energy of 1460

the CZT detector and the conventional Ge detector. Both were

keV is calculated to be around 0.02. This supports that the CZT

obtained at the same plain and open field in JAEA and detectors weredetector has less sensitivity to energetic gamma ray from 40K and/or

set at the height of 1 m so that the detector axes can be vertical to ground

Tl. Value for gamma ray from 137Cs (662 keV) was obtained to be

208

surface. As expected before, pulse height spectrum obtained by a CZT

0.06 and one-tenth of conventional Ge detector used for in situ

detector was ten times lower than those obtained by the Ge detector.

environmental radioactivity measurement.

This clearly reflects the differences of sensitivity to gamma rays. Peaks

Figure 3 shows the angular dependence of a relative net peak area fordue to gamma rays due to 134Cs and 137Cs are clearly found in bothfull energy absorption to incident gamma rays with various eneries up

spectra. However there is no identified peak around 1460 keV due toto 1333 keV. In Figure 3, 0 degree corresponds to a direction of the

gamma rays from 40K in the spectrum by the CZT detector. This might

detector axis and 90 degree is a horizontal direction to the ground.

be a crucial disadvantage for natural radionuclides measurement. In

Values in the figure were normalized by those obtained at 90 degree.

contrast, this low sensitivity leads to suppressed background levels

From the Monte Carlo calculations results by MCNP-4C, relatively

when determining surface deposition densities on soil for 134Cs andhigh peak efficiencies were observed between 40 and 50 degrees for

Cs from identified peaks.

137

gamma rays with energies of 60 and 122 keV. On the other hand,

In order to demonstrate the performance of in situ environmental

almost identical peak efficiencies were obtained regardless of incident

radioactivity measurement using the CZT detector, surface deposition37

Table1 comparison of surface deposition densities on soil for 134Cs and 137Cs measured by the CZT detector
Coordinate oflocation

Location

Distance fromFDNPS (km)Measured surface deposition density
on soil at 11th March,2011(kBq m-2)
134Cs

Ohkuma-town,
Chuodai
Ohkuma-town,
Ohno station
Futaba-town,
Kamihatori

37:25:26 N
141:00:08 E
37:24:32 N
140:59:07 E
37:27:25 N
140:59:22 E

Measured surface deposition density
on soil at 11th March,2011 by Ge detector *(kBq m-2)

137Cs

134Cs

137Cs

2.7, W(1.10 ± 0.02) × 104(1.05 ± 0.03) × 104

1.40 × 104

1.50 × 104

4.4, WSW(3.29 ± 0.24) × 103(3.37 ± 0.08) × 103

4.50 × 103

5.10 × 103

5.6, NW(1.89 ± 0.13) × 103(1.88 ± 0.05) × 103

1.10 × 103

1.20 × 103* data are available on line. (http://radioactivity.nsr.go.jp/en/) Note that measurement points are NOT exact the same.
Table2 comparison of estimated air kerma rates from the same pulse height spectra by the CZT detector
Location

Coordinate oflocation

Ohkuma-town,
Chuodai
Ohkuma-town,
Ohno station
Futaba-town,
Kamihatori

37:25:26 N
141:00:08 E
37:24:32 N
140:59:07 E
37:27:25 N
140:59:22 E

Distance fromFDNPS (km)Ambient dose equivalent rate by
the conventional NaI(Tl)scintillation survey meter(μSv h-1)

Estimated air kerma
rate due to 134Cs and137
Cs at measuring date
(μGy h-1)

Estimated air kerma rate by theG(E) function method(μGy h-1)

2.7, W

45.3 ± 0.4

35.8 ± 0.5

37.1

4.4, WSW

12.9 ± 0.1

10.7 ± 0.5

14.1

5.6, NW

1.63 ± 0.02

6.11 ± 0.26

3.29

densities for 134Cs and 137Cs were measured from 27th to 28th May

and/or 1 m above the ground per unit surface deposition density of each2013 in the measurement campaign . The CZT detector was set at theradionuclide of interest , according to the measurement condition.

height of 0.7 and/or1 m in a level and open field, using a conventional

Gamma rays from 134Cs and 137Cs were taken into account in the study.

5)

tripod. The entrance window of the CZT detector was set downward.

The value of φ/ Aa depends on the migration of soil from the surface ofAmbient dose equivalent rates at measurement points were also

ground and depth profile of concentration of radionuclides in soil varies

monitored by the NaI(Tl) scintillation survey-meter and ranging

as time elapses from the initial deposition. The parameter define as a

between 0.2 and 45 μSv h . Measurement time for each point changed

relaxation mass per unit area, β (g cm-2), is used to express the verticalaccording to the dose rates and was set to 600 sec for high dose rate

distribution of radionuclides deep inside soil 1),2). In this study, β was set

areas and 1200 sec for lower dose rate areas, respectively.

to 3, in accordance with the recommendation of reference 2.

-1

Surface deposition densities on soil for Cs and Cs, Aa (kBq m ),Table 1 shows the measured surface deposition densities for 134Cs andwere determined by dividing peak areas per second Nf (cps) due to

137

134

137

-2

Cs using the CZT detector. In this table, monitoring data obtained by

gamma rays from Cs and Cs by peak efficiencies with energies ofJapanese government (http://radioactivity.nsr.go.jp/en/) were also listed.

gamma rays, Peff (cps (kBq m-2)-1). The equation (1) shows the surface

Note that monitoring data by the government were not obtained thedeposition density on soil, Aa;

exact same position. For the case of the Chuodai, Ohkuma-town, soil

134

𝐴𝐴𝑎𝑎 =

137

𝑁𝑁𝑓𝑓

𝑃𝑃𝑒𝑒𝑒𝑒𝑒𝑒

was sampled 0.3 km away from our measurement point, according to(1).

the location recorded in the monitoring campaign. Considering

The peak efficiency, Peff, for an incident gamma ray with energy of E

uncertainties accompanying measurement results and difference of the(keV) was derived in accordance with the following equation (2),sampling point, results seem quite reasonable. This also supports that

𝑃𝑃𝑒𝑒𝑒𝑒𝑒𝑒 =𝑁𝑁0 𝑁𝑁𝑓𝑓 𝜙𝜙

𝜙𝜙

𝑁𝑁0 𝐴𝐴𝑎𝑎

the CZT detector allows to properly determine surface deposition(2),

density even in high dose equivalent rate area.

where N0/φ is a net peak area for full energy absorption of incident

Table 2 shows the comparison of air kerma rates estimated fromgamma ray per unit gamma ray fluence, determined in terms ofevaluated surface deposition densities on soil and G(E) function

measurement and calculations. Nf/ N0 is the correction factor formethod from the same obtained pulse height spectra. Ambient doseangular dependence of a net peak area for full energy absorption of theequivalent rates obtained by the survey-meter are also listed for

CZT detector used and set as 1, according to the evaluation mentioned

comparison. Almost identical results were obtained in high dose

above. φ/ Aa ((cm s ) (kBq m ) ) is a gamma ray fluence rate at 0.7

equivalent rate area. On the other hand, estimated air kerma rates vary

-2 -1

-2 -1

38

References
1) Beck, H. L., DeCampo, J. and Gogolak, C. In situ
Ge(Li) and NaI(Tl) gamma-ray spectrometry for themeasurement of environmental radiation. USAEC
Report HASL-258 (New York, NY: USAEC)(1972).
2) International Commission on Radiation Units andMeasurements. Gamma-ray spectrometry in theenvironment. ICRU Report 53 (Bethesda, MD:
ICRU) (1994).
3) Moriuchi, S and Miyanaga, I., A Method of Pulse
Height Weighting Using the Discrimination Bias
Modulation. Health Phys. 12(10), 1481-1487 (1966).
4) International
Commission
onRadiologicalProtection (ICRP), Conversion coefficients for use
in radiological protection against external radiation.
ICRP Publication 74 Ann. ICRP 27(4), Pergamon
Press, London and New York (1997).
5) Shibahara, Y., Kubota. T., Fujii. T., et al. Analysis
of cesium isotope compositions in environmental
samples by thermal ionization mass spectrometry 1. A preliminary study for source analysis ofradioactive contamination in Fukushima prefecture.
J. Nucl. Sci. Technol., 51 (5), 575-579 (2014).

with methods for results in low dose equivalent rate area. The
overestimation of air kerma rate obtained by surface deposition
densities on soil might be explained by low counting rates of peak areas.
Low counting rates may lead to difficulty in identification of each peak
and their higher counting errors. Results also imply that determinationof the surface deposition density and the air kerma rate by the CZT
detector should be applied only in relatively high dose equivalent reteareas.

4. Summary
A CdZnTe semiconductor detector (CZT detector) tuned out to be a
promising candidate as a detector applied for in situ radioactivity
measurement in high dose equivalent rate areas, throughout theinvestigation by means of a series of experiments and the Monte Carlosimulation techniques. Before the field tests in Fukushima areas, theenergy dependence of peak efficiency and the angular dependence ofpeak efficiency for the CZT detector were measured using sealed
radioactive sources in laboratory. Field tests were then carried out in
JAEA and Fukushima areas. From pulse height spectra obtained by afield test, surface deposition densities on soil for 134Cs and 137Cs were
evaluated and compared with those obtained by monitoring campaign
organized by the Japanese government. Results of surface deposition
densities on soil for 134Cs and 137Cs seemed reasonable, considering
uncertainties accompanying measurement results and difference in thelocation. Using the same pulse height spectra, air kerma rates atmeasurement places were also estimated by G(E) method and fromestimated surface deposition densities on soil. Results of estimated air
kerma rates show that a reasonable air kerma rate would be obtainedeven in in regions whose dose equivalent rates exceed more than 40
μSv h-1. A series of performance tests also strongly supports theapplicability of the CZT detector to in situ environmental radioactivity
measurement for verification of the effect of decontamination works
and an easy and effective long-term monitoring in deeply
contaminated areas.

Acknowledgements
The authors thank all staff members of Hotel Matsushimaya Ryokan
in Fukushima-city for their heart-warming hospitality and continuing
support for our research project.

Funding
This research work was supported by the KUR Research Program for
Scientific Basis of Nuclear Safety.

39

Prediction of Ambient Dose Equivalent Rates
for the Next 30 Years After the Accident

Sakae KINASE1)*, Tomoyuki TAKAHASHI2), Satoshi SATO1),
Hideaki YAMAMOTO1), Kimiaki SAITO1)
1) Japan Atomic Energy Agency Tokai-mura, Naka-gun, Ibaraki
2) Kyoto University Kumatori-cho, Osaka*kinase.sakae@jaea.go.jp

To support recovery and rehabilitation in Fukushima, prediction models have been developed for ambient dose
equivalent rate distribution within the 80 km-radius around the Fukushima Daiichi nuclear power plant. The prediction
models that are based on bi-exponential functions characterized by ecological half-lives of radioactive caesium for landuse, enable Fukushima residents to obtain distribution maps of ambient dose equivalent rates for the next 30 years after
the accident. Model parameters such as the ecological half-life of the short-term component and the fractional
distribution of the short-term component were evaluated using ambient dose equivalent rates through car-borne surveys.
The ecological half-lives for the short-term component and the fractional distributions of the short-term component indeciduous and evergreen forest areas were found to be different from those in other areas. In addition, it was found that
distribution maps of ambient dose equivalent rates for the next 30 years after the accident, created by the prediction
models would be useful for follow-up of the radiological situation since they provide information on the space variationof the ambient dose equivalent rates in inhabited areas.
Keywords: ambient dose equivalent rate, ecological half-life, prediction model

1. Introduction

fractional distributions of the short-term component were re-evaluated

It is essential to establish a radiation monitoring system allowing

using ambient dose equivalent rates through car-borne surveys. In

follow-up of the radiological situation in long-term contaminatedaddition, distribution maps of ambient dose equivalent rates for the1)

areas . To assess current levels of contamination and its space andnext 30 years after the accident were created using the prediction

time distribution, radiation monitoring such as car-borne, airborne,

models in conjunction with the updated model parameters within themeasurements using survey meters has been performed after the

80 km-radius around the Fukushima Daiichi nuclear power plant.

2)

Fukushima accident in 2011 . At the Japan Atomic Energy Agency(JAEA), to assess the evolution of the long-term exposure situation

2. Materials and methods

after the Fukushima accident, prediction models have been developed
for ambient dose equivalent rate distribution within 80 km-radius(1) Radiation monitoring
Radiation measurements have been carrioud out using various

around the Fukushima Daiichi nuclear power plant3) - 5). The

mobile systems such as car-borne, airborne and simply walking on

prediction models were expressed using bi-exponential functions

the ground after the Fukushima accident2). In particular, ambient dosecharacterised by ecological half-lives -the time for half the radioactive

equivalent rates over wide areas in northeastern Japan were measured

caesium to disappear from the local environment due to natural

through a series of car-borne surveys. Eight car-borne surveys were

removal phenomena and human activites- for land-use. In the present

carried out by JAEA in collaboration with many organizations until

study, ecological half-lives of the short-term component and thethe middle of 2014: The first survey (June 4-13, 2011), the second40

survey (December 5-28, 2011), the third survey (March 13-30, 2012),

created using the prediction models. The maps were made for thethe fourth survey (from August 20 to October 12, 2012), the fifth

next 5, 10 and 30 years after the accident. To predict ambient dose

survey (from November 5 to December 10, 2012), the sixth survey

equivalent rates within living areas, corrections were made to the(from June 11 to July 19, 2013), the seventh survey (from November

initial ambient dose equivalent rates obtained using the mobile

5 to December 12, 2013) and the eighth survey (from June 23 tosystems. That is, the ambient dose equivalent rates obtained using theAugust 8, 2014). The ambient dose equivalent rates obtained using

mobile systems were corrected using the relationship of ambient dose

the KURAMA II systems in moving car were converted to thoseequivalent rates between those on roads and those around roads so as

6)outside the car . Inside the evacuation order areas, seventeen car-to be consistent with those within living areas2). On the maps relative

borne surveys were also performed under the comprehensive

to the categories in ALOS, the ambient dose equivalent rates

monitoring plan7).

including the background radiations were indicated using image
colors in 100m mesh units.

(2) Prediction models and model parameters
According to previous studies on prediction models8)-11), the3. Results and discussion

change with time in the ambient dose equivalent rate contribution
from radioactive caesium on grounds can be expressed using the(1) Model parameters
Cumulative distribution functions of the ecological half-lives of thefollowing equation:short-term component Tshort were obtained for both inside and outside
the evacuation order areas. For inside the evacuation order areas

𝑌(𝑡) = 𝑌(0) �αshort exp �+ (1 − αshort )exp �

−ln2

∙ 𝑡�

−ln2

∙ 𝑡��

TshortTlong∙

𝑘exp(−λ134 ∙𝑡)+exp(−λ137 ∙𝑡)
𝑘+1

+ 𝑌BG

consisting of the difficult to return, the restricted residence and thecancel preparation areas, the cumulative distribution functions of Tshortwere plotted in Fig. 1 (a), based on whether or not the land-use area
falls under deciduous and evergreen forest areas. On the other hand,the cumulative distribution functions of Tshort for outside theevacuation order areas were plotted for each land-use in Fig. 1 (b).

(1)

From the figures it can be stated that the model parameters in

where Y(t) is the ambient dose equivalent rate at time t; Y(0) is thedeciduous and evergreen forest areas are different from those in otherambient dose equivalent rate at time zero; αshort is the fractional

areas. In a similar fashion, cumulative distribution functions of the

distribution of the short-term component; Tshort is the ecological half-

fractional distributions of the short-term component αshort for inside

life of the short-term component; Tlong is the ecological half-life of theand outside the evacuation order areas were plotted in Figs. 2 (a) andlong-term component, 92y; λ134 and λ137 are the physical decay(b), respectively. In view of the current situation that there areconstants of 134Cs and 137Cs, respectively; k is the ambient dose

differences of human actitities among the areas, the model parameters

equivalent rate ratio of 134Cs to 137Cs at time zero, 2.7(as of March 15,

for areas where human activities occur might change.

2011); YBG is background radiation.
The model parameters such as the ecological half-lives of the(2) Distribution maps of ambient dose equivalent rates

short-term component and the fractional distributions of the short-

Figures 3 (a)-(c) show the distribution maps of ambient doseterm component were evaluated using the changes with time inequivalent rates for the next 5, 10 and 30 years after the accident.

ambient dose equivalent rates through the car-borne surveys. They

These maps provide the radiological situation based on the prediction

were obtained from the best curve fit when plotting the ambient dosemodels in conjunction with the 50th percentile model parameters. The

equivalent rates over time. To identify key parameters in the

figures indicate the ambient dose equivalent rates over 0.2 μSv/h. It

prediction models, the model parameters were categorized according

was found from a comparison with the results that the ambient doseto land-use/land-cover. The categories were made using the precise

equivalent rates decrease certainly. The ambient dose equivalent rates

land-use and land-cover map by the advanced land observing satellite

in 2015 might decrease to one fourth of those values by 2041. It is“Daichi” (ALOS)12). Eight categories were classified: water, urban,

concluded that the distribution maps of ambient dose equivalent rates

paddy, crop, grass, deciduous forest, evergreen forest and bare surface

for the next 30 years after the accident would be essential informationin ALOS.

to support the implementation of all protection strategies after the
Fukushima accident.

(3) Distribution maps of ambient dose equivalent rates
Distribution maps of ambient dose equivalent rates within the 80

4. Conclusions

km-radius around the Fukushima Daiichi nuclear power plant were

Prediction models for ambient dose equivalent rate within 80 km-

41Ecological half-life of radioactive caesium within the 80 km
radius of the Fukushima Daiichi nuclear power plant,
Online.Available:
http://www.irpa2014europe.com/wpcontent/uploads/2014/07/IRPA2014_AbstractBook_22-07-14.pdf(2014, July 14) .
5) Kinase, S, Sato, S., Sakamoto, R., Yamamoto, H., Saito, K.,
Changes in ambient dose equivalent rates around roads at
Kawamata after the Fukushima accident, Radiat. Prot.
Dosim. doi:10.1093/rpd/ncv275.
6) Tanigaki, M., Okumura, R., Takamiya, K., Sato, N.,
Yoshino, H. and Yamana, H. Development of a car-borne
γ-ray survey system, KURAMA, Nucl. Instr. Meth. A, 726,
162-168 (2013).
7) Ministry of Economy, Trade and Industry, METI measuresand requests in response to the great east Japan earthquake,
Online.Available:
http://www.meti.go.jp/earthquake/nuclear/20140527_01.
html
8) Gale, H. J., Humphreys, D. L. O., Fisher, E. M. R.,
Weathering of caesium-137 in soil, Nature, 4916, 257-261(1964).
9) Jacob, P., Meckbach, R., Muller, H. M., Meimberg, K.,
Abnahme der abgelagerten kunstlichen radioaktvitat in
stadtischer umgebung, GSF-Bericht 17/90 (1990).
10) Sprung, J. L., Rollstin, J. A., Helton, J. C., and Jow, H-N,
Evaluation of Severe Accident Risks: Quantification ofMajor Inpu Parameters, MACCS Input, NUREG/CR-4551
SAND86-1309 Vol.2, Rev.1, Part 7, Sandia National
Laboratories, Albuquerque (1990).
11) Andersson, K. G. and Roed, J., Estimation of doses received
in a dry-cntaminated residential area in the Bryansk region,
Russia, since the Chernobyl accident, J. Environ. Radioact.,85, 228-240 (2006).
12) Japan Aerospace Exploration Agency, Advanced land
observingsatellite,
Online.
Available:
http://www.eorc.jaxa.jp/ ALOS/en/index.htm(2013, July 31).

radius around the Fukushima Daiichi nuclear power plant have beendeveloped using bi-exponential functions characterised by ecologicalhalf-lives. Model parameters were obtained for each land-use. The
ecological half-lives of the short-term component and the fractional
distributions of the short-term component would be changeable byhuman activities. In addition, distribution maps of ambient dose
equivalent rates were created for the next 30 years after the accident. It
was found that the distribution maps would be useful for follow-up of
the radiological situation after the Fukushima accident. We plan in thenear future to update the prediction models using bi-exponentialfunctions.

ACKNOWLEDGEMENT
This study was conducted in a government-commissioned
research project from the Nuclear Regulation Authority of Japan.
The distribution maps of ambient dose equivalent rates for the next 5,
10, and 30 years after the accident can be created on knowledge thathas been obtained in the project.

References
1)

2)

3)

4)

ICRP, Application of the commission’s recommendations to
the protection of people living in long-term contaminatedareas after a nuclear accident or a radiation emergency,
ICRP Publication 111. Ann. ICRP 39(3) (2009).
Nuclear Regulation Authority, Monitoring information ofenvironmental radioactivity level, Online. Available:
http://radioactivity.nsr.go.jp/ja/list/560/list-1.html (2015,
August 6) (in Japanese).
Kinase, S, Takahashi, T., Sato, S., Sakamoto, R., Saito, K.,
Development of prediction models for radioactive caesium
distribution within the 80-km radius of the Fukushima
Daiichi nuclear power plant, Radiat. Prot. Dosim., 160(4),318-321 (2014).
Kinase, S, Sato, S., Takahashi, T., Sakamoto, R., Saito, K.,(a) inside the evacuation order areas.

(b) outside the evacuation order areas.

Figs. 1 Cumulative distribution functions of the ecological half-lives of the short-term component Tshort.

42(b) outside the evacuation order areas(a) inside the evacuation order areas.
Figs. 2 Cumulative distribution functions of the fractional distributions of the short-term component αshort.
“Difficult to return area”, “Restricted residence area” and “Cancel preparation area” mean “Areas where it is expected that the residents
have difficulties in returning for a long time”, “Areas in which the residents are not permitted to live”, “Areas to which evacuation orders
are ready to be lifted”, respectively.

(b) 10 years later(a) 5 years later(c) 30 years later
Figs. 3 Distribution maps of ambient dose equivalent rates after the accident.
Evaluated using the 50th percentile model parameters.

43

Part 3
Environmental radioactivity/internal exposureEffect of nitrogen and potassium fertilization
on radiocesium absorption in soybean
Naoto NIHEI1)* , Atsushi HIROSE 1) , Keitaro TANOI1) , Tomoko M. NAKANISHI1)
1) Graduate School of Agricultural and Life Science, The University of Tokyo,
1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657 JAPAN* anaoto@ mail.ecc.u-tokyo.ac.jp
Radioactive materials that were released during the nuclear accident contaminated the soil andagricultural products. It has become clear that potassium fertilization is effective for the
reduction of radiocesium concentrations in agricultural crops. However, apart from reports
about potassium, few reports have examined how nitrogen, which has a large effect on crop
growth, contributes to the radiocesium absorption. Focusing on this point, we studied theeffect of nitrogen and potassium fertilizer on the radiocesium absorption in soybean seedlings.
The concentration of radiocesium in the seed of soybean was higher in nitrogen-fertilized
plants than in plants grown without fertilizer. The radiocesium concentration in theaboveground biomass increased as the amount of nitrogen fertilization increased. But theconcentrations of radiocesium were higher in potassium-fertilized plants at high-N than inplants without added nitrogen and potassium. Further study is required to clarify the factorsthat incur an increase in radiocesium concentration in response to nitrogen fertilization.
Special care is required to start farming soybean on fallow fields evacuated after the accident
or on fields where rice has been grown before, which tend to have higher available nitrogenthan the regularly cultivated fields.
Key Words: Radiocesium, Soybean, Nitrogen, Ammonium, Potassium
concentration in soil to grow rice, approximately 25

1. Introduction
The

TohokuRegionPacific

Coastearthquake

mg 100 g-1 (dry soil) or higher. This prevention method

occurred on March 11, 2011, causing the immediateof radioactive cesium uptake was introduced because

accident at the Fukushima Daiichi power stationof recent clear results that potassium fertilization was

operated by the Tokyo Electric Power Company.

effective for reducing the radiocesium concentration inRadiocesium, the dominant nuclide released during the

agricultural crops5,6. On the other hand, some reports

accident, reached the agricultural lands in Fukushima

have suggested that nitrogen, showing a large effect on

and its neighboring prefectures and contaminated thecrop growth, promoted the radiocesium absorption7.

soil and agricultural products1,2. To guarantee the

However, only a few studies have examined how

safety of food and handling of agricultural, livestock,

nitrogen contributed the radiocesium absorption inforestry, and marine products, monitoring inspections

soybean plants as well as the relation to that ofwere established3,4. The monitoring inspection results

potassium. For the recovery and revitalization ofindicated that the ratio of soybean exceeding 100 Bq

agricultural industries, the mechanism to reduce

was high compared with that for rice and wheat

radiocesium absorption in soybean plants is an

and that the decreasing tendency of the contaminatedimportant and urgent issue to study. Focusing on thissoybean was low compared with that for rice and wheat.

point, we studied the effect of nitrogen and potassium

To revitalize agriculture, Fukushima Prefecture has

fertilizers on the radiocesium absorption in soybean

been trying to prevent radiocesium uptake by plants

plants.

kg-1

throughincreasing

theexchangeable

potassium

442. Materials and Methods
Soybean (Glycine max) was grown in Iitate Village,
Fukushima Prefecture (experiment 1). The radiocesiumof the field was approximately 13 kBq kg-1 (15-cm
depth), exchangeable potassium was 15.8 mg 100 g-1,
and pH was 6.2. Nitrogen fertilizer in the form ofammonium nitrate was applied at three levels: 0, 50,
and 100 kg ha-1 (hereafter non-N, low-N, and high-N,
respectively). We sowed the seeds for experiment 2 onJune 16, 2014 and collected the aboveground biomass
on September 2, 2014. We cultured soybean in a

Figure 2. Appearance of the laboratory test
（left; experiment 2, right; experiment 3）

greenhouse (experiment 1). For experiment 2, nitrogen
fertilizer in the form of ammonium sulfate was appliedat two levels: 0.4 and 1.3 g per 1 L pot (hereafter

3. Results and Discussion

low-N and high-N, respectively). The radiocesium

Figure 1 and 2 showed the effects of nitrogen

activity of the soil which was taken in Fukushima in
August 2012

was approximately 30

fertilizer on radiocesium concentration and those ofkBq kg-1,

base cations in aboveground part of thesoybean. The

exchangeable potassium was 13.4 mg 100 g-1 soil, andradiocesium concentration in the aboveground partpH was 6.0. The plants were grown until maturity, and(experiment 1) or the seed (experiment 2) were higher

the seed was collected. Finally, we studied the effect ofwhen grown in high-N condition than those in non-N

the nitrogen and potassium fertilization treatment on

or low-N. The concentration of the other elements wasradiocesium absorption by the soybean seedling

not affected by the nitrogen treatments. Table 1 shows(experiment 3). Nitrogen was applied as ammonium

thenitrate, at three levels: 0, 0.01 and 0.05 g per treatment

andpotassium

sulfate at high-N. The radiocesium concentration in thedays in a biotron (28°C, 16 h light). We collected theseed and the aboveground part was increased as theaboveground biomass. We used soil sourced from theamount of nitrogen fertilizer increased. We previously

same batch in Experiment 2 and 3. The radiocesium

reported that the amount of radiocesium extracted from

activities were measured using a sodium iodide
AM-300).

nitrogenconcentration was shown when treated with ammonium

soybean in a vessel (6.5 cm × 6.5 cm × 6.5 cm) for 18(Alokathethe aboveground part (experiment 3). The highest

potassium as potassium chloride at 0.03 g We cultured

counteroffertilization treatment on radiocesium concentration in(hereafter non-N, low-N, and high-N, respectively) andscintillationinfluencethe soil, which is considered to be potentially available

The

for

concentration of potassium, calcium, and phosphate inplant

absorption,wasincreasedbyammonium-nitrogen fertilization . It is reported that8

the sample was measured after acid decomposition

cesium ions are fixed to the clay mineral and, therefore,

using inductively coupled plasma-optical emission

the radiocesium adsorbed to the soil particles was

spectrometry (ICP-OES, PerkinElmer, Optima 7300).

probably not available for plants to absorb. But theionic radius of the ammonium ion is similar to that of
the cesium ion10, radiocesium ion seemed to beexchanged by ammonium ion and released from thesoil. It was found that the amount of radiocesium
extracted by ammonium-fertilizer was increased the
day after fertilization. Therefore, them the soybean wasable to absorb radiocesium.
The concentration of radiocesium in the abovegroundpart was lower in potassium-fertilized plants than that
under

Figure 1. Appearance of the field test（experiment 1）

potassium

deficientcondition(Table1).

Potassium and cesium are alkaline metals, located at45

the first group in the periodic table, and have similar

Soybean cultivation is the most important inbehavior. Potassium probably competes with cesium

Fukushima except for that of rice. To assist theduring membrane transport, thereby blocking therecovery and revitalization of agricultural industries intransport of cesium from the soil to the roots and from

Fukushima Prefecture, special care is required to selectthe roots to the shoots . However, the concentrations of

the appropriate kind of fertilizer as well as to start

radiocesium were higher in potassium-fertilized plants

cultivating soybean on fields that have lower available

at high-N than those under deficient condition of

nitrogen than the regular cultivated fields. It isnitrogen and potassium. It was suggested that whenimportant to clarify the mechanism of cesium

soybean plant is going to be grown again in theavailability in response to nitrogen fertilizers to cope

converted field or a fallow field, the uptake amount ofwith the cesium contamination in crops.

5

radiocesium is liable to increase when available
nitrogen is increased, and the potassium fertilization

(a)

(a)

1.0E+04

mg/100g20(c)

mg/100g

0.0E+00
40

0
3
2
1
0
20

(d)

10

(b)

5
0

Bq/kg

2.0E+04

400
300
200
100
0
30
20
10
0
30
20
10
0
10

mg/100g

mg/100g

mg/100g

mg/100g

Bq/kg

treatment might not be effective.

non-N

Low-N

0

High-N

Fig. 1. Radiocesium and base cation concentrationin aboveground part of the soybean plant after
nitrogen fertilization treatment (Experiment 1).
(a) radiocesium, (b) potassium, (c) calcium,(d) phosphate

(b)

(c)

(d)
Low-N

High-N

Fig. 2. Radiocesium and base cation concentrationin aboveground part of the soybean plant after
nitrogen fertilization treatment (Experiment 2).
(a) radiocesium, (b) potassium, (c) calcium,(d) phosphate46

Table 1. Radiocesium and base cation concentration in aboveground part of the soybean plant after
nitrogen and potassium fertilization treatments (Experiment 3).
K

Ca

Na

P

Bq kg-1

mg g-1

mg g-1

mg g-1

mg g-1

g plant-1

Non-N

440

21

3.3

0.09

2.0

1.6

28

Low-N

642

22

3.6

0.12

2.6

1.4

25

19

3.4

0.09

2.3

1.6

29

treatment(Control)Ammonium
nitrateHigh-N 1077

Ammonium

Chloride**weightHeight

cm

Low-N

366

24

3.0

0.09

2.1

1.6

25

High-N

686

25

3.0

0.11

2.2

1.6

26

Nitrate+Potassium

DryCs*p < 0.05, **p < 0.01 compared to the control (Dunnet's test).

4. Acknowledgment

riceThis work was supported in part by the research grant

Fukushima Dai-ichi Nuclear Power Plant accident.

for Mission Research on Sustainable Humanosphere

Scientificfrom8653-8658(2015/3).

theResearch

InstituteforSustainable

from

Fukushima
Reports

Prefecture
5,

Article

after

the

number:5) Zhu Y. G., Shaw G., Nisbet A.F., and Wilkins

Humanosphere (RISH), Kyoto University.

B.T., Effects of External Potassium Supply on
References

Compartmentation and Flux Characteristics of1) Yasunari T. J., Stohl A., Hayano R. S., Burkhart J.

Radiocaesium in Intact Spring Wheat Roots.
Annals of Botany 85, 293-298(2000).

F., Eckhardt S., and Yasunari T., Cesium-137
deposition and contamination of Japanese soils

6) Sanchez A.L., Wright S.M., Smolders E., Nayor

due to the Fukushima nuclear accident. Proc. Natl.

C., Stevens P. A., Kennedy V. H., Dodd B. A.,

Acad. Sci. USA. 108, 19530(2011).

Singleton D. L., and Barnett C. L., High Plant

2) Zheng J., Tagami K., Bu W., Uchida S.,

Uptake of Radiocesium from Organic Soils Due

Watanabe Y., Kubota Y., Fuma S., and Ihara S.,

to Cs Mobility and Low Soil K Content. Environ.

135

Cs/

137

Sci. Technol. 33, 2752-2757( 1999).

Cs Isotopic Ratio as a New Tracer ofFukushima7) Evans E. J. and Dekker A.J., Effect of nitrogen on

Nuclear Accident. Environ. Sci. Technol. 48,

cesium 137 in soils and its uptake by oat plants.

5433(2014).

Can. J. Soil Sci., 49, 349-355(1969).

Radiocesium Released

from the3) Nihei N.，“Radioactivity in agricultural products8) Nihei N., Hirose A., Mori M., Tanoi K, T. M.

in Fukushima, Agricultural Implications of the

Nakanishi T. M., Effect of nitrogen fertilization

Fukushima Nuclear Accident, Ed, Tomoko M.

onNakanishi ・ Keitaro Tanoi”, Springer, p.73-85,

Radiilogical issues for Fukushima's Revitalized

2013

Future, Springer,4) Nihei N., Tanoi K. and Nakanishi T. M.,
Inspections of radiocesium concentration levels in

47

radiocesium

absorption
In press (2015)

insoybean.

Biological Effect of Soil Sterilization on theCesium-137-Transfer to Plants* Tadatoshi KINOUCHI1, Yuki HATTORI1,2,3, Keiko FUJIWARA1, Tomoyuki TAKAHASHI1,3,
Satoshi FUKUTANI1, and Sentaro TAKAHASHI1,3
1) Kyoto University Research Reactor Institute2) SEIKO EG&G
3) Kyoto University Graduate School of Agriculture*kinouchi@rri.kyoto-u.ac.jp

In order to examine how soil microbes affect the dynamics of Cesium-137 (137Cs) between plants andsoils, different types of soils were collected at ume (Prunus mume, ‘a Japanese apricot’) orchards andpaddy fields about 50-55 km northwest from Fukushima Daiichi Nuclear Power Plant. Those soils, whichwere sterilized with gamma ray irradiation (60 kGy) or autoclave (at 121℃ for 20 minutes), were applied
to the cultivation of Radish cultivar (Raphanus sativus var. sativus). After harvesting, the concentrationof 137Cs in radishes was measured by a germanium semiconductor detector. As a result, transfer
coefficients of 137Cs to the radish cultivated in the sterilized soils were significantly higher than in thosecultivated in the non-sterilized soils. 137Cs and NH4+ released from organic matters, including soil
microbes, decomposed by sterilization would be the main source of an increased amount of 137Cs in theradish.
Keywords: Cesium, Transfer coefficient, Sterilization
1. Introduction

2. Materials and Methods
Cesium-137 ( Cs) is one of the most harmful radionuclides, which
137

were released into the environment by the Fukushima Daiichi(1) Soil samples

Nuclear Power Plant accident. Since

Cs has half-life of 30.17

Surface soil samples (0-5 cm depth) were collected at different sites,

years and is immobilized in the surface soil for a long period of time,from ume orchards and paddy fields, located about 50-55 km

137

there are concerns about a negative influence on the natural

northwest from the Fukushima Daiichi Nuclear Power Plant. The

environment and health.

Many experimental data about theume (Prunus mume, ‘a Japanese apricot’) orchard soil consisted ofenvironmental behavior of 137Cs has been reported, and mostclay loam and dry grass, and the paddy field soil was a considerably

especially, transfer coefficient (TC) is an important parameter towet kuroboku soil with slight fraction of clay. The concentrations

know the dynamics of Cs between plants and soilsof 137Cs in the ume orchard and paddy field soils were 21,000 and

137. However,1) - 3)considering the agricultural ecosystem (agro-ecosystem) in a

6,300 Bq/kg, respectively

comprehensive way, the effect of soil microbes on the Cs transfer
137

Fukushima Daiichi Nuclear Power Plant were collected and(2) Sterilizating methods
Autoclave sterilization and 60Co gamma ray irradiation were used
for sterilization of soil samples. Collected soils were put inapplied to the cultivation of radish cultivar (Raphanus sativus var.

polycarbonate containers (72×72×100 mm) by 200 g wet-weight,

sativus) with or without sterilization for evaluation of TCs.

and then autoclave sterilization at 121ºC for 20 minutes or 60 kGy

from soil to plants has not been studied in detail. Therefore,
different types of soils from agricultural fields located near48

gamma ray irradiation. The succcesful sterilization was verified byother hand, the NH4+ concentration in the paddy field soil extracts

colony formation assay.

after sterilization was 10 to 30% lower than before sterilization.
Additionally, in order to examine whether denaturation of organic(3) Cultivation experimentmatter by sterilization affects on the release of 137Cs from theRadish cultivar (Raphanus sativus var. sativus) was used in thisorganic matters, we preliminarily measured the 137Cs concentrations

study. Seeds of radish were sterilized by a sterilizing solution

extracted from the paddy field soil before/after sterilization by the(0.05% Tween 20 and 5% sodium hypochlorite), and thentreatment with hydrogen peroxide. As a result (data not shown), thegerminated on the sterilized filter paper.

137

Single samples ofgerminated radish sprouts were transferred to, and cultivated in eachCs concentration after sterilization was 30% higher than the 137Csconcentration before sterilization. Therefore, it was suggested that

aforementioned sample soil with and without sterilization,

denaturation of organic matters by sterilization did not affect on therespectively, for 45 days at 22.0ºC and 60% humidity under long-

release of 137Cs from the organic matter. At the present, it is difficult to

day condition (16 hrs light/8 hrs dark). Each sample was applied tostate precisely what is the main effect on the increase in the planta Ge semiconductor detector for Cs measurement.

available 137Cs.

137

Regardless of the kind of the soils, TCs were higher in the soils
treated with autoclave sterilization than the gamma ray irradiation.

(4) Ammonium determination
Ammonium in the sample soils was determined by a modified
indophenol method5). Photometric standards were prepared froman aqueous solution of NH4Cl, and the absorbance was measured at
660 nm by a spectrophotometer.

As indicated in other report, autoclave sterilization was more
effective for the elution of NH4-N from the soils than othersterilization techniques such as gamma ray irradiation9). The hightemperature and humidity by autoclave sterilization may cause adynamic change of the soil structure, which leads to the release of(5) Transfer Coefficient (TC)
TC is defined in this report as a ratio of the 137Cs concentration

not only NH4+ but also Cs+ from the soil.

(Bq/kg dry weight) in plant to that in soil.
4. References
3. Results and Discussions

1)

M. SAIKI, Y. OHMOMO, S. UCHIDA, H. OBATA, M.
CHINO, H. OKABAYASHI and S.YAMAZAKI, Transfer

The concentrations of Cs and the TCs were shown in Fig. 1 and 2,

Factors of Radionuclides from Soils to Agricultural Products,

respectively . The concentrations of Cs in the radish (leaves andRadioactive Waste Management Center, Tokyo, 1988 (intaproot) were increased by the sterilization. The absorbed 137Cs

Japanese).

137

4)

137

2)

concentration (3,100±25 Bq/kg) in the radish (1.1 g of dry-weght),

J. P. ABSALOM, S. D. YOUNG, N. M. J. CROUT, A.
SANCHEZ, S. M. WRIGHT, E. SMOLDERS, A. F.

which was cultured in the autoclaved paddy field soil (200 g), wasCs in the pod.

NISBET and A. G. GILLETT, “Predicting the transfer of

The TC from the autoclaved soil of the ume orchard to the radish

radiocaesium from organic soils to plants using soil

taproot was estimated to be 8.9 times higher than the TC from thecharacteristics”, J. Environ. Radioactiv., 52, 31-43, 2001.

equivalent to 0.25% of the total concentration of

137

3)

non-sterilized soil of the ume orchard.
The reason for the increase in the 137Cs-transfer from soil to

H. TSUKADA and H. HASEGAWA, “Soil-to-plant transfer
of 137Cs and other essential and trace elements in cabbage

radish by sterilization would be the increase in the concentrations ofplants”, J. Radioanal. Nucl. Chem, 252, 219-224, 2002.

NH4+, originating from organic matters decomposed by sterilization.

4)

Y. HATTORI, T. KINOUCHII, S. FUKUTANI, T.

As has been reported, the increase in the NH4+ concentrations

TAKAHASHI, K. FUJIWARA, K. IWATA, and S.

enhances the elution of Cs ions from the soil clay particles. The

TAKAHASHI, “The effect of soil sterilization on the 137Cs

decrease in the activity of nitrifying bacteria by sterilization would

transfer from soil to radish (Raphanus sativus var. sativus)”,also cause the accumulation of NH4+ in the sterilized soil and theJpn. J. Health Phys., 50, 2015 (in press).

6) - 8)following the absorption of Cs ion by plants. Therefore, the5)

E.D. Rhine, G.K. Sims, R.L. Mulvaney, and E.J. Pratt,changes of NH4+ concentration in the sample soils before/after“Improving thesterilization were measured. As shown in Fig. 3, the NH4+

ammonium in soil extracts and water”, Soil Sci. Soc. Am. J.,

concentration in ume orchard soil extracts after sterilization was

62, 473-480, 1988.

approximately two times higher than before sterilization. On the

6)49

Berthelot reaction for determining

N. YAMAGUCHI, Y. TAKATA, K. HAYASHI, S.

ISHIKAWA, M. KURAMATA, S. EGUCHI, S.
YOSHIKAWA, A. SAKAGUCHI, K. ASADA, R.
WAGAI, T. MAKINO, I. AKAHANE and S. HIRADATE,“Behavior of radiocaesium in soil-agricultural plants systems
and its controlling factor”, Bulletin of National Institute forAgro-Environmental Sciences, 31, 75-129, 2012 (inJapanese).

7)

H. TSUKADA and A. TAKEDA, “Latest agricultural
technology-Soil fertilization vol.4”, Rural Culture
Association Japan, Tokyo, pp. 1-6, 2011 (in Japanese).

8)

B. DELVAUX, N. KRUYTS, E. MAES, and E.
SMOLDERS; “Trace Elements in the Rhizosphere”, CRC
Press, London, pp. 82, 2001.

9)

C.F. ENO and H. POPENOE, “Gamma radiation comparedwith steam and methyl bromide as a soil sterilizing agent”,
Soil Sci. Soc. Am. J, 28, 533-535, 1964.
Fig. 2, Soil-to-radish transfer coefficient (TC) of 137Cs in the leaves,
taproot and total radish.

Acknowledgements

This work was supported by the Fukushima Agricultural
Technology Center, the Research Program for the Scientific
Basis of Nuclear Safety, Kyoto University Research Reactor
Institute, and the Grant-in-Aid for Scientific Research(KAKENHI) from the Japan Society for the Promotion of
Science (No. 23570272 to T.K., and No. 24510031 to T.T.).

Fig. 3, Concentrations of NH4+ in the sample soils before and aftersterilization.
Y-axis indicates concentrartion of NH4+(ppm).

Fig. 1, Concentrations of 137Cs in the leaves, taproot and total radish.
Y-axis indicates concentrartion of 137Cs (Bq/kg).

50

Radioactivity levels of vegetables, rice, fruits and drinking
water in Minami-Souma City
Kiyoshi Shizuma 1)* and Yushi Sakurai2)
1) Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527, Japan
2) NPO Corporation Furusato. 2-144-6 Takami-cho, Minami-Souma 975-0033, Japan*shizuma@hiroshima-u.ac.jp

Radioactivity concentration of 137Cs, 134Cs and 40K in vegetables, rice, fruits cultivated in Minami-Souma City after the accident ofFukushima Daiichi Nuclear Power Plant were measured and transfer coefficients from soil-to-vegetables and soil-to-unhulled rice were
determined. In 2014, 6 model farms were prepared and 15 kinds of vegetables were produced. The 137Cs and 40K concentration in soils of
paddy field and unhulled rice were measured and the transfer coefficient was determined. Japanese persimmon and chestnut sampledfrom the same tree in 2013 and 2014, and 137Cs and 40K concentration were compared for two years. Radiocesium concentration in tap
water and ground water were sampled in Minami-Souma City and the results were compared with the regulation limit. It was found that137
Cs concentration in vegetables and unhulled rice are much lower than the regulation limit (100 Bq/kg). Radioactivity concentration of137
Cs in chestnut was over the regulation limit at one sample, but those in Japanese persimmon and chestnut in 2014 were decreased about
half of radioactivity level in 2013. It is noticed that radioactive 137Cs was detected both in tap water and ground water but concentration
was much lower than the limit (10 Bq/L). Further continuous measurement is necessary to investigate the migration of 137Cs in theenvironment.
Key Words : Radiocesium in vegetable and rice, transfer factor, radiocesium in fruits, radiocesium in drinking watercompared with each other. The 137Cs concentration of soil in
paddy field and unhulled rice were measured to obtain the transfer
factor from soil-to-unhulled rice. Tap water and ground water
were collected and 137Cs concentration were measured. The
obtained data were informed to residents for understanding about
the present radioactivity levels.

1.Introduction
Four years have passed from the Tokyo Electric Power
Company (TEPCO) reactor accident occurred on March 11, 2011.
Due to this reactor accident, significant amount of radioactive
fission products 1) were released in the environment. Short-lived
radionuclides (≤ 30 d) such as 129mTe, 129Te, 131I, 132Te havedecayed out within several months, however, long-lived
radionuclides remain in the environment for long time and cause
external and internal radiation doses 2) to residents who are livingin the contaminated area.
Minami-Souma City is located at 10-40 km from the northof the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) of
TEPCO and the north-east and southern area of the city are highly
contaminated 3). Radioactive contamination on agricultural
products produced in their own town and drinking water areserious because radioactive contamination in various foods mightcauses the internal exposure. The purpose of this study is to makeclear the radioactivity level in agricultural products and drinking
water in Minami-Souma Cty. In 2014, we prepared 6 modelvegetable farms and produced 15 kinds of vegetables.
Radioactivity concentration in the soil and vegetables were
measured and transfer factors of 137Cs from soil-to-plants as well
as 40K were determined. Some fruits (Japanese persimmon andchestnut) were measured in 2013 and 2014 and the results were

2. Materials and Methods
2.1 Vegetable
Locations of the model fields, each field is typically 10 m ×
10 m, are shown in Fig.1. Typical farm (F1) is shown in Fig.2. The
fields were cultivated well and 6-9 soil samples were taken fromeach field. Soil samples were oven-dried at 80 ℃ for 24 hours,
and filtered through a 2-mm mesh sieve to remove stones andglasses. About 60 g of soil was packed into a the polystyrene
container (U9 container, 4.8 cm dia.×3.0 cm height).
Fig.1 Test farms F1-F6 in Minami-Souma City51

2.2 Rice
Since the monitoring of 137Cs concentration in riceproduced in 2011 in Fukushima Prefecture exceeded the foodsafety limits, rice production were restricted 5) in Fukushima
Prefecture.. Only rice produced at test paddy filed were permitted
for monitoring. In the present work, measurement ofradionuclides in soils of five paddy fields (P, Y, N, E, D) shown in
Fig. 5 are conducted in August 2014. Rice was produced only at
the paddy field D. Seven soil samples were taken around the rice
stubbles and the unhulled rice were directly sampled from thehead of the rice. An example of rice stubble and unhulled rice areshown in Fig. 6. Unhulled rice and soil samples were oven-driedat 80℃ for 24 hours. Soil samples were grind into powder under
2mm and about 40 g of soil was taken into a U9 container for
gamma-ray measurement. The unhulled rice of about 22 g werepressed into the container for the measurement.

Fig.2 Typical test farm F1.
Gamma-rays were measured with a low-background Ge detector(Seiko EG&G, GEM-110225). The detection efficiency of the Ge
detector was determined using nine nuclide mixed activity
standard volume sources (MX-033, Japan Isotope Association).
Radioactive concentration were determined for 137Cs, 134Cs and40
K. Produced vegetables are mini-tomatoes, potatoes, kidneybeans, garlic, onions, eggplant, pimento, cucumber, chinese
chives, mulukhiya, pumpkins, sweet potatos, chinese cabbages,
Japanese radish and welsh onions. Some examples are shown in
Fig.3. They were harvested from July to November. Vegetables
were not dried, but fresh samples were cut into fine pieces, andpacked in the U9 container for the gamma-ray measurement.
Typical gamma-ray spectra of cucumber produced at F1 field areshown in Fig. 4.

Fig.5 Paddy field in Minami-Souma City. Rice was produced
only at the paddy field D.

Fig.3 Vegetables produced at test farm F5.

Fig.6 Rice stubble and soil (left) and unhulled rice (right).
2.3 Japanese persimmon and chestnut
Japanese persimmon and chestnut were sampled fromthe same trees for two years 2013 and 2014. Locations of trees areshown in Fig.7 and examples of fruits are shown in Fig.8. Freshof fruits were cut into a small pieces and pressed into a U9container for gamma-ray measurement.
Fig.4 Gamma-ray spectrum of cucumber produced at test farm F1

52

low.

Fig.9 Sampling locations of 6 tap water (T1-T6) and 11 groundwater (G1-G11) in Minami-Souma City.
Table 1 Radioactive concentrations of 134Cs, 137Cs and 40K in soilof test farms F1-F6.

Fig.7 Locations of Japanese persimmon (P1-P3) and chestnut(C1-C3) in Minami-Souma City.

radioactivity. In the present work, the transfer factor was defined
as follows,

Fig.8 Typical Japanese persimmon and chestnut.
2.4 Tap water and ground water
Tap water in Minami-Souma City are supplied from threewater purification plants (Ushigoe plant, Ohtani plant andYagawara plant). Water sources of three plants are ground water.
In addition to public tap water, a boring well is equipped privately
to supply groundwater. Sampling locations of tap water (T1-T6)
and ground water (G1-G11) are shown Fig. 9. Sample water weretaken into a 1-L polystyrene bottle. One litter of water measured
correctly with a mass-flask was dried up on a heat plate covered
with a Teflon sheet kept at 100 ℃ for about 6 hours 6) The dried
sheet was folded into a size of 15 mm dia.× 40 mm length for
gamma-ray measurement with a well-type Ge detector.

TF =

137

Cs (Bq/kg − fresh weight ) in plant
Cs (Bq/kg − dry weight ) in soil

137

The TF 7, 8, 9) is normally defined as the ratio of radioactive
concentration (Bq/kg) of the dry weight of plant to that of the dryweight of soil. In some cases, the radioactive concentration of the
fresh weight is used 9). Fresh weight to dry weight ratios are also
given in IAEA-TRS-472 8). Since the purpose of the present work
is to know whether the radioactive concentration in plant is safe
compared to the Japanese regulation limit of food, the radioactive
concentration in fresh weight of plant was used. In the present
vegetables, the ratio of dry weight to fresh weight were typically
5 %.
The TF of 40K was also determined in the same way as 137Cs.
An example of TF for each vegetables produced at the test farmF1 is shown in Fig.10. The TFs of 137Cs for vegetables are about0.001 and those of 40K are about 0.2. Average concentration of137
Cs and 40K and their TFs for test fields F1-F6 are given in Table
2. It is shown that the 137Cs concentration in fresh vegetables areranged 1.2-2.8 Bq/kg, which is much lower than Japanese foodregulation limit of 100 Bq/kg. The 40K concentration were 68-128
Bq/kg and TF were 0.166-0.287 which were much higher than

3. Results and Discussion
3.1 Vegetables
Radioactive concentration of 137Cs, 134Cs, 40K and the ratio
134
Cs/137Cs in soil for six test farms are given in Table 1
Concentration of 137Cs in soil ranged in 791–1909 Bq/kg at July
2014. The ratio of 134Cs/137Cs was about 0.34. Concentration of
K were ranged in 391-565 Bq/kg. Radioactive concentration of
Cs and 40K in vegetables produced at six test farms are
determined. It was hard to detect 134Cs in vegetable because of its
40

137

53

Table 3 Radioactive concentration of 137Cs, 134Cs and 40K in paddy
field P-D.

Table 4 Transfer factor (TF) of 137Cs and 40K from soil-to-unhulled
rice in the paddy field D in 2014.

Fig.10 Transfer factor of 137Cs and 40K for fresh vegetables in thetest field F1.

FDNPP are reported as follows; Endo et al. 13) reported as 0.0060.013 for polished rice and 0.019-0.026 for unhulled rice (ear) in
2011. Fujimura et al.14) reported the TF from pot experiment as
0.011 in 2011 and 0.0061 in 2012 for brown rice. They also
reported from their paddy field work as 0.0008-0.17 in 2011.
Ohmori et al.15) reported as 0.0008-0.01in 2011. According to ourexperience, the 137Cs concentration in rice in husk decrease to halfin unpolished rice, decrease to 1/4 in polished rice and finallydecrease to 1/8 in washed rice. The present result of TF for 137Cs
is in agreement with the recent reports.

Table 2 Average concentration of 137Cs and 40K in vegetables andtransfer factors

those of 137Cs in 0.0009-0.0018.
Tsukada et al. 8) reported that stable potassium content insoil and uptake of 137Cs and stable Cs show negative correlation.
Tagami and Uchida 11) reported that the behavior of 137Cs and 40K
are different in giant butterbur and field horsetail. In the present
work, stable potassium amount in the soil were not measured, but
40
K was easily detected from the gamma-ray measurement. The
correlation of radioactive concentrations of 40K and 137Cs wasinvestigated in this work. Correlation coefficients was +0.365,
which indicates positive weak correlation between 137Cs and 40K
concentrations. Among 15 kinds of vegetables, mulukhiyas andchinese chives are relatively high concentration of 137Cs as well as
40
K compared with other vegetables,

3.3 Japanese persimmon and chestnut
Radioactive concentration of 137Cs, 134Cs and 40K for
three Japanese persimmon and chestnut in 2013 are given in Table
5 and those values harvested in 2014 are given in Table 6. The
results are also shown in Figs. 11 and 12. In the case of 2014, the137
Cs concentration were ranged in 3.3-33.4 Bq/kg in Japanesepersimmon and 19-156 Bq/kg in chestnuts. In the case of chestnut,
it is noticed the 137Cs concentrations exceeds the Japanese foodregulation limit in the southern area (Odaka area) in the city. The
40
K concentration was ranged in 32-79 Bq/kg for the persimmon
Table 5 Radioactive concentrations of 137Cs, 134Cs and 40K in
Japanese persimmons and chestnuts harvested in 2013.

3.2 Rice
Radioactive concentration of 137Cs, 134Cs, 40K and the ratio
134
137
Cs/ Cs for five paddy fields are given in Table 3. The 137Csconcentration are ranged in 824–1102 Bq/kg and the 40K
concentration are in 394-666 Bq/kg at August 2014. Since rice
was cultivated only at the paddy field D, the transfer factor of soilto-plant for 137Cs and 40K were determined as given in Table 4. TF
are 0.011±0.001 for 137Cs and 0.071±0.004 for 40K, respectively.
The transfer factor of 137Cs from soil to polished rice wasreported as 0.0016 by Tsukada et al.8) in 2005 and 0.003 by
Komamura and Tsumura12) in 1994. The radioactive 137Cs of their
TF were due to global fallout in 1950-1980 and also Chernobyl
reactor accident in 1986. The transfer factor after the accident ofTable 6 Radioactive concentrations of 137Cs, 134Cs and 40K in
Japanese persimmons and chestnuts harvested in 2014.

and 134-242 Bq/kg for chestnut. No difference in the area of thecity was observed in the case of 40K reflecting no relation to the54accident of FDNPP ,The concentration of Japanese persimmon and chestnut in2014 were decreased to about half of those in 2013 for the same
trees, nevertheless the 137Cs concentration in soil around the routeof the trees supposed to be almost constant. Such results arereported as ageing16) for agricultural products reflecting thechemical form of 137Cs compound changed to insolubility form
and uptake from soil to plants decrease. Further survey of the 137Csconcentration in these fruits is needed to clear the uptake process.

The radioactive concentration of 137Cs in tap water wereranged in 4.4 -13.4 mBq/L and 0-27 mBq/L in ground water. It isnoticed that the 137Cs concentration level both in tap water andground water are about 1/400 of the Japanese drinking water
regulation limit of 10 Bq/L. A background sample prepared fromthe tap water supplied to Hiroshima University was examined but
137
Cs was not observed. The radioactive 137Cs was detected inground water, however, 137Cs was not detected in the southern area,
Nakaohta, yagawara, and Katakura in Minami-Souma City.
Ohta et al.17) reported a prediction of ground watercontamination of 137Cs and 131I in the Kanto district after the
FDNPP accident. Based on the estimated 137Cs migration rate of
0.6 mm/y, they predicted that contamination of ground water by
137
Cs is not likely to occur in Kanto district. Since the soil layer ofthe Minami-Souma City is different from Kanto district, further
migration model estimation and continuous monitoring of 137Csconcentration in ground water in this area are needed to clarify theground water radioactive contamination of the ground water.

Fig.11 Comparison of the 137Cs concentration in Japanesepersimmon obtained in 2013 and 2014.

Fig.13 137Cs concentration in tap water for 6 samples andrelated water purifying plant.

Fig.12 Comparison of the 137Cs concentration in chestnut obtainedin 2013 and 2014.
3.4 Tap water and ground water
The 137Cs concentration in tap water and ground water are
given in Table 7 and also shown in Figs. 13 and 14.
Table 7 Radioactive concentration of 137Cs in tap water andground water in 2014.

Fig.14 137Cs concentration in tap water for 6 samples andrelated water purifying plant.
4. Conclusion
Six model vegetable farms were prepared and 15 kinds ofvegetables were produced in Minami-Souma City in 2014.
Radioactivity levels in the soil and fresh vegetables were
measured and transfer factors of 137Cs and 40K from soil-to-plant

55

K. Shizuma, S. Hamanaka, X. Q. Wen, K. Iwatani and H.
Hasai, A method for measuring accurate radon
concentration in water by means of gamma-ray
spectrometry. Nuclear Instrum. Methods in PhysicalResearch A410, 309-313 (1998)
7) C. Myttenaere, Absorpyion of radiocaesium by flooded
rice: relative importance of foods and shoot base in thetransfer radioactivity. Plant. Soil. 36 (1) , 215-218 (1972)
8) Tsukada, H. Hasegawa, H. HIsamatsu, S. Yamasaki, S.
Transfer of 137Cs and stable Cs from paddy soil to polishedrice in Aomori, Japan. J. Environ. Radioact. 59, 351-363(2002a)9) IAEA, Handbook of Parameter Values for the Predictionof Radionuclide Transfer in Temperate Environments.
Technical Report Series (TRS) No.472, Appendix I.
International Atomic Energy Agency, Vienna (2010).
10) M. Brambilla, P. Fortunati, F. Carini, Foliar and root uptakeof 134Cs, 85Sr, and 65Zn in processing tomato plants(Lycopersicon esculentum Mill). J. Environ. Radioact. 60
351-363 (2002)
11) K. Tagami and S. Uchida, Effective half-lives of 137Cs ingiant butterbur and field horsetail, and the distributiondifferences of potassium and 137Cs in aboveground tissue
parts. J. Environ. Radioact. 141, 138-145(2005).
12) M. Komamura and A. Tsumura, The Transfer Factors ofLong-lived Radionuclides from Soil to Polished Rice
Measured by ICP-MS. RADIOISOTOPES 43, 1-8 (1994).
13) S. Endo, T. Kajimoto,K. Shizuma: Transfer coefficient soil
to rice plant of 134Cs and 137Cs deposition due to Fukushima

were determined. The transfer factor of the fresh vegetables were0.0013 in average. Rice was produced in a paddy field and transfer
factor of 137Cs and 40K from soil- to-unhulled rice were
determined. The transfer factors were 0.015 and 0.071 for 137Cs
and 40K, respectively. Japanese persimmon and chestnut were
measured for the same tree in 2013 and 2014. It was observed the137
Cs concentration in these plants in 2014 were decreased from2013 due to ageing effect. The 137Cs concentration in vegetable,rice and Japanese persimmon are much lower than the Japanesefood regulation limit of 100 Bq/kg. Tap water of 6 samples andground water of 7 samples were collected and the 137Csconcentration 0-27 mBq/L were observed. The 137Cs level indrinking water are much lower than the drinking water regulation
limit of 10 Bq/L.

6)

Acknowledgement
We deeply appreciate Messrs. Mitsuyoshi Sato, Yuji Shiga,
Tsunekiyo Hanzawa, Masayuki Suzuki for kindly offering model
farms. We also deeply appreciate Messrs. Minoru Yamada,
Masayuki Suzuk, Kiyoshi Tateyama, Narufumi Sugi, Toshinori
Monma, Nobuo Shiga for offering Japanese persimmon andchestnut. We also thank to Messrs. Yuji Shiga, Masayuki Suzuki,
Matsuoka Kensetsu, Akiko Takahashi, MItsuyoshi Sato, Toyoaki
Horiuchi, Kazuo Endo, Kazuo Monma, Masakazu Sugi forkindly offering water samples.
References
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estimation. J. Environ. Radioact. 111, 18-27 (2012)
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Radioact. 110, 84-89 (2012)3) T. Kajimoto, S. Endo, T. Naganuma, K. Shizuma,
Distribution of radioactivities 137Cs and 134Cs in river waterand bottom sand for major rivers at Minami-Souma City in
Fukushima. Proceedings of International Symposium on
Environmental monitoring and dose estimation of residents
after accident of TEPCO’s Fukushima Daiichi Nuclear
Power Stations. pp. 96-100 (2013) (KURRI).
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pdf (in Japanese)5) Limit with product of the rice in 2012, Nuclear regulatory
agency, www.nsr.go.jp/archive/nsc/ad/pdf/20120405_1.pdf
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116 , 59-64(2012).
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T. Kobayashi, K. Yoshioka, Y. Ueda, Accumulation of
137Cs by rice grown in four types of soil contaminated by
the Fukushima Dai-ichi Nuclear Power Plant accident in2011 and 2012. J. Environ. Radiat. 140 , 59-64 (2015).
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accumulation among rice cultivars grown in the paddy fieldin Fukushima Prefecture in 2011 and 2012. J. Plant Res.
127, 57-66 (2014).
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Frissel, Impact of aging and weatherconditions on soil-toplant transfer of radiocesium and radiostrontium. J.
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K. Takamiya, H. Yoshinaga, H. Mizuochi, T. Igarashi,
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The amount of 137Cs deposition and transfer ratioof 137Cs to wild edible-wild-plants after theaccident at TEPCO's Fukushima Daiichi Nuclear
Power Station
Yoshiyuki Kiyono1)*, Akio Akama1)
1) Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba, Ibaraki, Japan*kiono@ffpri.affrc.go.jp

Using the data published by the government, we determined the relationship between the amount of 137Cs
deposition to the ground surface by the accident of Fukushima Daiichi Nuclear Power Station and 137Csconcentration in the edible portion of 12 wild edible-wild-plant species 2–3 years after the accident. The
relationship was approximated by power equations. The equations were statistically significant for the 12
species combined and for each species except Laportea cuspidata. The relationships differed among
species. For example, the 137Cs concentration was high in Eleutherococcus sciadophylloides, medium in
Aralia elata, Pteridium aquilinu, and Aralia cordata, and low in Petasites japonicus (leaf) and Hosta
sieboldiana to the same amount of 137Cs deposition. Using the equations as prediction models, 137Csconcentrations in the edible portion of each plant species and their transfer ratios (TRs) of 137Cs were
calculated when the amount of deposition was 10, 60 and 300 kBq m-2, respectively. The 137Csconcentrations of 11 species increased and the figures of TR of 10 species reduced as the amount ofdeposition increased. However, the figures of TR of Eleutherococcus sciadophylloides appeared scarcely
to change. This species probably has a mechanism of 137Cs absorption different from the other species andincreased absorption in proportion to the amount of deposition with respect to the range of data.
Keyword: aggregated transfer factors (TFag) of 137Cs, Eleutherococcus sciadophylloides, TEPCO's
Fukushima Daiichi Nuclear Power Station
plant species after the FDNPS accident (Note that samples

1 Introduction
The accident at TEPCO's Fukushima Daiichi Nuclearof cultivated edible-wild-plant species were not used in thisstudy). This paper reports the outline of the results. This study

Power Station (hereafter referred to as the FDNPS accident)

was implemented using the fund of Foresry Agency and JSPS

was the serious radioactive contamination accident first

KAKENHI Grant Number 15K07496.

occurred in the region where citizens gather a wide variety ofedible wild plants. The radiocesium concentrations of plant
body were nearly proportional to the air dose rates 1) and2 Materials and methods

edible wild plants are no exception . Since case studies are2)

insufficient, difference of contamination among plant species(1) The amount of 137Cs deposition to the ground surface by

was little known. Local governments like prefecture havethe FDNPS accident

monitored radiocesium concentrations in agricultural crops
and the considerable amount of data were published. We used

In most data of the local governments’ monitoring, thethe data in Fukushima Prefecture to analyze the relationships

locality of wild edible-wild-plant sample was shown in the

between the amount of 137Cs deposition to the ground surface

unit of city, town, or village. Therefore, the amount of 137Cs

and 137Cs concentration of the samples of wild edible-wild-

deposition to the ground surface by the FDNPS accident was57

estimated by reading the maximum and minimum amount of(3) Regression analysis

deposition classes (Fig. 1) and averaging them for each unit in
Fukushima Prefecture in the results of the airborne monitoring
survey of

We used the 2008 version of the Ekuseru-Toukei software

Cs by Ministry of Education, Culture, Sports,(Social Survey Research Information Co., Ltd., Tokyo, Japan)

Science and Technology and converted to those on November

for approximating the relationships between the amount of

16, 2012 3).

137

137

Cs deposition to the ground surface and radiocesium

contamination in the edible portion of wild edible-wild-plant
species.

(2) Radioactive contamination of wild edible-wile-plants
No particular difference was found in between 2013 and2014 about the radioactive contamination data of wild edible-

3 Results and discussion

wild-plants reported by Fukushima Prefecture and compiled
by Forestry Agency (http://www.rinya.maff.go.jp/j/tokuyou/(1) The radiocesium contamination in the edible portion of

kinoko/kensakekka/fukusimaken.html). We combined 2013–

wild edible-wild-plant species

2014 data of 137Cs concentration of 12 plant species and 685
samples. When the concentration was less than the detection

The relationship between the amount of 137Cs deposition tolimit (2.3–9.4 Bq f-kg-1), we used the detection limit as thethe ground surface and 137Cs concentration in the edible

measured concentration. Number of samples of each species

portion of 12 wild edible-wild-plant species after the FDNPS

was between 16 and 121. Some of radiocesium might haveaccident was approximated by power equations (Fig. 2). The

derived from the past. The

equation was statistically significant in the dataset of total 12

Cs in natural ecosystems derived

137

from historical nuclear tests and the Chernobyl nuclear

species (P < 0.0001) and that for each species (P < 0.0344)

accident were neglected.

except Laportea cuspidata (P = 0.5054), this species had arelatively narrow range of the amount of 137Cs deposition. The
relations differed among species. The 137Cs concentration washigh in Eleutherococcus sciadophylloides, medium in Aralia
elata, Pteridium aquilinu, and Aralia cordata, and low inPetasites japonicus (leaf) and Hosta sieboldiana to the sameamount of 137Cs deposition. The tendency of low 137Csconcentration of Petasites japonicus (leaf) was also reported
in Kiyono & Akama 2) as Petasites japonicus (leaf) <Hydrangea

petiolaris,

Schizophragma

hydrangeoides,

Eleutherococcus sciadophylloides.
Since the values of concentration at the detection limit wereused for some low contaminated samples in this study,
predicted values by the equations in Fig. 2 may be larger than
the true values for low contaminated samples.
(2) Transfer ratio (TR) of 137Cs
Using the equations in Fig. 2 as a prediction model, 137Csconcentrations of edible portion of each plant species werepredicted (Table 1). The 137Cs concentrations of 11 species
Fig. 1 The amount of Cs deposition to the ground surface by theincreased as the amount of deposition increased. Their ratio ofaccident at TEPCO's Fukushima Daiichi Nuclear Power Station

137

Ministry of Education, Culture, Sports, Science and Technology

deposition to the ground surface was calculated as transfer

137

Cs concentration in plant sample/the amount of 137Cs

and converted to those on November 16, 2012 (Ministry ofratio (TR) following the aggregated transfer factors (TFag) 4) of

Education, Culture, Sports, Science and Technology, 2013)

137

Cs when the amount of deposition was 10, 60 and 300 kBq

m , respectively. The figures of TR of 10 species reduced as
-2

58

137

Cs deposition increased. The figures of TR ofamount of radiocesium deposition and concentration in plant

Eleutherococcus sciadophylloides was much greater than theis considered to change chronosequentially by various reasons

other species and appeared scarcely to change. This species

such as radioactive decay, the movement of radiocesium inprobably has a mechanism of137

Cs absorption different fromthe ecosystem. By continuing the monitoring by thethe other species and increases absorption when the amount ofgovernments and appropriate methodology improvement, we

deposition increased in between 10 and 300 kBq m-2.

will be able to detect the trend of the relation between the

Regarding a taxonomic group (Table 1), 3 species ofamount of radiocesium deposition and its concentration in

Araliaceae including Eleutherococcus sciadophylloides had

plant body. However, the amount of 137Cs deposition per unit

not signifcantly higher TRs than the other 9 species of theland area widely different even in the same municipality (Fig.

different families (P = 0.40, ttest was done using figures of1). The accuracy of the present predicted values depends on

Cs TR when 60 kBq m , the same shall apply hereinafter).

uncertainties of the models that are based on the average

Between 9 species of Angiospermae and 3 species ofamount of the maximum and minimum deposition classes in

137

-2

each municipality.

Pteridophyta, no significant difference was found (P = 0.38).
Butkus & Konstantinova 5) found that a fern, Dryopteris filix-

As shown in Fig. 2, 137Cs concentrations of Petasites

mas was more contaminated than the grass species in the sitejaponicus (leaf) and Hosta sieboldiana were mostly far lesscontaminated by Chernobyl nuclear power plant accident

than 100 Bq f-kg-1 even in the sites where the amount of(April, 1986). A fern, Osmundastrum cinnamomeum var.

deposition was large. Determining the range of amount offokiense was found the most contaminated plant on a freshradiocesium deposition where the radiocesium concentration

weight basis in the FDNPS accident . However, as shownin plant body is below the standard level will be useful as anin Table 1, 3 fern species: Matteuccia struthiopteris,

information for making a decision for lifting shipping

2)

Pteridium aquilinum, and Osmunda japonica did not show

restrictions of wild edible-wild plants. It should be done based

significantly higher concentrations than the other species.

on the data like in Fig. 2 and with considering 134Cs

Generalizing "fern has high concentration" is not correct. Life

concentrations.

form is a kind of classification of living things based on theirfunction and morphology etc. as a result of adaptation to the

4 Challenges in the futureenvironment. Between 3 species of deciduous tree and 9
species of deciduous perennial herb, no significant difference

The locality of wild edible-wild-plant sample has so far

was found (P = 0.39). However, life form is sometimes

been shown in the unit of municipality in most local

influential to radioactive contamination of edible-wild-plant.

governments’ monitoring. Collecting higher spatial resolution

Edible-wild-plants with holdfasts (e.g., some lianas) are moredata, e.g., recording locality at the section of municipality

highly contaminated for a given air dose 2).

level, or by latitude/longitude, will reduce uncertainty of theTopography where the edible-wild-plant is growing is also

estimated amount of active cesium deposition models in Fig. 2

influential to radioactive contamination of edible-wild-plant.

and improve accuracy of predicted values of radiocesium

Plants growing at a lowlying site (where surface water andconcentration.

groundwater flow, such as valley bottoms and small hollows)

methodology to monitor radioactive materials in plants;

are at particularly high risk of dangerous contamination .

development of methodologies to predict radioactive material

2)

Challenges

includeimprovementofHarvesting season may also be influential to radioactive

concentration; and development of simplified methodologies

contamination of edible-wild-plant. The 137Cs concentration of

to lift shipping restrictions for wild edible-wild plants.

plant was high in young leaf in spring and reduced as the leaf
biomass grew large 6, 7). Petasites japonicus (leaf) and

References

Elatostema umbellatum are edible-wild-plant that mainly stem

1) Forestry Agency, “About the results of survey on theis edible. They are usually harvested after stems grow large

plant species using the monitoring results for special forest

distribution of radioactive materials in forest (the second
report)”. Press release, December 27, Forestry Agency,2011.
http://www.rinya.maff.go.jp/j/press/hozen/111227_2.ht
ml (in Japanese)

products based on radiocesium tests for food that were2) Kiyono Y, Akama A, “Radioactive cesium contamination

conducted by the governments. The relationship between theof edible wild plants after the accident at the Fukushima

and it may be a reason that the concentrations of them are low.
In this study, we showed the possibility of estimating thedifference in 137Cs contamination among wild edible-wild-

59

Environmental Sciences, 31 ， 75–129, 2012 (inDaiichi Nuclear Power Plant”, Japanese Journal of Forest

Japanese)

Environment, 55(2), 113–118, 2013

3) Ministry of Education, Culture, Sports, Science andTechnology, “About ①the measurement result of the
6th aircraft monitoring and ② the measurement resultof aircraft monitoring out of range 80 km fromTEPCO's Fukushima Daiichi Nuclear Power Station”.
1st
March
2013.
Press
releasehttp://radioactivity.nsr.go.jp/ja/contents/4000/3710/24/
1305820_20110506.pdf (in Japanese)5) Butkus D, Konstantinova M, “Studies of 137Cs transfer insoil-fern system”, Journal of Environmental Engineeringand Landscape Management, XIII(3), 97–102, 2005
6) Bunzl K, Kracke W, “Seasonal variation of soil-to-planttransfer of K and fallout 134, 137Cs in peatland vegetation”,
Health Physics, 57(4), 593–600, 1989

7) Rantavaara A, Vetikko V, Raitio H, Aro L, “Seasonalvariation of the 137Cs level and its relationship withpotassium and carbon levels in conifer needles”.
Science of the Total Environment 441, 194–208, 2012

4) Yamaguchi N, Takata Y, Hayashi K, Ishikawa S, Kuramata
M, Eguchi S, Yoshikawa S, Sakaguchi A, Asada K,
Wagei R, Makino T, Akahane I, Hiradate S, “Behavior ofradiocesium in soil-plant systems and its controlling
factor”, Bulletin of National Institute for Agro-Fig. 2 Relationship between the amount of 137Cs deposition to the ground surface by the accident the accident at TEPCO's

Fukushima Daiichi Nuclear Power Station and 137Cs concentration in the edible portion of 12 wild edible-wild-plant
species 2–3 years after the accident.

60

Table 1 Predicted 137Cs concentration in the edible portion and 137Cs transfer ratio to edible portion of 12 wild edible-wild-plant
species 2–3 years after the accident at TEPCO's Fukushima Daiichi Nuclear Power Station.
Predicted 137Cs concentration （Bq fresh-kg-2）
Species

FamilyTracheophyta

Sansho10 kBq m-2

60 kBq m-2

300 kBq m-2

410.000536

0.000262

0.000138

1888

0.005753

0.006032

0.006294

Taranoki

27

71

0.000894

0.000443

0.00023510180.000521

0.000167

0.000060

56

70.000504

0.0001030.000025

6

16

39

0.000623

0.000272

0.000129

7

11

17

0.000725

0.000188

0.000056

6

15

34

0.000616

0.000253

0.0001145--0.000500--

Asparagaceae

5

6

-

0.000469

0.000101-

Onocleaceae

8

14

25

0.000767

0.000239

0.000084

5

10

17

0.000517

0.000160

0.000056

7

23

70

0.000657

0.000382

0.000234

60 kBq m

300 kBq m

5

16

58

362

9
5

Deciduous tree

Koshiabura
Araliaceae

Aralia cordata
Udo

Petasites japonicus (leaf)
Fuki

P. japonicus (flower stalk)Fuki (fukinoto)

Asteraceae

Momijigasa

Elatostema umbellatum
Uwabamiso

Deciduousperennial herb

Urticaceae

Miyamairakusa

Hosta sieboldiana
Oobagiboshi

Matteuccia struthiopteris
Kusasotetsu

Pteridium aquilinum
Warabi

Osmunda japonica
Zenmai-2

Angiospermae

Parasenecio delphiniifolius

Laportea cuspidata-2

10 kBq m
Rutaceae

Eleutherococcus sciadophylloides
Aralia elata

Cs deposition amountCs deposition amount-2

Zanthoxylum piperitum

Predeicted 137Cs transfer ratio （m2 kg-1）
137

137

Life form

Dennstaedtiaceae

Pteridophyta

Osmundaceae

61

Examination of Iodine-131 Concentrations inFood and Drink in the Early Phase after the
Accident
Masaki Kawai1*, Nobuaki Yoshizawa1, Sachiko Hirakawa1, Kana Murakami1,
Mari Takizawa1, Osamu Sato1, Shunji Takagi1, Hirokazu Miyatake1,
Tomoyuki Takahashi2, Gen Suzuki31) Mitsubishi Research Institute, Inc.: 2-10-3, Nagata-cho, Chiyoda-ku, Tokyo2) Kyoto University Research Reactor Institute: Asashironishi 2-chome, Kumatori-machi, Sennan-gun, Osaka3) International University of Health and Welfare Clinic: 2600-6, Kitakanemaru, Otawara-city, Tochigi*makawai@mri.co.jp

Radioactivity concentrations in food and drink, represented herein by water and vegetables, have beenmonitored continuously since the Fukushima Daiichi Nuclear Power Plant accident occurred, with a focus
on radioactive cesium. Radioiodine, on the other hand, was not measured systematically in the earlyphase after the accident. The values of radioactivity concentrations in food and drink are absent, though
they are essential when estimating radiation levels resulting from internal exposure due to ingestion
pathway. When the internal dose from ingestion in the evacuation areas is estimated, water is consideredas the main ingestion pathway, and vegetables and milk are considered as not the main pathway,
considering effects of food distribution suspension due to the evacuation. In this study, we estimated theabsent values of radioactivity concentrations in water in the early phase after the accident, using
measurement values of radioactivity concentration and iodine-131 deposition rate on the groundcalculated from atmospheric dispersion simulation. We used a compartment model as an estimation
method, and considered how drinking water would be affected by radioactive materials deposited into thewater source. We estimated the values of transfer parameters in the compartment model based on themeasurement values. As for vegetables, we derived a correlation expression between measurement valuesof radioactivity concentrations and iodine-131 deposition rate on the ground using atmospheric dispersion
simulation. For our future work, we examine the internal dose from intake considering the situation offood and drink intake after the accident using the estimation method.
Keywords; radioactive concentrations in food, Iodine 131 and compartment models

1. Introduction

information dating back two years after the accident, released a report

Radioactive materials were discharged into the atmosphere after thein 2014. The report estimated more closely to the actual situation than

accident at Fukushima Daiichi Nuclear Power Plant of Tokyo

that provided by WHO2).

Electric Power Company, resulted from the Great East JapanFor this reason, we considered an estimation method to calculate theEarthquake which occurred on March 11, 2011. When trying toradiation dose of internal exposure due to intake of tap water,

assess health risks to local residents, it is important to grasp how muchvegetables and milk, in order to grasp the internal dose from food andradiation they were exposed to by radioactive substances. The reports

drink.

from the following two international institutions are typical in the

In this study, the estimation mainly covered the evacuation areas,

dose estimation systematically from the recent accident. World

where estimating the dose was considered to be particularly important

Health Organization (WHO,) with the aim of considering measuresin the early phase after the accident. For reference, we used the results

to reduce health effects of exposure to radiation through emergency

of WSPEEDI established by the Japan Atomic Energy Agency

response measures after the accident, conducted a temporary(JAEA), National R&D Corporation, in order to obtain deposition

evaluation using information obtained at that time, and released a

rate 3).

report in 20121). United Nations Scientific Committee on the Effectsof Atomic Radiation (UNSCEAR), taking into consideration

62

When the location of water source is not identified, a purifying facility

2. Estimation Method

is substituted. It is assumed that it takes twelve hours for tap water to(1) Estimation Method for Iodine-131 Concentration of Tap

be taken in after the deposition of radionuclides.

Water
To estimate iodine-131 concentration of tap water, we used a(2) Estimation Method for Iodine-131 Concentration ofcompartment model where radionuclides contained in tap water are
deemed to attenuate at a fixed rate to their concentration, and increase

Vegetables
As for iodine-131 concentration in vegetables, from both the rate ofat every new depositions. In estimating iodine-131 concentration ofradionuclide deposition on the ground, calculated via atmospheric

tap water through the compartment model, changes in radioactivity

dispersion simulation, and measurement values of radioactive

concentration in tap water are represented by the rate of radionuclides

concentration, the following estimation method is considered.

newly deposited into water and effective attenuation of radionuclides(3)
Where A=iodine-131 concentration in a vegetable (Bq/kg),

A = FS

contained in water.
dC= p − λCdt

F= conversion coefficient (m2/kg), and S= amount of accumulated(1)

deposition on the ground at the time of harvest (Bq/m2).

Where C=iodine-131 concentration in drinking water (Bq/kg), p=rate

Conversion coefficient necessary for estimating iodine-131

of deposition into water (Bq/kg･s), and λ= effective attenuation

concentration in vegetables is determined based on measurement

coefficient (l/s).

values, according to vegetable category (leaf and stem vegetables,

Formula (1) can be represented as follows, provided the rate ofmushroom vegetables, etc). As for leaf and stem vegetables, spinach,deposition into water is replaced by the rate of radionuclides

for which there is a wealth of measurement data, is utilized to obtain

deposition on the ground, which is calculated using atmospheric

conversion coefficients. As for mushroom vegetables, shiitake

dispersion simulation and conversion coefficient.
dC= ap '−λCdt( p = ap')

mushroom, for which there is a wealth of measurement data, is used
to obtain conversion coefficients. In addition, under the supposition(2)

that deposition effect due to rain can be excluded as it is protected byroof, for example, only dry deposition is taken into consideration, as
far as indoor-grown vegetables (incl. mushrooms) are concerned.

Where p'=rate of iodine-131 deposition on the ground (Bq/m2･s), anda=conversion coefficient (m /kg).
2

Conversion coefficient and effective attenuation coefficient are
determined using the least squares method and finding the best fit,(3) Estimation Method for Iodine-131 Concentration in Milk
To estimate iodine-131 concentration in milk, a model is considered

substituting measurement values of iodine-131 concentration in tap

where intake ratios of outside feedstuffs and the other feedstuffs, andwater.

transfer coefficients of radionuclides deposited onto each feedstuff are

Based on this estimation method, data necessary for estimatingtaken into consideration. Radioactive transfer coefficient of eachiodine-131 concentration in tap water are iodine-131 concentration

feedstuffs and ratios are estimated based on the measurement data.

values actually measured in tap water and the rate of deposition on theFig.1 shows the concept of the model considered. Based on the

ground calculated from atmospheric dispersion simulation. As formodel, iodine-131 concentration is estimated using the following

measurement values of iodine-131 concentration, we collected data

formula.
𝐴𝐴 = {𝛼𝛼𝐹𝐹1 + (1 − 𝛼𝛼)𝐹𝐹2 }𝑆𝑆
𝐹𝐹1 = 𝑇𝑇𝑓𝑓 × 𝑓𝑓1 , 𝐹𝐹2 = 𝑇𝑇𝑓𝑓 × 𝑓𝑓2

contained in publicly-available information, which was obtained atwater purifying facilities or drinking spaces of running water at local

(4)
(5)

municipal offices. In addition, tap water travels until it reaches each

Where A=iodine-131 concentration in milk (Bq/kg), S=accumulated

drinking space, starting from the source of tap water, then on to adeposition amount on the ground (Bq/m2), 𝛼𝛼 =intake ratio of milk

from cows fed with outside feedstuffs, f1=transfer coefficient of

purifying facility and a distribution facility. Radionuclides in theradionuclides onto outside feedstuffs (m2/kg), f2=transfer coefficient

atmosphere are more likely to deposit into water at the source and atsome parts of a water purifying facility, via these relay points. Waterof radionuclides onto the other feedstuffs (m2/kg), F1=transfer

distributed through a water purifying facility to each household, on thecoefficient from outdoor feedstuffs to milk (m2/kg), F2=transfer

other hand, seems less affected by radionuclides deposition, as mostcoefficient from the other feedstuffs to milk (m2/kg) and Tf =transferof the tap water piping goes under the ground or indoor. Taking into

coefficient from feedstuffs to milk.

account all these conditions, the water source is deemed to be theplace where radionuclides are deposited, when the rate of deposition

3. Estimation Resultson the ground is calculated from atmospheric dispersion simulation.

63

(1) Estimation Result of Iodine-131 Concentration in Tap

coefficients in the model using measurement values, as some reports

Water
The results of estimating iodine-131 concentration in tap water using

say that it can reduce the amount of iodine-131.
As for vegetables and milk, conversion coefficients were determined

a compartment model are shown. Fig.2 shows an estimation based onfrom measurement data of iodine-131 concentrations. By using thesemeasured data of Kawamata Central Park in Kawamata Town, andconversion coefficients, and by using deposition rates calculated from

Fig.3 shows an estimation based on measured data of Yamatama

atmospheric dispersion simulation, it is possible to estimate iodine-

Water Purifying Facility in Iwaki City. Estimation results change

131 concentrations in vegetables and milk from any point. As foraccording to rates of iodine-131 deposits on the ground calculated via

vegetables, the result showed that three points have a different

atmospheric dispersion simulation, and measurement values oftendency from the others. These points share similarities in that theyiodine-131 concentration in tap water.

are far from the nuclear power plant, from which we might as wellconsider setting different conversion coefficient according to distance.

(2) Estimation Result of Iodine-131Concentration in

However, we have confirmed that the estimation will not be an

Vegetables
The logarithmic graph below indicates actual values of iodine-131

underestimation, even though the determined conversion coefficientconcentration in vegetables (spinach and shiitake mushroom) andAs for milk, there is a problem that iodine-131 concentration in milk

amounts of deposition on the ground from atmospheric dispersion

is largely different in the same area, but it can be explained by thesimulation. Table.1 shows results of estimating conversion

estimation method of categorizing ‘animal feedstuffs’ into ‘outside

coefficients, obtained by following the model formula. The graph offeedstuffs’ and ‘the other feedstuffs’. However, as the ratio of eachspinach highlights three dots indicating a different tendency from thefeedstuff is an assumption in this research, it should be noted that there

others.

is a large uncertainty in our estimation models.

(3) Estimation Result of Iodine-131 Concentration in Milk
To estimate iodine-131 concentration in milk, we divided

5. Conclusions and Future Workis used for estimation at the points which have a different tendency.

measurement data obtained from milk into three classes, andperformed a fitting using as parameters, ‘the ratio of outside feedstuffs

We confirmed that iodine-131 concentrations of drinking water,and other feedstuffs’, and ‘transfer coefficients of outside feedstuffs

vegetables and milk can be estimated, even during the period or at theand the other feedstuffs’. As a result of parameter consideration, ratios

points without measurement data in the early phase after the accident.

of outside feedstuffs, measurement values, and amounts of groundWe have decided to consider internal dose from ingestion, taking into

deposition from atmospheric dispersion simulation are shown in

consideration the situation of food intake shortly after the accident. As

Fig.6. In addition, transfer coefficients for each feedstuffs, with which

for consideration of internal dose, we should use measurement data

fitting is performed, is shown in Table 2. The result of fitting indicates

for the period with measuring. For the period without measurementthat the transfer coefficient of radionuclides from outdoor feedstuffs todata, we use estimated values, with giving priorities to actual data as

milk is forty times that from the other feedstuffs to milk.

much as possible, and try to reflect them in the results. Furthermore,
we consider estimation uncertainty of models quantitatively andreduce uncertainty of internal dose from ingestion in the early phase

4. Consideration

after the accident. As for vegetables and milk, in particular, so as toEstimations of iodine-131 concentration in food find that it coincide in

and improve estimation models based on an actual situation.

two measured points where the amounts of iodine-131 deposits wereWe limited our estimations to iodine-131, however, we also need to

substantial and the values of iodine-131 concentration in tap water

undertake the estimation for other radionuclides, including cesium,

reduce uncertainty of models, we need to collect measurement data

were actually measured. These results proved that iodine-131

using the same model in the early phase after the accident. Cesium,

concentration in tap water can be estimated using the rate of iodine-different from iodine-131, has a longer half-life and the measurement

131 deposited onto the ground from atmospheric dispersion

data is usable during the period. For this reason, in case of cesium, we

simulation. However, we must take into consideration that estimatedneed to consider estimation methods for iodine-131 concentration andvalues may change according to different distance, becauseinternal dose that are more based on actual data.

deposition rate after the accident varies considerably, despite being
merely several kilometers apart. In addition, the facility effect of awater purifying facility is factored into parameters such as conversion

64Reference
1) Preliminary dose estimation from the nuclear accident after
the 2011 Great East Japan Earthquake and Tsunami,WHO, 2012.
2) UNSCEAR 2013 Report to the General Assembly, with
scientific annexes, UNSCEAR, 2014.
3) Terada H., et al., “Development of worldwide version ofsystem for prediction of environmental emergency
dose information: WSPEEDI 2nd version”, Journal of
the Atomic Energy Society of Japan, 7, p257–p267,
2008(in japanese).

Fig.3 Estimation Result in Iwaki City

Acknowledgements
This study was conducted in “Study of the Health Effects of Radiation
Organized by Ministry of the Environment, Japan”.

Fig.4 Iodine-131 concentration of spinach and ground deposition

Fig.1 Estimation concept for iodine-131 concentration in Milk

Fig.5 Iodine-131 concentration of shiitake and ground deposition

Fig.2 Estimation Result in Kawamata Town

Table.1 Estimation result of parameters for vegetables
Parameters
SpinachMushroom(Shiitake)
Conversion coefficient
2×10-2
2×10-4

Fig.6 Iodine-131 concentration of milk and ground deposition
Table.2 Estimation result of parameters for milk
Parameters
ValuesTransfer coefficient from outdoor feedstuffs to milk 4×10-3
Transfer coefficient from the other feedstuffs to 1×10-4
milk

65

The distributions of radiocesium in seawaters and sediments
collected off the Niida River estuary, Fukushima Prefecture
Miho Fukuda1) *, Shinnosuke Yamazaki1), Tatsuo Aono1), Satoshi Yoshida1),
Takashi Ishimaru2) and Jota Kanda2)
1) Project for Environmental Dynamics and Radiation Effects, Fukushima Project Headquarters, National Institute ofRadiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan
2) Department of Ocean Sciences, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku,
Tokyo 108-8477, Japan* Corresponding author：mhfukuda@nirs.go.jp
Lateral and vertical distribution of radiocesium, grain size and organic matter content off the Niida River estuary,
Fukushima Prefecture were investigated in mid-October 2013. The dissolved 137Cs activities in surface water samples
collected at NR1, NR3 and NR5 stations, which are located within 5.0-10 km from the Niida River estuary, were higher
than those of other stations outside the 10 km zone. In bottom water samples, the activities had a small variation with
distance from the estuary. The activities in surface water at most stations were higher than those in bottom water. There
were a negative correlation between dissolved 137Cs activities and salinity in surface water. These results suggested thatthe dissolved radiocesium in seawater have been transported to north-south direction in surface layer along thecontinent. High fractions for coarse to very fine sand particles in the sediments were observed at NR1 and NR2 stations,which are located in a northern direction from the Niida River estuary. At NR4, there were high fractions for granuleand very coarse sand particles. The grain size fraction became granular with increasing core depth. The 137Cs activities
in sediments at NR1 were higher compared to those of other stations. It seems that lateral and vertical distributions ofradiocesium in sediments were affected by the particle composition. It is necessary to get more station data because thevertical profiles of 137Cs activity were not especially similar to those of grain size and contents in sediments. Thus, it isnecessary to continue the monitoring in the estuary area in order to elucidate the effects of the grain size and contents on
cesium in the sediments found off the Fukushima Prefecture coast.
Keywords: off Niida River estuary, radiocesium, seawater, marine sediment, particle composition

It is insufficient to report just the transition process from ariver to the ocean. In this study, the Niida River estuary
was focused on, because the upstream portion of this riveris located in the Iidate Village, which was an area of highradio-Cs deposition from the accident. The distributions
and behaviors for radio-Cs were elucidated based on the
results of the radio-Cs activity, grain size composition andorganic matter contents in seawater and sediments.

1. Introduction
The Fukushima Dai-ichi Nuclear Power Station(FDNPS) accident in March 2011 resulted in large
releases of artificial radionuclides including 134Cs and137
Cs (radiocesium, radio-Cs) into the environment. There
are three input pathways of radionuclides to the marine
environment: atmosphere deposition, direct discharge andriver water input. As of January 2015, the 137Cs activities
in seawater had decreased1) more than 10 times comparedto these before the accident (in the early 2000s these
activities were 1.0~2.0 mBq/L2)) within the 20 km zone
from the power station. However, the activities in
sediments have decreased more slowly than those in
seawater and they have had large fluctuations with time.
In contrast, sediments consist of particles of several grain
sizes. In sediments, radio-Cs ions are strongly adsorbed
onto clay minerals such as vermiculite and smectite3).
Radio-Cs activities in riverine sediments tend to be highfor finer grains because these have a large specific surface
area4). It is necessary to consider the differences of grain
size composition in sediments in order to compare thelateral and vertical distributions of radio-Cs in sediments.

2. Sample collection and preparation
Seawater and sediment core samples were collected in
mid-October 2013 during the SY13-10 cruise of theTraining Vessel (T/V) “Shinyo-maru”, which is owned by
Tokyo University of Marine Science and Technology,(Fig. 1). The collection stations were located in a zone of
5.0-12 km from the Niida River estuary, Fukushima
Prefecture.
After transporting all the samples to our laboratory, we
filtered the seawater samples through a 0.2 μm filter.
Radio-Cs in the seawater samples was concentrated by an
improved ammonium phosphomolybdate (AMP) method5).
The radio-Cs activities were measured by gamma-ray66

spectrometry using a high-purity Ge detector (GX-2019;
Canberra), and the detection limits were ~1 mBq/kg.
Collected sediment cores were cut into 1 cm thickslices and dried at 60 ℃ . Radio-Cs activities were
measured with the same Ge detector as for the seawater
samples. Then, the dried sediments were separated into
four classes, based on grain sizes, using several meshsizes: granules (grain size larger than 2 mm); very coarse
to coarse sand particles (1-2 mm); coarse to very fine sandparticles (0.063-1 mm); and silt to clay particles (smaller
than 0.063 mm). The ignition losses of the sediment
samples were also measured in order to estimate organic
matter contents; for this, we used a high temperature
microwave muffle furnace at 550 ℃ for the 2 hours.
Radio-Cs activities in seawater and sediments werecorrected to sampling date of October 16, 2013.

respectively. The selections at NR1, NR2 and NR4 were
3.1-4.6, 1.9-6.2 and 2.4-5.0, respectively and is not good
based on the classification proposed by Compton7).
(3) 137Cs activities in bulk sediments
In bulk sediments, the only artificial radionuclides
detected were radio-Cs. 137Cs activities in sediments were
4.3-838 Bq/kg-dry (Fig. 5). 137Cs activities at NR1 werehigher than those of the other stations. There was a
maximum layer at the 5 cm core depth at NR1. At NR2and NR4 stations, vertical fluctuations of 137Cs activities
were small.
(4) Organic matter contents in bulk sediments
The ignition losses of organic matter contents were0.93-8.8 % (Fig. 6). Organic matter contents for NR1
station sediment samples increased slightly withincreasing core depth. These at the NR2 and NR4 stations
showed only a small variation.

3. Weather conditions at the time of sampling
In mid-October 2013, the typhoon “Wipha” passed
through the eastern part of the main Japanese island. At
the Haranomachi weather station, the total amount of
rainfall was more than 100 mm on October 16, 2013,
which was the sampling date for this study6).

5. Discussion(1) Potential for controlling dissolved 137Cs activities
in seawater
The 137Cs activities in seawater reported through 2012were 8.5-99 mBq/kg in the Niida River estuary1) and ourpresent values were within the range. In surface water, thesalinity at NR1, NR3 and NR5 stations (32-33) wereslightly lower than those at NR2, NR4 and NR6 stations(about 33). On the other hands, those values in bottom
water were 33-34 and the differences between the stations
had small compared to those in surface water. These
results seems that fresh water originating from the Niida
River has transported to north-south direction in surface
layer along the continent. It seems that the distributionsfor 137Cs activity in surface water reflect influence of river
input.

4. Results
The 134Cs /137Cs activity ratios in seawater andsediments corrected to March 11, 2011, ranged from 0.85
-1.2. Therefore, these samples have been influenced by
the FDNPS accident. Here, we report the 137Cs activities.
(1) Dissolved radiocesium activity in seawater
Dissolved 137Cs activities in seawater were 2.8-96
mBq/L (Fig. 2). In surface water, 137Cs activities at NR1,
NR3 and NR5 stations, which are located within the
5.0-10 km zone from the Niida River estuary, were morethan 40 mBq/L. These activities tended to be high forstations in the southern direction. 137Cs activities at NR2,
NR4 and NR6 stations, outside the 10 km zone, werelower than 20 mBq/L. In bottom water samples, it is notunclear whether there were relationships between these
activities and distance from the river estuary (Fig. 3). The
137
Cs activities in surface water samples were higher thanin bottom water samples (Fig. 2).

(2) Factors affecting distributions according to grain
size in sediments
The seabed north from the Niida River estuary mainly
consist of sandy and rudaceous textures, while the seabedto the south consists of coarse textures8). For this study,
the distributions we obtained according to grain sizes
were similar to these trends. There were very different
distributions according to grain sizes at each station since
the distances at each station were 6.2-7.1 km. At the
Haranomachi station, located in the Niida River,relatively coarser particles (grain size: 30-200 μm) wereobserved during the 2013 typhoon “Wipha” compared toparticles observed in normal weather periods9). It seems
that relatively coarse particles such as granules and very
coarse sand particles were transported eastward from thisriver. However, it is unclear whether these results were aparticularly effect of the rain event due to the typhoon ornot.

(2) Distributions according to grain size in sediments
Fractions for the classes of granules, very coarse sand,coarse to very fine sand, silt to clay particles were:0.0-35 %, 0.013-35 %, 38-99 %, and 0.0-29 %,respectively (Fig. 4). The fractions for coarse to very finesand particles represented more than 70 % of the total
particle amount for each sediment layer and the highest
fractions were obtained at NR1 and NR2, which arelocated northward from the river estuary. In contrast,
fractions for granules and very coarse sand particle at
NR4, which is located in an area of the same latitude as
the river estuary, were relatively high and the total
fraction for these particles ranged from 20-62 %. Grainsize fractions became granular with increasing core depth(Fig.4). Medium diameter (Md； mm) values at NR1, NR2
and NR4 were 0.14-0.15, 0.13-0.16 and 0.16-2.5,(3) Factors affecting 137Cs activity variation in sediments
In the estuary area, radio-Cs flux from rivers to theocean in Fukushima Prefecture was 30-50 % of the annual
radiocesium flux during heavy rain events in 201110). In

67

October 2013, 137Cs activities in sediments near the Niida
River estuary were 3.0-44 Bq/kg-dry1), 11). At the NR2 andNR4 stations, 137Cs activities were within the range andthose at the NR1 station were one order of magnitude
higher. The fluctuations for 137Cs activity with core depth
at the NR1 station were larger than those at NR2 and NR4(Fig. 5). In the area near the FDNPS, fluctuations for137
Cs activity with core depth for coarse to very fine sandparticles, and silt to clay particles were larger than thosefor granules and very coarse sand particles12). It seems
that 137Cs activities at the NR1 station were large because
the fraction for silt to clay particles was higher than at theother stations. However, vertical fluctuations for silt toclay particle contents were small. Therefore, it is unlikelythat the 137Cs activity distributions in sediments only
depend on the difference of Cs-adsorption according to
grain size. In the future, we will get data from morestations, in particular, temporal data.

Acknowledgement
We are grateful to Captain Hayashi and all crew
members of the T/V “Shinyo-maru” for their on-board
help during sample collection. This work was partially
supported by Grants-in-Aid for Scientific Research on
Innovative Areas, the Ministry of Education Culture,
Sports, Science and Technology (MEXT), Japan (Nos.
24110004, 24110005) and Research and Development toRadiological Sciences in Fukushima Prefecture.

References
1) MEXT (Ministry of Education, Culture, Sports,
Science and Technology) Available at http://radioactivity.nsr.go.jp/ja/list/428/list-1.html (2015).
2) P. P. Povinec, K. Hirose, T. Honda, T. Ito, E. M. Scott,O. Togawa, Spatial distribution of 3H, 90Sr, 137Cs and239,240
Pu in surface waters of the Pacific and Indian
Oceans-GLOMARD database, Journal of Environ.
Radioactiv, 76, 113-137: doi:10.16/j.jenvrad.2004.03.
022 (2004).
3) R. M. Cornell, “Adsorption of cesium on minerals: A
review” Journal of Radioanalytical and Nuclear
Chemistry, 171(2), 483-500, doi: 10.1007/BF0221987
2 (1993).
4) Q. He, D. E. Walling, “Interpreting particle size effectin the adsorption of 137Cs and unsupported 210Pb bymineral soils and sediments” Journal of Environ.
Radioact, 20 (2), 117-137 (1996).
5) M. Aoyama, K.
Hirose, “Rad io met r i c
Det er mi n at io nofan t hr o p o ge n ic
r ad io n uc lid es i n sea wa t er s a mp l es” Radioact.
in the Environ. 11, 137–162 (2008).
6) Japan Meteorological Agency (JMA) data, 2013.
Available online http://www.data.jma.go.jp/obd/stats/
etrn/.
7) R. R. Compton, Manual of field geology, Wiley New
York, (1962) p. 378.
8) A. Mogi, Y. Iwabuchi, “Submarine topography andsediments on the continental shelves along the coastsof Joban and Kashimanada” Geographical Review ofJapan series A, 34 (3), 39-58 (1961) (in Japanese withEnglish abstract).
9) JAEA reports, 2014. Abatable online http://radioactivi
ty.nsr.go.jp/ja/list/504/list-1.html.
10) Nagao S, Kanamori, M, Ochiai S, Inoue M,
Yamamoto M. Migration behavior of 134Cs and 137Cs
in the Niida river water in Fukushima Prefectre, Japan
during 2011-2012. Journal of radional Nucl. Chem
2014; 10: doi:10.1007/s10967-014-3686-9.
11) Fukushima prefecture fisheries experimental station
data, 2013. Available online https://www.pref.
fuku-shima.lg.jp/sec/37380a/suisanshikenjo20.html.
12) M. Fukuda, S. Yamzaki, T. Aono, S. Yoshida, S.
Naganuma, A. Kubo, K. Shimada, N. Takasawa, T.
Hosaka, K. Sato, S. Yamaguchi, Y. Ito, T. Ishimaru, J.
Kanda, “The distributions of radiocaesium according
to grain sizes in sediments collected from the
Fukushima coastal area in May 2014” to be published

6. Conclusions and future plans
Lateral and vertical distribution of radiocesium, grain
size and organic matter contents were observed in
October 2013 is seawater and sediment samples collected
off the Niida River estuary, Fukushima Prefecture. Our
main findings based on these observations are given
below(1) The 137Cs activities in surface water at the NR1, NR3
and NR5 stations, which are located within the 5.0-10 km
zone from the Niida River estuary, were higher than thoseof the stations outside the 10 km zone. In bottom water
samples, the 137Cs activities had a small variation with adistance from the Niida River estuary. The verticalprofiles of 137Cs activities in surface water at the stations,
except for NR4, were higher than those in bottom water.
(2) Fractions for coarse to very fine sand particles werehighest at the NR1 and NR2 stations, which are locatednorth from the Niida River estuary. In contrast, these for
granules and very coarse sand particles at NR4 were thehighest. Fractions according to grain size became moregranular with increasing core depth.
(3) The 137Cs activities at NR1, which had a high fraction
for silt to clay, were the highest among the stations. There
was a maximum layer near the 5 cm core depth at NR1. In
contrast, the vertical changes of 137Ca activities at NR1
were small. Vertical profiles of 137Ca activity were notsimilar to the distributions according to grain size.
(4) The ignition losses of organic matter contents at NR1
were slightly increased with increasing core depth. Thesevertical fluctuations at NR2 and NR4 stations were
smaller than at NR2.
(5) In this study, samples were collected after the typhoon“Wipha” had crossed Japan. It is unclear whether theseresults were particularly affected by rain events due to thetyphoon or not. Thus, continuous monitoring in theestuary area is necessary in order to elucidate the effectsof the grain size and organic matter contents on cesium inthe sediments, because there are many rivers inFukushima which flow into the sea, including 116 class B
rivers and 339 class A rivers13).

68

in Proceedings of the 16th Workshop on
Environmental Radioactivity, KEK proceedings.
(accepted)13) Fukushima prefecture, 2012 Available online
http://www.pref.fukushima.lg.jp/uploaded/attac
hment/10205.pdf

Fig. 3 Relationships between 137Cs activities in seawaterand distance from the Niida River estuary. Circles andtriangles are 137Cs activities in surface and bottom water,
respectively. The solid and dotted lines are regression
curves of surface and bottom water, respectively.

Fig. 1 Sampling locations in the Niida River estuary.

Fig. 4 Fractions for each particle size group in sediment:
granule (white), very coarse sand (light grey), coarse tovery fine sand (dark grey) and silt to clay (black).

Fig.2 Vertical profiles for137Cs activity in seawater.

Fig. 5 Vertical profiles of 137Cs activities in sediment.

Fig. 6 Vertical profiles of organic matter contents insediment.

69

Review of the gastrointestinal absorption rates
of cesium in human and animals from foodproducts and soil particles
Kayoko IWATA 1)* , Hiroshi YASHIMA 2) , Yuko KINASHI 2) ,Tomoyuki TAKAHASHI2) , Sentaro TAKAHASHI 1,2)
1)Graduate School of Agriculture, Kyoto University, Kitashirakawaoiwake-cho, Kyoto Sakyo-ku, Kyoto606-8502
JAPAN2)Kyoto University Research Reactor Institute, 2, Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka 590-0494 JAPAN* iwata.kayoko.86x@st. kyoto-u.ac.jp

After the Fukushima Daiichi Nuclear Power Plant accident in 2011, public health concern s
have arisen about internal exposure to the radioactive nuclides from ingestion of contaminatedfood products and soil. Internal exposure dose is estimated from the amount of ingested
radionuclides as committed effective dose by ingestion using the ICRP internal dosimetricmodels. The models take account of various parameters such as gastrointestinal absorption rate
(f 1 ). The ICRP recommended f 1 value of 1 for cesium (Cs) in any kind of chemical forms.
However, previous studies have shown, for instance, Cs which strongly adsorbed to clay
minerals is difficult to be extracted; therefore, the absorption rate of Cs in gastrointestinal
tract varies depending on its existing form. Thus, more accurate f 1 values for Cs in different
forms are important in order to estimate physiologically more realistic internal exposure dose.
In this study, we review previously published research on Cs absorption rates in human s andanimals from food products and soil particles, and compare the f 1 values among different
existing forms. The f 1 value for Cs varies among different existing forms (studied samples
containing Cs). For example, f 1 for humans has been reported to have a wide range of values
between 0.08 and 1.0. Nevertheless, the data for f 1 are still limited. In order to estimate
internal exposure dose of Cs more accurately, it is important to accumulate data on f 1 forvarious samples and construct an f 1 database for Cs.
Key Words: Cesium, Ingestion, Gastrointestinal absorption, Dose coefficientinternal exposure (Sv/Bq) recommended by the Internal

1. Introduction

Commission on Radiological Protection (ICRP)1). The
dose coefficient for ingested 137Cs, for instance, is 1.3 x

The Fukushima Daiichi Nuclear Power Plant accident
in 2011 led to a release of large amounts of radionuclides.

10-8 Sv/Bq1).The ingested amount of

One of the major discharged radionuclides wasconverted to internal dose (Sv) by the dose coefficient.

radiocesium. Since cesium-137(

137

137

Cs (Bq) is

Cs) has a relatively

The converted dose is expressed as the committed

long physical half-life (T1/2 = 30.17 years), theeffective dose (CED), which is the integration of dosecontamination in the environment is of both humans andover 50 years for adults after the intake.

animal health concern. Ingestion of the contaminatedfood products and soil particles causes internal exposure.
However, it is unfeasible to measure the internal(1)ICRP models
The dose coefficient for each element is determined

exposure doses (Sv) from radionuclides accurately.

based on multiple models. The models include intake

Therefore, internal exposure dose is estimated from themodels, biokinetic models, and dosimetric models. The

amount of ingested radionuclides (Bq) as committed

intake models, such as of ingestion and inhalation,effective dose by calculation using dose coefficient for

describe the intake pathway and process. The biokinetic

70

models describe the distribution and retention ofconcentration of animals, but also are possibly used as aelements in the body and specific organs. The dosimetricreference for f1 range in different existing forms, whichmodels calculate the absorbed dose in each target organ

human data is scarce. Furthermore, it may be utilizable

2)

from the element in the source organ .

for use in the estimation of f1 values in human.

The models take account of various parameters suchas gastrointestinal absorption rate (f1).The parameter f1 iscomprised in the gastrointestinal tract model of the

2. Review of f1 data for humans and animals

intake models. The ingested radioactive element isassumed to be quickly absorbed at a rate of f1 from thesmall intestinal tract to the blood after digestion in the(1)Humans
The collected data were summarized in Table 1

stomach.

Cs(experimental studies) and Table 2 (a model study). Most

3)

recommended by the ICRP is 1 in any chemical forms .

of these studies consisted of healthy volunteers who

Thus, for the ingestion of Cs, it is assumed to beingested Cs in each of the studied existing form after theabsorbed completely when it reaches the small intestinal

Chernobyl accident.

ICRP

recommended

The

f1

for

tract.

The studies provided volunteers with beverage with
CsCl or cooked food products contaminated with

However, a previous experimental study has shown

radioactive Cs. After consumption, their urine and fecal

that Cs which strongly adsorbs to soil particles issamples were collected and measured. Some studies alsodifficult to be extracted4). The f1 of Cs could varymeasured whole-body retention, using gamma-ray

depending on its existing form. The calculated CED is

detectors external to the body.

likely close to the product of CED (when f1=1) and f1.

The model study by Giussani and Risica (2014) used

Therefore, the f1 may have significant influence on thethe experimental data obtained in the study operated by

calculated CED result. Thus, more accurate f1 values Cs

Risica et al. 1992, 1997 5)-7). They modified adjustablein different existing forms are necessary in order toparameters, such as absorption rates for different foodestimate more physiologically realistic internal exposure

products, and fit the model to the existing data.

dose. In this study, we review the available experimental
data on f1 for Cs for humans and animals.

Data foranimals are important because they can not only be used(2)Animals
The collected data were summarized in Table 3. For

for evaluation of the internal exposure dose and Cs

animals, absorption factor (A) is generally used. The

Table 1. Human gastrointestinal absorption rate (f1) of radiocesium for various ingested forms
Ingested forms

Preparation

No. of volunteers

f1 (Mean)Reference

CsCl

Beverage

3

0.96-0.98 (0.97)

Raaf et al. 2004

CsCl

Beverage

40.87-0.90 (0.89)

LeRoy et al. 1966

Silicate

Gelatin capsule50.73-0.84 (0.80)

LeRoy et al. 1966

Fallout

Gelatin capsule30.29-0.36 (0.31)

LeRoy et al. 1966

Fish (Perch)

Fried

2

0.96, 0.97 (0.97)

Raaf et al. 2004

Mushroom

Fried

1

0.98

Raaf et al. 2004

Meat (Venison)

Meal*

10

0.65-0.90 (0.78)

Henrichs et al. 1989

Meat (Mutton)

Meat pie

80.80-0.94 (0.89)*

Talbot et al. 1993

Mushroom

Fried

1

0.98

Raaf et al. 2004

Shellfish (Cockles)

Boiled6

0.08-0.43 (0.21)

Hunt 1998*Cooking method is unknown
Table 2. Human gastrointestinal absorption rate (f1) of radiocesium estimated by model parameter fitting
Ingested forms

Preparation

No. of volunteers

f1 (Mean)Reference

Meat

Model calculation-

0.2-0.8 (0.66)

Giussani and Risica 2014

Fish

Model calculation-

0.2-0.9 (0.48)

Giussani and Risica 2014

Pasta

Model calculation-

0.9-1.0

Giussani and Risica 201471

reviewed animal experimental studies also consisted ofexperimental data. From the experimental results byfeeding Cs contaminated feed or materials to the

Hunt (1998) with shellfish, its f1 values show a very low

subjected animals and then collecting their urine andrange compared to other food groups10). Low digestion

fecal samples for analysis.

and absorption of Cs in the edible portion of shellfish or

Salbu and Østby (1992) and Cooke et al. (1995)

sediment in the digestive tract of shellfish may have led

performed extraction of Cs from the contaminatedto the low f1 values. However, because there is limited

materials, such as lichens and soils, using rumen liquid

data on f1, further study and consideration of theand estimated A

8)-9)

.

variation factors of f1 tendency are necessary.
The A of Cs in animals also shows a wide range. For
dissolved Cs forms, the A values were between 0.77 and0.98 while the values for lichens had a wider range

3. Results and Discussion

between 0.17 and 0.72. It indicates that ionic Cs is
The f1 values of Cs in humans are within a wide range

absorbed in the gastrointestinal tract more readily, but

between 0.08 and 1.0. The f1 values estimated for meat

the absorption rates of Cs in food products or otherand fish in the model study were lower than othercontaminated materials depend on what the ingested

Table 3 Animal gastrointestinal absorption rate (A)* of radiocesium in various ingested forms
Ingested forms

Studied animals

No. of cases

A (Mean)

Reference

SolutionRat

4(0.98)

Moore and Comar 1962

Ionic

Sheep

3

(0.86)

Mayes et al. 1996

Ionic

Sheep

6

(0.79)

Mayes et al. 1996

Ionic

Sheep

4

(0.77)

Mayes et al. 1996

Ionic filters

Sheep (lactating)3(0.84)

Beresford et al. 1992

Grass

Sheep

4

(0.82)

Mayes et al. 1996

Grass hay

Sheep

4

(0.68)

Mayes et al. 1996

Grass+ herbage+ fungi

Rumen liquid from sheep**

100.75-0.85

Salbu and Østby 1992

Grassy vegetation

Sheep

4

(0.88)

Beresford et al. 1992

HeatherSheep2(0.67)

Beresford et al. 1992

HeatherSheep2(0.67)

Beresford et al. 1992

Clover hay

Sheep

3

(0.83)

Mayes et al. 1996

Lichens

Reindeer

40.52-0.72

Ahman et al. 1990

LichenRumen liquid from sheep**

1

0.32

Salbu andØstby 1992

Lichen (fallout)

Reindeer6

0.17

Skuterud et al. 2004

Lichen (CsCl-sprayed)

Reindeer

80.65-0.67

Skuterud et al. 2004

LitterRumen liquid from sheep**8(0.06)

Salbu andØstby 1992

Fuel particle

Rat

4

0.0075

Talbot et al. 1993

Bentonite

Sheep

3

(0.56)

Mayes et al. 1996

Silt

Sheep

6

(0.095)

Mayes et al. 1996

Ravenglass silt

Sheep

4

(0.88)

Beresford et al. 1992

Ravenglass silt

Sheep (lactating)3(0.13)

Beresford et al. 1992

SilicaSheep

4(0.54)

Mayes et al. 1996

Soil (Alluvial gley)

Sheep

4

(0.19)

Cooke et al. 1996

Soil (Lysimeter peat)

Sheep

3

(0.03)

Cooke et al. 1996

Soil (Alluvial gley)

Rumen liquid**-(0.074)

Cooke et al. 1995

Soil (Lysimeter peat)

Rumen liquid**-(0.011)

Cooke et al. 1995

Soil (Peaty ranker)

Rumen liquid**-(0.13)

Cooke et al. 1995

*Absorption coefficient for animals, which corresponds to human f1,**Data from extraction method

72materials are and how they were contaminated. After theInt. Conf. One Decade After Chernobyl: Summing up theConsequences of the Accident. IAEA-TECDOC-964(Vienna: IAEA), pp 215-220 (1997).

Chernobyl accident, contamination of food animals(ruminant like sheep and cattle) was one of the major

8) Salbu, B. and Østby, G. “Availability of caesium isotopes
in vegetation estimated from incubation and extractin
experiments,” Analyst. March. 117, pp 487-491 (1992).
9) Cooke, A.L., Green, N., Rimmer, D.L., Weekes, T.E.C.
and Wilkins, B.T. “Development if an in-vitro method toassess the availability of soil-associated radionuclides for
uptake by ruminants,” J. Environ. Radioactivity. 28(2), pp
191-207 (1995).
10) Hunt, G.J. “Transfer across the human gut ofenvironmental plutonium, americium, cobalt, caesium andtechnetium: studies with cockles (Cerastoderma edule)
from the Irish Sea,” J. Radiol. Prot. 18(2), pp 101-109(1998).
11) Rääf, C.L., Falk, R., Thornberg, C., Zakaria, M. and
Mattson, S. “Human metabolism of radiocaesium
revisited,” Radiat. Prot. Dosim. 112(3), pp 395-404(2004).
12) LeRoy, G.V., Rust, J.H. and Hasterlik, J. “Theconsequences of ingestion by man of real and simulated
fallout,” Health Phys. 12, pp 449-473 (1966).
13) Henrichs, K., Paretzke, H.G., Voigt, G. and Berg, D.
“Measurements of Cs absorption and retention in man,”
Health Phys. 57(4), pp 571-578 (1989).
14) Talbot, R.J., Newton, D., Warner, A.J., Walters, B. andSherlock, J.C. “Human uptake of 137Cs in mutton,” HealthPhys. 64(6), pp 600-604 (1993).
15) Moore, W. Jr. and Comar, C.L. “Absorption of caesium
137 from the gastro-intestinal tract of the rat,” Int. J. Rad.
Biol. 5(3), pp 247-254 (1962).
16) Mayes, R.W., Beresford, N.A., Howard, B.J.,
Vandecasteele, C.M. and Stakelum, G. “Use of the true
absorption coefficient as a measure of bioavailability ofradiocaesium in ruminants,” Radiat. Environ. Biophys. 35,
pp 101-109 (1996).
17) Beresford, N.A., Mayes, R.W., Howard, B.J., Eayres,
H.F., Lamb, C.S., Barnett, C.L. and Segal, M.G. “Thebioavailability of different forms of radiocaesium fortransfer across the gut of ruminants,” Radiat. Prot. Dosim.
41(2/4), pp 87-91 (1992).
18) Åhman, B., Forberg, S. and Åhman, G. “Zeolite andbentonite as caesium binders in reindeer feed,” Rangifer. 3,
pp 73-82 (1990).
19) Skuterud, L., Pedersen, Ø., Staaland, H., Røed, K.H.,
Salbu, B., Liken, A. and Hove, K. “Absorption, retention
and tissue distribution of radiocaesium in reindeer: effects
of diet and radiocaesium source,” Radiat. Environ.
Biophys. 43, pp 293-301 (2004).
20) Talbot, R.J., Newton, D. and Segal, M.G.
“Gastrointestinal absorption by rats of 137Cs and 90Sr from
U3O8 fuel particles: implications for radiation doses to
man after a nuclear accident,” Radiat. Prot. Dosim. 50(1),pp 39-43 (1993).
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Wilkins, B.T., Beresford, N.A. and Fenwick, J.D.
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concerns in western countries. Experimental studies havebeen conducted with those animals as subjects. However,their digestive tract systems are quite different from thatof humans. Thus, more studies need to be done forfurther improvement of the Cs intake model for humans.
4. Conclusion
This review study showed that the f1 and A values
have wide range among different existing forms andindividuals in both humans and animals. For someexisting forms, f1 values were quite smaller than 1.0,
which leads to an overestimation of CED. Therefore,
validation of as many parameters as possible is important
for a more representative estimation of f1 values for eachexisting form. Currently, the data of f1 for food products
are still limited. In addition, it is difficult to obtain morehuman experimental data at present. In order to estimate
internal exposure dose of Cs more accurately, it isimportant to accumulate data on f1 for various samples
and construct a f1 database for Cs. Thus, moreexperimental data of animals and model studies need tobe performed.
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1) ICRP. “Age-dependent doses to the members of the
public from intake of radionuclides-Part 5 compilation ofingestion and inhalation coefficients, ” ICRP Publication
72. ICRP (1995).
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JAEA (2012).
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ICRP Publication 30. ICRP (1979).
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Savannah River site soils,” Health Phys. 83(4), pp
476-787 (2002).
5) Giussani, A. and Risica, S. “Considerations on the ICRP
model predictions of the transfer of 137Cs from food to themilk and urine of lactating mothers,” J. Radiol. Prot. 34,
pp N19-N30 (2014).
6) Risica, S., Campos Venuti. G., Rogani, A., Baronciani, D.
and Petrone M. “Caesium contamination in human milk
and transfer factor from diet,” Analyst. 117, pp 511-514(1992).
7) Risica, S., Rogani, A., Tancredi, F., Grisanti, A., Grisanti,G., Baronciani, D., Del Prete, A. and Zanini, R. “Caesiumtransfer to placenta, urine and human milk,” Proc. IAEA

73

Transfer of radioactive cesium to earthworms
after the Fukushima Daiichi nuclear power
plant accident
Sota Tanaka 1) *, Tomoyuki Takahashi 2) , Keiko Fujiwara 2) , Sentaro Takahashi 1)2)
1) Kyoto University Graduate School of Agriculture, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, JAPAN
2) Kyoto University Research Reactor Institute, 2, Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka 590-0494, JAPAN*tanaka.sota.57s@st.kyoto-u.ac.jp

The Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Pla nt accident occurred on
March 11 th , 2011 and large amounts of radioactive materials were released into the environment. In
Fukushima, approximately 70% of the land is covered with forests. Therefore, the majority of radioactive
materials were deposited in those forests. These radioactive materials were moved by material circulationin the ecosystem and were accumulated in high concentrations from the soil surface to the litter in theforest. Earthworms and other soil organisms, which decompose organic matter such as litter in theecosystem, have an important role for the circulation of organic materials. Studying such organisms would
lead to understanding the environmental dynamics and ecological impact s of the released radioactive
materials. In this research, we measured the radioactive cesium concentration in earthworms that inhabit
the forest located about 40 km northwest from the FDNPP. As a result, 6.5 × 103 Bq / kg-fresh ofcesium-137 were detected in these earthworms. The concentration ratio (CR) of the earthworm are 0.58 forthe soil, 0.10 for the litter. In addition, the distribution of the radioacti ve cesium in earthworms wasobserved using an autoradiography.

Key Words: Earthworm, Fukushima Daiichi Nuclear Power Plant accident, Radiocesium,
Radioecology

decontamination2). In order to understand the movementof radioactive materials circulated by complex
interactions of organisms and environment, it isappropriate to investigate the organisms that form the
dynamic ecosystem. Earthworms especially relate to thevertical migration of radioactive materials in the soil and

1. Introduction
The Tokyo Electric Power Company’s Fukushima
Daiichi Nuclear Power Plant (FDNPP) accident
occurred on March 11th, 2011 and large amounts ofradioactive materials were released into the environment.
In Fukushima, approximately 70% of the land is covered
with forests. Therefore, the majority of radioactive
materials were deposited in those forests. Theseradioactive materials were moved by material
circulation in the ecosystem and were accumulated inhigh concentrations from the soil surface to the litter

provide a migration pathway as a food source for otherorganisms.

layer in the forest1). Highly contaminated areas in thenortheast part of Fukushima are covered with mountain
forests. Therefore, the inflow of forest organic matterwith accumulated radioactive materials is one of thewhich are exposed to a dose of approximately 30Gy in
the forest near the reactor from the Chernobyl nuclear
accident, had been reported4). The earthworm was
assigned as a reference animal for assessing the effectsof radiation on the environment by the ICRP5).

Earthworms inhabit the highly contaminated soil surface
and thus they are exposed to higher radiation than otherterrestrial organisms3). Based on this, the population
decrease of soil invertebrates including earthworms,

factors that delay reconstruction activity such as74

In this research, to elucidate the ecological impact of
the radioactive materials and the movement ofradioactive materials in the ecosystem, we collectedearthworms and samples of their environmental habitat
and then compared the radiocesium concentrations.
It was previously reported that radiocesium ingested by
the earthworm is excreted rapidly and is notaccumulated in high concentrations in specific organs6).
In order to examine the distribution of radioactive
materials in the earthworm under the naturalenvironment 3 years after the accident, we used
autoradiography.

determined using a standard radiation volume
gamma-ray source (MX033U8PP; Japan Radioisotope
Association). The activity concentrations of Cs-137
were determined from 661.7 keV peak energies.
a) Earthworm
The earthworms (Pheretima group) were collected
between the litter layer and soil in the deciduous
broad-leaved forests in the sampling area. Seven
individuals were packed together in 100ml containers(U-8) and were measured for 2.7×104 seconds.
b) Soil and litter
Each sample was dried in an oven at 105°C. The soil
was screened with a 2 mm mesh and the litter was
crushed by a blender. These samples packed in 100ml
containers (U-8) and were detected with a Ge detector.

2. Materials and Methods(3) Autoradiography (ARG)
An imaging plate (BAS-IP-MS2025E) was used for 8
days after contact with the plate, and then the IP wasread with a reader (Typhoon FLA7000).

(1) Sampling area
The sampling site is located about 40km northwest of
the FDNPP (Fig.1)7). The earthworms (Pheretimagroup) were collected between the litter layer and soil
(Ao-layer) in the deciduous broad-leaved forest. The
collected earthworms brought to the laboratory with thesoil (Ao-layer: organic layer including the litter) in aliving state.

3. Results and discussion(1) Results on the Cs concentrations
The Cs-137 concentrations were 6.3×104 Bq/kg-dry in thelitter, 6.5×103 Bq/kg-wet in the erthworms, and 1.1×104
Bq/kg-dry in the soil (Fig.2). The CR value of Cs forearthworm by ICRP was reported to be 0.0488).

Fig.1 sampling area
Fig.2 Concentrations of Cs-137 in earthworms andenvironmental samples(2)
Measurement
methodsforCs-137concentration
The radioactivity was measured using a high-purity
germanium
detector(Model:
GC4020-7500SL-2002CSL) with a multi-channel
analyzer (MCA: DSA-10000, CANBERRA) andIn order to indicate the transfer of Cs-137 from theenvironmental samples to the earthworms, we calculated theconcentration ratio (CR) of Cs-137. The concentration ratio of
Cs-137 was calculated using the equation (1).

analyzed by gamma spectrometry. The activities were75

Concentration ratio =Concentration of 137Cs in earthworm (Bq/kg-fresh)⋯ (1)Concentration of 137Cs in environmental sample (Bq/kg-dry)

The concentration ratios from environment samples tothe earthworm shows 0.58 with soil and 0.10 with thelitter. To determine the concentration ratio (CR) of theearthworm, we detected the CR of wet weight. However,when converting the CR of dry weight under the same
conditions as the environment samples, the CR ofearthworm become 7 to 8 times higher than that of wet
weight. This CR value is lower than that of the litter CR
value which suggest that the main food resource of theearthworm is litter. Thus the results show that highof different species. Earthworms inhabit highly
contaminated soil surfaces and consume thecontaminated litter layer as food. Therefore they arehighly exposed internally and externally even three
years after the accident.
In the Chernobyl nuclear accident, it was reported thatthe net export of Cs-137 from the forest ecosystem wasless than 1%4). In addition, the radioactive cesium isretained on the soil surface and the litter, and not
significantly move to the deep layer of soil9). Therefore,biomagnification of cesium137 is not observed in theearthworm.

it is predicted that the radiocesium will be retained inhigh concentrations in the forest ecosystem ofFukushima for a long period time. To elucidate theecological impact of the radioactive materials, it isnecessary to carry out long-term investigations forearthworms, and to monitor the crowd density ofearthworms with relation to the levels ofcontamination.
In order for reconstruction of contaminated areas,
which are approximately 70% covered with forests, thedynamics of radioactive materials in the forest
ecosystem must be understood. It is necessary to use an
indicator organism which constitutes the interaction ofmaterial circulation in the ecosystem. Earthworms playa vital part in the materials circulation from the groundto the soil as the decomposer of an ecosystem.

(2)Result of autoradiography
The ARG result shows that radiocesium was highly
concentrated in the center line of earthworm body,specifically in the digestive tract of the earthworm. Thissuggests that the earthworm intake of cesium which is
attached to organic matter such as litter, remains in theirdigestive tract through digestive process. Thus, there ishigh possibility that most cesium exist in the digestive
tract of the earthworm.
This result suggests that the accumulation ofradiocesium to the muscle of earthworm rarely occurrs
under the natural environment 3 years after the accident.
It is estimated that the radiocesium ingested by the

Therefore, the earthworm is suitable as an indicatororganism for understanding the dynamics of radioactive
materials in the ecosystem. By monitoring such
indicator organism, there is a possibility to predict the
dynamics of the radioactive materials to understand thetotal contamination situation in the ecosystem. In thisresearch, we took the cesium concentration data of theenvironmental samples and the earthworm, and thedata of cesium movement in the earthworm body.
These data can be useful for the dose assessment ofinternal and external exposure on the earthworm in theecosystem in future. It is possible to predict theearthworm is excreted rapidly and is not accumulated
in high concentrations in specific organs and themuscle under the natural environment in Fukushima.
However, earthworms are annelids and thus theirdigestive tract is located close to the other organs.
Hence there is a limit to showing the distribution ofradiocesium in each organ by ARG. In order toelucidate the results in greater detail, we need toquantify the cesium concentrations of the muscle andorgans separately by using a Ge detector.

4. Conclusion

long-term dynamics of cesium in the ecosystem by datacollection of the relationship between various

The radiation effects on organisms depend on thecomplex interactions among radiation dose, dose rate, its

environmental organisms and the concentration valuesof cesium making it possible to determine thetemporal and spatial variations, and the radio-sensitivity

ecological impacts of radioactive materials. In the76

future we will establish a prediction method bymonitoring the indicator organism. This will contributeto the reconstruction of contaminated areas in
Fukushima.

References
1) Ministry of Agriculture, Forestry and Fisheries,‘Resultsof the radioactive materials distribution in the forest’,Web site of Forest Agency, March 29, 2013.
(http://www.rinya.maff.go.jp/j/press/kenho/130329.html)(in Japanese)
2) Brumfiel G, Fuyuno I ‘ Fukushima's legacy of fear’,
Nature, 483, 138-140
3) Satoru ENDO et al., ‘Estimation of β-ray dose in air andsoil from Fukushima Daiichi Power Plant accident’,
Journal of Radiation Research, 55, 476-483, 2014.
4) IAEA, ‘Environmental Consequences of the Chernobyl
Accident and their Remediation: Twenty Years ofExperience’, Report of the Chernobyl Forum Expert
Group ‘Environment’ , Radiological Assessment Reports
Series, 2006.
5) ICRP, ‘A Framework for Assessing the Impact ofIonising Radiation on Non-human Species’, ICRP
Publication 91, Ann. ICRP 33 (3), 2003.
6) K. Fujiwara et al., ‘Uptake and retention ofradio-caesium in earthwrms cultured in soil contaminatedby the Fukushima nuclear power plant accident’, Jornal
of Evironmental Radioactivity, 139, 135-139, 2015.
7) Extension Site of Distribution Map of Radiation Dose,etc., / Digital Japan, ‘Air dose rate’, November 07, 2014.
(http://ramap.jmc.or.jp/map/map.html) (in Japanese)
8) ICRP, ‘Environmental Protection: Transfer Parameters
for Reference Animals and Plants’, Annals of the ICRP
Publication 114, Ann. ICRP 39(6), 2009
9) Takeshi Ohno., Y. Muramatsu., Y. Miura., K. Oda., N.
Inagawa., H. Ogawa., A. Yamazaki., C. Toyama., M.
Sato. ‘Depth profiles of radioactive cesium and iodine
released from the Fukushima Daiichi nuclear power plantin different agricultural fields and forests’, Geochemical
Journal, Vol.46 pp.287-295, 2012.

77

Part 4
OthersCase Study of Radiation Education in Compulsory
Education for Fukushima's Revitalized Future
Hiroko MIYUKI*1
1

Graduate School of Energy Science, Kyoto University
miyuki.hiroko.77c@st.kyoto-u.ac.jp

This study investigates effectiveness of radiation risk education to Elementary and Junior High school
students (N=989) based on the classes-on-demand which delivered from April, 2014 to March, 2015. The
classes are designed as (1)45min. for elementary students, (2)90 min. (two consecutive 45 min. classes)
for upper elementary and junior high school. Common learning goal is to know radiation risk. Active
learning is emphasized when designing the classes. World Café Miyuki version (M-Café: discussion
method which based on chains of brainstormings that lead to discussion and presentation) has beenstrongly recommended as one of the learning activities in the radiation risk classes and performed in over
90 % of the classes delivered as the classes-on-demand. As change in the perceived reactions before andafter the class, the participants larned basic knowledge of radation risk and had interest in learning more.
Teaching radiation risk education as class on demand, not only the targeted students learned about
radiation risk, but also observed teachers have learned the subject. Also, it is suggested that M-Cafédeepens and broadens children's idea of radiation risk.
Keywords: Radiation Risk Education, Classes on Demand, Compulsory Education, Active Learning,
World Café Miyuki version (M-Café)
went off from curriculum guidelines4). These caused "Radiation"
became the inexperienced unknown territory learned by the school
education for a teacher of elementary and junior high schools5). (2)Teachers in practice feel that “the radiation risk education” has highspecialty, but they do not have time to learn as the new subject3). (3)There is no appropriate educational material which can be usedeasily6). (4) The concept of “risk” is difficult to understand6).
In order to make public about radiation and to make radiation
education spread widely, the Ministry of Education, Culture, Sports,
Science and Technology, Ministry of Economy, Trade and Industry
Agency of Natural Resources and Energy, Universities, education
facilities and research organizations published supplementary readers,booklets and various related materials about radiation and delivered toelementary and junior high schools throughout Japan. Howeveralmost no teacher training to those material is accomplished, and theteachers receiving the materials are responsible to implement thematerials to make radiation risk education to practice, thus teachingradiation risk education in schools by classroom teachers stayed quitedifficult. Further, some of the materials sent to schools are clearlymade from atomic promotion point of view as well as an opposite
point of view, anti-nuclear party. These issue were some of the cause
which disturbs the spread of radiation education6).

1. Introduction

Japan has a low self-sufficiency rate of the primary energy, and2010 before the eastern Japan great earthquake, including atomic
energy, it was 19.9%. In 2011, the year of the Fukushima Daiichi
Nuclear Power Plant accident (the NPP accident), the nuclear power
plants (NPP) suspended successively and the self-sufficiency rate fell
to 11.1 %. In September, 2013, the 3rd and the 4th unit of Oi NPP of
Kansai Electric Power were suspended thus the energy selfsufficiency rate dropped to 6% 1). After 2014, Japan’s self-sufficiency
rate of the primary energy is thought to fall below less than 6% fromall Japanese nuclear power plants' stopping2).
Problems caused by the NPP accident in 2011 is not only the
decline of the energy self-sufficiency rate. Danger of nuclear power
generation, radiation and radioactive waste management issue werebrought to light. Concern grew about the risks of exposure toradiation and the safety of food and the environment. However, thecurrent status of the radiation risk education in school education is not
put into effect sufficiently yet when over 4 and a half years havepassed after the NPP accident3). There are 4 main reasons for its
cause: (1) After 1981, management of radioactive materials becamevery severe. Also the teaching hours of the science in school
education were reduced. Moreover, teaching guidelines of radiation

On the other hand the meaning of the word “risk” is equivocal.
The word “risk” is used variously in the public, and is both negative78

project to the JPC, ICEEE entrusted by Ministry of Education,
Culture, Sports, Science and Technology Japan (MEXT Japan).
The contents regarding the topics about the radiation risk and theteaching method as well as teaching materials are transferred tolecturers depending upon the students’ developmental stage.
The class duration is 45 minutes (1 frame) session or 90 minutes(2 consecutive frames) session and their learning goals are to know
about radiation risk (Table 2 on next page).

and affirmative. It is important to understand the concept of risk.
What is risk, how to understand the risk and the ways to avoid it oruse it.
In keeping with these social issues, in order to satisfy pressing
needs of radiation risk education, the radiation risk educational classon demand program was put into effect in 9 prefectures throughout
Japan including Fukushima-ken from 2011 to 2015. In this paper,
practice result of the class-on-demand in compulsory educationdelivered in 2014 are summarized and discussed.

a)Concept of “risk”
Many technologists and scientists define risk as "the probabilityof something happening multiplied by the size of the resulting cost;"
however, here, the risk is a state of uncertainty to which Hazard and

2. Practical Studies

Benefit are in trade-off relation7, 8, 9). During the sessions, risk is
explained “Risk is not events that is only dangerous” “even if theevents may concern danger, would you like to take chances?”

The author visited schools and delivered radiation risk classes to4613 students started from September 2011 to March 2015 (Table 1).
Actual period when the practical studies performed are :(Fiscal Year starts from April, ends March of the following year)
FY2011: June 2011 to February 2012; 9 months
FY2012: October 2012 to March 2013; 6 months
FY2013: October 2013 to March 2014; 6 months
FT2014: April 2014 to March 2015; 12 months
The above durations include application period.
The visited schools are located in Hokkaido, Aomori pref.,Yamagata pref., Fukushima pref., Chiba pref., Wakayama pref.,Shiga pref., Osaka-fu, and Kyoto-fu as shown in Fig. 1.

(2) Teaching Methodsa) The class designed as “Quiz Show”
The classes are designed as “quiz show” to get the participants
attention and keep them enthusiastic. After explaining about the basic
knowledge which becomes the aim of learning, the understanding
confirmation tests called “quiz” are performed on each topic, andmore explanations are added while seeing children’s reaction.
Experiments were conducted to experience the knowledge they justhave learned. Confirmation test of the class contents (all items which
are taught as basic knowledge) was performed at the end of the class
to check the short-term level of proficiency (Fig. 2 on next page) 10).

(1) Contents of the lessons
A panel of experts (such as radiation specialists, educators andscientists) reviewed the topics to be taught on the subject of radiation.
The panel was called by Japan Productivity Center, Information
Center for Energy Environmental Education (the JPC, ICEEE).
Class-on-Demand in FY2011 is a government’s commissionedb) Active learning and World café Miyuki version
It is widely known that Active learning, which is a process
whereby students engage in activities such as discussion, problem
solving, evaluation, cooperative-learning, problem-based learning,
simulations and so on, has higher retention rate than passive learning

Table 1 Number of Participated Schools, Grades and Students（FY; from April to March, as of March 2015）
FY
Schools
visited
grade
1st
2nd
3rd
4th
5th
6th
J.H.
H
Teachers
PTA
Univ.
Total

2011

2012

2013

2014

total

25

13

8

21

67

0
0
5
193
317
1323
128

10
10
11
34
229
455
130

22
22
26
47
45
587
240
29

37
36
47
340
708
2685
594
29

50

110

27
1095

27
4613

participants

5
4
5
66
117
320
96

60
1966

939

613

Fig.1 Location of the Schools(from Sept. 2011 to Mar. 2015)79

Table 2 Class duration, Grades, Target of study
Class
Target Gradeduration

45min

Topics／objectives

Don't feel with fivesenses
1st & 2nd Around us
Elementary Dangerous but usefulProtect against
Radiation
Don't feel with fivesensesAround us
3rd & 4thDangerous but useful
ElementaryProtect against
Radiation
It can be measured
Don't feel with fivesensesAround us
5th & 6th Protect against
Elementary Radiation
It can be measured
Affect living things
Usefl
What is "Risk?"
Don't feel with fivesensesAround us

90min

Protect against
Radiation
Upper
It can be measured
Elementary
Affect living things
Usefl
What is "Risk?"
High‐level radioactive
waste
Disposal method
Radioactivity,
radiation andradioactive materials
Types of rays (α, β, γ,X ray)
Around us

100minJuniorHigh

Characteristic of theradiation
Relation between theradiation dose andsafetyRadiation use
What is "Risk?"
High‐level radioactive
waste
Disposal method

Experiments
Wilson's
ChaberActivities
Story telling
Experience
Demonstration
Visual aids,
Quiz

Wilson's
ChaberDemonstration
Experience
Visual aids,
Quiz
SurveyWilson's
ChaberRadiation
SurveyDemonstration
Experience
Visual aids,
Quiz
SurveyWilson's
ChaberRadiation
SurveyBentonite

Demonstration

Fig. 2 Structure of the Radiation class

Experience
Visual aids,
Quiz
SurveyWorld Café
Miyuki version

Wilson's
ChaberDemonstration

Radiation
SurveyExperience

Bentonite

Visual aids,Quiz(7) extracting issues and problems, (8) try to solve the problems, (9)summarize the ideas, (10) present the ideas during the class (Fig. 3).
When conducting M-Café, divide the class into small groups andeach group will have the same number of members (1 ≦N ≦6).
Number of the groups in a class and numbers of members in eachgroup can be adjusted according to the size of the class. Procedure of
M-Café is as follows. For example, first, divide the class into small
groups so that each group contain about the same number ofmembers. On the table of each group, place large sheet (A1 or A0size) of poster paper with various discussion topics. Students will
write anything they can think of about the topic in 2 minutes,
brainstorming. At the tone of 2 minutes, members of group 1 moves
to the group 2 table, leaving the group 1 poster sheet behind on theSurveyWorld Café
Miyuki version

which is a process whereby students are expected to "record andabsorb knowledge” mainly by “seeing and hearing” 11,12,13).
World Café Miyuki version (M-Café) is designed,
conceptualized and performed as active learning in order for all thestudents to continuously (1) think freely, (2) think about multiples of
topics, (3) think enthusiastically, (4) think at own ability, (5) listen toother’s ideas and opinions, (6) think about various ideas and opinions,Fig. 3 World Café Miyuki Version

80

expose a lot. etc). The quiz score during the class and the proficiency
test right after the class are given to students to diagnose the level ofshort-term proficiency. (Figure 4).．

table of group 1. Grope 2 moves to group 3 table, group 3 togroup 4 table and so on. Immediately after the groups moving to the
new tables, students start writing their ideas and thoughts on the newgroup’s poster sheet, brainstorming. Since there will already be someideas and thoughts written on the poster sheet, they have to thinkflexibly and consider carefully (Photo 1). Again at the tone of 2
minutes, students move to the next table till they come back to theoriginal table where they started from. When they come back to theoriginal table, students will read what’s written on the poster sheet andsummarize ideas and draw conclusion. Students will have time topresent their summarized conclusions and hypothesis in front of theclass (Photo 2) . M-Cafe is student centered active learning method.

Fig. 4 Survey page, Answer sheet for quiz andCheck-up Test

3. Analyses

Result of the classes-on-demand is analyzed by summarizing
respond words as (1) counting the numbers of respond words orgroup of words, (2) selecting top ten words of the first impression
words (words that are written first), (3) dividing the respond words orgroup of words into three categories (a) positive image, (b) negative
image, (c) neither positive nor negative, facts and knowledge. The
scores of the quiz given during class and the scores of theconfirmation test given right after the class were compared andanalyzed. The result of M Café is qualitatively evaluated according to
how the students involved in the activity.

Photo. 1 Children working on the M-Café posters（Photograph by H. Miyuki, Mar., 2013）(1) The numbers of respond words, the numbers ofletters used to form the group of words
The common features were seen by the respond words written
before the class, after the class, and after the M-Café activity. Before
the class, students wrote respond words to stimulus word “radiation”
as single word such as “danger, scared, cancer and so on.” After theclass, conditional words were seen with respond words such as“dangerous but useful, dangerous if you expose a lot, etc.” For after
M-Café, responds words are no longer just group of words, they
contain social issues and pointing out the problems such as “there aremany ways to the nuclear waste management, but they are all difficult,how should we deal with the nuclear waste, etc.” Fig. 5 next pageshows the comparision and change of the numbers of words andletters after the class and after the M-Café, setting the number ofwords and letters before the class as 100.

Photo. 2 Children presenting their M-Café posters（Photograph by H. Miyuki, May, 2014）(3) Survey Method
Right before and right after the class, 45 seconds of open-ended,association test are given to 3rd graders and older students and theresults are summarized and analyzed. Stimulus word for this survey
is “radiation” and the students are asked to wright respond words orgroup of words. By counting the words (i.e., dangerous, deadly, etc)
or the group of words (i.e., dangerous but useful, deadly if you get

81

Fig. 5

Change in the numbers of words and letters used in the survey taken after-class and after M-Café(Before-class = 100%, from Apr. 2014 to Mar. 2015)(2) The first impression words
In this study, the top ten of the first impression words of theclasses given in fy2014 are summarized. The open-ended association
tests were given before and after the class to the student from the 3rd
grade in elementary school to the 9th grade in junior high school.
Because M-Café activitiy is designed for upper elementary and older
students, for after M-Café survey was taken only by participatedstudents who were the 5th graders and older (Table 3 ).

Table 3 Top 10 First Impression Words(before and after the class, after the M-café)
Before Class

1

Danger,Dangerous

2 Scared(3) Conceived change in impression
The first impression respond words were summarized. The
words given before and after the class were categorized into threegroups; (a) positive image, (b) negative image, (c) neither positive nor
negative, facts and knowledge. Comparing before the class withafter the class, the bar graphs in Fig. 6 show the increase in positive
image, decrease in negative image and increase in facts andknowledges.

3

Bad effect onliving things

4 Cannot see

5

Nuclear Power
Plant(4) Comprehension Level of Learning Objectives
The class was designed as if we are in the quiz show. Eachquestion in the quiz show is aimed to a learning objective. Eachquestion in the confirmation test after the class is also aimed to thelearning objectives. Thus by summarizing the results of the both tests,
it may leads to the students’ comprehension level of learning radiation
risk. Fig. 7 shows averaged correct answer rate of the quiz during theclass and the test after the class. In elementary schools, 10 classes outof 12, correct answer rate of the after class test has increased. The 2
classes’ correct answer rate has decreased; however, they were by 2%
and 3%. On the other hand, in junior high school, 3 classes out of 7
have increased, 4 out of 7 have decreased.

Dangerous but
sometimes useful

Many ways to dispose theToo much exposureradioactive waste, but they all
may have bad effectare dangerous and cost a lot
to living thingsof money
Radioactivity
becomes weak

How should we dispose of thewaste?

Everywhere in theworld

It is dangerous to dispose of
the waste in the universe(outer‐space)

If you don't know
about it, it becomes
Isn't there any safe and lessa danger. If you
costly way?
know it, you will be
OK.
May cause cancer

Isn't there any idea not toleak radiation?

7 get cancer

Cant feel with fivesensesInstead of disposing,shouldn’t we expected to
manage?

The disaster ofeast Japan

It's in the food we
eat everyday

We could consider various
ways

Too much
9 exposure may
kill you

We can beprotected by it

I didn't think the radiation
was dangerous, but it isactually dangerous

α‐ray，β‐ray，
γ‐ray，X‐ray

If you don't understand therisk of radiation, it becomes
dangerous. If you understandit, it will be OK somehoweven though the radiation isdangerous

10 Useful82

After M‐Café
There are many ways forradioactive waste
management, and they are alldifficult and with a lot of
trouble6 It penetrates

8(5) Discussion

After Classthat the students having “emotional fear of radiation” tend to have"feeling of efficacy (the confidence that radiation can be controlled
and that danger can be evaded and the perspective from which
advantage is obtained)" though they still believe radiation to besomething we should be scared of 3, 14). The result suggests that thestudents in compulsory education have learned radiation risk in theschool time when the respective schools were limited.
b) Understanding of the learning contents
From Fig. 7, the students have learned and understood radiatin
risk through class on demand by accuracy of average correct answer
rate of 71% to 100%. 14 classes out of 19 classes scored higher inafter class test which is given after experiments compared to duringclass quiz, it is inferred that the students became interested in radiationand learned and experienced through scientific experiments.
97% of students who participated answered “enjoyed the class”,
on the other hand, students’ of 17% answered "it was difficult tounderstand," it is revealed that futher improvement andimplementation of class on demand are nessecary which include topace down the speed of carrying the class activity and making the
purpose of experiments much clearer.

Fig.6 3rd graders’ of elementary schools to Junior highstudents’ Perceived Changes on Nuclear
Radiation before and after the radiation class(from Apr. 2014 to Mar. 2015)a) The impression change by increase of the number of words
The Fig. 5 shows that the numbers of words and letters haveincreased by 24% in average compared before the class with after theclass, it is inferred that adding to the original impression, positive andnegative impression words as well as words that tells facts andknowledge have increased. The Fig.. 6 seems to show that the
impression of the radiation became more positive after the class;however, it does not suggest that the impression of the radiation risk
became something awful to something good by attending theradiation risk class. It is suggested that because the surveys wereconducted right after the class, students tend to write the facts andknowledge related words which they have just learned. Also, it is
widely known that impression received from the radiation class, evenfrom the same word, differes in an individual depending on theparticipant’s original image to radiation before the class. In addition,
more positive and negative images as well as facts are listed in thesuevey, not only analyzing by the first impression words, further
investigation such as analyzing all the listed words is necessary.
From Table 3, in spite of students age and experience ofevacuation, after class compared with before class, students
acknowledge more interest in radiation risk and have learned basic
knowledge of radiation3). By learning radiation risk, it is presumedc）World Café Miyuki version
Teachers and parents who have attended or observed the classhave commented that “it was against their imagination that many
students volunteered to present the M-Café poster in front of theclass.” “they were impressed with M-Café activity that almost all thestudents were enthusiastically thinking, giving ideas, extracting issues
and trying to solve the problem given by classmates.” Moreover, “thequiz show was well planned and was easier to understand than thepreviously attended radiation seminars.” World Café Miyuki version
enhanced students think deeper and broader about radiation risk
issues. Moreover, the comments and the result of the class on
demand suggest that even though the classes are designed for 45 min.
to 90 min., not only students who attend the class on demand learned
radiation risk, but also teachers and parents who observed the classhave learned radiation risk.

Fig. 7 The Correct Answer Ratio of the Check-up Test during the class and after the class835) Hideki Ono, “Problem of nuclear power plant ‘radioactivity’
education in elementary and secondary education and theconquest” The Japan Scientists’ Association e-magazine, No.16，
2013 ( In Japanese )4. Conclusion

When future Japanese energy issues are considered, we must
think critically, must gain the power of thinking and imagining ofwhat kind of energy gives what kind of influence on environment andhow the economy influence by, and how the energy and outcome ofthe energy use influence our everyday life. Not only must the benefitof the use of energy, but also hazards of the use of energy beconsidered. The citizens of the earth who makes those important
decisions concerning energy are generation of present children. We
must not only advance technology, but bring education into focus sothat "children" becomes confident in making important decision"decision-making of the energy".

6) Fukushima prefecture School Board，“Radiation Educational
Promotion Support Project” leader education workshop in fiscal
year 2014, Study Conference “Issues of the Radiation
Educational Promotion” subcommittee meeting group 2elementary school, group 3 junior high school，Koriyama-city,
Fukushima 2014.6.18 ( In Japanese )7) Naoki Yamano, “Rethinking of Risk Communication”，Journalof Atomic Energy Society of Japan, Vol. 57, 109-113, 2015.
( In Japanese )8) the International Organization for Standardization, Risk
management standard ISO31000:2009 2.1Risk “Riskmanagement-Principles and guidelines ISO31000:2009 2.1”

Acknowledgment

This research based on
FY2011; The government's commissioned projects to Japanproductivity center, information center for Energy Environmental
education by The Ministry of Education, Culture, Sports, Science andTechnology
FY2012; Kyoto University Golobal COE program
Nov. 2013 to March 2014 and FY2014; Sumitomo Foundation
133076
Special thanks to the schools and the teachers and students who letme practice class on demand program of radiation risk education.

9) International Risk Governance Council, White Paper on Risk
Governance towards an Integrative Approach, p.19, 2005
10) Hiroko Miyuki “Our everyday life and radiation risk --- What ishigh level radioactive waste?” Lesson plans, Learning activities,
Results of visiting lectures, Nuclear Waste Management
Organization of Japan<http://numo-eess.jp/class/2013/yachi.seibu.php> 2014. 3 ( In Japanese )11) Ben Johnson, “How Do We Know When Students Are
Engaged?”, Edutopia, Education Foundation, 2013, < http://
www.edutopia.org/blog/student-engagement-definition-benjohnson> , accessed Jul. 4, 2014

References
1) Energy White Paper 2015，Fiscal Year Heisei 26 Report，
Agency for Natural Resources and Energy，accessed Jul. 2015
http://www.enecho.meti.go.jp/about/whitepaper/2015pdf/

12) Hendrien Maat,“Working paper, The Active Teaching &Learning Method”, edukans, University of Amsterdam, Version
4, <http://www.edukans.org/images/International/The-ActiveTeaching-Learning-Method-2014.pdf> accessed June 20, 2015

2) The energy self-sufficiency rate of Japan will be 6 % which is
one-third before the great disaster, less self-sufficiency rate is
expected as all the NPP stop. Sankei news,<2015http://www.sankei.com/life/news/140519/lif140519 0002n1.html > accessed June 2015, ( In Japanese )13) Dean A. McManus, "The Two Paradigms of Education and thePeer Review of Teaching", School of Oceanography and Center
for Instructional Development and Research, University ofWashington, The National Association of Geoscience Teachers,
Journal of Geoscience Education,Vol. 49, No. 6, Nov 2001, pp.
423-434.

3) Hiroko Miyuki, Eiji Yamasue, Hideyuki Okumura, Keiichi
Ishihara, “Radiation Class given to 6th graders of Japanese
Elementary Students and their Perceived Changes on Nuclear
Radiation after the classes analyzed with locality”，The 49th
Environmental Engineering Research Forum Proceedings, Japan
Society of Civil Engineers, pp. 205-207（2012）( In Japanese )4) Minoru Eda, “Wishing the renaissance of the radiation
education” Radiation Education Forum Newsletter, No.37，p.1，
2007 ( In Japanese )8414) Hiroko Miyuki, Hiroshi Tamiya, Shigeyuki Haga, Yuji Kodama,
Naoki Yamano, Keiichi Ishihara “Radiation Risk Education in
Elementary schools --- results of Class-on-demand” the 51st
Annual Meeting on Radioisotope and Radiation Research,
Tokyo, 2014.7 ( In Japanese )Derivation of Apparent Diffusion coefficient (Da)and Distribution Coefficient (KD) from Evolutionof Depth Distribution of Radiocaesium in Soil
Contaminated by the Fukushima NPP accident
Haruo SATO 1)*
1) Graduate School of Natural Science and Technology, Okayama University, 3-1-1, Tsushima-naka, Kita-ku,
Okayama-shi, Okayama 700-8530, Japan*sato.haruo@cc.okayama-u.ac.jp

The authors have investigated the depth distribution of radionuclides (RNs) in soil at 11 locations in thecity of Nihonmatsu, the towns of Kawamata and Namie after about 3 months (1st investigation) and 1 year
(2nd investigation) following the Fukushima NPP accident, and reported the Da-values of RNs (Cs-134,
Cs-137, Te-129m and Ag-110m) obtained from depth distributions near the surface layer of soil and theKD-values of Cs-137 and I-131 on soil obtained by batch experiments so far. Many Da-values ofradiocaesium (Cs-134, Cs-137) derived from the 1st investigation were of order 10-10 m2/s, and tended tobe higher in soil of former farmland and organic soil than in mainly sandy soil. However, many Da-values
derived from the 2nd investigation were approximately of order 10-11 m2/s. The KD-values of Cs-137 on soil
were in the range 2,080~61,000 ml/g in both investigations. Considering the high KD-values, the Da-values
should be theoretically 2 or 3 orders of magnitude lower than those obtained in both ivestigations, but large
descrepancies were found between both parameters. The cause for the high Da-values is thought to be thatthe distributions include the effect of dispersion or permeation by advection near the surface layer of soil
which is unsaturated following the deposition of RNs, i.e., these high Da-values were considered that depth
distributions following the initial deposition were formed mainly by a dispersion process. This is evidenced
by the depth distribution of water content. Based on this, it is considered that depth distributions in deeper
part of the soil were formed by mainly diffusion process. Therefore, a theory to exclude the influence ofearly-time of dispersion or permeation by advection and derive Da for only the diffusion process wasconsidered based on the evolution of the depth distributions in deeper part from the 1st to 2nd investigation.
Furthermore, KD was calculated from the Da and compared to the measured data. The calculated results of
Da were of order 10-14 m2/s, and those of KD were in the range of KD=104~105 ml/g, which wereapproximately consistent with the measured KD-values. However, no evolution of depth distribution was
found for many data of sandy soil, which irreversibility was found in desorption experiments after sorption
experiments. Model construction considered irreversible reaction in sorption is needed.

Keywords: Fukushima nuclear accident, radiocaesium, diffusion, distribution coefficient, soil
forests, ponds, residential land, etc.) in the Fukushima and the

1. Introduction

surrounding prefectures. The inventory of RNs discharged by
The accident at the Tokyo Electric Power Company(TEPCO) Fukushima Dai-ichi Nuclear Power Plant (1F-NPP)

May 2011 is estimated to be approximately 900 PBq with thisvalue converted to radioiodine (I-131) (500 PBq for I-131 andoccurred following the Great East Japan Earthquake on March
11, 2011, and led to the release of volatile radionuclides (RNs),

10 PBq for Cs-137) 1). This amount is equivalent towhich were deposited on the surrounding environment (soils,

Chernobyl NPP accident which occurred in April 1986 2).

approximately 1/6th of the 5,200 PBq discharged by the85However, the 1F-NPP accident is evaluated as the worst level 7
on the International Nuclear Event Scale (INES). After theKD-values of Cs-137 on soil were in the range 2,080~61,000
ml/g in both investigations. Considering the high KD-values, thedecay of short-lived I-131 (half-life T1/2=8.021d), radiocaesium(Cs-134 (T1/2=2.065y), Cs-137 (T1/2=30.07y)) 3) are now thelower than those obtained in both investigations, but large

main contributors to radiological dose rate.

descrepancies were found between the KD-values and the Da-

Da-values should be theoretically 2 or 3 orders of magnitude

This work was a research project related to distribution

values. The cause for the high Da-values is thought to be thatmaps of radiation dose rate, which the Ministry of Education,
Culture, Sports, Science and Technology (MEXT) has

the distributions include the effect of dispersion or permeation
by advection (water flow) near the surface layer of soil which is

promoted as one countermeasure to the 1F-NPP accident, since

unsaturated, following the deposition of RNs. In short, these

March 2011. The authors have conducted two investigations onhigh calculated Da-values were considered that depth

the depth distribution of RNs in soil at 11 locations in the city

distributions following the initial deposition were formedof Nihonmatsu and the towns of Kawamata and Namie, whichmainly by a dispersion proess. It is also cleared from the fact

are located between 20km and 60km north-west from 1F-NPP,
in June 2011 after about 3 months (1st investigation) 4) andthat actually the Da-values obtained from the depth distributions

during February and March 2012 after about 1 year (2ndinvestigation) 5, 6) following the 1F-NPP accident, and reported

TeO32- 8) and Ag-110m of which species in the porewater is Ag+

those results so far 4-6).

KD-values on soil are significantly different between cationof Te-129m of which species in the porewater is HTeO3- and/or
were all similar levels as those of radiocaesium even though theTable 1. Overview of 2 times of investigations (1st and 2nd investigation)

The apparent diffusion coefficients (Da) of RNs were(Cs+) and anion (I-) 4). This is also evidenced by the measured

calculated based on the Fick’s 2nd law 7) from depth

results of water content distribution in the direction of depth,

distributions near the surface layer of soil, and the distribution
coefficients (KD) of Cs-137 and I-131 on soil were obtained bywhere the degree of saturation changed from unsaturated toa batch method. Many Da-values of radiocaesium (Cs-134, Cs137) were of order 10-10 m2/s in the 1st investigation and wereadvection does not come to take place with increasing depth.

saturated condition in depth direction. This means that
Therefore, it is considered that depth distributions in deeper part

6)

were formed by mainly diffusion process.

approximately of order 10 m /s in the 2nd investigation . The
-11

2

86

early-time of dispersion or permeation by advection or

investigations. Since details of each investigation are describedin literatures 4) and 6), only the outline is described here. As

permeation near the surface layer of soil which is unsaturated

shown in Table 2, many Da-values of radiocaesium were ofand derive Da for only the diffusion process was considered

order 10-10 m2/s in the 1st investigation and were approximately

based on the evolution of the depth distributions in deeper partof order 10-11 m2/s in the 2nd investigation 6). The KD-values offrom the 1st to the 2nd investigation. Furthermore, KD was

Cs-137 on soil obtained by batch experiments were in the range

calculated from the Da and the consistency between both

2,080~61,000 ml/g in both investigations.

Therefore, in this study, a theory to exclude the influence ofAs cleared comparing between the Da-values and the KD-

parameters and the validity of the theory were discussed bycomparing to the measured data (KD).

values, both parameters are quantitatively inconsistent at all, i.e.,quantitatively large descrepancies are found between both

2. Overview of the field investigations

parameters. As described above, concretely, although the highTable 1 shows overview of twice of the field investigations(1st and 2nd investigation) and Figure 1 shows the investigation

experiments, Da-values obtained from depth distributions nearlocations. Both investigations were conducted at 11 locations in
the city of Nihonmatsu (1 location) and the towns of Kawamata

those expected from the KD-values. The cause for the high Da-(2 locations) and Namie (8 locations), where are locatedinclude the effect of dispersion or permeation by advection such

between 20km and 60km north-west from 1F-NPP.
Table 2 shows the calculated results (conventional analysis

as rain water following the deposition of radiocaesium on

KD-values of radiocaesium on soil were obtained from batchthe surface of soil were 2 or 3 orders of magnitude higher thanvalues was thought to be due to that the depth distributions

ground surface. Soil near surface layer is unsaturated by water

Figure 1. Investigation location.
method based on the Fick’s 2nd law 7)) of the Da-values ofradiocaesium (Cs-134, cs-137) from depth distributions near
the surface layer of soil versus the type of soil (sandy soil,organic soil, soil which is supposed to have been used as
farmland (soil of former farmland)) obtained in both87

Table 2. The calculated results of the Da-values of radiocaesium from depth distributions near the surface layer of soil
versus the type of soil obtained in both investigations (1st and 2nd investigation)
Investigation location

Soil type1st Investigation（after 3 months）

Kozuka, Yamakiya, Kawamata T.
Kanaori, Nihonmatsu C.
Matsukiyama, Shimotsushima,
Namie T.
Teshichiro, Akogi, Namie T.
Kurabeishi, Hiruzone, Namie T.

Sandy soil

Organic soil

Ohshimizu, Yamakiya, Kawamata T.
Kozuka, Yamakiya, Kawamata T.
Mizuzakai, Tsushima, Namie T.
Matsukiyama, Shimotsushima,
Namie T.

Soil of former
farmland(including flower
garden)Shiobite, Akogi, Namie T.
Kunigidaira, Akogi, Namie T.

2nd Investigation（after 1 year）

Cs-134

Cs-137

Cs-134

Cs-137

1.70E-11
4.43E-11
6.63E-11
1.28E-10
1.06E-10
5.09E-10
1.12E-10
6.17E-11

1.71E-11
4.31E-11
6.78E-11
1.32E-10
1.12E-10
5.09E-10
1.14E-10
6.10E-10

3.38E-12

3.19E-12

3.41E-11

3.51E-11

7.85E-11

8.17E-11

1.04E-10
3.05E-10
1.98E-10
1.23E-10
4.97E-11

1.08E-10
3.31E-10
2.01E-10
1.78E-10
5.33E-11

9.18E-11
4.75E-11

9.28E-11
4.54E-11

8.32E-11

1.01E-10

7.49E-11
1.92E-10
4.03E-10

7.71E-11
1.91E-10
4.03E-10

2.26E-11
3.25E-10
1.77E-11
4.03E-11
1.51E-10

2.05E-11
2.54E+10
1.86E-11
4.23E-11
1.16E-10

The diffusion equation 7) for one-dimensional non-steadyvaporization from the surface layer excepting the case thatwater table is the same level as the ground surface such as

state considering decay term is expressed as follows.

topographically water catchment area. The degree of saturationnear the surface layer of soil was approximately 50 % at many∂C∂C∂= �Da � − λC
∂t ∂x
∂x

investigation locations from the measured results of watercontent distribution in the direction of depth, and increased with

(1)

Assuming that Da is independent of distance, Eq. (1) is

depth. As described above, the depth distributions of other RNs(Te-129m, Ag-110m) obtained at the same time in the 1st

arranged as follows.

investigation were also approximately the same as those ofradiocaesium at the same investigation location even though the∂2 C∂C= Da 2 − λC∂x∂t

KD-values between cation and anion are significantly different,
and the calculated Da-values were also all similar levels.
Synthesizing these facts, it is considered that initial depth(2)Where, C is the radioactivity concentrations of radiocaesium inunit volume of the soil (Bq/cm3), t the time elapsed from the

distributions near the surface layer of soil include the effect ofdeposition of radiocaesium (s), x the distance in the depth
direction of soil from the deposited surface (ground surface)dispersion or permeation by advection following the deposition
of RNs on ground surface. Therefore, it is considered that the(m), Da the apparent diffusion coefficient (m2/s), and λ thedecay constant (1/s).

evolution of depth distribution in deeper part where advection
does not occur reflects transport by mainly diffusion process.

For one-dimensional non-steady state diffusion of a planar

3. Analyses of Da and KD based on the evolution of
depth distributions

source consisting of a limited amount of substance such as

As described already, a theory to exclude the influence ofradiocaesium in a cylinder of infinite length, the analyticalsolution of Eq. (2) is written as follows based on the following
initial and boundary conditions.

early-time dispersion or permeation by advection and derive Da
for only diffusion process was considered based on theInitial Condition
C(t, x) = 0, t = 0, x ≥ 0evolution of depth distributions.

88Boundary Condition
C(t, x) = 0, t > 0, x = +∞1tan(θ2 − θ1 )+∞M = � C(t, x)dx0

C(t, x) =M�πDa tx2�−�
𝑒𝑒 4Dat 𝑒𝑒 −λt

1
4Da (t 2 − t1 )(7)

Where, Da is the apparent diffusion coefficient against timechange from t1 to t2 (m2/s).

(3)

Arranging Eq. (7), Da is expressed by the following relation.

Where, M is the total amount of diffusing subsatance per unit
area (Bq/m2) (equivalent to the amount of radiocaesium per unit

Da = −

area initially deposited on ground surface).
Taking logarithm for Eq. (3), the following relation can betan(θ2 − θ1 )4(t 2 − t1 )(8)

From Eqs. (5), (6) and (8), finally the theory to derive Da isderived.
LnC(t, x) = Ln �=−

expressed as the following relations.
x2
�−
− λt
4Da t
�πDa tM

1
1
tan �arctan � � − arctan � ��ba
Da = −
4(t 2 − t1 )(4)

A slope given by a plot of LnC versus x2 gives Da from therelation of diffusing time based on Eq. (4). Conventionally Da=−

was calculated by this method. That this correlation is valid with

tan{arctan(−4Da2 t 2 ) − arctan(−4Da1 t12 )}4(t 2 − t1 )(9)

a high relative coefficient means that KD which largely affects

Therefore, when plural concentration profiles in the depth

Da is reversible in sorption.
A slope (a) given by a plot of LnC (vertical axis) versus x2

direction of soil obtained at different elapsed times at the same

(horizontal axis) for time elapsed (t1) after the deposition oflocation exist, Da can be calculated from the changes of theconcentration profiles with time (equivalent to change of slope

radiocaesium is expressed by the following equation as θ1 forwith time) based on Eq. (9).

angle to vertical axis.

Next, the relation to derive KD from Da is explained. If soil
can be regarded as typical porous media, the relation between

1
1
a=−
=
4Da1 t1 tanθ1

Da and KD is expressed as follows.

(5)

Da =

In the same way as Eq. (5), a slope (b) for time elapsed (t2,t2 > t1) after the deposition of radiocaesium is expressed by the1
1=
4Da2 t 2 tanθ2(10)Where, np is the porosity (%), Dp the diffusion coefficient inporewater (m2/s), Do the diffusion coefficient in free water(m2/s), ρd the dry density (g/cm3), δ the constrictivity, and τ2 thefollowing equation as θ2 for angle to vertical axis.

b=−

np Dp
np Do
δ
=
� �
np + ρd K D np + ρd K D τ2

(6)

tortuosity.

Where, Da1 and Da2 are the apparent diffusion coeffients forelapsed times t1 and t2, respectively (m2/s) (in this case, Da1 and

The tortuosity τ2 for uniform and typical porous media isgeometrically τ2 = 3. In the case that pore size (pore aperture) is

Da2 are equivalent to the apparent diffusion coefficientsobtained in the 1st and 2nd investigation, respectively).

large enough compared to diffusion species, it is regarded thatapproximately δ =1. With respect to normal soil, pore size isconsidered to be fairly large compared to ionic sizes.
Therefore, Eq. (10) is arranged as follows.

The change quantity of slope against time change from t1 to
t2 is expressed as follows from Eqs. (5) and (6).

Da =

89

np Do

3�np + ρd K D �(11)Table 3. The calculated results of the Da and KD for Cs+ ions based on the evolution of depth distribution versus the type of soil
2

Physical property of soil
Investigation location

Soil type

Porosity（％）

Kanaori, Nihonmatsu C.
Kurabeishi, Hiruzone, Namie
T.
Ohshimizu, Yamakiya,
Kawamata T.
Mizuzakai, Tsushima, Namie
T.
Matsukiyama,
Shimotsushima, Namie T.
Shiobite, Akogi, Namie T.
Kunugidaira, Akogi, Namie T.

Sandy soil

50.9

Organic soil

59.0

0.969

2.566

44.9

1.378

69.8

Soil of former
farmland(including flower
garden)Dry density Solid density（Mg/m3）（Mg/m3）
1.159
2.719

Da（m /s）KD（ml/g）Cs-134

Cs-137

Cs-134

Cs-137

2.76E-14
1.99E-14
4.53E-14

2.74E-14
1.96E-14
4.64E-14

9.66E+03
1.98E+04
8.66E+03

9.74E+03
2.00E+04
8.46E+03

2.729

1.56E-14

1.37E-14

1.34E+04

1.53E+04

0.728

2.511

6.69E-15
1.76E-14

8.37E-15
1.06E-14

9.63E+04
3.66E+04

7.70E+04
6.08E+04

70.2

0.724

2.619

2.93E-14

2.06E-14

2.15E+04

3.05E+04

59.3
48.4

1.053
1.062

2.604
2.631

2.37E-14
1.23E-14

2.35E-14
1.06E-14

1.65E+04
2.04E+04

1.67E+04
2.35E+04

From Eq. (11), KD can be calculated from the following

sorption experiments on sandy soil, organic soil and clayey soil,
but the KD on sandy soil was irreversible 6). Model construction

relation.

considered irreversible reaction in sorption is needed.
KD =

np

(Do

− 3Da )
3ρd Da(12)

4. Conclusions

By using solid density (solid particle density) instead of dry
density of the medium (soil), Eq. (12) is finally arranged asvalues obtained by batch experiments and the Da-values offollows.

radiocaesium obtained from depth distributions near the surface

Since there were found large discrepancies between the KD-

layer of soil and the main cause was considered to be due to the
KD =

np

(Do

− 3Da )

effect of dispersion or permeation by advection near the surface(13)

3ρth �1 − np �Dalayer of soil, Da was calculated from the evolution of depth
distribution in deeper part and further KD was calculated from

Where, ρth is the solid (soil particle) density (g/cm3).

the relation with Da.
The calculated results of Da based on the evolution of depth

In this study, Da and KD were calculated based on Eqs. (9)and (13), respectively. In the analysis, the porosity and solid

calculated from the Da-values were in the range of 104~105 ml/g,

density of soil were based on the measured results of soil

which were approximately consistent with the KD-values

sampled at each investigation location, and the D for Cs ions
was used 2.1x10-9 m2/s (25°C) 9, 10).

measured by the batch method. This is consistent with the fact

Table 3 shows the calculated results of the Da and KD foris very slow and much percentage of radiocaesium stillodistribution were of order 10-14 m2/s and the KD-values+

that the movement of radiocaesium in the depth direction of soil
distributes near the surface layer of soil.

Cs+ ions versus the type of soil, together with physical property-14

On the other hand, since no evolution of depth distribution

m /s, and the KD-values calculated from the Da-values were in

was found for many data of sandy soil, those Da-values havethe range KD = 10 ~10 ml/g, which were consistent with the

not been able to be analysed. This is considered to be due toKD-values measured by the batch method.

irreversible reaction in sorption, and is consistent with theof soil used in the analysis. Many Da-values were of order 1024

5On the other hand, since no evolution of depth distribution

results of desorption experiments after sorption experiments.

was found for many data of sandy soil, those Da-values have

Model construction considered irreversible reaction in sorption

not been able to be analysed. This is considered to be due to thatis needed.

the KD of radiocaesium on sandy soil was irreversible. Actually
the KD-values on organic soil and clayey soil wereReferences
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